Why No One Has Measured The Speed Of Light
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- čas přidán 27. 03. 2024
- 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"
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.
Aaand subscribed
First
13 seconds ago
hey Dustin!
Use quantum entanglement
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.
Even after watching the video, I have a few questions. What terrifies me the most about the questions, isn't that I think that they'll find a way to solve the one way speed of light; but the fact that if I am thinking about these questions, someone else likely has already, and there is a reason these questions don't answer it, and when I try thinking of the reasons, it makes the whole concept seem even more bizarre than it already is.
For instance, we are trying to measure the speed of light in a vacuum. But we could also measure the speed of light in a medium; intuitively there should be a relation between them. But the intuition must be wrong right? Or at least unverifiable. Which means even with an instantaneous vacuum speed of light one way, and a 0.5c vacuum speed of light the other way, there is some very strong asymmetrical physics going on when light goes through a medium.
Even if I have a medium that slows light down to a crawl, there has to be a reason it doesn't show the asymmetricity in the speed of light.
There also has to be a problem with colliding objects at relativistic speeds, due to the vastly changed special relativity formula. Two objects with the same insane kinetic energy relative to their stationary mass, can be travelling at two vastly different speeds depending on which direction they are traveling. One could be moving near instantaneously, while the other can be moving just below half c. Intuitively there must be some way you could use this information to solve the problem; but the intuition must be wrong, otherwise it wouldn't be an open ended problem.
Probably the reason things act so asymmetrically weird if the speed of light in a vacuum is asymmetric, is because that isn't "just the speed of light", it is the speed of causality. It means cause and effect acts different speeds in different directions; and there is no experiment you can do that can get past the limitations of cause and effect. All physics basically goes bonkers such that the asymmetrical speeds will always work out.
----------------------------------------------
Anyways, other than my mind breaking, I do agree that the end of the video is very intriguing. A solution to figuring out if the speed of causality is asymmetrical or not, could exist in a unifying theory. So the mind breaking isn't all for not.
Or perhaps the concept turns out to be pointless. As what does it mean if the speed of causality is different in two different directions? What is differences in time and space even mean if causality is different in two directions, aren't time and space dependent on causality. Perhaps the entire paradox of asymmetric speed of light is dependent on our own ignorantly rigid view of space and time? And thus unifying theory will have nothing to do with answering our fallacy of a question?
Ugh, my head. Anyways, I can always find solace in that Hexagons are the bestagons.
Hexagon = Bestagon
I made a separate comment, but no one replied so ...here it goes:
"I honestly have no idea what I am talking about, but ... can you use quantum entanglement to measure the speed of light somehow?
The entangled particles are "already synced", so "hit" the one "far away" with "something" that changes it's state and observe it/measure the time on the one "near" you... and do the same speed of light test from/in all "directions", then just compare the times to see if it's the same.
Only objection I could find to this not working is that I have no idea what breaks entanglement, so stuff like lasers, photons, whatever ... might not break it.
In rest, it seems like a good idea. Obviously I am wrong, or else it would of been tried by now, but I would really like an answer for this, if someone could educate me. Like I said I have no idea what I am talking about, so don't jump me. :)"
Okay, I have a question is the solution of 10:00 in multiple ways correct to verify de one-way speed of light okay hear me out.
1. If you do this and film both the clocks you can see which one turned on the fastest. Or which one is further. Once again you need to time it perfectly by turning on the cameras at the same time. But this one could be possible
2. If you move the middle clock to the left or the right you would get another result out of it if the speed of the light is different if not you have done it. To this correct you nee to set the clock on both sides at 300 meters away from the middle
I hope my English wasn’t that bad and that you understood my brain thoughts
Think one more time: "are distances AB and BA the same or they are measured in terms of light traveling time?" and you will get your sanity back. You can easily simulate the entire special relativity universe defining your (name A) causal boundary as now. It looks like "c0 towards you is \inf", and "c1 away from you is c/2" and for every BA synchronization event all time travel distances pointing to you are just zero, and still (c0 dt0)^2 = dr^2 = (c1 dt1)^2 the metric invariant your coordinates must obey.
This kind of "absolute" distance independent from your speed of light choice came from you actually postulated the object B being at the same location for AB and BA synchronization events but how can you define "the same point" within the experiment? Observer from Pluto will surely note your signals were sent and received at different points of space.
And here comes the answer: how can you measure any kind of "directional" speed of light if you can not provide the same distances in different directions?
On another note, I enjoy your videos immensely! You explain things in a way that I can understand and I find myself spending more time watching your content. Your videos satisfy that itch to learn.
me too
Learning is fun as long as it's not forced...
He did PhD in physics on how to make physics more approachable to general public using media. So, he knows thing or two about presenting in a way that everyone can get along.
I have been a long time subscriber of yours but now when life is making sense to me i landed upon your videos and god i have been binge watching your videos ....every topic you choose is so interesting and really strings my chord.......🎉 Thank you
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.
XD
Underrated comment lol
Oh, same here
It is, for bank, a convenient model to embrace. You'd be a banker, you'd do the same !
Now , of course, you don't believe Einstein really had any clue what was the speed of light.
The number just fell into his hat. Actually Morley and Michaelson were trying in 1887 to measure the speed of light. But the 'ether" screwed up everything.
Einstein just took M&M experiment result and declared that "ether" does not exist, and that froze everything in place including the speed of light.
LOL my bank is involved in this inverse of equities and is complicit as far as I'm concerned....I speak into existence and impose the maximum penalty for their impetulance with the application of the converse of consequence to the algorithms restricting my transactions and unleash the acholaids of irreverence to expand and proliferate the funds available to be unlimited everyday and to exponentially grow... please and thank you :)
Light: "My speed is immeasurable, and my time is ruined"
That's..... actually quite brilliant 😐
Underrated comment!
@@sinpi314 yes it is
Lmao 🤣😂🤣
You made me laugh so much 😂😂😂
WOW
I really never looked at that this way and you're right its facinating. Keep creating videos like this
So in basic school we've learned, that light "moves" like waves, but reatcs like photons, as in atoms.
Why don't we send a laser beam through a wheel which has many flaps and it spins fast like Fizeau's, but the light would be blocked when the top flap is on top dead center, and it would let light through while the next flap is coming up to top dead center (when the flaps are making a V shape instead of a horizontal line). Then, you put a phometer on the other side, and u check all 6 directions, and compare them.
If the light doesn't go with the same speed in all directions, then when it's going "against" the flow, the photometer would measure less light.
if the light is traveling slower then so is the time so the rate of the spin of the photometer would still line up to give the same amount of light through in all directions. Unfortunately the speed of light affects the speed of time so no setup like this could possibly solve the problem
Mark on Mars is instantaneously fast at texting! Maybe he can observe the one-way speed of light!
oh hi
@@jabobthegod lol u win the youtube comments
@@TheSarancool lol you win the CZcams comments
@@TheAcExGalaxy lol u win the CZcams comments
But he doesn't have a synced clock!
"so someone has measured the speed of light... or have they?" Hey, Vsauce... Michael here
Hahaha exactly!
You look like vsauce but mexican
Lol
xD
VSalsa
@veritasium What about quantum entanglement? We already can with high precision to determine if the superposition has collapsed or not without actually collapsing the superposition.
We also know that information between entagled particles travel faster than the speed of light.
So at the same moment when we send the light pulse, we can collapse the particle on our end, thus collapsing the particle on the other end. Collapsing the superposition will cause the start of the timer. In this way, we can ensure that timer clock starts at the same time. Once the light reaches the B point, then the clock stops and we can measure the time difference.
I found a different video talking about the issue of light measurment in 1 way. Saw Veritasium had a video about this so came here (cause @veritasium rocks) with the intend of commenting just what you said. Quantum entanglement, as far as I know, could allow us to measure the speed of light in 1 way.
Hope somebody does this experiment at somepoint, would be amazing
This won't work because you cannot transmit information using quantum entanglement.
If we could instantly know if a superposition has collapsed w/o collapsing it we could treat any number of such particles as bits(0 - no collapse, 1 - collapse) - i.e transfer of information.
@@FCMaccabiHaifa I certainly don't know how it is done to detect changes on the state of entangled particles, but I had understood there are ways of knowing it.
I remember reading some articles about the development of communication technologies using entanglement, but I know very little about all this.
That won't work. When the superposition of one entangled particle is collapsed through measurement, the other particle's state is indeed (seemingly) instantly correlated. However, an observer at the location of the second particle cannot know that this collapse has occurred or that a measurement has been made on the first particle without receiving a classical signal (IE, a signal subject to the speed of light) to inform them of the measurement being taken. Until this signal arrives, any measurement taken on the second particle would be arbitrary, with no way to discern if the measurement was meaningfully correlated to a specific measurement taken on the first particle. Since you only get one shot at this (taking a measurement breaks the entanglement, otherwise we could just spam measurements on the second particle until we found the moment where correlation was no longer ambiguous), a synchronizing signal is still 100% required. Which, of course, brings us all the way back to the problem we were trying to solve for originally, and we're no closer to successfully measuring the one-way speed of light.
@@sasca854correct. But how do we know that information transfer from entanglement is instantaneous without measuring the time it took for the information to transfer?
If there is a mechanism to prove that information transfer from quantum entanglement in instantaneous, it should be possible to know the status of the second particle without breaking the superposition.
Thank you so much, your content is mesmerising
"So someone has measured the speed of light...or have they?"
Huge Vsauce moment right there
They both never really were the same after the "Is anything Random?" collab.
Or were they?
*vibrophone intensifies*
what about quantum entangle ment to start the two clocks on both sides
@Windigo Jones that is why you watch flat earth videos lol
"We've invented an FTL drive but you can only turn left."
Lol
If you turn right you go backwards.
It's not an ambi-turner!
Douglas Adams Likes this comment!!!
NASCAR is going to have to build bigger tracks...
@veritasium I love your videos! I have a comment on this one in particular. If the speed of light returning to us was immediate, we couldn't then explain the cosmic microwave background or the red/blue shifting from stars right? As you explained, we cannot measure the speed of light directly, but evidence shows that it may be the same in both directions. What do you think? Thank you again for your wonderful videos!
Can we use some ohter signal than light to reset the 2. clock? Use sound signal to clear the clocks and then send the laser light after a predefined timedelay eg. 1s, then measure the time it took light to travel between the clocks. We know the speed af sound, we know the delay, isn't the rest a simpel calculation.?
We are trying to measure speed of light in vacuum. Sound doesn’t travel in vacuum.
Yes, but it is a vacuum inside a cylinder, and sound do travel in the material the cylinder is made of.
@@danbroe5966 Even if so, the speed of light is actually the speed of information. The speed of sound is determined by the speed of light anyway. It doesn't matter what "other speed" you wish to use to synchronize clocks, because the speed of every wave is based and limited by the speed of light anyway.
I love how he called it right off the bat, “oh you’re talking relativity, you’re gonna something weird aren’t you?”
"You're gonna something weird"
This sentence makes me confused and or scared.
So is the speed of shadow the same as the speed of light?
Quay
@@Chadwicktrumpet No
@@Kristian-ql8zw but why is it not that speed. That is the question
I know for a fact that the speed of light depends on direction, because sometimes when I sit at a traffic light I can see the BMW driver behind me flashing before I see the light turning green.
I don't think the difference can be felt/measured through humanly senses. That bmw guy is flashing before it turns green.
@@yogi30303 that is the joke.
@@glinchdk yeah I guess among all the serious comments I took this seriously too.
@@yogi30303 r/swooosh
@@Majesticbro r/slamdunk
feel like since light seems pretty consistent you could use light to trigger a clock to get rid of the latency.
Certain audio cables have essentially an unused control line that detects interference and compares it to the signal with the desired "noise" and deletes anything they have in common. Which makes for a pretty clean signal
What about a laser a mirror and a receptor the mirror reflects and as soon as it reflects its caught by the receptor? But also how would you activate both the timer and the receptor at the same time? Via the phone as soon as a noise is made person 1 or p1 will wait 1 second then will turn on the timer and p2 will also turn on the receptor so it wil befome vise versa
Should have wrote this in my physics exams, "It is neither a supposition, nor a hypothesis, but a stipulation that I can make of my own free will"
i still believe that 1 is prime
@@gasun1274 0 is odd
Definitely would have gotten your word count up
0 is positive
Lets be honest or make a bet... when the time comes, it will be proven that the speed of light is same for both directions, its pretty obvious. Right now "Veritasium" got the free hall pass for making wild assumptions since speed of light can't be measured with synced clocks.
When a physicist comes to an engineer with a question: "OH you're gonna do something weird arent ya?"
+Science Revolution I see but the whole religion thing is better than science is defunct
Thing this deep makes me question the existence of this very video. Really.
@Science Revolution , You list SO many things which are not true here that I won't bother to point them out. You might as well be traveling instantaneously.
@Science Revolution If you write an article and prove that mathematically, you could actually become a reputed scientist. Go ahead and do that. That's the beauty of science, all scientist have that in their minds, a sentence that says: "we could be wrong, and we probably are". We have like 3 centuries of science and look around you, look what they've already done! 300 hundred years is nothing compared to the time that our species is in the planet and absolutely nothing compared to the age of Earth itself. Stop comparing Science to Religions, they have nothing to do with each other.
Guys don't reply to that revolution guy,he/she literally mass spams this exact paragraph on all science related channel nowadays along with bunch of his flat earther friends,
Well he's/she's literally questioning the very science which is allowing him/her to watch this video on his/her device, it's like if Elon Musk's son starts saying neuralink is fake.
I was watching a video where a psychiatrist explains why these kinda people exists who claim the earth that it's flat or all the theories are bs , it's like they want to feel special as if they possess a knowledge which is hidden from the general public,it's like the film 2012 where only few people knew about what will happen actually in the start ,these want to get a feeling like that forgetting the difference between real life and Christopher Nolan's fiction scriptures , however this is also a state of mental illness which must be treated and not like back in 1700s when if someone started seeing ghosts , people started excorism or drowned him/her in the water lol
This is similar to the problem I have regarding the speed of gravity effect: if gravity acts instantaneously there’s no issue but if it acts at c - or any speed - the effect on an orbit of another body surely must be at some angle other than the instantaneous direction between the bodies?
Anyway, another thought provoking video from V - well done!
Double film roll type of setup attached to light source that sends a beam to both directions at the same time. Any rate/distance needed. "Film" can be any futuristic material that leaves a mark when a light beam hits it. Both rolls would have precise markings as close you would need. Both rolls would have the same controlled distance. Start both rolls at the same controlled speed (any). Send light ticks and make sure both films end close to each other. The rolls should end the exact same time. This wouldn't measure time, and would only show dots of light at the identical order... But there would be markings at different position in the film when starting at top to bottom. If the light went faster the other way, let's say right, the right dot would appear first when films are put side by side. Identical, but one would hit the film later than the other.
I have no idea how small / large it would have to be, or do we have that sort of film or equipment. But at least in my mind, an identical controlled dual rig would show the difference in light speed. In reality, film could be replaced with anything, but it would have to be identical in both direction, so that you could verify it with precision. I may be just an idiot and forget something important. It's just way too simple test that 1/100 would have thought. This would be just one way light. The only thing you would have to control is the "film". Starts and ends at the same time (next to each other). When comparing dots on the film, you could even verify if the films were out of synch, because both side have identical pattern, but they would arrive to the film in different time. If the light speed is even slightly different in both ways, this should show it.
Nope. Time and space dilation due to movement.
@@idkman4748 The time and space dilation would be the same for both identical systems. If the light speed is the same for both ways, these should be 100% identical. Now do this in every direction possible for multiple times. If they were off, then make sure what is causing this issue. You could even add the space dilation as one of the variables to the system. The only thing we don't have is the light speed for both ways.
You would see all the timings on the film material when light beam hits and compare all the tiniest changes. My bet is that this would work in reality and both would output identical results. It would be just insanely expensive experience for "nothing".
@@Monsux relative to an outside observer yes but not relative to the light
I swear this channel is a gold mine for educational and entertaining content
Indeed
True
Very much so
Why are you watching this on the same day I am
@@autoclockk the comment man works in mysterious ways
My real takeaway is that two clocks, regardless of precision, will never be truly synchronized. This explains why I am frequently late.
@Steven Moore
Since I am the moving observer, it's my timepiece that runs slower. Only when traffic is unusually light can these relativistic effects be mitigated. It's just physics.
That’s what I told my boss for getting late at work, and I got fired...
Would like but your count fits into 8 bits exactly, don't wanna be the one to change that :)
*Edit* Damn someone changed it, oh well, added the like now it no longer fits into a perfect 0xFF
@@markm8188 ...but are you...or are you the observed standing still...
I think about that all the time, how two things can’t be happening at the same time, EXCEPT for two things touching each other.
I think we should take a straight (line) path and take 3 equidistant points A,B&C on the path and synchronize both the clocks at point B and then move both of the clocks to each's opposite directions at same relatively speed at points A & C
Check a paper published by Andrzej Dragan and Artur Ekert "Quantum principle of relativity". Reading it you can see that if you would have a observer who travels faster than light (in your case this would be the information carrier about the time on Mars if you consider return speed as nearly infinite) from his perspective reality would be much different than for observes that are traveling with the speed
thanks for giving me another thought I can't talk to most people about cause they'll just say I'm crazy.
yeah xD also with the gravity video
They probably don't even have the intelligence to understand what you are telling them so it's easier for their little brains to consider you crazy than to accept that they are stupid.
Toooo true
This is just him wanting to think is so smart conjecturing that c is different one way than the other
@@r3kpwner303 Not true. People have different things to focus. No one has the capability to be smart in every thing.
Debunk this: There is no way to measure a people's intelligence.
4:06 - "Or have they?"
I feel like this was a missed chance to put the vsauce theme on
Also noticed VSause referenceh
Here
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this is depressing here the right url czcams.com/video/xuCO7-DLCaA/video.html
Moon Men by Jake Chudnow
(Vsauce theme) - czcams.com/video/TN25ghkfgQA/video.html
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Great video as always! I had one question which I could not wrap my mind around. What if we put two light sources inside an object pointing at each other and mark where both sources point at. Then we accelerate the object and measure the distance of deviation from the original point they were pointing at. Couldn’t we see if the deviation is different between the two oppositely directed light sources, and by extent measure the speed of light using the deviation?
Thank you in advance to anyone who sees this and answers!
Love the video and the way you explain things making it easy to understand.
Alright here is my idea, assuming our nomber for c is correct then given a long enough test area we could set up a test with a gate programed to close on a percice delay to be some distanc light travles over that delay. Could we then wait back at the start for the reflection and adjust the timed gate untill we know exactly what timing it takes for the light to be blocked?
In my mind you could do this in any direction and since you are blocking it before it hits the mirror then your getting the one way messurment
For me it seems you replaced second clock with gate, but the problem with synchronizing them still occurs
I like the extra effort you put into the short acting parts to visualize the concepts.
Have a big clock display of a super accurate clock suspended on a roof or tower. Aim two cameras at this display. Let the clock run, its start time doesn.t matter. Have the first camera triggered instantly, the second camera triggered by a beam of light activated the same time as the first camera. Compare the photos to see yhe time difference. Depending on how powerful the camera, depends on how far away you could feasibly place the static clock and second camera
@@Raythe But how both cameras will activate in the same time?
@@Raythe but because the speed of light is different for different directions, two cameras will see differently delayed images so that the time difference you see in the images will be c.
Destin was probably having a perfectly fine, normal day and then the phone rings. Now he has a broken brain.
Have a rocket exactly half way between earth and Mars. The ship will send one message to earth and the other the Mars and then instantly back to earth. You would expect that the message that was sent to Mars first would take exactly three times as long to reach earth as the one sent straight there. If this does happen then the speed of light is the same in both directions.#big🧠
@@jontisaurusrex9851 In order to measure that, the clocks on the ship and on earth would have to be perfectly synchronized. How are you going to do that?
And that makes it an even better day.
@@Anton-cv2ti Maybe one way would be to accurately calculate at what time exactly the ship would be in a specific place between mars and earth and when the ship knows it's in the correct spot, just set the time to the predetermined on earth time, then proceed with the experiment suggested above.
Rotate a tube or a some type of gear with slits on opposite sides and have a detector to see if light made it through. At a certain velocity of rotation light won't be able to traverse it. That speed and however large the slit is (the distance it would need to rotate to stop the light from making it through) gives you the time. Use that time and distance between the slits to get the speed of light
@veritasium, couldn't quantum entangled bits solve some of the clock sync issues? Or are we running into other known limits in physics?
Instead of using electromagnetic waves in order to synchronize the two timers it's possible to use non-electromagnetic waves like audio waves in solid, liquid or gas media.
Actually no. The speed of non electromagnetic waves is limited by the speed of light anyway, because the speed of light is the highest speed that any INFORMATION can travel with, also when it comes to mechanical energy waves, they will never travel faster than light, so using them as a reference is pointless.
"Speed of light is the universe's refresh rate." -Stephan Wolfram
Has that got to do with his physics project?
speed = distance/time
refresh rate = 1/time
YES LOL
I haven’t got to the end yet but can you use some kind of quantum entanglement trigger in the future.
Are we living in a simulator?😢
“We don’t you reply quicker?”
“Sorry babe I’m at Mars rn”
That's the way to measure the one-way speed of light. Send babe to Mars.
@@majidaskari8306 it doesn't matter; no matter if light is same or different in all directions, it will take 20 mins.
That whole thought experiment about light moving in different speeds in different directions reminds me that this is exactly that: a thought experiment. It reminds me of my astrophysics class that I took in college and the professor talking about extremely impressive sounding hypotheticals. Until you realize it's, again, all hypothetical. And that's the case for the theory of relativity in the form of matters like time dilation. There's a reason experiments for time dilation are onto something in getting the right direction in estimates, but tend to be pretty far off the mark, relatively speaking, in their results versus estimates. We don't seem to consider that in the case of something like a GPS satellite that uses time dilation correction, it's not any sort of actual time dilation, but the system itself that's facing anomalies. Atomic clocks are effected by environmental factors like magnetic and gravitational forces. Those would explain why the Hafele-Keating experiment had opposite directions in results for east versus west travel. It makes you curious what would happen if this was done flying over a pole instead. I also like the experiments of trying to just fly a slower plane to control for the velocity effect. Which makes absolutely no sense that the speed a clock travels would have any effect in this theory as opposed to having moved the same distance over a longer period of time. But for some reason it's a point taken.
I’m stuck at 02:55 when the two clocks are not synced anymore. How is it possible to change the clock electronics or quartz and slow down a clock whatever its speed or position? It doesn’t make sense to me. Can someone explain this to me? Is there any obvious simple application that can help understand this ? Thank you so much
That’s why going to work feels like a drag and coming home feels quick.
Lol
Hahaha
I know this is a witty joke but there's a video about this kinda time where u feel vs time that is real in vsauce
The answer is easy, if u wanna measure the time delay in one direction, u send an impulse between this two clock's in each of this two directions and u will see if one starts later ....
Quick maths
@@babylebron6119 I'll take it you didnt watch the whole video when you wrote this. He explains that the problem is that it remains unknown if light travels the same speed in all directions.
This is the best explanation of "WHEN WILL THEN BE NOW?" I've ever seen.
Isnt it the best 'lack of explanation' of 'WHEN WILL THEN BE NOW'?
**i really like your point
Soon.
Get two clocks that are 100 meters away from each other. Start them at the same time. Shoot a light across from one clock to the other. When the light reaches the first clock it will stop. When the light reaches the second clock it will stop. You have 2 times and you subtract them to find one. And convert to the larger scale
@@jordanammons4851 How do you start them at the same time?
@@jordanammons4851 2:07
I just have one solution to this(a thought): c = displacement / time. You said we can not synchronize the time for far distant location(which you think distance is constant) referring wrt measuring speed of light. Now at that light speed what if i say we can never measure distance precisely at different time instants ( mind it we are working at light speed ). Time dilation says space ( length) changes time which is significant at light speed, so at that speed how we define distance is important. Similarly if time changes ( which is very fast at c) length should also change significantly, if time dilation follows reciprocity. So what if c=kd/kt=d/t,where k is just constant which just shows if time reduces, length reduces or vice versa. So at the end c remains fixed. Basically if direction changes your speed, so should the distance!!! Now the only question is how correct is c value, well know that depends on how correctly we have captured the time to distance proportional constant. So how correctly we have captured c will tell how correct we are at calculations which involves "c". Either if it's incorrect only the definition changes not the meaning. It's just like saying instead of 1-meter now my new reference is 0.80-meter. I might have 20% error in value but it's just my new reference now. As long as my all observations / calculations are at far lower values wrt to my new reference the delta error i generate is very small in new observation. The same is the case with c, more close my observation reach to c, more error i would encounter.
New thought: in your earth/mars spatial diagram you said c= infinity = distance/Zero ( as per your case), it also hold true for my explanation above which says c=0/0, distance is zero here which still makes c infinite!!!
Can we shoot 2 rays from one emiter distance between them to be x and after put a mirror in the path of first and reflect it back like x/3 distance and again a mirror at x/3 to send it back the original path so if light have same speed then distance between them is x/3 if it is instantaneous then distance is 2x/3 is it possible to do like that
"Stars look exactly as they are right this instant." Gave goosebumps.
czcams.com/video/nRGCZh5A8T4/video.html
We saw past of star coz it take millions of year to reach star's light to earth
@@ABHEEeeee Watch the video
@@ABHEEeeee how do you know? Are you saying you can prove the return trip isn't instantaneous?
Have a rocket exactly half way between earth and Mars. The ship will send one message to earth and the other the Mars and then instantly back to earth. You would expect that the message that was sent to Mars first would take exactly three times as long to reach earth as the one sent straight there. If this does happen then the speed of light is the same in both directions.#big🧠
“No Officer. I was not speeding. You see, the speed of light different depending on the direction.”
Officer:
“lol. Here’s your ticket.”
Actually this argument has held up in court. Google it, it’s pretty awesome.
@@epicvillain8308 I tried to but couldn't find it. Mind sharing?
@@epicvillain8308 you are lying
@@lilsabin 🤣
@@epicvillain8308 No but the dopler effect has, even though it works in the driver's favor. Far as I know this argument does not work anymore because of that factor (I just drive a truck though 😅).
What about instead of using 1 km we used 1 m or 10 m and light detecting sensors on both ends so when light passes through starting point the timer starts and when it reaches end it stops also we have to use timer with 10^-20 or 10^-30 decimals ???
cant you sinchronize the clocks in the midle and then when they started separate them on both sides with the same speed? cus the special relativity says that a moving clock ticks slower than a stationary one but what if both are moving at the same time?
"So some one has measured speed of light"
"Or have they??"
*Vsause theme plays*
I kinda expect there's a theme song... But left disappointed
*vibrophone intensifies*
Is he even alive
Vsauce must have run out of topics. Loved his channel.
yes what a garbage clickbait channel this has become....
The worst part about me watching this video, is that I understand everything he says, but at the same time, I understand nothing.
Dude is too smart
@@abrahamsanchez7455 indeed
Understand the words, but not the meaning, it's what happens
He does speak English pretty well
Same here...
Move clock a and clock b equal distance and move equal speed. Relativity will be synced then measure?
10:48, little question. If the speed of light depends on direction. Why not move the clocks back to the middle after te experiment, this way the clocks moved the same in both directions ? And 1 where you do not do this and check what the diffrence is in autocome. What would be the problem in this case? :) thank you
He said "or have they?" I was kinda sad no vsauce music played
yea
If the pulse to start the second clock us traveling at the speed of light(2:27), then why can't you just subtract the number of seconds the second clock has been running for from the first? I feel like this is a stupid question and I'm missing something...
I know, right?! At 4:05 I thought I was watching a Vsauce video. lol
@@mahirshyam4127 because if the speed of light is potentially different in both directions, then how could they know how much to subtract it by?
The experiment would be trying to measure the speed of light, but you’d need to know the speed of light in order to know how much to subtract the second clock by.
For example, imagine trying to solve for the length of the hypotenuse of a right triangle, but the only information you’re given is the length of the bottom leg.
Asking why you can’t just subtract the speed of light from the clocks to get the answer would be kind of like saying “why not use the length of the bottom leg and *the length of the hypotenuse* to find the other leg? Then from there, just use this other leg to find *the length of the hypotenuse.”*
Hopefully this example makes sense, I’m not the best at explaining things.
yeahhhh
Old Derek: makes people on the street feel stupid
Present Derek: make rocket scientists feel stupid
True
only by asking a dumb philosophical question that reality refutes on every level... This is why philosophy is garbage. Possabilities dont matter, reasonable probabilities do.
@@terryfuldsgaming7995 bro my mans said Einstein himself did the two way measurements and he has many points in this video based on relativity not philosophy
Past derek and present derek is meaningless according to this video
@@terryfuldsgaming7995 Reasonable? Take a good, hard look at our current understanding of physics and come back when you're ready to call it reasonable. The very reason philosophy _is_ interesting is precisely because there are possibilities about reality that sound completely bonkers to us, and yet there's strictly nothing explicitely fordidding those possibilities... so what rational reason could you possibly have to dismiss them entirely? Symmetry? That sounds like a good argument, but there are plenty of situations in the real world where symmetries are broken. You could say that, on a purely a priori basis, more symmetrical options are more likely, but because it's a continuum between being completely symmetrical and being completely asymmetrical, without changing anything about causality, physics or your everyday experience (since if there was a difference you could measure it), the probability that the situation is _perfectly_ symmetrical would be zero. Even as a thought experiment, this entire thing is fascinating because it completely breaks our intuitions.
in one of your examples light can travel at c/2 from Earth to Mars and infinite from M to E...if this were the case, shouldnt the reverse speed also be applicable from M to E and vice versa? Love this channel and your work...also huge fan of @smartereverday
I would like to know if the two way speed was tested in 3 directions at the same time (XYZ), same clock at origin? Ex: For z, lets put a mirror at the bottom of a 1km deep mine shaft. Does it make a difference? Is there a preferred direction in the universe? Like foucault pendulum? Is there decomposition of this preferred orientation or is there a cap on maximum speed?
Lol when Destin realizes Derek is about to drag him into relativity
yeah, that was hilarious.
That got me good when he realized what was about to come up XD
Thank you for putting a camera on Destin when you had this conversation with him. I wanted to see his pondering/puzzled face so much! 😁😁😁
We* wanted
@Veritasium, Is the impact force of a photon (as used in solar sails) affected by the speed of light? If so, could this phenomenon be used to infer (indirectly) a different c, based on the force imparted to some detector, the experiment repeated in different directions? Or is the force imparted the same because, assuming a perpindicular reflective surface to the direction of photon travel is used, the sum of the two speeds (before and after reflection) is still 2c? Wouldn't there be a different force imparted at a different vector with a variable c? If not, would this violate conservation of momentum? Also, would a similar experiment, but using an angled reflection, work better because the light would not be going in the opposite direction as before, making it more likely that the variable c speeds would not add up to 2c? Am I thinking about this too much? Now my brain hurts...
All the energy of a photon is baked into its wavelength. Its velocity is not subject to conservation laws. Electron-positron pair creation never generates particles at light speed, but their annihilation leads to the generation of two photons (charge is conserved in each photon, hence why there's two). For what's it worth, it's almost correct to say photons don't have a velocity at all, due to how it's not part of any quantum interactions, nor is it ever conserved.
i have a question... at 9:52 .. when we place the synchonizing clock.. why cann't we use this particular apparatus itself to measure the difference in speed of light????
i mean..if the speed of light is truly diffferent in both the directions.. then the outcome of the " simultaneously sent pulses " will and must be different.. why cann't this help in understanding the speed difference of light..
just a thought..
I love when Destin is presented with something he genuinely didn't know/understand before. His face lights up with extreme excitement and intrigue.
That moment led me to evaluate my whole existence on whether I could share something interesting enough to impress Destin that much.
Us to aliens: "We measure a meter as the distance a light takes to travel in 1/299 792 458 seconds"
Aliens: "Which way monkeys?"
Lol
But the aliens can't know what a monkey is and they probably won't be able to speak English (I know it is just a joke)
@@shivannapv4262 nasa would like to hire you
@@omniyambot9876 why (I still know its a joke)
@@shivannapv4262 because biden is gonna be the new president😄😄😄😄
Is it possible to use audio to trigger the clocks? We know the speed of sound and we can essentially start the clocks on the third beep of a series of beeps. But using the speed of sound the clock predicts the third beep based of the other two...... both clocks are synced without moving and they start at the same time with zero latency. The light beam gets shot simultaneous with the third beep.
Any problems with this?
Two light sources 1km apart, two sided sensor, if sensor recieves light from both sources when exactly positioned at 0.5 km then light speed in each direction is the same, if not sensor can be moved until it recieves both light from both directions at same time to calculate speed in each direction
But then how do you trigger the lights at the same time..
"Ok, let's synchronize our watches!" - 2070 Nobel Prize winner
SEND THE REINFORCEMENTS THIS GUY IS LOW ON LIKES
Also there were two nobel prizes awarded for breaking the assumption scientists had about the charge parity and time simmetries so this wouldn't be a first but would probably be one of the best
You could just move both clocks at the same speed for half a mile then measure the exact time the light was turned on, and then the exact time it reached the destination and do the math
i meant move them In opposite directions
I thought this said witches... Happy Halloween!
This video really changed the way I look at “simultaneously”
haven’t seen the video yet, but based off psychedelic experience i know exactly what you mean
@@vast5853 could you explain ?
Simultaneity*
Now when i do simultaneous equations, i do the calculation for one, and i instantly get the other one.
This is an awesome, very thought inducing video. A follow up video on what could be causing this potential asymmetry would be fascinating as well. However the centered clock synchronizer at 9:50 doesn't exactly equate to the GPS example he introduces next because in the first example, the A/B clocks agree (correctly) that they are stationary relative to the other. In GPS, the clocks are in relative motion. This creates a larger problem when trying to keep the satellite clocks running at the same "rate" as the ground clocks. They in fact have to run at the same ongoing rate for the system to function accurately but this (like it or not) is in contradiction with special relativity. I cover this in my twin paradox video.
2:40 could you not just start the timer when you send the signal to the other timer and then subtract the times to calculate the speed of light?
Would you be able to use the transfer of energy due to pendulums to synchronize the clocks? Then measure it?
I love that all these guys are friends and all they care about is figuring stuff out, learning and showing us.
They couldn’t care less about figuring stuff out. All of these stupid ideas are absolutely incorrect, and have been put to grave with actual experiments over 100 years ago
All they care about is showing their sponsors how many people watch their anti scientific horseshit
Go buy some kiwico and support the huckster
@Zach Comstock me and 11K other people who actually studied Physics
The rest of you should go buy kiwico
@@MarchelloMastrayani I'm actually interested in reading the experiment. Do you have any reference to papers that I could follow through?
@@MusicNewb absolutely, there were two brilliant scientists who set out to measure the difference of the speed of light in different directions over 100 years ago. Their names were Michelson and Morley and if you search “Michelson-Morley experiment” you will find many articles because what they have measured was an important stepping stone in the history of Physics
@@ENikolaev huh
"Or have they?"
**strong flashback of Vsauce*
Why didn't he queue the song?! haha
@@KingR787 He'd need a colab and permission to use the song =)
It's a shame Vsauce doesn't really do these types of videos anymore
Us to aliens: "We measure a meter as the distance a light takes to travel in 1/299 792 458 seconds"
Aliens: "Which way monkeys?"
Ok
I was watching and thought about a quantum clock ? I'm ont very knowledgeable about the subject but if i remember correctly 1 set of quantum particules can change their state at the same time regardless of distance ! Would that be possible then to mesure the one way speed of light ?
Can you not shoot two or more equal intensity laser beams from opposite directions to the same opposite generation point/site, instigated from the center point of the distance so triggering is simutanious and compare the measurements?
Everyone gangsta until someone calculated the speed of shadow
Heyyyy vSauce, Michael here
Its istantaneous because it doesnt carry information (so it could go above c)
Hey Michael, vsauce here
@@giacomogroppi5768 No, the shadow is not instantaneous. The light that passed the object before the rest is blocked will still be visible until the last unblocked light reaches the surface of the observation.
@@ozciva but it’s still the same thing... how do you measure the speed of the shadow accurately?
"Or have they?"
Hey VSauce! Michael Here
Tohba tohba tohba mood kharab kar diya
Abbe saale
🤣🤣🤣
That would be such a collab!
Derek already did one with Michael but not with Destin in one video.
@@NimbleBard48 We all want that to happen💥💥💥
What about having one clock at the start that times from when the light is emited, when it hits the second clock the clock starts timing and the first clock stops when the light hits it again.
Sound doesn't change when reflected, so I would make the assumption light also being particles would act the same way. Couldn't you trigger a light to turn on at the distant location the moment it receives the light and have both the reflected light and direct light pointed at source location and measure any difference between the 2 at the source?
4:07 *Vsauce music starts* and im anticipating a round head will pop from the bottom of the screen.
Hey, just to let you know someone else in this comment section named Nihab Khan copied your exact comment word for word soon after you posted. Control + F to find the bastard. Go give him hell lmao.
I’m glad someone else thought this😂
IKR
Or is it,,😂😂
yeah my brain stopped working.
I long for the days of before I saw this video
Even if we figured out the exact speed of light and KNEW what it was, it doesn’t change the fact that I have to go to work tomorrow
and that's facts
the speed of work is always c
@@rsolsjo unless it's Monday. On Monday it is C/2
@@michaeldivens7570 bruh in a maths lecture its c/5
When's the lay off?
Here's an idea how to measure the one way speed of light:
Put a photosensitive material at the other end of the light's path. When the light touches the material, it will start a reaction (similar to developing a photo). That's one way. Now, I know that in order for us to notice that reaction we either need to observe it (which means light would have to bounce back for us to see it, which creates a return travel for light) or measure the time in which the photo reaction occurred (but here we arrive at the two clocks problem). BUT! What if we create a sort of a tube made of entirely photo sensitive material, that would be constantly monitored by ultra high speed cameras and we measure the "speed" of photo reaction progressing towards the end of the tube?
I have a feeling that what I just described is based on a cartoon logic, but... I don't know. Maybe it will inspire someone :D
Could a device connected to points A an B record the trigger times like “lap time” in a stop watch in both directions AB and BA and then compare? What would make those the same?
Me a smol brain: light travels at 1 lightyear per year.
edit: turns out, this aint smol brain; this is big brain
r/3likecomment
Jk you don’t get a subreddit
@@LargestLuke 😀😭
in fact that smaller size of brain is the faster neuron work on brain Wich make it more smarter
@Waldel Martell even if it small it has 1 Petabyte or 1 million Gigabyte of room
"so someone has measured the speed of light? or have they " sounds like vsauce
Veritasium, Derek here...
*Vsauce music starts playing..*
**Camera zooms to michael**
Rip vsauce
@@debo325 is michael dead????
So if we can only measure the round trip of light by bouncing it off a mirror and then back then would it be possible to bounce light off multiple mirrors and stop the clocks when the light hits each individual mirror and then just use the time differences to get a general idea of what the one way speed could be? Idk just an idea
I don't know if this would work, but if a string is suspended between the two watches and before sending the ray of light we take a weight perfectly in the center of the string to break and thus activate the watch, wouldn't that make the watches synchronized? Posted again bacause I'm interested in the answer.
One thing we can know: Click-bait travels at superluminal speeds.
Why is Donald Trump pretty and I am not? But why does he only have a wife but I have TWO HOT GIRLFRIENDS who I show off in my masterpiece YT videos? Do you know the answer, dear pat
True
someone's about to get reported
To quote or at least paraphrase the late great Douglas Adams: Nothing travels faster than light - except for bad news, spacecraft powered by this technology were rather unpopular when they arrived at their destination.
@@freds2150 I did report him. This dude keeps on spamming on a lot of channels, probably hired a program to it.
Law zero of physics: Einstein always has the last laugh.
Until Veritasium was born.
Very unscientific
@@ebrelus7687 How is it unscientific if it's based on all evidence so far and is testable?
As a general theorie of relativity nerd i agree
Laws of this universe;
-- Perfection, is Imperfection !
-- Never use the word "never" !
************
-- Time-frames of 1*ly to 1/ly
(by mathematics)
-- Universe has Non-uniform properties
-- Universe demonstrates effects of outside forces
>>> "Perfection"
In cmb,we see almost same picture in all directions that mean the light speed is same in all directions.
(If that is not true,we will see different picture in all directions because the time of different direction's photos will be different that means,we see stars in one direction and cmb in another direction)
That was my thought too. Weird that Veritasium did not address that.
有些疑惑,比如:1.现有EIT技术可以使光在其中传播速度显著减慢到肉眼可辨,如果让光在其中反射不就可以看出正反两个方向的传播速度是否有区别吗? 2.如果光速是单向瞬达的,那么将不会受到折射反射的作用,没有红移现象,甚至不受黑洞视界的影响,不会产生光晕现象。3.假如某个方向光速无限,是否可以因此窥见黑洞内部的反射光线?
Aliens b like “yo they finally found a glitch”
Devs: Oh shoot the playerbase knows! Fix it!!!
lol
"someone has measured the speed of light....
...or have they?"
Don't you VSauce us like that
Hahaha exactly! I expected Michael to pop up out of nowhere
@Florentin sound happens because of pressure waves, which happen because of the fluid (air?) Moving, which is made of various particles, that interact with each other by means of electrical forces. And those are linked to electrical fields, which propagate.. at the speed of light... 🙈 Therefore I guess it's checkmate again
Brow if they send massage to Mars at 12:00 and send another massage to Mars after 20 earth minutes. So the man in the Mars kan take the first massage at 12:10 and he can take time and he can se how long it will take to get the other massage so he can find the light speed.
It is to easy.
Believe me
@@tthozan7632 Stop spamming this.
Veritasium basically is VSauce nowadays
I might have solution for special relativity problem. We should use two clocks. Sync them, at centre of two mirrors i.e 0.5 km then take one clock to starting point and other to end point.
Am I wrong?
while watching this great video, it got me thinking. If time space is curved than it means that the light will never travel the same path as the time will change but also the position of the earth in the univrs, so if the light is deflected using the mirror, thus the speed of light will be different in each direction.
This certainly has interesting legal implications for speeding tickets based on laser detectors (previously mistakenly referred to as "radar guns".)
I'll try to explain this to the cop the next time I get pulled over. I might get a ride down to the station instead of a ticket.
Apparently it doesn't. Lol
@@Future__martian Fair point. I made a poor choice of words. I was referring to laser-based detectors. In addition to radar, police commonly use laser guns as well. These are completely different than radar guns. They function differently from the police officer’s standpoint, they have a number of advantages and limitations compared to radar, and they require completely different tools to combat as a driver. Thank you for point that out.
@@Future__martian soooo, you are saying radar waves are as slow moving as sound?
There's 2 types of devices used by police to determine a car's speed. Radar measures the doppler shift in the signal and uses the shift to determine the speed of the vehicule.
Laser ones, fire a laser at your car and it bounces back and then it does it again and measures the difference between both interval. So it's measuring the 2 way speed (going to and coming back) and not single way. So even if light was slower in one direction it wouldn't change the final result.
this video made me feel insanely smart for 19 minutes and 5 seconds.
True 😂
Um this made me feel insanely stupid for 19 minutes and 5 seconds...😂
Dunning-Kruger Effect?🤔😁
Imagine watching it high
same man wtf*
What if we create two clocks that has a trigger based on a particle that is in quantum entanglement? I.e. the clock starts counting down when the entanglement breaks? Wouldn't that allow us to have two perfectly synced clocks?
I thought he was going to say, it comes back slower, and then he said returns instantaneous.
Very thought provoking
A micro millisecond: The time between when you shut, and lock your car door, and realize you left your keys inside.
What if the realization happens before the door shuts, but too late to stop it?
@@davidpowers746 We are talking reverse space time continuum. Way past my realm of comprehension.
@@treeguyable The physics isn't ripe yet.
Or perhaps 15 years because she told you she was 18.
The onosecond
The moment when Destin realized "Oh snap, Derek is going relativity• is Golden!
Where does the quotation end?
I am experiencing 299,792,458 meters of life every second, and no one else gets to experience it from my perspective. I dunno about you, but I'd call that relatively beautiful:)
Could two different Laser Interferometers facing in opposite directions and completely synched be used to figure this out. Wait for a gravitational wave to pass and measure it using both observatories. If the warping of spacetime causes the same delay in two beams of photons travelling in opposite directions, we can agree that the light must travel the same speed in those two directions. Am I right?
What if you get the 2 clocks and bring them in the middle then move them at the ends. Also, would it be possible to use a giant laser to hit something that can sense electromagnetic radiation or maybe heat transfer.