I've always kept in mind how one lecturer described it to me: _light propagates like a wave and interacts like a particle._ You can't go too far wrong with that. Glad to see the video comes to the same conclusion.
@@kaushalsuvarna5156 , Following the same line of reasoning, I've always thought of it is as a wave passing through the two slits, and a photon detected at the screen. That dispenses with any question of "which slit the photon passed through" -- there's no photon until it is detected. And the wave propagation instantly answers the question of why the interference disappears when you block one slit. The wave has spatial extent, while the photon is localised. Of course, it doesn't explain how we get from extended probability wave to localised particle, but we just have to live with that weirdness.
This description (the one given by the lecturer you heard) implies that most non-technical presentations of the famous double-slit experiment are based on incorrect reasoning. Is that your opinion?
How big is a visible photon? A good question, in particular, better choice of the word visible. How big is an audible sound or an electromagnetic wave? Alas, physicists must get their acts together and know what they're talking about. Are these pairs of concepts, light and visible light, photon and visible photon, etc., identical? Even better, the moon and the visible moon, the sun and the visible sun, are these two the same? Would you agree that the visible sun is much, much, and much bigger than the actual sun? So, physicists don't even know what the sun and the visible sun are or the difference between them because physicists don't distinguish them or don't have a definition for both.
@@schmetterling4477 what is the wrong part with the creators video? Pls explain. Take in consideration that for a photon travelling at C, time doesn't exist. Anthropic notions of space, size and time fail at both extremes of our understanding of the universe both at extremely small and insanely huge scales!
I've been searching over a year for a video like this, that actually performs the experiment and shows the results, not just an animation. Wonderful. Subscribed.
This is one of the best science videos on TH-cam. I cannot imagine how much time, work and thinking have gone into making this amazing video. For me, this is a better way of communicating science to people than publishing in Nature or Science. Thank you very much. Keep up the good work of educating people like me. Thanks.
@@smileyp4535 Peer review is a very nice concept and I fully stand behind it in principle. However, the way it is actually done is very flawed, as is the current practice of academic publishing in general. We should think about new ways to do this. Ways that don't have universities and society at large ripped off by publishing companies, that don't allow (and almost force) scientists to engage in dirty tricks exploiting the peer review process and that don't produce incredibly skewed metrics for gauging academic success.
@@bladdnun3016 it's all about the money, once journals become public and knowledge is free and we move past capitalism overall then there will a skyrocketing boost to scientific research, development and progress
The virtue of this video is not that it answered any questions, but that it intelligently and honestly raised some interesting ones, and showed how hard it is to do these kinds of experiments. Thanks for providing so much food for thought.
I love your silliness. It feels like I'm watching a 1940s scientist instead of a post 2000s one. There's a more human touch on this channel than on a lot of others, while still having legitimate science and engineering.
Elly Gatuno ; es muy facil calificar mal a quien presenta enfoques diferentes en materias conocidas. ? Tú haz hecho alguna aportación para ampliar el entendimiento de algún tema científico? Si no lo haz hecho, hazlo
Human's way of thinking that we are trying to abandon by starting our belief into theory that is a blind path ? Instead of assuming that photon behaves naturally when we dont look at it and starts being chaotic when we start looking at it, lets start thinking logically and on the base of experiments that we actually can conduct.
I love it! I never knew that coherent light would have additional assumptions compared to spontaneous emission in interference experiments. Maybe light really is a wave. The "duality" certainly seems less 50/50 and more like a wave with some extra features. Thanks so much for your videos.
Thanks Ben, I was aware of the fact that coherent light is essentially different, but because of quantization I thought "a photon is a photon".Which evidently is not the case. I used a more classical depiction here with the EM field as leading, because I figured it would make more sense to most people than dishing up a Hamiltonian.
@Michael Bishop A very neat way to see how classical thinking is not a sufficient explanation of a quantum effect. Particularly liked his realization that the quantization of energy (observable eigenvalue of the field state) is distinct from the continuous and extended wave function of the photon (a photon created around the big bang can still be detected today across billions of light-years). This is truly a quality channel!
@@HuygensOptics You have not yet reached the fun part of duality :) You only presented the argument for the wave side. Instead of attenuating the beam with grey filters, use a sequence of beam-splitters to see how many times you can split light before its coherence length is reduced so much that it destroy the interference. To see the particle side argument, use beam splitter and show that when you split a single photon, it is detected either left or right but never on both side simultaneously.
Wow. A logically consistent and scientifically consistent explanation of quantum mechanics. I've had trouble fully understanding the double slit phenomenon for years and now I suddenly think, "well duh, of course it works that way. It's obvious." You're an incredible teacher sir.
@@jamesmoran7511 Blue on black, tears on a river, push comes to shove, it don't mean much, joker on jack, match on fire, cold on ice, a dead man's touch.
This is the phase of QED pedagogy known as Socrates' Nutpunch. By this time, the OP has no doubt experienced several similar delusional epiphanies, followed by the inevitable complete collapse of understanding in the face of the next paradoxical twist. This is the only trajectory possible. No disrespect intended, and I agree with the sentiment. We've all been there.
Hello! Grad student working in quantum optics here. Great video! The coherence length of a photon is the same coherence length as the beam. Single photon experiments can be done with kilometers of distance between the photons, given a sufficiently coherent laser. The explanation you have given is spot on. Also, the attenuation method is not reliable to produce only single photons states. You're still in the right range, but the resulting beam will be "bunched", where you have a high probability of two-photon events. (think Bose-Einstein statistics) Either way, you're actually measuring the interference of the photons with your experiments, even if they are bunched up. Generating single photon states is an area of ongoing research, but the main methods are 1) quantum dots, or 2) SPDC single photon heralding. Both of those require expensive equipment. The second method is totally attainable if you can get a single photon detector second hand from somewhere on the cheap. They tend to be very expensive. Another interesting avenue to get single photons would be the SPDC part, where you could generate photon pairs from a single pump photon through interaction with a nonlinear cristal (like the ones found in green laser pointers). If you know about second harmonic generation, it's basically that process in reverse. Since you have photolithography equipment, you could DIY produce periodically poled materials that would even allow for colinear polarisation-entangled photon pairs to be generated.
This is fascinating - when you say that single photon experiments can have kilometers of coherence, are you discussing this same (or an equivalent) self-interaction experiment? As in, if this had used a single-photon source, would the result have been the same, or how far could the split-off beam have been retracted before interference faded?
Wow, this is was a super concise and delightful presentation on something I've often seen ignored in modern POPSCI TH-cam. You took a stab at explaining something I always imagined as black magic and I left with a greater intuition and understanding of something I don't even use day to day in my work. However it did make me think differently about EM in general, which is an amazing accomplishment for a such a short video.
I am a variant of Francis Bacon - I've taken all knowledge to be in my periphery... I find that the information of the Internet (our modern Library) is wonderful and strange. Now if I ever could focus and get just a few interests instead of 'all', I would pursue the knowledge through University studies and research at a institute or an other; for now YT will suffice for my scatter brain...
@@RobLocksley yeah, agreed, I feel the same. But when you choose an interest and go to university, you will be told to watch yt videos as your 'reading' assignments.
Yeah. This video confirmed to me that amount of light smaller than a photon exists even if it cannot be measured. You just need to add a bit more energy and boom it 'statictically' materialises. It becomes a 'particle' and sets the detector off. Black magic or what?
@@echelonrank3927 You don't need to add a bit more energy as measured by the power of the beam, you just need to add a bit more time (as long as the h•c÷𝜆 value is enough to exceed the energy level that has to be excited). So there are two energies we're dealing with here. The energy of the light beam itself, in watts, and the energy of individual photons as calculated by the photoelectric effect equation, h•c÷𝜆. This may also be written E = hv (that's a Greek letter "nu", not a vee), where v = c÷𝜆, and with dimensions of T^-1, or inverse time, represents frequency. Old joke: What's new? Cee over lambda. Just because I can give that explanation, above, doesn't mean that I have any deeper understanding of this process.
Excellent video, this is the first time I've listened to such a clear explanation in such a short time of the seemingly paradoxical behavior of photons. The graphics and narrative are just what is needed to explain this topic in a super-efficient way. Thanks so much for sharing!
@@HuygensOptics me too. This channel is a hidden gem. I discovered it via one of the later videos and got to the part where you said, "... with my DIY wafer photo-lithography stepper", and it was a bit of a record scratch moment, "wait, what did he just say?". I paused that video and immediately switched to the wafer stepper construction and watched everything in order from there. You should create a Patreon page so that we can help fund more experiments.
What a wonderful experiment and presentation. As a “radio person” the concept of a Photon has never been easy to swallow. I can appreciate that an emission of light is produced as a quantum event (photon) but from there the electromagnetic field created propagates without quanta limitations just as your experiment demonstrates. The same quanta effect applies to detection or attenuation as you describe so we end up detecting a photon from the wave. It is time for a resurgence in science to reconsider what a photon is and how light and radio waves propagate and I think you are on to it. Perhaps we need to set up quantum de- radicalisation classes for Photon believers. Well done.
Wow! Awesome to see the double-split actually demonstrated like this, whereas most discussions just illustrate it with graphics. Makes it seem even more mind blowing.
Graphic meaning.......of or relating to a pictoral representation,its a graphic.Your whole interaction with your phone or computer is a graphic.The law of the phantogram states that anything relative in size to your observation,is relative in size to the human condition.Wave mechanics......This is one of the most proven themes inscience.
You made my day, i cracked my head on multiple books but none give that much i sight. You really gave beautiful insights and you will always be remembered for years for spreading this level of knowledge of optics
@@schmetterling4477 representation they give you in high school is aimed at a very wide audience (that generally won't need this knowledge for their career in the future) and it's very lopsided and simplified. For example, they don't give you the deep connection of the wave function of a photon with its properties as a particle and they don't tell you anything at all about the Dirac equation and how the wave function experiences local time. And yes, once the wave function of a photon collapses and its position is measured, it indeed does localize to a point, so in this sense they can have a perfectly well-defined position (which's also emphasized in the video). They only explain it properly at uni's fundamental physics course.
@@schmetterling4477 photons don't have a particle-like wave function because they have 0 rest mass. But they do obey the same laws in their relativistic limit as do particles. "Collapse doesn't exist" in everettian interpretation, but the way wave functions entangle in the multi-universe interpretation by definition of word "interpretation" act exactly the same way how this happens in copenhagen interpretation with the wave function collapse.
@@schmetterling4477 I mean sure, you can keep on being a judgemental edgelord who obviously knows better than Everett, but then if you want people to start taking you seriously, it's probably worth achieving something first using your vision (as in, other than just criticizing). It absolutely does not matter how much you hate a theory if it actually works.
@@schmetterling4477 what makes you think that reading literature automatically gives you any understanding? You apparently read something about MWI that somehow gave you the confidence to judge that it's "complete nonsense" which implies that you're either a future nobel prize winner or just a classic edgelord who's full of himself and jumps on the internet to teach others.
Beautiful! Gravitational lensing, in particular, Einstein rings, is an example where the size of the photon is greater than the size of the galaxy. In other words, the distributed chunks of masses in the galaxy (stars, etc) gravitationally interacts with the very distant photon's wave function to make it become focused on a telescope here on Earth. In fact, due to the low luminescence, you can argue that the ring is a bunch of single photon interference experiments!
"Gravitational lensing, in particular, Einstein rings, is an example where the size of the photon is greater than the size of the galaxy. " reading comments this stupid is kind of depressing
It helps to think of the EM field as the propability to encounter a photon over any point in time & space. The energy at this point is the propability * the energy of the Photon. Since the ND Filter is randomly removing photons and not removing exactly every nth, the propability is reduced by a constat factor and remains constant. It's this propability field that interferes with itself. When measuring (in the sensor) photons will be measured distributed according to this propability field.
Very good, if you can wrap your head around it. I was taught it that way after I asked too many "but why" questions to my father, while he was teaching me about uncertainty, because it's an all encompassing way of viewing the ideas, that can't be further "but why"'d, which to me is a good wrap up
This is how I understand it - from reading and watching Feynman's explanations. As to how this probability "field" relates to physical space as we conceive it, I believe Feynman says: Nobody knows!
re: "It helps to think of the EM field as the propability to encounter a photon over any point in time & space. " Stated impossibility; EM **is** photon, and, in 3D space a propagating wave or waves DO NOT/does not affect propagating waves, i.e. photons!
Antenna theory with EM waves is adequate for all practical purposes in most of optics and all of electronics, but the rabbit hole is far deeper than this: Photons are probability wave functions that take all possible paths until they interact with something and collapse in one place even if they have had time to stretch over the entire universe before that happens, as his slit experiment shows and you also point out. What is worse, is when you also consider the rest of physics. Special Relativity says that particles moving at the speed of light are completely length contracted, so a Photon is flat and 2 dimensional and to the photon times doesn't pass, so to it, interaction is instant regardless of how far it has travelled and to it, the Universe has no length and by that no volume and time has passed instantly! This is not only a theoretical curiosity, but a reality as real as our way of perceiving the Universe. So the question is: Did the Universe really expand, or is it only to us meat computers that perceive space time as a "place"? Going deeper (or taking a theoretical step back): If you look into diffraction you realize that photons as particles are not needed here either for imaging, diffraction patterns alone give the illusion of particles coming from different directions creating an image on a retina or image sensor. A single photon does not carry other information than colour. Without interference from objects like a lens or a pinhole or other photons, there can be no image, i.e. no apparent direction that photon is coming from. Finally, as a curiosity, acoustics share 2 properties with photons however sound extends in time, so it has also a time diffraction based on its duration, so the shorter it is, the less precise its frequency can be defined. It might be obvious looking at a sinusoidal pressure graph of a note, but you can also hear it it. Very short notes on the same instrument or tone generator sound more rough and that roughness never goes completely away, regardless of how long you play the note, so to make a perfect sinusoidal clear note, it has to be eternal! That means that the sound "knows" it is being truncated sometime in the future before you lift the finger from the key! This roughness effect can also be seen in radio waves, where side bands extends further and increase in numbers from the center frequency, the further you increase the modulation or data rate. Maybe the conclusion to all this is that any type of wave regardless of propagation medium, share quantum properties like elementary particles, even sound waves that usually are considered purely in the realm of classical physics?
Fantastic presentation. I have been studying optical phenomena for many years (as an amateur) and thought I was alone in wondering how long a photon might be. Also, a great explanation as to the reduction in EM passing through filters without violating Planks law due it to being coherent & unconstrained by quantisation.
A photon, by definition, IS a quantum particle. For those not familiar, exploring QED or Quantum Electrodynamics. Feynman diagrams, and the double slit experiment (the origin of the go Copenhagen Interpretation of the double slit experiment..... WARNING- this may lead to many journeys down multiple rabbit holes....
I concur with Ben. Amazing! I was clueless to the differences between a photon from spontaneous emission vs. coherent from the laser. I will have to rethink my experiments from now on. I have been playing with interferometry since high school in the 80's when I first got my hands on a HNe laser salvaged from a supermarket scanner and first surface mirror fragments from an overhead projector. Added an interferometer to a vertical seismometer with a 20lb lead mass and then monitored the lunar tidal pull over a few days. Been a Zealot for interferometers ever since.
I would have loved to see the results of the experiment with the florescent light. The insight about the continuous nature of the laser beam was very interesting, I wonder why I don't here that talked about more when people describe these experiments.
Yes please. I know this is quite old, but please to do the experiment with some sort of non-coherent light source. I don't know if color filters can be sufficiently tight (meaning limit to a small enough wave length range) to make this experiment meaningful. Maybe you would need to use a prism to filter the light source? Or would a "gel" be accurate enough?
@@thorwaldjohanson2526 is it this?? Fluorescent tubes are filled with low pressure mercury, when an electric current is passed through, the electrons in mercury are excited and move to a high energy level, this high level state is unstable and so the electron moves back to its original state, but on doing so, it emits an electromagnetic wave with energy equivalent the difference in energy level. This is UV light !!! and the electrons in the phosphor coating inside the fluorescent tube are excited, and releases visible light(that is NOT very 'spectrum pure' ) when the electrons return to its original energy state, which provides the glow in fluorescent lights.
This is one of the best videos on TH-cam on the subject, I’ve reference people to this video all the time. An incredible number of people have the misunderstanding that the EM field is quantized. The photon did not go through one slot or the other, the wavefront went through both. then it is just the probability of detection there’s no magic science about this.
Modern physicists often don't really care about how this kind of stuff works. If the math works out they are happy. That's why I love your approach to try and develop an intuitive feel for it. Great explanation. Can't wait to see the experiment again with a more suitable beam attenuation!
That's pretty cool man. When it comes to extrapolating certain information from results or trying to infer a mechanism, it usually ends up necessitating at least a dozen different, highly controlled experiments all with their own interpretations as well. It usually makes me feel like we are trying to see the universe through a single pinhole in a 1 square mile cloth. Hopefully, our curiosity and individuality can be maintained after our physical death so we can prove for answers to these questions. In fact, I'd like to talk with Werner Heisenberg about some of these newer findings but I feel like he'd just say "uh, I don't know." Fitting for an uncertain bastard...
The best analogy I have read is this: Imagine disturbances in the EM field (which are by definition what photons are) as transverse water waves that ripple across the top of a completely still, shallow pond. Now you calculate exactly the amount of energy required to transfer one quanta to that field, lets say that's by using a small wooden sphere that you drop from exactly the right height so that its interaction with the water takes all of its energy (which is wxactly equal to one quantum) and converts it into a circular wave that spreads out from the point of impact (which would leave the wooden sphere sitting completely still on the surface of the water, with ripples of various sizes spreading away from it, carrying its energy away in all possible directions). Now imagine that there are other identical wooden spheres, floating completely motionless, on the top of the still pond. They are spaced few and far between, at random places on the pond, but all relatively far from the point where the wave is generated. More precisely, the radial distance, as measured via a straight line from the closest floating sphere, through the origin (the point where you are dropping a sphere and generating the wave) to the next closest floating wooden sphere, is long enough so that information traveling at the speed of light would take far longer to travel between them, than the time difference that exists from when the expanding wave 'hits' the first sphere to when it will 'hit' the second floating wooden sphere. This is so that once the wave reaches the closest sphere, the sphere directly opposite to it across the circle would have no way of 'knowing' when or if the wave has interacted with anything yet by the time the wave gets to it as well. After all that setup (sorry for how long winded and convoluted my explanation is. I know my English is not great, but I'm trying my best.), here is the interesting part: Imagine repeating the experiment multiple times, each time with the same setup and a completely still water surface. Each and every time after you drop the sphere, a circular wave spreads out from the impact point, traveling at a constant wave speed. However, once it gets to the first (i.e. radially closest) floating wooden sphere, one of 2 things happen. Sometimes the wave hits the sphere without it recoiling at all. It doesn't absorb any energy and doesn't move a single millimeter, but it does influence the shape of the wave going past it, diffracting and reflecting it without otherwise seemingly interacting at all. Other times, something even stranger happens. As the wave reaches the floating sphere, the whole wave instantly disappears from the entire pond all at once. It doesn't send out information that makes the wave disappear at the speed of light from the location of interaction. No, seemingly violating Einstein's theory of relativity (that is, "Spooky action at a distance", even without any special entangled states), it all vanishes all at once and, simultaneously, *ALL* of the energy that went into creating the original wave gets transferred into the single wooden sphere that the wave interacted with, sending it flying up into the air to *exactly* the same height that the original wooden sphere was dropped from. This is sometimes referred to more succinctly like so: Imagine dropping a wooden plank into a body of water, with other identical planks floating on top of the water, and seeing the waves it created suddenly disappearing whilst instantly transferring *all* of the energy of the spread out wave into one single plank, sending it shooting up into the air precisely just as high as the height that the original plank was dropped from. This is the essence of the weirdness. The EM wave could be thought of as 'guiding' where the photon 'goes' (i.e. Pilot Wave Theory), but still, how do you reconcile the fact that a single-photon-strength 'light wave' could have been spreading out for thousands of light years only to finally reach two atoms (also spaced thousands of light years apart) at the *exact* same distance with one atom suddenly, *instantly* gaining *all* of the energy contained in that wave, while the second atom never gets *any* information about the wave at all.
I would say that it is because the original model doesn’t accurately depict what is going on. The initial wave induced an oscillation in every sphere it interacts with. Each successive sphere creates a new circular wave that exists simultaneously with the original wave minus the portion absorbed to cause the next sphere to oscillate. Every sphere that oscillates creates a wave based on the energy it absorbed but converted into a smaller amplitude wave spread out over the surface of the new circular wave. Each successive wave induces an oscillation in other spheres in all directions. So while the original wave front propagates, multiple wave fronts created by every other sphere interferes with it in multiple locations. Every sphere creates its own wave front. I would set it up with acoustics rather than hydrodynamics. If you use harmonically similar spheres, you would more closely resemble the absorption, oscillation inducement, and transmission of new waves that you see in the Raleigh Scattering of light waves in an optically transparent material. It is difficult to replicate that effect with wooden spheres and water. Perhaps metal disks of the same material and size floating between two transparent liquids of different specific gravities and different colors so you can easily see the interface between the liquids. If you set up a strobe light that forms a plane which intersects perpendicularly with the the interface, you should be able to adjust the pulse rate of the strobe to visually “freeze” the interference pattern created in the interface at any location in the system. By moving the strobe beam around, you should see how the wave evolves over time/distance from the original oscillation and all subsequent oscillations generated by sympathetic harmonic regeneration of each successive sphere. At least, that’s what I imagine.
This was similar to how I visualized it in my head as well and I love the detailed explanation. Set a single pulse of light off at the center of a large sphere of empty space and envision the spherical wavefront expanding at lightspeed in all directions, ready to interact with anything, and have only a few randomly spaced "spheres" floating different distances from the center that can absorb that light energy. If these spheres were, say, atoms that could absorb only a specific quantized amount of energy, and that is precisely how much you set off in the center, then presumably whichever atom encountered the wavefront first would absorb the entirety of the energy leaving nothing for other atoms to absorb lest you violate the conservation of energy. Much like the one wooden ball suddenly absorbing the entire wave. If the wooden ball were a quantum ball then I imagine that is how it would work. It would then presumably decay from it's excited state releasing another wave in all directions for some other atom to interact with, but due to it's quantum nature it could only either absorb the whole wave, leaving no energy left in the wave anywhere else (in spite of it having expanded in all directions initially) or not interact with the wave at all. Assuming it's closed and ignoring losses, if you just watched this system it could appear from the outside that a "photon" is just bouncing from one atom to the next closest one and you don't need the wave explanation at all. But indeed to your point, why would one atom absorb the whole wave immediately and how could this occur? In the real life example, wouldn't the available energy just fall off with distance and thus not match the needed quanta to be able to be absorbed at all? The wave would just pass all the balls and never get absorbed. Thus the example isn't a quantum system, the surface of the water is continuous and can take any energy value. If you could, for example, construct an elliptical tank and drop one ball in at one focus and place the second ball at the second focus, the wave would reflect off the sides and come back together at the other focus at full strength and thus be able to be absorbed and return all the energy to the second ball. The probability of absorption would be higher where the wave is greatest and I think in a real example would be the only way you could get the second ball to absorb all the energy. It would be a cool experiment to see. I love thinking about this stuff, thank you for your insightful post!
" how do you reconcile the fact that a single-photon-strength 'light wave' could have been spreading out for thousands of light years only to finally reach two atoms (also spaced thousands of light years apart) at the exact same distance with one atom suddenly, instantly gaining all of the energy contained in that wave, while the second atom never gets any information about the wave at all " How about throwing away the assumption of locality ? I prefer to think that this only happens probabilistic, so it doesn't matter which atom gets the wave, that is decided at random when the atom absorbs the energy, it could be even that for this single event both get the energy, this just happens with very little probability, effectively doubling the energy for that amount of time for that single event, but it is statistically conserved in the long run. Basically, I break conservation of energy on best effort basis, for a small bit of time, but for longer times, it is statistically conserved.
@@deprivedoftrance 'lest you violate the conservation of energy" what's the problem with violating it for a single event if it is statistically conserved in the long run after more events ? perhaps I'm presuming time is also quantized, it wouldn't be any problem if that was the case, the math would kind of work the same
If you consider time as quantized, you could define the outcome of the event even before it occurred, by the simple arrangement of the fields and the distances, and the end result when more than a single event occur would be impossible to differentiate by experimentation, even because you would to actually cause more events, sending the information back to the source to be able to even know what happened, so it would even out by definition, the moment you try to analyze the system, thus conservation of energy isn't violated, not cumulatively, only in that specific single time frame. I don't see a problem with this approach. Its not like the universe make computation errors that accumulate, the calculations are perfect (I presume), so statistically it would always even out in the next "frame". (basically, I disregarded the entire chaos "theory", as just an artifact of imprecise macroscopic experiments, and the fact that you can't know all the state of the system to avoid errors that accumulate, I basically consider it is not of nature)
An amazing video and props to you for explaining the possible issues with your experiment. Still very impressive to say the least. I spent a few months this past summer performing a very similar experiment in the quantum optics lab where I work as an undergraduate physics student. I used a 405nm coherent laser to pump an SPDC crystal to convert "one" 405nm photon into two 810nm photons. I then split these photons up using a beamsplitter and sent them on two different paths. One path was sent to a single photon detector which would convert these detections to electrical signals. The other path was sent across the lab onto another table where I used this as my source for the actual optics setup with a pricy Andor ICCD. The idea was to trigger the camera's intensifier at the moment I expected a photon to arrive. Without doing this, you will observe a lot of unwanted photons since the intensifier is on in between these single-photon events. So, you tell the camera "okay, I need you to expose when you get this signal from the one arm and you'll catch it simultaneously at the other table with the ICCD. Well.....Obviously, by the time the trigger signal would reach the camera from the single-photon detector, the photon that was sent across the table will have long since arrived at the sensor and you would miss its arrival. So, I delayed my source using a 50-meter fiber spool. This allowed the arrival of the "across the lab" photon to be LATER in time than the camera's trigger pulse (which can be delayed between each intensified instruction pulse to match when the source photon should arrive at the sensor). It was quite fascinating to get this setup working properly. When it was done, I think I was left with more questions than I had answers. I was able to determine these events within 5ns and have a lot of messy notes determining how I managed to find what time I expected this photon to arrive. Correlated photons are very strange and I'm not sure I'll ever fully understand what I was able to do through that experiment. It's a bit difficult to explain without writing a full paper on the experiment. It had already been performed previous to my doing so a full paper would have been a waste of time. I'm now using the setup to perform other experiments. I learned a tremendous amount and made A LOT of mistakes in the process before achieving the results I was looking for. Thanks so much for making this video. It's nice to see other's question and perform similar experiments --- and at home nonetheless! I'm looking forward to going through the rest of your vids. Cheers, Josh
I'm an engineer and these videos always make me try to remember if what I learned matches the content. Frankly, one thing struck me, how is the field not quantized like a photon? How much of the field/wavelength is the photon? Serious questions. I'll never figure those out, I know my line of work will never take me there either. I'm just human with a finite lifespan. Sad we can never live long enough to know all the answers. Doubt we can remember them either if we knew all the answers.
This is a fascinating and well carried out experiment. Thank you for sharing this! In the hope it might be of interest, I would like to share some words on the subject from Albert Einstein. In his publication on the photoelectric effect, he writes: "According to Maxwell's theory, for all purely electromagnetic phenomena ... the energy is to be understood as a continuous space function." "However, it is ... conceivable, that the theory…, which operates with continuous spatial functions, leads to contradictions with experience if it is applied to the phenomena of light generation and light transformation." "It now seems to me that the observations about black body radiation ... and the generation and transformation of light, ... are more understandable under the assumption that the energy of light is discontinuously distributed in space." ( This is my own translation from German to English. So, please handle with care! ) Mathematically he treats the electro magnetic field like an "ideal gas" of photons, but these only appear during the transformation of energy. So, during propagation light acts like a wave, during emission and absorption it acts like a particle. And those particles, have no extension.
this is a fair assumption by him but it's wrong (or maybe it's true, but that would imply a near fractal universe) quantum field theory is also wrong but for other reasons, einstein was just likening it to something he was familiar with, the behavior of gasses that are large compound structures of individual atoms, meanwhile QTR is just pants on heads retardation that should be ignored and ridiculed lest time and braincells are certain to be lost
You narrate these videos as if you were a professional narrator. It is pretty cool. I have the impression I am watching one of these older (and better) science documentaries.
@@vvs6476 Taking the view that as a quanta, photons experience zero time; and that the field can hold fractional values... you'll find that the photon is always the exact size of the detector; and it will continue to do so until you reach the Hubble volume.
A nanosecond laser would be enough given the path length of his setup. A 905nm pulsed laser diode with a 2ns pulse width would do it. Not cheap, but a lot cheaper than a fs laser! Though his camera probably wouldn't detect that wavelength.
Add in a SPAD and picosecond precision Event Timer and you will be able to tell which path a photon took because you can compare travel times of individual photons.
Yes, I also want to know. In my undergrad physics I learned that a single photon will show the interference pattern with a double slit. But never was the path length issue discussed.
Indeed, as I understand it you would also see interference... But this is QED, way over my head... There are actually many philosophical discussions about the Mach Zehnder interferometer.
Amazing video with good explanation! This confirms my old believe that we can have a continuous wave with infinitely small amplitude. And all the discreteness comes from the detection side, when the sufficient amount of the energy is accumulated the detecting atom jumps to a higher level (and the detecting atom is the "size" of a photon). By the way Plank was explaining exactly this, the light matter interaction, and the discreteness was assign to the EM wave! although you have the system with discrete levels on the matter side! And I also think this applies not only to EM waves but to all matter waves.
One of the key sentences for me is the "particle event" takes out the energy out of the field in quantized portions. So it seems a lot easier to think of an excited field which allows interactions with probabilities correlating to the strength.
According to QM, which is not "physical". It's a math model, a model which may __Not__ be valid in all cases beyond which **observations** were made to write the model in 'math' form.
I think (likely wrong) that the "probabilistic" behaviors have more to do with our inability to measure things with sufficient precision. My reasoning is that things aren't "probabilistic" on the macro scale. Stuff is happening that we have no idea about...just a hunch.
@@rustyosgood5667 I believe what you think of is akin to a hidden-variable theory. There's a nice Wikipedia article on that. According to this article this interpretation implies non-locality. Whereas locality is normally one of the other key assumptions we make.
@@neur303 Thank you. I will go check that out. I also recently purchased "Quantum Mechanics and Experience" by David Albert...It is supposed to be pretty good.
I did read that article and was aware of the "Pilot Wave" theory. I do tend towards "deterministic" interpretations simply because they scale. Nondeterministic ones do not scale unless one claims (equally ridiculously, in my opinion) that the macro and micro worlds experience different "physics". I'd rather believe that the very act of engaging an electron or photon (to measure it) produces the same. In other words, there is no "there" there until you shove something in the way (like a silicon semiconductor, vapor, magnetic field or wall). Imagine that you have a matrix field of UV laser beams. Since they are UV, you can't see them. Now imagine that you place something with fluorescence (like a piece of paper with phosphor on it) in the field. You can suddenly see the field in the form of a dot. Now imagine that this field permeates the entire universe (spacetime) but unlike the UV lasers, it is the thing we call "Phosphor" when we "charge" the field to that level which corresponds to "Phosphor". The instant we turn on a light or collide "packets" of quanta, the field produces the photons or said "quanta" respectively. Prior to "charging" the field, there isn't any measurable thing. We don't know that this "field" is there because it is not visible...until you charge it. It could be like tiny lines or like soup. I can imagine fields within these fields that likewise, can't be seen or measured because we simply don't have the tools to do so. We can see that the universe extends to a similar scale in the "larger" direction. I find it hubris to think that when we scale it down, it stops at "Quanta" simply because that is the smallest thing we can detect. I somewhat understand the notion of gravity being a "force" but it doesn't need to be. You can imagine that there is no such thing and everything still works. We are falling towards the center of the earth which is falling towards the Sun which is falling towards the center of the galaxy etc... Spacetime is bending this "field". We can't see it, but it's there. We call it "Dark Matter". On the other hand, it could be that I am completely ignorant and these ideas have been put to rest long ago....I am almost certain this is the case. This is why I intend to read, read and read some more especially after I retire.
I have to admit I really liked the original explanation that H. O. / Jerome just Kicked over lol. Still it does make me wonder how many experiments in physics don't take into account the possible 'Maximum size" of an effect or interaction ? Leonard Susskind's conjecture of matter being a holographic projection from a 2D surface at the furthest extents of "the universe" kind of bothers me (even though he seems like a cool dude and very practical guy ~ much like Jerome. ). Somehow this much needed (atemporal) 2d surface disposed in three space + 1 of time - seems that it must lurk much closer to home (rather than at the "Edge" of the universe or some unfathomable 'Distance" away. ), but at a scale much closer to home not normally "experimented" for ? Well at least that's my totally unsubstantiated "Hunch" :-) Soooo many experiments are carried out at the scale of an optical table and the 4 walls of a lab ? Maybe we are missing something because of that more usual range of scale we choose experiment at just out of convenience. + I'm nor really sure how visible a 2D entity really is in the 3d universe we occupy especially if such entities are comparatively large - very faint energies over a large volume ? At least this experiment pulls some focus on that idea and helpful further explanation. + David Nadlinger chiming in was super nice / super helpful. [Something that has no Z in and XYZ universe shouldn't be "Visible" other than extremely vague changes in energy / radiation. ??].
What of the quantum eraser or delayed choice experiment where (superficially) the future seems to influence the past ? Does David Nadlinger's reasoning squash that as well ? th-cam.com/video/0ui9ovrQuKE/w-d-xo.html
@@HuygensOptics it clears up a lot about its behaviour, certainly at the macroscopic level. I think perhaps a lot of text books overemphasize the quantum nature, but I suppose it's a case of choosing the correct model, for the situation.
truly amazed, u have solved the double slit puzzle, and discovered how and why light is a wave and behaves like a particle when obseved with your eye sensor or any other measuring device. a true scientist you are.
I added quite a few videos of yours to my watch later. And I also subscribed so I can add future videos to watch later. I quite enjoy the educational and engineering bits of your videos. During this winter semester I didn't manage to sign up for an optics course at university, but I feel like I am learning quite a bit here. Always loved the idea of a photon trap. Perhaps in the future we manage to trap photos easier and keep them as souvenirs stuck in one point in space. Is a photon a particle or wave is an older question in physics. And the answer is that a single photon behaves like a particle but more photos behave like a wave. Waves aren't single entity. But if even the dimmest light is continuous, this means that photon counting sensors (in astronomy for example) do just make up a threshold. e: I still don't have an answer to what "destructive" interference does. You mentioned it in a different video a while ago - but this question leaves me wondering at times.
I always suspected that they are not sending single photons or electrons in the experimental double slit setups. When you are using filters, you are just reducing the amplitude of the light beam to below the single photon energy. The wave function is still continuous though and not a signal photon. To do a single photon would require a burst of energy with a start and stop time equal to the wavelength of the light used then a space of at least a wavelength of time. For red laser light at 635 nm, you would have to pulse the light at (635E-9/3E8) 2 Femto seconds on and 2 Femto seconds off or longer. The amount of energy in the photon should then make no difference. I think even if you used electrons instead of photons, you still would have a problem switching the electron beam on and off at a Peta Hertz. Giga Hertz oscillators we can do, maybe even a Tera hertz oscillator, but I don't think we can do a Peta Hertz oscillator yet. I also think that a photon just like an electron has a probability wave shell associated with it. I think that a traveling photon has a finite probability of being just about anywhere until it is detected and then the wave function is collapsed. When detected the photon wave function disappears and the energy packet position is detected. We are seeing the probability waves of the photon interfering with themselves causing the interference pattern. The dark spots in the interference pattern is where the probability of the photon being there is zero.
You are right about the basic point of bursts vs. continuous light. Fortunately, however, it is not necessary to make them quite as short as a single em field cycle, as you can space them out much further. For instance, one type of physical system that can produce "clean" single photons are single atoms. If you trap one of them and excite it with a laser pulse to some short-lived state, it will emit exactly one photon when it decays back down to the ground state. The photons will have an exponential profile in time, typically on the order of ~10 ns. Just make the space between the pulses exciting the atom much longer than that, and you have a series of "perfect" single photons. You'll still observe interference in this case, but as you introduce a path length difference, the contrast will go down as the overlap of the ~10 ns exponential decay envelopes is reduced. > but I don't think we can do a Peta Hertz oscillator yet This is a tangent, but we actually _can_ produce such short pulses. You can get down into the single femtoseconds using mode-locked laser techniques. The trick here is to realise that a short pulse is a superposition of many frequencies, and arrange the many modes of a laser cavity so that they naturally overlap in the right way, rather than trying to actively switch anything on this time scale (which is indeed pretty much impossible). You can go even faster (attoseconds!) e.g. by high-harmonic generation techniques. Of course, confirming that you have made such pulses is quite a challenge by itself (see e.g. doi.org/10.1364%2FOE.25.027506).
This is what I've been saying for years that there is so much dishonesty in this experiment and to add to what you said , when they "observe" the interaction they fail to realize that inorder to observe it there has to be an interaction of some form inorder for us to "look" at what's going on and by "looking" we are sending light there and back in order to "see" what's going on and that's going to interfere with the light they are calling photons
I would be interested in seeing the results of repeating the experiment with a high speed electronic shutter chopping the beam. this would probably require increasing the long path length, perhaps by sending the beam through a coil of fiber optic line.
@@rdizzy1 given that the beam travels at 300,000,000m/s, you can calculste how fast a 'chopper' would need to revolve in order to chop the beam into segments 1m long.
very provocative video, i like that you ask many questions that make me think. in my intuition, a photon is a debroglie wave that is infinitely stretched on space along its path. another way i see it is a particle that travels at the speed of light and has infinite time dilation, so in the reference system of that particle the entire world is relativistically contracted to have 0 "length". while photon "length" is relatively clear to me, its "width" is more obscure. as a wave packet i would on one hand expect it to have variable size, but on the other hand all photons of a given wavelength are supposed to be identical.
@@schmetterling4477 I'm not really asking you if I'm right or wrong, because I worked enough in the field to know when my intuition is correct and when it's just a convenient way of thinking about something (and when this convenience stops working). I also have a PhD in physics, so you can go and give your valuable high school advice to somebody else.
@@schmetterling4477 I did measure plenty of cosmic rays, including gamma rays, but I see 0 point in proving you anything considering how full of yourself you are.
@@schmetterling4477 sure, they are not photons, they are particles that have rest mass, but they move very close to the speed of light and exactly due to that, they travel longer distance that they would in their decay time if there was no time dilation in their local frame of refence that you called "total bullshit".
No, the answer is photons are BS. There is no such thing as a photon, whoever named it was an idiot. Should've just called it "EM field touch" or "EM field energy transfer".
@@coenraadloubser5768 so what you're saying is that the answer to how big a photon is, is "no" in general relativity, because in actuality photons are quantum waves of electromagnetic energy, which are also either waves or point like excitations. So to summarize your counter argument it would go something like; General relativity: no. Quantum mechanics: yes. but also no. ? Dude your trying to explain my point back to me.
You can force temporal localization on photons by passing them in a narrow beam through a rotating disc with a small radial slit. Making slit and beam narrower will eventually force photons to be so much localized in time that you will get into proper single photon regime, at least in comparison with ToF over the longer leg of the setup. This would be much cheaper than a nanosecond lazer;) Of course you can also artificially elongate your second optical path by adding a bunch of fiberoptic cable (or just a glass rod), thus making light travel a lot slower. If you go that path you'd need to dim the main path a bit to compensate for losses, of course.
Late to the party, but fascinating stuff as always! I'm continually impressed (or irritated hah) by how counterintuitive light is... right when you start to understand it, a new phenomenon shows up and you realize you have no idea how it works :) If you're taking suggestions for future experiments, I've always thought a Ghost Imaging setup would be very cool, and maybe doable on a home budget (mostly a matter of getting the delay lines setup and figuring out latency in the electronics). Great video! Looking forward to the next!
There are a few answers to that question with various levels of meaning which could be zero, infinity, some finite value or a distribution of values. In the sense of the size of the particle itself it would be zero, but the closest things to a meaningful size for a photo would be either one wavelength of a plane wave or more often and more usefully the full width at half maximum of the envelope function of a wave packet.
I'm impressed with your use of the experimental equipment. An antique, some crystals, a couple mirrors, A BUNCH OF NUTS AND BOLTS? Wow, I've seen people sharpen pocketknives with what looks like more precision equipment and you are recombining low powered laser beams on a table with a CARDBOARD BOX on top of it. I am serious, I'm amazed at your use of those tools.
I would be extremely interested myself! It is, after all, the point of the initial experiment. That would finally give the answer (or added clues) that he started out looking for.
Thank you for explaining how I think about light in a simple way. I did physics at university and I got the impression that light is continuous in free space but acts in a quantised way when it interacts with matter because matter is quantised (because the particles it interacts with, such as electrons, are in potential wells, such as atoms). Since we always detect light by using its interaction with matter we always see it as being quantised. But when I asked professors about it, they would shy away from accepting that explanation. Maxwell's equations explain perfectly how light behaves in free space. They haven't been superceded in a century, they are correct relativistically, and they don't have any quantisation in them.
@@schmetterling4477 We didn't do QED at university so I don't know in what regime or for what precision you need to consider the light as being quantized even when it is acting on a free particle in space. But in our "normal" quantum mechanics classes we were introduced to the effects of light on a quantum system (like an electron bound in an atom) by taking the oscillating field as a continuous wave and putting it in the Schrodinger equation as a modification to the energy term. That gave apparently plausible results. But maybe that was an approximate bodge just to keep us quiet and avoid discussing QED 😄 I'm not sure if this technique gives good enough results to work with for engineering/ chemistry in "everyday life" or if it is just wrong?
The idea of degrees of coherence is interesting. I'd still love to see the experiment done with a fluorescent lamp so the expected difference in interference could be showcased. The question of an intuitive answer of where the energy is in the photon's quantum state before interaction is definitely a strange one. It seems to me that it should have some weird intricacies with momentum and minute internal forces in the optical system. did the single photon interact with and exchange momentum with the mirrors? or did it travel straight? if you could measure the forces involved would you see quantized events in the expected distribution? If anyone knows, please respond!
Thank you for confirming my picture of the double slit experiment. Why anyone would suggest that a photon would go through two slits at once has always blown my mind. The only time you 'see' a photon is when it interacts. It's where it starts it life and ends its life. Photons don't travel. Huygens optics indeed, carried by continuous superposable EM fields.
Amazing!! You answered so many questions I had burning inside me for so long! And you did it so elegantly and throughly, just incredible. To take such a heady subject like point like particle sizes; which really aren’t anything but different fields interacting, and make it coherent and easily digestible. Bravo. Explaining the issues with diagrams versus reality is truly eye opening. Love the experimental evidence you show. Thanks for the lessons!
You have a great understanding of how light works, thanks for sharing this in a simple way that others can understand. A lot of people would be mind blown of the true nature of em waves.
@@schmetterling4477 yeah, just like you. No content, no proof to back anything up. If it takes just a couple minutes to explain it all with experiments made to back up your claims, why haven't you made a video of it yet? Obviously you seem to place yourself more knowledgeable about this than most, yet fail to provide an explanation yourself
@@schmetterling4477 you gave me approximately nothing, as per usual. If he is wrong he can be proven wrong. As for the repeating ad nauseam part, you seem quite adept at it as well, consistently saying the same things without thought. If its not X, then what is it, and if its Y instead, how do you prove Y is correct? In other words to make it abundantly clear: you right now are claiming the earth is flat because someone made a mistake some time ago, and when asked to provide proof you say someone else made a mistake and that's all the proof you need. You do not give an alternative because quite frankly I dont think you know of one, or are otherwise not able to share it. Tldr: a mistake was made, I ask you to prove it
We should always keep in mind that models describing physical world are more or less good for making predictions, but we should not think of them as describing true nature of reality (which may be fundamentally non discoverable BTW). In this regard the weirdness of quantum world makes me think that we are missing something here. There 'must' be something hidden, something 'behind the scene' that would explain this weirdness more naturally and logically than the current models do (or don't).
they are not good at making prediction, like the fuck they are, have you even looked at that stuff? QFT has no predictive abilities at all, all the QFT calculation are just applying interractions between distinct objects but magically overallped in an infinite of ways, but of course they don't calculate an infinite of ways, they just calculate the most numerous alternate realities they larp about, and how do they decide which ones are the most numerous/(aka which unproven interraction) has the higher chance of happening? through experimental data of course! it's literally just writting a mathematical model that makes no sense and hitting it with a hammer until it has the same shape as the experimental data, it doesn't predict anything that just drawing a curve between the experimental datapoints wouldn't predict, it's an absolute joke same with general relativity, good luck trying to make a model of the solar system (the movement of which is very well known) with einstein's equation, when you try that it flies appart, you literally need to cancel out the equations of general relativity to make it work aka you take newton, add einstein, then cancel einstein and declare einstein's theory works same for literally any observed movement, do the movement of galaxies match general relativity? BWAHAHAHAHAHAHAAHAHA, GUESS there's a reason the trajectory of probes launched by space agency use proper movement equations and none of that garbage
One thing is space. Space seems to be treated as a place for electrons and protons to reside in. May be space is a catalyst that instead of just being some where to put stuff, works with electrons and protons to do the things they do. Space may be an integral part of every interaction. It is just not understood as such so basically ignored. There is some thought that the proton and electron is just concentrated space. This kind of makes sense. Look how much space there is compared to how much protons and electrons there are. It is lopsided to space being predominant. May be a balance has been struck in that not much more concentration of protons and electrons is possible. If so, it is a good thing as otherwise there would be no space just protons and electrons. It is something to consider.
Super great explanation which takes out the misticism given by many people about whats really going on in the double slit experiment. The reason the interference pattern in the double slit experiment resemble so much the patterns created by water waves is that the actual laser beam is a continous field similar to the liquid water which is a bunch of molecules connected by vandelwaal forces. Your approach to takle the issue by readjusting out the optical set up in different ways is what a scientist should do in experiments. Use your set up in several ways to get to a more complete explanation.
This explanation destroys a large part of the double-slit experiment conclusions I've seen over the years. So, lasers are the wrong tool for this, but they are *always* used. I feel fooled.
Either we as humans love regurgitating things we don't understand..... or maybe it's been the biggest magic trick of the 21st century... misdirection... we've been subtly manipulated in the spirit of nuclear proliferation. Personally I think it's the latter... I think it's all been part of a strategy to keep everyone as dumb and controllable as possible while "they" figure out how to surveil or control us even more... you know how the pace of technology is exponential? Now imagine how much further ahead someone would be today, who just had a 1 year head start say ... 50 years ago? You know, because they're afraid we'll blow up the planet if we know too much and play with matches? Atheists who do not understand the metaphor that "the world is already saved"... two year old mentalities that think "mine mine mine" and very sneaky about controlling things... sure, someone properly motivated to do something terrible, can do something really terrible... but how much of those things are motivated by the terrible in the first place? That's the age old question, I guess. When will all of humanity wake up to the same truths that what we see is what we are... (and if you don't like it, look somewhere else!!!) One would hope that'd be enough for people to stop trying to take what can not be taken? Maybe we just need a new language that can explain this better.
@@coenraadloubser5768 Take your meds. How does using the wrong tool for light experiments involve what you're talking about? If there was a they trying to stop us from using the correct tool for double-slit experiments, why was this video published?
There's nothing wrong with the laser. The experiment is exposing our assumption that the interaction of the detector and the field is quantised. If you can produce a detection event with less than a quantum of energy it can't be.
I struggled with this for many years until someone offered an explanation that really made sense, and this experiment is a perfect illustration of what I was told: Forget about photons. Just think about light in terms of classical EM theory, with the following additions 1.) Energy is added to or taken away from the classical EM wave only in discreet amounts 2.) When the wave has only a single photon's worth of energy, there is the issue of figuring out where it will be detected (since the wave can't deposit fractional hv to many places over a surface, for example). It's simple: it just follows the Born rule of quantum mechanics. The probability of a single photon's energy being detected at a particular spot is equal to the square of the wave(function) amplitude at that spot. Bing bong that's it. For large numbers of photons, this will reproduce classical EM. 3.) Thinking too hard about how the detection probability "works" will always give counter-intuitive and confusing results. That's just QM. Just think of things in terms of classical EM, with going into/out of the wave in quantized amounts, with the location of detection being probabilistic according to QM. Thinking about it this way, it is very hard (impossible?) to conceive of an experiment where a high-intensity EM field produces an interference pattern while a "single-photon" intensity field does not.
Ah, interesting. In physics labs we did a double-slit (or maybe diffraction grating?) experiment with both incandescent and laser light. The laser light had a proper pattern at any path difference, while the incandescent lamp would only have a diffraction pattern at path difference 0, as only then would all of the harmonics line up. But a monochromatic incoherent light source? I hadn’t thought about it, if it would really give a different result to a coherent source like a laser then that would be rather interesting to see. Of course, coherence is relative, a nice gas or diode laser might be incoherent enough at a few metres (or maybe kilometres). A spool of optical fibre would make things a bit easier. And yes, in general I treat all systems as classical systems up until where a quantum interaction happens, like with the CCD. I do not understand Stern Gerlach.
@@josephcoon5809 I meant that, in any optical system, you assume the light is behaving as a wave until the point at which it interacts with something in a quantum manner. Not on an system-by-system basis, but inside each system.
I came here from your later coherence series, where you attempted to model quantized emission and absorption processes with speakers and a string. I took quantum chem in college and did alright with the problem solving, equation manipulating aspects, but I never felt like I had an analogy for it that made it all any less mysterious. Also, my dad was always really into musical instrument acoustics, and your beat frequency insight brought back all his old explanations from my childhood (standing waves in open/closed tubes with cylindrical/conical bores, etc.) and connected it to the old chem diagrams, and to my current interest in radio as well. You've really provoked me to a lot of thought this past week, thank you. Ok, physics crank time: You and others have articulated this idea that "light propagates like a wave but interacts like a particle." Could it be that light interacts with matter only mostly like a particle, but rarely also like a wave? In this video it seems like there are two forms of matter that interact with light in a seemingly unquantized way, at least as far as its amplitude is concerned. One is the laser itself (since apparently spontaneous emissions won't interfere) and the other is the series of attenuating filters, which can apparently attenuate the wave to subphoton amplitudes. If light can be emitted without quantization and then attenuated without quantization, then could it be absorbed without quantization too, for subphoton-energy detection? Experimentally, I'm imagining shining very attenuated coherent light into the partially-silvered end of a laser at its pump frequency, to cause population inversion, and then somehow detecting the lower frequency transitions at the lasing frequency. If you are using high frequency photons to stimulate the emission of lower frequency ones, could you then cause more lasing-frequency detection events than there are pump-frequency photons to detect? For example, if the pump transition is between energy levels A->C, and the mirror resonator somehow lases at both C->B and B->A, then you would be producing two photons for every input photon, and possibly measuring the amplitude of the original beam at a greater resolution than the process that produced it. In other words, can a laser deputized as a detector be used to convert high-frequency, low-amplitude signals into low-frequency, high-amplitude ones for easy detection? That's the idea anyway. If I'm just the crank in the comments, I want someone to set me straight! Either way, my spontaneous ideations are only proof of how stimulating this channel's content has been. Appreciate your work Jeroen!
@@c.chouinard3282 An indoctrinated person sees things which do not exist and they cannot see things which do exist. You have been indoctrinated to believe photons exist, that's why you can't see that every slit and double slit experiment shows that lights is always waves, never particles. The photo-electric effect also has explanations which have nothing to do with electromagnetic radiation as "particles". Photons do not exist.
@@dreamdiction Correct, and there is a lot in modern Physics that is much more associated with religious dogma than actual physics. Like the other "theories" of Einstein, SR and GR. His explanation of the Photoelectric effect is clearly also just as wrong.
Thanks, this made much more sense than the 'single' photon explanations. The presumption that a laser fires off a single photon is just wrong. It is a continuous stream.
Who would even assume that? I got so confused when that part of the video started, like obviously it's not a single photon, how would you even be able to feasibly detect one single photon
I think the mistake you made, was only considering that the light is quantized, forgetting that it is also a wave, at the same time. . . Or something like that. ;) It seemed odd to me from the start that you would be able to split a single photon, because that should logically not be possible. So something seemed fishy about the single photon claim... as you eventually found out. Sometimes, I guess, we take things for granted, and miss something important. But as long as we eventually figure it out, it is science at work. ♥
You can split a single photon in the same way you can split a single electron: The particle isn't split, its probability distribution function is split. The probability distribution function can be divided arbitrarily, even for single particles.
You’re going to have your mind blown. A single photon can indeed “split” and travel multiple paths at the same time and interfere with itself. This is what the double slit experiment shows when you do it one photon at a time.
Dude, love your videos, especially the endings. Unfortunately, I dont remember 1985 so well: as I was 15, in high school, listening to lots of Led Zeppelin, Black Sabbath and a very new band, named Metallica. You get the point. But somehow we grew up to be Photonics Engineers!? In 1985 my parents thought I would be an absolute FAILURE. My dad (who was a surgeon) said to me: When in the city, how does one find an engineer? call a taxi. What does one say to a civil engineer? One BigMac, no pickles, large diet coke and xtra ketchup for my french fries please ... What does one say to a Photonics Engineer (which is far more technical) = I'd like a double chai latte, soy milk, no foam and served in a hand-made clay cup made by a guy with dread-locks wearing an organic flax shirt, while listening to Bob Marley, please... And an especial thanks for addressing my ignorant question regarding quantum mechanics and the splitting of a single photon by your beam splitters... Now I have the answer. I am 53, engineer, working for a major brand name camera company that every specialist knows, and still learning new things from your videos. I am grateful. Why were my professors not even half this good at explaining things? Is it possible, they didnt know and just repeated dogma?
@@marcelzuziak9954 The more you talk, the more of a joke you look like. When your philosophy (or model of reality) can predict something that quantum electrodynamics cannot predict (or even explain completely) and that can then be validated by experiment, you can call QED a waste of time and BS. Until then you are just another fringe lunatic.
@@bogywankenobi3959 1st of all: I do not talk I write...if U can read and think, but it is very doubtful. and 2nd which confirms the 1st: my human spirit can predict things and events anything that quantum electrodynamics cannot predict (or even explain completely). So please stay in your pseudo reality and do not pull nobody else into it. Period.
"on all counts" except maybe judging feinman so harshly, from the admittedly EXTREMELY LITTLE of him I know, he seemed genuine and honest in his demarch, and he appeared to me to have been rather speculated with high uncertainty in what he was saying rather than just declared that's how things were, which of course which was the case would warrant your opinion of him fully considering the contents
Could we all agree that photons don't exist? Why do we keep going down that street? A field is not a point source. Light is a field, not a bunch of BBs flying all over the place.
Thanks -I always hate the standard explanation taught in books of the slit experiment. I was just a tech in an engineering (ICs) but I was always the one to set up or design experiments to prove the design of this or that and measure it. The light detectors cause artifacts in the data because of the way they worked, this lead to hours of auguring about things like what in your video. One guy from MIT the head designer was the only one that support my data or see the other artifact of setup. Your is the best sofar.
y'know that you're not observing interference between one and the same photon but from stream of them? a lot of photons will create interference in your experiment regardless of delta-length of paths taken by the beam. just time for light to travel would be different. if you would have fast enough camera to observe the screen you would see first: a round circle without interference and then after some time that circle would be having an interference pattern on it because second wave have arrived. So i think you explanation of experiment completely wrong based on 2 things: 1. You are not measuring single photons, 2. You aren't observing interference from a photon interacting on itself
Excellent video. I have struggled with the understanding of light for years. Although I still don’t fully understand the totality of lights nature, your video explanation gives me a closer understanding! Thank you!
Wow! Thanks for making this video!!!! Now I get this experiment and its results!!!!! (And it only took 50 years of looking!) What I positively hate in Physics is everybody showing and explaining stuff, and always leaving out some pivotal information. It seems to take decades for each question one has, before, at random, one stumbles on it.
That is a beautiful demonstration of what a quantum field actually means. EM is a field, but its measurable/interaction properties are quantized. We call "photon" an specific interaction in which a quantized amount of energy is transferred to/from the EM quantum field.
Just this week I did an experiment that more-or-less measures the length of a photon. The source was a germanium vacancy defect in diamond, which emits single photons at a wavelength of 602 nm - we can confirm that this single defect emits single photons using the Hanbury-Brown & Twiss setup, a straightforward experiment in itself. Anyway the photon length is extracted from a measurement of the first order coherence, which you can obtain by doing one photon interference. Excite the defect so that it emits photons, then direct those photons through a Michelson interferometer that has a fine-adjustable short arm and course-adjustable long arm. The output of the interferometer goes to an avalanche photodiode which counts single photons. Fix the length of the long arm, then scan the short arm over a range of about 10 micron, this will produce an intensity oscillation (i.e. an oscillation in the rate of photons counted by the detector, which was averaging around 5 thousand counts per second) due to the single photon interfering with itself. The intensity oscillation has a certain visibility (ratio of oscillaiton amplitude to average intensity), and you record this visibility for many displacements of the long arm over a range of a few centimetres. The shape of all the visibility data has a gaussian distribution, and the full width half maximum of this distribution is essentially the length of the photon. In my case, the ensemble of observations which produced the visibility data yielded a length of about 3 cm.
I've always kept in mind how one lecturer described it to me: _light propagates like a wave and interacts like a particle._ You can't go too far wrong with that. Glad to see the video comes to the same conclusion.
Exactly my thought, but the double slit explanations had me confused all these years
@@kaushalsuvarna5156 , Following the same line of reasoning, I've always thought of it is as a wave passing through the two slits, and a photon detected at the screen. That dispenses with any question of "which slit the photon passed through" -- there's no photon until it is detected. And the wave propagation instantly answers the question of why the interference disappears when you block one slit. The wave has spatial extent, while the photon is localised. Of course, it doesn't explain how we get from extended probability wave to localised particle, but we just have to live with that weirdness.
This description (the one given by the lecturer you heard) implies that most non-technical presentations of the famous double-slit experiment are based on incorrect reasoning.
Is that your opinion?
When you realize that the so called particle is still a wave... 'cause everything is wavy (de Brouglei matter waves)
How big is a visible photon? A good question, in particular, better choice of the word visible. How big is an audible sound or an electromagnetic wave? Alas, physicists must get their acts together and know what they're talking about. Are these pairs of concepts, light and visible light, photon and visible photon, etc., identical? Even better, the moon and the visible moon, the sun and the visible sun, are these two the same? Would you agree that the visible sun is much, much, and much bigger than the actual sun? So, physicists don't even know what the sun and the visible sun are or the difference between them because physicists don't distinguish them or don't have a definition for both.
One of the most original, well spoken, informative and amazing videos in TH-cam. 1 million likes by me!
@@schmetterling4477 what is the wrong part with the creators video? Pls explain. Take in consideration that for a photon travelling at C, time doesn't exist. Anthropic notions of space, size and time fail at both extremes of our understanding of the universe both at extremely small and insanely huge scales!
But how big is a like?
I've been searching over a year for a video like this, that actually performs the experiment and shows the results, not just an animation. Wonderful. Subscribed.
You can perform these simple wave experiments at home. You can even do it in your bathtub. Waves are waves.
Searching for over a year? Where?
@@SchmelvinMoyvillemy guess.
he’s been searching in his pocket pool sized pants
@@kamakaziozzie3038 got his ass
@@schmetterling4477 Yeah but I can't perform a single photon experiment at home. Waves might be waves, but light isn't just a wave.
This is one of the best science videos on TH-cam. I cannot imagine how much time, work and thinking have gone into making this amazing video. For me, this is a better way of communicating science to people than publishing in Nature or Science.
Thank you very much. Keep up the good work of educating people like me. Thanks.
Couldn't agree further, you're totally right!
I totally agree, but you should DEFINITELY publish if you can, like peer review is one of the staples of modern science
@@smileyp4535 Peer review is a very nice concept and I fully stand behind it in principle. However, the way it is actually done is very flawed, as is the current practice of academic publishing in general. We should think about new ways to do this. Ways that don't have universities and society at large ripped off by publishing companies, that don't allow (and almost force) scientists to engage in dirty tricks exploiting the peer review process and that don't produce incredibly skewed metrics for gauging academic success.
@@bladdnun3016 it's all about the money, once journals become public and knowledge is free and we move past capitalism overall then there will a skyrocketing boost to scientific research, development and progress
The virtue of this video is not that it answered any questions, but that it intelligently and honestly raised some interesting ones, and showed how hard it is to do these kinds of experiments. Thanks for providing so much food for thought.
Easy to do, easy to see what happened, impossible to know why.
:-/
I love your silliness. It feels like I'm watching a 1940s scientist instead of a post 2000s one. There's a more human touch on this channel than on a lot of others, while still having legitimate science and engineering.
Elly Gatuno ; es muy facil calificar mal a quien presenta enfoques diferentes en materias conocidas. ? Tú haz hecho alguna aportación para ampliar el entendimiento de algún tema científico? Si no lo haz hecho, hazlo
@@jorgelopezvargas7251 don't know to use translator?
Human's way of thinking that we are trying to abandon by starting our belief into theory that is a blind path ?
Instead of assuming that photon behaves naturally when we dont look at it and starts being chaotic when we start looking at it, lets start thinking logically and on the base of experiments that we actually can conduct.
I love it! I never knew that coherent light would have additional assumptions compared to spontaneous emission in interference experiments. Maybe light really is a wave. The "duality" certainly seems less 50/50 and more like a wave with some extra features. Thanks so much for your videos.
Thanks Ben, I was aware of the fact that coherent light is essentially different, but because of quantization I thought "a photon is a photon".Which evidently is not the case. I used a more classical depiction here with the EM field as leading, because I figured it would make more sense to most people than dishing up a Hamiltonian.
@@HuygensOptics You know how good your videos are, when even Ben learns something from them. Thank you both for such wonderful videos!
@Michael Bishop A very neat way to see how classical thinking is not a sufficient explanation of a quantum effect. Particularly liked his realization that the quantization of energy (observable eigenvalue of the field state) is distinct from the continuous and extended wave function of the photon (a photon created around the big bang can still be detected today across billions of light-years). This is truly a quality channel!
@Michael Bishop "Segues."
@@HuygensOptics You have not yet reached the fun part of duality :)
You only presented the argument for the wave side.
Instead of attenuating the beam with grey filters, use a sequence of beam-splitters to see how many times you can split light before its coherence length is reduced so much that it destroy the interference.
To see the particle side argument, use beam splitter and show that when you split a single photon,
it is detected either left or right but never on both side simultaneously.
“Let’s not keep you in the dark any longer” ..very light on your puns there , really brightens my day.
I see what you did there
@@karlkarlsson9126 I’ll switch off the light on my way out
Wow. A logically consistent and scientifically consistent explanation of quantum mechanics. I've had trouble fully understanding the double slit phenomenon for years and now I suddenly think, "well duh, of course it works that way. It's obvious." You're an incredible teacher sir.
If you think you have anything that even vaguely resembles an answer, please share it with the world.
@@jamesmoran7511 Blue on black, tears on a river, push comes to shove, it don't mean much, joker on jack, match on fire, cold on ice, a dead man's touch.
This is the phase of QED pedagogy known as Socrates' Nutpunch. By this time, the OP has no doubt experienced several similar delusional epiphanies, followed by the inevitable complete collapse of understanding in the face of the next paradoxical twist. This is the only trajectory possible. No disrespect intended, and I agree with the sentiment. We've all been there.
Look, it's a VR
@@amarissimus29 lots of words, yet you say nothing.
Hello!
Grad student working in quantum optics here. Great video!
The coherence length of a photon is the same coherence length as the beam. Single photon experiments can be done with kilometers of distance between the photons, given a sufficiently coherent laser. The explanation you have given is spot on.
Also, the attenuation method is not reliable to produce only single photons states. You're still in the right range, but the resulting beam will be "bunched", where you have a high probability of two-photon events. (think Bose-Einstein statistics) Either way, you're actually measuring the interference of the photons with your experiments, even if they are bunched up.
Generating single photon states is an area of ongoing research, but the main methods are 1) quantum dots, or 2) SPDC single photon heralding. Both of those require expensive equipment. The second method is totally attainable if you can get a single photon detector second hand from somewhere on the cheap. They tend to be very expensive.
Another interesting avenue to get single photons would be the SPDC part, where you could generate photon pairs from a single pump photon through interaction with a nonlinear cristal (like the ones found in green laser pointers). If you know about second harmonic generation, it's basically that process in reverse. Since you have photolithography equipment, you could DIY produce periodically poled materials that would even allow for colinear polarisation-entangled photon pairs to be generated.
Now this seems like a neat path to explore.
This is fascinating - when you say that single photon experiments can have kilometers of coherence, are you discussing this same (or an equivalent) self-interaction experiment? As in, if this had used a single-photon source, would the result have been the same, or how far could the split-off beam have been retracted before interference faded?
Wow, this is was a super concise and delightful presentation on something I've often seen ignored in modern POPSCI TH-cam. You took a stab at explaining something I always imagined as black magic and I left with a greater intuition and understanding of something I don't even use day to day in my work. However it did make me think differently about EM in general, which is an amazing accomplishment for a such a short video.
I am a variant of Francis Bacon - I've taken all knowledge to be in my periphery... I find that the information of the Internet (our modern Library) is wonderful and strange.
Now if I ever could focus and get just a few interests instead of 'all', I would pursue the knowledge through University studies and research at a institute or an other; for now YT will suffice for my scatter brain...
Well said. I agree 100%
@@RobLocksley yeah, agreed, I feel the same. But when you choose an interest and go to university, you will be told to watch yt videos as your 'reading' assignments.
Yeah. This video confirmed to me that amount of light smaller than a photon exists even if it cannot be measured. You just need to add a bit more energy and boom it 'statictically' materialises. It becomes a 'particle' and sets the detector off. Black magic or what?
@@echelonrank3927 You don't need to add a bit more energy as measured by the power of the beam, you just need to add a bit more time (as long as the h•c÷𝜆 value is enough to exceed the energy level that has to be excited).
So there are two energies we're dealing with here. The energy of the light beam itself, in watts, and the energy of individual photons as calculated by the photoelectric effect equation, h•c÷𝜆. This may also be written E = hv (that's a Greek letter "nu", not a vee), where v = c÷𝜆, and with dimensions of T^-1, or inverse time, represents frequency. Old joke: What's new? Cee over lambda.
Just because I can give that explanation, above, doesn't mean that I have any deeper understanding of this process.
Excellent video, this is the first time I've listened to such a clear explanation in such a short time of the seemingly paradoxical behavior of photons. The graphics and narrative are just what is needed to explain this topic in a super-efficient way. Thanks so much for sharing!
Ìiùuĥù
I REALLY like the calm way you present these awesome experiments! ;) A nice contrast to show and shine channels like many others...
I've watched all your videos after discovering your channel two weeks a go. I'm addicted! Your explanations are superb!
Aha. So you are the guy driving up the views.
@@HuygensOptics me too. This channel is a hidden gem. I discovered it via one of the later videos and got to the part where you said, "... with my DIY wafer photo-lithography stepper", and it was a bit of a record scratch moment, "wait, what did he just say?". I paused that video and immediately switched to the wafer stepper construction and watched everything in order from there. You should create a Patreon page so that we can help fund more experiments.
@@HuygensOptics I recently found your channel too, via the spirit level video. I subscribed straight away, it’s that good.
Cheers.
Finally, algorithms are bringing good content to viewers
I discovered few hours ago, watched all the stepper videos lol
What a wonderful experiment and presentation. As a “radio person” the concept of a Photon has never been easy to swallow. I can appreciate that an emission of light is produced as a quantum event (photon) but from there the electromagnetic field created propagates without quanta limitations just as your experiment demonstrates. The same quanta effect applies to detection or attenuation as you describe so we end up detecting a photon from the wave. It is time for a resurgence in science to reconsider what a photon is and how light and radio waves propagate and I think you are on to it. Perhaps we need to set up quantum de- radicalisation classes for Photon believers. Well done.
Wow! Awesome to see the double-split actually demonstrated like this, whereas most discussions just illustrate it with graphics. Makes it seem even more mind blowing.
Agreed 100%! It is so much more instructive to see the experiment itself than just some graphics simulating it.
Graphic meaning.......of or relating to a pictoral representation,its a graphic.Your whole interaction with your phone or computer is a graphic.The law of the phantogram states that anything relative in size to your observation,is relative in size to the human condition.Wave mechanics......This is one of the most proven themes inscience.
You made my day, i cracked my head on multiple books but none give that much i sight. You really gave beautiful insights and you will always be remembered for years for spreading this level of knowledge of optics
I love it when you tackle material that no one dares to tackle and present it in an accessible way
@@schmetterling4477 representation they give you in high school is aimed at a very wide audience (that generally won't need this knowledge for their career in the future) and it's very lopsided and simplified. For example, they don't give you the deep connection of the wave function of a photon with its properties as a particle and they don't tell you anything at all about the Dirac equation and how the wave function experiences local time. And yes, once the wave function of a photon collapses and its position is measured, it indeed does localize to a point, so in this sense they can have a perfectly well-defined position (which's also emphasized in the video). They only explain it properly at uni's fundamental physics course.
@@schmetterling4477 photons don't have a particle-like wave function because they have 0 rest mass. But they do obey the same laws in their relativistic limit as do particles.
"Collapse doesn't exist" in everettian interpretation, but the way wave functions entangle in the multi-universe interpretation by definition of word "interpretation" act exactly the same way how this happens in copenhagen interpretation with the wave function collapse.
@@schmetterling4477 I mean sure, you can keep on being a judgemental edgelord who obviously knows better than Everett, but then if you want people to start taking you seriously, it's probably worth achieving something first using your vision (as in, other than just criticizing).
It absolutely does not matter how much you hate a theory if it actually works.
@@schmetterling4477 what makes you think that reading literature automatically gives you any understanding? You apparently read something about MWI that somehow gave you the confidence to judge that it's "complete nonsense" which implies that you're either a future nobel prize winner or just a classic edgelord who's full of himself and jumps on the internet to teach others.
Beautiful!
Gravitational lensing, in particular, Einstein rings, is an example where the size of the photon is greater than the size of the galaxy.
In other words, the distributed chunks of masses in the galaxy (stars, etc) gravitationally interacts with the very distant photon's wave function to make it become focused on a telescope here on Earth.
In fact, due to the low luminescence, you can argue that the ring is a bunch of single photon interference experiments!
"Gravitational lensing, in particular, Einstein rings, is an example where the size of the photon is greater than the size of the galaxy. "
reading comments this stupid is kind of depressing
Don't worry . They'll know when it's time
It helps to think of the EM field as the propability to encounter a photon over any point in time & space. The energy at this point is the propability * the energy of the Photon. Since the ND Filter is randomly removing photons and not removing exactly every nth, the propability is reduced by a constat factor and remains constant. It's this propability field that interferes with itself. When measuring (in the sensor) photons will be measured distributed according to this propability field.
Very good, if you can wrap your head around it. I was taught it that way after I asked too many "but why" questions to my father, while he was teaching me about uncertainty, because it's an all encompassing way of viewing the ideas, that can't be further "but why"'d, which to me is a good wrap up
This is how I understand it - from reading and watching Feynman's explanations. As to how this probability "field" relates to physical space as we conceive it, I believe Feynman says: Nobody knows!
re: "It helps to think of the EM field as the propability to encounter a photon over any point in time & space. "
Stated impossibility; EM **is** photon, and, in 3D space a propagating wave or waves DO NOT/does not affect propagating waves, i.e. photons!
Antenna theory with EM waves is adequate for all practical purposes in most of optics and all of electronics, but the rabbit hole is far deeper than this: Photons are probability wave functions that take all possible paths until they interact with something and collapse in one place even if they have had time to stretch over the entire universe before that happens, as his slit experiment shows and you also point out. What is worse, is when you also consider the rest of physics. Special Relativity says that particles moving at the speed of light are completely length contracted, so a Photon is flat and 2 dimensional and to the photon times doesn't pass, so to it, interaction is instant regardless of how far it has travelled and to it, the Universe has no length and by that no volume and time has passed instantly! This is not only a theoretical curiosity, but a reality as real as our way of perceiving the Universe. So the question is: Did the Universe really expand, or is it only to us meat computers that perceive space time as a "place"? Going deeper (or taking a theoretical step back): If you look into diffraction you realize that photons as particles are not needed here either for imaging, diffraction patterns alone give the illusion of particles coming from different directions creating an image on a retina or image sensor. A single photon does not carry other information than colour. Without interference from objects like a lens or a pinhole or other photons, there can be no image, i.e. no apparent direction that photon is coming from. Finally, as a curiosity, acoustics share 2 properties with photons however sound extends in time, so it has also a time diffraction based on its duration, so the shorter it is, the less precise its frequency can be defined. It might be obvious looking at a sinusoidal pressure graph of a note, but you can also hear it it. Very short notes on the same instrument or tone generator sound more rough and that roughness never goes completely away, regardless of how long you play the note, so to make a perfect sinusoidal clear note, it has to be eternal! That means that the sound "knows" it is being truncated sometime in the future before you lift the finger from the key! This roughness effect can also be seen in radio waves, where side bands extends further and increase in numbers from the center frequency, the further you increase the modulation or data rate. Maybe the conclusion to all this is that any type of wave regardless of propagation medium, share quantum properties like elementary particles, even sound waves that usually are considered purely in the realm of classical physics?
Fantastic presentation. I have been studying optical phenomena for many years (as an amateur) and thought I was alone in wondering how long a photon might be. Also, a great explanation as to the reduction in EM passing through filters without violating Planks law due it to being coherent & unconstrained by quantisation.
A photon, by definition, IS a quantum particle. For those not familiar, exploring QED or Quantum Electrodynamics. Feynman diagrams, and the double slit experiment (the origin of the go Copenhagen Interpretation of the double slit experiment.....
WARNING- this may lead to many journeys down multiple rabbit holes....
I concur with Ben. Amazing! I was clueless to the differences between a photon from spontaneous emission vs. coherent from the laser. I will have to rethink my experiments from now on. I have been playing with interferometry since high school in the 80's when I first got my hands on a HNe laser salvaged from a supermarket scanner and first surface mirror fragments from an overhead projector. Added an interferometer to a vertical seismometer with a 20lb lead mass and then monitored the lunar tidal pull over a few days. Been a Zealot for interferometers ever since.
"Added an interferometer to a vertical seismometer with a 20lb lead mass and then monitored the lunar tidal pull over a few days." I am impressed.
I would have loved to see the results of the experiment with the florescent light. The insight about the continuous nature of the laser beam was very interesting, I wonder why I don't here that talked about more when people describe these experiments.
Yes please. I know this is quite old, but please to do the experiment with some sort of non-coherent light source. I don't know if color filters can be sufficiently tight (meaning limit to a small enough wave length range) to make this experiment meaningful. Maybe you would need to use a prism to filter the light source? Or would a "gel" be accurate enough?
I would absolutely love to see the fluorescent light source experiment too!
@@thorwaldjohanson2526 and do you know how a fluorescent light works??
@@bobm4378yes?! Why do you ask?
@@thorwaldjohanson2526 is it this??
Fluorescent tubes are filled with low pressure mercury, when an electric current is passed through, the electrons in mercury are excited and move to a high energy level, this high level state is unstable and so the electron moves back to its original state, but on doing so, it emits an electromagnetic wave with energy equivalent the difference in energy level. This is UV light !!! and the electrons in the phosphor coating inside the fluorescent tube are excited, and releases visible light(that is NOT very 'spectrum pure' ) when the electrons return to its original energy state, which provides the glow in fluorescent lights.
This is one of the best videos on TH-cam on the subject, I’ve reference people to this video all the time. An incredible number of people have the misunderstanding that the EM field is quantized. The photon did not go through one slot or the other, the wavefront went through both. then it is just the probability of detection there’s no magic science about this.
Modern physicists often don't really care about how this kind of stuff works. If the math works out they are happy. That's why I love your approach to try and develop an intuitive feel for it. Great explanation. Can't wait to see the experiment again with a more suitable beam attenuation!
That's pretty cool man. When it comes to extrapolating certain information from results or trying to infer a mechanism, it usually ends up necessitating at least a dozen different, highly controlled experiments all with their own interpretations as well. It usually makes me feel like we are trying to see the universe through a single pinhole in a 1 square mile cloth.
Hopefully, our curiosity and individuality can be maintained after our physical death so we can prove for answers to these questions. In fact, I'd like to talk with Werner Heisenberg about some of these newer findings but I feel like he'd just say "uh, I don't know." Fitting for an uncertain bastard...
Thank you for explaining your double slit experiment and for correcting your original explanation.
The best analogy I have read is this: Imagine disturbances in the EM field (which are by definition what photons are) as transverse water waves that ripple across the top of a completely still, shallow pond. Now you calculate exactly the amount of energy required to transfer one quanta to that field, lets say that's by using a small wooden sphere that you drop from exactly the right height so that its interaction with the water takes all of its energy (which is wxactly equal to one quantum) and converts it into a circular wave that spreads out from the point of impact (which would leave the wooden sphere sitting completely still on the surface of the water, with ripples of various sizes spreading away from it, carrying its energy away in all possible directions).
Now imagine that there are other identical wooden spheres, floating completely motionless, on the top of the still pond. They are spaced few and far between, at random places on the pond, but all relatively far from the point where the wave is generated. More precisely, the radial distance, as measured via a straight line from the closest floating sphere, through the origin (the point where you are dropping a sphere and generating the wave) to the next closest floating wooden sphere, is long enough so that information traveling at the speed of light would take far longer to travel between them, than the time difference that exists from when the expanding wave 'hits' the first sphere to when it will 'hit' the second floating wooden sphere. This is so that once the wave reaches the closest sphere, the sphere directly opposite to it across the circle would have no way of 'knowing' when or if the wave has interacted with anything yet by the time the wave gets to it as well.
After all that setup (sorry for how long winded and convoluted my explanation is. I know my English is not great, but I'm trying my best.), here is the interesting part:
Imagine repeating the experiment multiple times, each time with the same setup and a completely still water surface. Each and every time after you drop the sphere, a circular wave spreads out from the impact point, traveling at a constant wave speed. However, once it gets to the first (i.e. radially closest) floating wooden sphere, one of 2 things happen.
Sometimes the wave hits the sphere without it recoiling at all. It doesn't absorb any energy and doesn't move a single millimeter, but it does influence the shape of the wave going past it, diffracting and reflecting it without otherwise seemingly interacting at all.
Other times, something even stranger happens. As the wave reaches the floating sphere, the whole wave instantly disappears from the entire pond all at once. It doesn't send out information that makes the wave disappear at the speed of light from the location of interaction. No, seemingly violating Einstein's theory of relativity (that is, "Spooky action at a distance", even without any special entangled states), it all vanishes all at once and, simultaneously, *ALL* of the energy that went into creating the original wave gets transferred into the single wooden sphere that the wave interacted with, sending it flying up into the air to *exactly* the same height that the original wooden sphere was dropped from.
This is sometimes referred to more succinctly like so: Imagine dropping a wooden plank into a body of water, with other identical planks floating on top of the water, and seeing the waves it created suddenly disappearing whilst instantly transferring *all* of the energy of the spread out wave into one single plank, sending it shooting up into the air precisely just as high as the height that the original plank was dropped from.
This is the essence of the weirdness. The EM wave could be thought of as 'guiding' where the photon 'goes' (i.e. Pilot Wave Theory), but still, how do you reconcile the fact that a single-photon-strength 'light wave' could have been spreading out for thousands of light years only to finally reach two atoms (also spaced thousands of light years apart) at the *exact* same distance with one atom suddenly, *instantly* gaining *all* of the energy contained in that wave, while the second atom never gets *any* information about the wave at all.
I would say that it is because the original model doesn’t accurately depict what is going on.
The initial wave induced an oscillation in every sphere it interacts with. Each successive sphere creates a new circular wave that exists simultaneously with the original wave minus the portion absorbed to cause the next sphere to oscillate. Every sphere that oscillates creates a wave based on the energy it absorbed but converted into a smaller amplitude wave spread out over the surface of the new circular wave. Each successive wave induces an oscillation in other spheres in all directions. So while the original wave front propagates, multiple wave fronts created by every other sphere interferes with it in multiple locations. Every sphere creates its own wave front.
I would set it up with acoustics rather than hydrodynamics. If you use harmonically similar spheres, you would more closely resemble the absorption, oscillation inducement, and transmission of new waves that you see in the Raleigh Scattering of light waves in an optically transparent material. It is difficult to replicate that effect with wooden spheres and water. Perhaps metal disks of the same material and size floating between two transparent liquids of different specific gravities and different colors so you can easily see the interface between the liquids. If you set up a strobe light that forms a plane which intersects perpendicularly with the the interface, you should be able to adjust the pulse rate of the strobe to visually “freeze” the interference pattern created in the interface at any location in the system. By moving the strobe beam around, you should see how the wave evolves over time/distance from the original oscillation and all subsequent oscillations generated by sympathetic harmonic regeneration of each successive sphere.
At least, that’s what I imagine.
This was similar to how I visualized it in my head as well and I love the detailed explanation.
Set a single pulse of light off at the center of a large sphere of empty space and envision the spherical wavefront expanding at lightspeed in all directions, ready to interact with anything, and have only a few randomly spaced "spheres" floating different distances from the center that can absorb that light energy.
If these spheres were, say, atoms that could absorb only a specific quantized amount of energy, and that is precisely how much you set off in the center, then presumably whichever atom encountered the wavefront first would absorb the entirety of the energy leaving nothing for other atoms to absorb lest you violate the conservation of energy.
Much like the one wooden ball suddenly absorbing the entire wave. If the wooden ball were a quantum ball then I imagine that is how it would work.
It would then presumably decay from it's excited state releasing another wave in all directions for some other atom to interact with, but due to it's quantum nature it could only either absorb the whole wave, leaving no energy left in the wave anywhere else (in spite of it having expanded in all directions initially) or not interact with the wave at all.
Assuming it's closed and ignoring losses, if you just watched this system it could appear from the outside that a "photon" is just bouncing from one atom to the next closest one and you don't need the wave explanation at all.
But indeed to your point, why would one atom absorb the whole wave immediately and how could this occur?
In the real life example, wouldn't the available energy just fall off with distance and thus not match the needed quanta to be able to be absorbed at all? The wave would just pass all the balls and never get absorbed. Thus the example isn't a quantum system, the surface of the water is continuous and can take any energy value.
If you could, for example, construct an elliptical tank and drop one ball in at one focus and place the second ball at the second focus, the wave would reflect off the sides and come back together at the other focus at full strength and thus be able to be absorbed and return all the energy to the second ball. The probability of absorption would be higher where the wave is greatest and I think in a real example would be the only way you could get the second ball to absorb all the energy. It would be a cool experiment to see.
I love thinking about this stuff, thank you for your insightful post!
" how do you reconcile the fact that a single-photon-strength 'light wave' could have been spreading out for thousands of light years only to finally reach two atoms (also spaced thousands of light years apart) at the exact same distance with one atom suddenly, instantly gaining all of the energy contained in that wave, while the second atom never gets any information about the wave at all "
How about throwing away the assumption of locality ?
I prefer to think that this only happens probabilistic, so it doesn't matter which atom gets the wave, that is decided at random when the atom absorbs the energy, it could be even that for this single event both get the energy, this just happens with very little probability, effectively doubling the energy for that amount of time for that single event, but it is statistically conserved in the long run.
Basically, I break conservation of energy on best effort basis, for a small bit of time, but for longer times, it is statistically conserved.
@@deprivedoftrance 'lest you violate the conservation of energy" what's the problem with violating it for a single event if it is statistically conserved in the long run after more events ?
perhaps I'm presuming time is also quantized, it wouldn't be any problem if that was the case, the math would kind of work the same
If you consider time as quantized, you could define the outcome of the event even before it occurred, by the simple arrangement of the fields and the distances, and the end result when more than a single event occur would be impossible to differentiate by experimentation, even because you would to actually cause more events, sending the information back to the source to be able to even know what happened, so it would even out by definition, the moment you try to analyze the system, thus conservation of energy isn't violated, not cumulatively, only in that specific single time frame.
I don't see a problem with this approach.
Its not like the universe make computation errors that accumulate, the calculations are perfect (I presume), so statistically it would always even out in the next "frame". (basically, I disregarded the entire chaos "theory", as just an artifact of imprecise macroscopic experiments, and the fact that you can't know all the state of the system to avoid errors that accumulate, I basically consider it is not of nature)
An amazing video and props to you for explaining the possible issues with your experiment. Still very impressive to say the least. I spent a few months this past summer performing a very similar experiment in the quantum optics lab where I work as an undergraduate physics student. I used a 405nm coherent laser to pump an SPDC crystal to convert "one" 405nm photon into two 810nm photons. I then split these photons up using a beamsplitter and sent them on two different paths. One path was sent to a single photon detector which would convert these detections to electrical signals. The other path was sent across the lab onto another table where I used this as my source for the actual optics setup with a pricy Andor ICCD. The idea was to trigger the camera's intensifier at the moment I expected a photon to arrive. Without doing this, you will observe a lot of unwanted photons since the intensifier is on in between these single-photon events. So, you tell the camera "okay, I need you to expose when you get this signal from the one arm and you'll catch it simultaneously at the other table with the ICCD. Well.....Obviously, by the time the trigger signal would reach the camera from the single-photon detector, the photon that was sent across the table will have long since arrived at the sensor and you would miss its arrival. So, I delayed my source using a 50-meter fiber spool. This allowed the arrival of the "across the lab" photon to be LATER in time than the camera's trigger pulse (which can be delayed between each intensified instruction pulse to match when the source photon should arrive at the sensor). It was quite fascinating to get this setup working properly. When it was done, I think I was left with more questions than I had answers. I was able to determine these events within 5ns and have a lot of messy notes determining how I managed to find what time I expected this photon to arrive. Correlated photons are very strange and I'm not sure I'll ever fully understand what I was able to do through that experiment. It's a bit difficult to explain without writing a full paper on the experiment. It had already been performed previous to my doing so a full paper would have been a waste of time. I'm now using the setup to perform other experiments. I learned a tremendous amount and made A LOT of mistakes in the process before achieving the results I was looking for. Thanks so much for making this video. It's nice to see other's question and perform similar experiments --- and at home nonetheless! I'm looking forward to going through the rest of your vids. Cheers, Josh
This makes it about as simple and easy to understand as possible. Well done.
I'm an engineer and these videos always make me try to remember if what I learned matches the content. Frankly, one thing struck me, how is the field not quantized like a photon? How much of the field/wavelength is the photon? Serious questions. I'll never figure those out, I know my line of work will never take me there either. I'm just human with a finite lifespan. Sad we can never live long enough to know all the answers. Doubt we can remember them either if we knew all the answers.
This is a fascinating and well carried out experiment. Thank you for sharing this!
In the hope it might be of interest, I would like to share some words on the subject from Albert Einstein. In his publication on the photoelectric effect, he writes: "According to Maxwell's theory, for all purely electromagnetic phenomena ... the energy is to be understood as a continuous space function." "However, it is ... conceivable, that the theory…, which operates with continuous spatial functions, leads to contradictions with experience if it is applied to the phenomena of light generation and light transformation." "It now seems to me that the observations about black body radiation ... and the generation and transformation of light, ... are more understandable under the assumption that the energy of light is discontinuously distributed in space." ( This is my own translation from German to English. So, please handle with care! )
Mathematically he treats the electro magnetic field like an "ideal gas" of photons, but these only appear during the transformation of energy. So, during propagation light acts like a wave, during emission and absorption it acts like a particle. And those particles, have no extension.
this is a fair assumption by him but it's wrong (or maybe it's true, but that would imply a near fractal universe)
quantum field theory is also wrong but for other reasons, einstein was just likening it to something he was familiar with, the behavior of gasses that are large compound structures of individual atoms, meanwhile QTR is just pants on heads retardation that should be ignored and ridiculed lest time and braincells are certain to be lost
You narrate these videos as if you were a professional narrator. It is pretty cool. I have the impression I am watching one of these older (and better) science documentaries.
Sounds to me like a good excuse to invest in a femtosecond laser :P
yes pls XD and adjust distance difference till interference appears/disappears XD
@@vvs6476 Taking the view that as a quanta, photons experience zero time; and that the field can hold fractional values... you'll find that the photon is always the exact size of the detector; and it will continue to do so until you reach the Hubble volume.
A nanosecond laser would be enough given the path length of his setup. A 905nm pulsed laser diode with a 2ns pulse width would do it. Not cheap, but a lot cheaper than a fs laser! Though his camera probably wouldn't detect that wavelength.
Add in a SPAD and picosecond precision Event Timer and you will be able to tell which path a photon took because you can compare travel times of individual photons.
@@vvs6476 you will find that the interference will disappear once the length of the laser burst is shorter than the longest distance traveled.
16:15 Will wait for results of the same experiment but with incandescent/halogen lamp as a source. Thanks for the video, btw)
Yes, I also want to know. In my undergrad physics I learned that a single photon will show the interference pattern with a double slit. But never was the path length issue discussed.
Yes! I would love to see that
Indeed, as I understand it you would also see interference... But this is QED, way over my head... There are actually many philosophical discussions about the Mach Zehnder interferometer.
I agree! the cardboard shielding did provide that high-tech look required for the experiment 👍
Amazing video with good explanation!
This confirms my old believe that we can have a continuous wave with infinitely small amplitude.
And all the discreteness comes from the detection side, when the sufficient amount of the energy is accumulated the detecting atom jumps to a higher level (and the detecting atom is the "size" of a photon).
By the way Plank was explaining exactly this, the light matter interaction, and the discreteness was assign to the EM wave! although you have the system with discrete levels on the matter side!
And I also think this applies not only to EM waves but to all matter waves.
One of the key sentences for me is the "particle event" takes out the energy out of the field in quantized portions. So it seems a lot easier to think of an excited field which allows interactions with probabilities correlating to the strength.
According to QM, which is not "physical". It's a math model, a model which may __Not__ be valid in all cases beyond which **observations** were made to write the model in 'math' form.
I think (likely wrong) that the "probabilistic" behaviors have more to do with our inability to measure things with sufficient precision. My reasoning is that things aren't "probabilistic" on the macro scale. Stuff is happening that we have no idea about...just a hunch.
@@rustyosgood5667 I believe what you think of is akin to a hidden-variable theory. There's a nice Wikipedia article on that. According to this article this interpretation implies non-locality. Whereas locality is normally one of the other key assumptions we make.
@@neur303 Thank you. I will go check that out. I also recently purchased "Quantum Mechanics and Experience" by David Albert...It is supposed to be pretty good.
I did read that article and was aware of the "Pilot Wave" theory. I do tend towards "deterministic" interpretations simply because they scale. Nondeterministic ones do not scale unless one claims (equally ridiculously, in my opinion) that the macro and micro worlds experience different "physics". I'd rather believe that the very act of engaging an electron or photon (to measure it) produces the same. In other words, there is no "there" there until you shove something in the way (like a silicon semiconductor, vapor, magnetic field or wall). Imagine that you have a matrix field of UV laser beams. Since they are UV, you can't see them. Now imagine that you place something with fluorescence (like a piece of paper with phosphor on it) in the field. You can suddenly see the field in the form of a dot. Now imagine that this field permeates the entire universe (spacetime) but unlike the UV lasers, it is the thing we call "Phosphor" when we "charge" the field to that level which corresponds to "Phosphor". The instant we turn on a light or collide "packets" of quanta, the field produces the photons or said "quanta" respectively. Prior to "charging" the field, there isn't any measurable thing. We don't know that this "field" is there because it is not visible...until you charge it. It could be like tiny lines or like soup. I can imagine fields within these fields that likewise, can't be seen or measured because we simply don't have the tools to do so. We can see that the universe extends to a similar scale in the "larger" direction. I find it hubris to think that when we scale it down, it stops at "Quanta" simply because that is the smallest thing we can detect. I somewhat understand the notion of gravity being a "force" but it doesn't need to be. You can imagine that there is no such thing and everything still works. We are falling towards the center of the earth which is falling towards the Sun which is falling towards the center of the galaxy etc... Spacetime is bending this "field". We can't see it, but it's there. We call it "Dark Matter". On the other hand, it could be that I am completely ignorant and these ideas have been put to rest long ago....I am almost certain this is the case. This is why I intend to read, read and read some more especially after I retire.
WoW 😳! Instantly in love with the content of your channel.😁👏👏👌👌
This is all pretty rigorous and heavy 🪨 or I should've said 'light' 🕯️ stuff 🧐🤓👌
This is a fantastic and clear explanation! Great!
Thanks Les. Hope this helps next time you take another laser apart. ;-)
I have to admit I really liked the original explanation that H. O. / Jerome just Kicked over lol. Still it does make me wonder how many experiments in physics don't take into account the possible 'Maximum size" of an effect or interaction ?
Leonard Susskind's conjecture of matter being a holographic projection from a 2D surface at the furthest extents of "the universe" kind of bothers me (even though he seems like a cool dude and very practical guy ~ much like Jerome. ). Somehow this much needed (atemporal) 2d surface disposed in three space + 1 of time - seems that it must lurk much closer to home (rather than at the "Edge" of the universe or some unfathomable 'Distance" away. ), but at a scale much closer to home not normally "experimented" for ? Well at least that's my totally unsubstantiated "Hunch" :-) Soooo many experiments are carried out at the scale of an optical table and the 4 walls of a lab ? Maybe we are missing something because of that more usual range of scale we choose experiment at just out of convenience.
+ I'm nor really sure how visible a 2D entity really is in the 3d universe we occupy especially if such entities are comparatively large - very faint energies over a large volume ? At least this experiment pulls some focus on that idea and helpful further explanation. + David Nadlinger chiming in was super nice / super helpful. [Something that has no Z in and XYZ universe shouldn't be "Visible" other than extremely vague changes in energy / radiation. ??].
What of the quantum eraser or delayed choice experiment where (superficially) the future seems to influence the past ? Does David Nadlinger's reasoning squash that as well ?
th-cam.com/video/0ui9ovrQuKE/w-d-xo.html
@@HuygensOptics it clears up a lot about its behaviour, certainly at the macroscopic level. I think perhaps a lot of text books overemphasize the quantum nature, but I suppose it's a case of choosing the correct model, for the situation.
@@extradimension7356 what "creates" distance in 3D space? That's the first Q for me as a layperson in physics
Great video! Light is fascinating. Please, can we see the experiment with a fluorescerende lamp as well??
truly amazed, u have solved the double slit puzzle, and discovered how and why light is a wave and behaves like a particle when obseved with your eye sensor or any other measuring device. a true scientist you are.
Your channel is amazing! Thank you for taking time out to share your knowledge!
I added quite a few videos of yours to my watch later. And I also subscribed so I can add future videos to watch later.
I quite enjoy the educational and engineering bits of your videos. During this winter semester I didn't manage to sign up for an optics course at university, but I feel like I am learning quite a bit here.
Always loved the idea of a photon trap. Perhaps in the future we manage to trap photos easier and keep them as souvenirs stuck in one point in space.
Is a photon a particle or wave is an older question in physics. And the answer is that a single photon behaves like a particle but more photos behave like a wave. Waves aren't single entity. But if even the dimmest light is continuous, this means that photon counting sensors (in astronomy for example) do just make up a threshold.
e: I still don't have an answer to what "destructive" interference does. You mentioned it in a different video a while ago - but this question leaves me wondering at times.
Thank you for this bit of validation and honesty. Most of the experts discussing the topic ruin it for me.
Many great scientific discoveries result from finding a glaring error in a previous theory and embracing the need to account for that error.
I always suspected that they are not sending single photons or electrons in the experimental double slit setups. When you are using filters, you are just reducing the amplitude of the light beam to below the single photon energy. The wave function is still continuous though and not a signal photon. To do a single photon would require a burst of energy with a start and stop time equal to the wavelength of the light used then a space of at least a wavelength of time. For red laser light at 635 nm, you would have to pulse the light at (635E-9/3E8) 2 Femto seconds on and 2 Femto seconds off or longer. The amount of energy in the photon should then make no difference. I think even if you used electrons instead of photons, you still would have a problem switching the electron beam on and off at a Peta Hertz. Giga Hertz oscillators we can do, maybe even a Tera hertz oscillator, but I don't think we can do a Peta Hertz oscillator yet. I also think that a photon just like an electron has a probability wave shell associated with it. I think that a traveling photon has a finite probability of being just about anywhere until it is detected and then the wave function is collapsed. When detected the photon wave function disappears and the energy packet position is detected. We are seeing the probability waves of the photon interfering with themselves causing the interference pattern. The dark spots in the interference pattern is where the probability of the photon being there is zero.
You are right about the basic point of bursts vs. continuous light. Fortunately, however, it is not necessary to make them quite as short as a single em field cycle, as you can space them out much further. For instance, one type of physical system that can produce "clean" single photons are single atoms. If you trap one of them and excite it with a laser pulse to some short-lived state, it will emit exactly one photon when it decays back down to the ground state. The photons will have an exponential profile in time, typically on the order of ~10 ns. Just make the space between the pulses exciting the atom much longer than that, and you have a series of "perfect" single photons.
You'll still observe interference in this case, but as you introduce a path length difference, the contrast will go down as the overlap of the ~10 ns exponential decay envelopes is reduced.
> but I don't think we can do a Peta Hertz oscillator yet
This is a tangent, but we actually _can_ produce such short pulses. You can get down into the single femtoseconds using mode-locked laser techniques. The trick here is to realise that a short pulse is a superposition of many frequencies, and arrange the many modes of a laser cavity so that they naturally overlap in the right way, rather than trying to actively switch anything on this time scale (which is indeed pretty much impossible). You can go even faster (attoseconds!) e.g. by high-harmonic generation techniques. Of course, confirming that you have made such pulses is quite a challenge by itself (see e.g. doi.org/10.1364%2FOE.25.027506).
This is what I've been saying for years that there is so much dishonesty in this experiment and to add to what you said , when they "observe" the interaction they fail to realize that inorder to observe it there has to be an interaction of some form inorder for us to "look" at what's going on and by "looking" we are sending light there and back in order to "see" what's going on and that's going to interfere with the light they are calling photons
@@DavidNadlinger great info. fyi the extra parenthesis at the end of your link breaks it
What is a non-traveling photon like?
In some mirror trap?
I would be interested in seeing the results of repeating the experiment with a high speed electronic shutter chopping the beam. this would probably require increasing the long path length, perhaps by sending the beam through a coil of fiber optic line.
yes!
You could use a sideways drone motor with the prop to "chop" the light beam, can get the small ones up to like 50,000 rpm.
@@rdizzy1 given that the beam travels at 300,000,000m/s, you can calculste how fast a 'chopper' would need to revolve in order to chop the beam into segments 1m long.
very provocative video, i like that you ask many questions that make me think.
in my intuition, a photon is a debroglie wave that is infinitely stretched on space along its path. another way i see it is a particle that travels at the speed of light and has infinite time dilation, so in the reference system of that particle the entire world is relativistically contracted to have 0 "length".
while photon "length" is relatively clear to me, its "width" is more obscure. as a wave packet i would on one hand expect it to have variable size, but on the other hand all photons of a given wavelength are supposed to be identical.
@@schmetterling4477 I'm not really asking you if I'm right or wrong, because I worked enough in the field to know when my intuition is correct and when it's just a convenient way of thinking about something (and when this convenience stops working). I also have a PhD in physics, so you can go and give your valuable high school advice to somebody else.
@@schmetterling4477 I did measure plenty of cosmic rays, including gamma rays, but I see 0 point in proving you anything considering how full of yourself you are.
@@schmetterling4477 sure, they are not photons, they are particles that have rest mass, but they move very close to the speed of light and exactly due to that, they travel longer distance that they would in their decay time if there was no time dilation in their local frame of refence that you called "total bullshit".
Here's the answer for those not wanting to watch;
General relativity: no.
Quantum mechanics: yes. But also no.
No, the answer is photons are BS. There is no such thing as a photon, whoever named it was an idiot. Should've just called it "EM field touch" or "EM field energy transfer".
@@coenraadloubser5768 so what you're saying is that the answer to how big a photon is, is "no" in general relativity, because in actuality photons are quantum waves of electromagnetic energy, which are also either waves or point like excitations.
So to summarize your counter argument it would go something like;
General relativity: no.
Quantum mechanics: yes. but also no.
? Dude your trying to explain my point back to me.
QM: A crutch, non-reality using fancy maths to describe 'what is seen' but NOT how it works; no "First Principles" of physics needed or required ..
@@roger_isaksson but there must be something exciting "about" the EM field, mustn't it? Just a poetic question from a non-native speaker....
@@roger_isaksson BTW if universe is the fields than it's maybe not that lazy after all: it fluctuates even at "absolute zero" energy
You can force temporal localization on photons by passing them in a narrow beam through a rotating disc with a small radial slit. Making slit and beam narrower will eventually force photons to be so much localized in time that you will get into proper single photon regime, at least in comparison with ToF over the longer leg of the setup. This would be much cheaper than a nanosecond lazer;) Of course you can also artificially elongate your second optical path by adding a bunch of fiberoptic cable (or just a glass rod), thus making light travel a lot slower. If you go that path you'd need to dim the main path a bit to compensate for losses, of course.
The problem with that is that you lose your narrow beam due to diffraction with the radial slit.
@@orsonpeters And then you can confine it back by just restricting the optical path.
20-30% isn’t really “a lot slower”
@@alexpyattaev according to QFT sure, according to reality no you can't realign light by restricting the light path
Light is a wave but also behaves as a particle. The field is continuous, but the energy within the wave is quantized! This explains so much!
Late to the party, but fascinating stuff as always! I'm continually impressed (or irritated hah) by how counterintuitive light is... right when you start to understand it, a new phenomenon shows up and you realize you have no idea how it works :) If you're taking suggestions for future experiments, I've always thought a Ghost Imaging setup would be very cool, and maybe doable on a home budget (mostly a matter of getting the delay lines setup and figuring out latency in the electronics). Great video! Looking forward to the next!
There are a few answers to that question with various levels of meaning which could be zero, infinity, some finite value or a distribution of values. In the sense of the size of the particle itself it would be zero, but the closest things to a meaningful size for a photo would be either one wavelength of a plane wave or more often and more usefully the full width at half maximum of the envelope function of a wave packet.
Wonderful invitations to an experiment. Wish it included another run with the non-coherent source, or preferably un-entangled and entangled compared.
I'm impressed with your use of the experimental equipment. An antique, some crystals, a couple mirrors, A BUNCH OF NUTS AND BOLTS? Wow, I've seen people sharpen pocketknives with what looks like more precision equipment and you are recombining low powered laser beams on a table with a CARDBOARD BOX on top of it. I am serious, I'm amazed at your use of those tools.
So, are you planning to repeat the experiment with a different light source or a sufficiently pulsed laser? I hope so :)
I would be extremely interested myself! It is, after all, the point of the initial experiment. That would finally give the answer (or added clues) that he started out looking for.
Thank you for explaining how I think about light in a simple way. I did physics at university and I got the impression that light is continuous in free space but acts in a quantised way when it interacts with matter because matter is quantised (because the particles it interacts with, such as electrons, are in potential wells, such as atoms). Since we always detect light by using its interaction with matter we always see it as being quantised. But when I asked professors about it, they would shy away from accepting that explanation. Maxwell's equations explain perfectly how light behaves in free space. They haven't been superceded in a century, they are correct relativistically, and they don't have any quantisation in them.
@@schmetterling4477 We didn't do QED at university so I don't know in what regime or for what precision you need to consider the light as being quantized even when it is acting on a free particle in space. But in our "normal" quantum mechanics classes we were introduced to the effects of light on a quantum system (like an electron bound in an atom) by taking the oscillating field as a continuous wave and putting it in the Schrodinger equation as a modification to the energy term. That gave apparently plausible results.
But maybe that was an approximate bodge just to keep us quiet and avoid discussing QED 😄 I'm not sure if this technique gives good enough results to work with for engineering/ chemistry in "everyday life" or if it is just wrong?
A photon is the property of space itself. Imagining it as a separate entity is a mistake from the very beginning.
The idea of degrees of coherence is interesting. I'd still love to see the experiment done with a fluorescent lamp so the expected difference in interference could be showcased.
The question of an intuitive answer of where the energy is in the photon's quantum state before interaction is definitely a strange one. It seems to me that it should have some weird intricacies with momentum and minute internal forces in the optical system. did the single photon interact with and exchange momentum with the mirrors? or did it travel straight? if you could measure the forces involved would you see quantized events in the expected distribution? If anyone knows, please respond!
Thank you for confirming my picture of the double slit experiment. Why anyone would suggest that a photon would go through two slits at once has always blown my mind. The only time you 'see' a photon is when it interacts. It's where it starts it life and ends its life. Photons don't travel. Huygens optics indeed, carried by continuous superposable EM fields.
10:20 "just to give the experiment a nice high tech look and feel" had me rolling 🤣🤣🤣🤣
10:10 “the give the setup a nice high-tech look and feel” :)
Yeah, that was 10 point from 10 👌
It was cardboard from Asus
Best video ever on electromagnetic waves. It really helped clarify a lot of concepts from me. Thank you!
Amazing!! You answered so many questions I had burning inside me for so long! And you did it so elegantly and throughly, just incredible. To take such a heady subject like point like particle sizes; which really aren’t anything but different fields interacting, and make it coherent and easily digestible. Bravo. Explaining the issues with diagrams versus reality is truly eye opening. Love the experimental evidence you show. Thanks for the lessons!
You have a great understanding of how light works, thanks for sharing this in a simple way that others can understand. A lot of people would be mind blown of the true nature of em waves.
This clears a lot of my misgivings about the double slit explanations available everywhere
I clicked on a new Huygens Optics video like a [insert fast analogy here]!
similie?
fantastic, more confused but better informed ... must be quantum not-able-to-visualise effect. thank you
@@schmetterling4477 yeah, just like you. No content, no proof to back anything up. If it takes just a couple minutes to explain it all with experiments made to back up your claims, why haven't you made a video of it yet? Obviously you seem to place yourself more knowledgeable about this than most, yet fail to provide an explanation yourself
@@schmetterling4477 you gave me approximately nothing, as per usual. If he is wrong he can be proven wrong. As for the repeating ad nauseam part, you seem quite adept at it as well, consistently saying the same things without thought. If its not X, then what is it, and if its Y instead, how do you prove Y is correct?
In other words to make it abundantly clear: you right now are claiming the earth is flat because someone made a mistake some time ago, and when asked to provide proof you say someone else made a mistake and that's all the proof you need. You do not give an alternative because quite frankly I dont think you know of one, or are otherwise not able to share it.
Tldr: a mistake was made, I ask you to prove it
Woah!!! This is the best explanation I've ever heard about wave-particle duality.
Thank you so much for making these great videos!
Loving the nice high tech looking feel :p
Easily one of the most insightful and brain shifting videos I've watched in a long time.
This is burning a hole in my brain.
We should always keep in mind that models describing physical world are more or less good for making predictions, but we should not think of them as describing true nature of reality (which may be fundamentally non discoverable BTW). In this regard the weirdness of quantum world makes me think that we are missing something here. There 'must' be something hidden, something 'behind the scene' that would explain this weirdness more naturally and logically than the current models do (or don't).
they are not good at making prediction, like the fuck they are, have you even looked at that stuff? QFT has no predictive abilities at all, all the QFT calculation are just applying interractions between distinct objects but magically overallped in an infinite of ways, but of course they don't calculate an infinite of ways, they just calculate the most numerous alternate realities they larp about, and how do they decide which ones are the most numerous/(aka which unproven interraction) has the higher chance of happening? through experimental data of course!
it's literally just writting a mathematical model that makes no sense and hitting it with a hammer until it has the same shape as the experimental data, it doesn't predict anything that just drawing a curve between the experimental datapoints wouldn't predict, it's an absolute joke
same with general relativity, good luck trying to make a model of the solar system (the movement of which is very well known) with einstein's equation, when you try that it flies appart, you literally need to cancel out the equations of general relativity to make it work
aka you take newton, add einstein, then cancel einstein and declare einstein's theory works
same for literally any observed movement, do the movement of galaxies match general relativity? BWAHAHAHAHAHAHAAHAHA, GUESS
there's a reason the trajectory of probes launched by space agency use proper movement equations and none of that garbage
One thing is space. Space seems to be treated as a place for electrons and protons to reside in. May be space is a catalyst that instead of just being some where to put stuff, works with electrons and protons to do the things they do.
Space may be an integral part of every interaction. It is just not understood as such so basically ignored. There is some thought that the proton and electron is just concentrated space. This kind of makes sense. Look how much space there is compared to how much protons and electrons there are. It is lopsided to space being predominant. May be a balance has been struck in that not much more concentration of protons and electrons is possible. If so, it is a good thing as otherwise there would be no space just protons and electrons. It is something to consider.
Super great explanation which takes out the misticism given by many people about whats really going on in the double slit experiment. The reason the interference pattern in the double slit experiment resemble so much the patterns created by water waves is that the actual laser beam is a continous field similar to the liquid water which is a bunch of molecules connected by vandelwaal forces. Your approach to takle the issue by readjusting out the optical set up in different ways is what a scientist should do in experiments. Use your set up in several ways to get to a more complete explanation.
That sounds great... right until somebody asks you to calculate the anomalous magnetic moment of the electron to ten decimals and you can't. ;-)
This explanation destroys a large part of the double-slit experiment conclusions I've seen over the years. So, lasers are the wrong tool for this, but they are *always* used. I feel fooled.
Either we as humans love regurgitating things we don't understand..... or maybe it's been the biggest magic trick of the 21st century... misdirection... we've been subtly manipulated in the spirit of nuclear proliferation. Personally I think it's the latter... I think it's all been part of a strategy to keep everyone as dumb and controllable as possible while "they" figure out how to surveil or control us even more... you know how the pace of technology is exponential? Now imagine how much further ahead someone would be today, who just had a 1 year head start say ... 50 years ago? You know, because they're afraid we'll blow up the planet if we know too much and play with matches? Atheists who do not understand the metaphor that "the world is already saved"... two year old mentalities that think "mine mine mine" and very sneaky about controlling things... sure, someone properly motivated to do something terrible, can do something really terrible... but how much of those things are motivated by the terrible in the first place? That's the age old question, I guess. When will all of humanity wake up to the same truths that what we see is what we are... (and if you don't like it, look somewhere else!!!) One would hope that'd be enough for people to stop trying to take what can not be taken? Maybe we just need a new language that can explain this better.
@@coenraadloubser5768 Take your meds. How does using the wrong tool for light experiments involve what you're talking about? If there was a they trying to stop us from using the correct tool for double-slit experiments, why was this video published?
Double slit experiment has been done with electrons and even molecules.
There's nothing wrong with the laser. The experiment is exposing our assumption that the interaction of the detector and the field is quantised. If you can produce a detection event with less than a quantum of energy it can't be.
@@Seagaltalk this! I still think he will see the interference pattern with a single photon spontaneous emission source.
love your content, ty for sharing
I struggled with this for many years until someone offered an explanation that really made sense, and this experiment is a perfect illustration of what I was told:
Forget about photons. Just think about light in terms of classical EM theory, with the following additions
1.) Energy is added to or taken away from the classical EM wave only in discreet amounts
2.) When the wave has only a single photon's worth of energy, there is the issue of figuring out where it will be detected (since the wave can't deposit fractional hv to many places over a surface, for example). It's simple: it just follows the Born rule of quantum mechanics. The probability of a single photon's energy being detected at a particular spot is equal to the square of the wave(function) amplitude at that spot. Bing bong that's it. For large numbers of photons, this will reproduce classical EM.
3.) Thinking too hard about how the detection probability "works" will always give counter-intuitive and confusing results. That's just QM. Just think of things in terms of classical EM, with going into/out of the wave in quantized amounts, with the location of detection being probabilistic according to QM.
Thinking about it this way, it is very hard (impossible?) to conceive of an experiment where a high-intensity EM field produces an interference pattern while a "single-photon" intensity field does not.
Ah, interesting. In physics labs we did a double-slit (or maybe diffraction grating?) experiment with both incandescent and laser light. The laser light had a proper pattern at any path difference, while the incandescent lamp would only have a diffraction pattern at path difference 0, as only then would all of the harmonics line up. But a monochromatic incoherent light source? I hadn’t thought about it, if it would really give a different result to a coherent source like a laser then that would be rather interesting to see. Of course, coherence is relative, a nice gas or diode laser might be incoherent enough at a few metres (or maybe kilometres). A spool of optical fibre would make things a bit easier.
And yes, in general I treat all systems as classical systems up until where a quantum interaction happens, like with the CCD. I do not understand Stern Gerlach.
In what optical system does a quantum interaction not occur?
@@josephcoon5809
I meant that, in any optical system, you assume the light is behaving as a wave until the point at which it interacts with something in a quantum manner. Not on an system-by-system basis, but inside each system.
"Single photon" is a mathematical thing.
@@schmetterling4477 The wave function is mathematical thing, understanding what exactly you measuring is not.
@@schmetterling4477 All is energy - proton, electron etc., yet they are different.
I came here from your later coherence series, where you attempted to model quantized emission and absorption processes with speakers and a string. I took quantum chem in college and did alright with the problem solving, equation manipulating aspects, but I never felt like I had an analogy for it that made it all any less mysterious. Also, my dad was always really into musical instrument acoustics, and your beat frequency insight brought back all his old explanations from my childhood (standing waves in open/closed tubes with cylindrical/conical bores, etc.) and connected it to the old chem diagrams, and to my current interest in radio as well. You've really provoked me to a lot of thought this past week, thank you.
Ok, physics crank time: You and others have articulated this idea that "light propagates like a wave but interacts like a particle." Could it be that light interacts with matter only mostly like a particle, but rarely also like a wave? In this video it seems like there are two forms of matter that interact with light in a seemingly unquantized way, at least as far as its amplitude is concerned. One is the laser itself (since apparently spontaneous emissions won't interfere) and the other is the series of attenuating filters, which can apparently attenuate the wave to subphoton amplitudes. If light can be emitted without quantization and then attenuated without quantization, then could it be absorbed without quantization too, for subphoton-energy detection?
Experimentally, I'm imagining shining very attenuated coherent light into the partially-silvered end of a laser at its pump frequency, to cause population inversion, and then somehow detecting the lower frequency transitions at the lasing frequency. If you are using high frequency photons to stimulate the emission of lower frequency ones, could you then cause more lasing-frequency detection events than there are pump-frequency photons to detect? For example, if the pump transition is between energy levels A->C, and the mirror resonator somehow lases at both C->B and B->A, then you would be producing two photons for every input photon, and possibly measuring the amplitude of the original beam at a greater resolution than the process that produced it. In other words, can a laser deputized as a detector be used to convert high-frequency, low-amplitude signals into low-frequency, high-amplitude ones for easy detection?
That's the idea anyway. If I'm just the crank in the comments, I want someone to set me straight! Either way, my spontaneous ideations are only proof of how stimulating this channel's content has been. Appreciate your work Jeroen!
12:25 You clearly have some interference in the X-direction, as well as the Y-direction. Time for some more investigation!
This is amazing! Have you tried the experiment with a source that can send one photon at a time?
Wonderfully detailed video, superbly presented. Wish I'd had this available when I was a physics student.
So photon is simultaneously infinitely large and infinitely small... My brain hurts :(
Your brain hurts because you believe photons exist.
@@dreamdiction so, you are trying to say that they don't exist ?
@@c.chouinard3282 An indoctrinated person sees things which do not exist and they cannot see things which do exist. You have been indoctrinated to believe photons exist, that's why you can't see that every slit and double slit experiment shows that lights is always waves, never particles. The photo-electric effect also has explanations which have nothing to do with electromagnetic radiation as "particles". Photons do not exist.
@@dreamdiction Correct, and there is a lot in modern Physics that is much more associated with religious dogma than actual physics. Like the other "theories" of Einstein, SR and GR. His explanation of the Photoelectric effect is clearly also just as wrong.
@@dreamdiction I would agree that a "photon" is more like a concept rather than an actual object
How big is a Photon?
He's probably around 6ft, has a short beard and about 11kv @1amp. That should make it pop...!!!! 🤓
induced current by photons, or sometimes just a hammer
Thanks, this made much more sense than the 'single' photon explanations. The presumption that a laser fires off a single photon is just wrong. It is a continuous stream.
Who would even assume that? I got so confused when that part of the video started, like obviously it's not a single photon, how would you even be able to feasibly detect one single photon
The cardboard gave it a high tech look and feel. 😂
I think the mistake you made, was only considering that the light is quantized, forgetting that it is also a wave, at the same time. . . Or something like that. ;)
It seemed odd to me from the start that you would be able to split a single photon, because that should logically not be possible. So something seemed fishy about the single photon claim... as you eventually found out.
Sometimes, I guess, we take things for granted, and miss something important. But as long as we eventually figure it out, it is science at work. ♥
You can split a single photon in the same way you can split a single electron: The particle isn't split, its probability distribution function is split. The probability distribution function can be divided arbitrarily, even for single particles.
You’re going to have your mind blown. A single photon can indeed “split” and travel multiple paths at the same time and interfere with itself. This is what the double slit experiment shows when you do it one photon at a time.
Dude, love your videos, especially the endings. Unfortunately, I dont remember 1985 so well: as I was 15, in high school, listening to lots of Led Zeppelin, Black Sabbath and a very new band, named Metallica. You get the point. But somehow we grew up to be Photonics Engineers!?
In 1985 my parents thought I would be an absolute FAILURE. My dad (who was a surgeon) said to me:
When in the city, how does one find an engineer? call a taxi.
What does one say to a civil engineer? One BigMac, no pickles, large diet coke and xtra ketchup for my french fries please ...
What does one say to a Photonics Engineer (which is far more technical) = I'd like a double chai latte, soy milk, no foam and served in a hand-made clay cup made by a guy with dread-locks wearing an organic flax shirt, while listening to Bob Marley, please...
And an especial thanks for addressing my ignorant question regarding quantum mechanics and the splitting of a single photon by your beam splitters... Now I have the answer.
I am 53, engineer, working for a major brand name camera company that every specialist knows, and still learning new things from your videos. I am grateful. Why were my professors not even half this good at explaining things? Is it possible, they didnt know and just repeated dogma?
You really need to watch Richard Feinman's lectures on quantum electrodynamics.
Watching a bunch of BS and nonsense presented by fraudulent/quantum theorist like him will be pure waste of lifetime. No thanks
@@marcelzuziak9954 The more you talk, the more of a joke you look like. When your philosophy (or model of reality) can predict something that quantum electrodynamics cannot predict (or even explain completely) and that can then be validated by experiment, you can call QED a waste of time and BS. Until then you are just another fringe lunatic.
@@bogywankenobi3959 1st of all: I do not talk I write...if U can read and think, but it is very doubtful. and 2nd which confirms the 1st: my human spirit can predict things and events anything that quantum electrodynamics cannot predict (or even explain completely). So please stay in your pseudo reality and do not pull nobody else into it. Period.
@@marcelzuziak9954 fucking based on all counts
"on all counts" except maybe judging feinman so harshly, from the admittedly EXTREMELY LITTLE of him I know, he seemed genuine and honest in his demarch, and he appeared to me to have been rather speculated with high uncertainty in what he was saying rather than just declared that's how things were, which of course which was the case would warrant your opinion of him fully considering the contents
Could we all agree that photons don't exist? Why do we keep going down that street? A field is not a point source. Light is a field, not a bunch of BBs flying all over the place.
I will sign that petition.
@@realscientistflanders1688 Thank you. We need to pass it.
Thanks -I always hate the standard explanation taught in books of the slit experiment. I was just a tech in an engineering (ICs) but I was always the one to set up or design experiments to prove the design of this or that and measure it. The light detectors cause artifacts in the data because of the way they worked, this lead to hours of auguring about things like what in your video. One guy from MIT the head designer was the only one that support my data or see the other artifact of setup. Your is the best sofar.
y'know that you're not observing interference between one and the same photon but from stream of them?
a lot of photons will create interference in your experiment regardless of delta-length of paths taken by the beam. just time for light to travel would be different.
if you would have fast enough camera to observe the screen you would see first: a round circle without interference and then after some time that circle would be having an interference pattern on it because second wave have arrived.
So i think you explanation of experiment completely wrong based on 2 things: 1. You are not measuring single photons, 2. You aren't observing interference from a photon interacting on itself
Excellent video. I have struggled with the understanding of light for years. Although I still don’t fully understand the totality of lights nature, your video explanation gives me a closer understanding! Thank you!
Wow! Thanks for making this video!!!! Now I get this experiment and its results!!!!! (And it only took 50 years of looking!)
What I positively hate in Physics is everybody showing and explaining stuff, and always leaving out some pivotal information. It seems to take decades for each question one has, before, at random, one stumbles on it.
Please... more videos!! You're doing this better than any other TH-camr.
That is a beautiful demonstration of what a quantum field actually means. EM is a field, but its measurable/interaction properties are quantized. We call "photon" an specific interaction in which a quantized amount of energy is transferred to/from the EM quantum field.
Kudos! I stopped and rewatched several parts of this video and will rewatch the whole thing later!
Just this week I did an experiment that more-or-less measures the length of a photon. The source was a germanium vacancy defect in diamond, which emits single photons at a wavelength of 602 nm - we can confirm that this single defect emits single photons using the Hanbury-Brown & Twiss setup, a straightforward experiment in itself. Anyway the photon length is extracted from a measurement of the first order coherence, which you can obtain by doing one photon interference. Excite the defect so that it emits photons, then direct those photons through a Michelson interferometer that has a fine-adjustable short arm and course-adjustable long arm. The output of the interferometer goes to an avalanche photodiode which counts single photons. Fix the length of the long arm, then scan the short arm over a range of about 10 micron, this will produce an intensity oscillation (i.e. an oscillation in the rate of photons counted by the detector, which was averaging around 5 thousand counts per second) due to the single photon interfering with itself. The intensity oscillation has a certain visibility (ratio of oscillaiton amplitude to average intensity), and you record this visibility for many displacements of the long arm over a range of a few centimetres. The shape of all the visibility data has a gaussian distribution, and the full width half maximum of this distribution is essentially the length of the photon. In my case, the ensemble of observations which produced the visibility data yielded a length of about 3 cm.