@@jazzabighits4473 Shhhh, they don't need to learn that yet. You're at the top of your game snusheaven, totally invincible, and nothing can stop you! Do all of the things!
Ed Copeland has more faith in the level of understanding that teenagers have on average than I do. Still, always a pleasure to hear Tony and Ed speak on any subject.
หลายเดือนก่อน +20
It could just be that he thinks of teenagers as 19-yearolds. The ones he is most likely to meet at his job.
Tbf, all of the vocabulary he used, i.e. electron orbitals and wavelengths, were all covered in my high school physics and chemistry classes. So it’s well within reason that a high school student could grasp these concepts.
In middle school I learned about electrons and atoms and molecules, so the teenager explanation seemed pretty reasonable to me. By the time I was graduating high school I was definitely aware of the quanta of particle physics. I'm 34 now and from what I can tell, schools are pushing material to younger people sooner, I'm just trying to keep up by watching videos.
I just love listening to all of these guys. What Brady had captured over the years is just great science education from people passionate about their field of study.
A quantum communications professor I used to work beside used to ask this as a starting question during PhD vivas. He said the only acceptable answer to him was ‘a click in a detector’
Incidentally that is exactly what it is. That click is caused by a small amount of energy. You had a smart professor who was actually testing if students understand physics. If you can't associate a photon with a click in a detector, then you do not understand. Not even a tiny bit.
The special relativistic wave equation that accurately describes electrons is the Dirac equation. The Dirac Lagrangian density for electrons has got a local U(1) symmetry because of local causality and local charge conservation (Noether's theorem). U(1) symmetry, because we only ever observe the absolute value squared of the wave function. This can be modeled in gauge theory as an S^1 fiber bundle (or a U(1) Lie-algebra valued principal g-bundle) over a flat Minkowski spacetime base. Wave functions for the electron field are then sections in this fiber bundle. To make precise the comparison of geometric data between different spacetime points (gauge covariant derivative), we introduce a connection on this fiber bundle; the electromagnetic vector potential, A_mu (just like the Christoffel symbols/Levi-Civita connection of the tangent bundle in general relativity). Basis vectors/phase can change from place to place either bc. we are using some strange coordinate system (like polar coordinates fx.) or bc. our manifold/bundle is curved (to be precise, the connection is curved). So this connection might have a holonomy/curvature (responsible for geometric Berry phase), just like how spacetime can be curved. In this case, the curvature is caused by the 4-current, just like how spacetime curvature is caused by the stress-energy-momentum tensor. We can take the exterior derivative of this Ehresmann connection 1-form (A_mu), which yields a curvature 2-form, called the electromagnetic/Faraday tensor (or the Riemann curvature tensor in the case of general relativity). This new field, (A_mu) the vector potential has got its own dynamics. If we derive the equations of motion with the help of the Euler-Lagrange equation, we get back the Lorentz force and Maxwell's equations in the 'classical' case. We can also apply canonical quantization and make the 'A' field values into operators. At low energies, this A field behaves like a quantum harmonic oscillator at each point of spacetime; its energy levels are going to be quantized. The number of quanta in a given frequency mode is what we call the number of photons in that mode (pure numer state/Fock state).
Will you ask them about radio frequency "photons"? I know radio and light are just different energy levels or frequencies of the electromagnetic spectrum so I would assume quantization can be found at all levels, but I never hear anyone discuss quantization of the low frequency electro-magnetic spectrum. The way signal transmission from an antennae is typically described does not leave any obvious room for quantization.
@TheDuckofDoom. Photon energy is directly proportional to frequency. The energies of individual radio wave photons are so low that they're essentially unobservable. We simply don't have detectors that are sufficiently sensitive. (It's entirely possible that someone somewhere has built such a detector, of which I am blissfully unaware.)
It's because we are approaching the limit of what our theories can describe at the most fundamental level. A quantum wave function can be described as a vector in Hilbert space. After that, we don't have a more fundamental description of what a photon really is, we can only talk about what it does in our models.
It is only becoming more difficult to understand. Nobody has a clue what a vector in Hilbert space is or how it looks like. It is just mathematics. All the time physicists have been dreaming of and searching for a simple world formula like the simplified Einstein e=mc2 equation and the longer their papers get the more complicated are their suggestions. There is no tendency that things become simpler but they become completely nuts. I am afraid that humans are still not nearly intelligent enough to solve the riddle. And never will.
@@peppipeppi51 Of course things become more complex. These theories describe phenomena that are completely removed from the usual human experience. For example, classical mechanics is simple (not really) because it deals with phenomena close to the human experiecne, like the motion of objects. This makes it much easier to intuit. It is only logical that you cannot intuit something like quantum electordynamics (except for mathematical intuition I suppose) because as far as daily human life is concerned, it is completely alien to us. I think its a miracle that we have the ability to describe concepts at such different scales.
This is where my knowledge hits a wall. We have EM waves in 3 dimensional space that are obviously waves. But then we have single photons... but all all the experiments we do that show interference seem to be with waves generated from a large number of electron transitions, not with single photons. There seems to be a huge difference between attenuating an EM wave to produce "single photons" used in most interference experiments... but those aren't actually single photons, it seems. The is a difference between those and an actual singular photon from a singular electron transition. So what does this actually mean at the level of a single emission? For example, can a singular emission (a single electron transition in a single atom) create an EM wave that is able to interfere with itself as a quantum-emchanical object? Does the 2-slit experiment work with a singular emission? And can that probability wave result in all of its energy interacting at a single point elsewhere in space? Or is it something else entirely? -Matt
The double slit experiment still works for extremely dim light sources (on the order of a few photons per second). Photons are waves in the electromagnetic field until their wavefunction collapses and they're absorbed by a particular electron. So yes to these: For example, can a singular emission (a single electron transition in a single atom) create an EM wave that is able to interfere with itself as a quantum-emchanical object? Does the 2-slit experiment work with a singular emission? And can that probability wave result in all of its energy interacting at a single point elsewhere in space?
How is the wavefunction of a photon related to the electric and magnetic field? For a massive particle, the squared magnitude of the wavefunction is equal to the probability density. Can the same correspondence be made between probability density and the electric/magnetic field?
I don't think so. IIRC, there is no position operator for relativistic wave functions therefore what exactly you mean by the probability of finding a photon in a particular location is not well defined. I think the energy-density can be localised but not an individual photon.
I think of the photon as a "bump" on the electromagnetic quantum field that is tridimensional, extends through all the universe and surrounds all of us. Electromagnetism is mediated by the photon, so it is its "form of expression" in the material universe, its the way the EM field affects reality
That is not entirely what a photon is though. A photon, in quantum field theory, is understood as a fundamental excitation (or quantized disturbance) in the electromagnetic field. It’s often described in terms of virtual particles and quantum field disturbances because these concepts provide insights into how photons interact with other particles and fields. Quantum Field Excitations: In quantum electrodynamics (QED), the electromagnetic field permeates space, and photons represent the smallest possible excitations of this field. These excitations are quantized, meaning they have discrete energy levels associated with the frequency of the light they represent. So, a photon is effectively a "quantum of the electromagnetic field." Virtual Particles: When photons interact with other particles, such as electrons, they can be represented in intermediate steps of these interactions by "virtual photons." Unlike real photons, virtual photons are temporary disturbances or "off-shell" particles that don’t obey the usual mass-energy relations. They exist briefly to mediate forces between charged particles in accordance with QED, such as the electromagnetic force between electrons. Disturbances in Quantum Fields: In QED, all particles are excitations of their respective fields, and fields interact with one another through these excitations. A photon, as a disturbance, causes changes in the surrounding electromagnetic field, allowing it to propagate through space. The photon’s properties, such as having no rest mass and a specific spin, emerge from the symmetries and mathematical structure of the electromagnetic field. In this framework, photons are both fundamental excitations (with observable properties) and carriers of force (through virtual photons in field interactions). This dual role helps explain phenomena from light waves to the electromagnetic force between particles.
Still missing things like: "Photons always travel at the speed of light relative to the observer (299 792 458 meters per second) regardless of the observers speed", and "They are massless particles - all their energy is in their momentum". Your answer is still better than the video, though.
Correct! Thank you! The one way speed of a photon is not measured experimentally though! We can only measure the 2 way speed of a photon. So we infare that the speed of the photon (or the speed of light) will be half of what we find as its 2 way speed. Which is 2 * 299,792,458 m/s. We also know from Maxwell that c = 1 / sqr(ε*μ) where ε is the permittivity of empty (free) space ε0 = 8.8541878188(14)×10−12 F⋅m−1 (with ±0.00000000014 of uncertainty) μ is the permeability of empty (free) space μ0 = 1.25663706127(20)×10−6 N⋅A−2 (with ±0.00000000020 of uncertainty) This is where my personal knowledge stops. Chat GPT says that: If we could achieve infinite precision in our calculations using Maxwell's equations, the value calculated for the speed of light would approach "c" = 299,792,458 m/s as an exact number. Is that true? I don't know... Is that a hint that the one way speed of light is "c" ? Or could it be that the emited speed of light is smaller or bigger than the reflected speed of the same light? Can we even talk for light as being the same as the one that was reflected back to us? I guess we might find out in the future!
When I was in 6th grade my science teacher told me that light was made up of little particles called photons, and that made sense to me because I could imagine them bouncing around and off of things like billiard balls, and it explained how reflection worked since the angle of reflection would be equal to the angle of incidence on a smooth surface. So a sufficiently smooth surface like a mirror would reflect all photons uniformly to create a clear image, while a rougher surface like a fabric would reflect the light in a scattered way preventing you from seeing a mirror image even though both objects reflected light. But as I've grown older and learned more about electromagnetism I've come to the understanding that radiation is kind of just the result of waves in the electromagnetic field that permeates the universe. That makes sense to me too, but it begs the question about whether light is a particle or a wave, or if it is somehow both? I was starting to think that what my 6th grade science teacher was technically wrong, and that a photon is just an elementary way to think about how light travels and interacts with things, but that it's not really accurate to what's actually happening. But if these guys are talking about photons as if they are real physical particles that travel around, then I don't really know what to believe about light anymore. Doesn't the double slit experiment disprove the idea of light as a collection of particles flying around through space?
And even that is an oversimplification. Ordinary Schrodinger's equation is not relativistic, it's for slowly moving particles, not for photons which are totally relativistic.
For the English majors out there, a photon is a verb and a noun at the same time. If you look up the definition of "photon" it becomes one or the other.
The photoelectric effect paper established a connection between wavelength and incraments of energy absorbed or emitted, thatnis very important, but i would argue that has absolutely nothing to do with particles.
Does this mean frequently of light is quantified? Little changes of frequency related to the amount of energy an electron changing needs to change orbit level?
Yep, the energy levels between different quantum states in different atoms are quantised. That's why you can use spectrometry to detect the different elements in a chemical or in a star, etc. At least that's my layman's understanding.. someone with more knowledge will probably chip in with a better explanation
I think by that he meant that a Teenager is likely to at the very least have some knowledge of the standard model and maybe a little bit of stuff like what quanta are. They won't know the mathematics and stuff like spin, but at the very least they'll be familiar with stuff like the photoelectric effect.
A science-minded teenager who takes advanced physics/chemistry classes or likes to learn about physics on their own probably does know some about QM. A random teenager, probably not lol
We never seen photon it self. We only know about photon from experiments. So. To answer those three questions we need to tell about experiments. 1) Simplest experiment: look at light. You see light, that what photon is. 2) interference\diffraction. You show plank with holes to see wave pattern and particle pattern. 2.1) Dispersion. Use prism to see different light colors 2.2) Light speed. Using mirrors and gears. 3) And last one. This is actually the question. About how light being emitted from electron orbit change. That is the question: how exactly do scientist did that experiment and prove photon actually emitted from electron and not from atom it self? 4) PhD question, how light, light speed, gravity matter and antimater related to each other, how did ligth form the Universe. Those are missing from video.
I've seen explanations using quantum stuff for refraction, absorption, re-emition, interference and scattering, but I've never found a quantic explanation for reflection... Especially about why angles are conserved in such a precise way.
They are not. Light travels in all possible paths. Literally, in all possible paths. It makes loops, it bends, it goes rectangular. What we see is the path that is not cancelled out by interference of the light wave with itself.
I recommend reading Curt Jaimungal Substack, the entry called "what is light?" which answer what is light in a progressive fashion like this video, but in a more profound way
If a photon is both a particle and a wave how can it have directionality? I’m trying to visualize an individual photon being emitted from a star. Wouldn’t it propagate out in all directions?
I like to think as light as a particle not in the "usual" sense of particles but it's energy as being a "particle". It takes discrete values and comes in packets. I usually think of light as an EM wave where it's particle aspect it's the amplitude of the fields. But I'm not even a undergraduate physics student YET so correct me if I'm wrong please!!!🤗🤗🤗 BTW sometimes I think it's not even important to picture things in our head because that's not (I guess) the scope of physics.
Photons are small amounts of energy. We try to teach these six words in high school (and have been for over 40 years) but nobody seems to be paying any attention. ;-)
It’s interesting that light is always explained as a particle. When it’s a wave! The photon is just the mathematical abstraction that we use to encapsulate the quantum of energy level that the wave (the field) exchanges when it interacts with another field. In other words, Photons are _interactions_ of light.
Quantum of a field is what particle physicists call a particle. Not a little ball. So in this sense photons are particles all right. Just not the kind of particle a child would imagine.
This is a great question, and the answer is that photons aren't actually tiny. The small tiny ball of light idea just isn't a helpful picture. The only sense in which a photon is a particle is really just that the energy comes in bunches or quanta-- it says nothing about how much space it takes up. In quantum field theory there isn't actually a well-defined position for a photon, and it can't really be said to be localized in a particular space. The "size" of a photon is better thought of in terms of its interaction with matter, so physicists often talk about "cross-sections".
I'm still not convinced that photons exist outside of the photoelectric effect, which is actually a property of the electron not of the EM field (alias "photons") as such.
When I do not bother to really think about the quantum fields and how it makes phenomena work, I think that I get it…. But when I really stop to think about it I realize that I do not get it… I always imagined it would be the other way around.
Quite a lot. If you rotate a spin-1 particle by 360 degrees it gets to its original state, but if you rotate a spin-1/2 particle by 360 degrees its wave function changes sign, so you need to actually rotate it twice as much to get to its original state. Spin-1 particles, like photons, are bosons and may share the same state, while spin-1/2 particles are fermions and they don't want to share, making them avoid each other and effectively this is why you don't fall through your chair, and this is why electrons in an atom don't all sit at the same orbital, making all of chemistry possible. Spin-1 particles are quanta of vector fields, which brings stuff like polarization. Spin-1/2 particles are quanta of Dirac spinor fields, which gives us matter and antimatter, and 2 values for the spin property, so that only 2 electrons can share the lowest orbital...
I think everything is made out of helix like links, and the dimensions they are "spinning in" correlate to physical dimensions more(bosons) or less(fermions) etc. - Now, this does not say much, sure, but a helix is much more sensible to imagine to me than a "wave" (where we often omit the other dimension, so it looks very weird: the derivative) - and perhaps the length of the helix is not even always in time...
@@danfg7215 Well, yes and no. They're two separate quantities, one quantum and one classical, but they both contribute to a photon's angular momentum, which is an important quantity that's conserved if the system is symmetrical under rotations. Also, ChatGPT is wrong a lot. Like, A LOT. There's even a video here from maybe a year ago that tests it on an undergrad question and it's totally, "confidently" wrong. There are much better sources for this kind of information (even forums on stackexchange and the like, not only dense books and papers)
Yes! all* elementary particles have spin :) Like Professor Copeland said, a photon has an integer spin, which makes it a Boson. Fermions (e.g the electron) have a half-integer spin (electrons have a spin of 1/2). Afaik (just starting my master's next week) the greatest difference between the two is that fermions obey Pauli's exclusion principle, which means they can't occupy the same quantum state (same energy, angular momentum, spin..), and bosons don't. The elementary bosons are also the "force carriers", like photons and the electromagnetic force, and elementary fermions make up matter (electrons, quarks which make protons and neutrons.. all fermions). *The only known elementary particle with spin 0 right now is the Higgs Boson, and that explains some of its (and the field it's related to) properties.
The question itself implies a certain level of knowledge that the person may or may not have. The first thing one should do is ask what does the person already know about photons. That applies especially to a 13-19 year old person, who may be a precocious genius, a university student, or a below-average youngster interested only in Tiktok.
We are teaching in 12th grade high school that photons are small amounts of energy. In other words, every 17 year old should know what a photon is. Most people just can't remember a thing about that time of their life. For many it's due to binge drinking induced memory loss.
Yes, that wave function can be a sum of 1 or more simple waves, each with their own frequency & wavelength. Photon's energy and momentum are still defined by that frequency.
@thedeemon Than you. I've always noticed, BTW, that when scientists start e,plaining the wave function and its relation to probabities, they switch to talking about electrons. They get cadgey about using the Born rule on he proton's wavefunction.
I don't think most teenagers learn about quantum mechanics. At least not in the Netherlands. You have to be at a very difficult pre-scientific education and even than choose the bèta (science) part of it. So, my estimate is less than 10% of teenagers will get in contact with quantum mechanics.
The photoelectric effect has been part of high school curricula in Europe and the US for over 40 years. As part of that we teach that "photons are small amounts of energy". That alone is enough to derive many important properties of quantum mechanics logically, even though we don't expect high school students to be able to do that.
In fact, the visual is very mind-blowing... The image on the 2-dimensional screen resembles the 2-dimensional shape of the s orbitals. Other orbitals are projected to the 3rd dimension with a rotation operation. We actually use the number i for this reason, for rotation, but it is the projection of the information in these 2-dimensional planes. For this, a rotation operation to the 3rd dimension is required... Just like the relationship between electric and magnetic fields... They transform into each other with a continuous rotation operation... The function of the laser in the image is a clue that the universe can work with the holographic principle... For whom? For the sherlock holmes nature people who care about this...
Makes sense, unfortunately the simplified explanation makes many think there is a physical particle that fills space and not what it really is, a definition of a energy wave peak.
@@kjnoah Because an electromagnetic wave peak is not a small amount of energy. It's an emergent phenomenon formed by a specific statistical distribution of many photons. You need to learn to differentiate between one and many. Would you like a link to a Sesame Street video that explains one/many with cookies? ;-)
@@lepidoptera9337 I think you are confused. A complete waveform is many. the peak is singular. Being condescending shows we are at the limit of your knowledge here.
so,when we look at a light source we don't see photons, we see the photons emitted from radiation falling on our surroundings? I m kind of confused . I thought photons are emitted from the light source.
Yes, but they constantly change into other particles, get absorbed and re-emitted. Like all quantum particles btw. Reason: In between you and the light source are not only an almost endless stream of other particles but also quasi-particles. So, each photon constantly bumps into "stuff". Or simpler said: The photon emitted at the source is not the same photon you might later detect at the destination/observation point.
I think you are taking the particle analogy for light too far. Light is both a particle AND a wave at the same time, or perhaps it is neither. In our macroscopic world we do not experience any object with wave-particle duality and so we simply do not have any model to describe what light or particles in general actually are. When we describe light travelling from a light source to our eyes we really should treat it as one continuous electromagnetic wave as the individual character of the photons really do not describe accurately what is happening.
Even in fyenmans picture, of you try to visualize what happens along each paths in terms of amplitudes, tgere are rotating vectors that sort of form a field in space and it is absolutely analogous to a wave anyway. I have yet to hear any argument at all that establishes light as propagating as particles in any way. Photons are just abstractions as far as i'm concerned. All the arguments about there really being these localized particles in a sense all have to do with interactions or absorption and emissions, and all of that behavior can be described by classical wave mechanics with a twist that systems that absorb and emit radiation does so in chunks and energy and momentum is absorbed from the entire wavefront much faster tyan light, then it is basically like grw, once you sum over the right distribution of such classical states. Again, roughly speaking, a more comprehensive model is needed to reproduce qft with creation and annihilation and so on. I just never understood why people think of light as particles at all, it just seems like a very useless idea when all the dynamics come from the wavefunction and have essentially nothing to do with individual trajectories.
In modern physics a particle just means a quantum of some field, it's not a tiny ball. Which means it is often a wave, at least it behaves a lot like a wave, but at the same time interacts at only one particular location and by exchanging a particular amount of energy (E=hf). If you send one photon towards a camera, it will only fire 1 pixel even though it might propagate in all directions as a wave.
Light is a cluster of expanding electrons- objects with mass. No ‘photons.’ “The Final Theory: Rethinking Our Scientific Legacy “, Mark McCutcheon for proper physics including the CAUSE of gravity, electricity, magnetism, light and well..... everything.
And no, i know the wavefunction is in hilbert space, roughly speaking, and that this is not the same as a wave in space that is deterministic, but you move some dynamics over into classical states, sum over them, normalize and if the dynamics of the classical states is right you get back the exact same probability distribution that results from quantum mechanics, from a phase space, quantum mechanics mixes possible world statistics and dynamics in a confusing way, this is why so many simpletons are convinced there is something fundamentally different from classical mechanics going on, but imo this is just verbal nonsense and doesn't have anything to do with the mathematics.
Photons don't move. They are not "coming at you". That's just a false semi-classical picture. A photon is a small amount of energy that gets deposited in the "detector system". Before that deposition took place the photon simply didn't exist. The reason why light can have direction is because every photon of energy that gets absorbed also deposits an amount of momentum in the detector. If all these momenta are pointing in the same direction (or at least roughly), then we are dealing with a directional beam of light.
"a teenager, they probably learned a bit of quantum mechanics" Hum maybe it's just the french educational system but I never learned about quantum mechanics when I was a teenager. (Maybe he means like watching a video online on your own time about quantum mechanics ?)
Apparently there's some basic quantum mechanics in physics syllabuses for 16-18-year-olds in the UK, for qualifications called A-levels. Students only typically do three subjects at A-level, so there's time to cover some relatively advanced material compared to countries where students study multiple subjects until they leave school.
The US high school syllabus teaches the photoelectric effect. As part of that you are being told that photons are small amounts of energy. I was being taught this in Germany over forty years ago. It must have been taught that way since the 1970s, at least.
@@chocomalk ashton forbes is pushing the term and i wonder what he says about it. Veritasium got roasted about his video explaining the possibly wrong understanding of elictricity… lets see what happens here…
@@phasA100 Well I know for a fact that there is no way to draw energy from 0 point energy because it is the min state something can actually exist, there is nothing to take away because you would have to expend energy to destroy it to remove whats there.
p=mv is just an approximation for small velocities. If you take relativity into account, p=mv/sqrt(1-v^2/c^2). However, if you have a massless particle moving at v=c, this gives p=0c/0, which is undefined. You can't calculate the momentum of a photon using any of these formulas, so your contradiction goes away.
That is like asking: can the sea run out of waves? As long as there is stuff giving energy to the sea there will be waves in it's surface. As long as energy is supplied to an atom it can then emit that energy again as it falls back to lower energy states. But yes: completely isolate an atom and make it very cool such that it is in its lowest possible energy state and it will not emit any photons
@lepidoptera9337 wouldn't you say that quantisation is similar to atomisation? Of course it's not an atom of light, but it comes very close to being an atom of light. You can study a photon gas.
@lepidoptera9337 you mean light-quanta, a photon. What other types of quanta are there? In your definition, is electron an atom or a quanta (At this point it should be clear that we don't mean the same concept by atom as normally used)
@@Yashodhan1917 Of course an electron is a quantum. What else would it be? Quanta are combinations of energy, momentum, angular momentum and charges. These are all locally conserved quantities that follow trivially from the Poincare symmetry of the background. The entire idea of atomism was that atoms are immutable and identical building blocks of the world. That is true in chemistry. It is no longer true in nuclear physics. It is completely false in high energy physics and at the level of quantum mechanics in general. Energy is a property. Atoms are objects. Properties and objects are not even the same category. That's kindergarten level, really. Most people are simply not paying enough attention in K-12. These details matter.
I was a kid when I first saw prof Copeland on this channel now I am a grad student. He still looks the same
forsenNugget
plot twist, you're still a kid
@@jazzabighits4473 Shhhh, they don't need to learn that yet.
You're at the top of your game snusheaven, totally invincible, and nothing can stop you! Do all of the things!
That'll be time dilation, he's actually moving quite fast 😊
TRUE LULE
Ed Copeland has more faith in the level of understanding that teenagers have on average than I do. Still, always a pleasure to hear Tony and Ed speak on any subject.
It could just be that he thinks of teenagers as 19-yearolds. The ones he is most likely to meet at his job.
I imagine a lot of his interactions with teenagers involves those interested in physics
Probably about right for A level physics students
Tbf, all of the vocabulary he used, i.e. electron orbitals and wavelengths, were all covered in my high school physics and chemistry classes. So it’s well within reason that a high school student could grasp these concepts.
In middle school I learned about electrons and atoms and molecules, so the teenager explanation seemed pretty reasonable to me. By the time I was graduating high school I was definitely aware of the quanta of particle physics. I'm 34 now and from what I can tell, schools are pushing material to younger people sooner, I'm just trying to keep up by watching videos.
As a grown man, a ball of light sounds good enough for me.
Yes, the Sun is a photon.
@@toolbaggers a very large one
ok?
I just love listening to all of these guys. What Brady had captured over the years is just great science education from people passionate about their field of study.
i always forget how fun the animations are in this channel and am always pleasantly surprised by them when i come back lol
Fun, and a little disconcerting for some reason.
@@madLphntI agree it’s like a vibe from a childhood textbook I can’t remember that would scare me
I've been watching your content for more than 10 years. Keep the good work as always!
Thank you.
Always a pleasure listening to Prof. Copeland
I love listening to any professors on this channel. But prof. Copeland's aura of calmness is amazing.b
A quantum communications professor I used to work beside used to ask this as a starting question during PhD vivas. He said the only acceptable answer to him was ‘a click in a detector’
Incidentally that is exactly what it is. That click is caused by a small amount of energy. You had a smart professor who was actually testing if students understand physics. If you can't associate a photon with a click in a detector, then you do not understand. Not even a tiny bit.
The special relativistic wave equation that accurately describes electrons is the Dirac equation. The Dirac Lagrangian density for electrons has got a local U(1) symmetry because of local causality and local charge conservation (Noether's theorem). U(1) symmetry, because we only ever observe the absolute value squared of the wave function.
This can be modeled in gauge theory as an S^1 fiber bundle (or a U(1) Lie-algebra valued principal g-bundle) over a flat Minkowski spacetime base. Wave functions for the electron field are then sections in this fiber bundle.
To make precise the comparison of geometric data between different spacetime points (gauge covariant derivative), we introduce a connection on this fiber bundle; the electromagnetic vector potential, A_mu (just like the Christoffel symbols/Levi-Civita connection of the tangent bundle in general relativity). Basis vectors/phase can change from place to place either bc. we are using some strange coordinate system (like polar coordinates fx.) or bc. our manifold/bundle is curved (to be precise, the connection is curved). So this connection might have a holonomy/curvature (responsible for geometric Berry phase), just like how spacetime can be curved. In this case, the curvature is caused by the 4-current, just like how spacetime curvature is caused by the stress-energy-momentum tensor. We can take the exterior derivative of this Ehresmann connection 1-form (A_mu), which yields a curvature 2-form, called the electromagnetic/Faraday tensor (or the Riemann curvature tensor in the case of general relativity).
This new field, (A_mu) the vector potential has got its own dynamics. If we derive the equations of motion with the help of the Euler-Lagrange equation, we get back the Lorentz force and Maxwell's equations in the 'classical' case. We can also apply canonical quantization and make the 'A' field values into operators. At low energies, this A field behaves like a quantum harmonic oscillator at each point of spacetime; its energy levels are going to be quantized. The number of quanta in a given frequency mode is what we call the number of photons in that mode (pure numer state/Fock state).
Okay, now _that's_ a grad-level explanation.
@@tomkerruish2982 Grad-level in what? I have an MSc and I have problems with that :D
@laszlofarkas1895 Okay, post-doc maybe?
Are you saying the ball of light is rolling or bouncing?
@@milobem4458 It's rolling
That's why it's got spin. Duh!
2:02 Oops! The photoelectric effect is about photons knocking electrons off atoms, not photons being absorbed an re-emitted.
Will you ask them about radio frequency "photons"? I know radio and light are just different energy levels or frequencies of the electromagnetic spectrum so I would assume quantization can be found at all levels, but I never hear anyone discuss quantization of the low frequency electro-magnetic spectrum. The way signal transmission from an antennae is typically described does not leave any obvious room for quantization.
@TheDuckofDoom. Photon energy is directly proportional to frequency. The energies of individual radio wave photons are so low that they're essentially unobservable. We simply don't have detectors that are sufficiently sensitive.
(It's entirely possible that someone somewhere has built such a detector, of which I am blissfully unaware.)
Remember that photons are not quantized by energy, it's just the energy that they deposit in material that is quantized.
I would watch a sixty symbols video on that.
Funny how with the progression, the explanation is less "what" it is and more "how" it behaves
It's because we are approaching the limit of what our theories can describe at the most fundamental level. A quantum wave function can be described as a vector in Hilbert space. After that, we don't have a more fundamental description of what a photon really is, we can only talk about what it does in our models.
All we have are models. All we will ever have are models. All models are wrong, some are useful.
It is only becoming more difficult to understand. Nobody has a clue what a vector in Hilbert space is or how it looks like. It is just mathematics. All the time physicists have been dreaming of and searching for a simple world formula like the simplified Einstein e=mc2 equation and the longer their papers get the more complicated are their suggestions. There is no tendency that things become simpler but they become completely nuts. I am afraid that humans are still not nearly intelligent enough to solve the riddle. And never will.
@@peppipeppi51 Of course things become more complex. These theories describe phenomena that are completely removed from the usual human experience. For example, classical mechanics is simple (not really) because it deals with phenomena close to the human experiecne, like the motion of objects. This makes it much easier to intuit.
It is only logical that you cannot intuit something like quantum electordynamics (except for mathematical intuition I suppose) because as far as daily human life is concerned, it is completely alien to us. I think its a miracle that we have the ability to describe concepts at such different scales.
This is where my knowledge hits a wall. We have EM waves in 3 dimensional space that are obviously waves. But then we have single photons... but all all the experiments we do that show interference seem to be with waves generated from a large number of electron transitions, not with single photons.
There seems to be a huge difference between attenuating an EM wave to produce "single photons" used in most interference experiments... but those aren't actually single photons, it seems. The is a difference between those and an actual singular photon from a singular electron transition.
So what does this actually mean at the level of a single emission? For example, can a singular emission (a single electron transition in a single atom) create an EM wave that is able to interfere with itself as a quantum-emchanical object? Does the 2-slit experiment work with a singular emission? And can that probability wave result in all of its energy interacting at a single point elsewhere in space? Or is it something else entirely?
-Matt
The double slit experiment still works for extremely dim light sources (on the order of a few photons per second). Photons are waves in the electromagnetic field until their wavefunction collapses and they're absorbed by a particular electron. So yes to these:
For example, can a singular emission (a single electron transition in a single atom) create an EM wave that is able to interfere with itself as a quantum-emchanical object? Does the 2-slit experiment work with a singular emission? And can that probability wave result in all of its energy interacting at a single point elsewhere in space?
Teenager: Mr. Copeland, what’s a photon?
Copeland: Listen here, you lazy !@&$
How is the wavefunction of a photon related to the electric and magnetic field? For a massive particle, the squared magnitude of the wavefunction is equal to the probability density. Can the same correspondence be made between probability density and the electric/magnetic field?
I don't think so. IIRC, there is no position operator for relativistic wave functions therefore what exactly you mean by the probability of finding a photon in a particular location is not well defined. I think the energy-density can be localised but not an individual photon.
@@VinayRamji i see. If that's the case then, can we work bottom-up? Can electric and magnetic fields emerge from the quantum theory of photons?
The spatial mode of the photon is still given by Maxwell's equations for the field afaik.
I think of the photon as a "bump" on the electromagnetic quantum field that is tridimensional, extends through all the universe and surrounds all of us. Electromagnetism is mediated by the photon, so it is its "form of expression" in the material universe, its the way the EM field affects reality
You do a lot of thinking.
And that 'bump' is a high probability of interacting with other matter. And that 'interaction' is quantized because of atom energy levels.
Has a positive side, a negative side and holds 5% of the universe together.
That is not entirely what a photon is though.
A photon, in quantum field theory, is understood as a fundamental excitation (or quantized disturbance) in the electromagnetic field. It’s often described in terms of virtual particles and quantum field disturbances because these concepts provide insights into how photons interact with other particles and fields.
Quantum Field Excitations: In quantum electrodynamics (QED), the electromagnetic field permeates space, and photons represent the smallest possible excitations of this field. These excitations are quantized, meaning they have discrete energy levels associated with the frequency of the light they represent. So, a photon is effectively a "quantum of the electromagnetic field."
Virtual Particles: When photons interact with other particles, such as electrons, they can be represented in intermediate steps of these interactions by "virtual photons." Unlike real photons, virtual photons are temporary disturbances or "off-shell" particles that don’t obey the usual mass-energy relations. They exist briefly to mediate forces between charged particles in accordance with QED, such as the electromagnetic force between electrons.
Disturbances in Quantum Fields: In QED, all particles are excitations of their respective fields, and fields interact with one another through these excitations. A photon, as a disturbance, causes changes in the surrounding electromagnetic field, allowing it to propagate through space. The photon’s properties, such as having no rest mass and a specific spin, emerge from the symmetries and mathematical structure of the electromagnetic field.
In this framework, photons are both fundamental excitations (with observable properties) and carriers of force (through virtual photons in field interactions). This dual role helps explain phenomena from light waves to the electromagnetic force between particles.
and now to a teenager...
Thx ChatGPT
Still missing things like: "Photons always travel at the speed of light relative to the observer (299 792 458 meters per second) regardless of the observers speed", and "They are massless particles - all their energy is in their momentum".
Your answer is still better than the video, though.
Correct! Thank you!
The one way speed of a photon is not measured experimentally though! We can only measure the 2 way speed of a photon. So we infare that the speed of the photon (or the speed of light) will be half of what we find as its 2 way speed.
Which is 2 * 299,792,458 m/s.
We also know from Maxwell that
c = 1 / sqr(ε*μ) where
ε is the permittivity of empty (free) space
ε0 = 8.8541878188(14)×10−12 F⋅m−1
(with ±0.00000000014 of uncertainty)
μ is the permeability of empty (free) space
μ0 = 1.25663706127(20)×10−6 N⋅A−2
(with ±0.00000000020 of uncertainty)
This is where my personal knowledge stops.
Chat GPT says that:
If we could achieve infinite precision in our calculations using Maxwell's equations, the value calculated for the speed of light would approach "c" = 299,792,458 m/s as an exact number.
Is that true? I don't know...
Is that a hint that the one way speed of light is "c" ? Or could it be that the emited speed of light is smaller or bigger than the reflected speed of the same light? Can we even talk for light as being the same as the one that was reflected back to us?
I guess we might find out in the future!
@@-_Nuke_- Look up how 1 meter is defined today, and you'll see why c is exactly that integer number.
When I was in 6th grade my science teacher told me that light was made up of little particles called photons, and that made sense to me because I could imagine them bouncing around and off of things like billiard balls, and it explained how reflection worked since the angle of reflection would be equal to the angle of incidence on a smooth surface. So a sufficiently smooth surface like a mirror would reflect all photons uniformly to create a clear image, while a rougher surface like a fabric would reflect the light in a scattered way preventing you from seeing a mirror image even though both objects reflected light.
But as I've grown older and learned more about electromagnetism I've come to the understanding that radiation is kind of just the result of waves in the electromagnetic field that permeates the universe. That makes sense to me too, but it begs the question about whether light is a particle or a wave, or if it is somehow both? I was starting to think that what my 6th grade science teacher was technically wrong, and that a photon is just an elementary way to think about how light travels and interacts with things, but that it's not really accurate to what's actually happening. But if these guys are talking about photons as if they are real physical particles that travel around, then I don't really know what to believe about light anymore. Doesn't the double slit experiment disprove the idea of light as a collection of particles flying around through space?
2:14 "photon is a solution to Schrodinger's equation" -
And even that is an oversimplification. Ordinary Schrodinger's equation is not relativistic, it's for slowly moving particles, not for photons which are totally relativistic.
I love how the difference between a child and a teenage explanation is: "a little ball of light" to "a particle of light" xD
I was hoping you'd go deeper into it.
For the English majors out there, a photon is a verb and a noun at the same time. If you look up the definition of "photon" it becomes one or the other.
The photoelectric effect paper established a connection between wavelength and incraments of energy absorbed or emitted, thatnis very important, but i would argue that has absolutely nothing to do with particles.
Naming a thing with a more sophisticated word does not equal explaining
Does this mean frequently of light is quantified? Little changes of frequency related to the amount of energy an electron changing needs to change orbit level?
Yep, the energy levels between different quantum states in different atoms are quantised. That's why you can use spectrometry to detect the different elements in a chemical or in a star, etc.
At least that's my layman's understanding.. someone with more knowledge will probably chip in with a better explanation
What is the duration of a photon? How many wavelengths? Pulse width, if you will?
A teenager had probably learned a little bit about quantum mechanics😂
You all should have a talk about quantum mechanics with your kids, before they learn it on the street
I think by that he meant that a Teenager is likely to at the very least have some knowledge of the standard model and maybe a little bit of stuff like what quanta are. They won't know the mathematics and stuff like spin, but at the very least they'll be familiar with stuff like the photoelectric effect.
Quantum mechanics. Not even once.
Depends on what country the teenager has been educated in
A science-minded teenager who takes advanced physics/chemistry classes or likes to learn about physics on their own probably does know some about QM. A random teenager, probably not lol
We never seen photon it self. We only know about photon from experiments. So. To answer those three questions we need to tell about experiments. 1) Simplest experiment: look at light. You see light, that what photon is. 2) interference\diffraction. You show plank with holes to see wave pattern and particle pattern. 2.1) Dispersion. Use prism to see different light colors 2.2) Light speed. Using mirrors and gears. 3) And last one. This is actually the question. About how light being emitted from electron orbit change. That is the question: how exactly do scientist did that experiment and prove photon actually emitted from electron and not from atom it self? 4) PhD question, how light, light speed, gravity matter and antimater related to each other, how did ligth form the Universe. Those are missing from video.
Photons are small amounts of energy. That's six words. You can't even remember six words?
I think these sorts of video seem to work better when there are persons of the specified ages being present within the video.
Photons are the things that make Laser Guns go pew pew
real
I've seen explanations using quantum stuff for refraction, absorption, re-emition, interference and scattering, but I've never found a quantic explanation for reflection... Especially about why angles are conserved in such a precise way.
I think Feynman in his popular QED book does this. Explained via his path integrals approach.
They are not. Light travels in all possible paths. Literally, in all possible paths. It makes loops, it bends, it goes rectangular. What we see is the path that is not cancelled out by interference of the light wave with itself.
I recommend reading Curt Jaimungal Substack, the entry called "what is light?" which answer what is light in a progressive fashion like this video, but in a more profound way
Great video idea, keep them coming!
If a photon is both a particle and a wave how can it have directionality? I’m trying to visualize an individual photon being emitted from a star. Wouldn’t it propagate out in all directions?
I like to think as light as a particle not in the "usual" sense of particles but it's energy as being a "particle". It takes discrete values and comes in packets. I usually think of light as an EM wave where it's particle aspect it's the amplitude of the fields. But I'm not even a undergraduate physics student YET so correct me if I'm wrong please!!!🤗🤗🤗 BTW sometimes I think it's not even important to picture things in our head because that's not (I guess) the scope of physics.
But freely propagating light can have any energy, it does not take discrete values.
What about a 3 Hz photon? Is it possible to detect it?
0:55 Pretty sure I was not doing quantum mechanics as a teenager.
Its in the a level physics course
I learned about photos in highschool physics
I wish I learned quantum mechanics as a teenager...
Very fun video! ❤
I would love for Brady's channels to continue Wired's 5 levels series.
Photons are small amounts of energy. We try to teach these six words in high school (and have been for over 40 years) but nobody seems to be paying any attention. ;-)
I love photons, almost as much as I love these two young professors!
It’s interesting that light is always explained as a particle. When it’s a wave! The photon is just the mathematical abstraction that we use to encapsulate the quantum of energy level that the wave (the field) exchanges when it interacts with another field. In other words, Photons are _interactions_ of light.
Quantum of a field is what particle physicists call a particle. Not a little ball. So in this sense photons are particles all right. Just not the kind of particle a child would imagine.
@ the particle of the interaction.
But what about radio wave photons? If a radio wavelength can be meters long, then how can a radio photon be tiny?
This is a great question, and the answer is that photons aren't actually tiny. The small tiny ball of light idea just isn't a helpful picture. The only sense in which a photon is a particle is really just that the energy comes in bunches or quanta-- it says nothing about how much space it takes up. In quantum field theory there isn't actually a well-defined position for a photon, and it can't really be said to be localized in a particular space. The "size" of a photon is better thought of in terms of its interaction with matter, so physicists often talk about "cross-sections".
The wavelength of water waves can be many meters or even kilometers, but water molecules are tiny. So there's no contradiction there.
@beeble2003 But water molecules are bonded and thus transfer wave energy across bonded molecules. Photons aren't bound to create a larger structure.
I'm still not convinced that photons exist outside of the photoelectric effect, which is actually a property of the electron not of the EM field (alias "photons") as such.
I thought I had a pretty good understanding of photons, but I'm getting lost at the teenager level.
The Schroedinger Equation is all greek to me.
When I do not bother to really think about the quantum fields and how it makes phenomena work, I think that I get it…. But when I really stop to think about it I realize that I do not get it… I always imagined it would be the other way around.
What does he mean the light particle has an integer spin and the fermon has a half integer spin?
Quite a lot.
If you rotate a spin-1 particle by 360 degrees it gets to its original state, but if you rotate a spin-1/2 particle by 360 degrees its wave function changes sign, so you need to actually rotate it twice as much to get to its original state.
Spin-1 particles, like photons, are bosons and may share the same state, while spin-1/2 particles are fermions and they don't want to share, making them avoid each other and effectively this is why you don't fall through your chair, and this is why electrons in an atom don't all sit at the same orbital, making all of chemistry possible.
Spin-1 particles are quanta of vector fields, which brings stuff like polarization. Spin-1/2 particles are quanta of Dirac spinor fields, which gives us matter and antimatter, and 2 values for the spin property, so that only 2 electrons can share the lowest orbital...
@@thedeemon Thank you very much! I understand much better now!
Next question: What is a spin?
I think everything is made out of helix like links, and the dimensions they are "spinning in" correlate to physical dimensions more(bosons) or less(fermions) etc. - Now, this does not say much, sure, but a helix is much more sensible to imagine to me than a "wave" (where we often omit the other dimension, so it looks very weird: the derivative)
- and perhaps the length of the helix is not even always in time...
Its a tiny little ball of light, so small you cant even see it... Wait a minute.
A photon is like ketchup. you pump ketchup from the dispenser, It's a wave. When it moves from the tube and rests in the paper cup, it a particle.
"It's a particle. It's a very good particle. It's making light, It's fantastic. Photon is a great friend to America." (explained to Donald Trump)
@@aspexpl At the border there's a literal panorama of Mexican photons coming in to the States at the speed of light. He's not going to like that.
Make Bosons Great Again 😊
I don’t think there is any way to explain a photon below the level of kindergartener.
@@Sköldpadda-77 TDS
The teenager stopped listening when an old man called him lazy.
Didn’t know photons had spin
Does it have anything to do with polarization, or is it a separate thing? Guess I'll ask ChatGPT.
@@danfg7215 Well, yes and no. They're two separate quantities, one quantum and one classical, but they both contribute to a photon's angular momentum, which is an important quantity that's conserved if the system is symmetrical under rotations.
Also, ChatGPT is wrong a lot. Like, A LOT. There's even a video here from maybe a year ago that tests it on an undergrad question and it's totally, "confidently" wrong. There are much better sources for this kind of information (even forums on stackexchange and the like, not only dense books and papers)
Yes! all* elementary particles have spin :)
Like Professor Copeland said, a photon has an integer spin, which makes it a Boson. Fermions (e.g the electron) have a half-integer spin (electrons have a spin of 1/2). Afaik (just starting my master's next week) the greatest difference between the two is that fermions obey Pauli's exclusion principle, which means they can't occupy the same quantum state (same energy, angular momentum, spin..), and bosons don't.
The elementary bosons are also the "force carriers", like photons and the electromagnetic force, and elementary fermions make up matter (electrons, quarks which make protons and neutrons.. all fermions).
*The only known elementary particle with spin 0 right now is the Higgs Boson, and that explains some of its (and the field it's related to) properties.
Photon = *_Raindrop of light_*
"The photon is the quanta of electromagnetic field" is such an elegant and beautiful way to explain it
The question itself implies a certain level of knowledge that the person may or may not have. The first thing one should do is ask what does the person already know about photons. That applies especially to a 13-19 year old person, who may be a precocious genius, a university student, or a below-average youngster interested only in Tiktok.
We are teaching in 12th grade high school that photons are small amounts of energy. In other words, every 17 year old should know what a photon is. Most people just can't remember a thing about that time of their life. For many it's due to binge drinking induced memory loss.
Does the “wavelength” the teenager gets to hear about have anything to do with the “wave function” the graduate student gets?
Yes, that wave function can be a sum of 1 or more simple waves, each with their own frequency & wavelength. Photon's energy and momentum are still defined by that frequency.
@thedeemon Than you. I've always noticed, BTW, that when scientists start e,plaining the wave function and its relation to probabities, they switch to talking about electrons. They get cadgey about using the Born rule on he proton's wavefunction.
I don't think most teenagers learn about quantum mechanics. At least not in the Netherlands. You have to be at a very difficult pre-scientific education and even than choose the bèta (science) part of it. So, my estimate is less than 10% of teenagers will get in contact with quantum mechanics.
They would learn about it on youtube and tiktok, it's not just about schools
Apparently there's some basic quantum mechanics in UK physics syllabuses for 16-18-year-olds (qualifications called A-levels).
The photoelectric effect has been part of high school curricula in Europe and the US for over 40 years. As part of that we teach that "photons are small amounts of energy". That alone is enough to derive many important properties of quantum mechanics logically, even though we don't expect high school students to be able to do that.
My favourite name for a lamp is a photon chucker.
> Can you explain what a photon is?
Answer is no.
In fact, the visual is very mind-blowing... The image on the 2-dimensional screen resembles the 2-dimensional shape of the s orbitals. Other orbitals are projected to the 3rd dimension with a rotation operation. We actually use the number i for this reason, for rotation, but it is the projection of the information in these 2-dimensional planes. For this, a rotation operation to the 3rd dimension is required... Just like the relationship between electric and magnetic fields... They transform into each other with a continuous rotation operation... The function of the laser in the image is a clue that the universe can work with the holographic principle... For whom? For the sherlock holmes nature people who care about this...
sound is really quite quiet, isn't it?
guess i'm still mostly a teenager, i'll take that as a compliment
@dr Copeland: What if I use your explanation and my teenager asks why a particle would have a wavelength?
Send them to grad school
Makes sense, unfortunately the simplified explanation makes many think there is a physical particle that fills space and not what it really is, a definition of a energy wave peak.
It's none of that. A photon is just a small amount of energy.
@@lepidoptera9337 A wave peak is exactly a small amount of energy. Not sure why you think the two are different.
@@kjnoah Because an electromagnetic wave peak is not a small amount of energy. It's an emergent phenomenon formed by a specific statistical distribution of many photons. You need to learn to differentiate between one and many. Would you like a link to a Sesame Street video that explains one/many with cookies? ;-)
@@lepidoptera9337 I think you are confused. A complete waveform is many. the peak is singular. Being condescending shows we are at the limit of your knowledge here.
@@kjnoah And there is the kid who wasn't paying attention in math class, either. ;-)
so,when we look at a light source we don't see photons, we see the photons emitted from radiation falling on our surroundings?
I m kind of confused .
I thought photons are emitted from the light source.
Yes, but they constantly change into other particles, get absorbed and re-emitted. Like all quantum particles btw.
Reason: In between you and the light source are not only an almost endless stream of other particles but also quasi-particles.
So, each photon constantly bumps into "stuff".
Or simpler said:
The photon emitted at the source is not the same photon you might later detect at the destination/observation point.
I think you are taking the particle analogy for light too far. Light is both a particle AND a wave at the same time, or perhaps it is neither. In our macroscopic world we do not experience any object with wave-particle duality and so we simply do not have any model to describe what light or particles in general actually are. When we describe light travelling from a light source to our eyes we really should treat it as one continuous electromagnetic wave as the individual character of the photons really do not describe accurately what is happening.
Why os it so quiet?
Even in fyenmans picture, of you try to visualize what happens along each paths in terms of amplitudes, tgere are rotating vectors that sort of form a field in space and it is absolutely analogous to a wave anyway. I have yet to hear any argument at all that establishes light as propagating as particles in any way. Photons are just abstractions as far as i'm concerned. All the arguments about there really being these localized particles in a sense all have to do with interactions or absorption and emissions, and all of that behavior can be described by classical wave mechanics with a twist that systems that absorb and emit radiation does so in chunks and energy and momentum is absorbed from the entire wavefront much faster tyan light, then it is basically like grw, once you sum over the right distribution of such classical states. Again, roughly speaking, a more comprehensive model is needed to reproduce qft with creation and annihilation and so on. I just never understood why people think of light as particles at all, it just seems like a very useless idea when all the dynamics come from the wavefunction and have essentially nothing to do with individual trajectories.
Why are astrophysics professors so genial?
A photon is an excitation of the EM field, that fills all Universe. The end.
I'm confused about why people describe it as a particle. Isn't it much more a wave? What exactly indicates that photons are particles?
In modern physics a particle just means a quantum of some field, it's not a tiny ball. Which means it is often a wave, at least it behaves a lot like a wave, but at the same time interacts at only one particular location and by exchanging a particular amount of energy (E=hf). If you send one photon towards a camera, it will only fire 1 pixel even though it might propagate in all directions as a wave.
What does it "look" like?
Light is a cluster of expanding electrons- objects with mass. No ‘photons.’ “The Final Theory: Rethinking Our Scientific Legacy “, Mark McCutcheon for proper physics including the CAUSE of gravity, electricity, magnetism, light and well..... everything.
And no, i know the wavefunction is in hilbert space, roughly speaking, and that this is not the same as a wave in space that is deterministic, but you move some dynamics over into classical states, sum over them, normalize and if the dynamics of the classical states is right you get back the exact same probability distribution that results from quantum mechanics, from a phase space, quantum mechanics mixes possible world statistics and dynamics in a confusing way, this is why so many simpletons are convinced there is something fundamentally different from classical mechanics going on, but imo this is just verbal nonsense and doesn't have anything to do with the mathematics.
Why can we NOT see a photon of light in all directions? We can only see it when it comes straight at us, the detector?
Photons don't move. They are not "coming at you". That's just a false semi-classical picture. A photon is a small amount of energy that gets deposited in the "detector system". Before that deposition took place the photon simply didn't exist. The reason why light can have direction is because every photon of energy that gets absorbed also deposits an amount of momentum in the detector. If all these momenta are pointing in the same direction (or at least roughly), then we are dealing with a directional beam of light.
"a teenager, they probably learned a bit of quantum mechanics"
Hum maybe it's just the french educational system but I never learned about quantum mechanics when I was a teenager. (Maybe he means like watching a video online on your own time about quantum mechanics ?)
Apparently there's some basic quantum mechanics in physics syllabuses for 16-18-year-olds in the UK, for qualifications called A-levels. Students only typically do three subjects at A-level, so there's time to cover some relatively advanced material compared to countries where students study multiple subjects until they leave school.
The US high school syllabus teaches the photoelectric effect. As part of that you are being told that photons are small amounts of energy. I was being taught this in Germany over forty years ago. It must have been taught that way since the 1970s, at least.
Brilliant video!
Pun not intended lmao
well guys a photon to R. Feynman was a "particle" .
Yeah, but what particle physicists call "a particle" is often described mathematically as a wave.
Please next: What is Zero-Point Energy?
I think it's the lowest level of energy a system can be in before it ceases to be able to be a system. But I am not a physicist, I play guitar....
@@chocomalk ashton forbes is pushing the term and i wonder what he says about it. Veritasium got roasted about his video explaining the possibly wrong understanding of elictricity… lets see what happens here…
@@phasA100 Well I know for a fact that there is no way to draw energy from 0 point energy because it is the min state something can actually exist, there is nothing to take away because you would have to expend energy to destroy it to remove whats there.
What do you think he’d do if someone called him Professor Cope-Cope one day
I'm old but still a teenager....🤪
Illuminating
A vibration/traveling wave in the fabric of space-time.
those are gravitational waves
@thedeemon You're right. I'm tired.
If I was a flat-earther, I'd say that light didn't exist because I cannot see it.
Literally the only thing you can see. 😂 sounds like a flat earther
NOW I get it....😁
Light is made of particles just like the ocean is made of water buckets.
Yes, that was 100% false.
That explains why my teenage son glows in the dark.
The photon is a subatomic thing with momentum but no mass. Given that p=mv photons don't exist.
That Newtonian formula doesn't work in QM. Momentum operator is a spatial derivative of the wave function, up to a constant.
p=mv is just an approximation for small velocities. If you take relativity into account, p=mv/sqrt(1-v^2/c^2). However, if you have a massless particle moving at v=c, this gives p=0c/0, which is undefined. You can't calculate the momentum of a photon using any of these formulas, so your contradiction goes away.
"Imagine an idealized teenager..."
The explanation of photons to teenagers was really poor. No use of the words “skibidi”, “gyatt”, or “rizz”. No teenager would understand it.
Easy answer: it depends.
Photon rain makes some cool sounds.
meh.. dissatisfying to say the least.
better luck next time!
I still don’t get it, can atoms run out of photons?
Once an atom gets to the lowest energy state, it doesn't emit any more real photons until you excite it again by giving it some energy first.
That is like asking: can the sea run out of waves?
As long as there is stuff giving energy to the sea there will be waves in it's surface.
As long as energy is supplied to an atom it can then emit that energy again as it falls back to lower energy states.
But yes: completely isolate an atom and make it very cool such that it is in its lowest possible energy state and it will not emit any photons
I don't think they knows what a photon is...
It's an atom of light
It's a quantum of energy. A quantum is NOT an atom. Quite the opposite. Quantum mechanics is many things, but it is not an atomistic theory.
@lepidoptera9337 wouldn't you say that quantisation is similar to atomisation?
Of course it's not an atom of light, but it comes very close to being an atom of light. You can study a photon gas.
@@Yashodhan1917 No, it isn't atomism. If I put an atom in a jar, what I get back out later is the same atom. That is simply not true for quanta.
@lepidoptera9337 you mean light-quanta, a photon. What other types of quanta are there?
In your definition, is electron an atom or a quanta
(At this point it should be clear that we don't mean the same concept by atom as normally used)
@@Yashodhan1917 Of course an electron is a quantum. What else would it be? Quanta are combinations of energy, momentum, angular momentum and charges. These are all locally conserved quantities that follow trivially from the Poincare symmetry of the background. The entire idea of atomism was that atoms are immutable and identical building blocks of the world. That is true in chemistry. It is no longer true in nuclear physics. It is completely false in high energy physics and at the level of quantum mechanics in general.
Energy is a property. Atoms are objects. Properties and objects are not even the same category. That's kindergarten level, really. Most people are simply not paying enough attention in K-12. These details matter.
There is no balls of light in that wave