Why The Speed Of Light* Can't Be Measured

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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.
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"

Dane Villarreal
Dane Villarreal 2 minuter sedan
What if you did a laser and clock experiment in both directions and if you get a different number each time then you know that one direction is different and therefore C is not same in all directions
Daniel Robert Herr
Daniel Robert Herr 2 minuter sedan
Thanks for this....
Dane Villarreal
Dane Villarreal 13 minuter sedan
Why don’t you just move the 2 clocks away from each other 1/2 km so they both move the same speed and distance keeping them synced?
Stephen Albarran
Stephen Albarran 24 minuter sedan
What if you simultaneously pass light through a medium (like water) that slows down c and a vacuum one way, compare the difference in speeds, then repeat the experiment going in the other direction and compare the differences of the differences? It seems to work out for me, but please tell me where I'm wrong! The only way there could be the same difference is if c is the same in both directions. However, this experiment would only work if the medium slows down c proportionately to c (% change), not if it slows down c in an absolute way (by 500,000 m/s in all directions, for instance, which would be very weird). Let c be Einstein's conventional roundtrip average of c between points A and B. Let S be the absolute difference in c traveling through a vacuum and a medium. Let m be the proportion of c traveling through a medium to c traveling through a vacuum. Let d be the true unknown difference in c going from A to B compared to c going from B to A. Let S1 be for light traveling from A to B, and S2 be for light traveling from B to A. If Einstein's convention that c is the same in all directions, then S1 must equal S2, i.e. d = 0, when m is proportional to c. Math where m is proportional to c: S1 = (c+d) - (c+d)(1-m) = (c+d)[(1-(1-m)] = (c+d)(m) = cm + dm S2 = (c-d) - (c-d)(1-m) = (c-d)[(1-(1-m)] = (c-d)(m) = cm - dm S1 = S2 --> cm + dm = cm - dm --> dm = -dm, only if d = 0 and c is symmetrical in all directions Example: Assume we conduct this experiment and c actually travels at different speeds in opposite directions. For instance, assume c from A to B is 400,000 m/s and c from B to A is 200,000 m/s in a vacuum, or d = 100,000 and Einstein's conventional c = 300,000. Assume that we know from previous "round trip" experimental evidence that the medium slows down light by 10%, or m = 10%. As such, we would find that: S1 = (300,000 + 100,000) - (300,000 + 100,000)(1-10%) = 40,000 S2 = (300,000 - 100,000) - (300,000 - 100,000)(1-10%) = 20,000 S1 != S2 --> 40,000 != 20,000, therefore c has directionality and is not symmetrical in all directions. If we get results like this, we would prove that c has asymmetrical speeds depending on the direction it's traveling, right??? I must be wrong about something because many greater minds have surely thought of this already. And just for fun, here's the math where m is absolute, which, if true, would mean the experiment wouldn't prove anything new about c. S1 = (c+d) - (c+d-m) = m S2 = (c-d) - (c-d-m) = m S1 = S2 --> m=m, true for all values of m If I'm right and you win a Nobel prize, just thank Veritasium for the inspiration and donate the money to charity. ;-)
not who you are
not who you are 30 minuter sedan
Two things come to mind. 1. If it is half c on the initial trip to the object and instantaneous on the return. This would help explain the "red shift" 2. Maybe what we know as light is merely just a "shadow" representation of energy on a higher dimensional plane. Edit: could we somehow use quantum entanglement to measure the time? Have the laser agitate one side as it passes through, immediately notifying the other side, then have it agitate the end, immediately notifying the beginning. Edit 2: what if it is instantaneous both directions on a higher dimension but it takes time to process it. Kinda like a sphere passing through a 2d field? I've stopped making sense. Sry
93sikky 32 minuter sedan
Interesting video. (1) Light is also an electromagnetic wave and thus obeys the Maxwell equations from Electrodynamics. In Electrodynamics you have (well-defined) field constants which only depend on the properties of the materials through which electromagnetic fields pass through. From the Maxwell equations you can show that these field constants are related to the propagation speed of the electromagnetic wave via: v = 1/sqrt(epsilon * mu), where epsilon and mu are the material-depend field constants. Since light is an em-wave (there is various proof of that) it follows that c = v from above. Especially from this you see that the speed of light in vacuum is direction independent. (2) In your video you yourself mentioned that for the speed of light being direction depend there has to be a property of space in order to impose such an dependency. After getting know that light is an em-wave, over 120 years ago it was thought there has to be a propgation medium for these waves (as for waves in water). Therefor a background field, the so-called Äther, was introduced to be this medium and in general it could have a non-vanishing relative speed to objects (the so-called Äther wind). Due to the Galilei-addition of velocities this would lead to an direction dependent propagation velocity of light. How ever Michelson and Morley showed in a very famous experiment that this Äther does indeed not exist (or equivalently that the Äther wind is always everywhere zero - see Michelson-Morley-Experiment). This lead to the formulation of the Lorentz-transformation and thus to Special Relativity. (3) There are further various fundamental reasons why the vacuum speed of light has to be a universal constant. In Physics there is the homogenity, isotropy and relativity of spacetime (i.e. the laws of physics are the same everywhere in the universe and it does not dependent on in which direction I look from any position). The formulation of modern physics is based on these properties. And of course in general there is no strict proof of that but violations of these would be detectable e.g. in particle physics experiments and in fact that is what it is searched for (for example the search of so-called CPT violations which would indicate the violation of relativity). Hope this helps. Cheers
Roxy Lindholm
Roxy Lindholm 58 minuter sedan
Maybe I'm making myself a complete fool here, and maybe this can't be done in reality, but at least theoretical, which won't be helpful, wouldn't it? So my idea is to make use of quantum entanglement. Let's say we can make a particle "A" changing its spin every second, that means its entangled counterpart "B" is changing instantley its spin every second as well in the opposite direction. (At least, that's how I understood it) We put the first particle "A" at the first clock and put its entangled particle "B" at the second clock. Now we measure the speed of light with two clocks as described in the video. In the video, it has been said it is not precise, because of time dilation when moving the second clock. The trick would be to move that second entangled particle "B" with that second clock. Because this second particle "B" remains always in syncronicity with the first one "A", we must see, that this second particle "B" does not change spin in that one second periode according to the first clock, but it would according to the moving second clock. Am I right? If we only knew the second clock and observe our particle "B" spin, could we tell our time dilation this way? So we had a time stamp coming from the entangeled particles, which could be included in our light beam measurements, in order to calculate out that dilation from moving the second clock. Sorry, hard stuff anyway and english is not my native language. Hope this doesn't sound to stupid
Jakob Gabriel
Jakob Gabriel Timme sedan
I just thought about this. Let me suggest follow constellation (similar to the origin experiment according to Fizeau-Foucault). You have a rotating cogwheel in a distance of 10 km (or whatever). The rotating cogwheel is different. You have instead of a tooth, you have an area with an mirror (which reflects the light) and you have variantly an absorptive area. Now you start rotating this cogwheel with a slow known rotating speed. Your light source is also not a continious source, it is a laser with short pulses (nano or better femto seconds with known pulse length and pulse repetition frequency). Now to the tricky part. You know start to accelerate the rotating speed (this must be preciously and known to the Signal Generator. The result, when the first puls will be absorbed, is independent of the direction. Of course to see the result is still 2 times the distance, but it doesn't matter, because you only "measure" in one direction. Do I have made a mistake?
Frazer Kirkman
Frazer Kirkman Timme sedan
What if you had a laser at both clocks, and took a measurement in each direction.
Zack Coenen
Zack Coenen Timme sedan
Doesn’t bent space time around planets and things like that effect the speed of light
Jacob Romano
Jacob Romano Timme sedan
What about figuring out the time of the signal between the end clock and beginning clock. Then set two timers on the end clock. The first timer would be to tell the clock when to start. Therefore having both clocks starting at the same time.
Wander The World
Wander The World Timme sedan
What if you had 2 clocks that were synced by a clock that was at an equal distance from the other two. Say in a triangle formation. Then the 2 other clocks, now synced up with each other because they both share a reference point that is the third clocks signal. And maybe check if there's a difference if the triangle is equilateral vs not equilateral. That being said, I've often thought of how the universe is expanding so light will get a boost going one way and have to "go against the current" coming back, and every variation between that depending on where the center of the universe actually is, which coincidentally happen to be right where I'm standing.
PressRecord 2 timmar sedan
1. Build two clocks, both of which will instantaneously reset upon receiving a special RF pulse, and place them 1km apart. 2. Transmit the RF pulse from the apex of a triangle equidistant from the two clocks*. 3. Voilà, clocks synchronized. * The further the better to maximize angular coincidence, and thereby reduce any possible directional-temporal asymmetry.
Ace _
Ace _ 2 timmar sedan
So why cant you take a clock from earth to mars to tell the same time i know theres a reason but cant tell why
JDM forever
JDM forever 2 timmar sedan
Next video, 🤔how fast is warp speed
Edward Feldman
Edward Feldman 2 timmar sedan
Starting clock A as soon as the light goes through and starting clock B as soon as the light goes through, then stop them at the same time (potentially hours later). A-B/1km = c. Alternatively you could sync up the clocks by standing directly in the middle of the clocks and putting out a signal (using light) to each clock (to ensure light didn’t prefer one direction you would have to repeat experiment by setting clocks up in different positions, and changing which clock was the start and which was the end)
Squizei 2 timmar sedan
ive got no academics whatsoever so feel free to prove me wrong and explain why it wouldnt work, but why not have two experiments? two one-way trips? that way, if the times are different, we can determine that light moves faster in one direction than the other? i may be missing a crucial piece of the puzzle but its 8:30am
S Ali
S Ali 2 timmar sedan
You have simply ignored or forgotten what if your entire apparatus including the distance between the distant clocks is in a region of space or on Earth which has different gravitational pull than that in other regions of the space or earth or your experimental platform is close to a black hole. :D Or there is an unseen higher dimension bubble between the distant clocks trapping the light for sometimes in it like a diamond. Visible light ? Red or Violet? :D
Leslley Scotte
Leslley Scotte 2 timmar sedan
Retro reflectors. They bounce back on the same beam in the same atmosphere.
Lee Carrillo
Lee Carrillo 2 timmar sedan
Well that would explain why the universe expanded so fast. Just kidding I don't know what I am talking about. My mind is blown. You truly are the Morphious of physics.
TehWeirdo 3 timmar sedan
I don't understand what the issue is with the one at 2:30, if we can get the delay from subtracting the two numbers, and that delay is equal to the speed of light, isn't that a way to calculate the speed of light?
Boris 3 timmar sedan
So the whole thing makes no difference we can measure...
Jonathan Araujo
Jonathan Araujo 3 timmar sedan
Well if one way of light were instantaneous couldn't we see past the observable universe tho?
An Other Wolff
An Other Wolff 3 timmar sedan
The Speed of light can be measured. Scientist did it so many times.
An Other Wolff
An Other Wolff 3 timmar sedan
type in you internet search machin or take a good science book: "how to measure lightspeed"
Heefie 86
Heefie 86 3 timmar sedan
just a theory, but if you took a beam and split it, bounced them off a mirror with one mirror being twice as far, and checking if the time difference was divisible by 2; wouldn't that prove one way or the other?
EraPrestigeX 3 timmar sedan
Say we use the directions of earths polarization to defime direction, but we do so in space. In this case I would be looking 'north' which is the 180⁰ opposite of 'south'. If I use the two way measurement method in my 'north' facing orientation, then use the same method in the 'south' orientation, and then get the same exact numbers, couldnt that disprove that light has a preferred direction of travel in the universe? Furthermore, what if this was done in all infinitely possible 3 dimensional directions, and then came out with the same values. Wouldnt that imply that, within a vacuum, light-speed is a constant? At this point, what logical reason would we have to assume that light would have any reason to return the journey instantaneously. There would be no purpose to that. Finally, I do not believe that a two way measurement can ever be truly accurate because, and I may be incorrect about this, wouldnt light lose energy when bouncing off the mirror? Even if only a little bit?
Scott Huddas
Scott Huddas 3 timmar sedan
Can you work with quantum entanglement to use two entangled particles to synchronize the clocks?
James 3 timmar sedan
What if in the Mars example, just fly Mark home after sinking the clocks. If the speed of light is different in different directions, and Mark’s clock is 10 mins behind, wouldn’t we be able to check that after flying mark back to earth?
Jeffery Talosborn
Jeffery Talosborn 4 timmar sedan
So if we can't assume that the speed of light is the same based on direction, are we assuming that it is accelerating, or decelerating? If so, what forces are acting on the light to do this? To me, it seems impossible that light is instantaneous in certain directions, because, as far as I am aware, there are no cases of these tests on light being instantaneous, they always make it in some amount of time. Consider this comment an open discussion thread.
Shugar Kane
Shugar Kane 4 timmar sedan
Why talking about direction without defining it? All your "different directions" are all just direction pointing at the light source/observer and directions pointing away from the light source/observer. So if a point of light is emitting light all around, there's a chance that light will travel slower to some place where the observe is not located ? Which "direction" is that then?
Jacob Autrey
Jacob Autrey 4 timmar sedan
Hi, what if for the clock idea you had both clocks and just shot two beams of light. The first clock would start when beam (A) and beam (B) are first launched. Beam (A) would follow the normal route, heading to the second clock and reflecting back to hit the first clock. Beam (B) would go off and hit a second mirror that is the same distance as the second clock, positioned to reflect towards the second clock. As beam (B) hits the second clock, stopping the timer, beam (A) should hit the first clock. Would this be able to give you an idea of what the single trip speed of light is and show you the difference between the two if lights speed is not constant? Idk if that makes sense but cool vid 👍
Charlie 4 timmar sedan
Interesting topic. Its irrelevant until we can prove it. By proving it, it may be an accident in another experiment. Happens all the time🤣
Chach Wa
Chach Wa 4 timmar sedan
Dis hewts my bwain i fewl duhmer
Mj Ogundeyi
Mj Ogundeyi 4 timmar sedan
Correct me if I'm wrong. But why cant we test this? We have objects that have passed Mars. Or we could send a unmanned probe to Mars and have it designed to record how long it took for a message to be received from earth.
Alfons Gunawan
Alfons Gunawan 4 timmar sedan
Can light slows down in space, then finally stop?
Soopa Poopa
Soopa Poopa 4 timmar sedan
In order to prove that quantum entangled clocks are synchronized, you could have two identical clocks that are at any distance and use some sort of quantum entangled remote controller-Esque device that tells these two clocks to turn on at the same time, and after a little amount of time passes you can turn tell the two clocks to stop, using that same quantum remote. Then you could mark down the times the clocks say after you stop the clocks and if the times match then you have proven that the clocks are synchronized. (Note: for this example to work properly you must not be observing the clocks when they are activated). you could test this at multiple distances with different observer circumstances. for example, you could have two clocks right next to each other with one observer who is in the exact center of these clocks to the very Planck length and has both of the clocks in view and then repeat the experiment. you could figure out if an observer has any effect. also, you could have the observer in different positions with respect to the clocks to see if the time the clocks are observed has any effect. Then you could figure out if these clocks are synchronized, and if the observers truly have an effect on the end result.
reality check
reality check 5 timmar sedan
Just ummmm what bnov how why
tyler mills
tyler mills 5 timmar sedan
What if we sync up to the clock on earth and the one on mars then see the difference when the clock returns? Would that work or be affected by special relativity? And if so would we be able to determine how off it is?
Alexander MacKenzie
Alexander MacKenzie 5 timmar sedan
I know Veritasium said that the most extreme version was that it was c/2 in one direction and instant in the other direction, but has that actually been shown or is that just assumed? For example if we use the earth-mars transmission scenario it could be that it actually takes 30 minutes from earth to mars, and -10 minutes from mars to earth. The logic would still work out: Earth sends signal at 12:00 Mars receives it at 12:30 and sends reply [marks it as 12:10]. Earth receives it at 12:20.
Jay Hu
Jay Hu Timme sedan
There are problems and paradoxes of causality if you propose negative times. In your example you have earth reading the message from mars before it is written, which is impossible.
Nightowler 5 timmar sedan
First if speed of light was infinite in one direction then wouldn't we have a weird area in space where when we look farther and farther the stars seem same and not necessarily newer (and never see things from starting pf universe)? Also what if you have two clock A B but you synchronise with another clock C where C sits away from A at a distance AB (not towards B and inline with AB) and do the experiment and then repeat the same experiment but C sitting now away from B at the same distance AB (again not toward A and inline with AB). Wouldn't you see some sort of difference in both the experiment if the speed of light depended upon direction?
Nightowler 5 timmar sedan
Wait I got it, the experiment wouldn't work. I'm dumb
Zachary Hardgrave
Zachary Hardgrave 5 timmar sedan
just make it reflect twice instead of once so you can see if its different the third time boom btw this is a joke i dont actually think this would work
Drew Schwartz
Drew Schwartz 5 timmar sedan
What if we put a laser and clock on a rocket. Then fire the rocket towards the moon. While the rocket is at a constant fast speed we send the laser to the moon and time how long it takes to return. The light would travel further towards the moon and shorter on the way back. So we can tell which leg of the trip light went slower or faster based in the result being faster or slower than C. Would time dilation on the rocket ruin the result?
Chi 5 timmar sedan
14:08. Different speeds of light in different directions? All I can think of are birefringent materials. The refractive index of any given material is measured in relation to its value in vacuum. Are you saying that vacuum is birefringent?
Vince Slime
Vince Slime 6 timmar sedan
i can get with this
Jedi Master1976
Jedi Master1976 6 timmar sedan
I have a solution
Jonathan Farmer
Jonathan Farmer 6 timmar sedan
So is light subject to the rules of entropy? Can lights speed be unmeasurable due to the direction of time?
Frank Moran
Frank Moran 6 timmar sedan
But why would like be instant in the return? If that was true, would that imply the speed of light is dependant on where it's sent, when and why?
Halit Özgür
Halit Özgür 6 timmar sedan
svfrom.info/history/video/gsulqqWbnrN_l5k The guy finds the speed of light using standing waves. Does that mean we know the speed of light?
will 6 timmar sedan
maybe something to do with energy, the more the two travel times are synchronized, the less energy detected.
tycoon whibbey
tycoon whibbey 6 timmar sedan
Atomist. Senseless. Broken logic. The speed of light is a rate of induction.
keith kiminsky
keith kiminsky 7 timmar sedan
keith kiminsky
keith kiminsky 7 timmar sedan
the have slow motion cameras that can see photons travel thru space now
John Wing-Wessels
John Wing-Wessels 7 timmar sedan
So when you say the speed of light... do you mean red or blue? Or white.. red is the fastest ofc but what about in a vacuum, or in an atmosphere, with all these variables gone unchecked, "speed of light" seems highly unreliable.
Uru Sledge
Uru Sledge 7 timmar sedan
This video is actually subtly but extremely narcissistic.
Uru Sledge
Uru Sledge 7 timmar sedan
Doesn't this assume the speed of light is about light?
Gilder von Schattenkreuz
Gilder von Schattenkreuz 7 timmar sedan
Thats the Biggest rubbish I ever heard. 1. Why the Hell would you Sync the Second Clock using a Lightwave Cable? Just use a frigging Electric Signal with a Speed You know. Alternatively use a different method whose Speed we know. You could effectively have a Railwaycart travel at an accurately set Speed for a Predefined Distance before it Starts the Second Clock. That Distance would Equal a preset Time hence no light involved for Syncing the Clock. 2. Why would you need to clock this in a Single Instand ? You can have the Setoff Remotely. Meaning you set the Light Emitter Clock to Emit a Lightwave after 10 Minutes. Then you. With a Clock also set to 10 Minutes which Started out Synchronized. Move to the Target Point. After that. You measure the Difference between the Light Impact and your Stopclock. If your Theory is Correct and Clocks get slowed by exactly the same Speed as Light. There would be no Difference. 3. Option 3. Just use a known Speed to remotely Trigger the Light. Position the Only Clock at the Impactpoint. Then send an Object with predefined Speed to activate the Light. You know exactly how fast the object Travels. Hence you dont need a Synced Clock at all. 4. Use a Radio. We know how fast Radiowaves Travel. We also know how fast they come back. So setup a Radio Emitter that you can remotely activate via Radio but also via light Impulse. Now Activate it once via Radio and Measure the Time. You now have 2 Way Radio Wave Speed. Then use the light to trigger the Radio. Bam. You have 1 way Radiowace + 1 way Lightwave Time. Not sure whats Supposed to be Difficult about this.
HeLL HoRZe 8 timmar sedan
You have 2 clocks that are set over entanglement, light travels from A->B, hits the opposite end, triggering the clock at B , because both clocks are entangled they both are updated at the same time irrespective of distance....would that work?
Mark M
Mark M 8 timmar sedan
My real takeaway is that two clocks, regardless of precision, will never be truly synchronized. This explains why I am frequently late.
Bobby Shrimpton
Bobby Shrimpton 8 timmar sedan
Light travels different speeds in different directions? Me smellum big bullpoopie.
Alex Smith
Alex Smith 8 timmar sedan
What if you set off two clocks and lasers in opposite directions using a mechanical switch/lever from the centre of the two devices?
Aldarones 9 timmar sedan
If light was instantaneous one way wouldn't that object emiting that light never disappear? Even when outside of the observable universe, I mean, with this the observable universe would be different and not really like a sphere, the point is, light tends to get more "red" the more distance it covers, but with this it shouldn't happen that right? I mean, it should appear like it's just in front of us no?
Clarissa Smith
Clarissa Smith 9 timmar sedan
What about with clocks synchronized using quantum entanglement?
Jonathan Ho
Jonathan Ho 9 timmar sedan
According to hubble's law, all distant objects become increasingly redshifted due to the expansion of the universe. If the speed of light were faster on one side, celestial objects to that side of earth would appear less red shifted, and objects on the other side would appear more red shifted. This is of course assuming that the expansion of the universe is symmetrical. I'm not a physicist or astronomer, but I have never heard of such a pattern.
PucK3001 9 timmar sedan
Signal/Local times: 12 : 00 @ 12:00 12 : 10 @ 12:10 12 : 20 @ 12:20
CaptainK 9 timmar sedan
What if yo used quantum entanglement which is instant to sync the clocks?
spaceminers 9 timmar sedan
Put the entire laboratory test on a merry-go-round silly. Run the test repeatedly over and over and then spin the merry-go-round. If you see a change in the speed of light as it is rotating then you will have your answer as well as the direction of flow. Maybe you’re detecting frame dragging effects.
Eric Zhang
Eric Zhang 10 timmar sedan
Mr Eboric
Mr Eboric 10 timmar sedan
It gets even more complicated when you think about observation. Just looking up collapses the wave form and can potentially effect what happened to the light millions of years ago. Try cumming up with a mathematical solution to explain all those unknown variables.
kn6ft 10 timmar sedan
My head hurts....
Precision Lead Throwing
Precision Lead Throwing 10 timmar sedan
Challenge to youtubers - make an experiment demonstrating that increasing the concentration of CO2 in parcel of air from 00.029% to 00.038% has the effect IPCC claims and that it will bring the temperature up by the IPCC claimed amount of ºC WITHOUT increasing the energy input.
Yours Truely
Yours Truely 10 timmar sedan
So send the local send time with the message. En when you send it back do the same. Checkout albert michelson Het did some experiments.
RG Media
RG Media 10 timmar sedan
hmmm so if c is expected to be the same whether it's pointed N to S or S to North for example, then if you turn it 90 degrees to the E to W direction, wouldn't the measurement "HAVE" to be different because you turned it into a completely different direction?
felix lemaire
felix lemaire 10 timmar sedan
Couldn't they use two mirrors ? The light starts from the clock and go towards mirror 1, bounce towards mirror 2, bounce back to the clock. You do it once from clock - mirror1 - mirror2 - clock then you do clock - mirror2 - mirror1 - clock. Then you compare the two, the time to go from clock to mirror is the same for both but the mirror1 to mirror2 is inversed in each essentially allowing you to compare the time it takes to go from mirror 1 to mirror 2 and the time it takes to go from mirror 2 to mirror 1. Edit: that wouldn't allow us to calculate the true speed of light since for all I know the acceleration probably is not instantaneous but it would allow us to see if light has different speed based on the direction its going towards
ny4rlath 10 timmar sedan
Why can't you send light from A to B, and when B is hit, send a signal back to A with something you perfectly know the speed (by wire, soundwave, ...)? You then substract the known time (B to A) from the total, and you get the one direction time. I don't get where the problem is...?
Jakub Borowski
Jakub Borowski 10 timmar sedan
Cant you fire a laser beam around a curved space time so it comes back to the same clock without being reflected?
Stephen Albarran
Stephen Albarran Timme sedan
That could work if you assume the asymmetry of c is only related to spacetime. It could be that there’s another field (did someone say “ether”?) through which light travels that causes the asymmetry. If this is true (I really don’t think it is), then it would mean the curved spacetime would effectively be a round trip.
potatobearkelm 10 timmar sedan
I think I thought of one way: You have both clocks start in the middle, start at the same time, then move away from each other at the same speed. Why would *this* not work?
Yours Truely
Yours Truely 11 timmar sedan
OK redo the video on gravitational waves
Dominik Joder
Dominik Joder 11 timmar sedan
What about this? Combine the mirror experiment with a high speed camera. I will see the laser beam going from left to right and back (so only on the x axis, measuring like the baseball). If we measure the time until the light is back on the left, we don't know if the speed was equal in both directions. If we see the light via deflection in the high speed camera, this might cause the uncertainty (so it would be the fault of our y axis). But since the direction towards the camera does not change, if the light appears in the same speed from left to right as in the opposite direction, we are least know that the speed is symmetrical on the x axis.
ᅠXenockz 11 timmar sedan
What if you sent an astronaut into space with the order to send a signal back to mission control when he reaches 1 light minute away from Earth? You should be able to predict when he will reach 1 light minute away, you should be able to figure out if light is traveling faster or slower in one direction, as you should be able to accurately predict when the message should get to you. So let's say the astronaut is expected to get to 1 light minute away at 11:59 as predicted by his motion after the engines were shut off. Should light travel instantly, you would get the signal from him at 11:59, if it were c, at 12:00, 12:01 if c/2, and anything in between. I might be stupid though, but this does seem like a sound way to figure this out since you're only getting the signal from him based on his surroundings, not you sending him a message and getting the two-way problem.
Jonas 11 timmar sedan
How would a non uniform speed of light effect things like interference of two waves of light and other wave like behaviour of light? As i understand it we could infer if a forward moving wave had the same wave length as a backward moving wave by seeing if they can destructively interfere. And we could check if a forward moving wave had the same frequency (and due thus the same energy) as a backward moving wave by seeing if they can excite a particular atom or get absorbed by a material with a particular bandgap. And then we could get c from the combination of wavelength and frequency. I wonder if these things would still work with a non uniform speed of light though likely our understanding of the wave mechanics of light would also need to be be adjusted in case of a non uniform speed.
Ben Keyte
Ben Keyte 11 timmar sedan
Couldn't we look at the age of stars in different areas of the sky?
lixo999 11 timmar sedan
As someone who has got here by accident and whose main language is not english: why can't you just use the camera the camera that shoots 1 trillion frames per second (as shown in the 9min00sec) and send the light to a mirror to see if the light behaves differently it bounces back to the direction it came from?
Marco Boscolo
Marco Boscolo 11 timmar sedan
svfrom.info/history/video/YNWtZaLTma6ToZU&ab_channel=DefconOkay Someone can answer about a potential double fizeau toothed wheel experiment used to measure the one-way speed of light?
Boogdoggggg 11 timmar sedan
Technically if you built something 29x,xxx meters long and did the one way laser beam experiment you could measure the one way speed of light. Right?
Kean4711 DUB
Kean4711 DUB 11 timmar sedan
I dont know where I heard this but but I heard the 1 way direction was measured with planets going by each other casting a shadow then allowing a visible ray of light each the next celestial body.... but then ig there would be a reflexion that bounces off both bodies and omg this video just broke me
Nethaniel S
Nethaniel S 11 timmar sedan
You can use two light sources in space light second away from one another and have simple logic to activate each light: when you see the other light flash, flash yourself. And then observe from another point in space that is in the same distance from each source of flashing light and log when each light flashes. Then repeat experiment multiple times when your position changes but distance from flashing light sources remains. If the light moves in different speed in different directions then you covered enough directions to notice it, no?
nom chompsky
nom chompsky 12 timmar sedan
If one way is half c and the other is instant wouldn't you be able to measure a red shift in one direction and none in the other?
Hunter SENPAI 12 timmar sedan
one watch on earth two watchs on Mars (Mars one watch editable version & second one not editable) 🧐 the earth ask and tell the time - the mars edit and tell the non edit time!. The point is from sending the message till the Mars received it we can measure the delay and then we can focus on which signal is faster (in my opinion I think the bigger equipment the fast response just like the size of the sun, so when he sending from mars is differently slow!!!) sorry bad english still learning.
fermin fernandez
fermin fernandez 12 timmar sedan
For the people that are thinking in the sun we don't exactly know when the photon is emitted so we can't exactly know what's th speed of light
Bert Hoffman
Bert Hoffman 12 timmar sedan
What about the Michelson-Morely experiment in 1887 and the subsequent analysis by Lorenz and FitzGerald?
Tristan Heartt
Tristan Heartt 12 timmar sedan
why can't you just reflect the light back and divide it in half
Tristan Heartt
Tristan Heartt 12 timmar sedan
now I feel like a fool because I could have just watched another 10 seconds
Thurston Bibian
Thurston Bibian 12 timmar sedan
What boggles my mind is people decades ago with "primitive equipments" were able to measure things, hats off to their ingenious mind
Artemis von den Sternen
Artemis von den Sternen 12 timmar sedan
This is so stupid! Maybe you heard about something called blue- or red shift! Think about it, i dont will comment this nonsense any further!
derken /gamer schule
derken /gamer schule 12 timmar sedan
hey also after my first comment i thought about the thing where you sayd what if you see mars in real time lets asume mars suddenly has no light anymore and they planned to shut off the light at this specific rotation around the sun the the mars should instantly be dark
Daniel Boylan
Daniel Boylan 12 timmar sedan
Too easy, but what if lasers are fired from each end at the same time, assuming the clocks are perfectly synchronized.
Canem Cave
Canem Cave 12 timmar sedan
if the light we see took no time at all to reach us and therefore light had infinite speed towards us, wouldn't that immediately invalidate the big bang theory of the universe?
derken /gamer schule
derken /gamer schule 12 timmar sedan
bruh i have a super simple solution just get a atom clock at both clocks and let them start when as an example the clock reaches 8pm (yes i know thats wrong but easier for everyone to understand) and at the same time at 8pm start the laser and yeah
Lavikka Photography
Lavikka Photography 12 timmar sedan
My head hurts now.
0MindSwept0 12 timmar sedan
4:03 Michael who? 8:18 that's because if it's just going one way it's not bouncing, it's only projecting SuperVinlin 15:21 so why the fruit doesn't matter? It's like that stupid question "if a tree falls in a forest and no one's around to hear it, does it make a sound?" Like yeah, obviously, it doesn't matter if someone observes something for it to have happened; you may as well ask if the tree even fell in the first place XD The only thing I'm questioning at this point is why this arbitrary question even came up in the first place 🤔 and that's truly something the world may never know LUL 16:45 ...ya I still don't care, but anyway, have fun wasting your time thinking about something that really doesn't change anything SoonerLater
Attila Szabo
Attila Szabo 12 timmar sedan
You make a long stick from earth to mars, and instead of sending radio signals, you just pull the stick. Or... Does the stick's end will be moved on the other end by delay?
Alberto Eusebio
Alberto Eusebio 12 timmar sedan
As a former Metrologist for several decades, I've calibrated many atomic clocks and various optics, and this one still stumps me.
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