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Why No One Has Measured The Speed Of Light

Veritasium
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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 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"

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2020/10/31

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コメント数 90 806
srikanth konatham
In my opinion, as time is relative to the observer it creates an illusion. So, to measure an absolute value there should be another determining factor other than time such as the force of gravity on particles. Which is not constant but it is when it gets relative to a particular object's gravity. I love the way you challenge scientific theories. Continue to do what you are doing and fill the world with ample food for thought. Cheers, Srikkanth Kontham
Dylan Watters
Dylan Watters 2 時間 前
What if you moved one clock away from the other, found the delay, compared it to how far you moved the clock to figure out the the delay in the clocks when moving them apart, tested the time then subtract the difference in the times that you have already figured out :) thats my idea
vic tor
vic tor 2 時間 前
To measure the one way speed of light, you send the light beam around a set of black holes arranged to “lens” the light back to it’s original spot.
SumGoodChow
SumGoodChow 3 時間 前
Just have one guy on mars and one guy on earth, flash a light from earth to mars, and mark how long it took, then do the same but mars to earth, if the speeds are different, we have our answer.
Michaël X
Michaël X 3 時間 前
You lost me at "astronaut on Mars".
Mile Gedojzna
Mile Gedojzna 4 時間 前
Sir, I am really sure thinking that we are inside a simulation, inside a simulation, inside a simulation, inside a simulation of base reality. And then realized that we are actually inside the emulation. Unless I find a way how to pass that start that is "nothing" where nothing are something and that something is nothing. xD
Prakash Das
Prakash Das 5 時間 前
The speed of light is : 2,99,792 km per second
Jate Litherius
Jate Litherius 5 時間 前
Why couldn’t the speed of light be negative in some direction?
Jate Litherius
Jate Litherius 5 時間 前
I’ve often thought that, were FTL travel possible, it would be equal to time travel backwards, also impossible, because you would reach your destination at a time relatively before you left, you’d be able to see your own approach, perhaps even see yourself arriving ahead of yourself
Frank DiMeglio
Frank DiMeglio 6 時間 前
WHY AND HOW EINSTEIN WENT WRONG REGARDING WHAT IS BALANCED BODILY/VISUAL EXPERIENCE, AS E=MC2 IS F=MA: E=MC2 IS F=ma. Get a good look at the BLUE SKY. The Earth is ALSO BLUE. Get a good look at what is THE EYE !!! Consider THE MAN who is standing on what is THE EARTH/ground. Touch AND feeling BLEND, AS ELECTROMAGNETISM/energy is gravity. Balanced BODILY/VISUAL EXPERIENCE is the reason that objects AND MEN fall at the SAME RATE (neglecting air resistance, of course), AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. (Accordingly, the rotation of WHAT IS THE MOON matches it's revolution.) "Mass"/ENERGY involves BALANCED inertia/INERTIAL RESISTANCE consistent with/as what is BALANCED electromagnetic/gravitational force/ENERGY, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Gravity IS ELECTROMAGNETISM/energy. E=MC2 IS F=ma. This NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE, AS ELECTROMAGNETISM/energy is gravity !!!!!!! It ALL CLEARLY makes perfect sense, AS BALANCE AND completeness go hand in hand !!! E=MC2 IS F=ma ON BALANCE !!!!! Think QUANTUM GRAVITY !!!!!!!!!!!! TIME dilation ULTIMATELY proves ON BALANCE that E=MC2 IS F=ma, AS ELECTROMAGNETISM/energy is gravity. INDEED, TIME is NECESSARILY possible/potential AND actual IN BALANCE; AS E=MC2 IS F=ma; AS gravity IS ELECTROMAGNETISM/energy !!! The stars AND PLANETS are POINTS in the night sky !!! Consider what is the speed of light (c). Great !!! E=MC2 IS F=ma. This NECESSARILY represents, INVOLVES, AND DESCRIBES what is possible/potential AND actual IN BALANCE, AS ELECTROMAGNETISM/energy is gravity. GRAVITATIONAL force/ENERGY IS proportional to (or BALANCED with/as) inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. The stars AND PLANETS are POINTS in the night sky. Carefully consider what is THE SUN. (Very importantly, outer "space" involves full inertia; AND it is fully invisible AND black.) Great. E=MC2 IS F=ma, AS ELECTROMAGNETISM/energy is gravity. Gravity IS ELECTROMAGNETISM/energy. Gravity/acceleration involves BALANCED inertia/INERTIAL RESISTANCE, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Now, ON BALANCE, carefully consider what is the speed of light (c) !!! The stars AND PLANETS are POINTS in the night sky. A given PLANET (INCLUDING WHAT IS THE EARTH) sweeps out EQUAL AREAS in equal times consistent WITH/as E=MC2, F=ma, AND what is PERPETUAL MOTION, AS ELECTROMAGNETISM/energy is gravity; AS E=MC2 IS F=ma. Gravity IS ELECTROMAGNETISM/energy. Gravity AND ELECTROMAGNETISM/energy are linked AND BALANCED opposites, AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity. Great !!!! SO, it all CLEARLY makes perfect sense; AS E=MC2 IS F=ma; AS BALANCE AND completeness go hand in hand. SO, I have CLEARLY explained why objects AND MEN fall at the SAME RATE (neglecting air resistance, of course); AS E=MC2 IS F=ma; AS ELECTROMAGNETISM/energy is gravity !!! GREAT !!! Gravity IS ELECTROMAGNETISM/energy ON BALANCE !!!! E=MC2 IS F=ma !!!! By Frank DiMeglio
Joevious
Joevious 6 時間 前
okay but what if you start the timers together next to each other and then move them both .5 kilometers with one going left and the other going right wouldn't that make them still synced? Then you just have to shoot the laser to stop the clocks and subtract the difference.
EgoBlackな
EgoBlackな 6 時間 前
TIME CAN STOP THE SPEED OF LIGHT OR JUST SLOW IT DOWN....
James Jeffery
James Jeffery 6 時間 前
three ads in 19 minutes? Really? You value $ over information. I get it now. Good by veritasium.
Leopard
Leopard 7 時間 前
Why not just separate both synchronized clocks at the same speed, same direction and opposite sense to get the disered separation?
jwinexe
jwinexe 7 時間 前
someone said in roblox that it’s 13000000 somthing idk but I’m am sure it is
bob saget
bob saget 9 時間 前
Did anybody get his reference to the book/movie “The Martian” ? It is about an astronaut named Mark Watney who gets stranded on Mars
Jack Carter
Jack Carter 10 時間 前
If you unironicaly comment on this video thinking you have solved how to measure the one way speed of light, with some absolute garbage that makes no sense and was likely explained why it doesn't work in the video itself, you have an IQ of about 70
Sam Gielen
Sam Gielen 12 時間 前
What if you reflect it an uneven amount like 3 or 5 times with multiple mirrors
Elijah Farley
Elijah Farley 12 時間 前
couldn't we physically start both clocks at the same time with a really long bar?
Jack Carter
Jack Carter 10 時間 前
If you were off by one millionth of a degree when you lowered the bar it would drastically change the measurement because of how fast light is and how long the bar would be. this would be completely impossible to do
Juho Takalo
Juho Takalo 13 時間 前
What about E=mc^2? If the speed of light is different to other directions, then this equation is not true.
Adrian Bogdan
Adrian Bogdan 13 時間 前
I was thinking about your example with Marc seeing distant object exactly as they are right now if the speed of light would be instantaneous in some direction. But when we look at very distant objects, we see the light has been redshifted due to it traveling to expanding space-time. Isn’t that a proof that the speed of light is not instantaneous?
The Stop Motions
The Stop Motions 14 時間 前
Why limit the 1km experiment to 2 clocks? Would an array of clocks along the path of the laser make a difference? Would that allow us to account for any variance in the speed of light along its path? The sum of all the clocks along the path should be equal to the clocks on each end. Any difference would hint towards the speed of light not being constant.
Casanova
Casanova 15 時間 前
quantum entangled clocks would help
Djordje Dragic
Djordje Dragic 16 時間 前
You are making an assumption that distance (between Earth and Moon) doesn't change while light is travelling.
Paul wuttke
Paul wuttke 16 時間 前
Is that the reason we just use the speed of light to define the "meter", so we don't have to actually measure it?
FaisalAlhathal
FaisalAlhathal 18 時間 前
It's possible to do many trials in many different situations and around 360x360 degree directions then we can proof if light has a favorite direction or not. And the distance of travel doesn't necessarily have to be 1 km. We can do 1 m.
Lawrence Pugh
Lawrence Pugh 20 時間 前
Wouldn't it be logical that the one way speed of light can never be measured because it takes observation, the seer or measuring means to determine light's speed, thus 2 (2 ways) 'is needed' for measurement to be said measured!
pETER
pETER 21 時間 前
How to prove that the "speed of light" is the ultimate speed of the universe? Why the larger the diameter of the "celestial body", the longer it takes to rotate one circle, because the "circumferential speed" of the celestial body will exceed the speed of light Therefore, "the speed of light cannot be exceeded" limits the time for the celestial body to rotate once. So the rotation of celestial bodies proves that "the speed of light cannot be surpassed"!
Craig Peterson
Craig Peterson 21 時間 前
what of you synced up the clocks in the Center of the 1 meter and then moved Both Clocks away from each other then they would still be synced :)
Matt Me
Matt Me 23 時間 前
Can't you set the time of the remote clock using another system that does not rely on light? Like a physical, tangible motion (robot on train rails) that is travelling at a known speed. It leaves clock one at 12:00, takes ten minutes to travel the distance to clock two and the moment it reaches clock two it sets the time as 12:10. We're not relying on light to set the second clock so we can evidence that light does travel the same speed in all directions. I mean, realistically, light is surely affected by gravity, as can be evidenced by a black hole, so the likelihood is that the speed of light is entirely environmental.
Rolfson Cobb
Rolfson Cobb 23 時間 前
Because star in any direction, the older star is always further, so the speed of light in any direction is the same. but measure the speed of light still difficult..
Epic What**
Epic What** 日 前
ok, yeah but what if you just got two perfectly placed sundials and did it. You got this camera that is extremely detailed like, 1000 k definition and the two cameras send in the same deriction above or below the sundials or cameras. And then you did it in the same place later? MIND BLOWING! 1905! It takes 115 years to fail and just a day with one person? DUMB! But yeah, i hope you leant something. :)
Jake Ryan
Jake Ryan 日 前
Well, at least not by Pfizer.
LightsOut McInnes
Its should be simple, move pre synced clocks away from each other at exact same speed and at exact distance, then do the measurement
Ashwini N
Ashwini N 日 前
i have an idea. how about we take a 1km and 10cm long tube and place the clock at the end of the tube (imagining the clock is 10cm long). you start ticking the clock as soon as you let light pass through the tube. then, the clock will stop ticking as soon as it detects the light
Andika Pradipta Suardi
What if we have: 2 light with timer 1 light so we place it like this LT1 ----- L ----- LT2 The point is, let's assume left is instant, and right is C - turn on L - because left is instant, LT1 start timer and shoot light - L goes to LT2 (1/2 C), LT1 goes to L (1/2 C) - LT2 start timer + shoot light - because left is instant, LT1 immediately stop the timer at 1/2 C - light from LT1 goes another 1/2 C to LT2 - LT2 get the light and stop the timer at C
Andika Pradipta Suardi
did I miss something here ? if left C is instant, timer goes different if left & right C is the same, timer goes same
faisal alyafei
I think I know how to find out how to tell if light is traveling at the same speed or not.
TheDarkYnder
TheDarkYnder 日 前
• => IF the speed of light is indeed different in opposite directions, wouldn't we see a hint of it in what we observe of the deep Universe? Let say that light coming from direction, "A", comes to us much faster than light coming from the opposite direction, "B". We would see a brighter Universe from direction A than from B. We would be measuring different temperature value of the cosmic microwave background in direction A and B. We would see younger galaxies and stars and also much further. The Universe would appear be very isotropic to us. OR, the Universe IS isotropic, and it if just the right amount such that it is older in direction A and younger in direction B, such that the light speed delay is juuust compensated. Quite strange. Such a physical model looks highly fine-tuned.
Jose Ruiz
Jose Ruiz 日 前
3 synchronized clocks. One at the start one in the middle one at the end, starting when the light leaves the source, tag at mid point, tag at end, bounce back then tag again at Midway back and at return?
Benjamin v.B
Benjamin v.B 日 前
Put both clocks in the middle and move them 500 meters in opposite directions, now they are still in sinc
Epic Shadow Boy
Ok so @Veritasium What if we do this, we have a huge clock on earth that can be seen even from Mars, we send someone to Mars and he looks at the clock at the same time as we send him a message telling him of the time, if the numbers differ the speed of light differs depending on direction if the number doesn’t differ, it isn’t different depending on direction. Does this work or is there a flaw, please tell me in the comments :D
Arcx cm
Arcx cm 日 前
in the experiment with the astronaut, the astronaut would recive it at a "wrong" time so when he would get back to earth wouldn't you notice, because only on earth we got the signal at the estimated times.
Charismatos Labiskun
Another theory over theory without any proof..!! Come on tell me exact things that you can measure exactly..?? No..!! You can't measure something on exact number.. you just use the closest measurement that you think it is but it is not. And please use the GPS as antena, as it was an antena not a satelite..!! And yes speed of light can be different on where or how you move... if you move away from the light it will take bit more then if you move towards the light... for example if you send signal to someone who follow you from behind you they will recieve it faster than if they sended it to you.. please ignore it.. it just a stupid thought. And pardon me for my english..!!
Killing Abel Novel M. Tieman
Simple way to check the one way speed of light. In space, using three satellites...rotate a laser on the center satellite, another satellite is say 49.712 km away and another is 45.712 kilometers form the laser and at an angle of 5 degrees radius apart from each other, that will give you a 45 degree angle between the two satellites targets, with the mean radius at 47.712 KM Spin and or rotate the center satellite laser on its axis at the rate of 1,000 Rev/per/sec. At the mean distance the tip of the laser is moving roughly the conventional believed speed of light. When the light hits both places at the same time, use the rotational speed of the laser to calculate the speed of light. If the light never hits them both at the same time either light is instant or you need to keep going higher rotational speeds and or at further distances. Timing, if that is the right term... gets interesting. If you use a clock to measure the sequence of the two beams hitting the two satellites, which is not absolutely necessary, When the light hits them both at the same time, that would mean that the clock doesn't move, when the correct speed is achieved. If you use a clock to measure "0" time are you measuring time and or using the clock ???
Efthimos Karagiannidis
Doesn't the light that reaches the earth from the sun travel in one direction. Measure the time that it takes light to travel from the sun to the earth. I understand it's around 8 minutes. Doesn't this overcome the 2 direction problem?
Vivs Mumbs
Vivs Mumbs 日 前
What if they took a video of the light being shone, then put it in slomo enough to measure the speed then multiply it with the slomo speed amount.
WTH doom Beasts gamers
ok this is very correct what if the same thing could follow for sound?
gandalforb
gandalforb 日 前
If light speed isn't the same in different directions it should change the shape of visible universe ? I mean at least if light go instantaneously in one direction it should make cosmic background radiation unobservable in that direction right ?
gandalforb
gandalforb 日 前
@Nali Tikva maybe if the speed of light isn't the same in all directions it also cause change in how energy moves (cuz light is energy) and that might have an impact on density of matter in the universe... Or maybe I'm pulling mumbo jumbo out of my *** ^^
Nali Tikva
Nali Tikva 日 前
Yeah, I think that if the speed of light was significant different in one way you might see it in the shape of the observable universe. Or maybe not the shape but the amount of stars in 1 direction vs the other direction.
Hasan Da Top
Hasan Da Top 日 前
What if, as usual, we‘d send a message to Mark at exactly 12pm, wait for him to reach the message and tell him that Mark should send a message at 12pm on the next day? If we assume that if the speed of light is c/2 in one direction and instantaneous in the other direction, we know that Mark‘s clock is 10 minutes behind the earth‘s time. So: if Mark would send a message at exactly 12pm saying that his message was sent at 12pm, it‘d arrive at 11:50am (I think it‘s am, don‘t know this certain time format), by which we‘d be certain that the speed of light is c/2 in one direction and instantaneous in the other one.
Dylan Rowin
Dylan Rowin 日 前
What if, you shine a laser from the earth, to the moon and back? Then, what if, you ran this test, every 2 weeks, 26 times in a year? Relative to the moons orbit around the earth (assuming the placement of the mirror on the moon works for this test) the moon will be at a different angle. Measure the difference of timings, relative to the moons orbit around earth.
Aakash Singhal
That's because nobody could run neaide light to measure that.
Treivix
Treivix 日 前
Excellent. But what if we send two lasers with period, for example, 10 minutes. When first laser reaches the Mars, timer starts working after exactly ten minutes, which can be counted by a human. And when the second laser reaches the timer, it stops. And now we get the time it takes it to travel from Earth to Mars. Divide distance by time and we get the speed of light in one direction.
kenny iwound
kenny iwound 日 前
You have no evidence that light travels at a different speed. Or any theory or reason. You are digging yourself a rabbit hole, jumping into it and then saying "Do you see". Why? Because it make you lots of money. Light is a cup of tea!
Paul L
Paul L 日 前
If the speed of light is not equal as your hypothesis, you will see things around you distorted.
Nirav Parmar
Nirav Parmar 日 前
can we make 1 km long clock so no need to synchronise?
Gaurav Suvarna
What if you make a set up with 2 clocks and a reflective object. clock 2 is exactly in between clock 1 and the reflective surface. this way you can check the time for when it passes through clock 2 on both sides. set up 2: 2 reflective surfaces R1 R2with clocks on them. when the ray of light hits the reflective surface the clock starts. SO u send a ray of light towards R1, when the ray of light hits R1 the clock starts. After hitting R1 it reflects back to R2. When it hits R2 the clock for R2 starts. The difference between the times of the clocks of R1 and R2 is the time it took to travel from R1 to R2. You can do the reverse and make the ray of light hit R2 first to get the time light took to travel from R2 to R1
Max Marmor
Max Marmor 2 日 前
I came up with the following approach: send two pulses simultaneously close to the event horizon of a black hole in opposite directions. The receiver is to be placed in such a way that both impulses arrive at it. Since the two in the curved space-time continuum move on a straight line, so do not change their direction, they must arrive simultaneously or just not (which would be much more exciting). What do you think about it?
Nemo Goldfarb
This is where his question from around the end comes into play: is "one way" a well-defined term? The pulses don't change direction only from the perspective of an observer that travels with them; for an outside observer, they curve.
Adam Capstick
Adam Capstick 2 日 前
We could just entangle two particles using quantum entanglement. Particle 2 will know exactly when energy was released to make light. When light hits Particle 2, we could then see the instant increase in energy of Particle 1 and Particle 2 and we would use the clock to measure the one-way speed of light.
Jack Carter
Jack Carter 10 時間 前
That does not work. That is not how quantum entanglement works. If that was possible, don't you think we would have measured it by now? It is not possible to measure the one way speed of light
Heaven Vibes
Heaven Vibes 2 日 前
hey got a solution!! what if we dont only bounce back the light what if we let it travel on triangular path or rectangular or any else... I guess we can get the answer like that!!! Edited- Well it might not be the answer but it might be a way for the solution!...
Vincent Licitra
Vincent Licitra 2 日 前
So what would be the relative difference even when considering apart from the speed of light, the speed of a thought?
ThePittsStops
ThePittsStops 2 日 前
The never ending question...
velatos
velatos 2 日 前
Ok did anyone else guessed the name of the astronaut before hearing it ?? Mark
Cherry Beats
Cherry Beats 2 日 前
Your theory has been debunked due to a camera that can see the speed of light and it is the same
betorka
betorka 2 日 前
i know you won't read or even see this comment but i have actual proof that the speed of light is constant in all directions. i would love to explain this to you but i don't know how to reach you directly
DegenWoW
DegenWoW 2 日 前
It shows how nothing in real world is statically defined but rather relative, altough we can mesaure the workings, it's not a static definition but rather describing an outcome that we don't know how happened in reality, but just assume to be for the ease of description.
Tom Sinclair
Tom Sinclair 2 日 前
What if the the clocks were synchronised as in the the message example assuming a constant speed, but a powerful telescope were used at one end to observe the clock's assumed time at the other?
Icyvivid Prism
Icyvivid Prism 2 日 前
Wait wouldn’t all we have to do is test the accuracy of lasers in any direction like have someone shot a laser at a specific spot on the moon and measure the offset of the miss to measure light speed then shoot another laser in the other direction and measure its offset
leck meng ness
leck meng ness 2 日 前
What if you have 2 mirrors, 2 clocks and 2 lasers, so you can measure both ways of light and see if one direction is faster/slower/equal to the other direction
Bjorn Ottevaere
Bjorn Ottevaere 2 日 前
I think I found a way to measure it, can u get in touch?
Muhammet Serhat Soyer
If the speed of light were c/2 in one direction and infinite in the other, we would not observe the cosmic microwave background in all directions.
Colin Worf
Colin Worf 2 日 前
Hey, so I was thinking, what if the light receiver triggered a sound wave which traveled back to the origin, knowing the one-way speed of sound and the distance, one could subtract that time from the overall experiment. Would this not suffice as a one way measurement?
Colin Worf
Colin Worf 2 時間 前
@BadPunzLord in this scenario light is only going one way, therefore if the light teleported instantly to the receiver, the sound wave would be calculated to have gone off instantaneously, knowing the speed of sound does not depend on the direction
Colin Worf
Colin Worf 2 時間 前
@Syed Umer Ahmed the clock is at the begining only. The only thing at the other end is the sound producer. The clock at the light source is stopped when the sound is registered.
Syed Umer Ahmed
Syed Umer Ahmed 21 時間 前
If there is only one clock at the end How will you know when to start the clock You only know when to stop it …
BadPunzLord
BadPunzLord 日 前
Remember that time dilation also depends on whether light is one-way. So when the sound reached you, maybe the light got to the receiver instantly and the sound took, relative to you, c + time it should've taken. It's like the "sending a message to mars" solution but with your ear as earth and the receiver as mars.
Ville Valste
Ville Valste 2 日 前
If light was faster in one direction and slower in another, wouldn't that mean that the observable universe, which we understand as a sphere, would in reality be more like an egg shape? Or any irregular shape really, as every direction light could go, it could have a different speed. Meaning that we can actually see much further in one direction than another, but because we have to assume that the speed of light is constant in both directions, we couldn't know this and have to also assume that the furthest we can see in every direction is equally far away. Then about measuring the one way speed of light. A crazy idea that probably cannot be done. But anyway. How about, if we use quantum entanglement to synchronize the clocks? I personally have no idea how it could be actually done, but maybe someone someday can figure that out.
Péter Szabó
Péter Szabó 2 日 前
But, if we don't know the speed of light, how did we know how many light years take to travel to eg.:Neptune?
SHREYAM PANDEY
SHREYAM PANDEY 2 日 前
Mark and you can use whatsapp 😂
Rosento
Rosento 2 日 前
Okay, but what if you move one of the clocks, and then record that number, and move the other. It would prove that one way is faster then the other.
Kev Musicluva
Kev Musicluva 2 日 前
You remind me of Pumba with all those flies/mosquitoes buzzing around your head XD ... did you film this in Africa -_-
Pedro
Pedro 2 日 前
another wrench to the question is that the speed of light is not constant in time, to account for the big bang the speed of light has changed and is changing all the time
Vanessa RA
Vanessa RA 2 日 前
Ýou are the best!!!!!!
Abnormal
Abnormal 2 日 前
13:50 but what if you let the clocks run and then compare them when Mark gets back!
Fort Cube City
Fort Cube City 2 日 前
The thumbnail and the title tell you everything The title: why has no one measured the speed of light? The thumbnail:it’s impossible
Martin Swanepoel
I can watch this kind of content all day - i was constantly thinking how we can solve this
Aaron
Aaron 2 日 前
Synchronize two clocks, that both have a light source and receiver. Set the light source to transmit ever X amount of time, and to log every signal received. Then move the timers to each end of the vacuum tube and collet the results. You just measured one the speed of light in one direction. To verify results are valid switch which timer is on which side of the vacuum tube and repeat the test. The results should be the same on the respective side but different on the respective timer.
Copynat
Copynat 2 日 前
What I find interesting is why would light travel different speed depending on direction: huge black hole, some unobservable curvature of the universe, massive planet/gravity (can bend light, right?), or maybe the light going one way makes for a temporary portal/stargate and then can go back instantaneously :D fun to think about. Another question, would there be a way to use entangled atoms or is there no way to use light to cause their spin to change or to read that speed change in the atom you have fast enough? :D Another question: seeing how the light is also a wave, can we compare it to other waves behavior and even though we don't know if it really bounces back and goes the same speed, we can sort of extrapolate that it likely does? I can't remember if normal waves actually travel the same speed every time. When is the follow up movie about the waves and light as a wave? :P
Alan Falk
Alan Falk 2 日 前
We All and the entire univers could actually have been created 1 second ago, with all (what we call ) our memories created at the same time. There is No way to find out, but then again it could also be 2 seconds ago, or 3 or 4 , ad infinitum.
skytec123
skytec123 3 日 前
what if we used sound to sync instead of light
Baibhav Sharma
Baibhav Sharma 3 日 前
Just reduce the distance to measure it
Ralfs Barakausks
you hurted my brain
Kevin Hanna
Kevin Hanna 3 日 前
Am I the only dumb one who likes watching these stuff
macchiato_
macchiato_ 3 日 前
What about using quantum entanglement? Use some system of 2 entangled particles to start the clocks at the same time. Just food for thought i'm no physicist.
Fuad bare
Fuad bare 3 日 前
Well that was a lot of math my brain can’t operate that
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Gerry B
Gerry B 3 日 前
Place the clocks 1 kilometer apart on the same longitude, at dawn when the sun is say 5 deg above the horizon start the clocks they are then synchronized.
Sami Ali || سامي علي
Is this the justification for quantum entanglement?
Evan
Evan 3 日 前
could you move both synced clocks apart by the same amount and then account for the difference?
sweet heart
sweet heart 5 時間 前
I thought it was said in the video that it wouldn't work?
51HankySpanky
51HankySpanky 3 日 前
Einstein's Theory of Relativity is simply an illusion. It is a mathematical trick. Here is proof: Given the common example shown @ 8:14, light dispatched from the originating point (A) will travel in a straight line and therefor miss the reflecting point (B) if B is moving, regardless of A's position relative to B. Even if A and B are synchronized, traveling light is independent of it's origination A and its destination point B. The illustration @ 8:14 does not show this, but rather demonstrates that A and B are not parallel, disproving the theory. Light has no mass and therefor no inertia to influence it's movement. If A and B are stationary then the light would reflect back and forth for a very, very long time however, due to the rotation of the Earth, B will eventually lose sync because of it will be traveling further than A, thus rendering the light to miss B and continue on until it meets a different object. Sorry Albert.
RemnantsOfBeauty
Why would the speed of light be different in any direction? Who actually thinks it's different? Could the speed of light increase if it's moving towards more gravity, and slow down if it's moving away from a large gravitational force?
RemnantsOfBeauty
@Colin Worf Not sure that logic follows.
Colin Worf
Colin Worf 2 日 前
Why wouldn't it be different? Both scenarios are unprovable and therefore equally likely.
Fighter178
Fighter178 3 日 前
Wait what if you don't use light, but a syncing device between 2 clocks, and then you pause each clock with the same syncing device, then you can use the time on the clocks to figure out how long the time dilation without moving the clocks.
+creative
+creative 3 日 前
clickbait
+creative
+creative 3 日 前
clickbait
+creative
+creative 3 日 前
clickbait
Tom Panhuise
Tom Panhuise 3 日 前
If the total, measurable value c is the sum of both parts of the journey (either two speeds, or instants), is a negative part then also possible (i.e. Traveling back in time)?
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