Why No One Has Measured The Speed Of Light

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"


  1. TeslaTheJolteon


    3 minutter siden

    10:48 doesn't that give you the same effect as moving one of the two (as mentioned earlier) since their motion is always relative to one another.

  2. Christopher Thiessen

    Christopher Thiessen

    3 minutter siden

    If light travelled at uneven speeds in different directions, wouldn't that cause the event horizons of black holes to be asymmetrical as light could have an easier time escaping in one direction than from another?

  3. Piddy


    39 minutter siden

    So if we could potentially be seeing distant galaxies as they are right at this very moment, does that break our assumptions on how old the universe is? Are those distant galaxies potentially their assumed age minus the amount of years equal to their distance in lightyears?

  4. Rodj


    Time siden

    If thé speed of light is not measured how we can know it’s unsurpassable ?

  5. Артём Ворохобин

    Артём Ворохобин

    2 timer siden

    It's an old video, but may be someone will see this comment. What about curved space? The light issued from one point will travel one direction, but because of space-time curvature itself it will hit this same clocks, then you can calculate one-way speed of light.

  6. Poor Gamer *at games*

    Poor Gamer *at games*

    2 timer siden

    If the speed of light is different in different directions...then there's no point in giving it a constant value

  7. Raagul Raguraman

    Raagul Raguraman

    3 timer siden

    Can't we use two clocks in an quantum entanglement to start and stop itself and measure the speed of light in one direction (if not now inthe near future).

  8. sri ram

    sri ram

    3 timer siden

    It's interesting to talk about this

  9. Gregg Gustafson

    Gregg Gustafson

    3 timer siden

    We know that clouds and atmosphere affect light, so why are we trying to measure the speed of light on earth? Then we know that space moves with the energy of black holes, planetary collisions, etc, and therefore the speed of light will change as it gets bent (the shortest distance between two points), so the best we could do is measure the speed in the vacuum of space when there is no "ripple" in the fabric of space,,,,, put that in your request for funding!

  10. sri ram

    sri ram

    3 timer siden

    This was told by feynman's in his lecture.

  11. Pyzard


    3 timer siden

    I don't know if I'm "sciency" enough to say this, but why can't humans build some sort of machine that fires a laser and keeps track of the timestamp exactly after firing the laser and have a high tech camera that gets the current timestamp immediately after it sees light on the other end? This way, if you get the timestamps from both devices and subtract the first timestamp from the second one, you'll know the number of seconds light took to cover the distance from the "laser machine thingy" to the high tech camera. If it takes a while for the devices to get the current timestamp, they can get it before the laser is fired and keep track of the number of seconds from then. Will this work?

  12. Abhinandan Malhotra

    Abhinandan Malhotra

    3 timer siden

    "The stuff that's correct is theirs. Any errors are mine" LOL

  13. Spicy potato

    Spicy potato

    3 timer siden

    Okay I was thinking alot about this vid and the thing about "speed of light in other direction" I think it's same both ways, beacuse when you throw a ball upwards the time it takes to reach maximum height is equal to the time it takes to reach the ground back (if thrown from the same level ofcourse) Just like the equation of motion, where max Height is v = 0 We use u = gt 0 = u - gt t = u/g Time of ascent (t₁) = u/g The time taken to fall down through the same distance Time of descent (t₂) = u/g T = t₁ + t₂ = 2u/g But, this was all under gravity not forget that light is completely different thing from matter, well my ideology has a lot of holes in it, I am not even sure if my logic is right. But I did wanted to share what I thought, tell me your ideas or any critics towards mine! Also, I'm still in highschool so I don't know much of the higher stuffs, another reason why my comment might seem especially dull in comparison of others! XD

  14. Diederik Luyt

    Diederik Luyt

    4 timer siden

    Just use sound to sync the clocks.

  15. Derva Kommt von hinten

    Derva Kommt von hinten

    4 timer siden

    regarding your mars experiment. wouldnt a second measurement solve that problem? if they agreed to instantly send a second message he would know that a message takes 20 minutes for a round trip. so he would either receive the message after half the expected time or not.

  16. Derva Kommt von hinten

    Derva Kommt von hinten

    4 timer siden

    so what if you have a light source and you know that at a very specific time, the light will be cut off? that way you could measure the delay of cutting the light off and measuring the absence of light? a one way measuring.

  17. Satoaki E.

    Satoaki E.

    4 timer siden

    Shoot in different directions

  18. teqeri


    4 timer siden

    maybe im dumb but what if you had a kilometer long pole suspended from one point on the ceiling and you could release it so that it would hit the ground along this entire kilometer at the same time. then you could have the start button for the clocks on the ground and drop the pole onto both at the same time

  19. Piper Mahon

    Piper Mahon

    4 timer siden

    also it shouldnt be c, it should be v

    • Piper Mahon

      Piper Mahon

      4 timer siden

      becuase v shows the idea that its 10 minutes to, and 10 minutes back

  20. JL Martin

    JL Martin

    5 timer siden

    thanks for your video. Just one reflexions : - I never realy understood why we don't say (on Earth) that present on Mars is what we see now. I think it's just a convention, but it seems to me more natural to say what i consider present on a distant place is what can have effect me now.

  21. Piper Mahon

    Piper Mahon

    5 timer siden

    10:00, thats still worth tring becuase wouldnt that confirm the idea that lights/energy, i forget which moves differents speeds in different directions? also maybe you could mesure the speed it takes to send the signals, and that could help with the study of speed of light

  22. Sathiyanarayanan Manivannan

    Sathiyanarayanan Manivannan

    5 timer siden

    Can we measure the shift in the wavelength? The blue shift and red shift should help us figure out the frequency change in different directions. As frequency times wavelength gives the speed the controversy can be put to rest?

  23. Matt Lambermon

    Matt Lambermon

    5 timer siden

    The round trip speed of light question is one that kept me awake at night over many years when I was a child, I loved documentary about space but they frequently glossed over specific details like the fact the earth and sun are moving, frustratingly leaving you with unanswered questions to spend your nights pondering over. Maybe in the long run it was a valuable mechanism training your own mind to answer its own questions.

  24. asdf


    6 timer siden

    i think answer is not getting stuck on synching the clocks idea at all. all you need is properly recording signal output and signal recieved times in two seperate clocks. later you can find the one-way light speed by getting these clocks together and analysing time difference between them.

  25. C Luke

    C Luke

    6 timer siden

    And here all this time I thought somebody was smart enough to use a mirror and then use a highly precise atomic clock to measure the light going away and then the amount of time it would take to come back as one complete unit of measure. After all the mirror we have on the moon is how we measure the distance using a laser and the amount of time it takes for laser to go from the Earth bounce off the mirror on the moon and then return. If a suggested late had a preferred direction then such experiments as CERN which shoot photons into a loop would not work.

  26. SpaRool


    6 timer siden

    Here's an idea for y'all. Let's say that light coming from one direction of the universe traveled to earth at 0.75 c and light from the opposite direction traveled at 1.25 c. Also lets consider that when we look back to the most distant objects in the universe they appear as they were some millions of years ago. Would this not mean that we could infer the existence of this directional light speed difference from observing systematic differences when looking at distant objects in these opposite regions of space? Perhaps we could find more indicators of an early universe in one region 50 million light years way as compared to the polar opposite region. Or perhaps the irregularities found in the CMB map could also be an indicator of this.

  27. Vie De Chercheur

    Vie De Chercheur

    7 timer siden

    Thank you very much for this very interesting video. I work on studying light and I didn't even know this! Blow my mind ! Btw, I don't know if you would be interested, but we published a work where at we consider a sequence of two light pulses at the input of a nonlinear system carrying information. At the output, whereas both pulses have experienced exactly the same optical path, there is the creation of a third pulse at the central delay that carries the information of both pulses. This means that the information carried by the last pulse arrives at the output before the pulse itself !!! Honestly, before the experimental demonstration we performed, we were just scratching our heads thinking "it is what the equations tell us, but how on earth this really occurs?". Fascinating :D If you are interested, here is the publication "Lassonde, Philippe, et al. "Information transfer via temporal convolution in nonlinear optics." Scientific reports 10.1 (2020): 1-8." Cheers

  28. Ivan Olsen

    Ivan Olsen

    7 timer siden

    how about you ACTUALLY cook an egg Einstein

  29. himanshu chaurasia

    himanshu chaurasia

    7 timer siden

    can't we use atomic clocks ?

  30. klaas Beute

    klaas Beute

    7 timer siden

    What if you start with 2 clocks in the Middel move them do the test en move them back to the middle

  31. Nut All

    Nut All

    7 timer siden

    Sounds like a political activist arguing about science🦖

  32. antoine-marie Bourdon

    antoine-marie Bourdon

    8 timer siden

    Why are people surprised by this? We don't even have a real picture of the Earth from space.

  33. James Harwood

    James Harwood

    8 timer siden

    Don't we use 'redshift' to understand the constant?

  34. Gertjan van der Goot

    Gertjan van der Goot

    8 timer siden

    Four Clocks moved from the center in East, West, North and South, and four rays of light shot from each direction. The difference in time dilation in the East-West axis would not be visible in the North-South axis and vice versa.

    • Diederik Luyt

      Diederik Luyt

      4 timer siden

      But wouldn't the speed of the light make up for it?

  35. An Anattan

    An Anattan

    8 timer siden

    Couldn't you use a system that utilizes a qbit(Entangled Pair) as the message transmission tool. Entangled pairs appear to communicate instantaneously over any distance so you have one of the entangled pairs at the detector which flips on detection of the light source. This then resolves the other member of the pair which acts as the "stop" button for the clock. Has this been tried?

  36. Dario Karnincic

    Dario Karnincic

    8 timer siden

    Wouldn't universe in some directions look significantly younger than in other directions if the speed of light was influenced by direction?

  37. Ana Maria Rossell

    Ana Maria Rossell

    8 timer siden

    I'm not an expert. god forbids. but what about this experiment: at the start we send, at regular intervals of 1 second (or whatever time you agree), pulses/signals/whatever not only at speed of light but at a known, and verified, speed. for example each second is sent a signal at 20,000,000 m/s, simultaneously we also send another signal at 30,000,000 m/s, another at 50,000,000 m/s and another at the speed of light. at the destination, we start counting the signals as soon as we get simultaneously one of each and we stop the next time all pulses arrive at the same time. now we can count how many light speed signals we get between the start and the end of the period of time we measure at destination. there's no need to use mirrors or sincronized clocks. note: we use multiple non-light signals for the sake of redundance. the more signals the better. so long as they are all send simultaneously and periodically.

  38. Operational 117

    Operational 117

    8 timer siden

    If we ever make the Alcubierre-drive (aka. a Warp Drive, which moves an object along space by moving space itself, which (according to theorists) would permit true FTL-travel) a reality, we could send a signal through the unwarped space, reach the signal’s destination (trying not to accidentally hit and destroy the signal) before its expected arrival (taking with us a clock ticking at precisely 1 second per second), then see if the signal arrives at that point and when. If, in any direction, the signals would take exactly the expected time, then we can be certain that the one-way speed of light is a single constant in all measurable directions. If, however, the signal takes *different* amounts of time depending on direction, we can be certain that the one-way speed of light is a variable, based on the exact angle that the light travels. And *if* the signal never arrives (which means we missed the signal), we can be equally certain that the one-way speed of light in *that* particular direction is greater than the average speed that our Warp Drive-powered spaceship flew at. This obviously assumes that the Alcubierre-drive completely isolates us from the unwarped space in such a way as to make time dilation non-existant within the space bubble (such that time will flow at the same absolute speed regardless of the “relative” speed of the spaceship itself), which may still be up for debate. I believe that *if* the one-way speed of light is a variable, it’s because of the constant (and accelerating) expansion of the universe. In that case, I believe that the difference will be minor (but still measurable).

  39. Vytautas .J

    Vytautas .J

    9 timer siden

    I have a solution how to prove that it is same speed at both directions (or disprove), by using calculated speed of light (average from 2-way) you can check if its the same on one way and another, by having at first end a light emitter and light detector, but on the over side have some kind of device which could only reflect light one time per time which light travels one way ("average speed of light on one-way") the distance you made beetween device and light emiting source. Main problem would be synhcronising it, but after that, if you detect light on detector, that means light is same speed in any direction

  40. Jean-luc Chessher

    Jean-luc Chessher

    10 timer siden

    As a thought experiment you could have a force scale that is infinitely sensitive in a steral vacume in a room that is infinitely dark

  41. Jean-luc Chessher

    Jean-luc Chessher

    10 timer siden

    So what I'm getting from this is technically light could be a finite speed or infant

  42. rohandrummer


    10 timer siden

    If I were to vote for the best video made on NOnet. This one would be it.

  43. Harsh Shah

    Harsh Shah

    10 timer siden

    10:01 if we find out that the clocks are not synchronized then we know that the speed of light is not the same in all directions. and then we can find the ratios of both the speed with the help of the difference in time in the clocks and then equate the ratios with the speed of light and find out the speed of light in all directions. I am not sure if this is right.. just an idea.

  44. Victor Njagi

    Victor Njagi

    11 timer siden

    I'm not a scientist, I don't even have a degree in anything... but here is a question from layman's point of view: If light travelled at different speed depending on the direction to which it's travelling, wouldn't that be observed from other observations, eg the expansion of the universe, or in measuring the distance between us and other stars beyond our solar system?



    12 timer siden

    How about using timmer in both clock on same time

  46. Suhaib Ghazanfar

    Suhaib Ghazanfar

    12 timer siden

    What if you stood two individuals in such a way that the sunrise was exactly in between them. If light travels at different speeds in different directions, wouldn't one individual see the sunrise before the other? If we say light travels at c/2 in one direction and instantaneously in the opposite direction, wouldn't one individual see the sunrise approximately 9 minutes before the other? Even though the light from the sunrise that reaches the individuals is not completely opposite (imagine it like a triangle with the sun at the top and the two individuals make the two bottom corners) wouldn't there still be some difference in speed since the light each individual sees follows a unique path to the other?

  47. b2a5


    14 timer siden

    2:45 how about move those two clocks opposite direction exactly 500m each, so that they are 1km apart, and still in sync?

  48. KreVor


    14 timer siden

    Another convention: That light always travels at the same speed in one direction.

  49. TheInfernoFrenzy


    15 timer siden

    what if you moved two clocks in opposite directions and had 2 people stop them after motion has ceased when they reached a given time as they were still on the machine that moves the clocks further apart. then you have 2 people waiting at the end of the given distance to record the time that their clocks reached that given time which can only be reached after they have stopped motion.

  50. Mmmm Hmmmm

    Mmmm Hmmmm

    15 timer siden

    What would be the problem with having the light trigger other sources of light to begin as it moved towards the end point? For example, if we were "shooting" the light 100m, then we would have clocks stationed every 10m along the path that were capable of "shooting light" as well. When our original photon hit one of those clocks, it would trigger and shoot light back at the starting point. Would that not give us the one-way speed by adding up the time from all those secondary shots? What would keep that setup from working?

  51. Guinea54


    15 timer siden

    That would be pretty unusual if you shine a light in one direction it travels a different speed than if you shine it in another...

  52. Tomas Razelo

    Tomas Razelo

    15 timer siden

    I bet Rupert Sheldrake likes this video

  53. Mashca


    15 timer siden

    just use a ruler lmao

  54. MR. BANK-E

    MR. BANK-E

    17 timer siden

    What if you were to take two quantum entangled particles and in some way have the light react with one particle and then the other at a distance, the state from one would affect the other and then the light would ultimately hit the second particle changing both particles state I suck at explaining and please correct me if I am wrong or got anything confused or wrong lol but light hits particle A changes to A+ and changes particle B to B- and then light travels hits B- turns it to B+ turning A+ to A- does this work can entangled particles “spin” be changed ? And if I am wrong please tell me I know very little if anything at all about this but I try lol this would be the measure of one way light speed wouldn’t it ? but can quantum particles be used in such a manner ?

  55. yanninotmyname


    17 timer siden

    Could you not use quantum entangled clocks?

  56. Rohail Naqvi

    Rohail Naqvi

    17 timer siden

    Can't we record the one way and 2 way speeds of light through denser mediums (i.e. water and other substances) and determine whether light travels at a different speed on its way back?

  57. Vagossssssssss


    17 timer siden

    Can you just shoot 2 light guns and see where they hit???

  58. E-man Smith

    E-man Smith

    18 timer siden

    Wait, what about blackholes? Can't you see the back of your head because the light travels around it? Can't you measure it that way?

  59. Brewskiman


    18 timer siden

    What if you send the 2nd clock out and back 1km, divide the difference in time of the 2 clocks by 2 then preemptively change the time on the 2nd clock so that when you send it out 1km it can match up with the 1st clock.

  60. Javier Caballero

    Javier Caballero

    18 timer siden

    Sinchronise both clocks in the center in the center. Move them back at the same time, same speed and them shoot each other a measure how fast the opposite shoot reach each other.

  61. Javier Caballero

    Javier Caballero

    18 timer siden

    What if you star in the center, move both clocks from the center back , at the same distance, same speed same same hight and then shoot each other, and then measure how fast the opposite shoots reach each other.

  62. TheXen


    18 timer siden

    The inference that the return message from earth is absurd. The Information is inherently different and for it to return to earth instantly implies the violation of the speed.

  63. theufwik


    18 timer siden

    in your experiment (12:34 until 14 :15) were you claim various directions you are actualy experimenting various distances wich by the way confirms Einsteins theory that light travels the same in all directions but riches differently in verious points in space

  64. Stephen Anderle

    Stephen Anderle

    18 timer siden

    The Apollo space craft did not travel instantly from the moon back to earth!

  65. Winston Reynolds

    Winston Reynolds

    18 timer siden

    What if you set a clock and at exactly 10 seconds you have it go at a consistent speed from point A to point B and at the exact second it gets to point B you stop the clock and then do the exact same in reverse.

  66. Filippo Ilya Neri

    Filippo Ilya Neri

    18 timer siden

    I swear this is one of the most interesting video I've ever seen

  67. Stephen Anderle

    Stephen Anderle

    18 timer siden

    Light from a specific type of star at a specific distance is the same in all directions. Twice as far it is still the same in all directions. The speed of light HAS been measured very closely.

    • Stephen Anderle

      Stephen Anderle

      18 timer siden

      And the difference between the two is also the same in all directions.

  68. Bell Luna

    Bell Luna

    18 timer siden

    It was just a little cringe how you looked away from the camera at the end. I like you videos.

  69. Emily Rose Lacy-Nichols

    Emily Rose Lacy-Nichols

    19 timer siden

    Using light to measure the speed of light feels like using a ruler to measure the length of a ruler and concluding that an inch does in fact equal an inch… my brain hurts 😂

  70. isaiah rubio

    isaiah rubio

    20 timer siden

    Why doesn’t someone just test it all the ways you can to find out and in different directions

  71. wa da

    wa da

    20 timer siden

    If it is true that light travels at a different speed from different directions, there should be applications where you can prove this hypothesis?

  72. DJ Terror

    DJ Terror

    20 timer siden

    I think light would travel differently in darkness than in light/daylight!

  73. אמיר וויסבלאי

    אמיר וויסבלאי

    21 time siden

    doesnt black hole would be bright if so?

  74. Resistivewig6


    21 time siden

    Wait what about redshifting I know I'm perfectly hundredth person to say this but what about red and blue shifting?

  75. Deku_BMGO


    21 time siden

    The speed of Light can Not be Instantaneous Because If it instantly Going from point B to Point A It is so called Infinite Speed And If its instant it could be possible that it would seem like it has stretched into infinity so it is physically impossible to know how fast light is going

  76. Michael Blaine

    Michael Blaine

    21 time siden

    It's like trying to measure the length of an infinitely long wall with a finitely long measuring tape.

  77. St. Brian The Godless

    St. Brian The Godless

    22 timer siden

    If this were true, the universe would look younger in one direction and older in the opposite direction. It would not be a uniform looking universe.

  78. Muhammad Naeem

    Muhammad Naeem

    22 timer siden

    You could align clocks directly connected to each other for the whole 1 km distance, no matter how many clocks it takes to fill the space. All the clocks would then be synchronized, you would shoot light in one direction, each clock capturing the time when light hits it only once. You will then have a progression of time stamps, that data could be used to measure the speed of light in one direction.

  79. Anonymous


    22 timer siden

    Use 3 mirrors and measure the 3 way speed of light using different types of triangles.

  80. OnlineDater69


    22 timer siden

    Nice quality video. I didn't know this. What if your consciousness is light & everything radiates away/forward from you in the form of fluctuations & functions collapses???

  81. Scyrex Core

    Scyrex Core

    22 timer siden

    this is just me, but what if you connect the two clocks at each end with a Y connection switch, where the lines are exactly the same length from the clocks, and the trigger for the light is connected directly to the first clock. In other words both clocks and light all start at the same time, then its just a matter of when the light hits the 2nd clock to indicate the stop time.

  82. JP


    22 timer siden

    I’m no physicist by any stretch of the imagination but maybe it’s assumed that the speed of light is how it’s currently measured not because it’s easier but because it’s an accepted measure of the numerical value we currently have. Maybe your right and it’s not 100 percent dead on but if no other value exists then what else do you have?

  83. jimmy Ryan

    jimmy Ryan

    23 timer siden

    But if the light from the universe was instantanious the formations we see in the deep universe wouldnt make sense. Gasses would have time to concense into stars and planets

  84. Wooper is our lord and savior

    Wooper is our lord and savior

    23 timer siden

    Have we actually mesured the one way speed of anything ?

  85. Cz łowiek

    Cz łowiek

    Dag siden

    But why we are the ones that see the light instantly?

  86. Борис Дзюбенко

    Борис Дзюбенко

    Dag siden

    Quantum entanglement, why not use it?

  87. Clinton Johnson

    Clinton Johnson

    Dag siden

    So, if the moving clock vs the stationary clock is an issue, move both clocks in different directions for the same subjective time and distance. This should keep the clocks synchronized. If you feel that somehow the preferred direction affects this, move the clocks at right angles. Do left and right handed tests and compare the results to ensure you don't have more preferred directions. Doesn't seem that complicated to me.

    • Clinton Johnson

      Clinton Johnson

      Dag siden

      Speaking of, that is pretty much how Ligo works.

    • Clinton Johnson

      Clinton Johnson

      Dag siden

      Oh, and after an agreed upon duration, move them back together again to compare the results.

  88. Kaan Keklikoglu

    Kaan Keklikoglu

    Dag siden

    what if we look at a star before it becomes supernova and record the time it became supernova and after supernova we can look at the ruins of it and calculate how long ago it became supernova ...... i may have described very bad

  89. Ray Berczik

    Ray Berczik

    Dag siden

    All of a sudden my brain hurts.

  90. Florian Klein

    Florian Klein

    Dag siden

    what about using an object so massive that you measure a one-way trip that simply bends in circle? you just need a black hole :)

  91. Pelle Chamliden

    Pelle Chamliden

    Dag siden

    I haven't read if anyone else has commented this before. But light had assymetric speed during its travel in vacuum you would be able to note CE frequency difference between say "leaving direction" and "going back direction". Meaning you would see interference pattern in a light measured on a "mirror bounce" riig... So it is excluding that the light has a assymetric speed in different directiond

  92. Александр Попов

    Александр Попов

    Dag siden

    No problems.... 1)(a1+b1+a2)/2 (2km.) constant 1905 ears. Mi version 1) distant #1) a1+c1(=1Km) sinhronisation a1 end c1 =(t1).... distant #2) a1+b1+c1 (=2km) (a1+b1+c1(2Km))-(a1+c1(1Km))=(a1+b1+a2)/2 ??????

  93. Chirag Kalra

    Chirag Kalra

    Dag siden

    What if we put put the clocks 1 km apart and hang a rod from the middle of length 1 km (just one point in the middle) and the clocks at the end. Then we release the middle joint and the rod falls on both of the clocks at the exact same time and starting the timer? (Just hypothetical)

  94. Julio Calderon

    Julio Calderon

    Dag siden

    Mind blown

  95. Julio Calderon

    Julio Calderon

    Dag siden


  96. Abhinav Sharma

    Abhinav Sharma

    Dag siden

    Is it possible to understand the speed of light by realising the time lag between the clocks if we try to synchronise them from the middle...?we will eventually know if the speeds are different and if so by how much! PS:correct me if I m wrong If right contact me thro insta @abhinav_08

  97. Shane Dancer

    Shane Dancer

    Dag siden

    How about this: We calculate a path for a rocket to take from Earth to Mars. We know exactly how long it should take and even put a person and a supercomputer on the rocket to guarantee that the plan was followed exactly. As soon as they touch the ground, they send a message to Earth saying they have landed. Of course we could never measure this so accurately and be able to account for the effect of special relativity but this would at least guarantee that light speed isn't more than a few percent off what we measure it as. Of course, that only covers the exact path that the light used to communicate with us took to come back to us, any other path could theoretically be different.

  98. Matt LaBonte

    Matt LaBonte

    Dag siden

    What if you could observe two clocks from far enough away to see both in the same reference frame?

  99. Yash Dubey

    Yash Dubey

    Dag siden

    This absolutely broke my brain🤯🤯

  100. Mark Bothum

    Mark Bothum

    Dag siden

    Why do the clocks need to be synched? Just looking for elapsed time, not absolute time.

    • Mark Bothum

      Mark Bothum

      Dag siden

      Never mind, that was really stupid.