Why No One Has Measured The Speed Of Light

Physics students learn the speed of light, c, is the same for all inertial observers but no one has ever actually measured it in one direction. Thanks to Kiwico for sponsoring this video. For 50% off your first month of any crate, go to kiwico.com/veritasium50
Huge thanks to Destin from Smarter Every Day for always being open and willing to engage in new ideas. If you haven't subscribed already, what are you waiting for: ve42.co/SED
For an overview of the one-way speed of light check out the wiki page: ve42.co/wiki1way
The script was written in consultation with subject matter experts:
Prof. Geraint Lewis, University of Sydney ve42.co/gfl
Prof. Emeritus Allen Janis, University of Pittsburgh
Prof. Clifford M. Will, University of Florida ve42.co/cmw
The stuff that's correct is theirs. Any errors are mine.
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"

[@brstrom1914]

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.

[@MARCO-rq2ph]

XD

[@fancygamer5896]

Underrated comment lol

[@rosauradiaz9842]

Oh, same here

[@novusmundi9131]

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.

[@jedpeltier3320]

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 :)

[@smartereveryday]

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.

[@daenite2480]

Aaand subscribed

[@dylancorkindale]

First

[@cjyt4115]

13 seconds ago

[@homunculus3646]

hey Dustin!

[@VellianoRosso]

Use quantum entanglement

[@vibhavaggarwal237]

I am an engineer and was working on time synchronization between two devices on the same network. We encountered cases where network delay from A to B is higher than from B to A and such cases resulted in inaccurate synchronization. I was working on solving this problem and after watching your video I realized it’s essentially the same concept- sending signals from earth to mars is like sending network packets from A to B. So the conclusion was, without the help of any external device it’s impossible to accurately sync time! Thanks a lot for your video :))

[@shinyconcepts3805]

My kids and I love your channel and I love the conversations induced afterwards. This video covers a topic that I’ve wondered about for quite some time. How can an object like the andromeda galaxy that is 200,000 light years across “appear” as a single object instead of a smear? Especially since it is also moving through space? These are the things my sons and I ponder. Thanks again for the great content!

[@rigel442]

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

[@brankelly1921]

That's..... actually quite brilliant 😐

[@sinpi314]

Underrated comment!

[@realo3503]

@@sinpi314 yes it is

[@pardeepgarg2640]

Lmao 🤣😂🤣 You made me laugh so much 😂😂😂

[@justharshad2044]

WOW

[@CGPGrey]

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.

[@josephburchanowski4636]

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.

[@amon7816]

Hexagon = Bestagon

[@andu2oo6]

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. :)"

[@thijsmas1359]

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

[@drozdovkonstantin]

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?

[@DevinHenkel]

Wouldn’t red shift be different in different directions if light traveled faster in one direction than another? Unless we make another huge assumption that the universe is lopsided?

[@JMScibra]

No or not without it mitigating itself to some degree. Strictly on expansion, the blueshift in its direction would be countered by the redshift caused by further objects expanding faster, because gravity.

[@michal88gno]

Derek, you have blowed my mind today. Great video and even greater attitude into science mystery.

[@bent.5687]

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

[@VivekYadav-ds8oz]

They both never really were the same after the "Is anything Random?" collab.

[@controlequebrado4455]

Or were they?

[@MikeTaffet]

*vibrophone intensifies*

[@joesimamura223]

what about quantum entangle ment to start the two clocks on both sides

[@ViratKohli-jj3wj]

@Windigo Jones that is why you watch flat earth videos lol

[@TheRealGuywithoutaMustache]

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

[@AquarialTV]

Indeed

[@Frilabird]

True

[@justsomeguywithoutamustach8695]

Very much so

[@autoclockk]

Why are you watching this on the same day I am

[@AquarialTV]

@@autoclockk the comment man works in mysterious ways

[@SpartanFilms1997]

What about using quantum entanglement to measure the speed of light? Fire the light, it sets off the entangled particle, and when the light reaches the end, the entangled particle there would immediately send the info back to the first one.

[@MagruderSpoots]

No information is exchanged when entangled photons decohere.

[@SpartanFilms1997]

@@MagruderSpoots what about before they decohere? There is information transmitted while entangled...

[@MagruderSpoots]

@@SpartanFilms1997 None. Entangled particles can't be used for communication.

[@johan85100]

What if we get 3 timer-clocks that have an internal mechanism that ticks every second, with extreme accuracy. They start synchronized, but it doesn't matter if they get slightly desinchronized. as long as the mechanism inside of all 3 keep independently cycling exactly every second We move two of them 1km on each side, and leave one of the center. The ones on the sides are programmed to start counting passed time after a given period of time (an hour?). The one of the center is programmed to emit a light beam a few milliseconds before that same amount of time (enough to cover for distance but still trigger first) and then and then keeps cycling every second. The clocks at the two sides start counting time every second after that and stop every time they receive a light beam/signal, the timer never resets, keeps starting and stopping, building up cumulative delay. If there was any desyncrhonization due to moving the clocks it doesn't matter, because that will only count once, while the repeated cycle will continue adding up and stacking possible delays caused by possibly different speed of lights. We then move the clocks back together and confront the amount of total delay built up. The difference caused by desyncrhonization will count once, but the the difference caused by possible different speed of light will be cumulative, so we can still spot differences...? I don't genuinely believe i solved a century-old problem in 10 minutes, but can someone help me undertand why this wouldn't work?

[@dead-claudia]

⁠@@SpartanFilms1997when two particles decohere, if you only have one, you have no way of knowing if or when it decohered.

[@bertheinrich586]

Fascinating as are all of your videos even though I am no Physicist but just a humble sailor and safari guide. I think I better have a drink now or sleep is out of the question tonight. Thank you

[@markm8188]

My real takeaway is that two clocks, regardless of precision, will never be truly synchronized. This explains why I am frequently late.

[@markm8188]

@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.

[@seanzhang3873]

That’s what I told my boss for getting late at work, and I got fired...

[@zxuiji]

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

[@icedefundthepol8770]

@@markm8188 ...but are you...or are you the observed standing still...

[@yeetmeat_]

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.

[@priyathgregory9055]

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"

[@gasun1274]

i still believe that 1 is prime

[@ghostoftheuchiha526]

@@gasun1274 0 is odd

[@lesserevil8136]

Definitely would have gotten your word count up

[@finmat95]

0 is positive

[@ShopperPlug]

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.

[@alperarkan6495]

2 synchronized clocks starting at the same point. Move 1 of them in a direction towards the sun for 1km (or something with a more stable position in the space like a far galaxy/star). Wait ~12 hrs so earth rotates. (something close to 12hrs, calculating all the planetary rotations, just be sure now the same direction is inverted relative to the space, this is the hardest part since you may need to wait a lot to be sure its the same direction again when moving back) Then move it back to the initial position. (now it actually moves on the same direction that it moved at the first trip) Once they are together again check the difference between clocks. Divide it by 2 and now you know that direction's time dilation for 1km. Next time synchronize the clocks again and do all again but with a completely different target, so completely different direction. (another far star, preferably in the opposite direction) Measure the second difference of the clocks once they are back together. If they don't have the same difference with the first test, you proved that the direction matters. If not you are close to prove that direction doesn't matter. Just do it again with different directions to be sure. Good luck

[@SolderingIronMen]

What about the wavelength? After all, we can determine the length of a standing wave (experiment with a chocolate bar in the microwave) and, knowing the frequency, calculate the speed of light. In general, a standing wave would not work if the speed of light were different depending on the direction.

[@sjeason]

Somehow I feel like that would have been tried before and we still can’t answer if the one way speed of light is c, soo

[@johnnyregs2378]

When a physicist comes to an engineer with a question: "OH you're gonna do something weird arent ya?"

[@creatorboii3012]

+Science Revolution I see but the whole religion thing is better than science is defunct

[@Heero5308]

Thing this deep makes me question the existence of this very video. Really.

[@BruceNitroxpro]

@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.

[@joselucas9398]

@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.

[@sashishekhar8266]

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

[@v10011011]

I love how he called it right off the bat, “oh you’re talking relativity, you’re gonna something weird aren’t you?”

[@RileyBanksWho]

"You're gonna something weird" This sentence makes me confused and or scared.

[@Chadwicktrumpet]

So is the speed of shadow the same as the speed of light?

[@bradbarker8527]

Quay

[@Kristian-ql8zw]

@@Chadwicktrumpet No

[@TheMelbournelad]

@@Kristian-ql8zw but why is it not that speed. That is the question

[@jmbrown3502]

Another idea… set your 2 clocks at the vertices of an equilateral triangle, and a light source at the 3rd vertex. The light source sends out a single light burst traveling in a spherical wavefront which initializes the 2 clocks to t=0 & starts the experiment. Clock A immediately sends out another spherical light burst which travels to both Clock B, the receiver, and Clock C, the initializer. Both clocks B & C record the time from initialization to the receipt of clock A’s burst, & then clock B immediately sends out its burst to clocks A & C upon receipt of burst A. Both A & C record this burst from B. Assuming you have all your light sources & clocks precisely positioned, & other factors such as electrical paths from the sensors to the clocks are the same & accounted for, clock A will measure 2c, clock B will measure 1c, and clock C will measure 2c & 3c. If all the c measurements are the same within a small degree of error, then this is your 1-way speed of light within that error. Of course to verify, you’d rerun the experiment again with B sending out the first burst after initialization so that clock A measures 1c in the other direction, & you could repeat the experiment 4 more times with each vertex being initiator, sender, & responder in turn and in both directions. Then you summarize all the data, calculate the maximal %error, & this would be the limit, within a calculated level of confidence, say 99.99999%, that the speed of light could vary without us knowing it. QED.

[@plooj1260]

The problem here is that A and B won't meassure the same 0 time. Your're adding a dimension by using a triangel. So you have to take in account that the light in y direction can also be different going up or down.

[@plooj1260]

If the speed of light is digferent if it's going left, right, up or down, it won't sent a spherical wavefront

[@medigoomnis]

Wow, those flies really love your hair...almost as much as I'd love seeing a supernova in real time. I doubt infinite velocity is the answer but the points you bring up are great.

[@TheRealMirCat]

"We've invented an FTL drive but you can only turn left."

[@ConceptHut]

Lol

[@ConceptHut]

If you turn right you go backwards.

[@WilliamAndrea]

It's not an ambi-turner!

[@showcase-me]

Douglas Adams Likes this comment!!!

[@corwinchristensen260]

NASCAR is going to have to build bigger tracks...

[@DJejbarros]

"so someone has measured the speed of light... or have they?" Hey, Vsauce... Michael here

[@arjunsubrahmanian7535]

Hahaha exactly!

[@hiftylonghead892]

You look like vsauce but mexican

[@Jacobcr93]

Lol

[@illusions66]

xD

[@mangckyatmamon]

VSalsa

[@KalSunrider]

What catches my attention is the c/2 "limit" to the discussion. What if light could be slowed to less than c/2? Then even an instantaneous trip back wouldn't make up for it.

[@betzalelhughes4546]

Didn’t the Michaelson Morley experiment prove that there was no ether so light moves at the same speed in a vacuum regardless of direction.

[@MagruderSpoots]

What they showed is that if there is an ether the motion of the earth through the ether has no effect on the speed of light.

[@Dr.Kay_R]

It's not only ether that can slow down light. We are talking about symmetry and quantum mechanics. There is weird stuff happening on small scales. Maybe the "vaccum" itself has this property of favouring one direction. It's possible.

[@danielrutschman4618]

No. That experiment proved that the properties of the ether are not what scientists had expected. Subsequent experiments proved that the ether does exist, but because their assumptions about it were so incorrect they gave it a new name, the "Higgs Field", to avoid the embarrassment of admitting they were wrong.

[@egecaglar2265]

​​@@Dr.Kay_R I thought everyone agreed that light travels in the same speed no matter the direction nor matter?

[@teiull9388]

@@egecaglar2265 but its just a universal agreemwnt we have, the point of this video is to tell us that its JUST that, a assumption which makes sense, but we can't prove

[@godzillaxred]

4:06 - "Or have they?" I feel like this was a missed chance to put the vsauce theme on

[@kagebushinmailru]

Also noticed VSause referenceh

[@physicsrox184]

Here kzbin.info/www/bejne/moLaZapvjMyLmbM

[@JanSeewald]

this is depressing here the right url kzbin.info/www/bejne/rqamgGpjebF2l6M

[@DumKump]

Moon Men by Jake Chudnow (Vsauce theme) - kzbin.info/www/bejne/in-VZpqeoMuah6M

[@Necrodzentelmenel1]

kzbin.info/www/bejne/j5jMqop9rq-Wf8U

[@ristopaasivirta9770]

I like the extra effort you put into the short acting parts to visualize the concepts.

[@Raythe]

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

[@higorss]

@@Raythe But how both cameras will activate in the same time?

[@ProblemFactory]

@@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.

[@kristofkarvazy3349]

Wouldn't redshift and blueshift disprove the c/2 and ∞. I mean sure we can't know if it's the same in both directions but I guess we can know that it cannot be instantaneous. Or if it doesn't work this way please explain why.

[@AngelOfDeathAc]

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!

[@Blimbus-Blombo]

As far as I can tell this should work.

[@matthewe3813]

The problem then would be that you would have to fire both the sources at the same time, which would not be possible due to having 2 clocks be synchronized and separated as he stated in the video

[@thanasismpoulionis2493]

You don't need to measure the speed of light in every direction, in order to check if it travels with the same speed in every direction. There is a method to prove that, you can check the Michelson-Morley experiment in which they were trying to prove that the "aether" exists. They ended up proving that the "aether" doesn't exist and that the speed of light is the same in every direction. They developed an instrument that was named after Michelson, called the Michelson interferometer. I really love most of his videos and I am a huge fan, but this video is straight misinformation. What @veritasium is saying in this video is simply wrong. It's shocking to me, given the reputation of his channel. :/

[@MrBaconbyte]

thanks for giving me another thought I can't talk to most people about cause they'll just say I'm crazy.

[@kilmersklassiskakanal]

yeah xD also with the gravity video

[@r3kpwner303]

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.

[@logangentry2365]

Toooo true

[@firstnamelastname8790]

This is just him wanting to think is so smart conjecturing that c is different one way than the other

[@moochoopr9551]

@@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.

[@NitePHX]

Destin was probably having a perfectly fine, normal day and then the phone rings. Now he has a broken brain.

[@jontisaurusrex9851]

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🧠

[@Anton-cv2ti]

@@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?

[@vigilantcosmicpenguin8721]

And that makes it an even better day.

[@crisbercutov7405]

@@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.

[@ericherrmann8012]

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

[@EricK-bw2mj]

I think the problem with measuring the 1 way speed of light is the fact that we are thinking about time and space being mutually exclusive when in fact they are the same exact thing

[@06boh]

Send light from A to B, once the light arrives at point B use this as a trigger to send another light from B to A. You can now measure: - the round trip A-B - the round trip B-A - the difference between the A-B signal coming back and the B-A signal going forward. Should be everything we need to solve it, right ? What am I missing?

[@wifparanoid304]

BA cannot be measured. Clock starting at a recieves the signal to be stopped either at lightspeed, not instantly, or it's instant with lightspeed being half

[@ClikcerProductions]

He explains in the video that you could not synchronize the clocks in A and B properly if c is different in each direction as they would experience different time dilation even if they were move at the same speed

[@Lightning-Shock]

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.

[@yogi30303]

I don't think the difference can be felt/measured through humanly senses. That bmw guy is flashing before it turns green.

[@glinchdk]

@@yogi30303 that is the joke.

[@yogi30303]

@@glinchdk yeah I guess among all the serious comments I took this seriously too.

[@Majesticbro]

@@yogi30303 r/swooosh

[@AcidArmy_]

@@Majesticbro r/slamdunk

[@fr3nchy226]

This is the best explanation of "WHEN WILL THEN BE NOW?" I've ever seen.

[@kimberlystratton7585]

Isnt it the best 'lack of explanation' of 'WHEN WILL THEN BE NOW'? **i really like your point

[@gavros9636]

Soon.

[@jordanammons4851]

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

[@gavros9636]

@@jordanammons4851 How do you start them at the same time?

[@Yrvo12345]

@@jordanammons4851 2:07

[@charlesbrouillette9707]

Great video, really got me thinking

[@dasireddysaijoshan6122]

We can use two clocks When the beam hits the first clock timer start And when it hits the second clock the another timer stars Clock are individual And we can get the diff between the clock

[@jptbaba]

That’s why going to work feels like a drag and coming home feels quick.

[@tarunyelakanti4710]

Lol

[@hoangphatnguyen3271]

Hahaha

[@ShadoryKaine]

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

[@babylebron6119]

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

[@averagejoe9040]

@@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.

[@skeleton208]

“We don’t you reply quicker?” “Sorry babe I’m at Mars rn”

[@majidaskari8306]

That's the way to measure the one-way speed of light. Send babe to Mars.

[@energyzap9484]

@@majidaskari8306 it doesn't matter; no matter if light is same or different in all directions, it will take 20 mins.

[@JacksonJey]

What about measuring the speed of light around the event horizon of a black hole. Space should be bent in a circle there, so technically light moves in the same direction yet circles the black hole and can be measured accuratly. This is pretty hypothetic, but it could be possible, right? Thanks for the video, your really good at revealing and presenting new perspectives!

[@azbz9075]

It still wouldn’t confirm that it moved at the same speed all the way around the circle.

[@matthj9480]

I was thinking that if the speed of light is different in different directions, then the event horizon should NOT be a sphere.

[@user-sb4gf8dh7g]

Your videos are amazing, I don´t speak english but I'm learning as fast as I can cuz I don´t want to miss your videos in both english or spanish. Thanks Derek.

[@Dr.Kay_R]

Learn English. You are missing out on a lot of things.

[@suvratarya]

"Stars look exactly as they are right this instant." Gave goosebumps.

[@user-hc9qv9yb9m]

kzbin.info/www/bejne/pIOqdI2eaqZripY

[@ABHEEeeee]

We saw past of star coz it take millions of year to reach star's light to earth

[@calebmcnevin]

@@ABHEEeeee Watch the video

[@xx_1dreamstanlegend_xx422]

@@ABHEEeeee how do you know? Are you saying you can prove the return trip isn't instantaneous?

[@jontisaurusrex9851]

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🧠

[@feedmyintellect]

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! 😁😁😁

[@justamanofculture12]

We* wanted

[@YusufTANA]

Hi mr veritasium, I think that it is key to understand what the medium that light travels through is made of. It could be that space and light and all kinds of matter are essentially made of the same thing. Just like sound waves are the vibrations happening in different kinds of materials, like solids and liquids and gases. These vibrations mean there is energy causing them to happen. Maybe, it is the same (the energy) that we see happening with space, light and matter.

[@andyabajo]

4:07 *Vsauce music starts* and im anticipating a round head will pop from the bottom of the screen.

[@TheProGam3rHD]

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.

[@ethangutierrez359]

I’m glad someone else thought this😂

[@-MVP-]

IKR

[@princetyagii]

Or is it,,😂😂

[@DudeWhoSaysDeez]

yeah my brain stopped working. I long for the days of before I saw this video

[@tmylve3495]

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

[@boycy69]

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

[@guinessgoin7836]

All other methods are using light as a mode to transfer information, however if you use sound which we do have a one way direction for, we could base the speed of light on its comparisons so the speed of sound

[@charlieagutter3789]

The escape velocity at the event horizon a of a black hole can be used to measure the speed of light in one direction. vesc = Square root of√2GMr

[@Birginio420]

He said "or have they?" I was kinda sad no vsauce music played

[@donottrustanyonelol]

yea

[@mahirshyam4127]

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...

[@BillAnt]

I know, right?! At 4:05 I thought I was watching a Vsauce video. lol

[@HaydenTheEeeeeeeeevilEukaryote]

@@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.

[@kartikchaturvedi7146]

yeahhhh

[@FranticEnemy126]

"So some one has measured speed of light" "Or have they??" *Vsause theme plays*

[@alijayameilio]

I kinda expect there's a theme song... But left disappointed

[@MikeTaffet]

*vibrophone intensifies*

[@sharofs.6576]

Is he even alive

[@sharofs.6576]

Vsauce must have run out of topics. Loved his channel.

[@bestonyoutube]

yes what a garbage clickbait channel this has become....

[@kentprovn]

I think that to be able to determine if the signals have an equivalent round trip or not, we might use a device that will receive signals within a specific time frame. Let’s say that [Device A] on Earth will change its receiving channel every 10 minutes. Meanwhile, [Device B] on Mars will send signals to the expected channel 10 minutes ahead of time, after receiving the message. For example: DEVICE A active channels 0:00: Channel 0 0:10: Channel 1 0:20: Channel 2 0:30: Channel 3 0:40: Channel 4 ... DEVICE A 0:00 SEND>>> It's 0:00 here in Earth DEVICE B 0:00 (Assuming the time will be synced after receiving the signal) 0:10 RECV

[@yveice]

The bigger paradox for me: 1m is defined as how far light travels in one direction in 1/299,792,458s. The speed of light is defined as how many meters light travels in one direction in one second. The speed of light must therefore be the same in all directions, because if it were different, 1m in one direction would be longer/shorter than 1m in another direction. And that would correct m/s of the speed of light. And then what's about gravity? How can we be 100% sure that our light took a straight path and was not bent by gravity (took a longer path as assumed)? So can we measure the speed of light at all? Whether one-way or two-way?

[@mongke1000]

Lol when Destin realizes Derek is about to drag him into relativity

[@kevinrasmussen1748]

yeah, that was hilarious.

[@WyattCayer]

That got me good when he realized what was about to come up XD

[@yeahuh4128]

"Or have they?" **strong flashback of Vsauce*

[@KingR787]

Why didn't he queue the song?! haha

[@WickedMuis]

@@KingR787 He'd need a colab and permission to use the song =)

[@Retotion]

It's a shame Vsauce doesn't really do these types of videos anymore

[@dianereid587]

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?"

[@ishworshrestha3559]

Ok

[@CaneBowl-fk3xk]

To measure the speed of light in the way you present it. Is take the distance of the timer 1 and timer 1 and put that distance between the light and timer 1 then make the wires for timer 1 and 2 is to do the length of the lights wire plus the length/ distance of timer 1 and 2

[@INSPIRED-GOLPO]

Take three clocks, For example Clock-a, clock-b and clock-c. Take points, point-1 and point-2. (The distance 1km) Clock-a and clock-c will stay at the point-1 and clock-b will stay at the point-2. Start clock-b and clock-c ( at the same time) before clock-a. Shot the light and start the clock-a. When the light will hit the clock-b the clock-b will stop. And now, do some calculation and you will get one-way speed of light.

[@theflyingmylle]

This video really changed the way I look at “simultaneously”

[@vast5853]

haven’t seen the video yet, but based off psychedelic experience i know exactly what you mean

[@Cameron-nf3nq]

@@vast5853 could you explain ?

[@Psionyc]

Simultaneity*

[@faizfrez2729]

Now when i do simultaneous equations, i do the calculation for one, and i instantly get the other one.

[@chriskennedy2846]

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.

[@emilianopisani9203]

"Ok, let's synchronize our watches!" - 2070 Nobel Prize winner

[@controlequebrado4455]

SEND THE REINFORCEMENTS THIS GUY IS LOW ON LIKES

[@controlequebrado4455]

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

[@tonylastname4752]

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

[@tonylastname4752]

i meant move them In opposite directions

[@mollykins8h]

I thought this said witches... Happy Halloween!

[@thaonpnguyen1852]

This video was so good! I understand so much More about the speed of light. But I propose a way to measure the one_way speed. So you have 2 clocks, one at the start and one at the 1km mark, and you use a 1km pole and you stand in the middle of thật pole and then you push ít. Thật way your clocks will bé synchronize and then you cần measure the one way.

[@abinnyc]

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

[@eds1942]

“No Officer. I was not speeding. You see, the speed of light different depending on the direction.” Officer: “lol. Here’s your ticket.”

[@epicvillain8308]

Actually this argument has held up in court. Google it, it’s pretty awesome.

[@puskywastaken]

@@epicvillain8308 I tried to but couldn't find it. Mind sharing?

[@lilsabin]

@@epicvillain8308 you are lying

[@orlanino]

@@lilsabin 🤣

[@aaronh8943]

@@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 😅).

[@jimovr7248]

“So someone has measured the speed of light......or HAVE they?” *Vsauce intro starts

[@phlosen7854]

I heard that music start...

[@foxtrotfelix9086]

Im your 69th like

[@Pacwerdna]

Agreed - thought this felt like a Vsauce video the whole time.

[@elig1976]

It is easy - set 2 sensors that send pulse when light passes thru them to perpendicular single clock, so there is no need for synchronization. Path from each sensor to clock and path direction should be same, so delay betwedn pulses will express exzctly time that took light to travel from first sensor to second - that's it, you will measure one direction light speed. Can make a such measurment in several dirdctions just to verify that result is same

[@elig1976]

you don't need to know when exactly they send it - you just need to measure delay between 2 pulses. Since each sensor sends its pulse in same direction for same distance , so time of travel of each pulse to clock will be same and delay measured by clock will express exactly time that took light to travel from sensor to sensor

[@flobiish]

This reminds me of the Jason Lisle articles on AiG trying to rationalize the creation story. Big difference in Lisle's view from the one way is presuming a self-centric zero-tick perspective on the directionality of light.

[@RichardT2112]

Puts an interesting spin on astronomy where we deem distances relate to time, as in the “early universe” due to time it would take light to travel.

[@booJay]

Found this on ​ @Brian Koberlein's blog: "Then in 2010 Jason Lisle revived the idea of anisotropic light. If light moving toward us travelled at infinite speed, and away from us at half the traditional speed of light, then it would allow the most distant light in the young universe to reach us while still agreeing with relativity. As crazy as that might sound, Lisle is right in claiming that such an effect would be indistinguishable from relativity, and this has made the work popular with young Earth supporters. However agreement with relativity isn’t enough. If light did actually reach us from distant galaxies instantly, we would expect galaxies at all distances (or more formally redshifts) to all look the same age. In fact, what we see is that more distant galaxies are younger than closer ones. If Lisle’s idea was correct, we wouldn’t see the magnification of distant galaxies due to cosmic expansion, nor fluctuations in a cosmic background, nor galaxy clustering in agreement with dark energy, nor a host of other observational results."

[@joshandromidas]

This is exactly what I was thinking. I'm curious if Derek has an explanation as to why we still observe distant galaxies the same way in every direction if lightspeed would vary based on direction?

[@anywallsocket]

The notion of instantaneous light speed breaks all of physics, unlike as is reported in this video. SR and maybe even GR would remain the same, but QM would explode instantaneously. You have to realize c is better understood as the rate of causality, not just the upper limit for relative object motion, let alone the ‘speed of light’. Much more likely then, if an asymmetry exists, it is a very subtle one, otherwise you’d run into CPT violations, and also have to extinguish the conservation of linear momentum - which itself predicates all other conservations.

[@SlimedogYT]

It's travelling one way to us though isn't it?

[@ineonfox4787]

@@joshandromidas The thing is, that if lightspeed fluctuates depending on which direction it travels, we'll still see different age of galaxies, because of the difference in speed, so it'll look the same as if lightspeed is constant.

[@joeytje50]

So wouldn't your comment then prove that there is no direction in which light moves instantaneously? Also, considering the uniformity of the cosmic microwave background, wouldn't that show that the speed of light is indeed isotropic? Any directionality of the speed of light would then show in the CMB, right?

[@Vitor-gz6fn]

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

[@MarchelloMastrayani]

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

[@MarchelloMastrayani]

@Zach Comstock me and 11K other people who actually studied Physics The rest of you should go buy kiwico

[@MusicNewb]

@@MarchelloMastrayani I'm actually interested in reading the experiment. Do you have any reference to papers that I could follow through?

[@MarchelloMastrayani]

@@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

[@sonjaschellevis188]

@@ENikolaev huh

[@axle.student]

I think the more important question is: What if the measurement of the velocity of light is off by -0.00...1 compared to 'c'. It changes the the entire context of GR, event horizons and singularities. > We could potentially use the Hippolyte Fizeau but use 2 mechanical connected gears at each end of the kilometer. As long as the connection between them is tight and precise, and we have enough granularity (precision) in the placement of the holes timed at each end to allow the light through at exactly 'c' then we should get a truth test for the speed of light. If it goes through the second hole and strikes a photo sensitive plate it is true and 'c', else it misses the second hole then it is not 'c'. If the truth test fails then you could recalculate the hole timing of the second wheel lower of higher until you get eventually get a truth test. Obviously we would be using a good quality narrow laser, and exceptional small through holes on the gears to get as much precision as possible. > You could add some large centrifugal weights to stabilize the timing connection over that distance and taking a statistic of many tests to reduce error. > Sounds kool yeah :)

[@Robloxninja391]

Dumb ahh me thinking why can’t you divide by 2 from A-B and B-A💀

[@lauyulesamuel6392]

4:07 "or have they?" *Vsauce music intensifies*

[@themostwanted774]

Lmao

[@NarutoShippuuden921]

@@themostwanted774 was looking for this kind of comment, ty

[@danpeer5908]

17:01 "And we'll wonder, why we didn't c it before?" Amazing!

[@chriskennedy2846]

g, I'm not sure...

[@Hank520Tube]

In 1881, 24 years before Einstein's hypothesis, A.A. Michelson and E.W. Morley demonstated that the speed of light is the same no matter what direction in space it travels. Hence the "ether theory" was disproved. Also, rather than by brut force one could just measure the permeability constant Uo (=1.26E-6 henry/meter) as well as the permittivity constant Eo = 8.85E-12 farad/meter and find the speed of light (from Maxwell's equations) to be c= 1/SQRT(Uo x Eo) = 2.99E8 meters/sec. Done. Still a very worthwhile video. Thanks

[@Longest-Word-In-English]

(1:02) How to measure speed: Formula: Speed = distance ÷ time

[@teja8575]

"so someone has measured the speed of light? or have they " sounds like vsauce

[@joseville]

Veritasium, Derek here...

[@Hermann493]

*Vsauce music starts playing..*

[@ricobrawlstars4880]

**Camera zooms to michael**

[@debo325]

Rip vsauce

[@mcknorth]

@@debo325 is michael dead????

[@wShadow1]

The worst part about me watching this video, is that I understand everything he says, but at the same time, I understand nothing.

[@abrahamsanchez7455]

Dude is too smart

[@wShadow1]

@@abrahamsanchez7455 indeed

[@nemeryel6482]

Understand the words, but not the meaning, it's what happens

[@seanpeters7284]

He does speak English pretty well

[@dharmeshvala9886]

Same here...

[@carlpfister110]

build a circle with four light sourses on the outside pointing in the middle, let some weights of equal mass fall from the same hight on the „lightswitches“ and messure if the light out of the four different directions is appearing in the middle at the same time

[@pirotehs]

Button in the middle/center. Two sets of lasers and mirrors are in opposite directions. Button turns on both lasers at the same time and scientists measure not only time laser go forward and back, but they measure when lasers hits mirrors. At least You have rough idea if speed is different in both directions.

[@khizirmohdismail9149]

The moment when Destin realized "Oh snap, Derek is going relativity• is Golden!

[@R0TEK]

Where does the quotation end?

[@bullpuppy7455]

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:)

[@WishMount]

This was the most elaborate, philosophical, mind-boggling, brain bending, insightful, confusing way of saying: We Can’t.

[@noorjahan4679]

Love your videos :) but I really need an explanation for the part where you showed an equation for different speeds of light in different directions...

[@billdouglas1721]

As a lay person (i.e., as a retired guy fascinated by science in general and Veritasium in particular but with no formal education in physics), can we bring entanglement into this discussion? Can we imagine, in some future time, a scientific instrument based on entanglement that we could use in order to synchronize two clocks at two different locations, or that we could use to undertake some of the other experiments you described for learning more about the true nature of c? As I understand entanglement, it is instantaneous, i.e. faster than light. Perhaps my limited understanding of "spooky action at a distance" may be revealing a woeful lack of knowledge about entanglement and about physics in general, etc. On the other hand, perhaps my comment here will inspire some undergrad physics student who follows Veritasium to pursue the line of inquiry I've described above and end up becoming the Nobel laureate in Physics in, oh, let's say 2030. Remember folks: You heard it here first!

[@plooj1260]

Quantum entanglement can't send information (a better name fore c is actually the speed of information). So sadly you can't synchronize clocks that way.

[@billdouglas1721]

@@plooj1260 Thanks for the info. I'm a novice astronomy/cosmology buff, so such information interests me greatly. The speed of information (I like that term) is something I've pondered my whole life (76 years so far). I think of so many now-commonly accepted things (heavier than air flight and a sun-centric solar system, for example) that earlier scientists had declared to be physical impossibilities, only to later be proven wrong. Those reversals of scientific thought bring to mind one of my favorite quotations, from Arthur C. Clarke: “When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong.” I may not see such a "faster than the speed of information" discovery in my lifetime, and probably the originator of that "law" (Maxwell, I think) was right. In any case, science is wonderful, and I thank you for taking the time to reply to my comment and expand my cosmic horizon.

[@bigjoes.1545]

Thanks you’ve distracted me from my engineering finals by making me question a convention of physics.

[@quickestturtle2951]

So someone has measured the speed of light. Or have they? **Vsauce Music intensifies*

[@MatthewHughes811]

What is light? This feather is light. Feathers are used by birds to fly. *Flips you the bird* But what about this bird? Why is this called "the bird"?

[@themafsguy999]

@@MatthewHughes811 accurate

[@donaldalm2293]

Hey guys Micheal here

[@divyakant3534]

Thief

[@AzaliahE]

@@MatthewHughes811 lol this is gold hahaha

[@ellieallen115]

Destin’s idea with the super long fiber spool could work. Run the experiment in several orientations and look for discrepancies. Rotate the spool 90 degrees, capsize it, etc.

[@ShaunDYST]

So take a mirror shoot a beam of light at it and get the time it takes to hit your sensor where it reflects to. Then do the same thing but put your timer at the mirror not the point where it reflects to. Compare times find your difference then you will know if the speed is different for going and coming back.

[@mcmamad]

"Speed of light is the universe's refresh rate." -Stephan Wolfram

[@minerscale]

Has that got to do with his physics project?

[@a.yashwanth]

speed = distance/time refresh rate = 1/time

[@AP05_]

YES LOL

[@Jahooliix]

I haven’t got to the end yet but can you use some kind of quantum entanglement trigger in the future.

[@samusam5853]

Are we living in a simulator?😢

[@rabbitskywalk3r]

After spending all the time to synchronize the the clock, mark then realized he actually had forgotten to take care of the potatoes he had planted in the greenhouse and eventually died, still not knowing what the single way speed of light was

[@sunandinighosh6037]

I understood that reference

[@Bazzwano2nd]

Hello, This is an interesting thought that i can't stop thinking about.. Lets imagine spacetime is moving faster in one direction like you suggested.. couldn't we test the speed in different directions.. would we be able to detect curvature of the light? I imagine it would corve more in one direction if spacetime was moving as in your example? And i then determine if we could detect the curvature it would then prove if spacetime is moving faster in any given direction?? Great video

[@jfh667]

move the clocks at same speed in opposite directions. edit : if possible, while free falling. Also, c = λf and we dont observe radical changes in frequency from one direction to another.

[@treeguyable]

A micro millisecond: The time between when you shut, and lock your car door, and realize you left your keys inside.

[@davidpowers746]

What if the realization happens before the door shuts, but too late to stop it?

[@treeguyable]

@@davidpowers746 We are talking reverse space time continuum. Way past my realm of comprehension.

[@davidpowers746]

@@treeguyable The physics isn't ripe yet.

[@rapidrabbit7175]

Or perhaps 15 years because she told you she was 18.

[@WilliamSmithIV]

The onosecond

[@Tomeroche]

It turns out the speed of light is C/3 and the return trip goes back in time.

[@lexxfirecore123]

correct until proven wrong :D

[@greenanubis]

Or irrelevant until proven right. So prove it!

@@lexxfirecore123 Nope, not how physics works. Not how *any* of this works.

[@rebelquadronfpv1065]

Photos dont experience time.

[@higorss]

@@rebelquadronfpv1065 it was a joke

[@lazthegreat10]

I thought he was going to say, it comes back slower, and then he said returns instantaneous. Very thought provoking

[@FriesOfTheDead]

This is easy, send 2 beams of light. Beam one through a medium that slows it down on the way there, and medium that has no impact on it's speed on the way back. Beam two is similar but opposite, no speed impact on the way there, but through a medium that slows it down on the way back. If there is no difference between the times that the light takes then light travels at the same speed in both directions. if there is a difference between the times, then you can calculate how much it was slowed down in either direction.

[@ethzero]

One thing we can know: Click-bait travels at superluminal speeds.

[@AxxLAfriku]

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

[@sohampatil1392]

True

[@freds2150]

someone's about to get reported

[@paulcoe7511]

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.

[@vasudevraghav2109]

@@freds2150 I did report him. This dude keeps on spamming on a lot of channels, probably hired a program to it.

[@miklos.]

"Or have they?" --- Thanks VeritasiumSauce.

[@Riccardomihaylov]

bro braken my brain

[@durhamgrigg3125]

Love your youtubes!!!❤

[@thegamecity8393]

Lets say on the thing you said about someone on earth telling someone on mars the time and the time won't be the same Cant you just bring the clock from mars to earth and see if it tells the same time?

[@Dalek_Scientist]

4:03 so some one has measured the speed of light. Or have they? 🤨 *Vsauce music plays*

[@romanyoder9266]

I seriously thought Michael from Vsauce was gonna show up in the moment! 🤣

[@Dalek_Scientist]

@@romanyoder9266 yeah, me too, or at least use Vsauce music.

[@MrHatoi]

Kinda disappointed he didn't use that music tbh

[@steve.b8872]

I know you guys saw that fly

[@SaurabhL2012]

I was about to comment the exact thing and saw your comment at to instead.

[@canaldoxerxes]

Mark the Astronaut sends a message. Me, on mission control: "Oh hi, Mark..."

[@4.0.4]

You're tearing me apart, expansion of the universe!

[@thePronto]

"Oh, hi Mark. What did you have for dinner last night? Potatoes!"

[@canaldoxerxes]

"So, how's your research life?"

[@darioinfini]

ha ha ha what a story Mark.

[@Hemebean]

With enough gravity, you could bend spacetime, curve the pathway of light and send that light right back to the same position for measurement. If that's too difficult (probably), you could just bend the light slightly then reflect it back form a distant point. Depending on the position of the gravity well in relation to the outgoing and incoming light beams, the outgoing and incoming distances traveled by the light could be made to be different. We could therefore measure the ratio of the speed of outgoing light compared to the speed of incoming light.

[@kyorith6132]

Im sure someone already came up with a counterargument but there are two things that i believe could work. Firstly, what if you used Quantum Entanglement to synchronize the clocks because that doesn't seem to be dependant on the speed of light. Similarly, what if you could measure some Universal value which is consistent no matter where you are, which is measured at the beginning of the track, where it activates a light beam and the beginning clock right as it measures some predefined variation and at the end of the track where it starts the clock at, what i would assume to be, the actual exact same moment.