Why No One Has Measured The Speed Of Light

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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.

References:
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 Ivy 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"

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25 Mar 2023

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SmarterEveryDay 2 yıl önce

This was a very fun present to unwrap. When you called me and told me to turn the camera on I knew something weird was going to happen and you certainly delivered. As long as I’ve known you Derek you’ve been destroying assumptions. Thank you for this friendship. It’s certainly enjoyable from my perspective.

geometric art Aylar önce

assumptions aren't destroyed they're only converted into something else.

David Micek Aylar önce

Would it be possible to use something else with a known speed to sync the clocks? For example, start with 2 clocks that are not in sync and space them a set distance apart. Clock A says to clock B, "when my clock says 12:00 I will fire a gun. When you hear the gunshot, set your clock to 12:00 plus the time it takes for sound to travel the set distance." Wouldn't that sync the clocks? Then clock A says, "Furthermore, when my clock says 12:01 I will fire a laser at you. Record what your clock says when you detect the beam of light." Then it's a matter of doing the calculation to see what the 1-way speed of light is. That being said, couldn't you use anything other than light that we already know the velocity to sync the clocks? Seems simple enough, so it's probably flawed. But I would like to know.

Marscom Aylar önce

If this would be the case the universe would look different in two Directions.

godzilla47111 9 aylar önce

@Cédrick Greenoak how do you verify that it's the same time on both devices?

Dan Kaufman 10 aylar önce

@Lindorosso if we could send information with these entangled electrons, I wonder if we could ever "know" that entanglement happens at the same moment since al the observations or confirmations would be round trip to transfer the information. All the proofs and experiments about entanglement probably make the same assumption about C being the same in all directions.

nekoill 18 gün önce

Don't you just love it how Destin was spelling out how they measured that ball's speed and immediately realized what you were up to? 😸 Can't help but love that guy

Justin Brockel Aylar önce

I love hearing about everyone's ideas of how to solve the problem. It shows the passion of finding the solution with individual ingenuity and creativity in one's thought processes. Very neat. It will be an exciting day when we know undoubtedly.

music b 5 gün önce

@Enrico Ramos I'm not stating it to be an estimation or a convention by the way, a convention would rather be like 'agreeing to make meter as the standard unit of length'. In this case, it has been pretty evident that the speed of light is the same in all directions, cause all the experiments in real conditions have proven that time and again. The phrase suitable for this scenario is 'just because you can't see the thing doesn't mean it isn't there'. Just like the influence of dark matter is pretty evident, you cannot dismiss the modern calculated speed of light simply because it is not measured in one way. Otherwise people that are way more intelligent than you or me wouldn't be using it's value to actually standardize units of time itself.

music b 5 gün önce

@Enrico Ramos what if we use a mechanical system that spans the full distance of the two clocks, it is designed such that the timer in both clocks will be stopped at an exact time period. If we make that time greater than the estimated speed of light to reach the distance, then when the clock stops at both points in my first scenario, we would get the time taken for light to travel by calculating the difference in each times recorded by the clocks.

Enrico Ramos 5 gün önce

@music b So you’re not mesuring the one-way speed of light, that you already admitted. What you’re saying is that for all practical purposes the round trip divided by two is the one-way speed of light, cause it works in all the experiments we had untill now. So what you want to propose is a convention that stipulates what the one-way speed of light is for practical purposes? Man, you’re some 118 years late.

Lalu Wahyu 19 gün önce

@music b watched it again then, but now carefully dissect every bit of information the vid gives you. Everything you said about your experiment is literally there in the video especially in the “other method” part. Look at the mars and earth communication part of the video, it literally what u said, sending signal from point A to point B. The video said that we dont know 1 way speed of light and it could be different from one direction to others, but you keep assuming that it is the same for all directions?? Which could be true as well as it could be not. And your way of measurements relies on speed of light being the same on all directions which einstein himself said that “we dont know and just have to agree that it is”. And ur gonna say that its not the light we are measuring its the pulse that travels at the speed of light. But its literally the same thing. Its masless particle that obey the rules same rules of physics. Now the video is talking about what if there is a preferred directions in our universe??? Rather than debate me in here, why dont you write this experiments in a form scientific paper and submit it to be peer reviewed?? If you re so persistent that you are right about your experiments??? Cuz this is literally a breakthrough in science if you are right. And it would be interesting to see that it all happen first here in this comments sections

Abhishek Dhar Aylar önce

If the speed of light were instantaneous in one direction, we would have one portion of our night sky, really lit up with no darkness. This is because all the light emitting heavenly body would have light reaching us simultaneously from even beyond the current observable universe.

Abhishek Dhar 24 gün önce

@Himadri Mandal What the universe shows has nothing to do with what we are assuming or hypothesising. If light had Double the speed in one direction, and half in the other direction, we would see a non uniform night sky, irrespective of our assumptions. Ofcourse, unless you wish to postulate that even the number density of the heavenly bodies, were distributed in such a manner that it would offset this non uniform speed of light. In that case, I would ask, we remember the Occam' s Razor.

Himadri Mandal 24 gün önce

It wouldnt light up the night sky because intensity is a thing but yes we would have an infinitely long bulge in the shape that is the observable universe. But who says such a bulge doesnt exist? The images of the observable universe are afterall a depiction of it on the assumption that light travels equally quickly in all directions.

Indy Z 10 gün önce

This is interesting. Imagine being in combat situation and some observer infinitely far away can instantaneously warn you of a coming attack, but by the time the enemy locates the observer, so much time has passed that their observation is worthless.

Hoshiumi Korai 10 saatler önce

So how about this as an idea. We know from the resonance synchronisation video that when two ‘pendulums’ are kept nearby they tend to synchronise. So now lets keep multiple such pendulums in a line such that they all synchronise to each other. That way, we are sure that the two pendulums have the same time period. Now, using a clock, you measure the time taken for each swing of the pendulum. Now given that your pendulums are synced, you can know launch a beam of light and use the pendulum swing as your measure of time taken. So now, you convert that into time it took light to reach and you have an answer for one-way speed of light. Now, you repeat this in any direction you can think of, and you will have your answers. I know it is incredibly hand wavy, but since we need two objects for time-keeping to sync, I thought it should be pendulums, not clocks.

CGP Grey 2 yıl önce

Great video. Despite getting a physics degree and teaching physics for years, I never came across this or thought about it. I was treating the video mostly as a 'fun to think about' sort of video, but your point at the end is really intriguing.

latthoff123 Aylar önce

@Joseph Burchanowski Would make sense, if the universe is just a creation of your (central point) brain. If any individual had its own universe and the "outside" is created from within. You see Mars "now" because you create it. Mars cant see you, becsuse it is a part of you. Question is: Am i part of your creation or vice versa?

ALTALT evan 4 aylar önce

Hey CGP love your videos, surprised to see you here, I am just trying to find this out: If light is Infinitely fast on the way back wouldn't we see reflections of light from far away galaxies and there would be no observable universe barrier?

GrillHike. 6 aylar önce

@George Alexander WoW! I was just thinking about entanglement and connection to this idea.:) Its such a great feel to know many people are thinking along that line too.

GO 6 aylar önce

@Joseph Burchanowski I hate you because before I even started reading I was getting at this same line of thinking about causality but you put into words my late night (also sick) brain could not and I appreciate someone else writing it out for the world to see and pontificate on. I truly do believe our view of space time is too rigid and we are one acid trip or sci show away from thinking of something extraordinary. And I hope it doesn’t take another to get to a new leap. I mean in my life time we have almost solved fusion reactors, something a section of ppl thought were not capable for another generation or two, not sure if the need for a solution for ecological or societal reasons are driving it. But I do hope more than anything that we solve wealth gap in our society and we make a shift so that it pays to have degrees in science and do research again w/o the need to profit on the results or create a weapon.

eee yyy 6 aylar önce

Why not sync the clocks in the middle of the tunnel then move them to the end at the same speed. They would still be at sync as they moved together at the same time and the same distance, therefore the same speed, therefore still be in sync. Does this not therefore mean that you could still stop it when the laser reaches it as they are at sync

Ran Mazor 7 gün önce

Suggestion for measuring the speed of light using computational models What if you repeat the experiment of miving the synchronized clocks to the opposite direction multiple times, each time use different asimut i the 3d space, and plot their results (the speed) on a graph and look for meaning in the maximum point and the minimum point?

Juran Aylar önce

I think it would be interesting to see when we get to the point where we have a greater understanding and control of quantumly entangled particles as we could potentially leverage them as a method to (potentially) ensure synchronicity between two clocks at great distance, thereby allowing us to at least "more" confidently measure the one way speed of light.

Ancient To Modern 8 gün önce

@Musarat Jahan oh so u must tell me by what means or medium are the particle communicating during Quantum entanglement bec bohr's result were later proved to true that the result shown by the particles is not predetermined rather they use some communication means which is surely faster that speed of light so who knows

Musarat Jahan 8 gün önce

@Ancient To Modern quantum entanglement? Funny enough, no it doesn't break this law. That's probably why Einstein called it spooky action at a distance

Musarat Jahan 8 gün önce

This is precisely what I was thinking. If we could just leverage quantum entanglement to ensure synchronized clocks this problem is done for. Surely, Einstein must've thought about leveraging this too, he very much knew about quantum entanglement

ayush sood 8 gün önce

yes ... and that is the only way to measure it.... the spooky action ....

Ancient To Modern 8 gün önce

But doesn't that break the conception that something is faster than light

FerumFist Aylar önce

Ever since you put this out it comes up in my head now and again and I always get so desperate and angry trying to come up with a solution in my head...two years, you make me angry and my brain hurt Derek 😭

Ryan Leadenham 11 gün önce

@Spood Beest filming something and measuring it taking into account relativistic effects are two different things

Spood Beest 11 gün önce

Slo Mo Guys did a video where they filmed the speed of light, at Cal Tech. So, Derek is wrong on this one.

iceman23 20 gün önce

@Ryan Leadenham Thanks. Probably should have explained the question better. Given that one way light speed has not been measured, if we accept that one way speed of light may differ from c, then should we also accept that our understanding based on things like the cosmic background radiation may potentially be uncertain. I don’t know much about physics at this level, but just wanted to know what you thought of it

Ryan Leadenham 22 gün önce

@Kerry Hebert that is based on theory and not testable. May be highly likely, but not provable.

Kerry Hebert 22 gün önce

At the extrema of C/2 and instantaneous, looking through a telescope you would see many super novas in the distant early universe in the C/2 direction and very few in the instantaneous direction.

pedrosura 14 gün önce

I really think its important to remind ourselves what things we know and are fairly certain and what things are assumed or convenient conventions. Another example is the red shift. It is assumed to be recessional velocity but we have never measured this velocity independent of the red shift.

J Mi 8 gün önce

I know that when they defined the speed of light, they set it at a point when everything based off it would not change much, but I think they should have gone all out and defined it at 3e8. Then the second could be based on a defined cesium-133 frequency of 9e9 Hz instead of 9,192,631,770 Hz. Put together these would be easier to remember, easier to use in calculations, and far more reflective of their defined vs measured state.

br│ström Yıl önce

My bank uses the same theory, but vice versa. When the money leaves my debit card, it goes really fast. When something is to be repaid, it takes much longer.

Brian Lopez 2 gün önce

Unless your SVB, then it never returns.🤣

Foodies at home 3 gün önce

😂😂

Roderick Daniel 4 gün önce

Boom!😂

Mihail Milev 6 gün önce

@MARCO u have my friends name but my pfp

Mihail Milev 6 gün önce

Lmao

WavePlasma 2 gün önce

Idea: take not two, but four clocks, two on each side, and each side syncs their two clocks, moving one of them to the other side. Light is fired in both directions, the first two clocks stop once light reaches them, then the remaining two stop once the light reflects back. The clocks are then moved to the centre and compared. If the speed of light is different in either direction, the clocks would not have measured the same difference in time. And if it were the same, the time taken for both single trips would approximately add up to the time taken for the round trip.

Thorben Schneider 22 gün önce

This randomly popped back into my head and I was wondering if this would be solvable by relating it to a on-Quantum-based speed. Like - Sound is just particles beung compressed to Form a wave. Sound has a fixed speed in a given Medium - if there's only one clock to measure but it starts when the Light Hits the sensor and stops when the Sound Hits, one could measure the delta in every direction. If it does not differ and there is no reason to beliebte that Sound also has a preferred direction (and I Do not See any reason since again, particles doing particle-stuff without Quantum wibbly wobbly) then this should at least Show whether speed of Light is the Same in any direction.

rob shmit 3 gün önce

Here are two ideas: 1. Use the concept from 9:50, except instead of triggering the two clocks with electronics/photons, you just mechanically sync the two clocks using a huge rod connecting them. 2. Have two tubes, one is a vacuum for sending light and one has a stable atmosphere for sending sound back. A timer is on one end to measure one-way speed of sound + one-way speed of light. The other end has a detector and speaker combo to detect light and send sound back. Obviously making precise measurements with these setups would be a nightmare in practice, but they should work just fine in theory, right?

Drew McGowen 2 gün önce

The problem with #1 is that, when you move the rod by applying a force at one point, it takes time for the rest of the rod to "feel" that force, ultimately because the particles that carry the force between the rod's atoms are limited by the speed of light, so you're still stuck with the possibility that the two ends of the rod are out of sync. For #2, I believe you could argue that, in a similar manner, if the speed of light is direction-dependent, then so too is the speed of sound. After all, sound emerges from interactions of air molecules, which are mediated by force-carrying particles limited by light-speed.

Someone Aylar önce

You set up 1 clock and a speaker at the other end. When the speaker gets the light, it will project a sound. On the other side, the clock starts at exactly when the laser hits a sensor, and stops when it gets that sound. After this, you subtract the time that you got with the speed of sound for the area. What you get should be extremely close, the only problem is that the speakers have wires that travel at the speed of sound, and so does the microphone.

Jade Neoma Aylar önce

the speed of sound is a compression wave affected by time dilation. This time dilation means that the result of your experiment would also be C regardless of if that is correct

Jared White Aylar önce

What if in the mars scenario we had a wormhole teleporter that connects two places without moving you instantly over large distance, but making the distancr shorter and you observed at either end, and sent the signal around the long way?

tempodude 20 gün önce

yes, if we could communicate instantly this whole illusion would break, but we can't and there are some really good arguments saying that it is impossible to do so, not only impossible with our current science but impossible by definition.

Just Some Guy without a Mustache Yıl önce

I swear this channel is a gold mine for educational and entertaining content

Sir Nicholas 5 aylar önce

Fax

Mik 7 aylar önce

It's becoming more clickbaity every day

peter gibbs 7 aylar önce

Please dont tell me you understand it, as i dont. I watched one about gravity but i was just totally confused.

Rishom Evans 7 aylar önce

And I swear you're in the comment section of at least 80% of all videos I have watched.

Tim Cummings 16 gün önce

Proposed experiment: Take a series of entangled pairs of photons, split and send them in opposite directions of equal distance towards a measurement tools on either side. The act of measurement determines the state of both photons. Measure the time to get a determination of spin state. Change the distance of one measurement device, leaving the other fixed. Time again and compare. This may work to measure the velocity of one photon by using the other photon to act as a 'return trip'. Perhaps to test if a ' directional bias' exists for the speed of light, a chamber may be built so that a 3d measurement can happen. Time to elimination for a set amount of time may prove or disprove this. Just a guess from a layperson.

Typhon Gün önce

This is quantum physics

Bill Pii 10 gün önce

Please tell me what Holiday Inn you stayed at last, there must be peyote in the water. ")

Jonathanbass1990 12 saatler önce

In my view, the high speed camera solution would work. The light isn't reflected *back* at the camera because the beam doesn't originate from the camera. If you can film at a right angle from the light beam and shine the light from opposite directions, you take the distance after reflection/refraction out of the equasion

Puck Povier 23 gün önce

I think the convention is plausible because every other causality seems to be the same speed in any direction. If we speed up the objects that are causally connected, the equation in any direction allways seems to be kept up. I mean we theoretically can converge to c and maybe never see violation of this equation. But, I know there could be a weird violation near c, or something like that. Thanks for this video btw.

Max 18 gün önce

What about Coriolis force for example?

James Hancock 25 gün önce

Couldn’t you just use entangled photons and fire another at the start and hit it one of the entangled photons on the far side? The one at the start would move in opposition instantly so you’d get the one way speed of light.

Yannick Wouters 6 gün önce

Could be a very simplistic thinking but: If you setup your mirrors in the shape of a "Z" (each leg being at the same length) and measure each leg you can calculate the time difference 1 > 2 is just the 2-way measurement so you know the speed for the 2 legs. So if you do the legs 1 > 2 > 3 a 1/3 of that time plus leg 1 > 2 equals 1 > 2 > 3. Then you should know if it's the same in every direction, right? You could even expand using more mirrors if they're setup in only 2 directions, but that requires more sections to measure.

Rigel Yıl önce

Light: "My speed is immeasurable, and my time is ruined"

hypocratus 2 aylar önce

You son of a lily , take a like

goldenxande golder 3 aylar önce

slow mo guys at 10 trillon frames per second

1Mountinman 3 aylar önce

@Zhinku Nakur : this video presented zero evidence that c is not symmetrical. It only pointed out that we haven't proved that is (yet).

Zhinku Nakur 3 aylar önce

@1Mountinman this video is the most direct reference i think , assymetrical em wave propagation speed is the topic of this video

1Mountinman 3 aylar önce

@Zhinku Nakur I haven't found any information that EM propagation through space is asymmetrical. If you have a reference, please share.

Salogalaxy 29 gün önce

I think this is fascinating. I also am curious how gravity would tend to affect this. If light travels at a certain speed on earth, how fast will it travel when out in space. We know that gravity can have an effect on light, so what would the difference be? Even something that is very slight over a long enough distance could effect it substantially.

Joshua Battaglia 26 gün önce

Gravity should have no effect on the "speed of light". What you might be confusing is that gravity warps space, giving larger distances for light to travel by "bending" it around celestial bodies, but the distance is what is changing, not the speed.

Frank Van Der Steur 27 gün önce

What if.. you put more measuring spocketed rotating station wheels between the origin of the light and the mirror? Like Newton's and Leibnitz's calculus, speed differences in opposite directions would average out.

Fews News 9 gün önce

Thank you for this video. There is a way to capture one way of speed of light. Place both clocks and ur desired locations. let them run at 1 minute. see the time difference. make the faster clock slower so that both clocks gives the same reading at 1 minute. test it if the clocks are going in sync if yes. run both clock in sync let them running and capture the time on both clocks when laser touch the sensors and vice versa. check if both directions gives same reading or not. (Beauty of technology is that we can amend the rules as per our need)

Olorin Istar 3 gün önce

I wonder if there could be a way to use quantum entanglement to measure the one-way speed of light

J Mi 8 gün önce

Can't you just sync multiple clocks and then move them in all different directions and velocities and record data from the moment they're synced until they are brought back together. This would measure so many different possibilities at a time that the only thing we would have to define where we calculate the frame of reference

5MadMovieMakers Yıl önce

Mark on Mars is instantaneously fast at texting! Maybe he can observe the one-way speed of light!

Cloak and Dagger's Papa Aylar önce

@ObyX Your assumption is pretty much correct except for the fact that, as you already said that "we could synchronize clocks on all three objects ", but in reality even if we want to synchronize the clocks, we need to know the time dilation which absolutely depends on the so-called 'C' or one way speed of light which we are trying to measure. So this process according to me won't work because at the end you will get the very exact result and as long as the result remains same and the laws of physics don't break, WE WON'T BE GETTING 'C'.

Mislav Horvat Yıl önce

He did not hit the transmiter he did not hit it!

MemeYeeter Yıl önce

@Biglyp wtf man u gotta continue it proper

Rashdan Ridzuan Yıl önce

@AlmondButton lol you lose the TRvid comments

AlmondButton Yıl önce

@Biglyp lol you lose the TRvid comments

The Gunslinging Hero Gün önce

why not have an AI try to solve this issue and see the results? I'd be very interested in seeing how they tackle this question.

Alpha Hill 7 gün önce

I'm missing something in the experimental setup, because I don't see why it's an issue to synchronize clocks at a distance. Yes you'll have a delay from the synchronization pulse, but then your measurement is 2*c one-way, and not 2*c two-way.

T Baker Aylar önce

I'm thinking of a laser shining down thru holes "poked" thru disks attached to each end of the axis. Measure the luminosity when stationary. Then spin up the axis at ultra high rate; and measure for luminosity loss. May not be feasible due to weight limitations to make a motor to spin an axel with tiny disks on either end at a speed that would probably need to faster than possible. But, making an extremely small hole is possible (I worked in lithography at a FAB; ultra small holes are possible). Any how; sophisticated astronomical tools are used to determine luminosity changes of stars when determining the stars planetary makeup; and are capable of the most minute changes in luminosity. Anyhow; I'm probably missing something basic (or, designing the "spinner" is impossible to get enough space between the 2 disks (perhaps a series of aligned disks). Anyhow, measuring the static illumination, and compare it to the light loss that is not fast enough to get thru the 2nd disk, might be a way to measure?

Sophie Cooper 5 gün önce

Could you use quantum entanglement to sync the two clocks?

Pradip Rimal 12 gün önce

Nice Video. Regarding the unknowability of reality, I think you should make a video about the implication of the violation of Bell's inequalities.

Ben T. 2 yıl önce

"So someone has measured the speed of light...or have they?" Huge Vsauce moment right there

D M 11 aylar önce

What's more funny is how people are unaware that speed of light was discovered about 40000 years ago (earliest available writing is 8000 years old). It's in Rig Veda, one of the 4 vedas of sanatan dharm (Hinduism).

Franklin Dsouza Yıl önce

without synchronizing the clocks, I think I found out a way of calculating the speed in one way. Please check my comment today.

805atnora Fertsera Yıl önce

Ha!

jamie marsden Yıl önce

no we have only tried to gain a poiint of reference ie the >> 299*

Prince Desirion Yıl önce

@Shomex Shome You 're remarks are easy and good. But, light travels bringing informations, and as far we know once you break that limit information won't be carried away. From you're perspective classical physic is ok, but quantun physic would have you to be on a superposition to be right or wrong. So unless you can keep your superposition argument collapses.

sergio loza Aylar önce

That is why a journey always feels longer in one direction than coming back 😂

Kanars Gaming 5 gün önce

Which also means once it hits your retina the time it took to get to your retina is the speed of light based off it going through a light sensor and then clicking right when you see the light

Ulug`bek Jumabekov Aylar önce

Hi. I`m seeing your videos for a while now. I want to know if it is technically possible. Start from the center sync your clocks (accurate as possible) and move it to opposite directions at the speed of light (at least, close as possible) and for each end put one person and say stop the clock at the moment clock comes to you, and observer will go to each location and see the difference if any "C" for different directions will be different if not then "C" is equal in both direction.

HonkMok 28 gün önce

you should be able to measure it by accelerating mass in opposite directions. since the energy you need is dependent on how much percentage of the lightspeed you accelerate you can find out if the light speed is the same in both directions, or not.

Autarch Kade 24 gün önce

Unless the mass needed varies by direction too, making it appear the same.

A Pro Player 16 gün önce

Such mind breaking physics truths cause me to never skip any of your video.

Garance A Drosehn 2 yıl önce

I will say it's pretty impressive that Einstein realized that this was a significant issue before he started to tackle relativity.

Mike Clahsen 6 aylar önce

@Bill Lynch No, because the effect would be different every six years, when Jupiter is on the opposite side of the sun and thus the direction that the light is travelling reverses. If the speed of light were infinite in one direction then moving towards or away from a moving object reflecting light in that direction of infinite speed would not change the appearance of that object's motion, because Io's motion is affected the same way and by the same amount when Earth is moving directly towards or away from Io, regardless of the stage of Earth's orbit, the speed of light must be constant no matter which direction it travels, unless it varies depending on which direction it travels relative to Earth and only Earth.

Bill Lynch 6 aylar önce

@Ognyan Gerasimov I wondered this as well. However, isn't the establishment of the period of the moons of Jupiter by its appearance to us essentially synchronizing clocks?

Bob Terry 6 aylar önce

Too bad for him. Even old Al can have a brain fart now and again.

Ognyan Gerasimov 2 yıl önce

I would like to add that Mr Muller is not right for measurement of speed of light moving in one direction. The speed of light was measured at first, by two astronomers Ole Roemer in 1676 and James Bradley. Both astronomical observations measures the speed of light moving in only one direction. Roemer observes the eclipses of Jupier moon Io, and the observed orbital period of Io is getting slower if the Earth is moving away from Jupiter or getting faster if the Earth is moving closer to Jupiter. Stellar aberration of light observed by James Bradley in 1728, all stars makes a small ellipses during the year in the same direction as Earth orbital movement, clockwise if you look at the North pole. So astronomical observations are available long time ago and the same speed of light in all direction from everywhere is an astronomical observation fact, not a convention.

Pratik Ray 2 yıl önce

Impressive!! Is there another way to describe that man?

Luis Enrique Alfonso Rubio 2 gün önce

So, light is interesting in the sense that the paradox about measuring also will surely apply to any (I mean any) kind of measurement tool. The best synchronized clocks for this experiment are two clocks at a distance of thee photons from each other, that stills carrying the paradox: the only thing about the speed of light we know is when we measure it (C instead of C/2) I don't so much about particles, but I think they liberate a lot of energy when colliding at speeds near C. Photons doesn't carry the same characteristics: they are not tiny tiny...tiny monsters! they behave as particles and waves (as i know): so, what if photons are as small as their movement could be affected from their own electromagnetic field? they would carry the speed of traveling their own magnetic field, at colliding they lost a lot of energy, but they are traveling on their own magnetic field. They still particles, they could potentially lost speed, so much that any measurement tool will miss them. Little changes in its frequency but a huge change in its initial speed could change totally the amount of space that particle needs to travel (initial speed under C) bigger particles wont travel on its own magnetic field

Rob C. 6 gün önce

I find this incomorehensibly interested. It seems like such an easy thing to accomplish.

Kable Aylar önce

I think you missed option C. To have both clocks synchronized to a 3rd clock without the need to move the second clock to the other side of the km. I believe thats how quantum speed has been "measured". Update: I continued the video when I had time and I noticed that you mentioned it around @10:00

Sudheer acharya 23 gün önce

I’m not understood time synchronisation beginning of the video . Two clocks ⏰

Kiruba Karan 20 gün önce

If the speed is different in different directions then can we just keep varying the distance so that we can measure how fast or slow the light travels in that particular direction?

A_ManCorporation 20 gün önce

What if you place just a single clock in between two mirrors, and then shine teo beams of light in the opposite directions?

Atlas 2 yıl önce

I love when Destin is presented with something he genuinely didn't know/understand before. His face lights up with extreme excitement and intrigue.

boycycy 2 yıl önce

That moment led me to evaluate my whole existence on whether I could share something interesting enough to impress Destin that much.

AZLE Norsworthy Aylar önce

If we put a synchronizing tool in the middle of the two clocks and they were not synced up after it was sent, couldn't we immediately assume that light does move faster in one direction?

Mahogany FPV 15 gün önce

Ya but if you used the same gear setup and just rotated the entire system by 1° until you covered 360°, couldn't you figure out if the speed changes in different directions?

Tim Young 3 gün önce

To measure the speed of light in one direction, then do just that. Maybe you can measure it near a black hole, where it bends the light back to its initial starting point. Or could you use “lensing”and measure it from initial starting point maybe more accurately, one point of the lensing around a black hole back, this gives you the speed of light measured from only one direction. Very curious I wonder if there is a way to do this? Tim Young

Destroyer 11 gün önce

Would it be possible to make a laser that records exactly when it's fired and a receiver that records when it receives the laser?

Miszellleq Aylar önce

what if you turn on the clocks at the same time and move them in the opposite direction, and then measure the time delay to clock A and clock B? Then you can synchronize clocks and measure the speed of light

Jade Neoma Aylar önce

he does discuss this in the video but turning on two clocks and then moving them means they will have countering time dilations which makes it exactly the same as syncing two clocks then only moving 1

Vitor143 Yıl önce

I love that all these guys are friends and all they care about is figuring stuff out, learning and showing us.

jayspeidell 11 aylar önce

He should have called a quantum physics TRvidr like Matt O'Doud.

James Barnett Yıl önce

Maybe the real speed of light is the friends we meet along the way

Sonja Schellevis Yıl önce

@Nik hahahaha lol

Nik Yıl önce

@Sonja Schellevis yeaaaa delete your comment and then play victim, ok

Mathias DK 21 gün önce

Could you have two clocks, where you put them apart aswell, but this time the light activates both clocks, and after 1 second or so, you would send a new beam of light, which this time then deactivates the clocks?

Mike Davis 20 gün önce

could you use quantum entanglement to trigger the stop of the timer ?

simon van Rijs Aylar önce

I love these videos and the thought experiments they pose. But, should this not be able to be tested once we have interlinked communication between three or more relative bodies? Much like we can't know a 3d location without 4 GPS satellites, we can't know a 2d time calculation without three dislocated sources (or use many and damp the errors as much as possible). For relative issues could we use our local galactic stars as something to interpolate from?

Alysson Anselmo Aylar önce

you need to add an additional mirror and measure with an extra bounce. Repeat it in both directions. And finally compare the results 2AB+BA vs 2BA + AB

umanitario Aylar önce

if a slowmotion camera sees the light, at the time the direction in which the light is going is different, because the light from one point to another takes a certain amount of time, but if it is seen by the camera before it reaches its destination it means that the light is faster in the direction of the camera, so you can try moving the camera in different directions and it may be that if in all directions (except in front) it is faster the light is propagating rather than the light going perfectly straight

Varasalvi2 2 yıl önce

Your last 3 videos have been absolutely mind blowing. Relativity is such a mind bending subject and you've done such a good job explaining the basic.

Brannock Taylor Aylar önce

Here is an idea. I think the speed of light is the same in all directions. My reasoning is because of the fact that if time dialation is relative to the speed of light, that would mean if you slowed the speed of light, you would also slow down time. Time does not feel like it is going any faster in January than it would feel in June.

Jade Neoma Aylar önce

your brain processes time isn't independent of how fast time is run. Hence, if time speeds up then so does your brain and that cancels to your brain experiencing time at the exact same rate regardless of how fast time is actually moving. If you could somehow detether your brain from time than this would work but as the two are very much tethered this doesn't work.

Hugo Buss 21 gün önce

Could you have 2 sets of clocks. Synchronise all of them. Then move one start clock and one stop clock to the new location. With a preset time to trigger. It wouldn't measure the true speed. But if they were different, then the sol is definitely effected by direction.

Brian Lopez 2 gün önce

I'm just going out on a limb here and asking a question... what would happen if we launched an object into space and were able to make it absolutely still. It has a propulsion system that can slow it down and keep it from moving in any direction, then measure the speed of light on board the device. Would that work?

Kerry Hebert 22 gün önce

At the extrema of C/2 and instantaneous, looking through a telescope you would see many super novas in the distant early universe in the C/2 direction and very few in the instantaneous direction.

Sagar H P 28 gün önce

i think by using quantum entangled particles it might be theoretically possible to solve the synchronization issue and can provide a wayout of this juxta position

2ToneCapone Yıl önce

I love how he always considers variables to problems that most people would never even think of in the first place. Like the possibility that light, or a signal, may change speed based on direction. Mind blown

Michael Yıl önce

He over complicated things it seems incredibly easy to measure one way light speed

Ashutosh Singh Yıl önce

This may be exiting, but one should also consiider the Electromagnetic Theory by Maxwell !

Mrbuck832 Yıl önce

@Gordon Seal measuring it going in different directions is still a two way trip, it goes from the source to where it hits something, and then to the camera after reflecting. you just watched a video that explains this in the middle of it. it is only a convention not a hypothosis or theory, and the universe doesnt make sense alot of the time anyway so thats not really a good point. i heard a saying once that dums it up pretty well "the first thing you think of isnt always the right answer". it made sense that the earth was flat or the center of the universe before we had ways to measure why thats not the case, it could be the same here.

Mrbuck832 Yıl önce

@CGN we dont know if it does or not, thats the cool part. just as veritasium explained we have only measured the 2 way speed of light, not the one way trip.

Gordon Seal Yıl önce

@Tim Bordasch Because A) it makes no sense and B) it would be measurable by recording light going into different directions and C) it would probably break the universe on a fundamental level, if light just behaved totally unexpectable.

Ben LaPoint Aylar önce

Wouldn’t a preferred direction of light cause a difference in astronomical observations? From what I understand quasars are from the early universe so if light was instantaneous in a given direction we would no longer see objects of the early universe in that direction, but would continue to see them in the other?

Manard 9 gün önce

I think the issue is that our knowledge of the timing of said observations is based on the assumption that light travels the same speed in every direction.

Mighty Owl Aylar önce

I have an idea, instead of checking exactly what the speed of light is we can check if it is c. My idea is to have a giant wheel with a hole in each side spinning really quickly. Have a laser pointing through those holes and if the light makes it through I think you should be able to figure out the speed of light with some math

Curtis Sharpe Aylar önce

Quantu entanglement can be used as an instant signifier over distance, as per the award winning experiment, so you only need one clock. Have the laser trigger a measurement for one of a pair of entangled particles, in order to trigger the second particle. Do this multiple times, at different distances, in different orientations and you should have a verifiable solution.

Tony Wells 25 gün önce

Quantum entanglement doesn't work like that. You still have to deliberately measure the second particle.

sekkei Aylar önce

Could you try shining a very very bright light on one end of a black hole that you knew all of the characteristics of, and then see how long it took for you to detect the light? Would that be the one way speed of light then? Technically you aren't curving the light, since the blackhole is curving space. Light is moving in a straight line still.

John Burrill Aylar önce

What about syncing the clocks at halfway, then move both clocks at the same speed in opposite direction? Then both are moving relative to the stationary starting point

Phillip Ionkov 21 gün önce

it doesnt matter where you sync them because you can always look at the situation from different reference frames. even if you look at it in the reference frame where they both move away from each other, the physics is necessarily the exact same as if you looked at the situation in the rest frame of one of the detectors (i.e. one of the detectors at rest and the other one being moved away)

Thurston Bibian 2 yıl önce

What boggles my mind is people decades ago with "primitive equipments" were able to measure things, hats off to their ingenious mind

Gaston Cito 2 yıl önce

@Muhammad Syafiq Thousands??

erick g.p 2 yıl önce

@HawksNest hahhaha what you doing here

S. Muller 2 yıl önce

@Muhammad Syafiq that is the most ridiculous comment i have ever seen.

Ry Hol 2 yıl önce

The art and science of measurement is quite interesting, complicated, and precise on an insane level.

Muhammad Syafiq 2 yıl önce

People thousands of years in the future would be thinking the same of us, its just a matter of perspective

Carlos Baquedano 13 saatler önce

What if you use more mirrors (one north and one south) and for the first model arrange the mirrors to make the light travel north for longer distance and for the second model arrange the mirrors to make the light travel south for longer distance and compare the time it took for each model to complete the journey. (I'm sorry for my English)

Stef 97 11 gün önce

So moving clock ticks slow relative to stationary observers, Does that mean that by syncing 2 clocks at the same location, moving 1 away from the other and then reuniting them, you should now be able to measure an anomaly?

Dana Duarte 12 gün önce

I like how this video is all "we can't know if the speed of light is the same in all directions" while simultaneously giving a least two ways to prove it

MeboDotExe Aylar önce

if you set two clocks and have a syncing device between them, with the wires connecting them being curved around a bit so that the distance it travels forwards and backwards is equal, would that cancel out the delay? then you could send a signal straight to each of them and see if there was any delay between them

Blonkerdook 19 gün önce

Do the round trip measuring method in a square, 4 directions. Then divide by 4. Compare that speed to 2 way round trips in 2 directions

Spencer Wiltse 2 yıl önce

I absolutely love when people can take something ordinary and make us step back and see how much we don't actually know! Even if you can't confirm or prove the knew idea. The greatest discoveries are made when people are willing to challenge the status quo. Thanks for another amazing video

TheSkystrider 2 yıl önce

Measuring the speed of light doesn't seem ordinary to me even if it's the same in all directions.

Ian Tullie Aylar önce

How about those extreme slow motion videos which show light in motion. That's a one-way trip (although of course you're viewing it at an angle), and then with the experiment I was expecting you to talk about was when this two-way measurement was done 6 months apart so that the Earth's motion through space was completely different - I think it was to test the either of the "aether".

Diego Olvera Aylar önce

This is the first science video I loved to watch but hated to think of, it’s an amazing and interesting video, but I literally hurt to think of it, it’s the first time I’ve hurt to think/theorize about something and I hate that

PlSm 7 gün önce

The thing is that time dilation is not linear; it starts off really slowly and jumps up at near lightspeed. So won't the difference in time when we synchronize the clocks and move them to their new location be very small, and enough to notice a difference in speed?

Johnlongears 7 gün önce

when you are measuring in fractions of a nanosecond, it is enough for there to be a difference, and if you are just assuming the difference is not noticeable, then you are not measuring the exact speed of light, you are measuring the relative speed

Robert 19 gün önce

Could we use quantum entanglement to create two clocks that are independent of distance and measure the one-way speed of light that way?

Ralor Penwat Aylar önce

I'd like to put forward one reason it seems unlikely to me, and others lightly touched on it, but I'd like to expand on it. Though I'm admittedly quite possibly missing information. So firstly, I think we can all agree with the idea that if light speed directionality exists, it would almost certainly not be relativistic itself, as in, it would not be dependent on going towards or away from the observer as then it would be impossible to consolidate that. Taking the c/2, ♾️ example, that would mean that for both parties, sending data would be one, and receiving would be the other. Following normal conversation dynamics, let's assume that sending is slow, receiving is instantaneous. This means that causality itself has to be broken, as you will be receiving a response that would be sent slowly instantaneously, meaning that information was obtained faster than it was sent. Even if this were true somehow because of quantum mechanics, which seems unlikely, it seems even more unlikely when you consider this would be happening without leaving evidence. No sort of interference patterns or anything. Going forward with this (admittedly very possibly flawed presumption), we would expect a distortion of the universe from our perspective, a very clear break in uniformity. Be it from the distribution of distant space objects, the CMBR, or redshifting and blueshifting, spectral analysis, or some combination of these data sets, no matter what, somewhere we would be perceiving one-way information from the favored direction, which should meaningfully change things.

noob_techie 7 aylar önce

I know its not enough but I would like to take out a moment and thank veritasium and all other similar channels like vsauce, numberphile, etc for the amount of research they do and provide us with such awesome informative stuff that is thoroughly backed by research and study and is not just hypothetical stuff or rumors. Also, the amazing presentations that they provide that make science so easy and fun and intuitive compared to text books. For all I can say, thanks a lot guys, and keep up the good work!!

noob_techie 6 aylar önce

Numberphile is a really nice channel for maths, do check it out

Don’t Know What Name to Use 6 aylar önce

lol i think its sciencephile not numberphile lol

TheDoomFan2004 🇰🇬 6 aylar önce

Never heard of numberphile

Michael Scarpelli 2 gün önce

Maybe 2 lasers facing each other, both measuring the incoming beam and their own reflecting beam in time sequence of several firing for synchronizing the time difference, not the time they are fired. It will either show that the light is moving at the same rate or that there is a difference. You are measuring both a round trip and a one way trip at the same time.

P Th 16 gün önce

If the speed of light differs per direction than we look at stars in the past at one direction and stars of the present in another direction. Which means if something is about to hit us from that direction, it will arrive faster than our calculations say. 😉

Lika a Boss Studio Aylar önce

have two clocks in the center synced, place them on a spiral turn table and rotate them around the start center point as they move away from each other. when they reach the required distance stop them moving away from each other but continue to rotate around the starting point. take readings every few degrees and see if there is any variation easy.

Jade Neoma Aylar önce

reading the clocks either requires you to move and be affected by time dilation, or see the clocks and be affected by the speed of light. neutralising any difference between the clocks

Sarmed Alwan Aylar önce

Do you mean that it might be 2c in one direction and instantaneous in the other direction? c/2 and instantaneous wouldn't make sense, unless I'm misunderstanding. Also I feel like a lot of big structures in the universe would fall apart if c wasn't symmetrical, but I'm not sure.

Kishi 27 gün önce

Just use the two clock method but find a way to calculate the time difference due to moving the two apart. It should be calculable

Noah Friedman 2 yıl önce

If the speed of light were not the same in every direction, then wouldn't the cosmos look very different in different parts of the sky? For instance we would look in one direction and see early quasars and a warmer cosmic microwave background, and in the other direction see nothing but red dwarfs. Of course, the universe might not be isotropic, but if it isn't then we have bigger theoretical problems.

frootloop edibles 10 aylar önce

Exactly what I was thinking; though I think that only rules out extremes in the difference of one way c, right? It could still vary by just a smidge, I guess. Since the CMB we observe is fairly homogeneous, I feel like that would have to mean c is, too.

Noah Friedman Yıl önce

@Ripcord I don't think anyone really believes the speed of light differs in different directions, but Relativity implies there's no way to prove that, unlike in a Newtonian universe where time is absolute everywhere. In a relativistic universe, I think the combination of expansion and isotropism provide good empirical evidence but there's no local experiment you can perform. And if the universe turns out not to be as isotropic as we think it is, that makes the case even weaker.

Jake Zee Yıl önce

@Thomas Horne you miss the major problem with the theory. The universe is expanding in all directions evenly (based on our perception). If light travelled differently in different directions that would mean catastrophic things for the universe, and would make the problem of what the universe really is a lot more complicated than it already is. Because you are basically saying, "no the universe doesn't look like it's expanding because the amount of light reaching us is equal on all sides, it looks like it's expanding because it literally is magically expanding." Just think about how dumb that sounds and try to still believe what this video is saying. Take some advice from a photonics graduate. The guy couldn't be more misinformed. If you are genuinely curious go study photonics too.

Jake Zee Yıl önce

@Siddhant Kanoi no, they can't elaborate because they didn't think before they commented.

Andy Hengst Yıl önce

We don't know anything first-hand about the distant universe. We also don't know, with certainty, the behaviour of light that is a million years old. Maybe we need to get a distant probe to get closer (or farther) from the gravity-lensed supernova that we expect to see again in a few months? years?... and take measurements. Unless we can't synchronize our clocks. Uh oh.

Clan shinko offical 26 gün önce

can't you just do the dual clock test twice but the second time you swap the laser and timers positions, in order to find if light goes the same speed both forwards and backwards? Just see if the delay is the same and boom

brnmcc01 Aylar önce

You can get two extremely accurate atomic clocks. Put them both together and sync them. Have each one transmit a radio "tick" each second. The tick would have to be a very short duration and strong, like a single spark. Put a receiver a precisely measured distance away from the pair of clocks. Start moving the two clocks apart. If there is any difference in the "tick" it will sound like a double tick at the receiver. Even if the 'tick' is like only 1 nanosecond apart. Once the two clocks are a significant distance apart, start moving the receiver to different locations. If the speed of light changes, then the measured time from each one will change, this can be double checked with simple triangulation from each clock to the receiver. For example one could move the receiver to a 3rd location that is in a straight line from the two transmitting clocks, and then move to the opposite end of the pair of clocks to check if the signal speed changes. However, I think if the speed of light wasn't constant, then the whole constellation of GPS/Glonass satellites would be off. We could also use something astronomical like the transit of mercury across the sun to synchonize two clocks one here and one on Mars. Then once the clocks are synchronized, measure the message delay from earth to mars, and then mars back to earch like the example shown in the video. Since the distance between Mars and Earth is in the order of 10 minutes +/-, this amount of time is way beyond the accuracy of even a cheap quartz watch so it would be obvious if the transmit time was instantaneous.

Jade Neoma Aylar önce

the ticks would travel to the reciever at the speed of light so they would both be heard at the same time even if the speed of light wasn't equal in both directions. the one that is ticking slower due to the time dilation would make up for that by the radio signal travelling faster

Alex Spittel 5 saatler önce

What about splitting a light in two, shot both a far distance, one hits a fluorophore, and the other bounces of a mirror and travels back hitting a fluorophore at the start. Assuming that both fluorophores react the same you could measure the time difference it took to light them up. Even if the Fluorophore takes a second to release light, if both are the same, the difference can be calculated

Nate Wronski Aylar önce

Let’s say a firework explodes halfway between two observers. You could measure the time between when the light was observed and the sound was registered. If the one way speed of sound can be verified to be the same in both directions in a separate experiment and the observed delta between the light and sound was also the same for both observers in the original experiment. It could be concluded that light travels the same speed in those two directions.

Peter 10 gün önce

@foljs you would use this information in combination with the original proof that shows the round trip time. If we know round trip time and know the speed of light is the same in both directions then we know the one-way speed.

Peter 10 gün önce

I think that would work perfectly. You could also have a line of 3 towers in a vacuum that are equally spaced. The center tower fires a laser to the outer two towers which are both rigged to fire a paintball gun back at the center tower when the light signal is received. Then you measure the time between impacts. If this is done in orbit then you maybe have to account for gravitational differences but you should be able to rule out gross asymmetry.

foljs 20 gün önce

It's not about conclude whether the speed of light is equal in both directions. We can conclude that all we want. It's about measuring the speed of light itself. The delta you observed wouldn't be able to verify any speed-of-light level time differences.

Sharpnetic Aylar önce

Just measure the shape of the observable universe... Oh, you do it with light? It will appear like a sphere!? This is the most fascinating and brain-hurting video I've seen! Great Video! ❤

Jack Hagerty 2 yıl önce

Dude! Your cinematography is killer! The shots of you on top of that hill with the Belt of Venus visible in the sky was positively cinematic!

Strange Man Yıl önce

If using not 2 timers, but 3 timers. Possible to get real speed)))

Adarsh Venkateswaran 2 yıl önce

Yolo 2.0 This should be fun.

Zach Wilbert Aylar önce

What if the clocks were synchronized before mark went to mars? Then when Mission Control said it was 12:00, and mark got it at 12:20, he could respond saying that so when the message arrived on earth if it was 12:20 then light speed would be instantaneous on the return trip but if it said 12:40 then it would be the same speed in both directions

Jacob 13 gün önce

I have two ideas - One is to shoot two lights at each other from a distance and measure where they collide, if light travelled at different speeds in different directions, the collision point would be further from one end and closer to the other. I would imagine this has already been done? Other would be to have something mechanical activate each clock so there is no delay. Something like a mechanical dial with solid arms connected to it to start both clocks at the exact same time. I didn't read through all of the comments and I am just coming around to this video so I apologize if this has already been talked about. Really cool stuff here though!

Jacob 13 gün önce

@V2AFHNF There should still be some way to measure when both meet, amount of photons or something increasing at said point?

V2AFHNF 13 gün önce

Light does not collide

D Reed Aylar önce

You can increase your confidence somewhat by repeating the experiment in different directions and locations on a round body like earth and see if you ever get another measurement.