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

Here is a solution that came to mind (I'm sure there are many loopholes and someone has already experimented with the idea and it did not work.) What if you use a long piece of a material which changes colour on exposure to light, i.e. the material has some distinguishable behaviour on interaction with light. Using a single long piece of this material we construct an arrangement in an arc/curved shape, such that the material passes through 2 slits, which are parallel to each other (basically the slits are the start and end point as shown in the video). 1st slit is where the light starts to travel form and the 2nd where it is going to be measured again. The distance between slit 1 and 2 is as mentioned in the video and the material moves through the slit at some constant known speed. This way we would have 2 exposed spots on the material and calculating the distance between them factoring in the geometry of the set-up, we should be able to measure the one way speed of light right?  This would remove the need for any synchronisation as it is a single piece of the material which is moving at a known speed. Not sure if relativity comes into the picture with such a setup, or if its practically possible. P.s. i'm not a physicist, this just came into my mind. I did not even try to see if this experiment has already been tried. I will probably try to search for it now :)

Not knowing the speed of light is the problem. You are using the speed of light as a measurement. Also the time returned to any unit that measured it takes the return time to signal

@brandon doner but the measurement is done after the experiment is done. Essentially only one photon will be used in the setup and it should not be reflected from the material.

I think this is a decent way to measure the distance, but how would you measure the time it took to get from point a to b?

@Bryan We know the velocity at which we were moving the material. As you said if we can measure the distance, we already know the velocity at which the material was moving, so we can calculate the time. Then use that time for calculating c. The distance for calculating c is the distance between the 2 slits. To summarise there are 2 distances, 1. distance between the 2 exposed areas on the material. 2. distance between the 2 slits. 1>2 because the material is curved to pass through the slits. There is only one measurement of time which can be made using the known velocity at which we move the material through the slits.

I'm no physicist either but I think this wouldn't work because you cannot know if the arc starts moving at the same time on both sides (beginning and end) = if you start the movement of the arc in the middle, the left side could start moving in c/2 and the right side instantaneously. In your example the moving material on the sides acts like the 2 clocks and there is no way of calibrating them (as explained in the video). PS: It's very fascinating how many beautiful ways people in the comments manage to "forget" that even solid material moves at the speed of light.

Your centered synchronizing device at 9:48 can be used by itself to determine if light has different speeds in different directions, thus proving if C qualifies as double your one-way measurement of light or if they do have different speeds, the difference in the time of the clocks will allow you to calculate that.

No it doesn't? What difference in time are you talking about?

@Noa I'm speaking of the numerical time difference between the two clocks he uses, it's shown about 20 sec after my timestamp

The problem is that the information of each clock's current time itself travels at the speed of light (either visually or through wires) so trying to compare the two clocks is just pushing the problem back a step without solving it.

We will never be able to measure the speed of limit. God created it.

@Trucker Rawb I could confidently argue that there is no god. Just like you can't prove the speed of light, you can not ever prove the existence of god. But there is logical arguments supporting his inexistence.

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

If his signal to warn you travels instantly to you then the light informing him about the combat situation traveled to him at half the speed of light. So either he'd see the situation in real time but his warning would be late or his knowledge of the situation would be late but the warning would be instant but arrive late anyways. Either way it doesn't help you any more than light travelling at the same speed in every direction would. It's just like the mars example in this video.

Of all things why would one choose “combat situation” ?

Sounds like the movie TENET. In their case it was....nah can’t spoil this movie

@Karamba why not

Star wars

As Destin said: it broke my brain. But I believe that regardless of the speed of light being the same in any direction or being instantaneous, things can really be happening simultaneously, this is just not possible to observe. Thanks.

It seems that one could know if the speed of light is the same in all direction by looking at far away galaxies: if a lot of galaxies seems too old in one direction only, then maybe the light travel faster from this direction to us, so we're just seeing the galaxies as they were recently.

Imagine you can see the galaxies in one direction in real time, so they look old, but galaxies in the other direction have been moving away from us at much higher time dilation, so they have been aging faster, so even though the light takes longer to reach us, the galaxy was older when the light left

Yes but maybe those galaxies were created after or before

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?

Use relativity to back out the speed light. Have two light sources in a line point at the same object in between them. Move the object towards one light source and measure the blue shift. If the red shift is the same from the other light source then the speed of light must be the same in both directions because the relative velocity is the same except for the opposite direction.

If nothing else, I think this demonstrates just how closely related light, space, and time are - so much so that they start to feel less like separate parts but rather one single thing.

Very interesting; great video! Doesn't this ultimately talks about the speed of the propagation of *causality* (as in 'c' for causality), rather than the speed of *light* (after all, the speed of light is dependent on the medium in which it propagates)? 14:08: It seems that there is a consistent *interval* of possibilities between [ (infinite, c/2) .. (c, c) .. (c/2, infinite) ] which are all *indistinguishable* (along the axis of propagation from the causer to effected observers)? Couldn't the speed of the propagation of causality, in fact, be *variable* rather than fixed/constant (e.g., at symmetric propagation speed (c,c))? This connects a bit with the "simulation hypothesis"?: This "semantics of the universe" would certainly give a lot of computational flexibility for "the simulation engine". It is as if there is a connection between quantum mechanics and "lazy evaluation" (programming technique whereby you only compute/evaluate/resolve something when(/if) it is needed). Just a [spooky] thought.

What if you sent pulses to both clocks simultaneously using a medium other than light or electricity? Maybe physical objects or sound waves. Would time dilation cause the same problem as moving the clocks in that case? Also even if that doesn’t work shouldn’t we be able to synchronize the clocks using quantum entanglement one day in the future?

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

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 :)

Would it maybe work to use telescopes to "see into the past" by looking really really far away, and comparing how far back can be seen in a given direction? if the speed of light was faster in one direction, maybe we could see further back in that direction?

The central problem is your single point of observation. What you observe could be past or present and it would be indistinguishable to you at that single point of observation. You have no other point to compare it to. When you add two observers, time dilation kicks in and you can't know if you are recording the same simultaneous point in time between each observer and what is being observed.

2:42 Can't you avoid the desynchronization problem by moving the first clock to the second as soon as light hits it (that way the time slow-down also affects the first) and stop both clocks once they touch each other?

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

What about using visual feedback on impact of the light to determine if the speed of light differs in one direction from another? For example letting light burn a hole in a sheet of paper placed on top of a mirror that is reflecting a laser beam back to another sheet. If the light burns a hole at the exact same time in both sheets than one direction is faster than the other, right? Im pretty bad at math and dont like to use my brain often but this got me thinking and gave you another sub. ;)

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

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

oh hi

@SkyLimited lol u win the youtube comments

@Saran Vashisht lol you win the YouTube comments

@Bearded Dragon Man 1997 lol u win the Youtube comments

But he doesn't have a synced clock!

If you take a fiber optic and make it travel around the world so you have the two ends at the same location, wouldn't it work ? You can also turn on a clock and send a light signal to another clock to turn it on and see the timer difference

If black holes or massive objects are used to warp space-time such that the light path is looped back to its spot of origin, then the experiment can be done in either direction around the warped space-time to see if each one way trip time was the same. 😁

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

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

The issue is all the speed we have calculated till date is fully related to derived speed of light and can not be put as reference point

Shouldn't it be possible to sync the clocks with an electrical signal that you send exactly from the middle?

@Mister Santa if the speed of light can depend on direction, then so can the speed of electrical signals (electrical signals are carried via electrons, which interact with each other via virtual photons, which travel at light speed).

How about having like a 2 stopwatchs like you have on your iphone and manage to start them together at the same time and sit on both ends , one the light reaches the first one the stop watch stops (lap) and when it reaxhes the second one then the second stopwatch stops (lap) then you end up with a number like you do it on your iphoe, 😂 sound funny but could that work somehow?

That hurt my head and i have delved into the layperson's pool of quantum mechanics! OUCH. I knew long ago no one can measure light because of the analog properties and quantum uncertainty, bu THIS specific way to put the idea? It really hit home. You are a great communicator my friend! I love this thought exercise

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

The redshift is a change in frequency and indicates a slower time frame and the shift to the blue indicates an increase in the time frame of otherwise stated as a increase in the recessional velocity.

@Mo King Doppler causes redshift but if you observe red shift it doesnt necessarily mean its caused by recessional velocity. Gravitational red shift for example. In the book Seeeing Red, Arp shows anomalies that put this assumption into question. Read it

@pedrosura I have never said that redshift is caused by recessional velocity. Redshift is a frequency shift that is caused by a time change because Gravity controls time and that is now a solid fact

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

@Automatiic the comment man works in mysterious ways

What about a single clock at the light source, with two mirrors so the light flows in a triangle, ie. 3 distances. You could test in both directions and see if they are the same (2 of the distances are round trip so cancel each other out, but the middle distance should tell you if the light travels at the same speed in both directions)? You could also then rotate one mirror so the light returns back, so travels 2 sides of the triangle, then bounces back through those 2 sides. Test that in both directions, and they should be equal, so proving the system is set up correctly, proving the first test results are accurate.

Criminally neglected option. You can even bump up the number of mirrors in different angles

So, what if there is just one intertial reference frame in the universe where the speed of light is equal in all directions? But if you move, even at a constant speed, the two values are different? You would never measure it because the laws of physics don't change, as you said. But it would be exciting if those values actually depend on your reference frame, it would mean that the universe is still :)

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

I thought of a solution to measuring the speed of light. Take both clocks, and start then via pressing the button with a 1 kilometre long plank (where the plank is lowered on the start button of both clocks). This would make the clocks start together.

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

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

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

Underrated comment!

@Comrade Pi yes it is

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

WOW

@Derek what about utilizing "Spooky Action at a Distance" as syncronization between point A and point B. This ensures that time dialiation doesn't come into play. on top of this, a mirror could be used to reflect the light back to measure the revese speed of light using the same "Spooky Actuib at a Distance". I'm no scientist, but it was just a thought 🙂

I would like to ask for something. My whole point would be about wormholes, which I shall consider here since even if we haven't seen any yet, they are theoretical solutions to general relativity equations. Considering their existence, wouldn't it be possible to use them to verify if time dilatation for 2 clocks sent in different directions but ending up at the same location is the same ? We would then have proof that c is the same regardless of the direction of measurement. Here's my thought, I'll let you debate about this :)

Doesn't space-time warping from highly gravitational influences give us this? For instance, viewing the light output of 2 black holes merging compared to the ligo detectors output? Wouldn't that give us a means to determine light generated one way?

I love your way of thinking and especially explaining truly

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

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

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.

I guess, it's because space-time is unified, but you need to use space divide by time to define speed, which is complicated on something with light speed.

I actually came up with an experiment to measure light, instead you can use a high speed camera, take a laser pointer shoot and shoot it at the camera and at the same time film your hand with another camera, see the time it takes for laser to hit the camera and the film of your hand pressing it and sync the footage in post and measure it by how many frames it took for the laser to appear in the high speed cam. Now maybe laser pointers aren’t the same speed but you could use a flashlight as well.

This is very interesting and should be considered when looking at dark energy. Galaxies seem to be moving away faster the further they are from us. But maybe it's because the speed of light is different the further away we look.

Dark Energy is the result of hidden black holes bypassing time. When you look at an expanding galaxy from a great distance you will see the effects of differing gravity changing time.

Could the Large Hadron Collider measure the speed using the same clock as the start and end point? Wouldn’t they need to know the speeds the particles achieve to understand the reaction of the experiment?

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

@MarchelloMastrayani U sound hurt.

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

If the two clocks were synced by quantum entanglement communication (supposing we someday find a way to use QE for comms), would we be able to measure the one way of speed of light?

Two questions: 1.)If this is true, would that imply something in the universe could travel faster than C 2.)Wouldn't Occams Razor suggest that this is unlikely to be the case?

1) Nothing would be able to travel faster than the speed of light in it's given direction of travel, which is functionally the same as if c is universal 2) Occam's Razor certainly does suggest this (he even mentions it in the video), but that's not a proof. "Probably true" is not the same as "is true"

​@Wheeler Pryor God could travel far faster then the speed of light. There's a reason why there's SO MANY gaping holes in every field of science. Look into the origin of life. When the planet was ready to sustain life, there was only 2 things on the planet, mass and energy, guess what those 2 things can't create lololol life and before you say ohhhh a meteor, that has been completely ruled out by Christian and secular scientist. God is amazing and we will never figure this out ❤😂

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

This was a fun video! There are ways to measure the one way speed of light, but I doubt there would be a consistent answer. It would vary each time the speed test was run. Using entanglement and coherent light to trigger a measurement is only giving you the speed along the path the light took. How many variables are you contending with? We are dealing with all sorts of gradients in time, not just gradients in space. Also, the speed of light is not the 'speed limit'. Isn't more likely that the speed of light is dependent of the speed at which information can propagate through space-time. Even all of this is based on the supposition that space-time is fundamental. It is more likely that it is not. All in all, I really enjoyed this and got me thinking about when I was a kid and I wanted to solve problems with interstellar communication.

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

This does not work because in moving one clock in one direction and one clock in the other direction, we would have to assume a constant speed of light in both directions. If the speed of light is not constant, then each set of clocks will change relative to the change in the speed of light in the direction those clocks are going. So if the light travels x speed one way and y speed the other way, the clock moving in the x direction will change based on the x variable, and the clock moving in the y direction will change based on the y variable. This is because the formula for the change of clocks over space includes 'c' in it's equation. Edit: Your suggestion is actually a variation on the satellite suggestion on the video, just with the satellites crossing each other instead of moving tangentially.

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

Unfortunately it shouldn’t be.

@Michael Frankel — It shouldn't be impressive, or it shouldn't be that this is an issue? 🙂

Garance A Drosehn impressive (thanks!)

@Michael Frankel Why shouldn't it be?

The paper Derek quotes from is the one where Einstein laid down special relativity for the first time, so it wasn't before he started tackle relativity

I think If you use the example of Destin to calculate the speed of the ball with high speed cameras from a LONG distance from both ways, record and measure the speed of the ball, if it is the exact speed on both cameras we can conclude that the speed of light is the same in both ways otherwise it is different.

Why not use the centered synchronization clock method, and take a picture from a third vantage point of both clocks and see if they match. You could use this method to determine if there are any variables depending on the angle of the camera relative to the clocks.

Pictures also measure light... And you don't know how fast it travelled from each clock, so the clocks might be synched but still show different values on the pictures because the light travelled faster from one clock than from the other. At least that's what I think.

Can you measure the speed of light in an L shape, similar to how we do for gravitational waves? Measure it in an L, then rotate/flip that L in various ways to get the full range of directions for the speed of light? If the light is faster in one direction than the other, each orientation of the L shape will have a slightly different return speed. You still wouldn't be able to measure the actual speed, but you could prove that there is a difference in speed based on direction.

Their more talking about light returning than if light goes faster east than west.

I wonder if they've ever tried to measure the speed of light by bending it. Make it move in a circle. Shoots light from one side and captures it from the other. Maybe they could try something like using a fiber optic cable. I don't know if it will work because I never tried it either.

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

"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

Could you not just do the gear experiment, but with the lantern where the mirror is and a much faster gear?

Hey @Veritasium, I really like your Videos I have to say. I have thought quite a while about this experiment. The reason why the two planets earth and mars cannot differentiate between the light traveling 10 minutes each way or 20 minutes one way and instantly the other, is because the sum of times in both ways is always the same in the experiment. And in order this to be true there has to be the relation given between the two speeds C1 (earth to mars) and C2 (mars to earth) and C (regular speed of light) : C2 = ( C * C1)/( 2 * C1 - C) And what physical background should there be behind that light behaves like this? And it also means that the slower light is in one direction, the so much faster it must be in the other ( in your experiment C1 = C/2, C2 = C * infinity). And this also does not make sense what force is so differently having an effect on light. Therefore we can be sure that if we cannot measure any time difference that light travels from earth to Mars and from Mars to earth and the sum of both being the same as we expect to be at equal speed in both directions, we can be super sure the speed of light is the same in every direction. This being said my friend, there has been measured a time difference of the speed of light in one direction versus the opposite direction: that was in the experiment when gravitational waves were proven to be true, you can Google it. It was proven that gravitational waves exist and they distort the distance between to objects thus the light is faster at the destination as it is supposed to be. Check it out.

Ok, so I would love to see this experiment run. Have 4 timers, 2 on each side with a laser, and a mirror at each side. Start the timer the same time the Laser starts, and then the Laser travels to the mirror on the other side, triggering the 2nd timer that stops when the original Laser returns.Would that not measure the speed of light in one direction? If not explain why.

Could you sync the clocks by pulling apart. Then shoot laser from the middle and split the beam to go both (or many) directions. Stop clocks when light reaches them. Then compare times? Light would be going the same distance in different directions and measurable.

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

When we look at the stars, we look back in time (at least if c is isotropically constant as usually assumed). The furthest look we can have is to observe the microwave background, isn't it? And as it changes smoothly the speed of light should change continously depending on the direction. Moreover, if we assume c is infinite for a particular direction, we should therefore be able to see indefinetly far into the universe and thus indefinelty much galaxies. So, if we compare the galaxies visible in different regions of the sky, we should be able to estimate an upper limit for deviations from an isotropically constant speed of light?

Came to the comment-section just to point this out as well.

This exactly, an interesting video nonetheless but this was not mentioned

they had that tired photon theory

Arguably, the distance of those far away galaxies cannot be determined if C is not constant. So basing the value of C on how much more "primitive" a galaxy looks depending on how far away it is only reinforces the unknown presented in the video. If we look at different patches of the sky we see that there is no standard/constant change in the development of those galaxies, and this is generally explained as the result of gravitational lensing. However, the same observation can be explained by the variability of C as well.

I was just wondering the same thing. If direction matters, wouldn't we see parts of the sky more or less as what they were some time ago (and therefore having dark gaps in which light hasn't reached us yet) and at the same time other parts that are much much brighter since that direction is the "realtime view" (if we can call it that) and we see much much farther away (and more stuff too)? Anyway, cool video as usual :)

Probably way more complicated (and probably already been disproven), but why don't we just set up a single starting switch that would relay a signal through two equal length wires at the same time so that the signal reaches both the light cannon and the stopwatch at the same time. This way both the light cannon and stopwatch would receive a signal to send off a beam of light and to start the stopwatch (Which would be at the end of the distance) at the exact same time. You could then use the light as a trigger to shut off the stopwatch and time how long it took light to make it to the other side. The hard part of this would be making sure that the signal would reach both destinations at the same time, but I still think that could be figured out...

I'm no physicist, but I've heard of slowing light down through different mediums and under very low temperatures. We could slow light and measure speed in various direction in the normal sense. Although speed will not be normal we could still prove velocity changes. Another idea is to use quantum entanglement to synchronise clocks over great distances.

I don't know if I am right or wrong, but let's consider a scenario where we question the synchronization of clocks and their dependence on each other. We can explore the possibility of a different speed of light, which would result in varying time dilation for moving clocks in different directions. To investigate this, let's perform the following experiment: First, we will move one of the clocks, let's say the right one, at a constant speed towards the right for a specific distance. We will then calculate the time difference, or the dilated time, between the two clocks. Next, we will move the left clock towards the left at the same constant speed and for the same distance, and calculate the time difference once again. If the dilated time is different in these two cases, it would support our assumption of a different speed of light. Conversely, if the dilated time is the same, it would indicate that our assumption is incorrect. It's worth noting that we should consider the distance the clock moves rather than the duration of its movement, as the distance should remain unaffected by the speed of light. I welcome any corrections if I have made any mistakes in my thinking.

If this is the case, could things in space actually be closer than we think since we are assuming the speed of light?

Interested in knowing how this would impact looking "back into the past" at ancient galaxies or the CMB?

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

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

Actually they (in error) took something pretty simple and made it unnecessarily complicated. The solution: Now that we have measured the two way speed of light, we can measure it one way. An observer on Mars can be told that precisely at Noon their local time, that Earth will send a communication. Precisely at that Mars Noon (which Earth also knows on its own clock's time from a previous two-way measurement to synchronize the clocks). Earth sends the communication. Mars then records when the communication arrives and compares the speed indicated to the assumed speed of light (based on the existing two way precedent of nearly 300m M/s). This tells Mars exactly how long it took the light to arrive - and whether it matched the assumed speed of light or took longer or took less time to reach Mars. And if we furthermore allow the communication to reflect back to Earth, Earth can use the same method to record that signal's speed back to Earth and show whether it matches the traditional assumption. To verify this, all Mars needs to do is confirm later for Earth observers at exactly what time the reflection on Mars occurred. This allows us to verify the speeds each way individually and whether light was slower or faster in either direction.

If there was a direction where the speed of light was infinite, then wouldn't the proportion of young and old stars be different (older) in that direction as you looked out at the universe?

What about doing the round trip time, but from every possible angle (North to south, North to East, etc all angles/combinations), could you math out the direction speeds?

I like this idea. This one seems like it should work. Even better is if you had a sphere of clocks. This way you can see the deviation in all of them from a 3D perspective. See if direction has an affect on spacetime.

This is good but there is a much easier way. See my reply to them beginning "This is not really true."

Could you use quantum entanglement to sync the two clocks?

I have an idea, that while doesn't tell us "c = this" could(assuming doing it isn't too difficult... which it probably is) tell us whether a guess is correct. Basically, have a light shoot(at a certain angle preferably) at a mirror that goes one way. If we're correct about the speed of light, we'll be able to calculate how to get the light to hit the mirror. If we're wrong, we'll get no signal of the light returning. So it doesn't measure 1-way, but it gives us feedback on whether our guess for 1-way works.

Lets go with the two clocks in the middle. If we have them syncronised in the middle, and then move them in oposite directions in the at the exact same speed, but stop them at a set distance. Or, further, four clocks, so that a set can be checked agains each other, one to test the timing when stopped to verify it is the same time, and the other set for light speed in one direction. There are clearly flaws, and functionally impossible to do in real life, but is the best i can think of for a one way test.

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

@trumpetbot No

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

Could we use quantum entanglement to calculate the one way speed of light? Have 2 sources constantly share the super position of their particles and use that information to calculate the time it took light to travel from point A to B and from B to A.

No, because quantum entanglement can’t be used to transmit any meaningful information. Very complicated to explain but there are great videos about this on PBS Spacetime

@Veritasium Has this been tried as a way to verify the uniformity of C in all directions? And please let me know if this falls short of this goal. A cube shaped clock is placed between “n” sources of light. There are light detectors on “n” sides of the cube, aligned with the light sources. Now in front of these light sources there are barriers blocking the light from being transmitted to their corresponding detectors. There is a mechanical, solid, structure designed to lift the barriers so that each barrier is lifted at the same time. Start the clock. Lift the barriers. As light is detected from each direction the time is logged. Compare the results and see if C is different in any direction. Repeat at various directions until C can be define with certainty… or mapped out.

I'm betting the way the light receptor works uses the 2 way speed of light. Or there would be a time difference that wound require you to know the speed of light to factor it out

@Charlie Hendrix tell me more

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

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

This is quantum physics

Always thought speed of light could be simultaneity, for me is very counter intuitive to accept it is 300.000km/s only… Could each mirror reflection slow down the speed a light as well? Or do you think only direction could affect it? I loved the video, fascinating area!

Is it possible to synchronise the clocks at a central point then move both apart from the central point at the same speed?

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

@cibo LOLLLL

yeah

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

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

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

If the two directions are different speeds then we have to do some weird particle physics for the one way.The best way I think is with a worm hole because light would be going in the same direction but that is weird in its self also because of the theoretical physics of worm holes.

The only way I can think of that could work to solve the measurement problem would be using "spooky action at a distance" to synchronise the measurement. However for this one would have to assume that "spooky action at a distance" has no delay, which is something I'm not sure of honestly.

Spooky action at a distance cannot be used to communicate... it's forbidden by modern physics, so doesn't do us any good

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

The clock isn't gonna be out of sync after moving it only a kilometer to any appreciable degree unless you move it near the speed of light. So, you could still measure the speed of light by syncing the clocks up next to each other first and then moving one a kilometer away with a truck or something else.

What if there’s another force in the universe, one that we don’t know about, one that one change how we think. This begs the question, would we even know light exists if we didn’t have eyes?

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

Very interesting question.

Yes but we would have never noticed the difference. Maybe if the speed of light was equal in every direction than many things would looks different.

@Jasper zdan Could you elaborate?

Depends how you define direction. I would think it would be from point source vs reflection more than a x/y direction

A fish doesn't realize it's in water until it comes out so how would we know the difference if we never seen it

True, I was going to say to see the difference in moving the next measurements further but it wouldn't change the % there and back final time. But if you change the distance and nothing changes doesn't that kinda mean it's one constant speed. So reverse shouldn't change that

The only solution i can think of (must be flawed) is using black hole, their gravity can "band" the light so it came back to its starting point while doing a perfectly straight line. Now we need to travel to a black hole manage the time dilatation due to gravity and here we go x)

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

So... this is something I have thought about: You are on a phone call (on the internet or land line) and you are speaking with someone on the other side of the world. That round trip time or one direction time can/could be measured. There should be a time difference (all be it very small). Why can I interrupt the person in what seems like real time. Is it because the delay is so small that we can not detect it?

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

The concept of light reaching a infinite speed on the way back is such a cool idea

the concept of stopping time and moving around while it’s stopped is also such a cool idea... if you catch my drift

Infinite speed....

There is something about infinite speed of light that makes me think being able to see into the future but there is definitely something that disproves it so I won’t think about it

@RIOT_ BABY22 I just read, for infinite speed to happen, both events have to happen at the same time. Traveling from a to b normally is limited. Yet for infinite speed to happen from a to b, both points would have to synchronize. Since only photons can travel at the speed of light. I think we’re not even scratching the surface upon light speed.

@Totodile 9:48 YOOOOO IF WE STILL DON'T KNOW IF LIGHT SPEED IS THE SAME IN DIFFERENT WAYS, WHY DON'T WE USE SOUND TO SYNCHRONIZE THE CLOCKS???? LIKE WE INVENT A CLOCK THAT STARTS COUNTING WHEN A SPECIFIC SOUND SETS IT, THEN WE LAUCH THIS SOUND IN THE MIDDLE OF BOTH CLOCKS, LIKE IN THIS EXAMPLE THAT THERE IS A SYNCHRONIZER DEVICE, BUT INSTEAD OF USING A SYNCHRINIZER DEVICE WE USE THE SOUND!!! THEN WHEN THE SOUND LAUNCHED IN THE MIDDLE WAY OF BOTH CLOCKS REACH THEM, THEY'LL BOTH START COUNTING!!!

Why can't you use a known speed to double check the speed of light? For instance, sending a beam of light to a repeater, which replies with a sound, a radio wave, or a bullet? If you can measure these values independently of the speed if light, you should be able to calculate one way trip.

Well couldn't you do the laser test by connecting two lasers at either end and activate them with a device linked by the exact same type and length of cable from the exact same batch and measure it 1 way both ways and see the difference if there is one?

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

Why not just synchronise the clocks then move them x distance away from each other simultaneously at the same speed? Won't that ensure that the clocks are synchronised and equidistant to the center?

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

If the speed of light was different in different directions, wouldn't one side of the universe look younger than another side?

Yes

But you never know because you are on one side

@Ayush Gundawar well, you ARE the center of the universe at all times with it expanding from you so (assuming swotiix is right) it would change from your perspective (I THINK)

@Undercoft You are the center of the observable universe. The universe as a whole has no center because it’s observed that all regions of the universe are moving away from each other in no respect to their individual positions within the universe.

@Horsepipe Thats what I was referring to, My bad if it didnt come across as such

Wouldn't the easiest solution for the time dilation problem be to place the 2 clocks 1 kilometre apart, set them both to zero, and then attach a mechanical device that will start both clocks simultaneously, by pushing down on their "ON" switch ? To have less inaccuracy due to bending materials, you could have a shorter distance between the two clocks.

Could the light of the big bang reveal anything perhaps? If constant in all directions it may proof Einstein's assumption I suppose. Nice video!

What i think can be done is Mark both clocks at 1km distance and set trigger point 750m from them and change relative position of trigger point keeping 750m constant and check variation for all readings that can be used to set time offset