Does light experience time?

[@Mahesh_Shenoy]

Go to ground.news/floathead to stay fully informed and access reliable information. Subscribe through my link to get 30% off unlimited access this month only. Also, first :D!

[@krislogy]

Minor correction. Fact. Tu. Ality. Not Faculty. :)

[@adamsheaffer]

But, what if an object travels so close to the speed of light that it travels across the entire observable universe in femtoseconds of proper time? Would the object continue on its trajectory until it hits into another object? Or would it wrap around the universe infinitely or stay in place in empty space as the universe expands so that the object HAS TO experience time?

[@tokajileo5928]

where to get that t-shirt? XL size

[@petevenuti7355]

So when I'm playing chess with my computer and our kings wind up next to each other, and im pissed because the computer wont let me take its king saying its an illegal move but it's king takes mine‽ I shouldn't be learning chess from a computer.

[@harrisbinkhurram]

I think your explanation is better, and it proves Tyson's experiment wrong: kzbin.info/www/bejne/eGPHdKmupbCKfM0

[@kyo_.]

man your topics are always so interesting i just have to watch

[@Mahesh_Shenoy]

Thank you :)

[@whykoks]

Do you have girl friend?​@@Mahesh_Shenoy

[@arkdark5554]

No. At the speed of light…the time stops. According to Gödel's interpretation of Relativity.

[@DABmonger]

I'm with that line of thinking, but then if equations are allowed to be blown up do we assume that singularities exist?! Perhaps time not moving and singularities are connected in some way, at least in telling us that we're missing something major in our knowledge!

[@kellyrobinson9564]

You don't understand inertial reference frames

[@mmicoski]

If an object travels almost at c, from its reference frame the universe is traveling at almost c and is extremely contracted in the direction of the movement. So, from its perspective, it would traverse the entire universe almost instantaneously. I think looking this way we could say this object experiences almost no time, meaning it does not see the universe evolve in the very short time (from its perpective) it took to traverse the universe. If you think regular objects do not traverse the entire universe, but a smaller distance between object creation and destruction, for this object it existed during almost no time and was almost instantly destroyed

[@QuantenMagier]

That is also how I see light, it's as if the photon was using a wormhole through space-but-not-time, and that wormhole is called the EM-field, but it's an imperfect wormhole due to redshift..

[@DABmonger]

I view light in the sense of limits and infinities, that blow up equations. Like singularities. We're clearly missing something significant in our understanding.

[@petejohnston5880]

You're absolutely right. As every point in the universe sees light traveling at the speed of light relative to it, then light in turn sees every point in the universe moving at the speed of light relative to it self and hence the whole universe is length contracted to be infinitely thin in the direction of travel. The universe becomes an infinitely thin but very wide pancake. This means that the point in space where it starts its journey is the same point in space where it ends its journey and it take zero time from its perspective to travel from start to finish. So does light experience time, well its life is over before it has a chance to experience anything. We see light moving but for it, it all happened and finished it's journey before time even moved.

[@DABmonger]

​@@petejohnston5880It can be argued that light does not experience time, and a photon is in all places on its path at the same time.

[@QuantenMagier]

@@DABmonger Nope, photons are just the exchange particles, there exist no photons on the path of light, just electromagnetic waves, the photons are only created from those electromagnetic fields by interactions with matter.

[@vyvianalcott1681]

I'm two minutes in and you are already blowing my mind about concepts I thought I understood. I absolutely love your videos, you are by FAR the best physics presenter and explainer since Feynman. Keep up the great work, I'm hanging on your every word now!

[@Mahesh_Shenoy]

Wow, that’s super encouraging to hear. Thank you :)

[@everythingisalllies2141]

I love it when people actually believe that they can really KNOW this stuff. They really have convinced themselves that they have actually understood what we can never possibly understand. Understanding what does light experience, is a classic case of over confidence. google the free ebooks, "Dave vs Hal 9001" for more information. You may change your mind about what you think is real and true.

[@auriuman78]

@@Mahesh_Shenoy it's true my man, I look forward to seeing your presentations when they drop in my notifications. They're actually fun dude, you make science what it's supposed to be, awesome 👍

[@Littleprinceleon]

​@@Mahesh_Shenoy, you help us to have some glimpses from the shoulder of science giants. That's the POV worth to achieve. Many thanks 🙏👍

[@Robienko]

Because it's not correct

[@luciddreamworks]

I have a masters in Math, and your videos have allowed me to appreciate axioms, postulates, and modeling so much more.

[@kriiistofel]

I read somewhere how we could imagine photon 'perspective'. From it's 'point of view' there is only act of creation and then instantaneous act of annihilation (when it interacts with some object). There is nothing in between for photon, it does not 'experience' time.

[@Vexas345]

But why assume it's instantaneous?

[@G0ldbl4e]

@@Vexas345 They experience infinite time and length contraction as per special relativity

[@auriuman78]

Well as far as it (the photon) is concerned, it might as well be instantaneous, even if it took 13.8 billion years in reference to me? Zero time experience is pretty well instant right? Kinda baffles the logic of normal intuition when you realize that time is truly based around the fastest thing in the universe, that's how it ought to be reasoned at least, if you want to truly understand what time is. Base your reference at the fastest thing known, kind of like temperatures and zero. There's a limit and we reference from there in science, hence Kelvin. Why not do the same with light\photons\emr? I'm not trying to turn our time reference understanding on it's head, Just like we don't use Kelvin in everyday life. But for scientific matters, yeah 👍 I think it would simplify the problem of medium speeds not matching to do that way, cause it's all light speed, just different frames of reference right? I'm not gonna even attempt to address the things that would happen sub-planck though, haha, not qualified. It'd be weird for sure, in case this isn't weird enough for you. I am in no way certain there's anything meaningful below Planck pixel, but I'm certainly not opposed to it being more than not meaningful, so what if the Schwartzchild radius = black hole. Another thing we don't really know anything about other than they're there and they're doing something deeply interesting.

[@Vexas345]

@@G0ldbl4e They do not. The math for time dilation/length contraction doesn't work for things moving at c. They don't have reference frames, so special relativity doesn't apply.

[@auriuman78]

The very idea that the photon does not experience time, as far as it's concerned it's just sitting there, good Lord man what a concept. I mean really if you think about it 🤯 trillions of trillions of trillions of photons, all different amplitudes and wavelengths, interacting with different interferences to form stuff, all infinitely small and large at the same time, this is weird stuff seriously. It makes me pull back to the holographic model, you know what I mean, if it's just there then not, everything else around it being what's in motion... Which is also a bunch of other photons at rest, blipping on and off here and there. Kind of leads to the idea that maybe it is in some way intricately holographic. I mean it's pretty much all electrical\em. I learned that some years ago during a heroic experience that I did not plan on taking but accidentally did anyway. Idk I think a lot about stuff but this one I think is above human thinking. I'm definitely not smart enough to grapple with that one, but I'd be willing to bet my life that it's so ridiculously elegant and simple that we're just looking right over it. It's probably right in front of us 😅

[@AS-zc8mr]

I followed your recommendation in a party, and the dude telling the story punched me in the face!!!

[@Mahesh_Shenoy]

What recommendation? :D

[@rodschmidt8952]

@@Mahesh_Shenoy probably saying "you're breaking the rules, you cannot use SR to conclude anything once you've broken SR"

[@jensphiliphohmann1876]

05:40 f _Looking from s.o.'s perspective basically means looking from s.o.'s reference frame._ I'd put it differently: By "looking from s.o.'s perspective" physicists mean *describing the scenario from a rest frame of her/ his.* ▪︎A frame in this context is a coordinate system which basically maps all of spacetime, so you can't really looking _out of_ it. Rather you express physical quantities in those coordinates. ▪︎Everything kind of has infinitely many rest frames with different orientations or origins. ▪︎Your reference frame is the frame you use to describe a scenario. This _might_ be a rest frame of yours but it _doesn't have to._ And in everyday life, it seldom is. Mostly we implicitly use a frame bound to Earth; otherwise, if I went to Cologne by train, I'd have to say "the train has come to rest (a very active rest like that of someone running on a treadmill) and lets Cologne approach it".

[@everythingisalllies2141]

google the free ebooks "dave vs Hal 9001" you will be surprised what you will discover.

[@siddhant5631]

I was literally looking for a person who could explain things that comprehensively. The way you crack things, like the scientists who are much more eager to break apart the subatomic particles in the Large Hadron Collider to understand the behavior or laws of this Universe. The power of visualization and the interpretation you have mastered is just Astonishing. I don't have words for you, you are just limitless. Keep continuing the series I am learning a lot by opening different ways to visualize things for Better interpretation. My regards to you.

[@CricketWithPranav314]

Hypothetically, if I make a phone call to my friend who is near the sun, than he would recieve it after more than 8 mins 16 secs and we will have conversation at each interval of more than 8 mins 16 secs?

[@manasyadav1993]

Duh

[@Farming-Technology]

I'd check with your mobile provider first to see if interplanetary calling is included in your package. Could be expensive 🤠

[@ashutoshsethi6150]

He is toasted.

[@Fluxikator]

The Interval would be double that. You Record your message and send it away. After 8min 16 sec your friend will recive it. He Records an answer and sends its back. After another 8min and 16 sec the answer has reaced you. So for you the time it takes from sening your message and getting an answer is 16min and 32 seconds. + the time he has used to reply to your message. Thus the interval is at 16mins and 32 seconds at a minimum.

[@CricketWithPranav314]

@@Fluxikator It means if I say "Hello", I would hear his reply "Hi" after around 17 mins?

[@PTGaonkar]

What a video! I think this series is one of the greatest assistant to understand special theory of relativity

[@Mahesh_Shenoy]

Wonderful to hear that :)

[@armaan7381]

Oh god I recognize your voice from khan academy

[@justinhageman1379]

As always these videos are amazing! By far the best most easily digestible explanations of physics concepts I’ve ever seen.

[@johnmagnotta8401]

Hear hear

[@johnmagnotta8401]

Or is it "Here, here?"

[@jonathanlister5644]

Excellent argument, your logic is very sound - it brings to mind constructor theory. Also love the chess analogy reminds me of Feynman's use of a chess analogy. Thanks very thought provoking.

[@Mahesh_Shenoy]

Thanks, Jonathan. :)

[@magnuszakrisson]

But you can have two kings next to each other in chess. That would have required an illegal move though but it can still happen. There has even been a real chess game where the judge ruled that the one who played a move after an illegal move lost, because it was illegal to to continue after this illegal position and create a new illegal position. When the player who made the first illegal move pointed that out the judge concluded that the last player who made an illegal move lost! ;) Not sure what conclusion we can draw about lights perspective from this though lol

[@dogcarman]

Mind duly blown. I had never considered that consequence of the second postulate. Wonderful. Thank you.

[@wootle]

I learn more from you in a 14 minute video than all my years of high school. Thank you sir!!

[@Jupiter1423]

And you might say, mahesh - i always wondered if we could have a beer together. But einstein says yes, of course you can have a beer with mahesh.

[@donnyfanizzi5360]

Thanks again great videos as usual. Love the energy!

[@Mahesh_Shenoy]

Thanks, Donny :)

[@kriiistofel]

The more I learn about special relativity, the more I think that our movement is just an illusion, rather we all stay in place and only light is truly moving.

[@nHans]

Lemme guess-still working from home? 😁😂🤣

[@bakshiavijit]

I really liked how you presented your understanding step by step emerging from your confessed confusion. Also loved how you made it a conversation between Mahesh, Einstein and Feynman chipped in, that made it both interesting and funny. A honest presentation full of excitement. Liked and subscribed!

[@IterativeTheoryRocks]

I studied this subject some decades ago. My interpretation of this question was somewhat different. You are focusing on time for the photon and the photons rest frame. You don’t have to do that. Instead think of travelling ‘almost at the speed of light’ and what you will see is that your own time passes normally, but the entire rest of the universe is Lorentz contracted in distance. In other words, you will (due to length contraction) arrive almost immediately after you leave - as the distance to travel is minuscule - even light years would (if you go fast enough) shrink to millimetres. The reason light does not experience time is nothing to do with rest frames, but rather that at the speed of light it arrives at the same instance it leaves / because the ‘length’ of its travel has shrunk to zero. This is in a perfect Vacuum. If the vacuum is not perfect, then the light will experience some minuscule time.

[@damc7456]

Excellent... Also, I think the video would better serve viewers by comparing clocks. If a photon were to look at its wristwatch, it would observe the hands moving in proper time. Sure, but an observer watching the photon go by would observe that the photon's wristwatch has hands that aren't moving at all. As you point out, this is explained by the photon observing that all the points through which it travels at the speed of light have contracted into one infinitesimal. I'm super curious how this topic relates to entanglement. Could it be that entangled pairs, despite potentially being separated by light years, "think" that they continue to occupy the same point because per their observation, zero time/space has passed between before they were split and when they become disentangled?

[@Jim-uq1mc]

In a reference frame the observer is at rest; not the photon is at rest. The photon needs to travel at the speed c with respect to any observer - even if the observer would himself travel at c with respect to some other observer . . .

[@Littleprinceleon]

​@@Jim-uq1mc two photons moving at the same direction: do they travel at c from each others' perspective?

[@damc7456]

@@Jim-uq1mc In my comment I make the photon the observer. "If a photon were to look at its wristwatch..."

[@kylelochlann5053]

Time cannot be applied to a null curve, that is, for a photon. Light in a medium will travel along a world-line (time-like curve) so there's no difference between us and light as far as time goes.

[@Simon-fg8iz]

There is another counter-attack: how much time does an observer experience between photon emission and photon absorption, if he is tracing the same path as the light, travelling with a speed limiting to the speed of light? In that sense, you do get that the events (emission and absorption) happen basically immediately one after the other, leading to a loose statement that a photon doesn't experience any proper time. In "photon's frame", it is born and dies at the same time - by definition, because the space-time interval is 0 on a light-cone.

[@Mahesh_Shenoy]

That’s because, from that frame, the emission and absorption locations were infinitesimally close to each other. If my neighbors house is infinitesimally close to my own, the moment I step out of my house, I would have stepped into the neighbor’s almost instantly. That doesn’t mean I don’t experience time, right?

[@Simon-fg8iz]

@@Mahesh_Shenoy If you only exist while traveling from your house to your neighbour's house, and the threshold is infinitesimally narrow, you could say that you only exist for a single moment, not any finite interval of proper time during which you could experience anything. I'm thinking of neutrinos here, who do have "time" to oscillate during their flight. Again, of course, Einstein's argument holds that the limit c→∞ isn't strictly reasonable. p.s. Just keeping the back-and-forth discussion with Einstein here, the conclusion in the video is of course correct :)

[@ramankhatri]

Photon experienced time but unfortunately nothing happens in that time as the space outside is not changing. It's as if it went out of the universe and popped right back in just before annihilation.

[@lewis7515]

Isn't that just sophistry? You've just used different words to suggest the same thing as an imagined frame of reference that is travelling in equality to light.. The logical conclusion of SR is that there is no, "basically immediately, one after the other", by Light's terms - that is is fudge the conclusion for the convenience of human interpretation. The natural consequence must be that Light does _not_ perceived Time - because by Light's terms, there is no such thing as, "Time": and there is no such thing as, "Space". Those attributes only mean anything, to us and other entities of those dimensions... For Light, there is absolutely nothing. That is: Time and Space are emergent properties - dimensions in a Universe that Light, by nature, has no access to: because they and that Universe are, by nature, coiled up to zero and contracted out of existence. Every single thing, is beyond Lights event horizon - where Light, is it's own event horizon. That's why the question makes no sense - but to say that the question makes no sense isn't necessarily a mature or complete answer to be shared among adults. The simple answer is that no, Light doesn't experience Time. The expanded answer is that Light cannot experience Time l, even if it wanted to - because neither Time nor anything else actually exist on Light's side of Light's own event horizon. That is to say: if Light could communicate, it couldn't process a question on whether it experiences Time? It wouldn't - couldn't - even have any single idea, whatsoever, of what you were even talking about: "Time", and, "Space"?..... Utterly meaningless.

[@leonardopizzini1443]

@@lewis7515 i don't realy get this. Why shouldnt light experience time if we see time as the change happening to matter in space . it should in my opinion. Giving light a perspectiv as a human doesnt make sense to me but looking at it from the outside its clear that change is happenig while it moves so how could it be different from the inside perspektiv of light? is it just a hypothetikal question that doesent realy apply to the real world?

[@daniellindforsbernholm3682]

I think the more intriguing point with the "experience" of something moving "almost" at the speed of light is that it would experience ending up at any destination "almost" instantaneously. If it keep going without any destination it would experience ending up infinitely far into the future (whatever that means) "almost" instantaneously. If it could do this indefinitely it would for sure experience the clock ticking as usually. But that it would even have time to experience one tick of the clock before either smashing into something or getting to the end of times is not likely.

[@ariaden]

1. I think "light does not experience time" is a good description of "proper time for light is meaningless". 2. There is still an affine parameter along any light-like geodesic, but there is no way to fix its unit (as we have fixed the second for proper time). 3. When gravitational lensing happens, you can connect two events by a family of time-like curves approaching a light-like curve in limit. In that case, proper time measured along those curves goes to zero as the curves approach the light. 4. Existence of singularities is proven using light-like geodesics, so even without proper time, the light can experience "something". 5. Not to mention interference and various electromagnetic interactions light can participate in.

[@photelegy]

I always just thought about it like: If you're nearly at the speed of light (c) others would see your time go very, very slow. But for you in this reference frame your time goes "normal" but everything around you seems to be very, very fast. So if you would be at the speed of light for the others your time stands still (∞ slow) but for you everything around you would be ∞ fast. So for you the whole age of the universe would be over in 0 seconds. So you can't experience anything outside of your reference frame. And that's the problem that arises like you described the problem in another way.

[@wailer27]

That's not how it works as you're skipping relativity. You see the universe moving slowly too as it is also moving relative to you, therefore your clocks would agree. Only when you accelerate or spend time in a gravitational field will your clock slow down relative to everything else.

[@sgiri2012]

Mahesh sir please cover quantum mechanics stuff also......

[@Mahesh_Shenoy]

Yes, yes! On my ever growing backlog of videos.

[@nikolayastashkin4834]

1.Being at rest is the same as moving at a constant speed. 2. To "experience time" means to experience change. 3. Only an observer of change can experience change. 4. The changing things themselves do not experience any “time”, they simply “change.” 5. The concept of “time” refers only to the observer who is aware of himself.

[@GIRGHGH]

I thought this was gonna talk about how light oscillates and if something changes throughout it's existence it must have time or something.

[@manasyadav1993]

Awesome video Mahesh. I wish you pointed out that when an object approaches speed of light although it would experience proper time, if it eventually stops, its time would be behind the proper time for the non moving reference frame. That’s an important bit of info. Yes ?

[@Mahesh_Shenoy]

Not sure how it would be relevant. If folks don’t already know it, it’s not that easy to make sense of it without diving deeper into it. I think.

[@manasyadav1993]

Well you have the other awesome videos. So it makes sense that you didn’t specify it. There is nothing wrong with my understanding tough right?

[@classicalmechanic8914]

@@Mahesh_Shenoy According to relativity it is equally valid to claim photon is travelling at the speed of light or photon is stationary and everything else is travelling at speed of light relative to a photon. Photon's perspective exist but it is not included in special relativity. If photon's perspective is not important is like claiming it is not important what happens to photons at the event horizon of a black hole. General relativity breaks down at the event horizon the same way as special relativity breaks at the speed of light. Einstein's theories break down at the speed of light which results in infinities that show up in physics when you are doing something wrong.

[@kylelochlann5053]

It's not important as at no point are any clocks actually ticking slower. It is fundamental to relativity that all identical clocks tick away at the same rate, everywhere, and under all circumstances of motion and orientation. What you're alluding is that the integral over the accelerating clock's world-line is simply shorter (wrt the global coordinates) which is not meaningful here in any obvious way.

[@amaze2708]

Dumb question perhaps.. if an object is traveling close to C does it appear colder to a stationary observer? My thinking is if time slows for that object including all particle momentum, average kinetic would appear lower. And I suppose all stationary objects would appear colder to the moving object too?

[@Mahesh_Shenoy]

I think “colder” is a very lose word here. If you are specifically thinking about the temperature, then you will have to measure it in its rest frame, no? (I mean you need to stick a thermometer in there somewhere, and now the thermometer is in the rest frame of that object). But, the average thermal energy should slow down. So, that’s an interesting question. Let me add it to my list of topics to research more. Thanks for the question. It’s anything BUT DUMB.

[@a64738]

That is actually a very interesting question...

[@amaze2708]

@@Mahesh_Shenoy thank you for the reply. To expand on this.. remote observation of temperature is possible (we measure temperature of everything in space remotely). Also colder == more red shifted.. what if part of the red shift we observe from distant objects is because they are at relativistic speeds from our reference frame due to expansion? Obviously Doppler shift is still relevant. If we see their “clock” moving slower, we should also detect the temperature as lower; all time based events are affected, and temperature is time based. I just solved dark energy (Kidding).

[@user-ks8mb7uo4l]

​@@amaze2708 Well , Temperature is time based as it measures total kinetic energy of molecule and kinetic energy is dependent upon velocity which depends upon time and as time is relative , temperature is also relative . I am not a physicist but I think a way to measure temperature can be thermal radiation, as thermal radiation is electomagnetic radiation it's speed is not relative but it's total power should as no of photon emitted in some time is different for both of them

[@sophiasalleythedawnofsadie3313]

Does Time experience Light? is the question i get asked the most. Right behind Do you know what time it is? And How are you doing? Thank the good Lord i have the answer now.

[@AdritoMitra]

Sir another question why the speed of light is less in water if the speed of light is always same for all observer? Love your videos

[@AdritoMitra]

And also if the speed of light is less than the speed of light then Photons will have mass. As you said in that video.

[@Mahesh_Shenoy]

I think I should cover this in a separate video. Adding it to the list. Short answer is, it doens’t make sense to think of “speed of photons” inside a medium

[@AdritoMitra]

​@@Mahesh_ShenoySir it will be very helpful for me because I can't find the answer. Love you and your videos from West Bengal ❤❤❤

[@Farming-Technology]

​@@Mahesh_ShenoyI would look forward to that video. Some points of interest for me would be, is causality slowed in a medium? When you say vacuum do you just mean free from baryonic matter? Also how does the light accelerate¿ when entering vacuum from a medium? I don't know enough to ask the questions correctly but it is very interesting to me and the way you explain mathematics to us laypeople is some of the best I've seen.

[@wynq]

@@Mahesh_Shenoy I also look forward to this video. Can you also include in that video an explanation of what's going on in the experiment where Hau and Harris "stopped" light in a cloud of ultra-cold sodium atoms? I'm having trouble understanding how the photon wouldn't see its own velocity as 0 instead of c.

[@thedeemon]

When light goes from A to B, we can compute the spacetime interval and corresponding "proper time" - for a photon it will be zero and it will be a valid computation. This is enough to say that time doesn't tick for a photon, and thus it "doesn't experience time". And it's an idea with practical measurable consequences: particles moving at light speed must not change along the way, they must be "frozen in time". That's why we now think neutrinos must move a bit slower than light, as they do change during their travel.

[@kriiistofel]

Photons also change, their wavelength gets longer as they travel through spacetime

[@thedeemon]

@@kriiistofel Not in special relativity ;) In GR yes, but there the topic gets more nuanced.

[@kylelochlann5053]

No, the proper time for a photon is not zero - it's undefined.

[@kylelochlann5053]

@@kriiistofel No, it is impossible for a photon to change, or have any intrinsic frequency/wavelength.

[@kylelochlann5053]

@@thedeemon No, there is no distinction between SR and GR (SR is simply describes the ground state gravitational field).

[@effectingcause5484]

"There comes a point in every man, woman, and child's life that they wonder - Does light experience time?" See, that's the mindset of a great theoretical physicist..

[@stevenjones8575]

I have a rebuttal. To invent an idea that breaks rules does not necessarily mean all rules must be thrown out. A clear example: sqrt(-1) used to be thought of as a meaningless question that broke foundational rules, until certain mavericks said, "Let's do it anyway and see where it takes us!" They didn't have to reinvent all of math, they didn't have to get rid of "a negative times a negative equals a positive," they just invented a new abstract concept that turned out to not break math when implemented. A tweak to the rules (i.e. overturning the rule that there's no sqrt to a negative) was enough. Likewise, tweaking the postulate to say "all *sub-c* inertial reference frames" (it already has "inertial" as a qualifier, after all) allows for everything special relativity claims to remain the same (since it's already assuming all reference frames are sub-c), while allowing for mavericks to break the rules beyond the limits and see what happens. So I don't think you can really say (at least as it was presented here) that you can't tweak the postulate while retaining all its current predictions, just like the introduction of the seemingly-nonsensical *i* didn't undermine the math of real numbers in any way.

[@Rationalific]

Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up (like a Doppler effect with a sound pitch getting higher)? And could you say that as you get arbitrarily closer to the speed of light, the passing of time of objects in front of you gets arbitrarily closer to infinitely fast? Or am I off base here?

[@renedekker9806]

_"Could you say that the faster you are moving, that the objects approaching you from the front seem to have their time speeding up"_ - if you are asking about the light that you see from the objects that approach you, then that is fully correct, yes. That is mostly due to the Doppler shift of the light. If you asking about what you would conclude about the clocks of the others, then your conclusion would be that they tick slower than yours. That is due to the relativistic time dilation.

[@Rationalific]

@@renedekker9806 I see... Thanks for the reply!

[@user-ks8mb7uo4l]

​@@renedekker9806I think you are saying opposite , if we are moving near speed of light our clock tick slower than theirs and other object appear travelling faster as they are moving fast in time relative to us

[@renedekker9806]

@@user-ks8mb7uo4l _"if we are moving near speed of light our clock tick slower"_ - our clock never ticks slower or faster. It always ticks at the same rate. It's that rate that is called proper time. It is always our perception of OTHER clocks that appear to tick slower (or faster in some circumstances). _"other object appear travelling faster"_ - other objects always appear to travel at the speed that they travel relative to us.

[@user-ks8mb7uo4l]

@@renedekker9806 If time is relative how can we say that clock ticks at same rate ,proper time should not exist even if proper time exist , then it is different for everybody If we are moving with speed near speed of light then other thing at rest only does not appear moving faster in time they are actually faster, and in this situation clocks at rest will always tick faster than our clock (if both clock have same mechanism)

[@stephanevernede8107]

Light is a null vector of space time which mean that is proper time is always 0 . This is can be seen from the equation of proper time `dtau^2 = dt^2 - 1/c^2 dx^2' which is always 0 for a photon whatever is the reference frame. So saying that light as zero proper time is perfectly legit, and this in all reference frames.

[@kylelochlann5053]

Well... not exactly. The equation you should have is general flat-space metric: ds^2=-dt^2+dx^2. It is only in the special case of a time-like curve that ds^2=-dτ^2. The proper time along a null curve is not 0, it is undefined.

[@stephanevernede8107]

@@kylelochlann5053 Thanks for your comment. If I understand well your point, you agree that light is a null vector of space time and has 0 norm, but you point that this norm can not be called `proper time` but should only stick to `norm`. How is this more that a play on word ?

[@kylelochlann5053]

​@@stephanevernede8107 Given a spacetime curve, S, in arbitrary spacetime coordinates with tangent vector, U, the "norm" is then the inner product on the tangent space, g(U,U). This would have nothing to do per se with how the curve is parameterized. For a time-like curve, the norm is a constant, g(U,U)=1, we can use a clock to measure off the distance along any time-like curve (if measurement shows that all identical clocks tick at the same rate, everywhere in the universe, and under all circumstance of motion and orientation). A null curve has no spacetime length, so in what sense can a clock be used to define time as a parameter to measure length along a length-less curve?

[@zemm9003]

​@@stephanevernede8107 you are correct in your original argument. He is just writing word salads.

[@zemm9003]

​@@kylelochlann5053proper time is by definition the length of the spacetime interval measured in the rest frame. However due to Lorentz invariance this number is always the same regardless of the reference frame. So we can just choose a different one to perform the calculations. We can choose any so it doesn't matter. The photon will always travel with spacial velocity c which means that Δs = 0 for all reference frames and hence Δτ = 0.

[@grayaj23]

I think some of the confusion comes in trying to understand length contraction in this context. Traveling very close to the speed of light, you experience proper time, yes. But the distance between the start and end points would be much shorter and take less time than it would for an observer watching you or for a traveler going at non-relativistic speeds. That makes it sound like you'd experience "no time".

[@bartomiejbadura499]

You are absolutely right - that kind of question uses lots of words with imprecise meaning. What I found talking about light not experiencing time is a person I talk to has in mind is what other reference frames look like from a reference frame approaching speed of light.

[@taggartaa]

Can you constantly accelerate to closer to the speed of light such that, from an outside perspective, the light never reaches the top of the clock and ticks? I suspect from inside the vehicle, you would just see space continually contract such that you would arrive at any destination point before light had a chance to tick the clock.

[@rodschmidt8952]

I like this question. I think you are right

[@varsha_1703]

Mahesh I have a doubt ... Why pair annihilation doesn't takes place in mesons ? I surf the internet and found some answers..i know charged pi mesons don't annihilate because the quark and anti quark are different flavours but what about the neutral pi mesons? Some of them said annihilation is not a instantaneous process..we know that mesons are unstable so before annihilate..it's starts to decay into other subatomic particle...is that right explanation ? Which property differentiate the lambda -0 and Sigma -0 in elementary particle because both are made of up quark-1 down quark -1 and strange quark - 1 ? If anyone have the answer let's start discussion 😅😊

[@Mahesh_Shenoy]

I have no clue about this. List most stuff in my life! But adding it to a list of my research topics

[@Krokodil986]

I also asked myself this question, and, hopefully, i have a similar answer to what Einstein would have given. I phrased the question like this: If I approach the speed of light relative to the centre of mass of the Milky Way, I see the Milky Way's length along my direction of travel as approaching 0. So I should cross the Milky Way in a length of my proper time that approaches 0. But an external observer (who is at rest with the Milky Way's centre of mass) will see my velocity as approaching c, and hence my length will approach 0, while the galaxy's stays "normal". So the external observer would see me cross the galaxy in a long amount of time, nowhere near 0.000...01 seconds. So whats the solution to this paradox? After 0.00..01 seconds have i, or have i not, crossed the galaxy? Who's right - me or the external observer? The answer i could come up with is this- There is no shared definition of "right now" between me, and the external observer "B". So while my journey takes 0.00...1s in my time, it takes some years in B's time. B and I, however, are using different standards to measure the distance between two events - me setting off, and me crossing the galaxy. That's why we don't agree on the time between those events. As you can see, until now, the situation is perfectly symmetrical and both of us are equally "right". So we just don't agree on the time between two events. But thats ok, it happens all the time in special relativity. Also B would agree on the length of *my* time it would take me to cross the galaxy because he sees my clock as very slow, approaching not ticking at all. So he would agree that it takes me less than a second of *my* time for me to cross the galaxy. I think it's beautiful how this fits so nicely - i measure so little time due to velocity which manifests as length contraction, while B measures the same length of *my* time, again, due to velocity, but this time it manifests as time dilation. And the result is exactly the same in both measurements. Maybe this shows the deep similarities between space and time, and why one can't be without the other, why we speak about spacetime together, not separately. But what if i turned around and came back to B, and we compared our ages? This is called the twin paradox. To come back, I'd have to accelerate. Time, space and simultaneity are relative but acceleration is absolute. So the moment i accelerate towards B, i break the symmetry. Now both of us have traveled thru spacetime, between two events - me leaving and me coming back. However my path was more thru my space and less thru my time, B's was more thru B's time and not at all thru B's space. So B has aged more than me when we meet again. And this comparison is only valid if and when we do meet up, otherwise you can't ask both of us how old we are right "now" because there is no meaningful way to define a shared right "now" for both of us.

[@bobpower9189]

Supposing you were to introduce a third perspective into the twin paradox scenario. One in which a spaceship is always manoevred to be halfway between the two. Putting myself in this third perspective, I find it implausible that two people, always equidistant to myself, could be ageing at such dramatically different rates. Similarly, consider the graphics at 0:53 to depict time slowing down for a moving clock. The inverse would also be true, from the top clocks perspective, the lower clock would be ticking slower. Then consider a third perspective 'C' where the top clock 'A' travels west-east at the same speed that the lower clock 'B' travels east-west. A and B would see each other ticking slower. But C would calculate A to be ticking at the same rate as B. Logically, it would seem, this is truly a profound 'paradox' - or these presentations are a little muddleheaded.

[@Krokodil986]

​​@@bobpower9189 you are correct - the middle clock, C, will see both A (who is at rest with the Milky Way) and B (who is crossing the Milky Way) as aging both slower than C and at the same rate as each other, as they are moving away from C at equal but opposite velocities. As you pointed out near the bottom of your comment, this situation is 100% symmetric. *If A and B are in relative motion, A sees B slow and B sees A slow.* That is, until acceleration happens, or more specifically, until one of these observer assumes a distinct inertial frame, and abandons his initial inertial frame. Everyone would agree on who changed their inertial frame and he would be found to have aged less when all three observers meet up again. This is consistent with the time animation you provided a timestamp to. Try drawing out a spacetime diagram for this accelerating observer. Initially, in the first inertial state, the light bounces off between two lines parallel to the proper time. But when the proper time changes direction, the light suddenly starts bouncing off much less frequently than before. So when your three observers meet up again, we can assert that B accelerated the least (didn't accelerate at all), C accelerated a little bit (less than A) and A, who travelled at nearly c, accelerated the most. Hence A ages the least, C a bit more and B the most.

[@bobpower9189]

@@Krokodil986The effects of acceleration breaking time symmetry seem credible enough, but I could not imagine putting the 'pedal to the metal' for a duration of half an hour could result in years of age disparity, as is often presented. Presumably, different rates of acceleration yield different results. Also, have you ever come across any explanation whereby the effects of deceleration cancel, to any extent, the effects of acceleration. Just a thought - I've never come across it. How would this configure in a spacetime diagram.

[@Krokodil986]

@@bobpower9189 amazing question So rate of acceleration is how much you are accelerating per second, "jerk". The lower the jerk, the slower the change to the new inertial frame, but also the more time spent in acceleration. So I think it cancels out (to be honest I'm not too sure about this) Deceleration is the same as acceleration, but viewed from a different perspective. Imagine me walking along the street. I can start running. I think I'll be accelerating, right? Well someone who is already running will think I'm decelerating, because I'll be decreasing the relative velocity between me and that person. But for me I'm still accelerating - so the effects of acceleration and deceleration must be the same, time dilates. Put in other words, the direction of acceleration does not matter because the universe is fair - it treats all directions equally. In a spacetime diagram, deceleration may be shown as acceleration to the left instead of to the right. Directions are equal, the universe is fair so it doesn't matter. The only thing that may change is simultaneity lines may bunch up or spread out depending if you're accelerating toward or away from an observer onto his world line But the only meaning of this spreading or bunching is it changes from what point in time causal action propagating from this observer can reach you in your own "right now". I didn't explain this last point very well, if you don't get it I'll try to explain it better, let me know

[@Krokodil986]

@@bobpower9189 I've done some digging around... also let's define two velocities u and f let's say u -> c And f -> -c If you go from v = u to v = f, even if your change in velocity is instantaneous, ie delta t = 0, the age disparity will still approach infinity. In fact the quicker you get the acceleration part over, the quicker your two two inertial frames will reach their maximum difference. The quicker this happens, the longer they will be maximally different from each other. And the age disparity comes from this difference. So the longer the difference exists for, the larger the age disparity. So rate of acceleration does play a small part, but what's more important is the difference between the two inertial frames - ie the difference in initial and final velocity, rather than the time spend in transition.

[@rcatv7750]

This highlights an important distinction between pure mathematics and physics. Math is an excellent tool for describing the reality (maybe the best tool we have?) but still will never "be" reality itself. The hard part is knowing where the math diverges from the physics.

[@pacolibre5411]

There is a sense in which light does not experience time, because it is impossible to define “proper time” for light. Proper time measures the experience of time, so because light has no proper time, it does not experience time. You don’t need a light reference frame to come to this conclusion.

[@Nuovoswiss]

That asterisk "ignoring length contraction" is doing a lot of work here, since in "light's reference frame" the universe is 2-dimensional, and its velocity is zero in what we would call its direction of travel (because for a photon, that direction doesn't exist). But real photons don't travel in only one direction, they propagate with a probability cone. Might be some insightful math to be done there...

[@lewis7515]

How have you concluded with such certainty that Light's universe is 2-Dimensional?..... Light's velocity is zero in its, "direction of travel" - purely from our, practically-useful, perspective, of Light's perspective. However, surely, Light only has a, "direction of travel", at all, from our perspective, of Light's perspective? That is: isn't it the case that Light's, "travel", is only perceived? Light doesn't travel, it cannot - we call how it presents in our Dimensions, "travelling", because it's intuitive and helpful. Meanwhile, isn't it actually the case that Light only simply _propagates_ - from the point that it manifests? If that is the case, then Light must propagate, at the speed of Light. If that is so, then Light simply propagates, from wherever it manifests, in every Dimension, in every direction, equally - which is: at the speed of Light. Wouldn't that then mean that every direction and every Dimension: is zero? Isn't the conclusion, then, that while there is no, "direction of travel", from Lights perspective - the exact same terms apply to all other, "directions": that it could only move to, at the speed of Light....So, wouldn't there, equally, be, no, "Direction" - in any non-direction it could move to?.. Must it not then be the case that there are no, "Directions", whatsoever - and, by that token, no, "Dimensions", in any non-direction, for Light to not, "travel", to? Isn't it the ultimate conclusion that, for Light, there is no, "Direction", at all, that it could travel to at anything less than the speed of Light - meaning there is no, "Dimension", whatsoever, to not, "traverse": with the result that there is no, "Space"; no, "Time"; no, "Thing"; no, "Where" - and there was not, is not, and never could be... Would it not be that, for Light, _all_ is simply null - and moot?

[@polariss0i]

I like this explanation, however I think quantum physicists use light experiencing no time to mean that it has no ability to change its state. Like an electron can flip it's spin because it travels less than the speed of light, but a photon can't change its state. That's my limited understanding anyway.

[@that80sLoverboy]

I watch a lot of these types of videos, and you just make things so much easier to understand than pretty much any other channel or there.

[@Guido_XL]

Naturally, inside a reference frame, the speed of light remains c, regardless the reference frame's speed in relation to any other reference frame. The speed of light is actually the speed of causality. Inside any reference frame, it is constant. If we sit inside a space ship that travels very fast, approaching c, we still experience everything inside the space ship as normal. The issue is the relationship with other reference frames that are not traveling that fast. The imaginary photon that is bouncing up and down the cart, is indeed perceived as traveling at c inside that cart, constituting a reference frame. But, if we could somehow register that photon's movement from outside the cart, standing still, events inside the cart would seem to freeze. An imaginary particle that was moving at the speed of light inside the cart could not be perceived on one spot, moving laterally "up" and "down" with regard to the non-moving observer. That movement would be extended along the vector of the cart's trajectory. It's Special Relativity's space contraction that does the trick here. If the cart was moving very fast, approaching c, the imaginary particle at the speed of c inside the cart would actually not traverse the same distance anymore, as it would at a low speed. It's forced to traverse a much larger distance, as seen from the outside observer, whereas the inside observer in the cart still perceives the particle to move at c. This is exactly the core concept of Special Relativity. What an inside observer sees , while moving very fast, is not the same as what an outside observer sees, when standing still. So, light that travels through the Universe experiences space contraction so that all of Space becomes contracted into one point. Time dilation is stating the same mechanism here: to traverse a point does not take any time at all. A hypothetical space ship that approaches the speed of light is seeing the Universe as contracted into almost one point, a distance that takes almost no time to traverse. And that while inside the space ship, light still travels at the speed of c, without any contradiction.

[@kylebushnell2601]

We are the frame of reference- the observer? Every time I hear something is meaningless to ask regarding cosmology or physics, I realize it It’s probably one of the most meaningful questions you can actually ask.

[@theredstonehive]

I think the argument is that because all photons tend to have a finite life if we pretend the photon is a normal object with mass that is approaching the speed of light, its experienced lifespan (time between its creation and absorption) will approach 0. However a photon that flies away to infinity and never interacts with another object cannot be said to not experience time in the way most people mean.

[@adirmugrabi]

we can say that: from my reference frame, no time passes for light. and almost no time has passed for something moving close to C

[@_abdul]

Now that the "experience" part is ingeniously taken care of, Shall we move to the next innocent but tricky term i.e, "Time"?. What is it? is there any intuitive sense of this term? Is it universal or it's just an emergent phenomenon as a statistical byproduct of entropy? I thought I almost got it from the Arvin Ash's video on the topic but would really love to have it reimagined with your enthusiasm and care. Great work brother, I absolutely admire your explanations. ❤

[@karmakamra]

Ok, so just modify the question. Does light experience distance? It seems to me that if you have three spatial dimensions, and could move at the speed of light along one of them, that dimension would contract completely, and your experience would be that you were stationary in a 2 dimensional universe. And so what would happen if you could accelerate more, until you exceeded the speed of light? The dimension you are traveling along cannot contract any further. From your frame of reference, there is no direction of travel. And so you would have to accelerate in a different dimension. So lets say you do that, and now reach the speed of light in 2 dimensions. The universe, from your perspective, would now be one dimensional, and you would appear to be at rest within it. And so lets say you accelerated to the speed of light in the final dimension. Then you would perceive no dimensions. The universe would appear to you as a singularity.

[@LinkenCV]

The 2 king situation in chess is known. Indian GM (if I remember correctly) makes that move one time. Calling Referee by opponent and lose as a result:reason - illegal move.

[@tomasvanderlaan2375]

I think you are confused by what a frame of reference is in physics. A frame of reference is a set of coordinates to describe a velocities of objects in that frame. A key feature of an INERTIAL frame of reference (the one we use in physics, which you are describing) is the frame is not accelerating, which does not mean that the speed is zero (which is also a “loose” term as describing velocity in respect to something, like the ground or earth)

[@ToyyinnAuslander]

Exactly. At rest also extends to straight line, non-accelerated motion which is exactly how photons travel through the vacuum of Space. I think this explanation is inconsistent with the very foundational basis on which it claims to sit. In another video, he explains why everything at rest in the universe is moving through Time at the speed of light. Using that thought experiment, he goes on to agree that the faster one travels, the greater their displacement through Space and the less their displacement through Time, till, eventually, the particle in the thought experiment reaches c and employs all its speed in the spatial dimension with nothing left over for Time hence, objects travelling at c experience no time. This video appears to contradict that. 🤷🏾‍♂️

[@undercoveragent9889]

@@ToyyinnAuslander Yes, I agree. To be honest, I always had a problem with the proverbial 'light-clock' being used in these thought experiments. I never understood how it was possible for the path-length between the reflector and detector to be altered by the velocity of the clock as it travels through space. These experiments seem to assume that the motion of the clock provides some forward momentum to the photon being emitted and detected in the clock but doesn't that contradict the postulate that all observers experience the same 'c'? I mean, if the clock is traveling along the x-axis and the photon is emitted along the y-axis then the photon would travel along a path that is perpendicular to the direction along which the clock is traveling, right? The photon would have traveled in a straight line but the location of the detector would have changed during the time of the photon's journey. Also, one would assume that each photon can be detected only once but in the model used here, the photon is depicted as a wave travelling from the emitter to the reflector. The fact is, according to the postulate, when the clock is at rest, the experiment is set up so that the photon travels the path between the emitter, the reflector and the detector. When the clock is in motion however, we can see that 'at rest' is a 'special case' since from the photon's point of view, the positions of the clock-parts are arbitrary. As soon as we put the clock in motion, the photon is no longer traveling the path between emitter/reflector/detector; it travels from point 'a' on the y-axis to point 'b' on the y-axis and arrives back at point 'a' on the y-axis. Right? The photon _never_ deviates from the y-axis but the emitter of the photon does. It's not the photon traveling along a path that is 45° to the direction of travel, it's the emitter that has moved to a new position on the x-axis that is at a 45° angle with respect to the photon's position along the y-axis; the photon is 45° _behind_ the emitter. The length of the photon's journey however remains constant. In other words, if you had a photon emitter firing photons between two parallel plates, the top one is uniformly reflective and will reflect any photon back the way it came; the bottom one will detect and register any photon that interacts with any point on its surface and we can have the plates spaced at some arbitrarily small distance so that even at light-speed, no photons will be lost to the system. There is a tiny hole at the centre of the detector where the emitter injects photons between the plates. With a clock like this, no matter how fast you travel, the clock will tick at a rate that is proportional to the distance between the two plates and the speed of light, both of which remain constant in all frames. And even assuming that 'length contraction' is an actual thing, that would not change the rate at which the clock ticks either. One might argue that the length of the clock becomes so contracted that its displacement along the x-axis takes the reflector out of the space occupied by the photon which is never detected. In that case, the clock simply stops but until then, the rate at which it ticked remained constant. So yeah, these thought experiments make it appear that the velocity of the clock alters the path of the photon somehow but how, no-one ever explain that to me.

[@topexmystery]

I believe there's no term "wrong question" Questions and curiosity are diamonds

[@I_SuperHiro_I]

The cart just needs to unlock Ultra Instinct.

[@FelipeCantalic3]

When I look at a lamp, and close my eyes a little, I see some lines. What is that? Eyelash?

[@andymccracken4046]

I had always imagined that photons would think they are travelling at infinite speed and therefore always arrive instantly from their point of view.

[@AbhiramGSrivathsa]

I have a doubt (not on this topic) : WHY DOES RESISTANCE DECREASE WITH INCREASE IN AREA? it may be a silly question, but how? when we increase area, the atoms are also more right? then resistance must remain same

[@otaku-chan4888]

my intuitive (disclaimer: I'm not a physicist or electrician) answer to this is: most of matter _is free space._ With an increase in area (and hence increase in the region where matter exists to provide resistance) there are more atoms but a LOT more free space as well. You'll understand it easier this way: imagine there's a tube with the free area of an atom inside. If there's atoms inside the tube's hole, the hole is blocked- except for the bit of space between the nucleus and the electron orbits. (assume) 40% of the 'stuff' inside can provide resistance. Now imagine the space increases to have a free area of two atoms inside the tube. Sure, there's one more atom- but twice the amount of free space. 80% out of 200% provides resistance, but a whopping 120% of 200% doesn't. Percentage wise nothing much's changed, but there's a lot more room for the same probability of resistance to _not_ play out.

[@superman00001]

Hmmm… I think you switch from talking about one thing to talking about another. First thing: a clock moving RELATIVE TO YOU appears TO YOU to slow down. That DOES mean (which you do NOT acknowledge) that a clock moving RELATIVE TO YOU at the speed of light, appears RELATIVE TO YOU to stop completely. Second thing: For a clock moving at the speed of light RELATIVE TO YOU, anyone travelling WITH the clock will see it running at normal speed. So this switch (which you don’t acknowledge) makes this part of your video unclear. You go on to make the valid point that light itself cannot be said to have its own reference frame (ie a frame in which light is at rest) because Relativity states that light travels at the same non-zero velocity in ALL reference frames.

[@BabyHoolighan]

This was so much fun. I laughed all the way through. "That question is meaningless" but delightful!

[@johnstebbins6262]

Great show! I suppose that one could make the argument, that light doesn't experience time precisely because photons going at the speed of light don't experience reference frames, so they couldn't experience time either. The only way they could experience time in the first place would be through a reference frame.

[@skoobastories]

hi, should not the light appears to bend from the moving perspective just like what you said in case of the gravity?

[@Rising_Pho3nix_23]

TLDR at the end. So the relationship of the stationary clock is relative to its speed ratio to the moving clock. Your animation showed that as the moving clock moves at the speed of light, then the photon never moves. But when the moving clock travels at half the speed of light, half the movement is horizontal. So we can divide by half. Using this, we can refer to division and multiplication to see the solution in both reference frames, for this very rough analogy. If the moving clock moves at 90% the speed of light, the photon takes 9x as long, meaning that for every 9 tick of the stationary clock, there is 1 tick of the moving clock. We can see a direct linear comparison. Without going too far into the weeds, we know what I'm getting at. From the stationary observer, the moving clock's photon never moves. It's T = 0. Now, we look at it from the photon's reference frame. 1/0 = infinity. Remember that from the perspective of the photon inside the moving clock, the outside is speeding up as the moving clock speeds up. Therefore, when the moving clock reaches light speed, the photon inside of it experiences regular time locally, but externally it witnesses infinite time. If we look at the photon, we observe no time. It would take infinity seconds of our time to observe the photon experience 1 second. Or, to switch reference frames, it would take 1 second of the photon's time to observe infinity seconds of our time. TLDR; As the moving clock approaches light speed, we observe it slowing down and it observes us speeding up. Using this linear relationship, we can conclude that when the moving clock reaches light speed, we observe it have 0 ticks, and it observes us having infinity ticks. It will experience infinity big bangs and big rips.

[@ObiWanCannabi]

the funny thing about the 1 light year cube of space is you wouldnt know where that photon was until you observed it, you would have a general idea, sound familiar? the old uncertainty principal is just that, you have no idea where something is until its information transmits to the receiver, we need to either poke something or have it poke us.. you wouldnt see it until its light propagated out, so that photon would appear dark.. Like you have 3 things, that 1 light year cube of empty space, a photon and the ability control time, place the photon in the box and stand outside the box, for all observers its dark, no one can see it but its there, you wont see it for up to half a year until its energy ripples its way to you, but hit play on the remote and space unifies to spacetime, the photon disappears from its source, sends its information onto space and it ripples away in the dimension of time. You wont know if its worked for up to half a year as an outside observer, and inside you would just see a flash of light as it passes by you, but it goes in every direction at the same speed unless it is influenced by something else, another kind of energy field, and in an "empty" box there is nothing other than space for it to ripple time with its remnant the photon died the moment it transmitted its energy, it never moves and it never really hits the source with anything other than a ripple in spacetime which our eyes process as light, so yeah what we see is actually just a burp in space as time sends it flying our way, the spacetime excites our eyes into processing an image, but its all just illusions of the past, everything we see and touch based on that limited perspective, even typing now im not feeling the keys, im feeling the electromagnetic fields of energy push my fields away, things arent solid they have energy barriers and fields holding things together on the smallest of scales When i look at something that i consider yellow, its actually rejecting that colour, to it, it would say it is every colour but yellow. Our perspective and understanding of things makes it really hard to see the big picture, but its all fields, a field of space wrapped up with time and packets of energy in stable or non stable forms, everything is just trying its best to exist for as long as it can and transmit its information into the void. Hoping something hears it

[@huytruonguic]

that segway to the sponsor segment is crazyyyyy good 😂 anyways, I have a question, if the speed of light is the speed of causality is the speed of time, shouldn't light be time?

[@daubert4892]

In fact, in the Lorentzian interpretation of special relativity this question does make sense, and the answer is no, light does not experience time. One can argue that for this reason no massless particle can decay.

[@randomarsh9817]

Your channel is incredible. I really cant wait to see you at 1 million subscribers. I have little doubt.

[@puffin88]

Okay, but I can say that from the perspective of someone traveling very close to the speed of light, it takes almost no time to travel even the hugest of spatial distances, right?

[@godfreypigott]

From the perspective of that person, those huge distances are tiny.

[@billt3922]

Love watching floatHead Physics! Your enthusiasm is infectious and I will be showing my teen daughter your videos to help her intuition of physics. Thanks, Mahesh!

[@nHans]

Or, as we say in mathematics: You can't divide by zero, but you can take the limit as the denominator approaches zero. At v = c, you're literally dividing by 0 to get quantities like γ, length contraction, time dilation etc. So those quantities are no longer well-defined. This is where the next genius wonders what happens if one were to allow division by zero, and thereby revolutionizes math as we know it.

[@DABmonger]

Anything travelling at the speed of light blows up the equations of relativity, but I'm with the physicists that say that light/photons does not experience time. But then does that mean that singularities exist, as they also blow up the equations?! One thing that can be agreed upon: infinities tell us that we're missing something major in our understanding of physics/nature.

[@aliptera]

I reached the same conclusion following this thought experiment: consider a massless observer, accelerating along a beam of light. Since it is massless, it can accelerate to C. Now what does it observe? As it accelerates, the speed increases, and it sees the beam of light redshifting. From the observer perspective, the beam of light loses energy. When he reaches C, the beam of light he was following practically lost all of its energy and is not detectable, ceases to exist. A photon does not exist from it's own perspective, nothing exists from the photon perspective. A photon that traveled since the big bang,13.8 billion years, traveled 13.8 billion light-years. Form the photon perspective that is meaningless, he has travelled 0 attoseconds, 0 attometers. Maybe here is the next physics breakthrough, since this does not make sense from the quantum perspective as well.

[@michaelwhalan9783]

If time is only a perception then it is in the eyes of the beholder.

[@youztuber5000]

I'm loving your vids, currently binge watching, thanks!

[@frankmcclusky7870]

Fascinating, so even if time is massively dilated (compared to our standard day-to-day reference frame) the experience of it is the same. It's interesting that time can subjectively pass quickly or slowly in a cognitive sense when the physics itself is rigid.

[@Sol-En]

It is possible that the photon has an incredibly small mass and is moving incredibly close to the maximum speed in the universe

[@kylelochlann5053]

Sure, though this would no bearing on relativity.

[@catastrophe3049]

Bhai re addict ho jata hu teri video ka Mat banaya kar aisi itni badhiya video Subah 5 baje teri video ko play kar diya dekhna nhi tha bas yuhi save karne ka irada tha Ab nahane nhi ja paa rha. Teri wajah se school jane me late ho jaunga😢 BTW I am physics teacher Feynman lecture ki book kharid ke rakhi thi padhne ka time nikalana bhul gya tha Ab tu aisi aisi chije lata hai to padhna padga😅

[@Mahesh_Shenoy]

Ab bas bi Karo bhai. Rulayega kya?

[@danielcopeland3544]

OK, fine. I can't help noticing the animations all say "length contraction ignored". So let's talk length contraction. Suppose we have three objects: P, Q, and R. P and Q are at rest with respect to each other, while R is moving with respect to both. P and Q can be road signs and R can be a car, or something. In P and Q's reference frame, they are some distance d apart. Due to length contraction, in R's reference frame they are some smaller distance d*k apart, where 0 < k < 1. As the speed of R with respect to P and Q approaches c, the factor k approaches what number? In R's reference frame, after P has gone past, it takes some time t for Q to reach it (since in R's reference frame it is P and Q that are moving). What happens to the time t as R's speed with respect to P and Q approaches c?

[@danielcopeland3544]

@silverrahul Then isn't that a meaningful way of framing the question?

[@danielcopeland3544]

@silverrahul ...the question in the title of the video? "Does light experience time?"

[@danielcopeland3544]

@silverrahul The thought experiment I started this comment thread with. Did you watch the video? Mohesh says that "does light experience time?" isn't a meaningful question, because it can't be framed in a way that has an answer within the laws of special relativity. I'm querying that.

[@danielcopeland3544]

@silverrahul Calculating what happens as one _approaches_ an unreachable limit, as a proxy for what happens _at_ that limit, is a routinely used and uncontroversial method in calculus. Mahesh himself discusses it in this very video (9:39--11:48).

[@danielcopeland3544]

@silverrahul I know that an object with mass cannot reach c. If you were concerned that I didn't understand that, you can rest easy. Thought experiments, in physics just as in mathematics and philosophy, reach out into the impossible, if only to understand _why_ it is impossible. We wouldn't say to Einstein "But you can't accelerate a train to half the speed of light, you'll kill all the passengers." We can turn my question around, if you like. Let's suppose again that we have objects P and Q, stationary with respect to each other, and object R, moving at speed v with respect to P and Q. P and Q are a distance d apart in their own reference frame, and a shorter distance d*k apart in R's reference frame due to length contraction. Let's ask now: what would v have to be to make k = 0? Now, is there any _other_ value of k that would yield the answer v = c? (There are certainly other impossible values of k. k can't be negative, or >1, or an imaginary or complex number. If you plugged _those_ values into the equation and solved for v, what answers would you get? Not c. v = c is associated with k = 0 and only 0.)

[@ytt8370]

Nice content! The moving clock ticking slower points directly to the twins paradox which has one of the hardest wikipedia pages I've ever seen lol

[@paulromsky9527]

Ok, there is no rest state for light. But if light could see a tick of its clock, that means it has to travel an infinite distance just to get off (one Plank length) of one of the mirrors. So light does experience time, but only as one Plank time no matter how far it goes: to the next Plank distance away or across the entire universe. To light, each distance was zero and thus instantaneous (or really just one Plank time) to its perspective. As you travel toward the speed of light, space seems to shrink ahead you and you get to your destination faster (by your clock) than you had planned. This has to do with time dilation and the Lorenz contraction. So if you travel at 99% of the speed of light to, say, the nearest star (4 light years away) you would get there in only about 3 years because of these effects. So, if you were to somehow travel AT the speed of light (mass can't) the space in front of you would shrink to zero and you get there instantly. It's the same for a photon, it still moves at the speed of light from its own inertial frame, but space is compressed before it and it too takes zero time to get to that same star... or ANY point in the universe... and "beyond".

[@jesusredondo513]

A video about inertial frames would be of great aid to understand Einsteins's postulates

[@Clock_Tune]

Q1 If a object is travelling at 0.9999999......c will it travel at speed of light because 0.999999.......=1??? Q2 In entanglement information can travel faster than light, doesn't it break causlity

[@NickUSHOR]

You should make an episode explaining a spaceship's point of view when accelerating towards the speed of light. Many people seem to not know that the ship can travel billions of lightyears in a matter of a few years of ship time.

[@logtothebase2]

I think sometimes because of the journey you experience getting to the right place it is worth starting in the wrong one.

[@vwcanter]

I keep running into this debate. It seems to me that the common sense meaning of a frame coincident with light would a frame coincident with one particular crest or one particular trough of the wave. A frame where the phase does not change. In such a frame, if it can be said to exist, the speed of propagation would still be c. But the phase would not change, and so it would simply look like a static field that varies in space. In other words, to light, light is a static field. Changes to the field would still propagate at c. But the field would not be changing with time. So there is no contradiction. The same phenomenon occurs in a frame just a tiny bit slower than c. The field appears almost static, because the radiation is red shifted almost to a static field. But changes would still propagate at c. The other argument I always hear is the the gamma factor of the Lorentz transform is mathematically undefined for a frame with a velocity of c. That's true mathematically. But math is a human tool, apart from nature. It is not the case that when human math stops working, natures must also stop working. There are plenty of other examples of natural phenomena that are obviously real, even though human effort to describe them with mathematics come up short. And last, assumes that Lorentz transform has to work for light, when it doesn't. There might be some reciprocal transform that is sensible for a light-like observer. And the massive stationary observer might not be able to make any sensible use of it. Curious what you think.

[@SaanMigwell]

Light is what defines the various frames, that's why It doesn't have it's own frame. Light does experience time, it just experiences it as distance. That's how I always made sense of it anyways.

[@vwcanter]

I keep running into the debate. It seems to me that the common sense meaning of a frame coincident with light would a frame coincident with one particular crest or one particular trough of the wave. A frame where the phase does not change. In such a frame, if it can be said to exist, the speed of propagation would still be c. But the phase would not change, and so it would simply look like a static field that varies in space. In other words, to light, light is a static field. Changes to the field would still propagate at c. But the field would not be changing with time. So there is no contradiction. The same phenomenon occurs in a frame just a tiny bit slower than c. The field appears almost static, because the radiation is red shifted almost to a static field. But changes would still propagate at c. The other argument I always hear is the the gamma factor of the Lorentz transform is mathematically undefined for a frame with a velocity of c. That's true mathematically. But math is a human tool, apart from nature. It is not the case that when human math stops working, natures must also stop working. There are plenty of other examples of natural phenomena that are obviously real, even though human effort to describe them with mathematics come up short. And last, assumes that Lorentz transform has to work for light, when it doesn't. There might be some reciprocal transform that is sensible for a light-like observer. And the massive stationary observer might not be able to make any sensible use of it. Curious what you think.

[@LucretiusDraco]

An amazing video I keep saved in my watch later playlist on you tube is called “Frames of Reference” it’s from the 50s or around there lol it’s in black n white. It explains this concept as well. It blows my mind every time I watch it! Thanx. This video was spot on at explaining this concept

[@asmodiasmobilemoba]

Man, my physics teacher is going to LOVE these videos. Thanks for explaining all of these things so well!!

[@BurningSandsOfTheLowLands]

Photons are created with the amount of time of their existence already built it, relative to the wattage of the source it was released from. As the photon travels through space, it releases/sheds mini photons in all directions in a varying amount in respect to the resistance from the already existing light or darkness in the infinite or inclosed environment that surrounds it.

[@dankellis1]

In light's reference frame, the entire universe is a singularity because of length contraction. So light always travels at the speed of light for zero distance and arrives at its destination before zero time passes.

[@godfreypigott]

That is one interpretation. Another is that in its own reference frame light is everywhere along its path at the same time.

[@mementomori7160]

One thing I disagree, when the cart moves almost with the speed of light, it will experience almost no time. Why? Not because it'll feel time different, but because of length contraction, the whole univers will get squished into a flat disk into the direction the cart is moving, so it will reach its destination and get destroyed(for photons, absorbed), so it's path will be approach 0, making the time needed to travel it also approach 0. So it does experience time normally, but it experiences 0 time because it's destination as well as any point on it's way are all in the same spot

[@Kaunkalakarindia_]

Dude these topics are so interesting . This type of analysis and critical thinking should be tought in schools . I am a 10th grade student ( like just passed 10th ) , the schools are just reducing syllabus so children dont gent stress but due to this our society , and country will face stress after some years. But i am here accepting you as my teacher to gain knowledge and pass it to others for benefitting my society and country .

[@zepkid5678]

I like to think of it in terms of definitions. In special relativity, time is defined by measuring how “fast” light travels. When a car moving at 90% speed of light relative to the ground sends out a light beam, to an observer on the ground, either the light beam is traveling at 1.90c (wrong) relative to the ground or the light beam is traveling c relative to the ground and the relative time is dilated and relative length is contracted (as well as simultaneity differences for the two observers). Both observers say “I must use c as my basis for time since it is actually the speed of causality / electric field changes etc” Thus we see why it makes no sense. How does a perturbation in electric field “experience” itself? It’s like asking a gust of wind how it feels to hit itself.. if electric field perturbations are how we measure rate of causality - eg how many times an block of radium decays in a period depends on rate of electric field flow C - then we can’t ask how does electric field disturbance measures itself. How many electric field disturbances did the electric field disturbance feel? Going in the same direction. It just doesn’t make sense. An electric field ripple in a direction can’t experience other electric field ripples in the same direction. It can’t measure time because it is how time is defined

[@arnavbandi-wq8qb]

Man you are the best. The concept best thing is that you use intuition for everything. Thanks man , helped me clear my curiosity

[@alexanderdede6354]

First, why are you so good at incorporating your sponsors in your videos? You're simply too good. Secondly, I totally agree with correcting people's understanding about certain subjects and misconceptions. Though, I would totally commend them for thinking about these things and being curious. I also can understand others telling others "click bait" concepts. I feel it is to get then intrigued and interested to learn more. Promoting education, critical thinking and scientific literacy is definitely a great thing to do.😊

[@Yaaalala]

I needed this channel for so long and didn’t even know 😱 Finally instead of just knowing the right answer I can understand what is going on. TY so much, great work! 👍🏻👍🏻👍🏻

[@deebznutz100]

Objects may not be able to move through space faster than the speed of light but they can interact or enter each other reference frames at or beyond that