Why The Speed Of Light* Can't Be Measured

31 okt 2020
2 903 673 Áhorf

Physics students learn the speed of light, c, is the same for all inertial observers but no one has ever actually measured it in one direction. Thanks to Kiwico for sponsoring this video. For 50% off your first month of any crate, go to kiwico.com/veritasium50
Huge thanks to Destin from Smarter Every Day for always being open and willing to engage in new ideas. If you haven't subscribed already, what are you waiting for: ve42.co/SED
For an overview of the one-way speed of light check out the wiki page: ve42.co/wiki1way
The script was written in consultation with subject matter experts:
Prof. Geraint Lewis, University of Sydney ve42.co/gfl
Prof. Emeritus Allen Janis, University of Pittsburgh
Prof. Clifford M. Will, University of Florida ve42.co/cmw
The stuff that's correct is theirs. Any errors are mine.
Einstein, A. (1905). On the electrodynamics of moving bodies. Annalen der physik, 17(10), 891-921.
(English) ve42.co/E1905 (German) ve42.co/G1905
Greaves, E. D., Rodríguez, A. M., & Ruiz-Camacho, J. (2009). A one-way speed of light experiment. American Journal of Physics, 77(10), 894-896. ve42.co/Greaves09
Response to Greaves et al. paper - arxiv.org/abs/0911.3616
Finkelstein, J. (2009). One-way speed of light?. arXiv, arXiv-0911.
The Philosophy of Space and Time - Reichenbach, H. (2012). Courier Corporation.
Anderson, R., Vetharaniam, I., & Stedman, G. E. (1998). Conventionality of synchronisation, gauge dependence and test theories of relativity. Physics reports, 295(3-4), 93-180. ve42.co/Anderson98
A review article about simultaneity - Janis, Allen, "Conventionality of Simultaneity", The Stanford Encyclopedia of Philosophy (Fall 2018 Edition), Edward N. Zalta (ed.) ve42.co/janis
Will, C. M. (1992). Clock synchronization and isotropy of the one-way speed of light. Physical Review D, 45(2), 403. ve42.co/Will92
Zhang, Y. Z. (1995). Test theories of special relativity. General Relativity and Gravitation, 27(5), 475-493. ve42.co/Zhang95
Mansouri, R., & Sexl, R. U. (1977). A test theory of special relativity: I. Simultaneity and clock synchronization. General relativity and Gravitation, 8(7), 497-513. ve42.co/Sexl
Research and writing by Derek Muller and Petr Lebedev
Animations by Ivàn Tello
VFX, music, and space animations by Jonny Hyman
Filmed by Raquel Nuno
Special thanks for reviewing earlier drafts of this video to:
Dominic Walliman, Domain of Science: ve42.co/DoS
Henry Reich, Minutephysics: ve42.co/MP
My Patreon supporters
Additional music from epidemicsound.com "Observations 2"

  • But, if c was extremely different depending on the direction, when seeing on different directions you could see infinitely more stars, and the observable universe would be infinite on one side.

    Lautaro LorenzaniLautaro Lorenzani3 mínútum síðan
  • can clocks be synced by two entangled particles?

    aleks parkaleks park8 mínútum síðan
  • "Filming the Speed of Light at 10 Trillion FPS" On youtube

    SizzleSizzle13 mínútum síðan
  • Subtitulos en español por favor!

    joseph Vicenjoseph Vicen18 mínútum síðan
  • *Noob question* : Let's say in future we can make quantum entangled clocks, could we measure light by this? *Another noob question* : Is there any way to measure light by observing black holes? *Last noob question* : Is there any possible way of computationally analyzing the speed of light in the foreseeable future?

    Salt ServiceSalt Service44 mínútum síðan
  • So relativity cancels out therefore showing light to be c no matter which direction or what speed your experiment is travelling at, or what gravitational field is affecting it because the only accurate measurement is only by 2 directions??. I know proponents state we can never reach the edge of the universe. But I think we can if you consider general relativity in the same context as en.wikipedia.org/wiki/Ant_on_a_rubber_rope

    Brett de Courcy HarrisBrett de Courcy Harris48 mínútum síðan
  • so lets say im on earth, and light is infinitely fast from mars to me. then lets say there was an asteroid or something to block part of the light coming from mars, if i saw the light come from mars and hit the asteroid at the same time from where i am on earth, then light is infinitely fast, however if i see it come from mars then shortly thereafter come from the asteroid then its not infinity fast? Wish i could explain better

    VaomondVaomondKlukkustund síðan
  • What about mechanically synchronizing a light emitter's clock and a reciever's clock? What's the issue there? I mean, other than needing a very precise clock. Wouldn't it be possible then? Consider the device being like 1m in lenght for example

    Agus RuibiAgus RuibiKlukkustund síðan
  • 🤔🧐🌌.

    Simón ValeroSimón ValeroKlukkustund síðan
  • Stupid video. Makes too many assumptions

    chicagocubs10601chicagocubs106012 klukkustundum síðan
  • Darkness is faster than light and that’s how you measure light one way...and you are right our current limitations are the key to link relativity and quantum mechanics.

    A GCA GC2 klukkustundum síðan
  • but wouldn't that negate the redshift in one direction?, unless the difference is small enough to not disturb too much to be noticed, and of course we have to make some assumptions, we can;t empirically be certain that tomorrow's speed of light will be the same as the one now, but we have to assume it, maybe laws of physics are different in other galaxies so what we conclude from our observations are skewed. We can also measure at the same tame the 2-way and the 1-way with two clocks, just with that we can discard that the difference from 1 way to the other can't be too big (not more than the error in sicronization)

    mz2281694mz22816942 klukkustundum síðan
  • If this is true, how do you explain this: 'The world's fastest camera shoots 10 trillion frames a second and is able to film the movement of light.' A ISpast Video is in the link below to this topic. I really would like to hear your oppinion on this. Btw I really like your channel, keep up the amazing work. Much love from Germany. ispast.info/losk/v-deo/a4qpj6-vrYOpiIo.html

    DiverhazeDiverhaze2 klukkustundum síðan
  • if light travels at different speeds in different directions that would mean the universe has some sort of universal direction system. (north south east west). if this was true, theoretically you could create a space compass which pointed in certain directions in accordance to the directions of light

    Grant ShermanGrant Sherman3 klukkustundum síðan
    • and what if the mars example was used so that when mars was in the opposite direction of earth, the two time differences were measured

      Grant ShermanGrant Sherman3 klukkustundum síðan
  • Could be possible to use the quantum entanglement in two particles in order to start two cloks separate from each other? Thus we wouldn't have to include a ray of light that generates conflicts with the measurement just like it is said in this video.

    Pavel Balboa FalcónPavel Balboa Falcón3 klukkustundum síðan
  • I have an idea, a possible solution with two clocks. Since I'm Spanish, I'm not sure if it's the proper word. But, what if we sincronise both clocks usin tho particles that are quantum interlaced (in case that's the right word)? If I understood it well, the information exchange between two interlaced particles is instantaneous. Then, all we need is the technology, in case we still haven't (honestly, I don't know). Am I wrong?

    RazielRaziel3 klukkustundum síðan
  • Michelson proved speed of light is same in all directions using interferometer

    Amarinder SinghAmarinder Singh3 klukkustundum síðan
  • Your example about the round trip message to mars is just not possible

    ReTNReTN4 klukkustundum síðan
  • ............

    YASER BUCHTAYASER BUCHTA4 klukkustundum síðan

    YASER BUCHTAYASER BUCHTA4 klukkustundum síðan
  • I have a question, although this might get lost in the comments. If we had the hipothetical case where c=infinity in one direction, wouldn't that mean that we shouldn't be able to observe psst phrnomena like Cosmic Microwave Background in one way? Since we would only be able to see the universe as it is today. Maybe I'm just confused but I appreciate some constructive criticism ♡ we are all here to learn

    MarcosMarcos4 klukkustundum síðan
  • loved this video. Broke my brain as well. It broke my brain further when I tried to throw in the notion that light speed is the speed of causality.

    Marcelo AguiarMarcelo Aguiar4 klukkustundum síðan
  • Súbelo a tu canal en español

    Paul Alberto Felix MartinezPaul Alberto Felix Martinez4 klukkustundum síðan
  • Subtitulos en español, please 👍

    Jose VJose V4 klukkustundum síðan
  • And why two toothed wheels would not solve the problem? This may have not been done yet but seems feasible to me.

    ChikeChike4 klukkustundum síðan
  • If the universe has a spherical or toroidal shape... or any shape that is closed on itself... let's wait for the ray of light to come back from the other side. It would just take a lot, a lot, a lot of patience

    Nicolas AntonelliNicolas Antonelli4 klukkustundum síðan
  • Light is instantaneous in the preferred direction? AWESOME, now I can see forever if I get a telescope and just look in that direction. Nothing will ever be out of view even if the universe is expanding faster than light.....INSTANTANEOUS is much much much faster than the speed of light. So which way do I look?😳

    Mark BurchMark Burch4 klukkustundum síðan
  • The direction is relative. So it is always forward direction. One direction is always future and not physical direction. So it make sense that light speed is constant.

    Pratik RathodPratik Rathod4 klukkustundum síðan
  • If one could measure the speed of light in one direction it will always be measured at C. Since both the starting point and end point are moving at the same speed. No one has ever measured the speed of light differently (different directions), we can assume light has a infinite speed though space only the observed speed in constant. The Doppler effect only measures the speed the starting point and end point are moving in relationship to themselves not the speed of light.

    jim sjim s5 klukkustundum síðan
  • Ok, let's think about this idea using time on mars an earth as an example. Rather than measuring the speed of light, let's just take pictures of mars at regular intervals as it rotates around the sun. Now, if light travels infinity fast 'in one direction' (honestly I'm not sure what direction in this context means, but anyway) and half the speed in the other, wouldn't we experience mars accelerating at a radically different speeds at weird times? Let's refer to the point in mars' orbit where light travels towards earth at an infinite speed as the 'c apogee' and the point where light travels at half speed as the 'c perigee'. Now, as mars orbits the sun from c perigee to c apogee, we should see mars speeding up in it's orbit. This is because at c perigee we would snap our picture of mars, but it would appear to us as behind it's true position in space time. As it moves closer towards c apogee, we begin to see mars in it's true current position. Likewise, as it moves from c apogee to c perigee it would appear to us that mars is slowing down as the true location of the planet would be ahead of where it appears. This of cours is assuming mars has a constant speed as it orbits the sun. Throw in the suns' gravitational pull and we're going to see some crazy moments of acceleration and deceleration at unpredictable times depending on our position relative to mars and it's position relative to the sun. This is just my thought... I'm curious where I'm wrong in my thinking as I'm sure there are much more intelligent people out there who have pondered this to death.

    Brett BalsamBrett Balsam5 klukkustundum síðan
  • If you started recording once the light hit the measuring device and stop when it reaches the end of this 1m stretch then the time it takes the light to go between the tube and the device is irrelevant. We have measured it! this is just philosophical pseudoscience

    Scott WallScott Wall5 klukkustundum síðan
  • Video tip : will you hear a more low pitched sound when an external speaker sends off a sound when ur in a car travelling away from the source?

    Azri HamdanAzri Hamdan6 klukkustundum síðan
  • How about using some quarks? I think Quantum physics could solve this

    Youssef OUARSEYoussef OUARSE6 klukkustundum síðan
  • Hey its Vsauce Micheal here....

    cuttyFLamm CRcuttyFLamm CR6 klukkustundum síðan
  • Might this give succour to Creationism trying to answer the objection to the age of star light? Is it possible to have the bias of speed in radial coordinates? Light leaving the origin (earth) travels at C/2 but arrives at the origin instantly.

    Paul DeCampPaul DeCamp7 klukkustundum síðan
    • how old was adam instantly after creation as he was created adult ?

      HbmdHbmd3 klukkustundum síðan
  • You can do one thing: In a horizontal vacuum tube one side with monochromatic light ray and on the other fluorescent gel or sensor to trigger the time the ray hit, time sync SOLVED*

    Shubham Raj ShristyShubham Raj Shristy8 klukkustundum síðan
  • What if we have a device that has 3 modules a light sensor, reflector and an emitter. The device emits light when the sensor is triggered, and we measured exactly how long it takes for the device to emit light when the sensor is triggered (device delay), we set that device a known distance and shine a light to trigger the sensor and reflector, we measure the time it takes for the light to travel to the device and pounce back to us from the reflector (2c) and the time it takes for the light emitted from the device to reach us while taking the device delay into consideration.

    Nour AlmustafaNour Almustafa8 klukkustundum síðan
  • I thought the particle accelerator was essentially measuring the speed of light?

    Syko RoseSyko Rose9 klukkustundum síðan
    • @Boodysaspie the very essence of matter has no mass according to science. More psuedo science by the guys that brought you the globe apparently.

      Syko RoseSyko Rose2 klukkustundum síðan
    • The velocity of the particles is limited by the fact that it's impossible to reach the speed of light (if you have mass). Particles in the LHC travel at 99.999999% of the speed of light, and if the speed of light varied then so would the speed of the particles.

      BoodysaspieBoodysaspie2 klukkustundum síðan
  • The "Speed of light" is the maximum speed information can travel, like a fundamental speed limit as a result of inherent internal energy. The idea that directionality plays a role here is just a futile practically impaired deduction of theory. But if you do what to verify this; maybe quatum entanglement might help.

    Jurrian Tjeenk WillinkJurrian Tjeenk Willink9 klukkustundum síðan
  • @Veritasium, if the clocks are mechanically synchronized. I mean, create a couple super long rods that will precisely start the timers?

    Allain MagyarAllain Magyar9 klukkustundum síðan
  • ...Synchronise your clocks in parallel with a host controller and equivalet length wire runs (regardless of the actuall amount of wire needed). After the synchronization signal is recieved, fire the laser. It's that easy. You don't even really need the first clock. You could actually just have the second clock recieve logic high to start the timer and have the other circuit element just be the laser. If the wire runs are the same, the clock will start the timer when the laser fires minus the time it takes to excite the laser, which can be measure and controlled for. If one was to argue that the signal may propogate at different speed then we could just at easily use a two 500 meter rods that are actuated by the same mechanism. So yes it is possible to do, I'm just surprised no one ever asked an indstrial engineer how they'd do this. Also, once you do this then you just measure the speed of both ways along each axis. The average between the measurements on axis will be the speed of light, and, because C is constant reletive to space itself and emmiter is moving in space, the 6-axis information will contain the information necessary to determine the absolute velicity of emmitter in space relative to space itself. Also, the flight time of light is absolutely different bi-directionally. Think about it, sniper have to think about it, the planet moves. If you fire a laser in the direction of rotation of the earth at a target, that tharget is moving away and down relative to the original flight path of the laser beam, it'll hit the target be relfected and then fly back at a target that is moving up and towards relative to the original flight path of the laser. Plus the sun is moving really fast through space, the earth is cirlcing on top of that, and god knows how fast galaxy is moving.

    Alex DesiletsAlex Desilets9 klukkustundum síðan
  • Interesting. But ez (ish) to solve. Entagle a bunch of particles. Send one half to some other place, keep your half with you. Shoot a laser from you to the other half. Now all you need to do is detect when the partickles get unentangeled.

    MrNeopoldMrNeopold10 klukkustundum síðan
  • Half of the research was done by albert einstein, we dont have anyone like him now. 💨

    ASIF KHANASIF KHAN10 klukkustundum síðan
  • So we can't directly measure C What about indirect observation?

    snowraider8snowraider810 klukkustundum síðan
  • This guy replicates the first ever experiment measuring the speed of light that Derek mentions. Highly recommend the video: ispast.info/losk/v-deo/jX6Faau52Z-7l4I.html

    Kathvard overherKathvard overher11 klukkustundum síðan
  • Why not put 2 timers 1 where the laser will start and the second timer with a sensor to stop time when hit with light. Why not make 1 button, when you hit the button the timers and laser will start when the laser/light hit the sensor of the second timer the timer will stop

    scenaz nathanscenaz nathan11 klukkustundum síðan
  • Someone just go and play the reverse UNO card on Albert Einstein grave it's time to come back buddy !!!!

    PiNeAppLe PiZZaPiNeAppLe PiZZa11 klukkustundum síðan
  • The fascinating implications are in special relativity. We often hear that the speed of light is the same in all frames of reference, it is actually true but for the two-way speed of light. A moving frame doesn’t look isotropic for me, regarding light circulating in it, however the two-way speed of light is the same.

    W0tchW0tch11 klukkustundum síðan
  • How about if we use clocks that sync' by quantum entanglement

    meng eekmeng eek12 klukkustundum síðan
  • We have measured the one-way speed of light. It can be done watching the moons orbit other planets. In fact, this was how we discovered that light had a speed in the first place (not instantaneous). The moons of Jupiter appear to lead and lag in their expected orbits exactly as required by the change in distance between the planets as we orbit. You can absolutely determine a one-way speed of light from that information. If there was a preferred direction in space the orbit of moons would apparently advance/retard not solely by a function of our distance, but also by a function of the relative angles. That is not observed. Additionally, I would love to see how a right angle interferometer could still work the same if a preferred direction in space existed. That would be some fancy cancellations. Your friends at LIGO might be able to help.

    Scott HurstScott Hurst12 klukkustundum síðan
  • what to do with the fundamental constants? since the 2-way speed can be calculated from those.

    ibiam10ibiam1013 klukkustundum síðan
  • Why do u say that speed of light is different in different directions??? Nothing will confirmed it. (Your speed is the same in different directions, so a photon's speed is the same in different directions)

    Adam NAdam N13 klukkustundum síðan
  • Interesting. Make a video on Ehrenfest paradox too!

    Ken TurtleKen Turtle13 klukkustundum síðan
  • Why don't we redefine 'metre' or 'second' or both such that speed of light in free space is 3 ×10^8 metre/second ? It will be easy for a lot of calculations.

    Raghavendran T BRaghavendran T B13 klukkustundum síðan
    • Because we want 'metre' and 'second' to be so close to the previous definitions of 'metre' and 'second', that the change in definition changes almost nothing at all in practice. We _could_ decide to suddenly change the definitions so that the speed of light in a vacuum is exactly 3×10⁸ m/s, but then we would either have to change all our rulers (every 1m would have to be 0.7 mm shorter), or all our clocks (every day would be 59.8 seconds shorter), or both. 0.7 mm on a metre might be pretty much negligible in everyday use, but for industrial/manufacturing purposes it matters a lot. All kinds of standards would have to be recalculated and redefined.

      RaizinRaizin45 mínútum síðan
  • you can see a universe in a mirror.

    Vimalakirti LotusVimalakirti Lotus13 klukkustundum síðan
  • What if you move two clocks appart of eachother at the same speed with a 45 degree angle ? That way you move them in a similar direction so the delta speed of light wont be that different ?

    Achdf BeatsAchdf Beats13 klukkustundum síðan
  • It seems like the speed of light can't possibly be instantaneous in one direction, because there would be no cosmic microwave background when we look in that direction. Everything we'd see in that direction would be the present, and the CMBR would have passed us by, leaving a blank patch in the CMB. If the speed of light is *finitely* faster in one direction than another, I don't think that would have a visible effect on the CMB? But I'm not sure, it's hard to visualise.

    D. TysenD. Tysen14 klukkustundum síðan
  • Can't you build a very long physical body and let it press down the buttons of the clocks and the beam of light? The delay would be same on all devices, wouldn't it?

    vivhiddvivhidd14 klukkustundum síðan
  • If you REALLY think about it the whole thing falls apart. If gravity can propagate instantly in one direction, but at the speed of light in the other direction, then wouldn't the pull of gravity cancel out expansion, since it would be unbalanced? Light isn't the only thing that travels at the speed of light.

    Josh MellonJosh Mellon14 klukkustundum síðan
  • Lovely video. Wasn’t this the issue questioned in the concept of the luminiferous ether? Also wouldn’t asymmetrical light speed have consequences for the redshift caused by expansion? Would love to know.

    Dan JonesDan Jones14 klukkustundum síðan
  • If the speed of light would be constant sending it from object moving fast would make it faster than the constant related to the surroundings, right? Let's think of sending the light to the two opposite directions on earths surface. Other against the rotation of the earth and other to the same direction. The source of light sent to the same direction is already at the speed of the earths surface rotating would it be that plus the speed of light. Or the opposite? Ofcourse the earth is already moving in the space at some direction! How does the speed of the light aource affect the speed of light?

    JonesgabeJonesgabe14 klukkustundum síðan
  • Hey guys, did you know Earth is the only place in the universe that you can look out and see everything as it is right now, but everywhere else has to abide by the speed of light? Lol I think a good place to start would be to find evidence that would lead one to believe that the speed of light WOULD be different in another direction. I would say that since police radar guns are equally effective in all directions that we could already say there is none. We can see the sun the same way all around it, and we detect gravitational waves from all directions as well. I think this notion ignores that we are MOVING through space, so if there WAS a bias in one direction it would "appear" to change; that is it would behave differently because we aren't always facing the same direction. I think there are even contradictions elsewhere. We would see particle jets that would instantly traverse the universe in one direction (just because we can't measure it doesn't mean it's effects wouldn't be observable), but obey physics in another.

    Josh MellonJosh Mellon14 klukkustundum síðan
  • When I said this in 2018 people laughed at me. Defining a meter in this way makes the speed of light invariant, even if the "distance" it travels in a second is variable.

    zane scheeperszane scheepers15 klukkustundum síðan
  • Hi. Why didn’t you mentioned how it would behave if you do several two-ways experiment in different directions (like in the 6 directions?)

    Gaetan SemetGaetan Semet16 klukkustundum síðan
  • Why cant you take two entangled particles separate them have a clock on the emitter end then have the receiver end change the state of the entangled particle once the light is received and then take the time difference from the state change on the particle?

    Matt LozoyaMatt Lozoya16 klukkustundum síðan
  • Does that mean that the assumption that the universe is expanding are based on a premis that may or may not be true? If that is true, then my mind is blown!

    Glenn IboiGlenn Iboi16 klukkustundum síðan
  • Send 2 clocks in opposing direction, thy both slow down, and just send a pulse at a given moment and than compaire when it was measured and check the clocks after the experiment. If needed, use a mirror so it travels 3 times and and try it in the other direction too. So one time it is 2 times to the right and once to the left and the other time it is 2 times to the left and 1 time to the right

    Kevin MichalikKevin Michalik17 klukkustundum síðan
  • Subscribed to and liked to look back at each other to support each other👍😍. सदस्यता ली और एक दूसरे का समर्थन करने के लिए एक दूसरे पर वापस देखने के लिए पसंद 👍😍 । 已订阅+点赞望望回访互相支持👍😍. 購読+いいね訪問は、お互いをサポートし、👍😍。 購読+ポイントの「いいね! は、この問題を👍😍。 Souscrit et aimait regarder en arrière les uns les autres pour soutenir les uns les autres👍😍. 구독 + 좋아요를 눌러 서로를 지원하기 위해 다시 방문 👍😍😂 👍 . Подписались и любили оглядываться друг на друга, чтобы поддержать друг друга👍😍.

    Just Funny VideosJust Funny Videos18 klukkustundum síðan
  • You have your 2 clocks 1 KM one east one west from each other, both displays facing south. From exactly between the 2 clock but 1KM south you have 2 very long lens telescopes, one on each clock. You can verify that the 2 clocks are synced that way. Boom, solved :)

    ElectricAfroManElectricAfroMan18 klukkustundum síðan
  • What if you had two pairs of quantum entangled particles. You send them to each location. At one location you do something to your particle from the first pair to indicate time started and then send a radio message. When the receiving party gets the message they change the second Quantum entangled pair to show it was recieved

    AJ SnarrAJ Snarr18 klukkustundum síðan
  • Put the clocks in the dead middle of the observatory.then take them to both ends at the same speed. Thus the time on the clocks may be THE SAME. Then you might measure ONE WAY TRAVEL...

    Watch It!Watch It!19 klukkustundum síðan
  • Okay so start with 2 synchronized clocks in the middle have them both move at a set speed to a set distance. If the clocks are diffrent then speed of light changes based on direction. It only confirms that it varies and not the actual speed but based on that experiment it can be compounded into an actual study.

    Clash of GamezClash of Gamez20 klukkustundum síðan
  • so if we actually cant measure the speed of light then all the other measurements we made must be inaccurate coz we dont know if the thing we saw, was at that very moment or it was late coz we dont know what speed the light has in different directions

    Merril BaijuMerril Baiju20 klukkustundum síðan
  • This Einstein guy seems to be a genius boy

    Shashwat JoshiShashwat Joshi20 klukkustundum síðan
  • Michelson - Morley Experiment .

    Abhijeet kumarAbhijeet kumar20 klukkustundum síðan
    • Exactly. If the speed of light is same in round trip can't we figure out speed of light in one direction from that.

      Abhijeet kumarAbhijeet kumar20 klukkustundum síðan
    • Proves the round-trip speed of light is the same in different orientations. Says nothing about the one-way speed of light

      VeritasiumVeritasium20 klukkustundum síðan
  • The real answer is develop light speed travel and have someone make the trip, if it takes 2x as long to get there and when they turn around they get home instantly, then it'll be proven that the one way speed of light is instant

    HeyBra2.5HeyBra2.521 klukkustund síðan
  • hold on... what? why would light move differently depending on the direction its traveling. sounds like a paradoxical statement; that somehow light gains more energy on its return than what it started with. the mirror experiment is fundamentally accurate, for C=(d1+d2/2)t, where d1=d2...? I think. you know you could synchronize timer if there was a median. rather, a separate third activator that starts both timers and activates the laser simultaneously. that way you're only measuring one distance rather than two. It's merely a hypothesis. I think mathematically the inclusion of a third party activator will cancel out, as it sends electricity in both directions.

    Prof. DemosdownProf. Demosdown21 klukkustund síðan
  • Can't you measure the one-way speed of light using gravitational redshifting? That doesn't depend on clocks.

    RJ HannaRJ Hanna21 klukkustund síðan
  • Can a light create a delay ? if we are to capture the light in the camera ?? or it’s just the camera is slow ?

    Imperial MomentsImperial Moments22 klukkustundum síðan
  • 13:45 If they knew that it took the man on mars 10 minutes to receive the message, if they sent it at 12.20 the man would have replied at 12.30 earth time, proving einstein’s theory?

    Aka RheligAka Rhelig22 klukkustundum síðan
    • If they actually tried this ^?

      Aka RheligAka Rhelig22 klukkustundum síðan
  • i still dont get it can someone explain to me why we dont have 1 km long stick and push it down from the center of it to the buttons(2 buttons connected to the each of the clocks with the same length cables) which will start the clocks for starting 2 clocks at the same time??????

    ulrike elibelindeulrike elibelinde22 klukkustundum síðan
    • @Veritasium thank you and im probably missing a giant point but it makes me restless, we start the clocks long before we turn on the light, straight hard stick which two end of it will start the clocks, we push the stick from exact middle and the stick simultaneously goes down at every point? So two ends of it will go down and start the clocks at the same time? Why couldnt we get synced clocks this way before we turn on the light? Then we turn on the light source and the clocks are going to stop when they see the light?

      ulrike elibelindeulrike elibelinde8 klukkustundum síðan
    • The push on the stick travels at best at the speed of sound to the other end of the stick

      VeritasiumVeritasium22 klukkustundum síðan
  • What if you were to use light detectors to start the timers??

    Patryk DziewitPatryk Dziewit23 klukkustundum síðan
  • Why you are changing thumbnail??

    Alone GamerzAlone Gamerz23 klukkustundum síðan
  • This is really cool. But wouldn't the idea of the speed of light changing based on direction simple to throw out considering the earth spins, the earth rotates around the sun, the solar system rotates around the galaxy, and the galaxy is moving in the Universe. Look towards the moon today is not the same direction tomorrow. So couldn't you start the experiment with two clocks in the center, slowly move them apart, stop halfway, then when you know the universal direction has changed move them the rest of the way to cancel the any effect, then perform your experiment?

    James BaileyJames BaileyDegi Síðan síðan
  • very interesting, physics can drive people crazy

    anywhere fromanywhere fromDegi Síðan síðan
  • What if you sent a spaceship towards mars or the moon and every minute earth sent a signal to mars/the moon and the space ship intercepted it and let it continue on its path to mars/moon then once the spaceship landed it went back to the earth and repeated the same experiment and altogether the earth, ship, and mars compared data points.

    CookieCrumbles222CookieCrumbles222Degi Síðan síðan
  • What about cameras that can film the speed of light? I recall the slow-mo guys doing a video on one, couldn't you just place two objects and see when each is hit with that. You would have the issue of the light traveling back to the camera, but the two objects should get hit at predictable intervals. Is this a viable method?

    CookieCrumbles222CookieCrumbles222Degi Síðan síðan
  • Could we use quantum entanglement to synchronize the clocks? I know it can't be used for sending messages since we can't change the state without breaking the entanglement, but if we wait for a natural change of the sort that would affect the entangled counterpart, then shouldn't both clocks detect a change at exactly the same time, allowing perfect synchronization?

    ArgenteusArgenteusDegi Síðan síðan
  • We know light can speed up matter right? So what if we just didn't measure the light itself but rather something that we know the speed of? What if we created a vacuum and shot a atom through it in both directions. And we measured the speed it took. Stay with me: not bounce back, but 2 separate experiments. Now we have the speed of an atom. Now we fire the atom again and with a delay shoot the light beam. The atom will now arrive at a different time at the other side. So if we know how much the light will speed up the atom, we can calculate the exact time, at which the light hit the atom. Now we could just take that calculated time, substract the delay and boom we have the one way speed of light. This is just a dumb theory I put together at 00:30 o'clock. What's your opinion?

    RotogasRotogasDegi Síðan síðan
    • This video is breaking my brain, well done

      RotogasRotogasDegi Síðan síðan
  • Seems fine to me

    Max KordonMax KordonDegi Síðan síðan
  • you could you quantum entangled particle to trigger the sync of the clocks, because they act in the same time with no time diffrence at any arbitrary distance

    Melodic Guitar Rock/Metal GuiltyGearRockYouMelodic Guitar Rock/Metal GuiltyGearRockYouDegi Síðan síðan
  • Simple solution...Just get a 1KM long stick to turn on the laser on the other side ...

  • "To move the clocks slowly won't help because of " reason>".. No no no.. the problem with trying to the affect the effects of time-dilation by slowing down how fast you move the objects is NOT what you said.. the problem is that even if you "slow down" the movement.. and because of this, reduce the "effects" of the dilation..... The TOTAL effect of the time-dilation is of course how MUCH something travels faster or slower.. AND!!... for how long time that difference is. (Oh; And just to say.. You seem to overlook the option of using a "bad" method of synchronizing the watches that by it's very nature can be CALCULATED how bad it is.. INSTEAD of using something that uses the speed of light to synchronize the watches... you can use sound.. no one have found any directional problem with sound.. but; It also has some flaws.. that are well known.. and we can use maths to compensate.. not ENTIRELY sure if the "corrections" that we would do would somehow relate to whether the bidirectional speed of light IS "constant"... )

    Roger LundströmRoger LundströmDegi Síðan síðan
    • I really should learn to watch an entire video before I answer.. Because.. I just realized that one of the MOST obvious ways to think of light as.. not randomly fluctuating (or being different).. is.. (besides of course occham's razor; MOST things don't care what direction, they just care about forces.. why should light be different?)...... is to ACTUALLY look at the stars... The thing is; The visible field of stars relates to the speed of light.. the stars that is the furtherst away; Their light just barely got time to hit us.. and as time goes on, we can see galaxies even further away.. but more importantly.. it doesn't matter WHICH direction we look from earth; The stars that is the FURTHEST away.. are still in their infancy.. so.. if we saw light from them in an "instance".. then we should see them as they are right now, but the "light" that hits us is the light when those galaxies were still in their infancy... Not a "deductive" logic styled proof (I would prefer that), but.. inductive logic ALSO has it's merits, when "final and conclusive absolutes" can't be reached.. it's just MUCH more likely that light travels at the same speed.. To keep ones mind open is always good.. and.. To imagine a world where the actual direction a light travels would affect it's speed... well.. a fun place to visit, but I doubt there are any good arguments (at least not yet) to move in and live there..

      Roger LundströmRoger LundströmDegi Síðan síðan
  • Maybe instead of getting the clocks in the centre to synchronise, maybe it would require a different medium that doesn't depend on the speed of light? Like, I don't know, a piece of uranium, that you then "break in two" and measure the atomic decay at the centre, and then again at the two clock locations? So that the atomic decay allows for the clocks to be set? Most likely I'm just talking rubbish lol

    big-eye101big-eye101Degi Síðan síðan
  • What would a black hole look like?

    TNB1TNB1Degi Síðan síðan
  • wouldnt the galaxies have tones of red in one direction of the galaxy and be somewhat more normal in the other? saying this since they are quickly mooving away from us and stuff

    Markus VdtMarkus VdtDegi Síðan síðan
  • First u have to measure if the speed of light in both directions is the same. This can be done by two clocks ⏰ 🕰 . The clocks dont need to be synchronised because the time difference is in both measurements the same. So if the speed of light is different in one direction then you know you will never be able to measure the speed of light in one direction. And if both measurements have the same results then c can be measured with one clock ⏰ and a mirror!

    Ano NiemAno NiemDegi Síðan síðan
  • Can't we measure the distance between sun and earth and the time taken for light to reach earth and then divide them to get the value of c?? 🤔🤔

    GrApHiC ErAGrApHiC ErADegi Síðan síðan
    • artificial puzzle.

      yasio boloyasio boloDegi Síðan síðan
  • 4:06 "... or have they?" I was actually expecting Micheal from VSauce to appear... :(

    Adil MhaiskerAdil MhaiskerDegi Síðan síðan
    • made using astronomy, by observing the eclipses of Jupiter's moons (Olaf Roemer in 1676) and the aberrations of the stars (James Bradley in 1728). Both measurements w

      yasio boloyasio boloDegi Síðan síðan
  • what if the man on mars sends a message with current time saying that I am messaging at 12.30. The people on earth will receive this message instantaneously according to your theory at 12.10. So, now they will know that the speed of light varies with direction, won't they?

    sujupravinsujupravinDegi Síðan síðan