I was born in the sun. But before I had time for anything, I was already here in this detector. Now I'm no longer light, I'm now just the heat I imparted. I lived for zero seconds 😢
Speaking of Time stopping for a Light, I once travelled with my boss to a small town in northern Michigan, which had only a single stoplight at the corner of Walk and Don't Walk. He was driving the rental car to the only restaurant in town and accidentally ran through the only red light in town and was immediately pulled over by the only Sheriff in town and handed a ticket.
Also, from the perspective of light, space doesn't exist. No perceived distances, as it happens all at the same instance. So, no space, no time for light. Those things are reserved for us mortals. It's crazy....
do any photons really travel at "c", tho? I mean at 1 Hydrogen atom per cc in space, then the index of refection minus one is ~1/2N_A (Avogadro's number) ..and that is NOT zero, so v is zero point 9 [24 times]....for a time dilation of ~ 10^24 < infinity. or a 1 ms delay of the CMB photons. Small, but not zero.
The photon can be involved in just two events which it perceives as being simultaneous, one which emits it, and potentially another which absorbs and destroys it. In the heat death of the universe some photons will never be absorbed and persist in a kind of limbo for eternity, which thankfully they will not be aware of anyway.
I love Sabine. She is the irrefutable manifestation of the differences between levels of intelligence. I click on her presentations several times a month, intrigued by the possibility that I might actually understand one of them from beginning to end... against the accumulating evidence of my experience. I follow her as far as I can, then come to the separation point where, like a rocket's booster dropping off to oblivion as the rocket soars toward space, I disengage and fall back to my accustomed level. Nevertheless, I love the ride, however brief, and return for more, grateful and perhaps a micro measure more enlightened than before. Danke, Sabine!
My grandfather used to tell me this when I was a kid and I had trouble believing it. Now I am 56 and the days go whizzing past. My dad is 75 and he told me "wait a bit more - you'll see!"
Maybe, the photon only knows its wavelength. When a wave travels at a certain velocity, an observer percieves the wave as oscillating at a certain frequebcy.
When you model light as a beam of photons you wouldn't talk about frequency, rather you would talk about momenta. Maybe that already hinted at you what the problem with your question is. When you say a photon can have a frequency that's only the case if it doesn't have a defined position in space due to Heisenberg uncertainty principle. You can only make sense of a perspective placing the photon somewhere in space and then it no longer has a defined frequency. If you define a frequency you spread his position along the path of the wave thus losing any meaningful way to talk about a perspective.
I think that the confusion for many of us non-physicists about timeless light arises from the common application of time based parameters to that light. Take Blue light for example: Say it has a frequency of 600 x 10^9 Hz, or (times per second). If a photon of that light travels for a light year in distance for a 'stationary observer' at it's destination. How many "times" has that light 'pulsed'/ vibrated in its travel? From the observer POV, it has vibrated maybe 1.9X10^22 times over the year. But if time has stopped for the light, then it's time clock cannot allow even one pulsation during the journey. How then can the concept of 'frequency' be applied to a photon of any em radiation? Or is this another of those things like "spin" for an electron (which is not "actually" spinning..)?
Good question! The frequency of a beam of light is defined by the number of cycles that pass a fixed point per second. The notion of 'a fixed point' and 'a second' are both with respect to the observer's frame. The frequency will be different as measured in different reference frames. The waveform of a pulse of light however is a fixed shape that moves through space and as it moves the 'wiggles' pass an observer at a given frequency. Since the waveform doesn't change as it moves it *is* like the state of the wave is frozen or fixed.
@@tysonprice5058 I am trying to picture it! One point though: Not only does time stop but also distance shrinks (to zero - for the photon). In that case, the frozen wave has effectively no crests or troughs, it is in fact acyclic!
I think it’s bizarre that a radio transmitter can emit a weak signal, yet a simple, small receiver can pick it up hundreds of miles away. It can’t be explained by a model of radiating discrete photons, but by fields which crystallise into photons when observed. Anyone care to explain the actual physics of it?
Well, you could consider a zero point field to which may travel into, or another perspective may be that photons aren't zero, but infinitesimally small, as in approaching zero by some order of Plank time or something
There's a bunch of problems that come from accepting a rest frame moving at the speed of light. The first problem is that light moves at c in all rest frames and thus the rest frame of light is one in which light is both at rest and moving at c, somehow. The second problem is that we observe light having a time varying behavior called "frequency." If light existed in an infinitely time dilated reference frame then we could only observe it as frozen - there would be no frequency. Another problem is that we observe light to have an extent in the direction of motion called wavelength. Again, if light existed in an infinitely time dilated rest frame then we shouldn't observe it to have a wavelength because there would be infinite length contraction, yet, it does have wavelength. These problems come from arguments where we let velocity approach c and jump to conclusions about what happens in the limit when v=c. This results in expressions of the form of one divided by zero, which, mathematically is not infinity but, instead, is UNDEFINED. If you allow division by zero you can prove anything. Now, light travels at exactly c in vacuum and not a smidgin less, so applying time dilation to light becomes undefined. We need to accept that light simply plays by different rules, which is what physics does because its job is to predict what is observable in the real world.
First of all, wavelength is a product of frequency and velocity. So it's an extension of your second point rather than it's own point. Secondly, Wavelength and frequency and all that are measurements we use to describe how it moves through spacetime. They are from our reference frame, not the reference frame of light. The two can't be compared so easily. Third point, the uncertainty principle comes into play. When you treat light as a particle it has a position and therefore has 0 meaningful time. But when you treat it as a wave, it has frequency, but can't have defined position in _spacetime_, so you can't say where or when it is.
@@wootcrisp It wasn’t the MOST rigorous I’ve ever seen, but frankly it was a fine description. Him criticizing it while offering nothing constructive points to trolling. If you’re interested in physics though, I recommend the channels “ScienceClic English” (S-tier stuff, literally feels like they should charge money for it), “PBS Space Time” (pretty good stuff, and covers a lot of topics. I like how they explain why relativity does not violate causality), and “Professor Eugene Khutoryanski” (also incredible stuff, although I haven’t seen his stuff on relativity really, just electromagnetism and thermodynamics. His thermodynamics playlist is so epic)
One explanation/clarification I've been very grateful for is that everything always travels at the speed of light - it's just that somethings (e.g. us) travel mostly in the time direction of spacetime, and somethings (e.g. photons) travel entirely in the space direction of spacetime.
the time direction in this case just means permeating bounded energy (e.g. Quarks oscilating at the speed of light because they are not moving), and the space direction means permeating free energy(e.g photon). one thing no one mentiones is that energy at the quantum level is always moving at the speed of c, the only difference is wether it is bounded or free
Is there any empirical evidence that everything always travels at the speed of light, or is this just some "thought experiment" contrived by a theoretician?
Question: If photons don't have "proper time", then they are all of the same frequency. Yet at the moment a photon is absorbed by an electron in an atom, it somehow "knows" its own frequency matches a frequency the atom's electron can absorb. How does that work?
Well 3D can be shown on a screen on youtube, and the 4rth dimention IS time / movement, so youtube is made for showing 4rth dimetional images, AKA 3d videos with movement...
@@a64738 The videos are often composed of filmed 3D reality or modeled 3D animation or even a 2D animation representing what 3D animation looks like, but even though the 2D screen can give an illusion of the dimension of depth, if it really was 3D and had depth in reality you would be able to walk around it and look at if from the top or bottom or go inside of it, like a character phasing through objects when a video game is glitching. Except, when you try to peek around to the other side of that barn on screen, you find that it’s really just a 2D plane whose perspective changes in 3D relative to you. For example, there is no parallax on TH-cam, which there would be if it was really 3D.
Good description. I always like summarizing relativity by saying that everything is always moving at the same speed through spacetime, even light, so if you're stopped in space then your speed through time is maximal, and if you're moving at the speed of light through space, your speed through time coordinates is zero. Kind of like a conservation law of speed through spacetime. Though this doesn't account for the subtlety of proper vs. coordinate time.
It's not a bad way of thinking about it. The only subtlety is that all inertial reference frames are equivalent, and so who is traveling how much in which direction is relative. Everybody in an inertial frame experiences themselves as moving 100% in time, 0% in space, and everybody else as having a different mix. These all turn out to be valid descriptions of the universe as long as you transform properly between different frames: no frame is privileged at a fundamental level.
Same. But I think of it as if we’re travel through different timezones. As each of the ‘fabric of space’ has its own local time, the faster I go through space, the less of the ‘local time’ I experience. But my internal clock always ticks the same. This also helps me make sense of time dilation by gravity as a non physicist. Because according to relativity, me standing still on a planet pulled by gravity is equivalent to me accelerating upwards at constant speed, therefore, it’s no different than me moving through space even I’m standing still. The stronger the gravity = faster I move = less of the local time I experience = my time slowed down from outsider perspective.
"Kind of like a conservation law of speed through spacetime" Indeed. This explains (some of) the length distortion we see with speed: it's the same effect as refraction. The speed at which light propagates inside a medium differs from one to another. Replace medium by reference frame. "Though this doesn't account for the subtlety of proper vs. coordinate time." But if you think proper time as quantity of interaction, then you may got it. The more movement there is, the less interaction there is, and the slower proper time seems to pass. Coordinate time is just a convention used to obtain the proportion of movements to interactions/proper time.
I asked this very question on Reddit, to the effect of “is there a place that is moving at the slowest speed relative to everything else, and therefore experiencing maximum time” They said it doesn’t work like that
I've always had a question about a story I heard about Einstein and Bohr discussing the nature of quantum physics. Einstein asked Bohr if he could not observe the moon, does that mean the moon does not exist. Bohr countered by asking if Einstein could prove the opposite: how can you prove the moon exists without observation of some kind? This led me to think about locality. If i continue to directly observe the moon, but then move backwards away from it until it is so small from my perspective that my eyes or my scientific instruments cannot detect it, does that mean quantum physics depends not only on the act of observation or the observer but also on locality or the relative position between the observer and the observed?
Do you have to prove the existance of the moon for it to exist? Does the moon not exist until the moment that you've proved it? The moon does not care about wither you prove it or not other than the effect of any interaction you might have with it
The moon doesn't really exist anyway, it's just a bunch of atoms that happen to be clumped together and our brains call it a moon to make sense of it. The real question is, can you prove the existence of all the quarks and electrons in it?
@@Loreroth It was an analogy for measuring quantum particles, where the act of measurement affects the outcome (see double slit experiment). But if the analogy holds, then it would imply a locality constraint as well.
Yes, observation and locality do affect the observation according to current Physics. See double slit experiment, although it’s not a completely settled theory.
@@richb2229 But if locality does have an effect, doesn't that imply a connection between space/time and quantum physics, and if so, isn't that a big deal? I don't recall ever reading about a double slit experiment that incorporated variable distance from the observed particles and whether it had an effect on particle/wave duality.
Thank you @Sabine for the great information as always. One very simple question that might be philosophical /as you mentioned/ to how light experiences time is "the distance of stars around", usually told in light years, example: Star X is 5 LY away from us. Of course we're talking about distance here (the distance the light travels in 5 years..), but it's also related to light and time, I mean, because it's 5 LY away, it means we're seeing the star, as it was, 5 years back, this can simply be understood. But, when we say that time stops at the speed of light, this gets confusing to me. So for the light itself, it wasn't actually 5 years, but instant? (So it actually passed 5 years - for the star itself, and for us the observers, but not for light?) It means the light itsel is fresh? No? (by fresh, I mean, it just got out of the star), but how come it shows us how the star was 5 years back? This video did not explain this point and I hope you could help with it :S. But maybe because light cannot experience time, this info is meaningless, and there's a difference between light photons and the shape they represent? Something like that?
Proper time is shorthand for saying all clocks run at the same rate for every observer. Coordinate time is shorthand for saying time runs at different rates when measured by a distant observer depending on the first observers acceleration or proximity to a gravitational field. I like to think of time as a wave. If you think of each wavelength as one second and make the rule that you can't experience a second until one wavelength has passed. Then you can understand why when you accelerate to almost the speed of the wave (light) you'll still measure Proper Time in your frame of reference and why a distant observer will see your clocks running slow in Coordinate Time. It's because you're chasing a wave. It's interesting that even though your Proper Time never changes you still see red shifted & blue shifted light. Which means Light doesn't experience Proper Time. Thanks for the videos Sabine.
You know how they say that space contracts the closer you go to the speed of light. I feel that saying time stops is the friendlier side of the equation. Its easier to think of time slowing down than space shrinking. Is it safe to say that at the speed of light space is contracted to 0 and at that point... youre not even moving, moving stops at the speed of light, which i guess if time stops youre also not moving. This doesnt feel as right as saying time is contracted to zero and it doesnt feel right to think of space as shrinking for an observer but not shrinking for an outside observer. At this point i feel that you need to define what it means to "move" in spacetime and rather than define movement in space and time independently since you cant just move in space and you cant just move in time. My question is "what is movement" in spacetime.
I feel like you might appreciate this... Motion is Time A proposed change of the Time coordinates name in General Relativity and the profound effects that it reveals. Motion is Time, and its implications, reveal that time is a conscious measurement of motion and is not a physical part of the spacetime continuum. Rising from the concept that only conscience thought can remember the past or project the future and the geometry of space and mass are merely moving in any given moment of observation. A thought experiment or more? Allow me to stretch your imagination and lets freeze the entire physical universe on the spot. We can now clearly see that everything is in the exact same moment regardless of its location or velocity or applied gravitational force. Pick any next moment and we see the same results and this demonstrates that as time flows everything remains in the same equal moment. Now lets imagine you are in an empty space with no visible or perceivable motion, no heart beat, no cell growth, nothing other than an observation point in space itself. How can you perceive time? (remember your a point of observation not a human, so no, you cannot count!) Now, taking the atomic clock experiment as an example, if a third clock is introduced visible from both points of observation through instantaneous quantum communication or other means (think of a sun sized clock in the middle) Time is revealed to be constant for the observed space from either perspective when observing the same measurement. It is from these observations that we can derive that - Time is not only constant in the physical universe but only exists as a conscious measurement of motion, so MOTION is the 4th physical dimension.
"Elementary particles don't experience time" - Oh? I learned in school that the radioactive decay of muons is an example of time dilation because the faster a muon moves, the slower it decays (on average). Doesn't that mean in some sense that muons experience time?
She was glibly pointing out that elementary particles are literally not capable of experience, i.e that they are non-sentient and asking how they "experience" time in this manner is meaningless
I'm fairly sure she meant it as in elementary particles don't have consciousness. She said immediately after "because elementary particles don't experience anything". Basically, there's no sense in wondering what something that can't experience anything experiences, since we couldn't ever experience it ourselves.
From my pov, even if elementary particules don't experience time, they experience evolution, like us. So we shouldn't talk about proper time but proper evolution.
I have a question related to the CMB. Let's say a photon in the X-ray region is emitted due to "whatever" and it travels across the universe for billions of years, where it strikes an observer. However, during the trip, the universe expanded, galaxies spread apart, and due to Doppler shifting, the observer sees it as microwave. My question is, did the energy that was lost by the photon contribute to the expansion of the universe itself? Or was the expansion of the universe drawing energy away from the photon the entire time? In a nutshell, do we know yet which is the cause and which is the effect?
I have always thought of the speed of light as in a certain sense infinite. If you think about it, from the perspective of a lone observer, there is no speed limit. If you made a journey at 90% the speed of light, and on the way back put twice the energy into the acceleration, the journey would take half the time as you expect, it is just that the time it has taken for you and the time it has taken for others is not the same. With this, it makes total sense for the speed of light to be unreachable. You would need to accelerate enough to reach your destination instantaneously (again, from your perspective), in other words infinite velocity which would require infinite energy.
For tge first time in my life, I understood the spacetime diagram. Your comparison of the Euclidean and Lorentz equations was really crucial. The effect of that negative sign in the Lorentz expression , so important.
A point of interest to me is that the more matter or energy in a given region the slower time flows. Time, therefore, flows the fastest when there is no matter or energy around. There then, should be, a maximum flow of time. Now, I stand to be corrected, but I dont believe that there is any other measure of a thing that ends as a maximal value, I believe they all instead start at their own version of zero. So with that in mind, I wonder if we havent just completely misunderstood time, and we experience zero time flow as fast, and infinite time flow as the stoppage of time, such as in the singularity of a black hole. Just a reoccurring thought.
@@ankavoskuilen1725 For clarification, it was learning about poetry not writing it, though that probably would have been tortuous for me too... and I was a teenager at the time. Hopefully poetry class is very different today. I have since developed an interest in etymology, but sadly still lacking an interest in poetry (I do appreciate song lyrics as a form of poetry though - it's a pity my English teacher didn't point that out to the class at the time...)
I know your comment was humour, but in all seriousness have you noticed your perception of time changing? I can actually remember how long a second was when I was at primary school. I can tap a finger to the ticking of the clock, and it's slower than what it is today. A second when I was 10 actually lasted longer than a present day second.
This comment was posted seven hours after the original comment: Light here, I’d love to help you but I don’t have time. It had 51 likes as of time of writing.
@@gregoryturk1275 I guess you are referring to the similar post by @sleightofmind2016 7 hours ago, Light: "I'd like to respond to your question, but I simply don't have the time!" I looked when I posted this to see if anyone else had already said something similar, and I didn't see his comment, but the joke does rather suggest itself, so I'm not surprised. It looks like they were posted around the same time.
@@crawkn There was another comment just like this one? I didn’t know that😅 I just commented that because sometimes people edit their comment after a few months and all the replies make no sense.
@@gregoryturk1275I just spent way too much time looking to see which one was posted first, and it was mine, but the other one got more likes and comments 😢.
When you think about it, a photon does not experience time. It simply exists everywhere. And the universe, to a photon, has shrunk to a dot. Must be kinda boring. That moment a photon slows down, time and the universe come into existence.....hmm, sounds like the big bang.
Do you find anything interesting in the idea’s of physicists, like Julian Barbour and some others, who claim that time is an illusion? (Maybe an illusion caused by entropy, I guess)
Personal perspective of time: Your brain speed isn't constant. It's faster when in your youth and slower in your elder years. When your brain speed is high, your perception of time is that it is running slower, and the opposite for when your brain is running slower. This variability can happen within a day also, your brain speeds up during an accident and people report that time seemed to slow down. It's almost like there's an internal calculation of how much information is being consumed by your senses relative to actual time and the resulting perception is not that the amount of information changed, but that time changed. The next step would be to look into how you can exercise your brain speed function and force it into a faster mode so your personal perception of time slows down, which would be quite nice
Our brain controls the time (unconsciously) just becase time is a contstruct, an illusion. Best example: dreaming. During dreams, time is highly variable. Yet, any interaction to reality (speaking or laughing during the sleep) consumes very same time, even the dream spans for hours or more.
A few questions? How does the direction of travel affect time; i.e. does time slow down in a centrifuge? Supposedly, the universe is expanding, while we are rotating on our little planet, revolving around the sun in a galaxy that is both spinning and travelling. What are these affects on time? In space, could one just stop moving, (except for the expansion of the universe), and if so, how would time pass for them, compared to us on earth?
The Concept of Time, which we created, came from our observation of change, therefore "change is time" as in "things moving, decaying, growing and so on indicate a difference between its present status and its past ones, and with enough data a prediction of future statuses may be doable". Since Time is not some kinda magic, but just change, we can say that time is just our reconstruction of the past with given present data, in the evermarching present, and possible predictions of the future. Time may be standardized in different situations, where it may flow faster or slower, by using a standard to measure it (nuclear clocks are the best) and that ACTUALLY DOES NOT create any problem because "if the more gravity there is, the slower time flows, then one place just has time flowing slower". More than this can not be said, because things like WHY the speed of light is what it is, and so on, is not yet known.
"The Concept of Time, which we created, came from our observation of change, therefore "change is time"" You're on the right way. If you choose to be cryogenic, you will age/change slower. But does this mean that cryonics slows down time ?
I prefer to think of time slowing down with velocity in terms of charged particles and 'feeling the force'... The faster a particle moves the less it feels the force of what it passes and what it passes feels the travelling particle force less too. At the speed of light what would have been lateral to forward lines of force when stationary become 45' backwards lines at light speed (as the speed of the charge force is the same as the speed of light, so exactly 45'). -- If two charges were travelling at light speed next to each other al their forward and lateral charge force goes as 45' backward, missing each other unless they're extremely close together (touching, if that's possible).. an electron and positron travelling next to each other at light speed would not annihilate until they slow. Time 'kind of' stands still for them.
A photon doesn't have a frequency, that is, not intrinsically. Rather, we assign a photon a number we call frequency. This should be perfectly sensible given that the number we assign to a photon frequency is observer dependent.
@@kylelochlann5053 Frequency (wavelength) has to do with probabilities of interactions at certain places and times, photon is point particle though in modern QED
@@kylelochlann5053 You can look it up, it can be and has been constructed. All elementary particles are point particles, anything "wavelike" about them are only probabilities
@@RWZiggy What do you mean "look it up" I have a graduate degree in physics. You're not making any sense. There is no such thing as a position operator for a photon, or any massless particle, for "point-like" to make any sense.
@@MichaelPizyea but sadly is has been (sort of) proven to be equivalent to the law of entropy which basically means time is only an illusion because it means that putting back the atoms of a broken glass is the same as reversing time. It’s sad cause I love clocks and many feel similar.
@@howmathematicianscreatemat9226 Clocks iz kewl. I've never been much into them but I admire their precision, especially watches with such tiny mechanisms. I find mechanical clocks more interesting than electronic or atomic for that reason. As for what time is, I was being tongue-in-cheek with the old saw about everything happening at once. Except for photons, apparently. 😁
Time is what particles that exhibit mass experience, like us and our everyday experience. Because we're made of particles that exhibit mass, we're the weird ones as we experience life 'slowed down' from the speed of causality's 'instantaneous' experience. Since light isn't known to interact with the Higgs mechanism and therefore exhibit mass, it is believed to be massless and therefore light and other 'massless' particles experience time instantaneously.
Time is motion. They are the same thing. We define time by the motion of a timekeeping device. Your perception of time is determined by the motion of particles in your brain. As to why? No idea.
I guess it would be better to say "the experience of time from the perspective of light" is rather undefined there than saying time stops at the speed of light. Einstein, in his Special Theory of Relativity takes the second postulate which is "Speed of the light in vacuum is observer independent" which implies the speed of light is always c no matter who the observer is. This would mean that, we cannot define a frame of reference (Here onwards known as FoR) where the speed of light (c) is 0. From our basic knowledge on relative motion, we know, when we are talking about the "Perspective of an observer" we are referring to it as, the velocity of the observer is 0 relative to himself. I.e. we just make the speed of the "observer" equals to 0 and adjust the speed of the other FoRs according to that. So, when we are talking about the "Perspective of Light" the same should happen. Which means, we have to define a FoR in which the speed of light is 0 since now the observer is the photon. And now we see the problem. How can we define a FoR where c=0, on top of Einstein's Relativity which is based on the postulate that c is same for all observers? So this means that we cannot define a FoR where c=0. It is simply undefined in Einstein's Relativity. So, Einstein's equations simple work for any speed but C, sine the 2nd postulate of Einstein's Special theory of Relativity literally means that "Apply these equations for any of the speeds you want but c". And the weird results of "Time stopping" occurs due to the fact that we just ate the apple of the forbidden tree of Einstein's Relativity.
I like to think about it as the path the photon travels has an infinite length contraction. From the photon’s perspective, its source and destination are in the same place. That’s why it experiences no time.
what about the expansion of space & time dialation? would that make the speed of light not enough to achieve the physical experience expected there then?
Not a physicist or math(s)metician but I get confused when she says things like "if you take a trip across the entire universe, the entire trip would taken zero seconds", because, I have been told, that when light leaves the sun (which, I have also been informed is 92,955,807.3 miles away) it takes 8 minutes for it to arrive at earth.
Silly question: Two photons take off together at the same time. Traveling in the same direction at the speed of light. One travels 9 minutes then hits an object. (and stops) The other travels for a year before it hits an object. (and stops) We can measure the distance and time that both have traveled. But to the photons, they have traveled the same time and distance? If you were on one photon and had a window to look out to see the other photon crash into an object. You could not do that because to you. You both starting off together, them crashing, then you crashing ALL happen at the exact same moment? Meanwhile, outside observers see this all unfold because they are in a different "time" coordinate? What if the outside observers were traveling at near light speed. Would they lose their ability to observe?
I read your comment quickly so don't hold me to this, but yes, that's pretty much what Sabine described and like you, I have an argument against its plausibility. I do believe its possible to separate time from general and special relativity altogether, which allows them to work more logically, and in unison. It doesn't even change the equations , why would you, since they are so brilliant, but reinterpret time as Motion and bingo , it all fits together 😉
Please talk about how your working day now differs from when you were working in academia. What are your fears regarding success? How do you stay motivated? How long do you expect it to last?
For simpletons like me it would help if the graph was setup in such a way that the words "shorter" and "longer" would correspond to shorter and longer lines on the actual drawing.
I thought in Relativity the concept of light's "perspective" makes no sense? Mathematically you're literally dividing by 0 which is also another concept that makes no sense either.
If you imagine that a particle can either move or interact, its speed becomes quantity of movement/quantity of interaction. In the case of light, the amount of interaction is zero, which effectively means dividing by 0 if we want to calculate its speed. And even if we don't know how to divide by 0 mathematically, the physical meaning of this equation is obvious enough to know that quantity of movement/0 = quantity of movement.
It means that our understanding of time is tied directly to light. Relativity explains our relative experience and we use light to track changes in the universe.
@@SabineHossenfelder I always thought the story about how cosmic ray muons reach the earth's surface even though the earth's atmosphere is too thick is a great example of space-time dilation and length contraction on things travelling that fast.
@@SabineHossenfelder except any experimentalist who's built a Cherenkov detector knows n = (1+eta) for a gas, and v=c/n so gamma = 1/sqrt(2eta) --> 43 for air. It has a little time at the end.
We see light take 8 minutes, but if you were traveling at the speed of light from the sun to the earth, you would "teleport" - it would appear instantaneous, no time would pass.
I know i'm off topic but i want to ask:what is the correct equation that expresses the irradiance on the surface of an object that travels through the interstellar medium at relativistic speed?what i mean is : what is the kinetic energy received per unit of time by a square meter of an object that travels in space at a good fraction of the speed of light? I thought like this : with a N of 1 particle per cm³ i got a density of 2e-21 kg/m³,then :if the object is travelling at 0.9c it means that in 1 of ITS seconds it's travelling 0.9*2.294*299792458=6.18e8 m,so 1.27e-12 kg are impacting each second at 0.9 c on a m²,so an irradiance of 140 kW/m².Is this correct? Thanks
@SabineHossenfelder Thats why the photographs don't move! The photons stopped the time, the moment they hit the emulsion of the film! Thank you Sabine you made me see, the Einsteinian mind! @SabineHossenfelder Deshalb bewegen sich die Fotos nicht! Die Photonen haben die Zeit angehalten, als sie auf die Emulsion des Films trafen! Danke, Sabine, du hast mir den Einsteinschen Verstand gezeigt!🌈
Sabine, I have a philosophical question (not necessarily covered in this presentation). Is it possible that as we become older, time appears to accelerate, ergo, when I was five years of age, the days seemed to be longer; now, in my sixties, those self-same days fly by - so much so, that they appear indistinctive (& no two days for me are the same). So then, is there a calculation that can explain this philosophical enigma - or is it a psychological imperative that progresses as we age ?
From Wikipedia: Proper time can only be defined for timelike paths through spacetime which allow for the construction of an accompanying set of physical rulers and clocks. The same formalism for spacelike paths leads to a measurement of proper distance rather than proper time. For lightlike paths, there exists no concept of proper time and it is undefined as the spacetime interval is zero
So if time and distance for an photon is 0 (no time and no length) the whole universe is a singularity in the frame of reference of the photon. And if all frames of reference are equally valid what can we extract from that? i'll have to rewatch the video i feel that some subtilness between time frames got over my head. Another question is why in space time diagrams do we always make the speed of light at a 45º angle wouldn't if be better to draw it at 90º from the perpendicular to better show time and distance being 0 for the photon?
The way I think about time "stopping" at the speed of light is this: it isn't that time has stopped, it's that local events have slowed to stagnation relative to an observer moving at subliminal speeds. Think of all the events that make up your conscious experience. Your cells divide. Your heart beats. Oxygen and carbon dioxide are exchanged in your lungs. Electrons are moved across the mitochondrial inner membrane. Your synapses send and receive trillions of neurochemical signals. All of that slows to a crawl. You become frozen, right down to the electrons in your atoms, while the universe around you zips by. If you, at any point, stop moving at light speed, you will notice that you're in a different location, but it will appear to you as if you instantaneously teleported there because you will have essentially been in stasis for the trip. However, you haven't actually teleported, because quite a bit of time will have actually passed outside of your immediate locality.
Na, time only appears to stop because objects become redshifted. It's known as the doppler effect. But that's just the way it appears. The objects still exist in the present. Actual time dilation doesn't have anything to do with light, photons or the way something appears. It's the actual rate at which time passes for an object relative to another in the present.
5:40 Eh, how do the units work out [„proper time“] = sqrt( s^2 + m^2 ) ? I would have expected [„proper time“] = s. I guess y is normalised by the speed of light? So [y] = m / (m/s) = s ?
In the above video, Sabine Hossenfelder is applying to light what is essentially the relationship of light to other things, to wit, objects with mass. Errors are made when attempting to apply that relationship to light itself, but they might not be apparent in calculating the Lorentzian distance for light. There is another way of calculating properties of objects relative to light's velocity that will show the error: using gamma. Gamma = 1/√(1 - (v^2/c^2)) If you try to calculate gamma for the speed of light, you get: Gamma = 1/√(1 - (c^2/c^2)) Gamma = 1/√(1 - 1) Gamma = 1/√0 Gamma = 1/0 but dividing by zero is not allowed in mathematics. Time does not stop for anything, not even light.
One of the things that bothered me was how a finite amount of energy could span an infinite distance intact. after thinking about it for many years I came to the conclusion that light only exists in one dimension, eliminating all concepts of distance, if you remove time the potential of distance is eliminated.
If it were true that things moving at the speed of light had slowed or stopped time, then photons would never be able to update as they moved from atom to atom getting absorbed and readmitted? I know they are said to have no mass, but how can you have no mass, but yet you have an energy value with an equivalent to mass.
Can you please explain to me gravitational aberration especially with respect to the solar system, I do not understand why it is proactively offset at constant velocities. I always thought that with the speed of gravity (light) that the Earth-Sun system would be rotating around the abberated position of the earth-sun system 8 1/3 minutes ago... so my world has fallen apart since discovering this would be unstable. Per S. Carlip, 1999 "I show that aberration in general relativity is almost exactly canceled by velocity-dependent interactions, permitting cg=c." So aberration cancels out, isn't that kind of flaky!? To my surprise this is also what also is described by Feynman for electric charges at a constant velocity, that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay due to any "signal" traveling (or propagating) from the charge, over a distance to an observer). What?!?! WHAT HAPPENED TO THE SPEED OF LIGHT AND CAUSALITY?!?! Why it being offset exactly?!? Then I read a paper by Dr. Krızek (2008) "Does a Gravitational Aberration Contribute to the Accelerated Expansion of the Universe?" and I'm totally lost on gravitational aberration (and the counter is argued to result in universal expansion). And what is this "quadrupole" nature of gravity?!?! WHY ARE WE ROTATING AROUND THE INSTANTANEOUS POSITION OF THE EARTH-SUN AND NOT THE ABERRATED POSITION GIVEN THE SPEED OF GRAVITY/LIGHT?!?! WHAT ARE WE ROTATING AROUND?!?! WHY DOES GRAVITY HAVE A QUADRUPOLE NATURE AND WHAT DOES THAT MEAN?!?!!? HELP PLEASE!!!!
I was talking to some friends the other day and was explaining that even though the a photon traveled a billion light years across the universe to get to our retina, for the photon itself the trip was instantaneous. It kinda blew there minds.
Can you explain that. It sounds like non-sense to me. I've always heard that ftl communication isn't possible and light travels at a finite speed. Seems like contradictory statement within relativity to say the photon travels instantly.
@@MatrixVectorPSI I can try. Its not contradictory at all, time stops when you reach the speed of light. if you are observing the photon, you are relative to it, so from your perspective it takes a billion years, from the photons perspective it was instant. This is exactly the time dealation effect relativity explains.
@@captcorajus That doesn't make sense really. Why would time stop when you reach the speed of light? Just because someone is observing my light waves doesn't mean time stops for me. Also, if a photon is supposed to travel to its destination instantly. Then why can something obstruct it's path after it's emitted? If light was instant there would be no way to obstruct it. I understand, GR's been church for such a long time, it's difficult to quantify anything else. It seems like non-sense to me.
@@MatrixVectorPSI Look dude, I told you how it works. I can 'understand it' for you. This is a proven thing. The faster you go, the slower time moves for YOU in relation to the rest of the universe. Time dilation has to be accounted for in GPS Satellites for example or they wouldn't be accurate. Its a mind bender to be sure, but its still true.
@@captcorajus Now that I'll agree with. Not so much the part about light, photons, perspectives and observers. Light and time dilation aren't really related. So it's not really an explanation for why you say "for the photon itself the trip was instantaneous". Still doesn't make sense.
One interesting way to think about it is that we, our body, is made up of matter. Matter that is held together by interactions and forces mediated by photons, gluons, things that are light and move at the speed of light. Those interactions are the tick of our internal clock. As we move faster and faster though space those interactions happen over longer and longer distances, but for us one second is always one second. For the more stationary observer their one second is different than our internal clock. As we travel closer and closer to the speed of causality, it takes longer and longer time for those interactions that make matter, eventually those interactions stop because the light can never get to the next interaction. And if interactions stop our clocks stop ... and time is no longer a thing.
It means time doesn't pass for a photon from its point of origin to its destination. To the photon, the two points, as well as all points between, are experienced at precisely the same relative time.
There was a time when I think I could have grasped this.With old age having found me I hear all the words but it's like when I talk to my dog. He hears all the sounds but doesn't have a clue about what they mean. I can almost touch understanding but then - no. Frustrating
Space time etc always fascinating, but what intrigues me more is why light starts at the speed of light and stops instantly. A medium can slow it down, and gravity can distort/bend it, but why no change in speed - no acceleration - always go or stop.
Without the maths, I've always thought about time from light's POV as: If you turn on your light at exactly noon on your clock, then turn if off one second later, the trailing edge of the light beam has the timestamp of noon+1 sec, whereas the leading edge is always noon. Time can't go backwards either because the tail would have to pass the head and you'd be arriving before you left. Funky.
I caught a layman's lecture that mentioned the relationship between light's uninterruptable nature, and the fragility of quantum memory. As i understood the theory: As light crosses the event horizon of a gravitational singularity it is ripped apart and drawn into a "wider " plane, where a segment may be interrupted leaving an unaltered trace of the original spreading into perpetuity. Thoughts?
Sabine, I have a question for you. Here's the setup: A photon is emitted from a star billions of light-years away towards my laboratory on Earth. I have a pendulum in my lab that I can control the weight of the pendulum to be to the left of the photon's path or to the right of the photon's path. (Basically, we're setting up a gravitational lens) If I have the weight to the left, the photon's path will be slightly bent to the left. Conversely, if I have the weight to the right, the path will be slightly bent to the right. When the photon is midway between the star and Earth, I make a choice to either position the pendulum left or right. If the photon does not experience time, this results in a contradiction. The universe was in state A when the photon was created, but now after I make my decision, the universe is in a different state, B, and the photons path will be different than what it would have been when it started because of my actions. If the photon does not experience time, how can two versions of the same universe, A and B, exist simultaneously for the photon?
Hi, are you saying that light has no speed and that it just is always there and therefore cannot take time to travel? Also, I don not understand current thought on the definition of photons.
What would “time stops” mean? Stop everywhere? Okay, but when? Stop everywhere “at the same time”? At the same time for all observers, regardless of their relative velocities? You see the problem …
You may help, if you say, that time can't really be measured, it can only be determined at best. For measurement you'll not only need a count or a rate, you'll also need a fixed unit and the last isn't given for clocks. The duration between two counts of a clock depends on the movement of the clock, because it's mechanic is amenable to the physical law, which is called classical Doppler effect. And for light in vaccuum (the fastest we know) there'll be no time, because no one can even determine it, because clocks can't count anymore at this speed. We need something faster than that, to do it. And while clocks can't count anymore the movement of light still happens and stays as cause for the clocks state not be able to count anything. Write it down: Movements do not depend on their speed measurement. That means: nothing happens in the same instant and thats also applies to light. In it's own instance light'll have an endless high speed, but all distances will stay the same for it. It doesn't matter, what your maths will tell you.
You don't measure time, you can't. Time is a definition. Make a clock, say it has 100 markings and rotates at the same rate as the moon. The number on the clock is time, or 'the time'. Time wasn't around before humans invented it and we invented based on clocks. Think about clocks, all they do is to present different numbers to you as they operate. Because they are mechanical - as you say - they also need power. Because there is no such entity as time - there is no portal for 'time' to be stuffed into the clock. Time is the oddest SI unit, unlike the other SI units - that are real - time is odd because it isn't.....
This diagram also VERY help when you try to think how gravity works. Any standing object moves perpendicular to space line and parallel to space line. And mass curves space-line, so time-line change it's angle and object now moves to center of mass, and while object get closer to boundaries of massive object, angle of time changes more => acceleration of free fall. Event horizon also understandable there extremely easy. Light always moves at angle on 45°, so event horizon is point, where curvature of space get an 45° anglel, so light starts move parallel to not curved space, what means it will not go away from this point, but if there will be second massive object going nearby it can curve space at event horizon from 45° to 45,00000000000....0001°, so light will escape that place. And more massive that object flying nearby to event horizon, more deeper light can escape event horizon. I think when two black holes of same mass interact, they can throw out of them huge amount of light(if light still there and didn't fall too deep). So particles aren't particles, they're rays through time-space, so only in space dimension they looks like dots. So, our world REALLY made from strings, but not from those in string theory. And yeah, singularity in black holes REAL time machine, they just travel you to Big Bang, so they're not very usefull. Or singularity doesn't exist(what also really easy to imagine if curvature inside massive objects aren't hyperbolic but parabolic)
Something I wondered, not being a physicus, nor mathematician: Why is in science the speed of light in vacuum not defined as 0, and all other velocities defined relative to that new absolute zero? Not sure if it would make sense, but in my naive view, this looks like a more coherent/peaceful solution to describing the universe. A video about this would be nice!
I love this stuff and the way you present it. I dropped out of high school in grade ten and so I missed the basics of physics. I have often said that I used to do drugs to blow my mind - now I just watch physics videos to do the same. Thank You
What would the light experience in an astrophysical light year traveling? Totally confused , I don’t know what the time is other than my repetitive heart beats. Could you please explain the relation of the coordinated universe Einesteinean time and the atomic clock?
Hi Sabine, if proper time stops at the speed of light, does that mean, photons, from their own perspective, are eternal standing waves, stretching from the infinite past, into the infinite future? Because, if that's the case, couldn't they be a medium, through which retrocausal signalling can occur, for photon interactions, being observed, from within coordinate time? If so, might that explain the seemingly retrocausal results of the double slit experiment?
I'm not sure I'm getting it. We know it takes light even from as close as the sun 8 minutes to arrive. How could proper time for light stop if the parts of spacetime it touches are in different times by the time it reaches them?
This video comes with a quiz which you can take here: quizwithit.com/start_thequiz/1713615419870x520177431082434560
Why not travel fare back in time as time is moving forward
Space Time diagram: ASSUMES both space and time change at the same warped rates. (Which they probably do not).
2:15 " ... coordinate time is physically meaningless"
6:42: "... coordinate time [that] describes the universe we inhabit"
Now I'm confused.
Nobody with an IQ over 80 cares
Light moves at the speed of time
Light: "I'd like to respond to your question, but I simply don't have the time!"
Light: "I'll take a potato chip.... and eat it!"
I thought you have all the time in the world! 🤷♂
I was born in the sun. But before I had time for anything, I was already here in this detector. Now I'm no longer light, I'm now just the heat I imparted.
I lived for zero seconds 😢
@@treeinthewood It's all relative....
😂😂
TH-cam's FINEST deadpan humor. Don't ever change, Sabine!
@@imilliemedina666 ... then her husband would be quite perturbed. :)
I am definitely looking for a way off the planet 😆😆💿
Love from North America. Ditto about never changing
Speaking of Time stopping for a Light, I once travelled with my boss to a small town in northern Michigan, which had only a single stoplight at the corner of Walk and Don't Walk. He was driving the rental car to the only restaurant in town and accidentally ran through the only red light in town and was immediately pulled over by the only Sheriff in town and handed a ticket.
Was that also the only ticket in town?
I truly wish I could live in there...
A photon checks into a hotel and is asked if it needs help with its luggage. It responds: "No thanks, I am travelling light.".
Well done! 8 out of 10
@@jonathangehman4005 A photon's wife tell's him to fix the leaky faucet. He tells her he's got no time.
wow...😮
Why didn’t he just say he didn’t have the time for it?
Receptionist: Mr.Light, here's your key, your room is...
Light: I'm checking out.
Quantum Bell boy: I'm having and not having your luggage.
From the perspective of the photon, it is absorbed the moment it is emitted.
which would imply that, from the perspective of the photon, it never existed.
@@3rdPartyIntervener Not much of a retirement plan...
Also, from the perspective of light, space doesn't exist. No perceived distances, as it happens all at the same instance. So, no space, no time for light. Those things are reserved for us mortals. It's crazy....
do any photons really travel at "c", tho? I mean at 1 Hydrogen atom per cc in space, then the index of refection minus one is ~1/2N_A (Avogadro's number) ..and that is NOT zero, so v is zero point 9 [24 times]....for a time dilation of ~ 10^24 < infinity. or a 1 ms delay of the CMB photons. Small, but not zero.
The photon can be involved in just two events which it perceives as being simultaneous, one which emits it, and potentially another which absorbs and destroys it.
In the heat death of the universe some photons will never be absorbed and persist in a kind of limbo for eternity, which thankfully they will not be aware of anyway.
I love Sabine. She is the irrefutable manifestation of the differences between levels of intelligence. I click on her presentations several times a month, intrigued by the possibility that I might actually understand one of them from beginning to end... against the accumulating evidence of my experience. I follow her as far as I can, then come to the separation point where, like a rocket's booster dropping off to oblivion as the rocket soars toward space, I disengage and fall back to my accustomed level. Nevertheless, I love the ride, however brief, and return for more, grateful and perhaps a micro measure more enlightened than before. Danke, Sabine!
eloquent reply! and a masterful metaphor
"I have always been everywhere I am."
- Light
.... you have more job to do to consider yourself
Photons are extreme extroverts.
They don’t need personal time.
Time slows down when at work and speeds up when you are not!!!! Time also speeds up after 50 years of age!!!!!!
My grandfather used to tell me this when I was a kid and I had trouble believing it. Now I am 56 and the days go whizzing past. My dad is 75 and he told me "wait a bit more - you'll see!"
@@anonydun82fgoog35 LMFAO I am 71 and he is correct!!
*Perception of Time
@@yestokindness99 To literal…..
The speed of time is directly proportionate to the distance of any bathroom when you have to pee.
I would love to see a follow-up video to explain how photons can have a frequency (cycles/T) given that T = 0 from the perspective of the photon.
Maybe, the photon only knows its wavelength. When a wave travels at a certain velocity, an observer percieves the wave as oscillating at a certain frequebcy.
Big head... lol
When you model light as a beam of photons you wouldn't talk about frequency, rather you would talk about momenta. Maybe that already hinted at you what the problem with your question is.
When you say a photon can have a frequency that's only the case if it doesn't have a defined position in space due to Heisenberg uncertainty principle. You can only make sense of a perspective placing the photon somewhere in space and then it no longer has a defined frequency. If you define a frequency you spread his position along the path of the wave thus losing any meaningful way to talk about a perspective.
And I always thought proper time was when one had to wear a tie.
Proper tiem
@@mikeycomics Proper item
@@yourguard4Proper tie 'em
I always thought proper time was using 24 hours instead of 12
These lowbrow pun comments representing how superficial this channel has become
I think that the confusion for many of us non-physicists about timeless light arises from the common application of time based parameters to that light. Take Blue light for example: Say it has a frequency of 600 x 10^9 Hz, or (times per second). If a photon of that light travels for a light year in distance for a 'stationary observer' at it's destination. How many "times" has that light 'pulsed'/ vibrated in its travel? From the observer POV, it has vibrated maybe 1.9X10^22 times over the year. But if time has stopped for the light, then it's time clock cannot allow even one pulsation during the journey. How then can the concept of 'frequency' be applied to a photon of any em radiation? Or is this another of those things like "spin" for an electron (which is not "actually" spinning..)?
In this case, from the photon's perspective, the photon would be one long wiggly line rather than a particle moving over time.
Good question! The frequency of a beam of light is defined by the number of cycles that pass a fixed point per second. The notion of 'a fixed point' and 'a second' are both with respect to the observer's frame. The frequency will be different as measured in different reference frames. The waveform of a pulse of light however is a fixed shape that moves through space and as it moves the 'wiggles' pass an observer at a given frequency. Since the waveform doesn't change as it moves it *is* like the state of the wave is frozen or fixed.
@@tysonprice5058 I am trying to picture it! One point though: Not only does time stop but also distance shrinks (to zero - for the photon). In that case, the frozen wave has effectively no crests or troughs, it is in fact acyclic!
I think it’s bizarre that a radio transmitter can emit a weak signal, yet a simple, small receiver can pick it up hundreds of miles away. It can’t be explained by a model of radiating discrete photons, but by fields which crystallise into photons when observed. Anyone care to explain the actual physics of it?
Well, you could consider a zero point field to which may travel into, or another perspective may be that photons aren't zero, but infinitesimally small, as in approaching zero by some order of Plank time or something
There's a bunch of problems that come from accepting a rest frame moving at the speed of light. The first problem is that light moves at c in all rest frames and thus the rest frame of light is one in which light is both at rest and moving at c, somehow. The second problem is that we observe light having a time varying behavior called "frequency." If light existed in an infinitely time dilated reference frame then we could only observe it as frozen - there would be no frequency. Another problem is that we observe light to have an extent in the direction of motion called wavelength. Again, if light existed in an infinitely time dilated rest frame then we shouldn't observe it to have a wavelength because there would be infinite length contraction, yet, it does have wavelength. These problems come from arguments where we let velocity approach c and jump to conclusions about what happens in the limit when v=c. This results in expressions of the form of one divided by zero, which, mathematically is not infinity but, instead, is UNDEFINED. If you allow division by zero you can prove anything. Now, light travels at exactly c in vacuum and not a smidgin less, so applying time dilation to light becomes undefined. We need to accept that light simply plays by different rules, which is what physics does because its job is to predict what is observable in the real world.
First of all, wavelength is a product of frequency and velocity. So it's an extension of your second point rather than it's own point. Secondly, Wavelength and frequency and all that are measurements we use to describe how it moves through spacetime. They are from our reference frame, not the reference frame of light. The two can't be compared so easily. Third point, the uncertainty principle comes into play. When you treat light as a particle it has a position and therefore has 0 meaningful time. But when you treat it as a wave, it has frequency, but can't have defined position in _spacetime_, so you can't say where or when it is.
I don't think I've ever heard this particular relationship between light and time worded so well. Thank you.
lol 😂. it’s worded incorrectly. sabine doesn’t understand special relativity.
@@mrslave41 I see. I don't either so I cannot adjudicate. To me it just seemed like a novel description.
@@wootcrisp
It wasn’t the MOST rigorous I’ve ever seen, but frankly it was a fine description. Him criticizing it while offering nothing constructive points to trolling.
If you’re interested in physics though, I recommend the channels “ScienceClic English” (S-tier stuff, literally feels like they should charge money for it), “PBS Space Time” (pretty good stuff, and covers a lot of topics. I like how they explain why relativity does not violate causality), and “Professor Eugene Khutoryanski” (also incredible stuff, although I haven’t seen his stuff on relativity really, just electromagnetism and thermodynamics. His thermodynamics playlist is so epic)
She had me within a minute, with "and who is not looking for a way to get off the planet at this point..."
Danke!
One explanation/clarification I've been very grateful for is that everything always travels at the speed of light - it's just that somethings (e.g. us) travel mostly in the time direction of spacetime, and somethings (e.g. photons) travel entirely in the space direction of spacetime.
the time direction in this case just means permeating bounded energy (e.g. Quarks oscilating at the speed of light because they are not moving), and the space direction means permeating free energy(e.g photon). one thing no one mentiones is that energy at the quantum level is always moving at the speed of c, the only difference is wether it is bounded or free
@@stefan24georgiev the channel float head physics is far superior in explaining this.
Is there any empirical evidence that everything always travels at the speed of light, or is this just some "thought experiment" contrived by a theoretician?
@@NondescriptMammal Yes it has been proven.
@@NondescriptMammal 'We all move at speed of light through spacetime'.. What does it really mean?
FloatHeadPhysics
149K subscribers
Light here: I'm not moving, you are.
Question: If photons don't have "proper time", then they are all of the same frequency. Yet at the moment a photon is absorbed by an electron in an atom, it somehow "knows" its own frequency matches a frequency the atom's electron can absorb. How does that work?
"last time I checked TH-cam didn't support 4-dimentional graphic" - this is gold
Perhaps just as well, given the amount of data it would take. A 256*256*256*256 object would take 4.2GB, if each hypervoxel was just one byte.
Not even 3, technically.
@@galacticminx
This does make me wonder, though, how far we could go with 4D visualizations in holograms or smth
Well 3D can be shown on a screen on youtube, and the 4rth dimention IS time / movement, so youtube is made for showing 4rth dimetional images, AKA 3d videos with movement...
@@a64738
The videos are often composed of filmed 3D reality or modeled 3D animation or even a 2D animation representing what 3D animation looks like, but even though the 2D screen can give an illusion of the dimension of depth, if it really was 3D and had depth in reality you would be able to walk around it and look at if from the top or bottom or go inside of it, like a character phasing through objects when a video game is glitching. Except, when you try to peek around to the other side of that barn on screen, you find that it’s really just a 2D plane whose perspective changes in 3D relative to you. For example, there is no parallax on TH-cam, which there would be if it was really 3D.
Good description. I always like summarizing relativity by saying that everything is always moving at the same speed through spacetime, even light, so if you're stopped in space then your speed through time is maximal, and if you're moving at the speed of light through space, your speed through time coordinates is zero. Kind of like a conservation law of speed through spacetime. Though this doesn't account for the subtlety of proper vs. coordinate time.
It's not a bad way of thinking about it. The only subtlety is that all inertial reference frames are equivalent, and so who is traveling how much in which direction is relative. Everybody in an inertial frame experiences themselves as moving 100% in time, 0% in space, and everybody else as having a different mix. These all turn out to be valid descriptions of the universe as long as you transform properly between different frames: no frame is privileged at a fundamental level.
@@jameshart2622 If you are travelling through space, you are through less time... if you want to think one can 'travel' through time.
Same. But I think of it as if we’re travel through different timezones. As each of the ‘fabric of space’ has its own local time, the faster I go through space, the less of the ‘local time’ I experience. But my internal clock always ticks the same.
This also helps me make sense of time dilation by gravity as a non physicist. Because according to relativity, me standing still on a planet pulled by gravity is equivalent to me accelerating upwards at constant speed, therefore, it’s no different than me moving through space even I’m standing still. The stronger the gravity = faster I move = less of the local time I experience = my time slowed down from outsider perspective.
"Kind of like a conservation law of speed through spacetime"
Indeed. This explains (some of) the length distortion we see with speed: it's the same effect as refraction. The speed at which light propagates inside a medium differs from one to another. Replace medium by reference frame.
"Though this doesn't account for the subtlety of proper vs. coordinate time."
But if you think proper time as quantity of interaction, then you may got it. The more movement there is, the less interaction there is, and the slower proper time seems to pass. Coordinate time is just a convention used to obtain the proportion of movements to interactions/proper time.
I asked this very question on Reddit, to the effect of “is there a place that is moving at the slowest speed relative to everything else, and therefore experiencing maximum time”
They said it doesn’t work like that
Time typically just about stops M-F at about 8am-12pm and again at 1pm-5pm.
Proper time - like tea and cake time
Half past 3: 00 to be specific☕🍰
and proper food - cucumber sandwiches and fruit cake
Yes, but proper tea is theft (Apologies for the old socialist joke)
Lunch time.
@@danielcomeau9880 Time is an illusion, lunch time doubly so.
I've always had a question about a story I heard about Einstein and Bohr discussing the nature of quantum physics. Einstein asked Bohr if he could not observe the moon, does that mean the moon does not exist. Bohr countered by asking if Einstein could prove the opposite: how can you prove the moon exists without observation of some kind? This led me to think about locality. If i continue to directly observe the moon, but then move backwards away from it until it is so small from my perspective that my eyes or my scientific instruments cannot detect it, does that mean quantum physics depends not only on the act of observation or the observer but also on locality or the relative position between the observer and the observed?
Do you have to prove the existance of the moon for it to exist? Does the moon not exist until the moment that you've proved it? The moon does not care about wither you prove it or not other than the effect of any interaction you might have with it
The moon doesn't really exist anyway, it's just a bunch of atoms that happen to be clumped together and our brains call it a moon to make sense of it.
The real question is, can you prove the existence of all the quarks and electrons in it?
@@Loreroth It was an analogy for measuring quantum particles, where the act of measurement affects the outcome (see double slit experiment). But if the analogy holds, then it would imply a locality constraint as well.
Yes, observation and locality do affect the observation according to current Physics. See double slit experiment, although it’s not a completely settled theory.
@@richb2229 But if locality does have an effect, doesn't that imply a connection between space/time and quantum physics, and if so, isn't that a big deal? I don't recall ever reading about a double slit experiment that incorporated variable distance from the observed particles and whether it had an effect on particle/wave duality.
Thank you @Sabine for the great information as always.
One very simple question that might be philosophical /as you mentioned/ to how light experiences time is "the distance of stars around", usually told in light years, example: Star X is 5 LY away from us.
Of course we're talking about distance here (the distance the light travels in 5 years..), but it's also related to light and time, I mean, because it's 5 LY away, it means we're seeing the star, as it was, 5 years back, this can simply be understood. But, when we say that time stops at the speed of light, this gets confusing to me.
So for the light itself, it wasn't actually 5 years, but instant? (So it actually passed 5 years - for the star itself, and for us the observers, but not for light?)
It means the light itsel is fresh? No? (by fresh, I mean, it just got out of the star), but how come it shows us how the star was 5 years back? This video did not explain this point and I hope you could help with it :S.
But maybe because light cannot experience time, this info is meaningless, and there's a difference between light photons and the shape they represent? Something like that?
Thank you for the video.
I have always admired you, Sabine!!! Love your work!
Proper time is shorthand for saying all clocks run at the same rate for every observer.
Coordinate time is shorthand for saying time runs at different rates when measured by a distant observer depending on the first observers acceleration or proximity to a gravitational field.
I like to think of time as a wave. If you think of each wavelength as one second and make the rule that you can't experience a second until one wavelength has passed. Then you can understand why when you accelerate to almost the speed of the wave (light) you'll still measure Proper Time in your frame of reference and why a distant observer will see your clocks running slow in Coordinate Time. It's because you're chasing a wave. It's interesting that even though your Proper Time never changes you still see red shifted & blue shifted light. Which means Light doesn't experience Proper Time.
Thanks for the videos Sabine.
You know how they say that space contracts the closer you go to the speed of light. I feel that saying time stops is the friendlier side of the equation. Its easier to think of time slowing down than space shrinking. Is it safe to say that at the speed of light space is contracted to 0 and at that point... youre not even moving, moving stops at the speed of light, which i guess if time stops youre also not moving. This doesnt feel as right as saying time is contracted to zero and it doesnt feel right to think of space as shrinking for an observer but not shrinking for an outside observer. At this point i feel that you need to define what it means to "move" in spacetime and rather than define movement in space and time independently since you cant just move in space and you cant just move in time. My question is "what is movement" in spacetime.
Yes, you have a good point there....
I feel like you might appreciate this...
Motion is Time
A proposed change of the Time coordinates name in General Relativity and the profound effects that it reveals.
Motion is Time, and its implications, reveal that time is a conscious measurement of motion and is not a physical part of the spacetime continuum.
Rising from the concept that only conscience thought can remember the past or project the future and the geometry of space and mass are merely moving in any given moment of observation.
A thought experiment or more?
Allow me to stretch your imagination and lets freeze the entire physical universe on the spot. We can now clearly see that everything is in the exact same moment regardless of its location or velocity or applied gravitational force. Pick any next moment and we see the same results and this demonstrates that as time flows everything remains in the same equal moment.
Now lets imagine you are in an empty space with no visible or perceivable motion, no heart beat, no cell growth, nothing other than an observation point in space itself. How can you perceive time?
(remember your a point of observation not a human, so no, you cannot count!) Now, taking the atomic clock experiment as an example, if a third clock is introduced visible from both points of observation through instantaneous quantum communication or other means (think of a sun sized clock in the middle) Time is revealed to be constant for the observed space from either perspective when observing the same measurement. It is from these observations that we can derive that - Time is not only constant in the physical universe but only exists as a conscious measurement of motion, so MOTION is the 4th
physical dimension.
"Elementary particles don't experience time" - Oh? I learned in school that the radioactive decay of muons is an example of time dilation because the faster a muon moves, the slower it decays (on average). Doesn't that mean in some sense that muons experience time?
I think she should have said massless particles don’t experience time. Surprised that such obvious error got through.
She was glibly pointing out that elementary particles are literally not capable of experience, i.e that they are non-sentient and asking how they "experience" time in this manner is meaningless
@@myusernamehere9972 this was my interpretation as well
I'm fairly sure she meant it as in elementary particles don't have consciousness. She said immediately after "because elementary particles don't experience anything".
Basically, there's no sense in wondering what something that can't experience anything experiences, since we couldn't ever experience it ourselves.
From my pov, even if elementary particules don't experience time, they experience evolution, like us. So we shouldn't talk about proper time but proper evolution.
I have a question related to the CMB. Let's say a photon in the X-ray region is emitted due to "whatever" and it travels across the universe for billions of years, where it strikes an observer. However, during the trip, the universe expanded, galaxies spread apart, and due to Doppler shifting, the observer sees it as microwave.
My question is, did the energy that was lost by the photon contribute to the expansion of the universe itself? Or was the expansion of the universe drawing energy away from the photon the entire time?
In a nutshell, do we know yet which is the cause and which is the effect?
dark energy seems to be the cause of expansion but not much is known about it yet
"If you're interested in space travel and.. who's not interested in getting off the planet at this point?" 😂
Never change Sabine, never change! 😁
Asians seems quite happy with how things are developing. I wonder why.
Only if you live in Germany .... 😁.... or the USA ... they are almost there where Germany was in 1940......
@@thechessmaster9291 in what sense? Going crazy with socialism?
Amazing line!
@@HR-yd5ib Just stop shoving your politics into everything 🙄
5:30 I'm disappointed there's no Light Yagami comments here :(
I was also looking for any. Only found yours, but that's still a win.
There's a Light Yagami reply in the first comment
Light Yagami will probably boast "I'll kill you in no time!"
I have always thought of the speed of light as in a certain sense infinite. If you think about it, from the perspective of a lone observer, there is no speed limit. If you made a journey at 90% the speed of light, and on the way back put twice the energy into the acceleration, the journey would take half the time as you expect, it is just that the time it has taken for you and the time it has taken for others is not the same. With this, it makes total sense for the speed of light to be unreachable. You would need to accelerate enough to reach your destination instantaneously (again, from your perspective), in other words infinite velocity which would require infinite energy.
That's how I think of it. 👍
For tge first time in my life, I understood the spacetime diagram. Your comparison of the Euclidean and Lorentz equations was really crucial. The effect of that negative sign in the Lorentz expression , so important.
5:30 I think Light is too busy with the death note to reply
😂👌
And eating potato ships
A point of interest to me is that the more matter or energy in a given region the slower time flows. Time, therefore, flows the fastest when there is no matter or energy around. There then, should be, a maximum flow of time.
Now, I stand to be corrected, but I dont believe that there is any other measure of a thing that ends as a maximal value, I believe they all instead start at their own version of zero.
So with that in mind, I wonder if we havent just completely misunderstood time, and we experience zero time flow as fast, and infinite time flow as the stoppage of time, such as in the singularity of a black hole.
Just a reoccurring thought.
At school we had triple period English poetry - time DEFINTELY slowed down during this time. The same with stats @ uni!
LOL
For me, that would have increased the speed of time.
@@ankavoskuilen1725 For clarification, it was learning about poetry not writing it, though that probably would have been tortuous for me too... and I was a teenager at the time. Hopefully poetry class is very different today. I have since developed an interest in etymology, but sadly still lacking an interest in poetry (I do appreciate song lyrics as a form of poetry though - it's a pity my English teacher didn't point that out to the class at the time...)
I know your comment was humour, but in all seriousness have you noticed your perception of time changing? I can actually remember how long a second was when I was at primary school. I can tap a finger to the ticking of the clock, and it's slower than what it is today. A second when I was 10 actually lasted longer than a present day second.
@@galacticminx It could be age related... time just seems to fky now I renember school terms seeming to last forever...
Light here, I'd love to help you but I don't have time.
This comment was posted seven hours after the original comment: Light here, I’d love to help you but I don’t have time. It had 51 likes as of time of writing.
@@gregoryturk1275 I guess you are referring to the similar post by @sleightofmind2016 7 hours ago, Light: "I'd like to respond to your question, but I simply don't have the time!" I looked when I posted this to see if anyone else had already said something similar, and I didn't see his comment, but the joke does rather suggest itself, so I'm not surprised. It looks like they were posted around the same time.
@@crawkn There was another comment just like this one? I didn’t know that😅 I just commented that because sometimes people edit their comment after a few months and all the replies make no sense.
@@gregoryturk1275I just spent way too much time looking to see which one was posted first, and it was mine, but the other one got more likes and comments 😢.
@@crawkn That sucks :(
When you think about it, a photon does not experience time. It simply exists everywhere. And the universe, to a photon, has shrunk to a dot. Must be kinda boring. That moment a photon slows down, time and the universe come into existence.....hmm, sounds like the big bang.
My kids and I were discussing this the other day. Referenced them to you for clarity!!
Do you find anything interesting in the idea’s of physicists, like Julian Barbour and some others, who claim that time is an illusion? (Maybe an illusion caused by entropy, I guess)
Yes, I find it interesting. But whether time is an illusion or not, it sure is very useful to order events that we observe.
Please do an episode on Julian Barbour
@@SabineHossenfelder well, it kinda stops everything from happening all at once!
@@andywason3414
That's not what I observe at work. Fan spins and everything hits it at once.
In a sense time is an illusion of the human mind and the senses.
Personal perspective of time: Your brain speed isn't constant. It's faster when in your youth and slower in your elder years. When your brain speed is high, your perception of time is that it is running slower, and the opposite for when your brain is running slower. This variability can happen within a day also, your brain speeds up during an accident and people report that time seemed to slow down. It's almost like there's an internal calculation of how much information is being consumed by your senses relative to actual time and the resulting perception is not that the amount of information changed, but that time changed. The next step would be to look into how you can exercise your brain speed function and force it into a faster mode so your personal perception of time slows down, which would be quite nice
Our brain controls the time (unconsciously) just becase time is a contstruct, an illusion. Best example: dreaming. During dreams, time is highly variable. Yet, any interaction to reality (speaking or laughing during the sleep) consumes very same time, even the dream spans for hours or more.
Doing good Sabine, thanks for asking 👍
I'm so glad that you took the time to make this video Sabine! 👍👍
A few questions? How does the direction of travel affect time; i.e. does time slow down in a centrifuge? Supposedly, the universe is expanding, while we are rotating on our little planet, revolving around the sun in a galaxy that is both spinning and travelling. What are these affects on time? In space, could one just stop moving, (except for the expansion of the universe), and if so, how would time pass for them, compared to us on earth?
I have heard some say it is not the speed of movement, but the acceleration that give the slowed down of time (and time is in essence movement).
The Concept of Time, which we created, came from our observation of change, therefore "change is time" as in "things moving, decaying, growing and so on indicate a difference between its present status and its past ones, and with enough data a prediction of future statuses may be doable".
Since Time is not some kinda magic, but just change, we can say that time is just our reconstruction of the past with given present data, in the evermarching present, and possible predictions of the future.
Time may be standardized in different situations, where it may flow faster or slower, by using a standard to measure it (nuclear clocks are the best) and that ACTUALLY DOES NOT create any problem because "if the more gravity there is, the slower time flows, then one place just has time flowing slower".
More than this can not be said, because things like WHY the speed of light is what it is, and so on, is not yet known.
Ngl this kinda sounds like mushroom talk
@@PlatypusMusiq It isn't.
Entropy + momentum
"The Concept of Time, which we created, came from our observation of change, therefore "change is time""
You're on the right way.
If you choose to be cryogenic, you will age/change slower. But does this mean that cryonics slows down time ?
@@noname8192 Not in the magical sense, yes in the physical and chemical sense.
That light can brag it went across the whole universe in a split second.
But it has no time for anything. As Sabine just explained. 😊
I prefer to think of time slowing down with velocity in terms of charged particles and 'feeling the force'... The faster a particle moves the less it feels the force of what it passes and what it passes feels the travelling particle force less too. At the speed of light what would have been lateral to forward lines of force when stationary become 45' backwards lines at light speed (as the speed of the charge force is the same as the speed of light, so exactly 45').
--
If two charges were travelling at light speed next to each other al their forward and lateral charge force goes as 45' backward, missing each other unless they're extremely close together (touching, if that's possible).. an electron and positron travelling next to each other at light speed would not annihilate until they slow. Time 'kind of' stands still for them.
The question that comes to my mind thinking about time stopping at the speed of light is: How does light have a frequency if it can't experience time?
A photon doesn't have a frequency, that is, not intrinsically. Rather, we assign a photon a number we call frequency. This should be perfectly sensible given that the number we assign to a photon frequency is observer dependent.
@@kylelochlann5053 Frequency (wavelength) has to do with probabilities of interactions at certain places and times, photon is point particle though in modern QED
@@RWZiggy So, how exactly is a photon a point particle if there's no photon position operator?
@@kylelochlann5053 You can look it up, it can be and has been constructed. All elementary particles are point particles, anything "wavelike" about them are only probabilities
@@RWZiggy What do you mean "look it up" I have a graduate degree in physics. You're not making any sense. There is no such thing as a position operator for a photon, or any massless particle, for "point-like" to make any sense.
Could you make video on What is time? Why is it? And current research too
Time is what keeps everything from happening all at once.
Except for photons, apparently.
@@MichaelPizyea but sadly is has been (sort of) proven to be equivalent to the law of entropy which basically means time is only an illusion because it means that putting back the atoms of a broken glass is the same as reversing time. It’s sad cause I love clocks and many feel similar.
@@howmathematicianscreatemat9226 Clocks iz kewl. I've never been much into them but I admire their precision, especially watches with such tiny mechanisms. I find mechanical clocks more interesting than electronic or atomic for that reason.
As for what time is, I was being tongue-in-cheek with the old saw about everything happening at once. Except for photons, apparently. 😁
Time is what particles that exhibit mass experience, like us and our everyday experience.
Because we're made of particles that exhibit mass, we're the weird ones as we experience life 'slowed down' from the speed of causality's 'instantaneous' experience. Since light isn't known to interact with the Higgs mechanism and therefore exhibit mass, it is believed to be massless and therefore light and other 'massless' particles experience time instantaneously.
Time is motion. They are the same thing. We define time by the motion of a timekeeping device. Your perception of time is determined by the motion of particles in your brain. As to why? No idea.
I guess it would be better to say "the experience of time from the perspective of light" is rather undefined there than saying time stops at the speed of light. Einstein, in his Special Theory of Relativity takes the second postulate which is "Speed of the light in vacuum is observer independent" which implies the speed of light is always c no matter who the observer is. This would mean that, we cannot define a frame of reference (Here onwards known as FoR) where the speed of light (c) is 0.
From our basic knowledge on relative motion, we know, when we are talking about the "Perspective of an observer" we are referring to it as, the velocity of the observer is 0 relative to himself. I.e. we just make the speed of the "observer" equals to 0 and adjust the speed of the other FoRs according to that.
So, when we are talking about the "Perspective of Light" the same should happen. Which means, we have to define a FoR in which the speed of light is 0 since now the observer is the photon. And now we see the problem. How can we define a FoR where c=0, on top of Einstein's Relativity which is based on the postulate that c is same for all observers? So this means that we cannot define a FoR where c=0. It is simply undefined in Einstein's Relativity.
So, Einstein's equations simple work for any speed but C, sine the 2nd postulate of Einstein's Special theory of Relativity literally means that "Apply these equations for any of the speeds you want but c". And the weird results of "Time stopping" occurs due to the fact that we just ate the apple of the forbidden tree of Einstein's Relativity.
I like to think about it as the path the photon travels has an infinite length contraction. From the photon’s perspective, its source and destination are in the same place. That’s why it experiences no time.
But measurably different places voids the principle that objective facts are true for everyone.
Dear Light, if you’re listening, please take me with you when you go! Let me be zero with you
what about the expansion of space & time dialation? would that make the speed of light not enough to achieve the physical experience expected there then?
Hi. Light here. I can tell you that the future is bright.
If you were really light you would know the future 100% dark untill you've gone through
Gravitational waves also move with the speed of light.
Though no one knows which kind of particles they are built from
Not a physicist or math(s)metician but I get confused when she says things like "if you take a trip across the entire universe, the entire trip would taken zero seconds", because, I have been told, that when light leaves the sun (which, I have also been informed is 92,955,807.3 miles away) it takes 8 minutes for it to arrive at earth.
It takes light 8 minutes in our reference frame. There is no reference frame for light so there is no elapsed time either.
Silly question: Two photons take off together at the same time. Traveling in the same direction at the speed of light. One travels 9 minutes then hits an object. (and stops) The other travels for a year before it hits an object. (and stops) We can measure the distance and time that both have traveled. But to the photons, they have traveled the same time and distance? If you were on one photon and had a window to look out to see the other photon crash into an object. You could not do that because to you. You both starting off together, them crashing, then you crashing ALL happen at the exact same moment? Meanwhile, outside observers see this all unfold because they are in a different "time" coordinate? What if the outside observers were traveling at near light speed. Would they lose their ability to observe?
I read your comment quickly so don't hold me to this, but yes, that's pretty much what Sabine described and like you, I have an argument against its plausibility.
I do believe its possible to separate time from general and special relativity altogether, which allows them to work more logically, and in unison. It doesn't even change the equations , why would you, since they are so brilliant, but reinterpret time as Motion and bingo , it all fits together 😉
Please talk about how your working day now differs from when you were working in academia. What are your fears regarding success? How do you stay motivated? How long do you expect it to last?
Please ignore this guy. Most of us are more interested in science than in your private affairs.
For simpletons like me it would help if the graph was setup in such a way that the words "shorter" and "longer" would correspond to shorter and longer lines on the actual drawing.
Einstein's Variable Speed of Light has entered the chat.
I thought in Relativity the concept of light's "perspective" makes no sense? Mathematically you're literally dividing by 0 which is also another concept that makes no sense either.
Yes, I thought the whole thing was that light has no proper time at all, and that it has no reference frame.
@@erinm9445 proper time is fine (and zero), but indeed it has no valid frame of reference
If you imagine that a particle can either move or interact, its speed becomes quantity of movement/quantity of interaction.
In the case of light, the amount of interaction is zero, which effectively means dividing by 0 if we want to calculate its speed. And even if we don't know how to divide by 0 mathematically, the physical meaning of this equation is obvious enough to know that quantity of movement/0 = quantity of movement.
It means that our understanding of time is tied directly to light. Relativity explains our relative experience and we use light to track changes in the universe.
I’ve read light travels from the sun in a certain amount of time. But are you saying it is zero time?
It takes 8 minutes in our coordinate time. It takes no time for the light itself.
@@SabineHossenfelder I always thought the story about how cosmic ray muons reach the earth's surface even though the earth's atmosphere is too thick is a great example of space-time dilation and length contraction on things travelling that fast.
@@SabineHossenfelder except any experimentalist who's built a Cherenkov detector knows n = (1+eta) for a gas, and v=c/n so gamma = 1/sqrt(2eta) --> 43 for air. It has a little time at the end.
We see light take 8 minutes, but if you were traveling at the speed of light from the sun to the earth, you would "teleport" - it would appear instantaneous, no time would pass.
@@SabineHossenfelderYES! The propagation of "light" is simply the transfer of information, the photons themselves may as well be stationary....
Amazing and interesting. Thank you for this amazing presentation ❤❤❤
I know i'm off topic but i want to ask:what is the correct equation that expresses the irradiance on the surface of an object that travels through the interstellar medium at relativistic speed?what i mean is : what is the kinetic energy received per unit of time by a square meter of an object that travels in space at a good fraction of the speed of light? I thought like this : with a N of 1 particle per cm³ i got a density of 2e-21 kg/m³,then :if the object is travelling at 0.9c it means that in 1 of ITS seconds it's travelling 0.9*2.294*299792458=6.18e8 m,so 1.27e-12 kg are impacting each second at 0.9 c on a m²,so an irradiance of 140 kW/m².Is this correct?
Thanks
Truly timeless and glowing
@SabineHossenfelder Thats why the photographs don't move! The photons stopped the time, the moment they hit the emulsion of the film!
Thank you Sabine you made me see, the Einsteinian mind!
@SabineHossenfelder Deshalb bewegen sich die Fotos nicht! Die Photonen haben die Zeit angehalten, als sie auf die Emulsion des Films trafen!
Danke, Sabine, du hast mir den Einsteinschen Verstand gezeigt!🌈
Sabine, I have a philosophical question (not necessarily covered in this presentation). Is it possible that as we become older, time appears to accelerate, ergo, when I was five years of age, the days seemed to be longer; now, in my sixties, those self-same days fly by - so much so, that they appear indistinctive (& no two days for me are the same). So then, is there a calculation that can explain this philosophical enigma - or is it a psychological imperative that progresses as we age ?
I understood nothing -(
me neither! but I like it anyway 🙂
There’s nothing to understand. Einstein was a psychopath
I'm always too high to get it.
"Im dope af, thanks for askin bro!" -light
"oh, and stop wearing sunglasses. Thats crazy offensive!" -also light
From Wikipedia: Proper time can only be defined for timelike paths through spacetime which allow for the construction of an accompanying set of physical rulers and clocks. The same formalism for spacelike paths leads to a measurement of proper distance rather than proper time. For lightlike paths, there exists no concept of proper time and it is undefined as the spacetime interval is zero
So if time and distance for an photon is 0 (no time and no length) the whole universe is a singularity in the frame of reference of the photon. And if all frames of reference are equally valid what can we extract from that? i'll have to rewatch the video i feel that some subtilness between time frames got over my head. Another question is why in space time diagrams do we always make the speed of light at a 45º angle wouldn't if be better to draw it at 90º from the perpendicular to better show time and distance being 0 for the photon?
The way I think about time "stopping" at the speed of light is this: it isn't that time has stopped, it's that local events have slowed to stagnation relative to an observer moving at subliminal speeds. Think of all the events that make up your conscious experience. Your cells divide. Your heart beats. Oxygen and carbon dioxide are exchanged in your lungs. Electrons are moved across the mitochondrial inner membrane. Your synapses send and receive trillions of neurochemical signals. All of that slows to a crawl. You become frozen, right down to the electrons in your atoms, while the universe around you zips by. If you, at any point, stop moving at light speed, you will notice that you're in a different location, but it will appear to you as if you instantaneously teleported there because you will have essentially been in stasis for the trip. However, you haven't actually teleported, because quite a bit of time will have actually passed outside of your immediate locality.
Na, time only appears to stop because objects become redshifted. It's known as the doppler effect. But that's just the way it appears. The objects still exist in the present. Actual time dilation doesn't have anything to do with light, photons or the way something appears. It's the actual rate at which time passes for an object relative to another in the present.
5:40 Eh, how do the units work out [„proper time“] = sqrt( s^2 + m^2 ) ? I would have expected [„proper time“] = s.
I guess y is normalised by the speed of light? So [y] = m / (m/s) = s ?
In the above video, Sabine Hossenfelder is applying to light what is essentially the relationship of light to other things, to wit, objects with mass. Errors are made when attempting to apply that relationship to light itself, but they might not be apparent in calculating the Lorentzian distance for light.
There is another way of calculating properties of objects relative to light's velocity that will show the error: using gamma.
Gamma = 1/√(1 - (v^2/c^2))
If you try to calculate gamma for the speed of light, you get:
Gamma = 1/√(1 - (c^2/c^2))
Gamma = 1/√(1 - 1)
Gamma = 1/√0
Gamma = 1/0
but dividing by zero is not allowed in mathematics.
Time does not stop for anything, not even light.
One of the things that bothered me was how a finite amount of energy could span an infinite distance intact. after thinking about it for many years I came to the conclusion that light only exists in one dimension, eliminating all concepts of distance, if you remove time the potential of distance is eliminated.
If it were true that things moving at the speed of light had slowed or stopped time, then photons would never be able to update as they moved from atom to atom getting absorbed and readmitted? I know they are said to have no mass, but how can you have no mass, but yet you have an energy value with an equivalent to mass.
Can you please explain to me gravitational aberration especially with respect to the solar system, I do not understand why it is proactively offset at constant velocities. I always thought that with the speed of gravity (light) that the Earth-Sun system would be rotating around the abberated position of the earth-sun system 8 1/3 minutes ago... so my world has fallen apart since discovering this would be unstable. Per S. Carlip, 1999 "I show that aberration in general relativity is almost exactly canceled by velocity-dependent interactions, permitting cg=c." So aberration cancels out, isn't that kind of flaky!? To my surprise this is also what also is described by Feynman for electric charges at a constant velocity, that static fields (either electric or gravitational) always point directly to the actual position of the bodies that they are connected to, without any delay due to any "signal" traveling (or propagating) from the charge, over a distance to an observer). What?!?! WHAT HAPPENED TO THE SPEED OF LIGHT AND CAUSALITY?!?! Why it being offset exactly?!?
Then I read a paper by Dr. Krızek (2008) "Does a Gravitational Aberration Contribute to the Accelerated Expansion of the Universe?" and I'm totally lost on gravitational aberration (and the counter is argued to result in universal expansion). And what is this "quadrupole" nature of gravity?!?!
WHY ARE WE ROTATING AROUND THE INSTANTANEOUS POSITION OF THE EARTH-SUN AND NOT THE ABERRATED POSITION GIVEN THE SPEED OF GRAVITY/LIGHT?!?! WHAT ARE WE ROTATING AROUND?!?! WHY DOES GRAVITY HAVE A QUADRUPOLE NATURE AND WHAT DOES THAT MEAN?!?!!? HELP PLEASE!!!!
I was talking to some friends the other day and was explaining that even though the a photon traveled a billion light years across the universe to get to our retina, for the photon itself the trip was instantaneous. It kinda blew there minds.
Can you explain that. It sounds like non-sense to me. I've always heard that ftl communication isn't possible and light travels at a finite speed. Seems like contradictory statement within relativity to say the photon travels instantly.
@@MatrixVectorPSI I can try. Its not contradictory at all, time stops when you reach the speed of light. if you are observing the photon, you are relative to it, so from your perspective it takes a billion years, from the photons perspective it was instant. This is exactly the time dealation effect relativity explains.
@@captcorajus That doesn't make sense really. Why would time stop when you reach the speed of light? Just because someone is observing my light waves doesn't mean time stops for me. Also, if a photon is supposed to travel to its destination instantly. Then why can something obstruct it's path after it's emitted? If light was instant there would be no way to obstruct it.
I understand, GR's been church for such a long time, it's difficult to quantify anything else. It seems like non-sense to me.
@@MatrixVectorPSI Look dude, I told you how it works. I can 'understand it' for you. This is a proven thing. The faster you go, the slower time moves for YOU in relation to the rest of the universe. Time dilation has to be accounted for in GPS Satellites for example or they wouldn't be accurate.
Its a mind bender to be sure, but its still true.
@@captcorajus Now that I'll agree with. Not so much the part about light, photons, perspectives and observers. Light and time dilation aren't really related. So it's not really an explanation for why you say "for the photon itself the trip was instantaneous". Still doesn't make sense.
One interesting way to think about it is that we, our body, is made up of matter. Matter that is held together by interactions and forces mediated by photons, gluons, things that are light and move at the speed of light. Those interactions are the tick of our internal clock. As we move faster and faster though space those interactions happen over longer and longer distances, but for us one second is always one second. For the more stationary observer their one second is different than our internal clock. As we travel closer and closer to the speed of causality, it takes longer and longer time for those interactions that make matter, eventually those interactions stop because the light can never get to the next interaction. And if interactions stop our clocks stop ... and time is no longer a thing.
It means time doesn't pass for a photon from its point of origin to its destination. To the photon, the two points, as well as all points between, are experienced at precisely the same relative time.
There was a time when I think I could have grasped this.With old age having found me I hear all the words but it's like when I talk to my dog. He hears all the sounds but doesn't have a clue about what they mean. I can almost touch understanding but then - no. Frustrating
I appreciate everything you do Sabine. Keep up the great work.
Ive thought about this before. A star can be millions of light years away, yet for the photon, the trip to earth is instantaneous.
Space time etc always fascinating, but what intrigues me more is why light starts at the speed of light and stops instantly. A medium can slow it down, and gravity can distort/bend it, but why no change in speed - no acceleration - always go or stop.
Without the maths, I've always thought about time from light's POV as: If you turn on your light at exactly noon on your clock, then turn if off one second later, the trailing edge of the light beam has the timestamp of noon+1 sec, whereas the leading edge is always noon. Time can't go backwards either because the tail would have to pass the head and you'd be arriving before you left. Funky.
I caught a layman's lecture that mentioned the relationship between light's uninterruptable nature, and the fragility of quantum memory.
As i understood the theory:
As light crosses the event horizon of a gravitational singularity it is ripped apart and drawn into a "wider " plane, where a segment may be interrupted leaving an unaltered trace of the original spreading into perpetuity.
Thoughts?
Sabine, I have a question for you.
Here's the setup: A photon is emitted from a star billions of light-years away towards my laboratory on Earth. I have a pendulum in my lab that I can control the weight of the pendulum to be to the left of the photon's path or to the right of the photon's path. (Basically, we're setting up a gravitational lens)
If I have the weight to the left, the photon's path will be slightly bent to the left. Conversely, if I have the weight to the right, the path will be slightly bent to the right.
When the photon is midway between the star and Earth, I make a choice to either position the pendulum left or right.
If the photon does not experience time, this results in a contradiction. The universe was in state A when the photon was created, but now after I make my decision, the universe is in a different state, B, and the photons path will be different than what it would have been when it started because of my actions.
If the photon does not experience time, how can two versions of the same universe, A and B, exist simultaneously for the photon?
Hi, are you saying that light has no speed and that it just is always there and therefore cannot take time to travel? Also, I don not understand current thought on the definition of photons.
What would “time stops” mean? Stop everywhere? Okay, but when? Stop everywhere “at the same time”? At the same time for all observers, regardless of their relative velocities? You see the problem …
You may help, if you say, that time can't really be measured, it can only be determined at best. For measurement you'll not only need a count or a rate, you'll also need a fixed unit and the last isn't given for clocks. The duration between two counts of a clock depends on the movement of the clock, because it's mechanic is amenable to the physical law, which is called classical Doppler effect.
And for light in vaccuum (the fastest we know) there'll be no time, because no one can even determine it, because clocks can't count anymore at this speed. We need something faster than that, to do it. And while clocks can't count anymore the movement of light still happens and stays as cause for the clocks state not be able to count anything. Write it down: Movements do not depend on their speed measurement. That means: nothing happens in the same instant and thats also applies to light. In it's own instance light'll have an endless high speed, but all distances will stay the same for it. It doesn't matter, what your maths will tell you.
You don't measure time, you can't. Time is a definition. Make a clock, say it has 100 markings and rotates at the same rate as the moon. The number on the clock is time, or 'the time'. Time wasn't around before humans invented it and we invented based on clocks. Think about clocks, all they do is to present different numbers to you as they operate. Because they are mechanical - as you say - they also need power. Because there is no such entity as time - there is no portal for 'time' to be stuffed into the clock. Time is the oddest SI unit, unlike the other SI units - that are real - time is odd because it isn't.....
@@chickenduckquack Well... is this a copy of one of my posts under other videos?
This diagram also VERY help when you try to think how gravity works. Any standing object moves perpendicular to space line and parallel to space line.
And mass curves space-line, so time-line change it's angle and object now moves to center of mass, and while object get closer to boundaries of massive object, angle of time changes more => acceleration of free fall.
Event horizon also understandable there extremely easy. Light always moves at angle on 45°, so event horizon is point, where curvature of space get an 45° anglel, so light starts move parallel to not curved space, what means it will not go away from this point, but if there will be second massive object going nearby it can curve space at event horizon from 45° to 45,00000000000....0001°, so light will escape that place. And more massive that object flying nearby to event horizon, more deeper light can escape event horizon. I think when two black holes of same mass interact, they can throw out of them huge amount of light(if light still there and didn't fall too deep).
So particles aren't particles, they're rays through time-space, so only in space dimension they looks like dots.
So, our world REALLY made from strings, but not from those in string theory.
And yeah, singularity in black holes REAL time machine, they just travel you to Big Bang, so they're not very usefull. Or singularity doesn't exist(what also really easy to imagine if curvature inside massive objects aren't hyperbolic but parabolic)
Something I wondered, not being a physicus, nor mathematician: Why is in science the speed of light in vacuum not defined as 0, and all other velocities defined relative to that new absolute zero?
Not sure if it would make sense, but in my naive view, this looks like a more coherent/peaceful solution to describing the universe.
A video about this would be nice!
I love this stuff and the way you present it. I dropped out of high school in grade ten and so I missed the basics of physics.
I have often said that I used to do drugs to blow my mind - now I just watch physics videos to do the same. Thank You
What would the light experience in an astrophysical light year traveling? Totally confused , I don’t know what the time is other than my repetitive heart beats. Could you please explain the relation of the coordinated universe Einesteinean time and the atomic clock?
Hi Sabine, if proper time stops at the speed of light, does that mean, photons, from their own perspective, are eternal standing waves, stretching from the infinite past, into the infinite future? Because, if that's the case, couldn't they be a medium, through which retrocausal signalling can occur, for photon interactions, being observed, from within coordinate time? If so, might that explain the seemingly retrocausal results of the double slit experiment?
This is the most profound concept to truly understand
I'm not sure I'm getting it. We know it takes light even from as close as the sun 8 minutes to arrive. How could proper time for light stop if the parts of spacetime it touches are in different times by the time it reaches them?