Why The Speed Of Light* Can't Be Measured

31 okt 2020
2 886 818 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"

  • IMHO This is elementary! To find out that the speed of light is equal in both directions (not to calculate it), you do not need to synchronize the timers, it is enough that they have sufficient stability and the ability to measure short intervals of the required accuracy. C (a-b) = (Tb - Ta + d) / L - where d is the discrepancy between the timers (can be negative) Substituting the known value of the speed of light (C), we find d: d = C * L - Tb + Ta We measure in the opposite direction and calculate C (b-a), substituting the found value of the error d. C (b-a) = (Ta - Tb -d) / L If C (a-b) = C (b-a) coincide then the speeds in both directions are equal. PS do not forget that the first measurements of the speed of light were 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 were "unidirectional", which may also indicate the equal speed of light in all directions. PPS The alleged paradox proposed by the author of the video is nothing more than a funny artificial puzzle.

    P060TP060T5 mínútum síðan
  • At first I wanted to propose to hook clock directly to the photon, launch this system towards a wall, and than go to destination to look an banged clock, but looks like it will also have no effect, because the time for any distance in this instance must be exactly zero. :)

    Roman SovetskikhRoman Sovetskikh30 mínútum síðan
  • Woudn't redifining the question to i'is the speed of light the same in both directions' make finding a solution easier? You woundn't have to go at lightspeed to test it out.

    Josh NievJosh Niev34 mínútum síðan
  • Hello. check this out: "isworlds.info/item/nLqslN-DqYWrhIg/v-deo" - The Slow Mo Guys/ About Speed of Light/

    Andrew DiatkoAndrew Diatko35 mínútum síðan
  • Veritasium this in theory can be verified on the photon shere around a blackhole. I just can't seem to think of a way to get there in tact. Maybe an insight to a solution here.

    Alejandro DirksenAlejandro Dirksen46 mínútum síðan
    • Wait, It is theoretically possible for matter to physically stay at a photon sphere with the right thrust and the right density gradient for this hypothetical rocket containing the laser and clock. It would require a complete redesign but I wouod have to investigate this further. And as you mentioned in your previous video, the photon sphere is the sphere at wich light traveled straight but looped back on to itself. Its the space that curved and not the light so in theory this should a one direction speed of light.

      Alejandro DirksenAlejandro Dirksen39 mínútum síðan
  • Maybe using one device that times and stops at the arrival of a light beam AND and object that emits a beam of light exactly every minute. Just place the object emitting the light at exactly 300 meters and then calculate the time it took to travel the distance between the object emitting the light and the one detecting it's arrival...

    Tony RodTony RodKlukkustund síðan
  • Can’t you shoot a light into a black hole to measure one way? According to physics nothing can escape a black hole. Not even light. Just a thought

    OpticsOpticsKlukkustund síðan
  • legend...

    PINGPINGKlukkustund síðan
  • Then we need to develop a quantum clock in order to be able to synch them on the dot.

    Tony RodTony RodKlukkustund síðan
  • What if you can slow the speed of light during the round-trip? Researchers from the University of Glasgow and Heriot-Watt University were able to create a device to slow speed of photon permanently. Depending on where you put the device on the round trip, and knowing by how much the device slows the light you'll be able to prove if the speed is the same in both directions. Once you measured one round trip, reverse the experiment and if the time is the same it means the speed is the same in all directions.

    Fennec NeeFennec Nee2 klukkustundum síðan
  • so, goku's instant transmission could be a reality. as long as we make sure we are transmitting in the direction in which light travels instantaneously.

    Why BotherWhy Bother2 klukkustundum síðan
  • I don't understand, it seems the hypothesis that light travels at different speeds in different directions is dependent upon 3D orientation. Can't you just run the reflection experiment many times over many different orientations in 3D space and see if that changes the clocked speed?

    Michael CallahanMichael Callahan2 klukkustundum síðan
  • One idea...keep one clock stopped and the other running

    Kim Kardashian UnKim Kardashian Un2 klukkustundum síðan
  • 2 timers at one end of a vacuum tube and 2 timers at the other end all set at zero. With a mirror at each end for the 2 way check. 1 timer at each end to measure one way speed and one at each end to measure 2 way speed. These timers along with 4 pulses of light will be triggered by plungers that are mechanically connected and calibrated to hit the start buttons at the exact same time when a plunger is physically engaged. This will remove time dilation from the equation. Send 1 pulse for one way measurement and 1 pulse for 2 way measurement from each end and if the 1 way pulses are timed at 50% of the two way pulses then you will know the one way speed of light. If the percentage is different then 50%, a little bit of simple math will tell you the difference in one way and two way speeds. I'm not a physicist but that's how i would approach the problem as an engineer.

    james williamsjames williams2 klukkustundum síðan
    • Objects don't move instantly when you push them and since that ultimately comes down to electromagnetic forces between the particles of the material, I highly doubt that you could eliminate c as a factor with your plungers.

      LünkelLünkel2 klukkustundum síðan
  • In curved spacetime: along some geodesics light will get back to us and yet technically go straight all the way.

    preme plugpreme plug2 klukkustundum síðan
  • By the way, we know from handling the rovers in Mars that this hypothesis is incorrect!!. Why is this being debated????

    Marco PereiraMarco Pereira2 klukkustundum síðan
    • 1. No, you can't just turn the setup 180% and run it again, you would always expect the exact same result. You're just testing the 2-way speed again. 2. Did you watch the video? He specifically used communication with a target on mars as an example.

      LünkelLünkel2 klukkustundum síðan
  • In the Martian example, isn't his message a one way light signal, and the message from Earth also one way? Also, stars away from us are sending that light one way. I understand the round trip analogy when using a mirror, but not in the case of the messages back and forth between Mars and Earth.

    Byron BatzByron Batz3 klukkustundum síðan
  • This is a trivial hypothesis to test. Just change the direction of the measurement to check for anisotropy.

    Marco PereiraMarco Pereira3 klukkustundum síðan
  • How about measuring the difference of the time it takes for light to travel between two points via different paths? Like different images of the same supernova through gravitational lensing? That difference, together with the difference in distance should give a single-trip speed.

    Frank RoosFrank Roos3 klukkustundum síðan
  • If we assume that the speed of light is c/2 in one direction and instantaneous in the other direction , then the schwarzschild radii of all objects in the "instantaneous " direction should be zero ... In effect , in one direction , we shouldn't be seeing any black holes .... Just a very weird hypothesis

    Manas AbhyankarManas Abhyankar3 klukkustundum síðan
  • Great information, Great Thinker 😊

    Problem SolverProblem Solver3 klukkustundum síðan
  • So long as no physics theory/concept/phenomenon is based on knowing the one way speed of light, we cannot measure it but nothing is affected by it either. The moment a theory/... like this does exist, we can use it to test whether or not the speed is the same in each direction. Personal opinion: the Michelson-Morley experiment shows no difference in directions perpendicular to each other, so there is no reason to think there would be a difference in directions parallel to each other, right?

    Sibe BleuzéSibe Bleuzé3 klukkustundum síðan
  • It is not about Einstein, it is about Maxwell and Hertz. Light moves with the speed c because it is an electromagnetic wave and that speed follows from the ratio between frequency and wavelength.

    Tomas PetterssonTomas Pettersson3 klukkustundum síðan
  • ɥɔnɯ os ǝlʇᴉʇ ǝɥʇ puɐ lᴉɐuqɯnʇ ǝɥʇ puɐ oǝpᴉʌ ǝɥʇ ƃuᴉƃuɐɥɔ noʎ ǝɹɐ ʎɥʍ

    Daniel MarchionattiDaniel Marchionatti3 klukkustundum síðan
  • 4:05 so someone has measured the speed of light. Or have they? He gone Vsauce.

    Jakub PiekarskiJakub Piekarski3 klukkustundum síðan
  • What if we start both clocks at exactly 12:00?

    Áron PanykoÁron Panyko3 klukkustundum síðan
  • Try out my türkish pizza recipe. Its easy to follow step by step... see it for yourselves.

    SOFRAMSOFRAM4 klukkustundum síðan
  • Why do you even need two clocks in the first place? Can't you simply connect the clock, the light transmitter and the light receptor physically; by running them on the same 'driveshaft' or whatnot? The clock and the transmitter starts at the same time and when the receptor receives light, it brakes the driveshaft to a halt, making everything stop instantly and simultaneously. Everything would be synced and there wouldn't be any need for sending a signal from the receiver back to the clock. Am I missing something?

    CarlCarl4 klukkustundum síðan
  • This might sound stupid But, let's say we tune two clocks together. Then, because space is expanding, then the two clocks will move away from each other, without gaining or losing or gaining any time (since they are not accelerating and just moving away due to increasing space between then due to expansion of space). Then when they spread far enough, we can shoot a beam of light and measure it's speed. Mabye its completely stupid or mabye this is a good idea. Please like so Derek can see this.

    Sanjog GuptaSanjog Gupta4 klukkustundum síðan
  • What if you put a laser on a spinning rod at the top. Vertical rod, horizontal spinning laser. You put a cylinder with a light sensitive inside and move it over de light source and rod. If light travels at the same speed in all directions you should see a perfect symmetrical spiral.

    Lime-NetworksLime-Networks4 klukkustundum síðan
  • But if the measurement is performed in a sufficiently isolated environment, there should be nothing there to define direction.

    Chocolate BunniesChocolate Bunnies5 klukkustundum síðan
  • "Clickbait" whats that? Anyone...... please ?

    abijithr quoraabijithr quora5 klukkustundum síðan
  • Light is fast ok....it's just fast, that's the answer...

    random dude teeheerandom dude teehee5 klukkustundum síðan
  • 10:05 Mechanical linkage with extreme tolerances.

    Nix Ryu The SergalNix Ryu The Sergal5 klukkustundum síðan
  • What about, sending a message to mars, the data package takes so many seconds to send, if the return was instant (im assuming its not like throwing ball off a moving platform, or is it?) Wouldnt you receive the package at different rates? Say mars is on the outer side (the way our solar system is traviling) data sent from mars, data colected on earth, then do it again on the behind side (on the end of our solar system relevetive to our travil) if one side is instant couldnt you tell by the time it took to recover the data?

    Matthew HartMatthew Hart6 klukkustundum síðan
    • Being the data transfer rate/receving being a different way mesuring cuz (from my understanding) frequency travils at the speed of light

      Matthew HartMatthew Hart6 klukkustundum síðan
  • Can't you synchronise two clocks, wait for the universe to expand a little (no acceleration involved) and then shoot the laser between the clocks? I.e. use the expansion of the universe to separate the clocks instead of accelerating one of them from the other.

    averas80averas806 klukkustundum síðan
  • How about measuring in rotating room...you got it ryt!?

    Mohammed RoshanMohammed Roshan7 klukkustundum síðan
  • If the speed of light changes with direction shouldn't the observable universe have another shape than spherical? Because the light could have traveled a greater distance depending on the direction we are looking. We might not know that the light traveled further but we should see more galaxies on one side than the other at least if the difference is substantial, right?.

    h4z4rd1000h4z4rd10008 klukkustundum síðan
  • If the speed of light wasnt constant gps would not work. But it does which leads me to think speed of light is constant in all directions.

    Ibaad FarooqiIbaad Farooqi9 klukkustundum síðan
  • It's been a long time without you my friend.

    AZZEDINE USMANAZZEDINE USMAN9 klukkustundum síðan
  • Plot twist: It's not the speed of light that is 10 seconds slow, its just the universe lagging from all our fancy machines

    Howie Still GamezHowie Still Gamez9 klukkustundum síðan
  • What if you turned the clock on with a string? Couldn't you pull it at one end, and it would instantly turn on at the other end? Even if it is not instant, you could calculate how long it takes to pull.

    Mark MalyshevMark Malyshev9 klukkustundum síðan
  • is anybody a kid here (if u arre is your he confuse?)

    Nevan Sanders SantosoNevan Sanders Santoso10 klukkustundum síðan
  • Wouldn't the appearance of stars in different directions appear to have a different average age?

    InAVanByTheRivrInAVanByTheRivr10 klukkustundum síðan
  • If space time is flexible, then can an object be at two places at the same time?

    Stephen BossStephen Boss10 klukkustundum síðan
  • What if you calculate the acceleration of light in a object? Light can push light weight objects in a vacuum so why don't you calculate how much time does it take this object to achieve a constant speed, so now you have a sort of measuring speed in which light its pushing this object, wouldn't this be by extrapolating the speed of the light moving the object?

    fergardglfergardgl11 klukkustundum síðan
    • how do you time that exactly?

      ERROR_AnythingERROR_Anything10 klukkustundum síðan
  • Can't you send something else alongside the laser, something that we know the speed, and compare the delay they arive?

    Igor HenriqueIgor Henrique11 klukkustundum síðan
  • Instead of observing the light what if you just absorb the light as it traveled?

    TheImmoralCookieTheImmoralCookie11 klukkustundum síðan
  • To start the timers at the same time, you need a very long stick, the ends of which will press on both timers when it comes down. A long stick doesn't care about your math, a long stick is faster than light! xD

    Efimka BroEfimka Bro12 klukkustundum síðan
  • Heeyyyyyy yes theory, poor choice in life motos cuz it looks like you have to do this!!!! I think itd be great if you teamed up to help @jacksepticeye. He and many other creatures are raising money for food for people who are in tight spots at the moment. It's called Thankmas, Every bit counts. Also spreading the word is great too. m.isworlds.info/item/vseDlNaspYuxn6o/v-deo at 4:18 forms.office.com/Pages/ResponsePage.aspx?id=kOKuLainZkyPQVS2-_F-RsCzQ-uZIS9IqzXK-NqxxxZURVZBVlY1RVFISzcwTUI0VVdZME9SNUI2My4u Like so he sees this, its great cause!!!

    Daniel WilliamsDaniel Williams12 klukkustundum síðan
  • hey doesn't the fact that the speed of light is different in different direction breaks the idea of isotropic nature of space?? I mean if space is isotropic in nature then in any direction one goes the property of the space has to be the same so the speed of light has to be the same in every direction.

    Shubhajeet DuttaShubhajeet Dutta12 klukkustundum síðan
  • So how do we know that we can't travel at the speed of light? maybe we already have? hmmmm...

    jasonj411jasonj41113 klukkustundum síðan
  • Can we experimentally prove it at least moves faster than %50 in all directions by accelerating something with mass to above 50% and measuring its speed. Afterall if it has mass it can't be moving faster than light. Perhaps put a particle accelerator to use? I'm not sure what the limit of this test would be, but presumably you could prove something of mass travelled at a high percentage of the speed of light in many different directions.

    Luke WilsonLuke Wilson14 klukkustundum síðan
  • The answer is to use entangled particles

    Helmer MussellHelmer Mussell14 klukkustundum síðan
  • Proof that you are wrong. isworlds.info/item/nLqslN-DqYWrhIg/v-deo light filmed at 10,000,000,000,000 frames per second.. you can see the photon of light move a measurable distance, hence the speed if light can and has been measured. Do some research before posting videos like this next time.

    797077970714 klukkustundum síðan
  • One way around this I may have found: Do not use timers. Fire a projectile at a known velocity. Measure the red-shift. The degree of red-shift or blue-shift is based on the speed of light. Normally physicists take an objects red-shift and the speed of light to calculate its relative velocity, but using a known velocity and measured speed of light to calculate the speed of light should work just fine. Measure the light as perceived from multiple points to find if it really is the same in all directions.

    Joseph JaroschJoseph Jarosch16 klukkustundum síðan
  • But what happened to the cat

    kingcarcas1349kingcarcas134916 klukkustundum síðan
  • Would it be possible to use a light source that is halfway between a sensor and a mirror. That is positioned to reflect light from the source back to the sensor. Let D be the distance between the light source and the sensor. If light travels at the same speed in both directions, then the reflected light will take three times as long to reach the sensor as the direct light from the source. If light travels instantly to the mirror, then the reflected light will take twice as long as the direct light from the source to reach the sensor. What is the flaw in this approach?

    garyz31garyz3116 klukkustundum síðan
  • I imagine the speed of light could be adjusted with gravity. Heavier the gravity it goes toward, the slower it goes on sending information back. Think about watching something fall into a black hole. Past the event horizon, that information stops until it red shifts out.

    James ParrottJames Parrott16 klukkustundum síðan
  • Hey @Veritasium, that was a thought provoking video. I recall back in 1983-ish when I was a physics student, we measured the speed of light using a pretty simple setup which used a laser, a spinning mirror to create a light pulse, a partially silvered mirror, a regular mirror, two detectors and a good oscilloscope to measure the time between the two pulses which arrived at the detectors. The light did not follow a straight line but it also did not make a "round trip". I just sketched an approximate diagram from memory (so it could be wrong) but I can't attach it. From looking on the internet, it seems to be a version of the Foucault method.

    Jeff SchaferJeff Schafer17 klukkustundum síðan
  • So, from Earth we see everything in real time and all other space objects are LAGGING?! XD

    Живко МиховЖивко Михов18 klukkustundum síðan
  • A couple years ago Cern conducted an experiment where they sent a particle to another lab only to have it arrive faster than the speed of light. Could this weigh into your inquiry?

    Jonathon ClaryJonathon Clary18 klukkustundum síðan
    • this was later debunked by the experimenters, something to do with a wire in the clocking system that was faulty, nothing can go faster than the speed of light

      Sibe BleuzéSibe Bleuzé4 klukkustundum síðan
  • Another issue with the high speed camera option is that you would also be measuring the time it takes the light to make it to the camera, so not just through the object but out and to the observer as well.

    Jonathon ClaryJonathon Clary18 klukkustundum síðan
  • You can try with one timer! At the moment when the beam of light is sent from point "A" to point "B" the timer starts, reaching "B" the sound signal is activated, then the sound waves return from point "B" to point "A" where they are caught by the device thereby stopping the timer. The received time is the time during which the light beam reached point "B" and the sound wave returned from point "B" to "A". And all that remains is, knowing the speed of sound and the distance between the points, calculate the time for which the sound has passed this distance, and subtract the result from the time on the timer, this will be the speed for which the light beam flew the distance between the points at one end!

    Slam Beats productionSlam Beats production19 klukkustundum síðan
  • Someone help me out here: if we suppose the speed of light is directionally dependent, why would NASA and Mark always get the same result? In the time it takes for Mark to see the message and send back a response, their relative positions have changed, meaning the direction the light (or electromagnetic radiation, to be more precise) travels is different. Wouldn't we expect the delta to vary as Mars and Earth change their relative positions, evincing an inconsistent speed of light? What makes the first message and the reply message linked events such that the delta is hidden? [mumbles] *something something* quantum entanglement?

    ncsupincsupi19 klukkustundum síðan
  • Doesn't the Michelson-Morley experiment prove that light travels in each direction with the same speed? The interference pattern would shift if that wasn't the case.

    prolarkaprolarka19 klukkustundum síðan
  • What if you toggle both clocks with a mechanical toggle? To make it simpel , arotating rod with cams to toggle both?

    Thijs VandeveldeThijs Vandevelde20 klukkustundum síðan
  • I remember watching this when first released and dismissed it due to SR. Now, something has clicked that compels a reply. The speed of light has nothing to do with a moment in time. The speed of light is the EMF. Imagine speeding up this vid by 10 trillion times or slowing it down by that amount. What would change with the information? Nothing. isworlds.info/item/qsaTgcmXlJq7pp4/v-deo - think GR when trying to find this medium (space.time) Part 2. Michelson Morley experiment. 32 views • Dec 8, 2019 isworlds.info/item/nLVpmZ2nmo-XX3w/v-deo - think EM shell of the Earth to understand the results (Tesla's weak electromagnetic resonance) Extended Michelson-Morley Interferometer experiment. English version 70,840 views • Sep 8, 2009

    Alpha OmegaAlpha Omega20 klukkustundum síðan
    • We are bound by temporal awareness! In truth: we (as with the universe) could have already lived and died and be unware of this fact (revealed in slow motion using the EMF).

      Alpha OmegaAlpha Omega19 klukkustundum síðan
  • Time to invent clocks which start ticking based on some quantum event, which could be synchronised with entanglement. Unless ofcourse entanglement itself occurs at different speeds in different directions.

    Mayank JhaMayank Jha21 klukkustund síðan
  • Philosophy of science is so interesting

    Dudok22Dudok2221 klukkustund síðan
  • Interesting. But sadly, not correct

    Debashish GhoshDebashish Ghosh21 klukkustund síðan
  • The best argument against the anisotropy of space (speed of light different in different directions) is that the way the universe appears to us today would be different. The observable universe would not be spherical, and in the c/2 and infinity case, we would see endlessly in one direction and not in the other. This is assuming that all regions of the universe began forming at the same time. By that, I mean simultaneity at the big bang. Maybe the universe was not point sized, but a finite-sized ball and one end of it began expanding, and the other regions followed. That way, we could still see a homogeneous universe of the same size in all directions because the speed of light in one direction could be faster by just the right amount to cancel any effect of delayed expansion.

    Mr CatMr Cat22 klukkustundum síðan
  • oh so i wasnt the only one who thought that speed was 300,000 m/s

    Vinicius 99Vinicius 9922 klukkustundum síðan
  • I could be completely wrong, but is this evidence that light can move differently in different directions? Say an object is moving and its mass suddenly halves. If the energy of the object stays the same and the object is in a friction-less environment (for example, space), then speed of the object will double. If the mass of the object were to gradually decrease (provided the energy stayed the same and a friction-less environment) then the speed of the object would gradually increase. The mass of an object changes based on the speed of the supposed object in relation to the speed of light (note that this relation could be a change in the speed of the object, of light or of both), if the speed of the supposed object decreased in relation to the speed of light, its mass too would decrease. Let's say that the speed of light is "fast" when moving east and "slow" moving west. If an object moved west (in the “slow” direction) and could suddenly switch to moving east (under the hypothetical that this could happen without the object stopping) then its speed would thus increase due to the decrease in mass. Now, instead, let’s say that the speed of light was “slow” at the center of the universe and “faster” as it moves away. An object’s speed, therefore, would then decrease in relation to the speed of light (this is not a decrease in speed. This is a decrease in speed relative to light speed.) and this would cause a decrease in the mass of the object. This decrease in mass would, in turn, make the speed of the objects greater. This would mean that objects propelled from the center of the universe would speed up. This is already observed to happen, as the expansion of the universe is increasing despite the “fact” that objects under motion with no propulsion do not increase in speed. Could this illogical increased expansion be proof/evidence that the speed of light increases the further you move from the center of the universe?

    James MacRandalJames MacRandal22 klukkustundum síðan
  • It is possible. After 'synchronization' time between the Earth and the Mars (13:47), we need some external event for register it and write down the time of the event using 'synchronized' time on the Earth and the Mars. It can be a large flash occurred on the Sun. The Sun, the Earth and the Mars must be aligned in a line. After that we can deliver wrote down the event time from the Mars to the Earth and compare they. We can use some interplanetary space probe instead of the Mars. It is possible to make this test in different positions of the Earth to the Sun. And finnally check if the Enstein's hypothesis works the same for directed light in different directions relative to the Sun.

    Volodymyr KusiakVolodymyr Kusiak22 klukkustundum síðan
  • That proofs that there is a God so wise and creative. also time... everything have time everything have a start and an end our life is time and it has an end the universe had a start and it's gonna end like it has started the universe is so temporary earth equal nothing to the universe, how about our God? may Allah keep me on his religion Islam till last second, and help me pass our life test. amen

    BasharBashar22 klukkustundum síðan
  • how can you say that you're receiving instantly?

    River RoadRiver Road23 klukkustundum síðan
  • If the postulation is that light speed depends on cartesian coordinates, couldn't you measure round trips on independent axes? For example have it travel +x, +y and -x in a staple-shape, then again for all permutations of XYZ and -/+? But then again the whole idea doesn't make sense since light travels along geodesics anyway and cartesian directions don't really play the same role.

    Alexander CohenAlexander Cohen23 klukkustundum síðan
  • Hey I want to give you a task or kind of a ''' challenge ''' if you want to accept it .You can do it with group of your friends do an explore on Nidhivan in india in vrindavan. Mainly about it's trees

    Catchy BeatzCatchy Beatz23 klukkustundum síðan
  • If the speed of light is different in different directions, then we don't have an event horizon...More like an event ecllipse or worse an open ended event parabola or something

    RanvirRanvir23 klukkustundum síðan
  • We can't measure it because time is not moving uniformly and because it's not moving uniformly it's going to change the rate at which the light is moving at any point.

    Morrigan Faye HaneyMorrigan Faye HaneyDegi Síðan síðan
  • Er... ah... the speed of causality ("light") has been measured accurately, and it also matches field theory.

    DesertphileDesertphileDegi Síðan síðan
  • To know whether light speed is the same in all directions or not, we can look at the cosmic microwave background. If the cosmic microwave background is the same in all directions, the light speed is probably the same in all directions. And if the cosmic microwave background isn't the same in all directions, the light speed is probably different according to the direction and we might be able to estimate how different. This reasoning assumes that the cosmic microwave background is curently the same in all directions and that simultaneity would has a sense, but as time depends on speed...

    Julien MarcinkowskiJulien MarcinkowskiDegi Síðan síðan
  • Hurr durr synchronize both clocks at midpoint, move to opposite ends

    archontarchontDegi Síðan síðan
  • 有中文字幕真好!

    朱家文朱家文Degi Síðan síðan
  • Big like and thanks

    NarcisNarcisDegi Síðan síðan
  • OK so. I might be missing something, but here is a question. What if: we take 2 clocks. Desync them by moving them that 1 km apart. Then send 2 laser pulses: one from clock A to clock B, and the other - from clock B to clock A. Let's say we were moving clock B. Then the time it shows is a little behind clock A, therefore the first pulse travels our measured time plus desync Δ. The other pulse, completely independent from the first, has travelled for our measured time minus desync Δ. What we get is two separate measurements that will only differ by double the desync constant _if the light speed is equal in both directions._ We could at least rule out the instantaneous one-way travel that way, wouldn't we? Or would that occurrence actually affect the amount of time dilation that occurred when moving the clock and therefore result in a massive desync capable of concealing the lack of travel time? Well, yes and no. While it is perfectly possible, we should not forget that Earth isn't stationary in Space. Therefore any directional effects may be absolutely irrelevant by the time Earth has moved tens of thousands of kilometers from where the initial clock movement took place...

    darth_Dandarth_DanDegi Síðan síðan
  • 3:08 Hah, "the only solution", he says. But what about having both clocks in the middle, and then moving them away to each side at the same speed? :) Edit: Happy it got addressed later in the video.

    MasterQuestMasterMasterQuestMasterDegi Síðan síðan
  • Okay, hear me out and please let me know what you think. If light traveled at C in one direction and INF in the opposite, could there be a scenario in which light traveling forward in time would be C, giving C/2 each way to mars, and backwards in time being INF, thus somehow collapsing the wave function of particles in the past ensuring the future is solidified?

    TristanSZTristanSZDegi Síðan síðan
  • Entangle the clocks, make the measurement, bring them back together and compare their records.

    Studio ProductionsStudio ProductionsDegi Síðan síðan
  • But could you measure speed of light to one direction like this: You have two lasers. First laser points straight to clock, and when light comes to the clock, clock starts. Then you have second laser in same point as first laser, but with small different angle pointing to mirror in half way to clock(lasers creates low triangle). Lasers send their light pulses same time. When second laser comes to same clock, clock stops. Now you have delta time and you measure delta distance from straight way and way of mirror. Then just calculate speed of two deltas and get speed of light (but is it one direction?). Now when I wrote this and started thinking more I'm sure it wouldn't work like this

    ManfrezoneManfrezoneDegi Síðan síðan
  • Time is a made up concept by man to give the illusion of understanding something, and if you ditch the time concept you will get in to another way of understanding this fiscal world

    Carlos ClsCarlos ClsDegi Síðan síðan
  • let me ask....WHY would it be different?

    Rick RhoneRick RhoneDegi Síðan síðan
  • Mars and Earth would set 12.00 on the clock then when earth sends them a signal he would think it is 10 minutes and send back the time of the signal that was sent than when earth receives the message and mars sends the message the clocks should be set 12 then we could know the travel distance like when mars sends it earth clock would be 12.20 but mars would say 12.00 and then when nasa sends another message with the time they sent it you would be able to subtract the numbers like 12.20 - 12.X (Mars clock ) and then you could have the value.

    wayubullyme hA?wayubullyme hA?Degi Síðan síðan
  • Use 2 clocks each on a planet then and you might know if the speed change concluding the signal

    Charbel feghalyCharbel feghalyDegi Síðan síðan
  • Isn't 'One-way' just an observer's perspective/interpretation of direction? If light didn't travel at the same speed in all directions, measurements to & from objects of equal distance away would be different depending on the position of the observer. I would venture to say all the measurements would all be the same. Forward can always be forward (one-way) depending on the observer's position.

    John DalzellJohn DalzellDegi Síðan síðan
  • How about using quantum entanglement to measuring one way speed of light?

    sungwon choisungwon choiDegi Síðan síðan
  • He said "or have they?" I was kinda sad no vsauce music played

    Mubasshir HossainMubasshir HossainDegi Síðan síðan
  • Just divide the two ways speed of light in to two the one half should be the one way speed of light 😆

    360360Degi Síðan síðan
  • You would need a clock that works with qbits, as 1 turns to 0 it does simultaniously with the other and so setting the clocks ?? maybe ?

    Sander Van eerselSander Van eerselDegi Síðan síðan
    • I'm not trying to mock your suggestion but throwing quantum mechanics to a physics problem is such a typical ISworlds comment thing to do

      Winnie PandaWinnie Panda17 klukkustundum síðan