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"


  • Dani Hernandez
    Dani Hernandez25 menit yang lalu

    What if you have an astronaught on mars with a watch perfectly synced to the time zone that the message is being sent. So if they send a message at 12pm and the astronaut receives it at 12:10pm then he sends a message back saying it was received at 12:10pm and they can go from there? Will that work?

  • nightmare_glitches
    nightmare_glitches36 menit yang lalu

    But what if we have realy good telescope whitch can se what someone is doing on mars and then writing it down and then sendjng it so then if he is doing it in the right that time he would send us that yes he is dooing that and even looking at clock when ha is doing that so when the massage reaches him then he would know how mutch time it took for light to travel from earth to mars so he could send back to earth the message of saying ether from earth the light speed was instantainius or it had some time delay? I hope my theory kinga helped out

  • rick mohamed
    rick mohamed44 menit yang lalu

    This was a cool discovery,,Lemme thibk about it well

  • rick mohamed
    rick mohamed50 menit yang lalu

    How about synchronizing the clocks before starting them

  • Étienne Beaudoin
    Étienne Beaudoin56 menit yang lalu

    how abouth lightning and tunder? cant we mesure the time diference between light and sound pulse at different distances in different direction from it to compare it?

  • Nich Froddle
    Nich FroddleJam Yang lalu

    why not have the two clocks on opposite ends and a lazer in the middle that fires one beam in both directions measure the 2 speeds

  • Marc Geurens
    Marc GeurensJam Yang lalu

    So, we live in a simulation

  • HYDRA Gaming
    HYDRA GamingJam Yang lalu

    The fastest is= mind energy.. the dark energy.. white energy.. spiritual energy dark matter 4 things around in exists world that is 2+2=5 that is truth.. 5 is real energy of life.. 5×5×5 =1:25 125 100_25 100 is century life.. century life is=1 1 is human 25 is B.B Big-Bang create every thing now... Bsquare proofs.. DIMOND BOY.. B.B=BELIEVE- 3 STARS IN SKY 7 STARS TO SEVEN WONDER.. 7 IS LUCKY 3 IS THREE TIMES COVERT EVERYTHING.. 3 IS LIGHT BLOOD AIR SOLID LIQUID GAS NEGETIVE POSITIVE NEUTRAL TIME SPEED EXIST...

  • Memetics
    MemeticsJam Yang lalu

    I suspect that if C varied based on direction in space, there would be some kind of observable variation, directly or indirectly, that would reveal the differential speeds. And everything that's discussed in the video relies on the ideal environment of a vacuum, which we know is not what space is. For example, if all light traveled instantaneously (or nearly so) in one direction, then it likely would affect the matter it encounters (such as the odd hydrogen atom) somewhat differently at different speeds. We still might not be able to measure the speed of a photon directly, but we might be able to observe the differences in the things that light interacts with and how they are affected. Based on everything we _have_ been able to observe to this point, I suspect that Einstein was right - the speed is the same no matter the direction of travel. And it still _does_ seem like an academic issue - the question of whether "now" here is the same as "now" on Mars is in fact a nonsensical question, as Einstein's theories showed - because "now" is relative to the observer's frame of reference. The only "now/then" that matters is what can be observed, so if the observations are _consistent_, that's all we need to know. The only interesting thing that could come from this discussion is the discovery that there's a meaningful _inconsistency_ in what we observe, which would then make it worth our while to continue exploring the question. Otherwise, I'm with the majority of physicists - apply Occam's razor and move on.

  • greennin
    greenninJam Yang lalu

    How about moving the clocks apart from the middle slowly. And then just doing the whole experiment again but turning the whole thing around? Meaning sending the light from the other direction. If the same result keeps coming out doesn't that at least help prove that light doesn't travel at different speeds in different directions? Unless you are saying light somehow "knows" from where you are measuring it?

  • escain
    escain2 jam yang lalu

    Can you constantly rotate the experiment around a center point? If the speed of light depends on some strange universe direction, you would see compression/dilatation of time.

  • John Henson
    John Henson2 jam yang lalu

    Time wasting

  • Bmddoe sntmatter
    Bmddoe sntmatter3 jam yang lalu

    Except for the fact that the speed of light has been measured... 670,616,629 mph.... IDdown will let any moron post a video.

  • tramar thomas

    tramar thomas

    3 jam yang lalu

    Guess you only made it five seconds into the video xD

  • Ben Chermside
    Ben Chermside3 jam yang lalu

    What about 1 light beam that makes a strate path and 1 that takes 2 legs of a triangle (with a meroe). You know how long after the 1st one hit before the 2nd one hit and you know the 2 disticest with a little pathagris or mesuring.

  • Ravi Rajyaguru
    Ravi Rajyaguru3 jam yang lalu

    16:13 - finally those flies left you alone! They were so annoying.

    PALEX XX4 jam yang lalu

    Okay, I watched until the end and I think I found something where I think you're confused or I'm confused about your position. "Light moves at the same speed in all directions." To me, this is a misrepresentation of special relativity. Special relativity states that light moves at the same speed in all directions WHILE IN A VACUUM. The speed of visible light and other forms of radiation can be interrupted and distorted just like any other instance of matter in motion.

    PALEX XX4 jam yang lalu

    I wasn't able to watch the entire video, but can't you just apply this concept to.... well, everything? Who cares if it's light that you're measuring, the point is that YOU'RE measuring it. Right? Greater point I took from this video was the flip of Einstein's relativity claims. We have no universal, objective reference when it comes to measuring how quickly matter moves. What do you guys think?

  • Shubham Todkar
    Shubham Todkar4 jam yang lalu

    But it may it mark set the clock on time even if it is 10 minutes late and came on earth and measure time difference. By this way calculating time difference. And create same situation for earth and calculator the difference in delay if they are different the speed of light may be different for both ways.

  • yodkagod
    yodkagod5 jam yang lalu

    Our body’s can react in that time

  • Odal
    Odal5 jam yang lalu

    You do not need to synchronize clocks, only make clear agreements. Mars and Earth agree that they will each send two consecutive signals one minute apart, or some other duration, according to their own local clocks. The first signal is to start the timer. You know then that one minute later, according to the clock of the sender, a second signal will be sent. It then becomes a simple comparison of all the data. The only problem is to distinguish the first signal from random ones. But that shouldn't be too difficult. All the difficulties reside in the idea that Einstein also could not let go off, that there is some absolute time that somehow keeps track of everything. Once we realize that time measurement can only be a (local) convention the problem disappears.

    TARUN SHARMA5 jam yang lalu

    Put two synchronising devices at equal distance and send signals two times to start and stop and the reading will be different in both the clocks that'll mean speed of light is different in both the directions.

  • Slobodan Milovanović
    Slobodan Milovanović5 jam yang lalu

    Wait!? If you shoot a light beam at a mirror on Mars and then move in that direction to a closer spot before it gets back to you, you will intercept it at a different distance and get all the details about the returning light speed.

  • shail patel
    shail patel6 jam yang lalu

    In this video you explain so much about light speed but i think the main issue is time synchronisation like you said in video its not possible to sync clocks;😄lol. I think i have watched a video of our great science which describes that time is synchronised by 1/627272.... Sec. If that's true, then may be we can measure exact speed of light in each direction and effect of gravity on light as well. Just an idea and i know i am not a scientist🙃.

  • Raj ‎
    Raj ‎6 jam yang lalu

    The last thing was a clear indication to the question - what if quantum entanglement works BECAUSE speed of light is C/2 and Infinity based on direction?

  • Anthony Reid
    Anthony Reid6 jam yang lalu

    Hey Veritasium, I just saw on QI that they measured light traveling through -260° sodium at 38 mph. Could this relatively sensible speed be used to reduce the theoretical problems with directional measurements? At 38mph you could stand at the other end of a large room and use a stopwatch, right?

  • Truth BeTold
    Truth BeTold6 jam yang lalu

    What If we shot out an astronaut in every direction and told them to return at a specific point in their journey. They would all get back at different points in time... Right? Somehow use this to discover times speed?

  • Bowen Creer
    Bowen Creer7 jam yang lalu

    What if you had two beams of light going in opposite directions triggering two clocks?

  • Babak Vaezi
    Babak Vaezi7 jam yang lalu

    Always felt like there is more to the speed of light. Awesome thinking and looking in new directions. “How about light speed from a moving source ?” “Maybe there is a positive and negative light “ Like magnets. Black holes are maybe negative speed of light, and opposites attract. Maybe I know too little 😁 But you are a great mind

  • †РаБоТяГа_ ek_FaStbik†
    †РаБоТяГа_ ek_FaStbik†8 jam yang lalu

    And what if you take one timer, move it away from the other, look at the error, take a third timer on which the error of the second is increased by 2 and move it in the same direction at the same speed, and at the time of connection, these timers are synchronized with 1😊

  • The_Animal
    The_Animal8 jam yang lalu

    one of those videos that you get it but you still dont know crap

  • Vincent Trotot
    Vincent Trotot8 jam yang lalu

    What if Marc and an observer on earth had some very powerful telescopes 🔭 ? If the speed of light is different depending the way light is travelling, wouldn’t they see that their watches are out of sync?

  • wefinishthis now
    wefinishthis now9 jam yang lalu

    Our inability to measure the one-way speed of light sounds eerily similar to our inability to properly observe whether light is a particle or a wave, so my thoughts are that the two problems are probably related. Since light's round-trip time is not actually about the speed of light, but the speed of causality, perhaps there's a way we can cheat by measuring other mass-less particles (which also travel at the speed of causality) to measure the one-way speed of light?

  • Rishi Achaibersing
    Rishi Achaibersing10 jam yang lalu

    Could gravitational forces be influencing the one way speed of light?

  • praharshitha josyula
    praharshitha josyula10 jam yang lalu

    wouldn't light travel through the path which takes the minimum time ?

    ARUNBAL VICKY11 jam yang lalu

    Out of the box thinking ❤️

  • Ronnie
    Ronnie11 jam yang lalu

    Could it also be, that light is less than 1/2 c in one direction and more than infinite c in the other direction, so ist travels back in time?

  • Hirnriss Lp
    Hirnriss Lp11 jam yang lalu

    Dumb question: What if you then wait, until Mars is at the other side of the earth and send the signal again. Let's say Mars is 10 Minutes back and the signal is infinitely fast in one way. It's 12:50 at earth and 12:40 on Mars. They send the signal, "hey, it's 12:50", and this signal instantly reaches Mark, then he would recognize the error. Only thing I'm not sure about: He travelled faster than the earth to reach the other side of our solar system. But doesn't that mean, his time went even slower than the earths?

  • Sg ///
    Sg ///13 jam yang lalu

    We should do multiple calibration of time from earth-mars. You calibrate once and then verify your theory...send a message from earth to mars, calibrate and respond from mars, then immediately send a second mesaage with the time when the message was received .. We should know if einstein was right or wrong

  • johnny hart
    johnny hart13 jam yang lalu

    this is why I will always trust and have faith in Jesus Christ

  • Elliot Lin
    Elliot Lin14 jam yang lalu

    The problem with your argument is simple: If light isn't consistent in both directions, then it violates the principle of relativity. The speed of light HAS to be constant in any direction in order for special relativity to work.

  • Nick Smith
    Nick Smith14 jam yang lalu

    Question... Is there not a way to use a T layout with a neutral clock? Lets call the top left of the T (A), and the top right (B). While the bottom will be N for neutral. Break the line from A to B exactly in the middle and put your mirrors to reflect to N and sync both clocks for A and B to N. A and B's one way trip to N and or vise versa should be identical. From that point just continue the experiment, Removing N and only going from A to B and B to A. I really have no idea here... but that popped up into my head.

  • Mario Portillo
    Mario Portillo15 jam yang lalu

    Tell me if this is dumb but it's just an idea get a really long plank of wood or whatever can stay straight for a long time and put one small square of glass at the start of the plank and one at the end then then shine a laser through one end and line it up with the other piece of glass and put some sort of sensor in the glass then goes off when I senses light you could measure the amount of time that it takes between One sensor to go off and the other and determine how fast it's going

  • Kara0ki
    Kara0ki15 jam yang lalu

    This is all nonsense. c = c. (regardless of the direction of travel) If c changed depending on direction, you would have blue-shift in one direction, and red-shift in the opposite direction. It could be measured and quantified.

  • Stephen Paul
    Stephen Paul16 jam yang lalu

    I think that while in theory you could have an infinite number of models for how light moves in the universe, it is more useful to use a simpler and more consistent model, so long as it remains consistent with all our observations of the universe. Most things that we recognize as proven fact could in theory be completely fade perceptions, but so long as they are consistent with all observations of reality, it remains practical to assume that we’ve proven them true.

  • radiodurans
    radiodurans17 jam yang lalu

    So those that think that light might be traveling instantaneously on its return path, do they think this is due to some quantum entanglement principle at work?

  • Ivan Sushkov
    Ivan Sushkov18 jam yang lalu

    why not put in a third mirror? and let the light in turn from different sides.

  • Isaiah Cutshall
    Isaiah Cutshall18 jam yang lalu

    Couldn't you connect the switches mechanicly to start both timers at the same time?

  • I Love Pizza
    I Love Pizza19 jam yang lalu

    I can think of two ways: 1) Two stop watches are set to start with a delay after x amount of time. Once they are in place then shoot the light beam with perfect synchrony. 2) Two stop watches are started at the same time/same place. We move one watch at a time at a constant velocity. Once the odometer reads a certain value the watch is stopped. Then this process is repeated in the opposite direction. Both times their face times are matched. If C is constant in both direction then both these watches should have the same difference in time. This method would require extremely high precision in distance and time measurement.

  • Del Scoville
    Del Scoville19 jam yang lalu

    The fact that earth is moving through space actually makes it impossible if we're measuring a reflected signal. It just won't be travelling at the same speed in both directions. We'd have to find a way to stand still in space.

  • Void X
    Void X19 jam yang lalu

    At 10:15 he talks about having a center clock to send the pulses out. What if you sent 1 pulse to start and a 2nd to stop it and record the difference. If light travels the same speed both directions then they would be the same when brought back together

  • Hastor
    Hastor20 jam yang lalu

    If you have two clocks in the first scenario, you could send a light pulse to the second clock, then use like something premeasured like electricity speed to send a signal back. Subtract the time it took for the electricity, and you get the one way speed of light, at least in that direction. Right? The electricity isn't affected by the speed of light, so it should work? I'm probably wrong though

  • I don't know any good names
    I don't know any good names20 jam yang lalu

    What if you set off an explosion really far away and measure the difference between when you see it and hear it, then do it again on the other side... surely that would work?

    AVINASH G21 jam yang lalu

    I was so much interested in science, but after watching video multiple times. Me: why should I care about speed of light😁

    AVINASH G21 jam yang lalu

    round way trip speed = 299792 km/s, then One way speed= could be 599584km/s🤣🤣🤣

  • Nick Fox
    Nick Fox21 jam yang lalu

    Two clocks. They start in the center, centered on the equator with the 1km path running perpendicular to the equator. Then use mechanical linkages to move them BOTH from the center to the ends of the 1km at a fixed, matching speed. Have a light source at both ends. Fire them off, bring clocks back to center, times should match.

  • Alvaro Navarro
    Alvaro Navarro21 jam yang lalu

    What if we put a atomic clock on the moon? It would look like the clock slows down and then speed up...

  • Dominic Gindoff
    Dominic Gindoff21 jam yang lalu

    I love the mark watney reference amazing movie

  • Champa Power
    Champa Power22 jam yang lalu

    I duno, use Sundials instead of digital clocks? lol

  • Siddharth Reddy
    Siddharth Reddy22 jam yang lalu

    I have a thought, in order to find out the speed of light in one direction. A to B, Try measuring from B? To A and C? Distance B to A and B to C = B as centre For example: Like you said if we have a satillite in centre of earth and mars shoots a signal to both sides Time taken to earth is different to mars then it proves light travels same speed in all directions?

  • lynn rathbun
    lynn rathbun22 jam yang lalu

    Can;t be measured , because it is defined, and it defines length.

  • Drift Simulator
    Drift Simulator22 jam yang lalu

    even if u find way to measure u cant say speed of light is this or this, because it depends on light, not every light are same not every light go so far and so fast , battery light cant move fsater than light from sun :D so all it depends on some power of light, use so low energy to a small light and there u can get slowest speed of light

  • TRONCO0013
    TRONCO001322 jam yang lalu

    Si ponemos 3 lásers que disparen al mismo tiempo, y para asegurarnos ponemos un medidor por cada láser a una distancia conocida, el láser A activará un segundo medidor a distancia de x, el láser B activará el medidor de inicio mediante rebote en un espejo y el láser c activará un medidor a 3x. Si c=3a b=2a indicaría que no existe diferencia entre una dirección y otra.

  • abdul_wasay 06
    abdul_wasay 0623 jam yang lalu

    Put a light source in between a circle of clocks if the clocks show different times for when light hits them we could know if the speed of light is different depending on direction if they all show the same time this means the speed of light is constant no matter the direction

  • Kelton Campos
    Kelton Campos23 jam yang lalu

    Wow so we could theoretically be seeing everything In the present rather than the past? The agreed upon speed of light could be wrong?

  • Filip Hoggen
    Filip Hoggen23 jam yang lalu

    What if you use 2 syncron clocks in the middle and send them to opposit sides with the same speed. The clocks have agreed tgat the light will be sendt on a spesifik time like 10s. So the clocks will count the time between

  • J B
    J BHari Yang lalu

    what if people on earth have really strong telescope and can watch the person on mars from earth? if light takes 10 minutes to get to mars, the people on earth would see the person on mars write down the time at 12:10, but if light takes 20 minutes to get to mars, wouldn't the people on earth see the person on mars mark the time 12:10 when the time on earth is 12:20 and know to correct it? or does that fall into the same problem? idk my brain feels like mush right now

  • Russian Bot
    Russian BotHari Yang lalu

    That's just visable light though right? The rest of the spectrums travel at different wave lengths this different speeds I would presume.

  • Banks Kaye
    Banks KayeHari Yang lalu

    Does anyone know if measuring two quantum entangled particles that changed polarity when a light beam hit them would work? Since the one at the end would instantaneously trigger the one on earth and let them know when the beam had hit Mars in real time?

  • jackson schmitt
    jackson schmittHari Yang lalu

    "how do u know FORSURE that the earth is round"

  • joel rogers
    joel rogersHari Yang lalu

    What about an experiment where you are in a vacuum have an observer in the middle and two people on either side both equally far away with lights. Both of the light bearers have come to an agreement on 2 oclock for when they turn on the lights and the observer records the difference. Please tell me if this is an unreliable experiment or what doesn't work.

  • Zealot
    ZealotHari Yang lalu

    When the astronaut comes back to Earth, wouldn't they notice the time isn't in sync? Following that logic: there should be a 10 minutes difference between Houston time and the synchronized time?

  • kevin ncube
    kevin ncubeHari Yang lalu

    A mirror may suffer some latency

  • Yuriy Kryvoruchko
    Yuriy KryvoruchkoHari Yang lalu

    I cant even imagine what the conversation would be like between Einstein (if he would be alive today) and Veritasium 😂

  • WolferDub Jazz
    WolferDub JazzHari Yang lalu

    i might have misunderstood the WHOLE video altogether but could this mean... 1. Events that happen in Earth and in space eg an eclipse or the celestial alignment of planets could have happened before we perceived them because if light doesnt travel at the same speed in different directions, this means that our perception of events might be totally different than our estimated or 'accurate' times. 2. If we technologically advance, we can measure the speed of light by trapping it in a black hole and building mirrors that have sensors built in around it, and, from the point of light entering the BH(black hole), record the time it takes for a ray to hit the sensor mirror 3. Since our very eyes rely on two way light or that for us to see, light has to go on an object and return to the eyes, we are unfortunately uncapable of coming up with a way to measure the speed of light and thus base future experiments on possible animals' eyes or machine life...though i must admit this is quite dark

  • Roger Phelps
    Roger PhelpsHari Yang lalu

    I have news for you. The speed of light has indeed been determined using one way measurements. In fact the first estimates of the speed of light were made using one way measurements. The moons of Jupiter are often eclipsed by the planet. If the distance between the Earth and Jupiter was constant the intervals between successive eclipses should be fixed but, since the Earth and Jupiter are in different orbits around the sun, the distance between the planets is constantly changing. This means that eclipse times, as measured on Earth, are sometimes early and sometimes late. The orbit of Jupiter can be determined using Newtonian dynamics together with parallax measurements of objects such as asteroids that pass close to the Earth. Given the orbits of Jupiter and the Earth the distance between Jupiter and the Earth can be determined. The speed of light can then be determined from the eclipse timing data. Note that different eclipse times are measured for different Earth to Jupiter directions, but the different directions no bearing on the results so this is a demonstration that space is isotropic. This was the way in which the speed of light was first estimated. The accuracy of this method will be limited and certainly a lot worse than modern methods. It is, however, a very strong pointer to the speed of sound being the same irrespective of whether a one way or two way path is used and also to the isotropy of space.

  • Himanshu Agrawal
    Himanshu AgrawalHari Yang lalu

    I have an thought ( in laymen term) the light move faster towards the object have higher mass, resulting in high gravitational force ( exp. Black holes) so when we sent the signals to mark at mars the time required was high due to lower mass of mars but when her replay back it will come faster due to Earth's mass, also if we add the sun gravitational force the message will receive faster , this just an idea i can wrong

  • Robert Gruener
    Robert GruenerHari Yang lalu

    This is probably stupid, but couldn't you have a set up like that at 2:14, so 2 clocks a distance apart but both start when hit by the laser? Then the difference between the clocks would be the time it takes for the laser to travel the distance. The clocks would continually count up, but at any time you could still take the difference (using cameras, etc). Or program the clocks to stop via a sound wave that starts at the middle or I'm sure many other clever ways to get them to stop without light being involved so that you could get directly at the time the light took.

  • AdamGa92
    AdamGa92Hari Yang lalu

    @veritasium if c in one direction was c/2 we would see half of night sky shining becouse of all of those stars which light didnt come to us yet.

  • Andrej Celko
    Andrej CelkoHari Yang lalu

    I am wondering, you mentioned to sync the 2 clock in the middle [kind of end of video], but I am pretty sure you could try to sync them lets say 3/4 vs 1/4 way [so not in the middle] and do a measurement, if what you measure using the syncing in middle and what you measure when syncing not in middle gives different results, it is a proof that the speed there and back is different, if you measure the same result it is a proof the speed is the same, I think.

  • Dawid Kaminski
    Dawid KaminskiHari Yang lalu

    Use fibre create big loop you can measure one way

  • Rani
    RaniHari Yang lalu

    cant we use the problem of time dialation itself to solve the problem? okay i was gonna propose another solution when i wrote the first sentence, but now i thought of something else, when we start two clocks at the same place at the same time like at 2:43. cant we start moving clock B, and since B is moving towards the other side at a constant speed, (or that we just know how much time its going to take to get there) lets say for example 1 minute. and we stop both clocks. so we sync them up start moving clock B to the right knowing that its going to stop after 1 minute, (each clock with relative to itself, since one minute is one minute (right?) even if clock A still sees clock B as moving it stops after 1 minute anyways (because of time dialation). stop both after 1 minute (when B finishes traveling) and we get the clocks back together to see how different is the time, and using that we can tell what is the speed of light in that direction. the only thing that im not sure of is that both of them have to stop after 1 minute of being separated, which im trying to say is "absolute time" when each of them counts it in their own local time, and without relation to its perspective. as in from a 3rd perspective, looking at both clocks from far away, would they stop at the same time? idk

  • Rani


    Hari Yang lalu

    okay nvm i remembered that then they would both have the same time on them because the minute itself would run differently in such a way that at the end they end up with the same time

  • Anubis __117
    Anubis __117Hari Yang lalu

    What if we synchronize the clocks using (when it finally becomes possible) quantum entanglement?

  • Fred Nimzowi
    Fred NimzowiHari Yang lalu

    you're overthinking this, really. Make any of your tests with the 2 clocks more or less syncronised, then make it in the reverse direction. And you'll see the difference, if any. And if you have not your answer right there, you at least have a basis to move on from there.

  • Creaters Refrigmenting & enjoy
    Creaters Refrigmenting & enjoyHari Yang lalu

    Well in the situation of the three clock we can measure the light speed through every angle (between line joining the two detectors and the line joining the detector and the clock) and can see if light speed is all the same.

  • Creaters Refrigmenting & enjoy
    Creaters Refrigmenting & enjoyHari Yang lalu

    Well we can use three clocks instead in order to synchronize the the clock seperated by some distance we can place a third clock at the middle point and perpendicular to the line joining the two detectors those are connected to the clock and may be at some time it sends a signal to the two detectors now as the distance between the clock and the detectors are equal the signal recieved by both are recieved at same time and so the two clocks are synchronised now we can do our experiment and can find the one way speed of light

  • Electrify Productions
    Electrify ProductionsHari Yang lalu

    What if you curved the path that the light travels on so that the light starts and stops at the same place?

    PRANAVHari Yang lalu

    if u suppose that speed of time isnt always the same then time dilalation doent even work

  • Ariea Ilezion
    Ariea IlezionHari Yang lalu

    what if we bounce the light off of multiple different mirrors back to the point? it wouldnt measure one way speed but if c is different it proves that c isnt the speed of 1 way light speed? not sure tho

  • Nivyan
    NivyanHari Yang lalu

    Something clicked. Here's a weird theory: 1) We, and everything in the universe are in orbit of something at the centre 2) The difference of the pull is so small, that we don't have the tools to detect it within the furtherest reaches we've ever gone. 3) If this is the case, we wouldn't know if going in one direction is vastly faster than going in the other. From our perspective, we've never experienced everything else. 3 Tangent) We're so rare in the universe, because not only is our planet ideal - but moving much closer or further from the orbit, has effects that render life unable to sustain itself. In other words, we're in a tiny, tiny pocket of the universe where (our type of) life is possible. 4) Furthermore, if 1 and 2 are correct, information could travel exactly like described: Very slow if directly opposite the centre, then essentially instant if fired directly at the centre.

  • Philip Soares
    Philip SoaresHari Yang lalu

    What If you start with 3 perfectly sincronized clocks, 1 in the middle, 1 in the right and 1 in the left, the clock in the middle sends two laser in the same moment in both ways, when the laser hits the clock(left/right) it stops. Maybe that can measure the speed If light in one way around

  • _
    _Hari Yang lalu

    So if the speed of light were infinite in one direction, would that affect how fast our space ships could travel in that direction? After all, isn’t the speed of light the only limit to the speed of massive objects?

  • Srishti das
    Srishti dasHari Yang lalu

    5:06 wowww🙏🏻👍🏻

  • Saberus Terras
    Saberus TerrasHari Yang lalu

    I've thought about this, and I have an idea on how to get a definitive answer... please break my logic: Synchronize two atomic clocks, and then send them both out on probes in opposite directions at the same speed. Program both probes to transmit their time to each other and the base station after they reach a proscribed distance. Both then transmit the other's message and the time it was received to the base station. Repeat to cover the 3 axes of normal space. Any discrepancy should become apparent pretty quickly?

  • EnchantedGamer9
    EnchantedGamer9Hari Yang lalu

    Thought Experiment here, feel free to debunk it. There may be a way to determine not the one way speed of light, but if light is faster going one way or another. Imagine you are a 10 lightyears away from earth, and looking at a clock with a telescope. You are stationary relative to the clock, so you see exactly what happened 10 years ago by the second (assuming that the light speed c constant from earth to the telescope.) 10 lightyears can be versatile in the scenario and the speed of light does not have to be C for the experiment to work, but I will use these values for the thought process. Now imagine that you start to move towards the direction of the clock, your hypothesis could be that the time on the clock will start to speed up relative the speed at which you travel towards the clock and the value of the constant c. If it does not, it proves that the one way direction is not the constant c. I'm not too keen on the idea of time relativity and if/how it would affect this excitement.

  • EnchantedGamer9


    Hari Yang lalu

    I also want to ask why would the speed of light be different in certain directions in the first place. Assuming that light is still a piece of matter, some force would have to be working on it to cause this discrepancy, which I think makes perfect sense. The force of gravity is infinite, and other forces for that matter, and I'm sure the universe ends at somepoint, so gravitational force should be stronger in one direction depending on where you are relative to the rest of the universe. Fundamentally, the speed of light has to be different in one direction, however, my hypothesis is that the difference is negligible.

  • Jimmy C13
    Jimmy C13Hari Yang lalu


  • Paul Snow
    Paul SnowHari Yang lalu

    What about Roemer's experiment? He measured the speed of light in one direction.

  • Andrew Beavis
    Andrew BeavisHari Yang lalu

    To quote the great DR Emmet Brown, "Marty Marty you are not thinking 4 dimensionally !" The starting assumption is that the speed of light IN A VACUUM is "c" and there is nothing to slow it down, physically so thats it. If you place the light beam in any medium thats not a perfect vacuum, even interstellar space, then the wave slow down minutely as its absorbed and reradiated. Furthermore, the purpose of the Michelson-Morely experiment was to show that space has no preferred direction because there is no "luminiferous aether" present to propagate the wave, indeed it travels fastest in a perfect vacuum. (although I suspect you may take issue with MM - have a go :)) ANOTHER, more relevant source of experimental error is the damn mirror ! Light does not INSTANTANEOUSLY reflect off the mirror , there would be a small time delay while the surface electrons absorbed and re-radiated the energy ! Ole Roemer's experiment gets around this....

  • Saibal Sinha
    Saibal SinhaHari Yang lalu

    Measuring anything in universal are assumptions from observations of patterns and repeatable results which are made references by us. This vast universe of infinite energy, our eyes captures an infinitely small band of spectrum of energy called light. It is like you are asking a plankton to measure the quantity of water of a pond from which it borns, lives and dies in it🙏🙏 Its all inside within us.

  • Agnovelli
    AgnovelliHari Yang lalu

    Maybe I missed something but why assume the way back is instantaneous?

  • Juzoh
    JuzohHari Yang lalu

    What if the light takes time to travel one way and instantly get back, because the light has to render textures going the way we are looking at, and 0 time to get back because it was already rendered. Would further support the theory that we are in a simulation.