I recall learning that scientists know neutrinos don't travel at the speed of light because they can change over time, which things bound to the speed of light can't do. So fascinating.

@-_Nuke_-

11 ай бұрын

Yes, things that travel at the speed of light can't travel at any other speed. A photon for example, if it could travel at any speed lower than the speed of light, it will gain mass, and it will simply stop being a photon!

@-_Nuke_-

11 ай бұрын

The reality is that all objects travel at the speed of light in spacetime. But only light travels at the speed of light in space. Stationary objects travel at the speed of light in time. And anything in between travel some γ (gamma) factor between space and time. γ = 1/sqr(1-(v^2/c^2)) where v is the speed of the object as measured by a stationary observer. And c is the speed of light. And it's the ratio between proper time and coordinate time. Or in other words the amount of time and space dilation and contraction an object traveling through spacetime will experience. For light γ is infinite. And for a stationary object γ is one*.

@user-qd2nd6hi8j

11 ай бұрын

@@-_Nuke_- speed of photon in glass/water/etc?

@nickcaruso

11 ай бұрын

@@-_Nuke_- of course this raises the question of the speed of light in a vacuum versus the speed of light in a material; I *think* photons do simply stop being photons of course when they are absorbed and re-emitted. if I am following along correctly. Which suggests the process of light "passing through a material" is a process of absorption and re-emission, or is it scattering? Are my concepts out of bounds here? I seem to recall a video Don made about this but I do not have the link to hand.

@markusmencke8059

11 ай бұрын

@@nickcaruso IIRC it is not a absorbtion/reemission thing, but a interaction of the Photon with the material’s atoms (iirc, the electrons, mostly) via the EM-Field (when you think of the Photon as an wavelike exitation of this field). The Photon then experiences something that is similar to „drag“. Absorption and Reemission does not work for transparent materials - iirc, the reemission direction is totally randomised, which would mean the material is only semi-transparent or opaque even.

Since you read most comments, here's another one. Thank you and the team so much, this channel really is outstanding for both people who don't study physics and people who need a little reminder of the beauty of physics when studying can be frustrating at times. You have the right balance between not being too complicated and not oversimplifying too much, a skill only few have. Outstanding!

@saramolet3614

10 ай бұрын

Yeah he didn't read yours bro to bad!

@savage22bolt32

10 ай бұрын

@@saramolet3614 maybe, in time...

@richardivonen3564

10 ай бұрын

Frequency is relative to time and every wave length has a frequency.

I just want to say how wonderful these videos are. I truly appreciate them.

Excellent program. These should be required viewing by every science class. We’ll set up and laid out. Thank you guys

@devalapar7878

7 ай бұрын

This would be too superficial.

The Don killing it as usual. Been thinking about this issue a lot recently, thanks for clearing up misconceptions!

I'm genuinely grateful for the time and effort you put into your fantastic educational videos Dr. Lincoln. You manage to make extremely complex concepts approachable and understandable for laymen, and that is quite an achievement. People like you maie our world a better, smarter place, so thank you so very much. All the best from Switzerland (living 10 minutes away from CERN)!

@spvillano

10 ай бұрын

Take advantage of the proximity, as they do give guided tours. Unfortunately, they don't give my kind of tours, as those would involve schematics, engineering diagrams, long talks with engineers about snubber circuits, early quench detection, etc. I also figured out to put Lorentz into mass-energy equivalence back in junior high school.

@johnf3326

10 ай бұрын

If he were a photon he would only have put effort into it and as effort takes time his input would also be zero!

I have been thinking about this question for years. Thank you for clarifying

When you mentioned you had people in the comments saying a photon experiences no time, I was very worried, because I am one of those people! I was worried you would bring in some concept I didn't know about and dash all my photon experience no time dreams! I was very relieved you didn't, but you gave a great explanation of this crazy phenomenon! Thanks!!! :)

@strangevideos3048

2 ай бұрын

There is no time 😅

@herbpowell343

Ай бұрын

@@strangevideos3048 Sure there is, it is just another spatial dimension. Though an argument could be made that time, as a measurement of change in general and motion in particular, is always a "higher dimension" than whatever an observer can perceive: A solid passing through a plane moves in time, but to an observer within the plane that motion also appears to alter the objects shape, because it presents the observer with a changing view without that it being obvious to the observer that that is all it has done. Meanwhile, photons thinks we're all nuts because they experience no practical difference between the current universe and the quantum singularity originally containing it. Concepts like space and motion break down as quickly as time for anything that exists everywhere simultaneously, which frankly makes sense if time, space and motion are just perceptual artefacts constituting no more than different perspectives on the same thing.

I always learn new things from you! I knew about the time thing, but had never considered the length contraction portion of it. Thank you for the great videos!

@DonovanCYoung

11 ай бұрын

Same, I never considered that a photon of light created at the big bang would also not "experience" any movement through the universe either. It makes sense though; from its point of reference the Big Bang just occurred, so of course it wouldn't have "traveled" anywhere either.

Any time I think 'Now I understand physics', this guy comes up with something wierd. Love what you do, Dan, and a huuuuge thanks for it!

@jackielinde7568

11 ай бұрын

"If you think you understand quantum mechanics, you don't understand quantum mechanics." - Richard Feynman. Classical physics is pretty easy to understand. There are rules, the rules are testable, and the rules don't change. When it comes to Quantum Mechanics, it's like "F*** THE RULES! I DON'T NEED YOUR RULES! I LIVE MY LIFE HOW I WANT TO LIVE!" It's like God asked some casino to manage things on the Planck scale, and the casino decided it was going to make it so the house ALWAYS wins. That's how we get a science ruled by probability, teleportation, things with no visible connections just magically talking to each other, and objects that are both particles (mass) and waves (energy) at the same time.

@AllenProxmire

11 ай бұрын

yah Dan is awesome😂

@zosothezephead837

11 ай бұрын

​@@AllenProxmireDon's even moreso 😂

@Onimirare

11 ай бұрын

There's a video called "What would we see at the speed of light?" by "ScienceClic English" at around the 10:50 mark, he gives an example that I haven't seen anywhere before. Makes it really easy to understand why reaching the speed of light is so hard, or what happens when you try.

@dugldoo

11 ай бұрын

@@Onimirare Just the nonsensical title of the video you quote gives away that it's weak.

Awesome. I hadn't thought to add length contraction into the mix when considering this until now.

Oh my... do I extremely enjoy this channel thank u for your work

This is such a cool channel. Not only is Dr. Don an amazing science communicator but stuff like this where they engage with the community is really cool.

@marioluna2957

11 ай бұрын

Dr Santa Lincoln rocks👍

That's awesome. I've wondered about that. So clearly explained every step. Thank you.

I was thinking about this a few weeks ago and this is exactly how i imagined it works, super cool!

How did I not find this channel earlier? This is great! Here I'm like, finally! Another good science channel after so long! 🤣 Really great!! 😁😁

"These equations don't apply to photons, but using these equations, let me show you how they apply to photons" - logic of the year award; there is no guarantee whatsoever that the trend that occurs up to c holds at c. That's like saying that an engine running for all values of having fuel close to zero will explain what happens when the fuel gauge hits precisely zero.

I love your videos. I do a lot of sci-fi writing and over the years have become more and more fascinated with particle physics and physics in general. I would love to see a video from you on Entropy :) !

Phantastic Video! Thanks a lot for the explanation. The universe is mind blowing.

I'm excited to watch your video on the combination of special relativity and quantum mechanics i.e. "relativistic quantum mechanics".

Hi! Thank you for showing me the math (which I'm not great at) that confirms my inference and instinct (which I'm great at) on this topic. I feel like you made this video just for me. 🙂 This is one of the single coolest things about reletivity I know about and I share it with people when it comes up because it's so damn cool. :-) Love. This. Vid.

@ytrrs

11 ай бұрын

Showing you the math? I thought he is intentionally avoiding it!

@jeraldehlert7903

10 ай бұрын

@@ytrrsWow. That username. Pretty sure someone needs to write a scientific paper on it.

interesting to hear the maths for this as i've been trying to get my head around what the photon may or may not "experience" since the idea came to me, after hearing penrose talk about "the size of the universe" being meaningless when there are only photons left. the idea that although the final minutes of the universe it may be an infinite size, but, also that size could be the next singularity was boggling.

@anywallsocket

10 ай бұрын

Yes the idea is CCC by Penrose

Don, what are you doing in my dream Vette? I'm so glad to see you doing this science communicator thing. You definitely do a good job. I've thoroughly enjoyed your content, and how you break it into chewy bits for us "non-maths". Keep it up! Hope all is well with you. Cheers!

Thank you. That fed my mind.

We are so lucky to have someone actually working in the field making these amazing videos! You and Matt from PBSSpaceTime have educated me so much about these amazing topics I am so passionate about but never studied formally. I cannot thank you enough, what amazing work you are doing! YEAH SCIENCE!

@cykkm

11 ай бұрын

Sorry, they haven't. I don't want to be a party crasher, but the whole point of popular science is to motivate one to _study_ science. There is no half-knowledge, only half-ignorance. The choice is yours, but for gossake, don't mistake it for education!

This is a lot clearer now, thank you. It helps that you point out that the formulas can't be applied to things traveling at c. It was also helpful that you pointed out how length contraction would basically shrink the universe to a flat, 2D circle for the photon. That explains how it flattens the time as well. Neat stuff. Thanks!!

@user-qd2nd6hi8j

11 ай бұрын

If you look at stationary objects at lets say 1 degrees aside of straight line, the speed of this objects for photons will be c*cos(Pi/90)=0,99939*c (projection on trajectory). Space also warps, but less and less with angle increase relative to movement of photon

@terrycole472

11 ай бұрын

I'm far from sure that relativity doesn't apply to things travelling at "c". The equations might need to be recast, though. As a secondary school student, Einstein created a thought experiment; what would it be like to travel so fast that you caught up with a light beam? Answer: the wave of light would seem frozen. That contradicts the picture given by (non-relativistic) Maxwell's equations, which assume motion. But in general relativity there is no contradiction.

Hi, Thanks for the explanation. I am eager to hear your answer to these two simple/intriguing questions: A. How about the photons that do not travel at the speed of light? Do they experience time? For instance in any material with refractive index greater than one. B. If photons do not experience time, how come their qualities can evolve in time? For instance (even in vacuum) their wavelength can change (red-shift) due to the expansion of spacetime.

@dexterPL

10 ай бұрын

A: photons do travel at C, always. But this is like in sun, photon from center need thousands years to get out to surface. Too many atoms and too many obstacles, they bounce a lot. B: i also want to know

@anhadhs

10 ай бұрын

Refraction also has light bouncing between atoms at c. Res shift and blue shift are not changing the light but only making us see it differently.

@EdwardChopuryan

10 ай бұрын

​@@dexterPL I'm afraid this is a misconception. This pinball model that ppl have in mind is incorrect. That would mean that the speed of light inside a medium depends on the thickness of the medium, which is not the case.

@dexterPL

10 ай бұрын

@@EdwardChopuryan not thickness but density and internal atomic structure. And not speed itself but the time it takes light to travel a given distance, speed of light beetwen atoms is constant.

@EdwardChopuryan

10 ай бұрын

@@dexterPL again, if you assumption is that photons get absorbed and re emitted then, even if we assumed your model is correct it would mean that if photons encountered more atoms on their way the overall time would be more than if they encountered fewer ones. Moreover, if photons got absorbed and re-emitted (well some of them do) then the material would be opaque because re emission happens in random directions

Excellent. Thank you. Staying on the subject of photons, would you maybe consider making a video that teases apart our everday classical EM field (radio waves to gamma rays) versus the quantum fields (EM, electron, magnetic, other?) that get perturbed resulting in a photon?

@johnconnor7501

7 ай бұрын

What’s wrong with EM fields? Are they not real either?

Thanks for the video. This has been a question in my mind for a long time. I get the analysis with limits. But, if a photon experiences zero time and zero distance, it can't experience change (∆t always = 0). How would the oscillations in E and B happen if ∆t = 0? Yet we *know* a photon is an oscillating disturbance in those two fields. How could photons red-shift if ∆t and ∆s are 0? Lastly, it seems that Heisenberg prohibits photons travelling at exactly c. Since any photos erector is *highly* localized and c is just c, it seems ∆s∆p

@kalyanchakrala9388

11 ай бұрын

Light or any massless quantum field is not localized. We preceive it as localized since we are measuring only after it interacts with another atom. We draw light as a 2d wave for shortform but it doesn't look like a wave. Light is a field that occupies every part of space from point A to point B (from transmission to absorption). It's a probability field. Please look up the images for electron S field/orbital of an atom. This field gives the approximate location of where an electron field can be located within an atom. The electron is the entire cloud/field. Think of a photon as a similar cloud between atom A and atom B. The quantum field/cloud extends from A to B. We perceive the field as traveling at 300,000 km per sec but from a photons point of view it occupies the entire space at once. The photon is the entire cloud/field between A and B. Objects with mass such as us experience time and can only measure the interaction (after it already occurred between 2 atoms). There is no way of measuring a massless quantum field between point A to point B (between 2 atoms). For example, a photon that left the sun and interacts with earth has one big orbital cloud that stretches the entire space from our sun to our earth. Technically the photon is the entire cloud/space between the two. From photon's point of view, no time or distance has elapsed. It's only our view. Our physical reality is an illusion. For example: the star Betelguese is 600 light years away but easily visible in the night sky. Since photons experience zero time/distance, it means the instant the photon was created 600 yrs ago, it also instantly hit your retina (even though you weren't born yet). This means everything in the universe is connected. You can further expand this logic to every photon/electromagnetic wave in the universe since big bang singularity. Everything is still part of a singularity. Past, present, future already happened. We just feel like we are experiencing time but its just a illusion.

'Undefined' seems like a better answer. You can't use calculus to make a number divided by zero equal zero. To observe requires time. To exist requires time. Exist is a verb, it requires action which takes place in time. It's not possible to understand, or even describe existing without time. There may be a better way of understanding space and time as emergent, which might resolve the whole dividing by zero problem.

@filonin2

11 ай бұрын

If that were true then existence would be subjective as the passage of time is subjective based on the relative velocity of the observer. Photons would both exist and not exist.

@filonin2

11 ай бұрын

Also, that's what calculus is for lol.

@DrDeuteron

11 ай бұрын

be careful when using the word "action" around a physicist, because Dr Don's action doesn't take time, it takes multiples of hbar.

@saelesbonsazse9919

11 ай бұрын

You can't observe a photon unless you interact with it and that interaction will be the only moment experienced by the photon since it came to be. P.S.: unless you consider the interactions with the very, very tiny ripples the photon produces on the spacetime, as its energy moves through the gravitational field. Does it exist or is it on the speculative realm of quantum gravity?

I've always wondered if photons were unable to experience time. Thanks for confirming my hunch that they don't! Love your channel (and your Great Courses work).

@freddiefox.

10 ай бұрын

Same here, although now I wonder what would happen if you slowed a photon down. The maximum unencumbered speed is c, but put light through a transparent or translucent medium and it slows a bit. So what about a light source in a gravity well? Not a black hole, but maybe a neutron star, where the escape velocity is about half of c. Presumably the photon would then experience some time delay on its journey.

@flyjet787

10 ай бұрын

@@freddiefox. Very interesting idea! Would it be accurate to say that, from the photons perspective, despite curved space around a massive object would "slow" it's progress from point A to point B? Not sure about the mechanics at work when light passes through a medium tho.....👍

@freddiefox.

10 ай бұрын

@@flyjet787 Interesting thought. The photon follows curved spacetime (e.g. as observed in gravitational lensing) at c I'd imagine. We know light can not escape a black hole, but presumably would still move at c - it's just that escape velocity of a BH is >c so it can't escape. But then inside the event horizon we don't know what happens, and the math breaks down at some point anyway, is my understanding. I think also we have to be mindful that relativistic effects really come into their own at very close to c. The video showed this with the differences in journey time at at 99.9, 99.99, 99.999 % c etc. as the value tends to infinity very rapidly, edging closer and closer to infinity which would be instantaneous travel/arrival. Regarding other media though, light is slowed minimally traversing water, glass, perspex, etc. yet photons still remain photons, even if their speed is reduced by a fractional amount, but I'd imagine still fast enough to count as relativistic in how it experiences time, because that's the nature of travelling so close to c.

I don't think I really understood a word of that.(physics was never my thing at School)...yet I still find it totally Fascinating. Thank you from this Mathlexic 68 year old Londoner, currently on Holiday in Spain..

If the photon experiences no time, would it not also experience no existence? If, from its perspective, it occupies the entire universe instantly, would in not also instantly red shift out of existence? It's puzzling, from light's perspective it seems to instantly fill the universe yet leave it totally dark!

@Guido_XL

10 ай бұрын

There is a popular misconception about photons, allegedly resembling small balls of light. In reality, photons only come into play whilst matter is involved. Empty space does not need the presumption of photons. The electromagnetic field is more than enough. That field is not quantized, as photons are. But, in order to ignite light, photons are required. Therefore, it may seem that photons are the bearer of light, whereas they are the dealers of light, making exchanges happen. There are only photons if matter needs them to complete the interference between the atoms and the electromagnetic field.

What happens to the energy of a photon in its own point of view while experiencing cosmological redshift (traveling through expanding space)? Also, where does the energy go from the perspective of an observer? Thanks for all the interesting videos - I've been watching Fermilab for years. Cheers, Dr. Don Lincoln and team!

@starcitizen890j5

11 ай бұрын

I literally asked the same question in the comments before I read your comment. Seems I am not the only one a bit confused by this.

@jurgel

10 ай бұрын

Good question.

so glad you did this video!!!!! ty!

I'm really glad you have done a video on this. I've had a bunch of questions about this for quite a while. I'd have liked to have seen you go deeper into the ramifications of this and go over some thought experiments. For example, I have thought about the following scenario but am not clear exactly what happens in practice. Let's suppose we have two planets A and B and those are stationary (and remain so) with respect to each other. Let's suppose a photon leaves planet A and moves in a straight line (as seen by a observer in planet A/B's reference frame) towards point B. Let's further assume that another body C is moving such that, according to the stationary observer, it will intersect the path of the photon before the photon can get to planet B. If the photon experiences the journey from A->B as instantaneous then it couldn't possibly hit the body C, but that of course is nonsense. So somehow, the universe, as "seen" by the photon, is one in which body C is already in between planets A and B at the time it sets off. Is this correct? It's kind of interesting then, from the photons POV, it already "knows" what it will collide with before the body C has moved into the position it'll be in when the collision occurs. This would be true in general and photons would in some ways predict what the state of the universe will be such that they do any interactions. Maybe this is obvious from space time diagrams, but I haven't studied relativity for 25 years so I'm way to rusty to know the answer to this now 😂

@JoshuaPTFan

11 ай бұрын

You're conflating photons not experiencing time with photons being able to travel any distance instantaneously, which is not true. As with all things in relativity, the key is frame of reference. From the photon's perspective, it may travel the distance instantaneously, but from the perspective of an observer stationary relative to A and B, the photon travels at the speed of light. Thus, there is time for C to move to intercept the photon after it has started moving. Because the photon doesn't experience time, from its perspective, C is at every position of its own path during the lifetime of the photon simultaneously, including being at the point of interception.

@andrewparker8636

10 ай бұрын

@@JoshuaPTFan Thanks for the reply. Your final paragraph seems paradoxical to me. I almost liked the explanation, but the problem is that seems to imply that the photo would collide with C if it took a path through any point in C's path, but that's not always going to be the case.

@IgnacioIF

10 ай бұрын

@@andrewparker8636 I understand you perplexity at the last paragraph. However, what he said is not wrong, but maybe the easier way for you to understand it is to think that the photon, from its reference frame, does not experience neither space nor time. That is, the photon "thinks" that it is not moving and that time is not passing. It is us, from our own frame of reference that we can say that time is passing and that the photon is moving during a length of time from A to B, being intercepted by C. The photon itself has no idea of this and, really, doesn't care.

Funny: last night I was wondering whether a photon can traverse the universe without experiencing time and today somehow this video appears in front of me ... As if KZread algorithms could read my mind. Anyway, this time dilatation could have been the reason for the wave vs. particle ambiguity of photons in the double slit experiment: the photon is not like a bullet shot at the slit. It is more like a spear with the shaft still in your hand and the spearhead already in the target (the screen). So, if you individually observe one photon's path it means that you follow the shaft from the emitter till the spearhead (screen), and you can only see a linear path going through one of the slits. The photon feels being observed at the same time at the slits and on the screen, instead of being watched first at the slit and then on the screen, because the photon occupies its whole path at the same very moment (from the photon's point of view). Probably this is why a photon behaves as a particle instead of a wave when being watched. Now, while this above seems like a possible explanation for the double slit experiment with light (even if light is slightly slower in air than in vacuum), but for a particle with weight >0 cannot be an explanation because particles with weight won't fly with C and thus cannot be present along their path at the same moment. Still, they can behave both as waves and particles in the double slit experiment.

@radfordmcawesome7947

2 ай бұрын

time dilation is not connected to wave-particle duality; we've performed the double-slit experiment with electrons it might be loosely connected to entanglement though, as some theoretical work suggests that ER = EPR

@jdmichal

25 күн бұрын

As mentioned, the particle vs wave duality is not unique to photons. A better fit for your thought experiment would be the delayed choice quantum eraser. The accepted explanation is superpositions. But considering photons as timeless would also resolve it, because everything happens to them all at once. So there is no delay in the choice.

Thanks Don, you're a legend. I was wondering whether the fact photons experiencing no time is how entanglement may actually work. A pair of entangled photons being everywhere in their path at the same time means there is zero distance at their source hence measuring the property of one immediately affects the other because they are in fact connected to each other. The fact "we" measure properties far away from the source is irrelevant and it is no "spooky action at distance" because in a sense, there is no distance in the first place.

@i_booba

10 ай бұрын

Entanglement happens with particles that have mass (electrons, for example, with entangled spin states), so the "spooky action at a distance" thing still applies. However, 2 things: First, this spooky action at a distance is not a problem because it involves particles associated with the *same* quantum state. A single quantum state that involves 2+ entangled particles is not sending any new information between the particles. They belong to the same state, so there's no violation of the speed of light happening. The speed of light is merely just the maximum speed at which information can travel, and if no information is being transmitted, then there's no problem. Second, some people think that entangled particles are connected with tiny, microscopic wormholes --- look up ER = EPR --- which if true, would explain geometrically why, physically, the particles are even entangled at all. As it stands now, the mathematics just tell us whether 2 particles are entangled or not, but we don't yet have a proven physical reason why.

@petergriffin383

8 ай бұрын

I have a question... Let's say I shoot a laser beam into the sky for one second then turn it off, that means there's a beam of photon's 186,000 miles long traveling on its way to deep space... My question is, do we have any idea how many photons are in that beam? Could we take 5 different measurements along the length of the beam all at the exact same instant and see 5 photons? Likewise, could we take 1 billion different measurements along the length all at the exact same time and see 1 billion photons? Or could there be just one photon in superposition?

@muhammadbilalmirajdin3764

7 ай бұрын

that's some whole essay not just one question@@petergriffin383

@clubx1000

5 ай бұрын

good question

@drdca8263

3 ай бұрын

@@petergriffin383 I think so, yeah. Or at least, kinda. If we assume that the laser is emitting photons with a particular frequency (or in a particular narrow band of frequencies), then each of the photons has a particular energy (or in a narrow band of frequencies). If we also know the rate at which energy is being put towards the energy of such photons, then, by dividing by the energy per photon, then we arrive at a rate for “how many photons is the laser emitting per unit time. Then, just multiply by the amount of time the laser is emitting photons at that frequency at that power level. Or, equivalently, divide the amount of energy in that laser beam by the energy per photon. However, I said “Or at least, kinda.” for a reason. The exact number of photons might not be strictly a well-defined quantity. Instead, it would, I think, be a superposition over a range of different numbers of photons. The computation I gave would, I think, be the expected value of the number of photons. (But like, I would imaging that the standard deviation of “number of photons” would be fairly small compared to the mean (probably as the time increases, the standard deviation divided by the expected value, should go to zero), so, like, I imagine it often works fine to pretend there is a single exact number of photons in the beam.) Oh, and also, I guess the uncertainty in the number of photons would correspond to uncertainty in the amount of energy that goes into them (as well as, I guess, uncertainty in the frequencies of the photons?)

If we implement the Planck constant as the differential in calculus then the differential can be carried to the front (outside) of the sum. Then many equations that become undefined when limits approach zero are defined.

Very thought provoking. Mind blown.

This is pretty cool! You're a very smart man Don! Thank you for making all of these wonderful videos so curious people like me can get a better understanding of the universe we live in ❤ P.S. I sorta thought that you were gonna go on and tell us that photons actually do experience something of time and debunk the timeless photon. Is there any evidence that points to the idea of photons experiencing time?

@benkusworl4934

11 ай бұрын

lets also credit those behind the scenes and not only the one who shows up in the video

@OmateYayami

11 ай бұрын

I will stir things up for you. C is speed of light in vacuum. Real photons obviously experience something - they at least experience gravity field, because we observe gravitational lensing. No real photon is in vaccum, so do real photons experience time?

@jamesh5743

11 ай бұрын

​@Łukasz Kucharski if gravity is simply curvature of spacetime, they don't necessarily "experience" gravity. They simply move in a straight line through a curved spacetime, which makes it *look like* they're experiencing a force

@estranhokonsta

11 ай бұрын

Note that the video didn't say that the photons didn't "really" experience time. First he said that one had to be careful since relativity didn't really work at the seed of light. And the showed how one could reach that ageless conclusion and steps one had to take. But it is just an argument done when stretching the theory of special relativity which as said earlier doesn't work for those speeds. An argument is not a proven scientific fact.

@OmateYayami

11 ай бұрын

@@jamesh5743 And what is the difference between experiencing a force and appearing to experience a force? What makes them bend from our perspective? If they would not experience gravity, that would mean they do not experience the curvature of spacetime. This is called equivalence principle for a reason. It needs to stay consistent when switching frames of reference. For a photon it might appear it goes straight in curved space time, but for us it is indistinguishable from experiencing gravity. Also, does photon feel the curvature? If not then how does it bend for us? It cannot appear that from a photon perspective it goes straight but it doesn't from a different observer. If an ant travels inside out on a spinning disk, it will make a spiral path for you only by going straight in it's own frame of reference, but it will experience forces that will give it a hint. That sounds awfully similar to the photon example.

Thanks for reading our comments, Prof. Lincoln and team. Also thanks for agreeing with me (even if it's at the limit, glory to Calculus!) The very related subsequent question (which it probably gets you in hot theoretical water) would be: can that explain "spooky action at a distance"... or even backwards in time (as per the DCQE experiment)? This I guess would have two sides: one for photon experiments/observations specifically (which requires no further elaboration AFAIK) and another for other particles (which may require of some sort of "pilot wave" explanation... assuming the pilot wave is made of photons/EM field). Cheers.

@boden8138

11 ай бұрын

2 dimensional “things” like light and electrons (in EM field state) don’t interact with space-time so distance is irrelevant.

@LuisAldamiz

11 ай бұрын

@@boden8138 - There are no electrons in the EM field, they are in the Electron Field rather. Only photons exist in the EM field, even if they are emitted ("created") and absorbed ("uncreated") by the Electron Field. Anyway a conventional light wave is not exactly bidimensional but rather three-dimensional because direction of motion and measure of wavelength all happen in the third dimension relative to the orthogonal electric and magnetic wave amplitudes. They do have dimension in that direction of motion, a static photon is unthinkable (even if caged photons have been produced in some experiments they are still in motion).

THANK YOU... PROF. LINCOLN ...!!!

I think, that when approaching light speed, distances contract to close to nothing, this would not only suggest that the photon-like object is everywhere at once (from our perspective) but from its perspective, all objects are in one place, lose their separation, so that space itself loses its quality. Could it then be possible that all we humans see is just one photon?

@PP-sj7pl

3 ай бұрын

I was thinking same thing.

Great video, thanks for doing this. Weird thought by me: consider that the Big Bang, if run far enough in reverse, arrives at the entire universe as a single point. Everything was everywhere at the same time. Now consider that photons apparently still experience the universe the same way. There is no distance between their end points, everything is adjacent to them. I don't know if that means anything, but it's kind of wild to think about.

@DavidBeaumont

11 ай бұрын

Read up on the transactional interpretation of Quantum mechanics, it uses this fact to make a really interesting hypothesis.

Great video. There is one point missing though which is what I was hoping to see explained: what happens when the photon enters a medium where it travels slower? Does it experience time then?

@limiNZ

7 ай бұрын

Its not actually traveling slower - its path just gets longer through those mediums

@LovethisNation

7 ай бұрын

Longer relative path and same time travel. Light is the only thing that behaves differently with respect to time

@GaryYates-pi9gy

4 ай бұрын

When a photon travels through such a medium it gets absorbed and reradiated with each particle it encounters... which takes time...a very very small amount of time. But during its travels between particles its back to velocity c. I'm not sure, but I think that is what is going on since photons can only exist at velocity c. ;)

@EikeDecker

4 ай бұрын

@@GaryYates-pi9gy Thanks for the explanation. I later looked it up and your explanation fits my understanding. So if I get it right, the refraction index is therefore describing the number of (average) photon absorptions that happen within a certain distance in that medium? I still don't understand how this results in light being refracted or total reflected... it would be cool to see a video on that specific part.

@GaryYates-pi9gy

4 ай бұрын

@@EikeDecker --- About refraction and reflection, I'm not sure. How does it change the path of light is still a mystery to me. I just see in my mind photons being absorbed and reradiated. I can see that I too still have a lot of physics to learn. Hope I never run out. ;)

It's really interesting how any particular piece of information is bounded in some way

Nicely done. Thanks 😊

I'm incredibly disappointed in this video. The presenter here is making statements which are patently false to anyone with at least an intermediate understanding on special relativity (SR). At 3:10 he says SR doesn't work for objects that travel the speed of light. More precisely it doesn't work for MASSIVE objects travelling the speed of light. Nitpicky? Maybe, but it gets worse. At 3:16 he says "relativity" fails for photons which is complete bunk. The gamma factor NEVER shows up in the equations of motion for the photon (e.g. look at the energy of a photon versus a massive object). This is clear from just evaluating the spacetime interval for a null light-like trajectory. More technically, you can just write down the geodesic equation for photons which is perfectly well defined. The whole crux of "photons experience zero time" relies on connecting the concept of the spacetime interval "ds" to proper time. The problem is the spacetime interval doesn't unique mean "time" (it means different things depending on context) and the assignment that ds^2 = 0 = dt^2 requires that we can write down a reference frame such that dt^2 (or photon time) is well defined. But it isn't. You can't write down a reference frame for photons, so the connection to proper time cannot be made. The limit argument (3:20 and onwards) also doesn't hold water as Lorentz transforms are completely symmetric. The limit works both ways and neither frame is considered privileged or unique letting you equally argue that *we* don't experience time.

@manipulativer

9 ай бұрын

You people missing such logical concpetion cause you trading time with speed of light.

Yet despite this incredible journey, the photon itself experiences none of what we know as time: it simply is emitted and then instantaneously is absorbed, experiencing the entirety of its travels through space in literally no time. Given everything that we know, a photon never ages in any way at all

@richardlinsley-hood7149

11 ай бұрын

So when does it pass our star, half way between this and the next star and the next star? The sequence will happen in that order for sure (otherwise lenses would not work).

@PoseidonWasTaken

11 ай бұрын

​@@richardlinsley-hood7149From our perspective light does travel and follows a set path. Though from the perspective of the particle it is timeless.

@LuisAldamiz

11 ай бұрын

True... assuming photons could experience anything, which AFAIK they can't. There is a paradox however: they do not experience time but we (or in general the massive universe, even electrons) do experience them in time (you're reading this, made of photons, now and not five minutes ago nor a week into the future). I may need to revisit the Twin Paradox video but it does look like a true paradox: timeless and perfectly timed at the same time, so weird!

@richardlinsley-hood7149

11 ай бұрын

@@PoseidonWasTaken But it must experience one face of a lens before it passes other oner one.

@richardlinsley-hood7149

11 ай бұрын

@@LuisAldamiz So how do lenses and prisms work?

I'm not sure, but I think you can switch the sides that the gamma is on. Then you can evaluate that at c, the delta t in the moving object moving at c is 0, irrespective of the delta t in the inertial frame.

i really enjoyed this video and it ties into an idea i myself have in relation to this but for speeds faster than the speed of light ie any matter inside of a black hole past the event horizon i’m going to make a video on my channel discussing why this could be a fun topic to tackle

This photon thing always amazes me. It has fascinating implications when you consider what photons are (EM bosons).

@charlesbrightman4237

11 ай бұрын

QUESTIONS: PHOTONS: (copy and paste from my files): A photon is usually depicted in a sine wave pattern with the 'e' and 'm' energy fields 90 degrees to each other. The 'e' and 'm' energy fields go out together and come back in together, over and over and over, doing so even across the vast universe as far as we can see. Where does the energy in the energy fields go when both the 'e' and 'm' energy fields go to zero? And what causes the 'e' and 'm' energy fields to come back to 'full' from zero? Over and over again over vast distances.

@juliavixen176

11 ай бұрын

@@charlesbrightman4237 The E and B ("m") fields never go to zero at the same time. The total energy is constant.

@gmfCoding

10 ай бұрын

@@charlesbrightman4237 I am not a physicists but it might be that we don't KNOW why they oscillate or HOW, it's just that the model we have for them currently predicts that they do, that pretty much can be applied to any subject in physics. Math describes phenomena, it predicts phenomena, but the more fundamental that you get, you have less and less explanations of why things are the way they are. Particularly with photons you can model the em field amplitude with a 3d complex plane. Just because, if modeled, the interference pattern of the E and B sine wave would be 0, doesn't mean the energy is 0, you can derive those sine waves from using that complex 3d plane, in the complex space the photon "sine waves" are flattened projections of a continuous helix. It's fun stuff I wish I knew more.

@charlesbrightman4237

10 ай бұрын

@@gmfCoding Speaking of things modern science does not know: THINGS MODERN SCIENCE DOES NOT APPARENTLY KNOW: (copy and paste from my files): Consider the following: a. Numbers: Modern science does not even know how numbers and certain mathematical constants exist for math to do what math does. (And nobody as of yet has been able to show me how numbers and certain mathematical constants can come from the Standard Model Of Particle Physics). b. Space: Modern science does not even know what 'space' actually is nor how it could actually warp and expand. c. Time: Modern science does not even know what 'time' actually is nor how it could actually warp and vary. d. Gravity: Modern science does not even know what 'gravity' actually is nor how gravity actually does what it appears to do. And for those who claim that 'gravity' is matter warping the fabric of spacetime, see 'b' and 'c' above. e. Speed of Light: 'Speed', distance divided by time, distance being two points in space with space between those two points. But yet, here again, modern science does not even know what space and time actually are that makes up 'speed' and they also claim that space can warp and expand and time can warp and vary, so how could they truly know even what the speed of light actually is that they utilize in many of the formulas? Speed of light should also warp, expand and vary depending upon what space and time it was in. And if the speed of light can warp, expand and vary in space and time, how then do far away astronomical observations actually work that are based upon light and the speed of light that could warp, expand and vary in actual reality? f. Photons: Modern science claims that energy cannot be created nor destroyed, it's one of the foundations of physics. First Law Of Thermodynamics: "Energy can neither be created nor destroyed." A photon is usually depicted in a sine wave pattern with the 'e' and 'm' energy fields 90 degrees to each other. The 'e' and 'm' energy fields go out together and come back in together, over and over and over, doing so even across the vast universe as far as we can see. Where does the energy in the energy fields go when both the 'e' and 'm' energy fields go to zero? And what causes the 'e' and 'm' energy fields to come back to 'full' from zero? Also, 'if' a photon actually red shifts, where does the red shifted energy go and why does the photon red shift? And for those who claim space expanding causes a photon to red shift, see 'b' above. * Note: My theory of everything idea, 'if' true (currently dependent upon the results of my gravity test, but 'if' true), can potentially answer all of the above items.

@charlesbrightman4237

10 ай бұрын

@@gmfCoding Do my gravity test for my TOE idea, and 'if' true, and 'if' it does not literally wipe out this entire Earth, all on it, and maybe more, potentially have the literal theory of everything for this entire universe: GRAVITY: (copy and paste from my files): WARNING: (CONTAINS EXISTENTIAL MATTERS): Here is the test for the 'gravity' portion of my TOE idea. I do not have the necessary resources to do the test but maybe you or someone else reading this does, will do the test, then tell the world what is found out either way. a. Imagine a 12 hour clock. b. Put a magnetic field across from the 3 to 9 o'clock positions. c. Put an electric field across from the 6 to 12 o'clock positions. (The magnetic field and electric field would be 90 degrees to each other and should be polarized so as to complement each other.) d. Direct a high powered laser through the center of the clock at 90 degrees to the em fields. e. Do this with the em fields on and off. (The em fields could be varied in size, strength, density and depth. The intent would be to energy frequency match the laser and em fields for optimal results, cancelling out the em modalities of the laser, thereby leaving behind the gravity modality.) f. Look for any gravitational / anti-gravitational effects. (Including the utilization of ferro cells so as to be able to actually see the energy field movements.) (And note: if done right, it's possible a mini gravitational black hole might form. Be ready for it. In addition, it's possible a neutrino might be formed before the black hole stage, the neutrino being a substance with a very high gravitational modality with very low 'em' modalities.) (An alternative to the above would be to direct 3 high powered lasers, or a single high powered laser split into 3 beams, each adjustable to achieve the above set up, all focused upon a single point in space.) 'If' effects are noted, 'then' further research could be done. 'If' effects are not noted, 'then' my latest TOE idea is wrong. But still, we would know what 'gravity' was not, which is still something in the scientific world. This test can speak for itself. It will either be true, partly true, or not true at all. It will either show what gravity truly is, might be, or is not. Science still wins either way and moves forward. * And note: Whether my gravity test or another's, a gravitational black hole would have to be formed to prove the concept as being really true. A gravitational black hole that 'if' self fed itself, could literally wipe out this Earth and all on it, possibly this solar system, possibly put a black hole in this section of our galaxy, and potentially even causing a ripple effect in this galaxy and surrounding universe. But hey, if it does, no worries. Nobody would be left to prosecute those who did so. (Possibly famous last words: "Hey, it worked. Ooooppppssss.................) But as NASA has already proven that low gravity conditions over a prolonged period of time is harmful to the human species, and large rotating space ships won't really work for space bases on planets and moons, those space bases probably being needed somewhere along the way out of this solar system and galaxy, we need to figure out what gravity truly is and see if we can generate artificial gravity so as to have smaller space ships and proper gravity conditions for space bases on planets and moons. Otherwise, at least all human life will most probably die and go extinct one day. Currently, no exceptions. * Added note: Just trying to save at least 1 single species from this Earth to exist beyond this Earth so that life itself from this Earth has continued meaning and purpose to. Gives me something to do while I exist, otherwise, what is it all and everything for? Even if my TOE idea were correct, but if it did not help species survive beyond this Earth, what good would it ultimately be? So, are you feeling lucky? Doing nothing and at least the entire human species eventually dies and goes extinct with a high degree of certainty. Doing a gravity test, (mine and/or another's), and there is at least a slim chance of literally wiping out this entire Earth and all on it, and possibly more. Do you and other's truly want me to prove my TOE idea as being really true? But also: Questions: Are at least some black holes in this universe due to a species who were trying to discern what 'gravity' truly was, came up with a test to do so, were successful, but the black hole generated (to prove what gravity truly was) self fed itself and wiped them and at least their entire planet out? What species might have existed where a black hole now resides? (Since all of life itself is ultimately meaningless in the grand of scheme of things anyway, do the gravity test and see what occurs?) * Added note: Suggestion: 'IF' society did not want to do the gravity test, one suggestion might be to at least create a model as if it were true, then see how that model matches with observations and predictions. It might be possible to discern the theory of everything without actually generating a gravitational black hole (which would definitely prove the TOE idea as being really true).

I would have liked to hear about the connection between length contraction and time dilation. Does one result in the other? and if so, which one is the causing part? It is a pleasure to watch your videos, but they have a habit of spawning new questions 🙂

@narfwhals7843

11 ай бұрын

Neither is causing the other. They always happen together. You can view length contraction as a result of the relativity of simultaneity, though. Because length is a measurement of where the two ends are "now".

@ivarwind

11 ай бұрын

I wouldn't say this covers all bases, but both things are what you observe in something else, as you always see yourself as stationary with the same length and your watch clicking away at a second per second, so while time dilation and length contraction are connected, which one matters depends on what question you're asking - and neither causes the other. When discussing how much time it takes to go from A to B - measured by your own clock and without regard to how much happens at A and B while you're travelling - only the length contraction is relevant. The faster you see the Universe go by, the "thinner" it is. It can never pass by at more than the speed of light, and the difference between e.g. 99% the speed of light and 99.9999% the speed of light is still only 0.9999% the speed of light (approximately 1/100 difference, if for instance you measure how fast an interstellar speck of dust passes by your spaceship) while the slice of Universe between A and B gets a lot thinner as the difference goes from 1% short of lightspeed to 0.0001% short of lightspeed. (Things also get a lot more energetic, so that interstellar speck of dust may go from an annoyance to plain lethal, if you were to hit it, but again, that wasn't the question) If, on the other hand, you're sitting at B and watching someone from A coming to visit you, the distance between the two places doesn't depend on the traveler's speed. What you would see with your amazing telescope, is that apparently everything happens very slowly on their spaceship, and if they move at 99.9999% rather than 99% the speed of light, things on the ship happen much more slowly, while as far as you're concerned, on your watch, the trip takes almost exactly the same time (Once you've corrected for the delay of the light from the traveler in reaching you). The end result is that in both cases, the traveler is observed to experience less time with higher speeds, but the explanations are different. To the traveler the explanation is length contraction of the Universe, while to the "stationary" observer the explanation is time dilation of the traveler. And I hope it's clear that this isn't because of some inherent difference between moving and "stationary" observers - which it is not - but rather because of the asymmetric questions - both the traveler and the "stationary" observer ask "how much time does the traveler experience." If the questions were changed to be about the "stationary" observer, the traveler would see time dilation at the destination while the "stationary" observer would see the traveller squashed thin (ignoring again the effects of the delay of the light, which would affect the uncorrected observations quite a lot).

@angeldude101

11 ай бұрын

They happen because acceleration is rotating between time and space. Since spacetime is hyperbolic, rotating away from the time direction actually makes the time component _increase_ rather than decrease while increasing the space component.

@adb012

11 ай бұрын

They are the logical and mathematical conclusion of just assuming that the speed of light is constant for all observares regardless of their relative motion. With that and middle school math (basically Pythagoras) you can derive time dilation and length contraction in minutes.

@anywallsocket

10 ай бұрын

Have you ever looked down on a city from an airplane window? You get the feeling as you go up that the world below is slowing down, and likewise it feels like it’s speeding up as you land. This is because the vanishing point is shrinking as the world contracts away from us and growing as the world expands towards us. Gravity and relative velocity have the same effect. In the case of gravitation, things contract and slow towards gravity wells, and vice versa. In the case of relative velocity things contract ahead and expand behind the direction of motion.

Hi, Dr. Don. I loved this video. I have a couple of takeaways. If a photon (or any other massless particle traveling at C) experiences no time and no distance, than from its perspective, spacetime doesn't exist. But for particles with mass, and things made of particles with mass (like you and me) spacetime is very real. Could the Big Bang and the accelerating expansion of spacetime be a consequence of previously massless particles suddenly acquiring mass? Could the Higgs Field be connected to this? I appreciate and enjoy your content here and your Facebook page. Thank you for being such a clear and honest voice for physics to the general public. You're the Carl Sagan of the 21st century. Keeps up the good work.

@wayneyadams

8 ай бұрын

@DeanBathaDotCom time dilation and length contraction are phenomena that only affect particle with mass. It is incorrect and nonsensical to apply those concepts to light.

One of my favourite thing is that you can pretty much derive the formula for gamma from pythagorans theorem and thus how highschool math can be found in such seemingly complicated topics like relativity

I love to think about this concept with Minkowski diagrams and light cones. Lights exist everywhere, everywhen on its lightlike worldline, and we happen to observe them like they're moving in our space while we're moving through time.

@bsadewitz

10 ай бұрын

Even though photons don't experience time, aren't they also moving through spacetime? I'm not trying to be pedantic. Spacetime is the thing they are moving through, isn't it?

@byungyoonchoi3744

10 ай бұрын

@@bsadewitz I figured out my comment had nothing to do with light not experiencing time... The comment by Tommy LaKindaSorta explains it quite well I think.

It blew my mind when I learned that it could take anywhere from a few thousand to millions of years for a single photon to exit a star

@johnnydoe3603

10 ай бұрын

Heavy Traffic It’s way too Dense

Thank you for these easy to follow explanations. I am puzzled about one thing though. Just before watching this video, I watched your video called "Why can't you go faster than light?" In that video, you said in spacetime everything is travelling at the speed of light but in this video you say that the equations of relativity do not apply to an object travelling at the speed of light. How do you reconcile these two statements?

There once was a young man named Fisk, Whose fencing was extremely brisk, So fast was his action, The Lorentz contraction, Reduced his foil to a disk.

Hi don, in classical electrodynamics we use the model of frequency modulation and amplitude modulation to transmit signals. Can you make a video on how those modulations are explained in quantum electrodynamics with photons? (I have an idea but am not quite sure...) thanks for your channel it's so good.

@kaitlyn__L

10 ай бұрын

I’m sure a video will be fascinating, but hopefully this is enough to get you looking into more things: the amplitude is the number of photons, while the frequency is the specific photon energy. Of course it gets fuzzier deeper down because each photon is itself really a wave function with its own complex amplitude and frequency over time… but the classical signalling effects we observe are determined by those two simpler counts of quanta.

I've always liked this way of thinking about it, and especially that, while mathematical limits and time dilation can be quite tricky and unintuitive, somehow the idea of the entire Universe getting squashed to a pancake from the point of view of something like a cosmic ray, and even thinner to a photon, makes perfect intuitive sense. Well, to me anyway; YMMV.

@anywallsocket

10 ай бұрын

If makes perfect intuitive sense you should seriously doubt your logic lol

Great video. A quick question regarding a single photon. I wonder if a single photon travels in a straight line or it travels 360 degrees into all directions. While electromagnetic waves (consisting of many photons) may travel in a certain direction, I always wonder how a single photon may behave.

The limit approach is a nice one and does help explain why many folks considered photons timeless. But I hope you don't mind if, in the style of the scientific method, I point out two issues worth considering. (1) The limit in question is quantized, not smooth. For example, by starting with 1 gram of matter and 1 gram of antimatter, the "at rest" end of the limit would be the two grams sitting next to each other. Converting increasing fractions of the two grams into pure linear momentum applied to the remaining matter and antimatter - an action-reaction pair - then can closely approach your limit, creating truly astonishing Lorentz factors. The trouble comes at the very end, when all that's left is one electron and one positron hurtling at incredible speeds in opposite directions. After that, there is _no_ smooth transition: You jump instead to pure gamma rays with _no_ rest mass. I suspect the safer path is still just to say, "Lorentz time dilation does not apply to photons." And it's funny to hear myself say that since I quite enjoy saying that photons are timeless. I'm just not sure the argument is completely sound. (2) I know it's popular for folks to say that length and duration between a fast spaceship and its destination both shrink as if divided by gamma. The problem is that both of these statements are flatly incorrect: (a) The spaceship-observed length to the destination does shrink dramatically, but by R, the relativistic Doppler factor, not the Lorentz factor, gamma. Since the Lorentz factor is nothing more than the average of R and 1/R, gamma and R converge at extremely high velocities. But they are not the same, and they deviate significantly from each other at more moderate relativistic velocities. (b) No matter how often it gets quoted, the claim that the passage of time in front of the spaceship slows as the ship approaches its destination is, well... spectacularly incorrect. What happens is that clocks in directly in front of the spaceship _speed up_ by a factor of R, the relativistic Doppler factor. This is not complicated. A spaceship traveling at high velocity to the Andromeda Galaxy encounters every photon emitted towards it during its passage. That translates into a huge increase in frequency and the speed of the events observed since the frequency is just another kind of clock. The relativistic Doppler factor has been around for decades, so I'm perplexed why this rather important message hasn't gotten out better. Why _none of this_ violates the Poincaré symmetries takes a few too many diagrams to describe here. Suffice it to say that people need to be more careful about who launched who, that is, which system got energized. Everything moving gets launched. Until you acknowledge and follow the full history of how and when momentum energy is added or subtracted to a given system, you can't calculate the _context_ over which the Poincaré symmetries of one system interact meaningfully and irreversibly with the symmetries of other material systems.

I wonder if the photon thinking it's everywhere along its path at once could be used to explain some interesting quantum mechanics effects, like interfering with itself in double slit experiment etc...

@a64738

11 ай бұрын

Yes I have been pointing that out for 20+ years now that light do not experience time and that you have to account for that and that it could explain lot of the "weirdness" with light...

@anywallsocket

10 ай бұрын

@@a64738 this is basic QM, lol. All quantum objects experience ‘self-interference’, whether it is constructive: the phases are aligning and the state is becoming more coherent, or destructive: the phases are misaligning and the state is decohering. The only way I can see this being related to time itself (experience is another matter entirely), is that the more coherent a state is the more reversible its dynamics, and so when a quantum state decoheres - say by interacting with an open system, it becomes more and more irreversible as the systems mix, leading to the a preferred direction in time and the 2nd law.

@scottmckeown1729

10 ай бұрын

interesting idea, I had a different take on the length contraction idea... If from its point of view, the distance it has traveled is infinitely short, that would explain why from the photon's point of view it takes zero time to get there. Presumably, (if a photon could be conscious) it can't even tell the difference between the start and end locations of its journey.

@anywallsocket

10 ай бұрын

@@scottmckeown1729 it is a silly idea. all you're doing is looking at the equation of velocity v=x/t, where c=x/t. as such, given basic relativity, you have u = (u'-v)/(1-u'v/c^2), i.e., the Galilean boost from seeing the light divided by the relativistic effect, i.e, 0. you're left with a mathematical fixed point which is undefined. therefore, it's a silly idea.

@scottmckeown1729

10 ай бұрын

@@anywallsocket I admit that I don't remember how to properly use the formula that you have provided, but that is a formula for adding velocities together yes? Like if I am standing still and you are on top of a train and you either throw a ball at me or shine photons at me that is a formula for adding the speed of the train to the speed of the ball, right? Anyway if I'm right about that, then the formula you provided isn't really relevant here. Consider the following uh..."story problem" 1) Imagine that Earth is 100% completely still. 2) Assume that Alpha Centauri is exactly 4.367 light years away. 3) Assume that Earth has sent out a ship to Alpha Centauri that is traveling at exactly 50% the speed of light. The question is... "how long will the spaceship think that the voyage took?" Obviously Earth will think it took 8.734 years, but how long will the spaceship say it took? Concider the following formula: ct' = γ(ct-βx) I will now go through and explain each term in the equation. Oh, and by the way other than the naming of γ(gamma) I find all the terms in this equation to be annoying and unintuitive. Like why does "β" mean velocity? Shouldn't it be "v" for velocity? Anyway whatever... the formula for gamma is as follows... γ = 1/(√1-(v/c)^2) in this case v = 0.5 so γ equals something like 1.155 ct is just how long Earth thinks the trip should take so 8.734 years. β is velocity so 0.5c x is distance, or to be more precise the distance Earth thinks it is. Cuz you know length contraction is a thing too. and ct' is our answer, this will tell us how much time the spaceship experiecned durring the journey. If you do the math the answer is like 7.5638 years depending on how much rounding you've been doing. Remember that Earth thinks the journey took 8.734 years so That's a discrepancy of about 1.17 years. ---------------------------------------------------------------------- Well what if you make the spaceship go faster? Say 90% the speed of light. Keeping in mind that you need to recalculate γ every time, if you do all the math you get an answer of ct' = 2.115 years. That is to say that Earth thinks the trip took 4.852 years and that there is a discrepancy of 2.737 years. ---------------------------------------------------------------------- You can keep plugging in speeds that are closer and closer to C and if you go really really really close to the speed of light, you experience almost no time at all, and if you go even faster than that you experience even less time still. I don't know about you, but I'm gonna say that the idea that photons experience no time at all is a pretty good assumption, based on the math. Could it be wrong? Yeah I guess. I mean you can't technically divide by zero, but you can take the limit, and in this case the limit as β gets arbitrarily close to C converges on zero instead of diverging. One of the reasons why you can't dived say one by zero normally is we can't say if the answer is -∞ or +∞. That is to say that the answer diverges as we take the limit of 1/0... but in the case of ct' = γ(ct-βx) as β approaches C it converges on zero time being experience by the fast moving object.

Yeah, this is pretty mind-bending. Just out of curiosity, how does redshift / blueshift factor into this? Does the light experience the red / blue shift, or is that something only the observer experiences?

@adamredwine774

11 ай бұрын

The number of wavelengths of light is basically set at the point of emission. Expansion of the universe means that the wavelength grows to accommodate. The photons obviously don't "experience" anything and even thinking of them as particles isn't quite right but since the total distance is zero, the "wavelength" functionally has no meaning for the photon anyway.

@garystewart3110

11 ай бұрын

I believe that the view it being a "doppler" effect is incorrect. I believe that it has to do with energy levels. As an example, light that travels a large distance will lose energy, and therefore be at a longer wavelength appearing red or infrared. This isn't an official answer, just my personal thought.

@adamredwine774

11 ай бұрын

@@garystewart3110 Distance traveled doesn't effect energy; no energy is expended in the travel. It might make a good sci-fi story to say that the energy lost by photons as they travel is dark energy or something, but I don't think there's any basis in known physics for such a model. I could be wrong; I'm not a relativity specialist and I'm pretty weak in theory, but that's my take at least.

@cloudpoint0

11 ай бұрын

Light doesn’t frequency shift over large distances. It is the observer moving rapidly towards or away from the source of the light emission that sees a frequency shift effect. It’s a bit like moving towards, passing and then away from a source of sound waves and hearing a pitch change at various distances and directions.

@garystewart3110

11 ай бұрын

@@adamredwine774 well, one thing that is for sure about science, is knowing that we really don't know anything ;)

This is pretty slick. Thanks.

I always found a photons ability to travel basically instantaneously (from its perspective) between two places oddly similar to the seemingly instantaneous transfer of information between two entangled photons in quantum entanglement.

@scribebat

11 ай бұрын

There is no 'information transfer' in entanglement, there is no data going anywhere in that. Thus it cannot be used for faster than light communications. Ya, it's hard to wrap a brain around that.

@charlesbrightman4237

11 ай бұрын

QUESTIONS: PHOTONS: (copy and paste from my files): A photon is usually depicted in a sine wave pattern with the 'e' and 'm' energy fields 90 degrees to each other. The 'e' and 'm' energy fields go out together and come back in together, over and over and over, doing so even across the vast universe as far as we can see. Where does the energy in the energy fields go when both the 'e' and 'm' energy fields go to zero? And what causes the 'e' and 'm' energy fields to come back to 'full' from zero? Over and over again over vast distances.

@IncompleteTheory

11 ай бұрын

@@charlesbrightman4237 I think that's some sort of momentum. Think of a pendulum which also frequently passes the resting spot, but keeps going due to inherent momentum.

@darrennew8211

11 ай бұрын

@@charlesbrightman4237 Since photons are emitted and absorbed by electrons, the answer would likely be that the energy/momentum of the photon winds up in the electron field.

@charlesbrightman4237

11 ай бұрын

@@IncompleteTheory Momentum would have the 'em' go past zero then and then come back from there to 'full' again, over and over and over, across the vast universe. And then also, electricity is electricity and magnetism is magnetism, varying possibly only in energy modality, energy density and energy frequency. The 'em' of a photon would be interacting with other 'em' as well as other electrical and magnetic forces in the universe along it's journey. Seems the 'em' should lose energy over time if momentum were the only reason why, at least to me. And yet, that is not what is apparently observed concerning photons.

The idea of a photon existing everywhere along its path at once makes the double slit experiment more interesting. But what about photons that go through thick atmosphere and slow down? Surely they experience at least a little time?

@aztronomy7457

7 ай бұрын

From the perspective of us they might, but from the perspective of the photon time doesn’t exist, therefor distance doesn’t exist, and if you have no time or distance something can’t slow down

@RowOfMushyTiT

7 ай бұрын

They don't have a path from their perspective since there is distance contraction.

@longlostwraith5106

7 ай бұрын

That is where the particle/photon theory of light breaks down. Light is a wave. Waves travel at a fixed speed (here, the speed of light) but when a bunch of waves are interfering with one another, their sum seems like it's moving more slowly. When light passes through our atmosphere, it lightly excites the electrons of nearby particles, causing them to produce their own light. The interference pattern that results from all that makes the light appear to be slower.

There are 5 levels or phases of time --- 1 ) Universal , 2) Psychological , 3) Atomic ,4) Mechanical , 5) Biological . Excellent Videos - Thank You .

This phenomenon (that photons travelling at c experience no time at all), is never, mentioned in any discussion about light-speed, or relativity. I'd realised some time ago that this effect must be the case, but wanted expert confirmation just to be sure, so this video is very much appreciated. Also important is the fact (also mentioned in the video) that the closer one's velocity approaches c, the journey time reduces exponentially. It doesn't matter that c is the universal speed limit because c is already infinite speed. Practically though this is not helpful at present because of the relativistic effects of accelerating mass towards c, but we may find alternative methods of travel in due course, when we have a better understanding of the nature of spacetime itself, and/or higher dimensions that we can not as yet perceive. Of course, we perceive that light still takes about 8 minutes to travel from the Sun to the Earth, because of relativity, and light reaching us from the edge of the visible universe has taken many millions of years to reach us by our measure, but then we are not travelling at relativistic speeds, so our perception is rather different from a photon's.

If a photon experiences no time, how can it have a wavelength? I know you are using abstractions in the video, because the real descriptions are mathematical, but these ideas just bend my brain . . . in good ways! =)

@geogrok8594

11 ай бұрын

This is also my question. Also, why does the wavelength stretch in the direction of travel due to the expansion of space but not in the width? Shouldn’t the amplitude also get stretched?

@cykkm

11 ай бұрын

Photon doesn't know that it has wavelength. _You,_ a massive observer, do.

@deltalima6703

11 ай бұрын

Classical description of what wavelength is cannot be correct, thats how.

@Jan-eh7nf

11 ай бұрын

@@geogrok8594 hmm the light became weaker from distance galaxies that we can observe on Earth

It's about time that this video comes to light ;)

@PaulPaulPaulson

11 ай бұрын

I c what you did there 😉

@wearemany73

11 ай бұрын

@@PaulPaulPaulson I see (C) what you did there with what he did there…😁

@andyk2181

11 ай бұрын

@@wearemany73 Ah the classic joke about the speed of light being a "c" and phonetically the same as "see", timeless!

What does it mean to ‘experience time’? Given the nature of the question, I think this should be explained prior to the presentation of your answer. Great video!

@minhdang1775

10 ай бұрын

From a purely mathematical perspective, the concept of "experience time" implies that an object traverses a non-zero distance in spacetime. In the realm of relativity, time is not merely characterized by change; rather, it assumes a role similar to that of a spatial dimension, along which a system evolves at a specific rate.

If you change the velocity of light to an imaginary number ic, the gamma equation becomes root 2/2 half the length of a basis vector at 45 degrees. It gives some mathematical support to the convention for the space/time diagram treating light as a line at 45 degrees and the presence of root 2 in Pauli matrices for quantum mechanics. Note vector calculus and its differential operators are derived from quaternions and the Schrodinger wave probability equation uses ih bar. There could be something in my observation if no one has not noticed already but what I have said clearly needs more work to see if its of value if that has not been done already. Experience has taught me that people on mass can overlook fairly obvious things. There are a few more things I can draw from this but not enough post space.

If photons don't experience time, how come their phase shifts as they travel over distance? The same photon could constructively interact with an object at time X, but destructively interact with the same object if it reaches it at time Y (when it had an opposing phase), so it doesn't experience all of its travel the same way?

@tommiller1315

11 ай бұрын

Think your answer lies in the expansion of space, causing the phase shift apparent to us the observer, but not to the photon. Maybe the loss of photon energy explains the expansion of space? Just a thought!

@suncat9

11 ай бұрын

They experience all phase shifts they undergo at once.

@drmilkweed

11 ай бұрын

Minute physics has some great videos about how things travel at relativistic speeds. He uses a cool physical model that displays how our intuition about things break down at those speeds. For example, things that appear to occur simultaneously can be viewed to appear at different times if your frame of reference is moving.

@smlanka4u

11 ай бұрын

Einstein's relativity helps creationists to make a singularity. There is no value for common sense sometimes.

@aaronwestley3239

11 ай бұрын

Because our theories of space and time is incomplete at best. It breaks down at the speed of light. Just because our math says that it experience no time doesn't mean it actually is. It's just a product of our incomplete understanding of how the universe works.

So do photons in space really move at "c"? There are atoms in space, and atoms have electrons, and electron cause an index of refraction. OM estimate: n = 1 + 1/Na (avagadro's number, not sodium). Taking limits: gamma = sqrt(Na/2) ~ 500 Billion. Could we even measure that propagation delay? I don't think so....but once v < c, there is a reference frame and photons experience time. Note: if their polarization rotates or changes, like in the ionosphere: they are moving at less than c.

This seemed to me what relativity was saying but it wasn't intuitive. I had not considered distance contracting. I also recently learned that while the speed of light varies with the medium, photons always travel at C. The implications are melting my mind, thanks.

Thank you for the videos, would you please address a confusion I have: the magnetic attraction between wires is a relativistic effect from the movement of electric charges but electromagnetic waves still have separate electric and magnetic fields. Thanks.

Life is a journey, not a destination...unless you are a photon. It's not the years in your life that count. It's the life in your years...unless you are a photon.

So you're sayin' photons exist in a frozen reference frame!? 🤯🤯🤯🤯 If that's true then how could they exhibit a time-varying behavior such as frequency? Also, they would travel zero distance in zero time so their velocity would be 0/0 in their rest frame - a resting velocity should evaluate to zero, no!? Furthermore, this frozen reference frame would imply that photons are immutable - so how could they red shift - such as when they emerge from a gravity well or are stretched by cosmic expansion? Also, aren't photons created moving at c? And doesn't that mean that your argument about limit-as-v-approaches-c doesn't apply? They don't start out moving at c-dv and accelerate to c, after all. Sorry for the snowball of confusion here. PS. Piling on one more confusion - if the photon is in a frozen reference frame then how could it have a wavelength? That wavelength should be zero for all photons, no?

@kylelochlann5053

11 ай бұрын

Your understanding is generally wrong, but first I want to point out what you are absolutely correct - the limit-as-v-approaches-c reasoning is indeed wrong and is a category error (the concept of time, etc, cannot be applied to null curves). Anyway... electromagnetic waves are a set of propagating values of the electromagnetic field. These field values of the electric/magnetic components are generated on time-like curves of some oscillator that propagate at c. As these variations in electric field strength pass over a detector it is the detector that is set oscillating and the oscillations then attributed to the em wave. A photon is a particle to which we attribute the em wave characteristics, but we don't measure photon frequency, only changes in detector states.

Those topics are exactly the reason why I will start studieing Physics in a few month.

But the speed of photons passing through a material, can fall below the speed of photons in vacuum, so in some cases photons are subject to time? I'm missing something. Is time quantized like space?

This also means that contrary to what we often hear from science educators, the speed of light actually isn't kinda slow on a cosmic scale, it's actually much faster than most people think since it essentially enables instantaneous travel to every available location.

@bengardener8928

10 ай бұрын

From lights perspective it never moved anywhere because space and time simply do not exist to it.

@manmanman2000

10 ай бұрын

It's still slow. From that point of view, if you were able to safely put yourself into some kind of cryogenic freeze and then safely unfreeze yourself again at your destination, you also could go anywhere at ANY speed and arrive there "instantaneously".

@markcarey67

10 ай бұрын

Yeah but only if you don't have mass

@wayneyadams

9 ай бұрын

No, it does not travel instantaneously to every location. It still takes time to travel from one place to another, that is why the light-year is such a convenient unit of measure. Since it is the distance light travels in one year, we can say that light takes x number of years to reach us if the body is x light-years away. For example, if we look at a body 10,000 light-years away, we know it took 10,000 years for the light to reach us. Since the visible universe is billions of years old, it takes light billions of years to reach us, so yes light is slow on cosmic scales. Even in our everyday world it takes light time to travel from place to another. In everyday terms, light travel about one-foot in one nanosecond.

@manmanman2000

9 ай бұрын

@@precisi0n86 Not if you're a wizzard ;p

Question: If photons don't experience time as they travel from source to detection, how is it that they change wavelength (redshift) as space stretches? Wouldn't they have to experience time in the same manner as leptons do when the lepton changes flavor? Or does the redshift have to do with photon density over said distances, and the stretching of space causes the pressure in the stream to reduce as there is now more space for the same number of photons, similar to an atmospheric pressure wave?

@kunjukunjunil1481

11 ай бұрын

'Redshift/Blueshift' is a subjective thing. It depends on the observer.

@johnbennett1465

11 ай бұрын

​@@kunjukunjunil1481 it also depends on the speed of the emitter. So how does the photon record that information?

@kethmarhkfy7luf.263

11 ай бұрын

@@kunjukunjunil1481 No. Photons red-shift due to the expansion of the universe. Every observer sees photons red-shift.

@kunjukunjunil1481

11 ай бұрын

@@johnbennett1465 "Speed of the emitter" relative to what ?

@johnbennett1465

11 ай бұрын

@@kunjukunjunil1481 the reciever. Red shift can be used to measure relative speed even when you are close enough that expansion of the Universe doesn't matter.

This guy is an excellent teacher

This is an excellent presentation. Now it’s up to us to draw logical conclusions. There is an ubiquitous a-spatial and atemporal force acting upon the universe. The cause of subatomic building blocks and their energy and propulsion is ongoing and not relegated to a single event in the distant past.

My problem with trying to wrap my head around this is that a photon is a traveling disturbance and it follows a frequency. Wouldn't a photon have to experience time for the disturbance to manifest?

@trevinbeattie4888

11 ай бұрын

Time relative to what? It is not the photons themselves which follow a frequency, but rather their passage through space. The time that the spend traveling is defined relative to the space they travel through.

@aliren6118

11 ай бұрын

@@trevinbeattie4888 Thanks, this kind of helps, I think. Photons following a frequency vs. their passage through space sounds a bit semantical to me though. At the end of the day, a photon is always under a state of change. A change that doesn't take 0 time. When the doc said a photon sees itself (relatively) everywhere along its path at once; is that in the peak of the frequency everywhere at once or the valley of the frequency, everywhere at once? And maybe it's both, I dunno, but it's very hard to intuitively say it doesn't experience time.

@AySz88

10 ай бұрын

​ @Aliren Does phase invariance help explain this? I'm not an expert, but I imagine that would say there isn't a set peak or valley "position" for any single photon, and phase only emerges in the relationship or interference between two photons.

Do photons experience time while going through substances like air, water and glass where they slow down a bit?

@groaningmole4338

11 ай бұрын

They don't actually slow down. They interact with the electrons in the medium, and that gives rise to a phase shift that gives the appearance of them having slowed down.

@DrDeuteron

11 ай бұрын

I say yes. If you can go into a calcite crystal and have your polarization rotated: you need time to change, hence: you're not moving at c. (you = photon, colloquially). Same for the ion-sphere and radio waves (and neutrino oscillations: that they change flavor means they have mass means v < c).

@dugldoo

11 ай бұрын

@@groaningmole4338 See Dr. Lincoln's presentation on the speed of light through transparent materials from 4 years ago. He debunks your explanation and shows how light really does slow down as it goes through glass, water, plastic, etc.

@estranhokonsta

11 ай бұрын

@@groaningmole4338 As said in the video, relativity doesn't really work at the speed of light. What on can say approximatively is that to an observer, using special relativity to describe a photon in a vacuum, it seems that the photon doesn't experience time. But a little better explanation is to say: whatever "time" or "experience" that the photon has, it is completely different from what we "experience" as relativistic beings. That is. We must admit our ignorance at this time. One must note that in quantum mechanics, they use wavefunctions rather than classical concepts of time to describe behaviour. Is a that better framework to describe photons? Possibly, since the quantum theory is more specialized on particles than relativity. But in the end the state of science today is still the same and our ignorance is still the end all conclusion of the whole thing.

@pattystephens8129

11 ай бұрын

All I know is photons don’t carry luggage because they’re traveling light.

Light is the extreme side of Heisenberg's uncertainty principle which i puts like measuring absolute speed missed out the absolute position of the supposed photon/wave. When light interacts with electric field, for instance: electron energy field variations are primary indicator of the interactions of the fields like say excitation of valence electrons. By that indication we can sum up the total observable energies and certainly light dips from it's superhero mode such as the photon to heat. we can be certain that light is source of external heat insertions. Relaying of reflections of light is fascinating and interesting.

Succinct and informative. Thank you. I've always wondered, if a photon experiences no time or distance, how can it have direction? In other words, without time or distance, it seemed to me as though all points in space coexist as a single point for the photon so direction would be meaningless. The way you phrased it as "experiencing all points along the path at the same time" gives me more to ponder (unless you want to do a video on it). I still don't see the solution because the term "experience" is necessarily temporal, but I understand that this is just an analogy.

Perhaps photons don’t move at all, what moves is ripples in the EM-field of space-time.

@kethmarhkfy7luf.263

11 ай бұрын

They take time to get someplace because they are moving.

When we use gamma we are only translating things to our euclidian minds.

Here's how I reasoned this out in about 1988: Anything with mass would have to achieve infinite mass to reach the speed of light, therefore it can't happen. However, since photons do travel at the speed of light, they are infinite without mass; therefore, every photon in space is, from its own point of view, everywhere in the universe at once. In fact, all photons might even be the same photon from their point of view

Time is a consequence of entropy gradient. Where there's an entropy gradient, the entropy changes by means of interactions and hence energy exchange. If there are no interactions, that in turn means there is no entropy gradient and hence no time. So if a photon is traveling with the speed of light and it does not interactiont with anything along it's direction of motion then it can't experience time. All photons travel without interaction between the place they were emitted and the place they are absorbed, by definition. This implies that they infact do not experience time themselves. If they did it would mean they interacted with something along the way and aren't really the same photon anymore.

I've tended to think of a photon as not so much an independent particle with its discrete bounds, but rather as an exchange of energy as two particles reach out and momentarily touch each other across space & time.

@wayneyadams

9 ай бұрын

Think of a photon as a packet of waves. A crude but usable way to do this is to think of what happens when sounds of two different frequencies interact. The result is packets of waves which we call beats. They still exhibit all the properties of waves but they also deliver their energy in discrete bursts much like a photon. This is only a very simple and crude way to think about it and you have to be careful not to take the analogy too far.

@ConsecDesign

7 ай бұрын

Tight

@dendrites

3 ай бұрын

Say you point a laser at a mirror 3 million km away, and briefly turn it on and off. In 20 seconds those photons will land back on your retina and you will see the light pulse. However let's say you start the experiment blindfolded for the first 10 seconds. If photons experience no distance or time, at what point on their return journey would they 'experience' the landing site change from a blindfold to a retina?

@FrankBlissett

3 ай бұрын

​@@dendrites The question does not make any sense if my assumption is correct. The photons in the first example would experience no time passing. The photons in the second example would experience no time passing.

@dendrites

3 ай бұрын

@@FrankBlissett If photons experience no time passing then from their perspective they will have returned back to you the moment you press the button on the laser. It seems like you are suggesting that photons don't experience *traveling* across space and time (because traveling is something that takes time); instead they "reach out" directly from their origin to their destination (e.g. from the tip of the laser to your eye). This is a notion I've also contemplated... what would the universe look like to a photon (given that no time passes and space is infinitely contracted). So if you are wearing a blindfold when you press the laser button, and the photon experiences no time passing between leaving you and returning to you (as if it's reaching out directly from your laser to your eyes), at what point does it experience the removal of the blindfold (given there is zero time for it to experience this change). Does that make sense?

As I thought then, there is no "spooky action at a distance", since there is no distance for the photon, the measurements are done at the same place, even if it appears differently.

@car103d

11 ай бұрын

Entanglement isn’t just for photons, and it’s instantaneous for the observer’s point of view, and undetermined, hence it remains spooky, and about the photon itself, well, being everywhere all at once is even spookier! Relativity itself was, and still is, spooky too! It’s a spooky Universe! 😂😅

If time speeds up the further it is from gravity/mass, does that change how fast you need to go to stop experiencing it? Or do they speed up and slow down at the same rate since light only reaches its max speed when free of gravity as well? Does time move at the speed of light? Does light move at the speed of time, hence it slows down when time does? Is it because nothing can move faster than time? If that was the case and we broke that speed, would we actually travel foreward in time, not backwards?

Thanks again, Dr Don. Maybe someday I'll have a chance to cross paths with you and share an inelastic collision of greeting.

What happens to space-time without time??

@drdon5205

11 ай бұрын

It's all space. However, in this case, it's even weirder - both space and time shrink to zero. Mind blown!

@LuisAldamiz

11 ай бұрын

Excellent question. Just for the speculative fun, I'll adventure that maybe time is tightly associated with mass. Which are the maths and logic around that plausible fact, it beats me.