The overly clever setup of the beam splitters, detectors and the clock reminds me of how designers of perpetual motion machines try to hide the energetic symmetry of their devices behind complex mechanics. The end result is the same: you just can't cheat your way around conservation laws and symmetries.
@@-danR 🤦♂🤦♂🤦♂ that's why I said "read my comment", because I meant MY ACTUAL EXPLANATION COMMENT ON THIS VIDEO 🤦♂🤦♂🤦♂ why would anyone think that "false, read my comment" 4 literal words would be the explanation of anything? I... I'm legit debufunged
@@raulkaap yes but not because of "cheat your way around conservation laws and symmetries", there are not "conservation laws" nor "symmetries", is just that if you measure it, it is the same, and it kinda makes sense because it would be a bit weird if it changed, but I don't necessarily see any clear reason why it couldn't, because there are no such "laws". but at the same time, your comment seemed to imply that there is no way to measure it, and in my comment I explain how there is, in fact, that is my point, that if you measure it, it is the same, because you can measure it
Somewhere, probably on PBS Spacetime, I learned that if I relabel the 'speed of light' as 'speed of causality', and light just going 'full speed', that makes the intuition slightly better. After a few years of mulling it over, I agree.
@@farhanrejwan surprinsingly, many ppl still enjoy oldtimes TV bc they don't need to choose something, just the channel and watch watever they give youl; I have a tiny amt of doubts and also no evidence, but I believe this could be cause by mental exhaustion,(which can come from anywhere), at least for ppl who do it for long periods of time......... also could be they don't want to bother looking for a youtube channel or whattever that plays random shit, like simpsons episodes or so,, due to ignorance or also lack of mental energy, there is a possible third scenario, which involves a third party showing the subject how to look for and/or setup such tvlike experience on phone, pc or whatever, but the subject will refuse, possibly due to lack of mental energy.... yea, i know, it's the root of all problems, even mine..... what am i even doing here, all coked up, writing pretentious nonsense..... ah.....
your videos have repeatedly inspired me to re-engage with scientific learning. you make scientific understanding feel within reach of anyone, not just labs with big grants. also you are precise, but also humble. thanks for publishing your videos.
learning is what makes it unique, whereas any of the many edutainment-type science channels can ultimately only offer a form of teaching or lecturing, the distinct ability this channel has is to just offer learning instead
This is a great a great video! I want to point out that you missed a simple (yet arguably not obvious) way to make opposing anisotropy locally: make the spring-mass setup MOVE! Or equivalently, make the wave generator move, so that it excites a different mass at each time step. From the resting frame of the wave generator the wave propagation is then opposing anisotropic. You might say that this makes no sense in the setting of the EM field because the field cannot have absolute motion. However, this is exactly the ether interpretation of the EM field (and spacetime itself): opposing anisotropy in the speed of light can be explained by assuming an absolute rest frame (the rest frame of the ether aka the rest frame of the CMB) and anisotropy resulting from motion relative to it.
But while this possibility doesn't suffer from the energy conservation problem, the aether has other problems, and all the old aether theories have been disproven, e.g. by the movement of the earth trough the aether. My takeaway is the following: The current theories describe most of our universe extremely well, so we often try to make small changes only. This video convincingly shows that an anisotropic one-way speed of light is not possible by making only small changes to our theories. But your comment hints that we can never consider every possibility. That is, unless we employ a much more systematic approach to the assumptions underlying our modern understanding of the universe. There are a lot of interesting ideas out there, but nowhere near enough manpower and funding to check every single one with all the consequences individually.
@@entcraft44the key thing here is that the *old* aether theories have been disproven. There is a way to have an aether field in such a way where you get the exact same equations that you get from relativity, where the speed of light is constant in the reference frame of the aether, and objects moving relative to the aether get length contracted and time dilated. This formulation gives identical math as special relativity so it is not possible to distinguish which interpretation is closer to reality through measurements
@@entcraft44 Aether has been disproved but an absolute rest frame has not. In big part because of the two-way speed of light. Once you assume that speed of light is the speed of transfer of information from one segment of space to another then you can have both the relativistic effects as well as an absolute reference frame, where the constant speed of light in any reference frame is just a result of slower processing of the thing moving close to the speed of light. (ie: imaging you have a clock that measures the passage of time by sending a short ray of light towards a mirror and waiting for a response, that clock would indeed slow down the closed you go to the speed of light, and stop completely once you reach the speed of light, since light would have to move perpendicularly to the mirror, the exact same thing happens when one particle sends our information and waits for it to come back) All the other space warping effects are also accounted for as being just a mirage caused by difference in processing speeds of information( photons in this case) that arrives perpendicular or and paralel to the motion as well as what just happens when light travels at a fixed speed.. First from the object's PoV the entire universe shrinks along direction of motion because its own processing slows (so everything just starts becoming very bright, and very blueshifted) Additionally the faster the object moves the more perpendicular to its movement the light has to be to actually hit it. I did the math and some simulations on this and it all checks out, tho I'm still unsure as to where the extra mass is coming from when you accelerate things close to the speed of light.
i think people are too afraid of "unsolvable" problems like this. if our current model does not predict any effects from this hypothetical and we do not observe any effects to prove our model wrong in that regard, it truly does not matter what the answer is. its like trying to prove the existence of an unobservable god with science. i appreciate the insight on how a closely related problem is much more approachable
@@YuriyKrivosheyev not quite. russel's teapot places some arbitrary "burden of proof" on the "positive claims". in reality, neither claim inherently has more merit than the other. the proper way to look at it is that whether this teapot "exists" or "doesnt exist" cannot mean anything unless it has observable effects (which it does not). embrace the fact that there is no useful answer rather than arguing one way and demanding proof from the one arguing the other way. otherwise its like trying to prove a god *doesnt* exist with science.
Yes, but… not really? Science has its dialectic in pure idealism, the imaginary, intuitive and creative. These “brain functions” are our pathway to pure empirical knowledge - ontology and epistemology, subject and object. More culturally, we depict someone getting a bright idea (lightbulb moment in cartoons), and then the “labour” to prove or disprove, calculate vs experiment, theory vs observation. As this video also shows, Einstein knew his Maxwell, and “imagined” how time, space, mass and energy interacted - and, well it still works, empiricism backwards and forwards to now. Einstein also put a nail in time travel, so the only way forwards is - unknown and undefined. Perfect for those “unscientific” traits we have, besides logic or reasoning. This is also how “wrong ideas” emerge, but are not empirically sound if they can be disproved. There are always “ideas” in a sort of superposition - before we are able to both prove and disprove. Both are necessary. If I’m wrong in this position, we have invented or discovered “everything”, there is no forward empirical path - nothing to imagine into the field. It’s a gloomy world at this time, but not _that_ gloomy?
@@jotch_7627Ultimately you can’t prove about a generic god with science, but many religions make enough additional specific claims about their gods that the gods they describe can be assessed
The best explanation of 0ermittivity and permeability ever, and the analogy with mechanics made so clear the concepts of isotopi and anisotropy of the material... literally wow, You deserve an honorary Professorship
It's fun that we can do this same experiment to measure the speed of light by reflecting a laser from the moon and timing how long it took the detector to pick up the same wavelength That folse guy makes reaction videos about everything, it's gross, can he not make his own video that he has to suck the attention away from a genuine creator, he adds Nothing.
The analogy to little springs reminds me of Feynman talking about the rubber band analogy for magnets: th-cam.com/video/MO0r930Sn_8/w-d-xo.html "I can't explain that attraction in terms of anything else that's familiar to you. For example, if we said the magnets attract like if rubber bands, I would be cheating you. Because they're not connected by rubber bands. I'd soon be in trouble. And secondly, if you were curious enough, you'd ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces, which are the very things that I'm trying to use the rubber bands to explain. So I have cheated very badly, you see."
Just like in math you get to axioms that cannot be justified, just accepted, in physics you reach a level where things just ARE and can't be explained.
@@HuygensOptics Nah it's very neat. I was trying to think in your spring & weight mirror example where energy is not conserved, what could we tweak to fix that? Inertia or the transfer of momentum could happen differently in different directions, and that got me thinking of how even in springs and weights at the smallest scale we're looking at forces and fields transferred at the speed of.... oh :)
Well done. It's one thing to argue that we cannot measure the speed of light in a single direction (always requiring a reflection), but quite another to assert that the speed of light in one direction could be different from the speed of light in the other. While the E=cp explanation is much simpler, I very much enjoyed the full exploration of the possibilities of anisotropy. Recall that it was Maxwell's equations that eventually led to special relativity, where only the Lorentz transformation could account for a constant speed of light. So if Maxwell's equations are fundamentally true (omitting quantum perturbations), then even if you can postulate the speed of light being different in opposing directions, it's impossible to model it in a self-consistent way.
If we can't measure the one-way speed, does it even make sense to consider to question what the one-way speed really is? In SR one-way speed of light is just a choice of coordinates. The problem with the argument from Maxwells equation is that in their standard form you have already chosen an isotropic, Einstein synchronized coordinate system. If you choose another coordinate system, you will have equations with anistropic light speeds (and hence not the standard wavequation with c = 1/√(ε₀μ₀))
_"even if you can postulate the speed of light being different in opposing directions, it's impossible to model it in a self-consistent way."_ - it is actually the other way around. Any anisotropic model of the light speed is self-consistent, as along as the two-way speed is c. The one-way speed is theoretically impossible to determine and is a matter of definition. You can choose any one-way speed you like for your model, and you will still end up with the current consistent physics model.
You can use curved space instead of a mirror. Shoot a photon to orbit a black hole near the event horizon. It will come back to you. Just time the orbital period. You know the distance so you will know the one way speed.
@@jeffbguarino And how would you prove the act of going around the black hole didn't slow down or speed up the photon in some way? And let me be clear, it doesn't. I feel very confident that c is constant in all directions but the point is, how do you prove it?
once again, what a brilliant video. one way speed of light is such a complex thing to wrap my head around, when I'm thinking about it i always get lightheaded.
exactly, that is how they do it, they try to " complex thing to wrap my head around" their way so that you don't try to put yourself on it, to try to understand it, to fight it, to bother with it, and to just accept what they say, they scare you, they make you think you just can't understand it, make you feel dumb, fight that, you are not dumb, put them in their place
@@NeroDefogger they don't make me feel dumb. they're making me smarter by making my brain work until topic makes sense. whatever you are saying is not the way to learn anything. my comment had an intended pun.
@@tsraikage "is such a complex thing to wrap my head around" and "when I'm thinking about it i always get lightheaded" does not "make me feel dumb"? whatever you say... "they're making me smarter" no they are not. "until topic makes sense" the topics never make sense. "whatever you are saying" I'm pretty clear on what I'm saying, did you not understand what I said yet you claim to understand the topic of the video? "is not the way to learn anything" what? you really did not understand anything I said... "had an intended pun" ... what?
I thought about this some time and realized that no matter what I try, I always end up with a two-way speed of light in the end. And I had some really crazy ideas that would be practically impossible to do even if we had access to materials that literally have unrealistic properties.
It's actually quite easy, technically you just have to take advantage of the non-linear nature of time dilatation. Basically you take some atomic clocks, move them rapidly in two different directions and graph the change in time. The time dilation on each clock should fit the curve t₀/√(1-v²/c²) where t₀ is the time for the 'rest' reference. If they fit to the same curve for each direction, then the one way speed of light is the same. The other way is that you just use a particle accelerator to spin a proton or whatever at like 99.9999% C. If the speed of light were different then the particle would have to slow down on one side of the ring in order to maintain it's mass. (or it's mass would fluctuate on each side) in either case you'd need to adjust the timing or strength of the magnets to maintain the particle in the ring - in other words every time the large hadron collider is use the one-way speed of light is verified to be equal.
@@takanara7 _"If they fit to the same curve for each direction, then the one way speed of light is the same. "_ - they will always fit the same curve for each direction, independent of what the one-way speed of light really is. _"in either case you'd need to adjust the timing or strength of the magnets"_ - you wouldn't need to, because the timing and current in the electromagnets would be subject to the same isotropic speed of the light. The one-way speed of light is theoretically impossible to measure. Trying to come up with mechanisms that could measure it, is like coming up with mechanisms for a perpetuum mobile. It is just a matter of determining why it fails.
@@rogerphelps9939 :"Romer's experiment!"_ - That's a difficult one. The mathematics for why Rømer's experiment is not a one-way speed of light measurement is described by L. Karlov in “Does Roemer's method yield a unidirectional speed of light?” Australian Journal of Physics 23, 243-258 (1970) I have a hard time interpreting what the correct interpretation of the math is, but I think it may be the following: Rømer's experiment measured the time between eclipses of Jupiter's moon Io. When the Earth in its orbit is moving away from Jupiter, there should be more time between those eclipses than when the Earth is moving towards Jupiter. Assuming the speed of the Earth wrt. Jupiter is the same in both case (but in opposite direction), you can calculate the (one-way) speed of the light from that difference. But how do we know that those speeds are the same? We measure that by measuring angles towards the Sun. Those measurements are based on the lines of sight to the Sun and Jupiter, that is, based on the (one-way) speed of light from the Sun to the Earth. Due to that, with an anisotropic speed of light, the Earth's speed would appear to be larger on one side of the Earth's orbit than on the other. That is, the orbit of Earth would appear to be more elliptical. The difference in travel time of the light between both side of the Earth's orbit would be attributed to that difference, rather than to the lower/higher speed of light.
@@rogerphelps9939 That is a difficult one. The mathematics for why Rømer's experiment is not a one-way speed of light measurement is described by L. Karlov, in “Does Roemer's method yield a unidirectional speed of light?” Australian Journal of Physics 23, 243-258 (1970) I have a hard time interpreting the math, but I think it may be the following. Rømer's experiment measures the apparent time between eclipses of the moon Io of Jupiter. It then compares those times at a part of the orbit of Earth when it is moving away from Jupiter, with the part where Earth is moving towards Jupiter. Effectively, it is a comparison of the Doppler shift in two directions. But the calculations assume the speed of the Earth wrt Jupiter is the same for both directions. The result depends on that, but that is merely a convention. To measure the "real" speed of the Earth, you would need to measure the distance Earth travels between two points in time. But how much you measure for that speed, depends on the one-way speed of light again. That is, you are measuring the one-way speed of light in relation to the one-way speed of light.
A couple points: 1) the expansion of space has the effect of slowing light in that the frequency is reduced and energy isn’t conserved. 2) the moving mass you mentioned in the end of the video you say we would not be able to detect, we do detect with LIGO. You are describing gravitational waves. I must say, I thoroughly enjoy your videos sir. Thank you and I always look forward to seeing the next! 👍🏻👍🏻
@@Holobrine You are correct, only accelerated masses in an asymmetric configuration (like two orbiting masses, but not one spinning mass) cause gravitational waves. But while a mass moving linearly with constant speed wouldn't radiate waves, it would still have a varying field that could in theory be detected locally with a LIGO-like system. In practice this particular case (e.g. caused by the sun moving relative to the earth) is absolutely impossible to detect with current designs, because the gradients in the field would be much lower, and several sources of noise like seismic noise and thermal noise, that are small in the region of interest for gravitational waves, explode in the low-frequency limit.
@@entcraft44 It would be a 'wave' but it would just have an extremely low 'frequency' If a large black hole zipped right past the earth you would probably be able to see it with ligo, lol. (and the 'frequency' would be higher if it were closer as well, if you think about it)
LIGO measures the 2-way length of a laser bouncing multiple times between two mirrors, it's the 2-way speed of light that determines the result. It uses interferometry so the laser has to go out and come back in order to work. So LIGO wouldn't be able to detect changes in the one-way thing.
Yeah, the final counter-example of a mass passing by during your measurement is just bad science. You are expected to keep black holes off your optical table and locked in a separate cabinet.
@@theterribleanimator1793 That does work, since the mass is pre-spaghettified but the BH can't have any angular momentum otherwise the noodles bunch up around the equator. Good luck finding a non-spinning black hole. Also, you'll have to remove the noodles to use the BH later.
The moment you said a spring with a different constant on one side than the other, I instantly realized as it vibrated, it would grow in vibration in a single direction and I was like: “Free energy machine!!!” 😂
Jeez time for an update guys the jokes are stale. It is hilarious to me that you think you are being cool by "joining in on the memes" when in reality you are repeating bot comments because you saw them and thought "this is how I can be cool and popular". This is the NPC mindset. Sees bot comment, thinks "popular meme, me be popular too if I mindlessly repeat comment everywhere." "All the cool bots are doing it"
It seems like this is just the simultaneity paradox in disguise. Alice and Bob meet up, get two clocks, and synchronize them. Alice moves a distance D left, Bob moves a distance D right, and they both stand still (relative to each other). Every second on the second, Alice flashes a light. Bob sees these flashes happening periodically, with a 1-second interval between each, and thus infers Alice experiences the same rate of time as he does. Moreover, Bob sees these flashes come slightly *after* each tick of his clock, with the delay given by dt=2D/c. When Bob also flashes a light every second on the second, Alice observes the exact same period of 1 second, and the exact same delay of 2D/c. If the clocks are still synchronized after having been moved, then the one-way speed of light necessarily equals the two-way speed. The only way for the one-way speed to differ is if the clocks are *not* synchronized. But, there is already a reference frame in which the clocks are not synchronized! Consider Charlie, who is on a rocket ship moving 0.5c to the right, relative to Alice and Bob. Charlie sees light take longer to get from Bob to Alice, than it does going the other direction, simply because both Bob and Alice are moving fast left from Charlie's perspective. Relatedly, Charlie *also* sees Bob's clock being ahead of Alice's clock, i.e. the clocks are desynchronized to account for the differing times required to cross the distance in either direction. The definition of "simultaneous events" is entirely dependent on your reference frame; simultaneity only makes sense for events at the same location. When events are at different locations, "simultaneous" depends on the observer. Measuring the one-way speed requires some notion of simultaneity across distances, which makes it inherently ambiguous. Even if the one-way speed were different than the two-way speed, then there would be some speed at which Charlie could move that results in the clocks being synchronized in his reference frame. We can simply redefine "simultaneous events" to be events which are simultaneous from Charlie's reference frame, which results in the one-way speed equaling the two way speed. This is a simple change of coordinates. The "one-way speed" is not unknowable in the same sense as Russel's Teapot. Rather, it's unknowable in the same sense that "which way's left?" is unknowable. It's an entirely semantic paradox, a simple matter of definition and choosing a coordinate scheme. It doesn't even qualify as a mystery.
Veritasium can be good sometimes, but he also pushes pseudoscience and click-bait like "Parallel Worlds Probably Exist", "Most People Don't Know ...", "The Big Misconception About Electricity", ... I'll stick to Huygens Optics 💖
@@TheOneMaddin EM waves always travel at maximum speed of propagation. Sound waves travel relative to the maximum speed of mechanical wave propagation in air. Maximum speed of propagation does not imply there is a medium. It just suggests waves can travel relative to maximum speed of wave propagation. The notion that light slows down in the medium is false. Light never slows down in a medium. Photons just takes longer path while travelling through medium at the same speed as outside of the medium.
Or ... one can actually trace the evolution of the constant evolved for denoting the speed of electromagnetic propagation, in a given medium, called "the speed of light" to Wilhelm Weber, read the old scientific publications, and literally understand that the speed depends on the inverse product of the magnetic and dielectric (permeability) constants in a give medium. Ones armed with such an "archaic" (and seems now days unconventional) knowledge one can ask the simple question, does any medium show dependency of the magnetic or the dielectric constants on its geometrical structure ( different properties based on the material spacial orientation). If that were to be the case, then it seems that either the magnetic or the dielectric permeability will have different values when an electromagnetic vibration propagates in space so the "speed" of ( light ) that wave propagation will be different in the different dimensions, if not, then clearly there will be no difference, exactly based on the physical (and formulated) definition of what the speed of light is.
The equivalence principal tells us if we do these experiments while in freefall we will always get the same results. This is even true if the experiment is done in free fall towards the event horizon of a black hole (one large enough to ignore tidal effects). However, observers in different reference frames may see things very differently. Light will always move at the same velocity, but clocks in different reference frames won't agree. Since the velocity is constant, the wavelength will appear different.
Best time resolution in a time-of-flight experiment with electronic triggers may be around 50 picoseconds. A 1 ppm error of c consequently can be achieved at a measuring distance of the light path of more than 15 km. Getting a stable signal transport over e.g. a coax cable of the same length looks almost impossible. However, if it may be feasible, rotating the whole setup 180 degrees might answer the question of whether the vacuum in space is anisotropic, of course only at the precision level of 1 ppm..
gps satellites can give a unique one-way predictable source of future information that could reduce need for timing data / start cues / synchronizing, right? and will be below margin of error, else you use a signal like the upcoming weird nova we expect, the arc difference will be minimal, but gps can be timed in midpoint, and as they are timestamped, reading the data means nothing then (but you can say speed of causality slows the clock?)
Derek makes excellent videos in general imho, though I maintain critique of his "impossible to know" video as mostly or pure notoriety rooted in unfalsifiable rhetoric - as well critique his rhetoric around defending clickbait "because giraffes," sigh
Aren’t the conservation of energy and momentum downstream of Noether’s theorems, which take symmetry as an assumption? Saying c must then be symmetrical is a circular argument.
Just had another thought albeit somewhat impractical. You could measure the one way speed of light if it was traveling around the circumference of a black hole such that its path was that of a closed circle. Who knows, maybe some super advanced aliens have done that :)
You don’t make mention of length contraction/time dilation in your proposal which depends on the speed of light in a given direction. Given that these depend on c, it’s likely that these effects would cancel out the infinite energy and there would be no observable difference if the speed of light was different in different directions. It would be interesting to see a follow up taking these into account.
Honestly I think that it doesn't feel like that's possible, because if it were, then wouldn't we see a little bit of redshifting if we look at something in one direction vs a different direction? Since, if the speed of light is different, that would mean the waves would get a little doppler shift if you look at them from a different direction.
*3 way* Could you just set up a “triangle”? So if the three-way speed is that same as the two-way speed, then each way is almost certainly the same speed.
every time I hear Huygens Optics talk I feel how much smarter than me he is, and even these long form videos can't fit all the knowledge he has to share
Now i might be missing something but we know the speed of sound is constant in air so could one not use spund to trigger the clock and the delay is the distance divided by speed of sound. Thus avoiding measuing the two way speed of light.
Why isn't it setup so the sensor detects the light twice? First the light directly from the source and second the light off the mirror? Distances and time between sensor detections are known
Well, you convinced me. But there again I'm more content to accept "common sense" explanations than any mathematician, or most scientists, would. So, for now, I'm going to ignore any "special pleading" attempt to introduce a possibility of there being a difference in light speed with a change of direction, while in a vacuum.
Now I am imagining that little green fempto-pulsed laser blip surfing a gravity wave and I am very happy with that. Thank you for the spring mass analogy. Love when EE concepts match up pretty well to mechanical concepts. Gives more intuition about the more abstract concepts which can be powerful. Love your videos by the way. Optics was one of my favorite courses in college and these videos solidify fundamental teaching while at the same time not shying away from more advanced concepts and topics. At the end of our course, our professor talked some about non-linear optics but treated it as dark magic. Would be awesome to explore some experiments or topics in that realm if your equipment would allow.
If in a Frame of Reference there is a shift in time as a function of shift in space, then light would effectively travel at different speeds depending on the direction it travels. This is exactly what happens in the equation t’ = gamma(t-vx/cc). In a moving Frame of Reference, time is shifted proportional to distance. It’s the x in the special relativity time dilation equation. Therefore the speed of light is different in the 2 directions depending on the Frame of Reference.
@@mikelord93no. From a moving Frame of Reference perspective, the distance is identically contracted in both directions of the round trip journey, and time is similarly dilated. But in one direction time is also shifted forward proportional to distance and then shifted backwards in the opposite direction proportional to distance. This means in effect from the moving Frame of Reference, light seems to travel at a different speeds in the two directions to compensate for this shifting of time as a function of distance.
Light can have different speeds in two opposite directions with respect to a moving frame of reference. The law of conservation of energy is still preserved.
The only issue with the conclusion is if we take the reference of an object in motion, let’s say traveling at say 1/2C then the speed of light forward of the object should appear to be slower (1/2C) while the speed of light aft of the object should appear to be faster (3/2C). This simple thought experiment seems to suggest that there MUST be a difference in 1 way speed of light for any object in motion.
A traveler moving at any speed would always measure the speed of light to be c in any direction, that's the fundamental observation that SR is based on.
Wait, I'm afraid that the definition of 'direction' was assumed, and never discussed or mentioned here. What exactly is a DIRECTION? Does the location of the observer (perspective) come into play with the definition of direction?
4:30 He mentions 'from the left' and 'from the right' to differentiate directions. Are these directions universal around some coordinate system? Or are they relative to the observer (in this case, the clock in the middle)?
Huygens Optics there is a channel called Dialect - do you know them? They are talking the same problem that you do - but they don't take for granted that the one way speed is 1/2 the 2 way speed... They allow it to be any value - even the one way being faster than the 2nd way... Thus they are trying to explain a different interpretation of relativity! I wish you could watch their videos and tell us what you think of them!
I don't think your asymmetric spring reasoning is correct. What you describe is a type of spring that generates different forces at its two end points for a given elongation, which as you point out violates conservation of momentum (and the action reaction principle). What I imagine as a (legal) two constant spring, for example, would be one that has k1 under compression and k2 under elongation (which isn't hard to achieve) but this would still result in isotropic propagation, so I'll come up with another spring. This third spring "detects" which of its ends is the first one to move (left or right) and "decides" if it will act as a k1 or k2 spring. A wave propagating from the left will encounter a medium with an elasticity given by k1, different from a wave approaching from the right (k2), resulting in two different wave speeds while conservation of momentum is preserved. Some possible issues with a system like this would be how the spring could "detect" and "decide" fast enough, intuitively this seems to require information to reach the spring's "decision" system faster than light travels in order to adapt to a traveling wave of light so as to slow it down. To be honest I also didn't find the last part of the video very convincing. It seems that reflecting light would violate conservation of energy but that is because we use formulas derived assuming C1 = C1' to start with, maybe we can come up with better ones. To be actually convincing I think you'd have to show how exactly that "illegally" obtained free energy could be turned into profit, but I can't really come up with any ideas about how. For example you could argue that these extra energy photons could be used to excite an atom, which will then emit a higher energy photon, which gets reflected for an even higher boost of energy, and so on. But then who is to say that atoms themselves would be excited isotropically? Thanks for reading so far down lol.
The arguments in the video cannot prove that c1 = c1' in the general case. Rather, they hint that such an effect would require a significant remodeling of our theories rather than just a small correction.
@@entcraft44 Absolutely agree with this interpretation. I just wanted to point out that you could imagine a sort of medium which propagates waves anisotropically without violating newton's principles. That being said, I'm pretty sure our whole current model of physics does assume that empty space is symmetrical or isotropic (I don't know which word fits here better). The fact that a model with this "extra" assumption that c1 = c1' doesn't fail experimentally is proof enough for me otherwise.
Yes, light propagating through space will be the same in any direction; but while the light is travelling, the receiver can move, which makes the detection at the detectors register different speeds. Your initial setup is indeed a two-way experiment... but you can change the setup: 1) 2 detectors in close vicinity, in the center, with a high precision clock that records the time when the detectors on left and right are triggered. 2) Put two emitters that have a stable clock, that will always tick at the same rate (more detail later). Each emitter will fire a short pulse (milliseconds are fine, you just mark the leading edge detection). Amazon has lasers that are good for up to 2 miles (10,000ft)... (light is approximately 1 foot per nanosecond, so over 10000ft is 10000ns or 10us.) Over the 10us, because of our motion through the universe towards VIrgo according to the redshift in the CMB, we move 370km/s or .0012 ft/ns... so it will move 12ft over 10us, and register a different speed from one side vs the other of +/-12ns... or a total difference in the speed of light of 24ns. (in the perfect arrangement).... so this would need to be aligned with the constellation virgo/cetus(opposite side constellation), so that there is a best-case... it's aligned to approximately +9degrees north; can't really just make this go any direction, or you can end up with a near null result, the orbit around the sun is 10% of the speed through the universe, and the rotation of earth is 1% of that... so +/-1.2ft or +/-0.012ft from those effects... the motion through the universe is much more on point. Mind you - the speed of light does not change based on the speed of the emitter... just the speed of the receiver - such speed is then c+v and c-v..... There may be additional skews to the stable clocks.... that once deployed they are not in exactly the same gravitational field... but this will be a constant effect, and the constant drift can be factored out. Air pressure is an insignificant factor; and since it's likely that the 4 miles the experiment covers (2 miles from one side of center and 2 miles from the other side) will likely be the same it ends up being non-measurable... and any change under like 100,000atm is barely notable... a few millibar is not going to change the experiment...same with humidity - the same amount of humidity is likely experienced across the apparatus. Another way to consider this is say you're playing catch with someone else, and every second they throw a ball at you at the same speed, if you move towards them, then the throw that happens while you are moving will be caught by you in a slightly shorter time. If you continue to stand in place, at this new distance per second, the ball will be registered as every 1 second. If you walk away during a throw, then the time it takes to catch the ball is slightly longer, again, until you stop. If the experimental apparatus is perpendicular to the velocity, that's basically initial conditions - and every pulse is received at 1 second intervals from both sides... as the apparatus aligns with the direction of motion, it's like the center detector is able to take a few steps forward, and pulses from one side will arrive in slightly shorter time or slightly longer time, whether the detector is moving towards or away from the emitters respectively. Once it reaches the maximum alignment, the pulses will still be every 1 second, but will be skewed from each other compared to where they started... if they start on every integer second, then it would be at +12ns and -12ns from the original state along a timeline. The times between each impulse registered from each side are subtracted from each subsequent sample, leaving a small delta change between each received pulse... at the end you'll have a net bias (probably) from clock skew, this can be removed by subtracting the final value from the initial value, and subtracting that sloped line from the result, biasing the beginning and and to 0. (This would mean a complete 24 hour cycle should be run... it would be less meaningful to do only 6 hours or even 12 hours - because at the 12 hour mark you're not necessarily in the same arrangement, since the apparatus is aligned with a specific point on the horizon, at 180 degrees of earths rotation, then the device is no longer in the same alignment as it started, but is tipped in a counter direction (that's not the right word but maybe you get the idea). I have been working on setting up this experiment, and if I can get the apparatus built, I would take it to the great salt lake, there are very few areas where there are 4 miles in an arbitrary direction that are entirely clear and flat, and wouldn't interfere with the line of site - could built something in the ocean maybe, but it would have to be tied to the ground. The two emitters and the center detector MUST be rigidly arranged - floating them, or launching them into space will not help. Anyway - I did setup a program for an FPGA that has a high speed clock, and two registers internally that can be latched when a signal from a light detector is received... the latched clocks can be read more slowly and stored in a computer over the next second between each pulse. The FPGA though is actually pretty slow, and although I'm almost able to get a 600ps clock, it's unstable, and a temperature corrected crystal oscillator that is more than a Ghz is expensive... That, and I don't know how many photons the photodetectors have to see, or how bright the intensity is - but I would expect actually quite a bit of noise from that receiver - plus, I don't know a good way to gate a laser pulse - for the same reason, propagation of all the voltage regulators, plus time to build up a signal to transmit are likely going to cause more noise in the experiment than +/-12ns. I've somewhat settled on using a synchronous AC motor that rotates 60RPM (once per second) and put a wheel with a 1mm slot on it - but even then, as that is actually pretty slow, it's going to uncover a fraction of the beam, and then the whole beam, and then start covering a fraction of the bean as it passes... which makes the signal leading edge not very concise... and is another point of noise. There are high precision frequency generators/counters but I find they are $16,000+ to be within a range of desired resolution, and then that is a bulky external thing, which introduces nanoseconds of delay with propagation of those signals... I just don't see it being done with off-the-shelf components. Probably have to make an ASIC with dedicated silicon for the clock and 2 latch registers (a super simple thing, though you do need about 52 bits of precision, which is quite a lot of bits, and a long chain to update.... which potentially makes the clock have grey bits in the middle while it's still counting a clock tick... the clock edge at one end will change even while the middle of the counter is still updating from the previous tick. That and the light detectors need to be pretty precise, and the module I got, the sensor is actually not JUST the sensor but has a transisitor the detector is attached to - which, again, signal jitter/noise. I don't know if maybe I got a DLP(?) sort of chip used in projectors that could gate small mirrors in two directions pretty fast... I would think those are still on the scale of 100s of microseconds... and far from the nano/picosecond gating I would want. Speaking of space, changes in space of the gravitational field only propagate at the speed of light also, which means ahead of our planet the field is somewhat compressed, and slightly more dense and is slightly weaker, so satellites will orbit just slightly further away (1 meter per kilometer roughly), and on the trailing side, the field will be elongated, and have slightly greater effect, making satellites on that side orbit slightly closer... This makes GPS signals always take the same amount of time to arrive. There is a thing in the solar system the 'Axis of evil' which is an overall alignment of the elliptical orbits of things that is always in the same direction. One could argue that GPS (multiple emitters some fixed distance away from a central detector that registers the time in the same location with 0 propagation time of the clocks signal) is the same as the above; that is, the same, except for the specification of being rigidly attached. On my channel the last few videos I did were on simulations I built (open source, links in descriptions to the demos and/or more information documents in the github repo) that are based on the one-way constant speed of light... and indeed, any two-way measurement will always be a constant time for a distance, in any frame, moving in any direction, while the individual one-way paths are neither the speed of light (as registered by a moving receiver). Light, once emitted no longer has anything to do with the source that emitted it, and it propagates in space regardless of what the source does afterward... Though the net combined effect does result in light aberration, both on transmission, and on reception of signals (see synchrotron radiation beaming effect for more about this aberration for electrons travelling close to the speed of light - the direction the light is detected is mostly all directed forward.
If the speed of light varied based on direction, then the observable universe would not be spherical and we would not be at its center. We'd see farther in some directions than others and thus see more stuff in those directions. We could (roughly) measure the relative speeds of light coming from different directions by counting the number of galaxies visible in those patches of the sky. I think it would also show up as an anisotropy in the size of the temperature fluctuations in the CMB. The relation between redshift and distance would be anisotropic. And probably other stuff too that I can't think of at 3 in the morning.
I thought of similar things. If there are enough stars with redshift to measure the expansion of the universe it should be possible to see a different speed of expansion in different directions if rhe speed of light would be direction dependent. The point of seeing more galaxies is brilliant as well (If mine has any merit & independent of that)
As someone who studies physics and electronics my brain got constant error 404 with the spring. It's a spring not a resistor, It's a spring not a resistor, It's a spring not a resistor...
Armand Hyppolyte Fizeau is one of the best names I've ever heard, holy crap P.S. how do you pronounce "Huygens"? Is part of that silent like the Vietnamese Nguyen (or are my white eyes just seeing the same letters and assuming a connection lol)?
I don't see why the "one way" speed of light is an issue of such concern to so many people. We fundamentally do not believe that there is any such thing as a "special direction" in space. Why WOULD the speed of light a long a path depend on which way it's going? The natural, obvious Occam's Razor assumption is that it travels the same speed both ways. And by the way - even if it didn't, it WOULDN'T MATTER, because if it did, then we could use that as a way to MEASURE the one-way speed of light. There very fact that we can't measure it means it's entirely irrelevant to us. People just like to "pick at things."
Exactly. Considering there is no way to say whether it is different or not, just assume that it is the same and move on. I guess people just can't understand that this doesn't change anything at all for us
they want to pretend they know more, but it is really to make up a hundred hidden variable, as long as they stay hidden.... that saying goes, part of one way speed of light is actually easy to disprove, specifically "directionally/opposing anisotropy" speed of light in 16:13/18:30 because they easily violate snell's law however snell's law can only only experiment locally
I think the speed of light is the same in both directions. Because if speed of light in one way was different even by a tiny amount, the universe would look completely different in different directions. Also, if speed of light was different in different directions, things like GPS would break because the time dilation would be different than expected.
If light was biased, half the galaxies on one side of the sky would looker younger and closer than the other half. Otherwise the question becomes "...within a sphere small enough to ruin your experiment idea"
No one actually thinks light moves at different speeds in different directions. That's not the point. The point is that no matter how obvious that we think that it MUST be that this is true, the universe appears to have conspired to make it so that we can never prove it to be true. So it may be obviously true, but it appears that even Einstein could not rigorously prove it so. And that's the point
no, if light was biased, then every interaction with light would cause a change in momentum, on average against the direction of the fastest emission of light. so things would move against light, and the doppler effect would appear to cancel the asymmetry
The speed of light being different in different directions breaking the conservation of energy explains why a lot of people very desperately want this to be the case since it would allow for infinite energy devices.
*Advanced Tinkering* channel just mentioned you in an absolutely lovely way in the video "Creating Ultra-Fine Details in Titanium - 20 Micron Resolution" ! 🤗
Well, if we did measure different times for different directions than it would mean that there was some additional moving gravitational potential somewhere in the vicinity of the light's trajectory and in fact we do use it cosmology when we measure the mass of black holes in a galaxy using long term gravitational lensing observations - recently covered by Anton Petrov on his channel discussing results from a Warsaw, Poland study on this exact subject. There's really no good reason to assume that light travels with different speeds in opposite directions when there's no change with respect to time in gravitational potential. If there was a difference we would not be able to infer anything about masses from any measurements, which would be contrary to experiments and day to day perception.
Good video. You compare the situation with an elastic medium that has different spring constants for the two directions, which leads to violation of conservation laws. But that is not the only way to achieve anisotropic propagation speed. The medium itself could be isotropic, but simply have a velocity in one direction. That would not lead to violation of conservation laws. I think the more profound observation is that there is a delicate link between the one-way speed of light, and how simultaneity of distant events is defined. The definition of simultaneity makes it theoretically impossible to measure the one way speed of light. You might want to do another video on that. Ever since I discovered this myself, I have marvelled at the following simple sentence in the introduction of Einstein's 1905 SR paper: _"We have not defined a common “time” for A and B, for the latter cannot be defined at all unless we establish _*_by definition_*_ that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A"_ Einstein already knew that what you have discovered as well: that the one-way speed of light is a matter of definition, not of measurement.
wow i’m so glad i didn’t click away after the first half lmao first half was amazing (for the viewer that’s not familiar w the conclusion) just excellent motivational context-building but the second half was an amazing next layer deeper of thought experiment / pre-analysis
There's an experiment that came to me today, just before this video came out, that I would love to see, but don't have the means to perform. I just recently learned that Neodymium-doped Lithium Niobate can be used as a lasing medium. I am incredibly interested in the interference and diffraction patterns produced by it, specifically when it is being used as a laser medium while also piezoelectrically oscillating. Lazing Lithium Niobate, even when not doped, is a parametric down conversion process too, producing more than typical entangled photon pairs! If you're interested at all I can link you to a few papers, and a source for Neodymium-doped Lithium Niobate on substrate. Love you so much!!
If the clock and the sensor is the same, i.e. a quickly rotating disc of photosensitive material, and the disc at both ends of the race track is coupled with a long axle that spins at a constant rotational speed, will this device show a different speed of light one way (angle between dots) if it is oriented horizontally and vertically in a deep shaft? I suppose the measured rotating speed of the disc at the bottom of the shaft will be higher than that of the top one, even if they sit on the same axle.
read Alberto Martinez' book Kinematics: The Lost Origins of Einstein's Relativity - he goes into how speed and velocity were confused in relativity. thanks
Would the difference in c result in different wavelengths for the same frequency propagating in opposing directions? Those quantities feel tractable to measure, and are a lot more local of a measurement, avoiding the whole loop problem. It felt like the video was about to go there a couple of times, so maybe I missed where the idea was dismissed as not even wrong 😅
You can't. When you have two detectors separated at a distance from each other, you won't be able to connect them to the "same" time measurement, because they are already in their own reference of time. Ponder on what "time-space" means. If you don't understand what I am saying, just go back to read the "train going through a tunnel" example again. Because if you want to compare the time of the two separated detectors, you have to bring them together, meaning at least one of them has to go through acceleration and deceleration, during which process their time reference is already changed.
Well you can always modulate a timestamp on a light pulse And then decode it to get the speed relative to the receiver you point a "laser" at tx an rx both have atomic clock, and you can synchronize both using a 3rd atomic clock half the distance between Rx and tx to average out any time dilation effect... How long does the second pulse take on average from the previous detected pulse, knowing the distance traveled and the time encoded on the radio signals
Sometimes I think that our universe is built this way because others have collapsed one way or another due to catastrophes from things like the mentioned "opposing anisotropy". There are similar issues arise with, for example, negative mass, infinite speed of light, time loopholes, perfect portals and so on. In other words, a world with free energy or an energy sinkhole will always destroy itself.
The graphics in the first half of this video are terrible! I seriously can't follow anything this guy is trying to explain. However, I was able to follow the Veritasium video perfectly even though I don't agree with it.
I thought the LIGO gravitational wave detector measures exactly this. I thought it worked because the speed of light is changing through the detector. but maybe my high-school education is failing me 🤔
And what if you pass the light beam through glass in both direction, same refraction angles, same diffraction angles, sam wave propagation speed, issue solved ?
Formulae assuming c to be constant would make predictions differing from observations in proportion to the specifoc error in c at time of the observation. We don't see this... C must be universal, no?
So, can you show a demo of speed of light vs speed of stick ringing a bell on the moon? Let the stick be stretched from earth to moon and the laser be located on earth. Now switch on the laser and push the stick at the same time. Which one will hit/ring the bell on the moon first? No need to search for an Internet answer; there is no response to this question.
Ok... so we put this clock on a train going thisaway, and we put that clock on this train going thataway and then we go choo choo real fast and then we put both clocks in the mail (DHL) back to the train station and THEN WE READ BOTH CLOCKS ON THE SAME DESK AT THE SAME TIME TO FIND HOW FAR AWAY THE CLOCKS ARE FROM EACH OTHER IN TIME or however you want to say the clocks experienced different rates of time... I am so fucking confused by how they managed to get both clocks into the same spot, doesn't that literally mean they're in the same frame of reference? (obviously we're not really talking about clocks here.) If you put them 'clocks' right next to each other, i mean straight up zero distance between them, how the fug can you say they're not in the same frame... so... there's no time dilation... wait what!? 😮
Aren't conservation laws written in their well-known form assuming isotropic speed of light? In other words, you would need a skew factor between conserved "to the right" energy and "to the left" energy if speed of light wasn't isotropic (same for momentum) (*). I'm just trying to think in terms of mass as photon boxes, then your mass on a k1,k2-spring scenario doesn't really violate the conservation laws (I think). So I don't buy the last argument. But I like the analogy, it does make it seem intuitive. But I think in this extreme example, the analogy does not apply, or at least you need one more assumption or piece of evidence to make it applicable. *) to clarify, conservation of energy and momentum are a consequence of Noether's theroem, they're a consequence of time and translation symmetry. But speed of light not being isotropic is no longer time and translation symmetric so you can't apply those conservation laws.
I will repost my comment from Veritasium's video HOW TO MEASURE SPEED OF LIGHT We can measure the time it takes light to go from point A to B in vaccum, bounce of the mirror and go back from B to A, BUT inside a glass Then repeat the experiment but in the opposite way. If the speed of light decreases by the same % going from vacuum to glass regardless of the direction, we should be able to see the difference in travel time. Furthermore, we can make 2 additional experiments (both ways in vaccum and both ways in glass), so that we have 4 measurements of time and 4 unknown velocities - easy to solve equations Great video btw :D
At 2:33 onward, you talk about seeking to prove C1 = C1' and therefore get C2 = C1 + C1' but my question is: Does a mirror reflect instantaneously (Tm = 0) or is there a delay (Tm > 0)? If Tm > 0, it must still be very small, but when you're talking about the speed of light, small is not zero. I'm no physicist so I'm not sure if this is important or irrelevant, but, at the very least, C2 = C1 + C1' + Tm and so inferring the one-way speed of light by halving the two-way speed of light would still not be correct.
you're never going to measure the one-way speed of light with a single clock, that I think is the fundamental problem with both this video and veritasium video. In order to measure the one-way speed of light you'll need two clocks, one at each end of a distance D, and those can be atomic clocks that are synchronized by GPS (signals that are perpendicular to D). The problem veritasium made is thinking that just because he wasn't able to think through how to do it he concluded that it was impossible, that's hubris. QED. anyone disagree ???
There is a miscalculation at 8:04 and it appears to be important. You accidentally have Δtr_31 = D/c_1 when it should be D(1/2c_1 + 1/2c'_1), you also committed this same mistake for Δtr_42. It is not an important mistake though, because you fix it immediately.
2:57 you say that C_2=(C_1+C_1’)/2 but this is completely false. You cannot just take the arithmetic mean. You have to use the harmonic mean when working with speeds. The right formula is C_2 = 2/(1/C_1 + 1/C_1’)
Wave propagation is instant difficulty in the emitter-receiver aspect of amplitude-frequency density-intensity in a holographic time-timing ratio-rates Perspective Principle of what is used in heterodyne radio and is a ubiquitous property of holography-quantization, eg the constants provided, such as permittivity are prime-cofactor products of collapsed Superspin/Epicyclic superposition identification in the general context of numberness probability differentiates dominance sequences, (have to draw the 0-1-2-ness in 3-ness -> 3D-T Physics drawing the picture of condensed form following functional concepts.., every possible movement is a potential focus of temporal thermodynamical superposition focus of reciprocation-recirculation relative-timing ratio-rates, and the speed of light is a 2-ness propagation of a differentiates rate of rate wave-packaging. Navigators must be living and breathing this duality of heterodyne transmission in Doppler shape shifting circumstances, but it takes time to accumulate a skill very similar to Euler's e-Pi-i superimposed fields sense. Of course the recognition of Euler's e-Pi-i Entanglement and 1-0-infinity instantaneous probability range according to wave frequency-amplitudes alignments is a Radar/Navigation Operator person's task, and you qualify for the tinfoil hat if you solve the orientation of Entanglement Fusion-Fission Function Fields positioning, and make the speed of light a trivial fantasy. Holographic Principle nucleation ensures.. We can't measure nothing in No-thing, only deny it's some thing else, which is trivial non sense putting some distance between POV.
To define a one-way speed of light between two different points, you must have a concept of simultaneity at those two points. According to special relativity, this is meaningless; you can pick a velocity v in any direction and define (x_1,t_1) to be simultaneous with (x_2,t_2) if (t_1-t_2) = (x_1-x_2) dot v. This gives you different speeds of light along the direction of v. Of course, this is not measurable by any experiment, which is why you can assume that the speed of light is the same in opposing directions as a matter of convention (although there is something more to be said about diagonal directions).
An interesting conundrum. But, the difference in speed is purely theoretical as the one way speed of light has no practical use in observation. Unless, of course you want to observe an observer, in which case ??? There is also the effect of gravitational lensing, the effect of gravity on light, there is an effect of bending the light and even Newton understood that things continues, at the same speed and direction unless forced not to, by a force. So, if you were on the edge of a supermassive black hole and shot a laser beam at the dearest dark object and measured the reflection time, it would seem obvious that the speed of light in both directions would not be the same, but the average speed would =C. And that's it realy. While I am here I will drop this little puzzle for budding geniuses. Tn + En = S n Sn + Tn = E n En + Sn = T n Think Fermat's Conjecture. With T= time, S = space E = energy.
But can't wee use a monochromatic light beam, say using FEL, whose frequency is exactly known. Then measure the wavelength precisely using a defracttion grating and figure out the one way speed by c=frequency X wave length? Won't that be a one way speed measurement? Yes, we're calculating c here from other stuff. But we do so in every experiment.
Holy smokes it's another masterpiece. Light is such a tricky subject to understand.
photons are downright fucking weird
the kid is a natural
@@defeatSpace Photons don't exist
no it is not
@@NeroDefogger yes it is
The overly clever setup of the beam splitters, detectors and the clock reminds me of how designers of perpetual motion machines try to hide the energetic symmetry of their devices behind complex mechanics. The end result is the same: you just can't cheat your way around conservation laws and symmetries.
false, read my comment
@@NeroDefogger
"false, read my comment"
@@-danR 🤦♂🤦♂🤦♂ that's why I said "read my comment", because I meant MY ACTUAL EXPLANATION COMMENT ON THIS VIDEO 🤦♂🤦♂🤦♂ why would anyone think that "false, read my comment" 4 literal words would be the explanation of anything? I... I'm legit debufunged
I read the comment and the comment seemed to agree that the speed of light is the same in both directions.
@@raulkaap yes but not because of "cheat your way around conservation laws and symmetries", there are not "conservation laws" nor "symmetries", is just that if you measure it, it is the same, and it kinda makes sense because it would be a bit weird if it changed, but I don't necessarily see any clear reason why it couldn't, because there are no such "laws". but at the same time, your comment seemed to imply that there is no way to measure it, and in my comment I explain how there is, in fact, that is my point, that if you measure it, it is the same, because you can measure it
Somewhere, probably on PBS Spacetime, I learned that if I relabel the 'speed of light' as 'speed of causality', and light just going 'full speed', that makes the intuition slightly better. After a few years of mulling it over, I agree.
Matt has saved us again 🤗
Nothing but garbage on TV tonight, what a brilliant timing!
you still watch TV?
@@farhanrejwan It's my excuse for laying on the couch.
@@Shokkwavez i think i'd still prefer my phone or my pc on a couch 😂
@@farhanrejwan surprinsingly, many ppl still enjoy oldtimes TV bc they don't need to choose something, just the channel and watch watever they give youl; I have a tiny amt of doubts and also no evidence, but I believe this could be cause by mental exhaustion,(which can come from anywhere), at least for ppl who do it for long periods of time......... also could be they don't want to bother looking for a youtube channel or whattever that plays random shit, like simpsons episodes or so,, due to ignorance or also lack of mental energy, there is a possible third scenario, which involves a third party showing the subject how to look for and/or setup such tvlike experience on phone, pc or whatever, but the subject will refuse, possibly due to lack of mental energy.... yea, i know, it's the root of all problems, even mine..... what am i even doing here, all coked up, writing pretentious nonsense..... ah.....
your videos have repeatedly inspired me to re-engage with scientific learning. you make scientific understanding feel within reach of anyone, not just labs with big grants. also you are precise, but also humble. thanks for publishing your videos.
learning is what makes it unique, whereas any of the many edutainment-type science channels can ultimately only offer a form of teaching or lecturing, the distinct ability this channel has is to just offer learning instead
Don't make me cry
This is a great a great video! I want to point out that you missed a simple (yet arguably not obvious) way to make opposing anisotropy locally: make the spring-mass setup MOVE! Or equivalently, make the wave generator move, so that it excites a different mass at each time step. From the resting frame of the wave generator the wave propagation is then opposing anisotropic.
You might say that this makes no sense in the setting of the EM field because the field cannot have absolute motion. However, this is exactly the ether interpretation of the EM field (and spacetime itself): opposing anisotropy in the speed of light can be explained by assuming an absolute rest frame (the rest frame of the ether aka the rest frame of the CMB) and anisotropy resulting from motion relative to it.
Like a wave on a river
But while this possibility doesn't suffer from the energy conservation problem, the aether has other problems, and all the old aether theories have been disproven, e.g. by the movement of the earth trough the aether.
My takeaway is the following: The current theories describe most of our universe extremely well, so we often try to make small changes only. This video convincingly shows that an anisotropic one-way speed of light is not possible by making only small changes to our theories. But your comment hints that we can never consider every possibility.
That is, unless we employ a much more systematic approach to the assumptions underlying our modern understanding of the universe. There are a lot of interesting ideas out there, but nowhere near enough manpower and funding to check every single one with all the consequences individually.
@@entcraft44the key thing here is that the *old* aether theories have been disproven. There is a way to have an aether field in such a way where you get the exact same equations that you get from relativity, where the speed of light is constant in the reference frame of the aether, and objects moving relative to the aether get length contracted and time dilated. This formulation gives identical math as special relativity so it is not possible to distinguish which interpretation is closer to reality through measurements
@@entcraft44 Aether has been disproved but an absolute rest frame has not. In big part because of the two-way speed of light.
Once you assume that speed of light is the speed of transfer of information from one segment of space to another then you can have both the relativistic effects as well as an absolute reference frame, where the constant speed of light in any reference frame is just a result of slower processing of the thing moving close to the speed of light.
(ie: imaging you have a clock that measures the passage of time by sending a short ray of light towards a mirror and waiting for a response, that clock would indeed slow down the closed you go to the speed of light, and stop completely once you reach the speed of light, since light would have to move perpendicularly to the mirror, the exact same thing happens when one particle sends our information and waits for it to come back)
All the other space warping effects are also accounted for as being just a mirage caused by difference in processing speeds of information( photons in this case) that arrives perpendicular or and paralel to the motion as well as what just happens when light travels at a fixed speed..
First from the object's PoV the entire universe shrinks along direction of motion because its own processing slows (so everything just starts becoming very bright, and very blueshifted) Additionally the faster the object moves the more perpendicular to its movement the light has to be to actually hit it.
I did the math and some simulations on this and it all checks out, tho I'm still unsure as to where the extra mass is coming from when you accelerate things close to the speed of light.
Huygens Optics Video: My favourite kind of photons 🤗
i think people are too afraid of "unsolvable" problems like this. if our current model does not predict any effects from this hypothetical and we do not observe any effects to prove our model wrong in that regard, it truly does not matter what the answer is. its like trying to prove the existence of an unobservable god with science.
i appreciate the insight on how a closely related problem is much more approachable
Exactly, Russel’s teapot
@@YuriyKrivosheyev not quite. russel's teapot places some arbitrary "burden of proof" on the "positive claims". in reality, neither claim inherently has more merit than the other. the proper way to look at it is that whether this teapot "exists" or "doesnt exist" cannot mean anything unless it has observable effects (which it does not). embrace the fact that there is no useful answer rather than arguing one way and demanding proof from the one arguing the other way. otherwise its like trying to prove a god *doesnt* exist with science.
Yes, but… not really?
Science has its dialectic in pure idealism, the imaginary, intuitive and creative. These “brain functions” are our pathway to pure empirical knowledge - ontology and epistemology, subject and object.
More culturally, we depict someone getting a bright idea (lightbulb moment in cartoons), and then the “labour” to prove or disprove, calculate vs experiment, theory vs observation. As this video also shows, Einstein knew his Maxwell, and “imagined” how time, space, mass and energy interacted - and, well it still works, empiricism backwards and forwards to now.
Einstein also put a nail in time travel, so the only way forwards is - unknown and undefined. Perfect for those “unscientific” traits we have, besides logic or reasoning.
This is also how “wrong ideas” emerge, but are not empirically sound if they can be disproved. There are always “ideas” in a sort of superposition - before we are able to both prove and disprove. Both are necessary.
If I’m wrong in this position, we have invented or discovered “everything”, there is no forward empirical path - nothing to imagine into the field. It’s a gloomy world at this time, but not _that_ gloomy?
@@jotch_7627Ultimately you can’t prove about a generic god with science, but many religions make enough additional specific claims about their gods that the gods they describe can be assessed
@@Holobrine and no proof for their gods
Fascinating! The examination of the asymmetric spring analogy was very intuitive
The best explanation of 0ermittivity and permeability ever, and the analogy with mechanics made so clear the concepts of isotopi and anisotropy of the material... literally wow, You deserve an honorary Professorship
I'm no scientologist but I always heard that read as "C1" and "C1 prime", not dash.
Probably I screwed up again, as a non-native speaker....
C1 dash is normal in the Britland afaik
@@HuygensOpticsYou're doing just fine! 👍
Thank you for all the time you put into these fascinating subjects. 🙏
The mea culpa, even when you are a non-native speaker speaks volumes about your scientific thought!
"scientologist"??
It's fun that we can do this same experiment to measure the speed of light by reflecting a laser from the moon and timing how long it took the detector to pick up the same wavelength
That folse guy makes reaction videos about everything, it's gross, can he not make his own video that he has to suck the attention away from a genuine creator, he adds Nothing.
The analogy to little springs reminds me of Feynman talking about the rubber band analogy for magnets: th-cam.com/video/MO0r930Sn_8/w-d-xo.html
"I can't explain that attraction in terms of anything else that's familiar to you. For example, if we said the magnets attract like if rubber bands, I would be cheating you. Because they're not connected by rubber bands. I'd soon be in trouble. And secondly, if you were curious enough, you'd ask me why rubber bands tend to pull back together again, and I would end up explaining that in terms of electrical forces, which are the very things that I'm trying to use the rubber bands to explain. So I have cheated very badly, you see."
Now I feel I've also cheated badly...
Perhaps if we involve gravity in the circular reasoning, we could get away with cheating a bit? :P
Just like in math you get to axioms that cannot be justified, just accepted, in physics you reach a level where things just ARE and can't be explained.
@@HuygensOptics Nah it's very neat. I was trying to think in your spring & weight mirror example where energy is not conserved, what could we tweak to fix that?
Inertia or the transfer of momentum could happen differently in different directions, and that got me thinking of how even in springs and weights at the smallest scale we're looking at forces and fields transferred at the speed of.... oh :)
Well done. It's one thing to argue that we cannot measure the speed of light in a single direction (always requiring a reflection), but quite another to assert that the speed of light in one direction could be different from the speed of light in the other. While the E=cp explanation is much simpler, I very much enjoyed the full exploration of the possibilities of anisotropy. Recall that it was Maxwell's equations that eventually led to special relativity, where only the Lorentz transformation could account for a constant speed of light. So if Maxwell's equations are fundamentally true (omitting quantum perturbations), then even if you can postulate the speed of light being different in opposing directions, it's impossible to model it in a self-consistent way.
If we can't measure the one-way speed, does it even make sense to consider to question what the one-way speed really is? In SR one-way speed of light is just a choice of coordinates. The problem with the argument from Maxwells equation is that in their standard form you have already chosen an isotropic, Einstein synchronized coordinate system. If you choose another coordinate system, you will have equations with anistropic light speeds (and hence not the standard wavequation with c = 1/√(ε₀μ₀))
_"even if you can postulate the speed of light being different in opposing directions, it's impossible to model it in a self-consistent way."_ - it is actually the other way around. Any anisotropic model of the light speed is self-consistent, as along as the two-way speed is c. The one-way speed is theoretically impossible to determine and is a matter of definition. You can choose any one-way speed you like for your model, and you will still end up with the current consistent physics model.
You can use curved space instead of a mirror. Shoot a photon to orbit a black hole near the event horizon. It will come back to you. Just time the orbital period. You know the distance so you will know the one way speed.
@@jeffbguarino And how would you prove the act of going around the black hole didn't slow down or speed up the photon in some way? And let me be clear, it doesn't. I feel very confident that c is constant in all directions but the point is, how do you prove it?
once again, what a brilliant video. one way speed of light is such a complex thing to wrap my head around, when I'm thinking about it i always get lightheaded.
exactly, that is how they do it, they try to " complex thing to wrap my head around" their way so that you don't try to put yourself on it, to try to understand it, to fight it, to bother with it, and to just accept what they say, they scare you, they make you think you just can't understand it, make you feel dumb, fight that, you are not dumb, put them in their place
@@NeroDefogger they don't make me feel dumb. they're making me smarter by making my brain work until topic makes sense. whatever you are saying is not the way to learn anything. my comment had an intended pun.
@@tsraikage "is such a complex thing to wrap my head around" and "when I'm thinking about it i always get lightheaded" does not "make me feel dumb"? whatever you say... "they're making me smarter" no they are not. "until topic makes sense" the topics never make sense. "whatever you are saying" I'm pretty clear on what I'm saying, did you not understand what I said yet you claim to understand the topic of the video? "is not the way to learn anything" what? you really did not understand anything I said... "had an intended pun" ... what?
I thought about this some time and realized that no matter what I try, I always end up with a two-way speed of light in the end. And I had some really crazy ideas that would be practically impossible to do even if we had access to materials that literally have unrealistic properties.
It's actually quite easy, technically you just have to take advantage of the non-linear nature of time dilatation. Basically you take some atomic clocks, move them rapidly in two different directions and graph the change in time. The time dilation on each clock should fit the curve t₀/√(1-v²/c²) where t₀ is the time for the 'rest' reference. If they fit to the same curve for each direction, then the one way speed of light is the same.
The other way is that you just use a particle accelerator to spin a proton or whatever at like 99.9999% C. If the speed of light were different then the particle would have to slow down on one side of the ring in order to maintain it's mass. (or it's mass would fluctuate on each side) in either case you'd need to adjust the timing or strength of the magnets to maintain the particle in the ring - in other words every time the large hadron collider is use the one-way speed of light is verified to be equal.
@@takanara7 _"If they fit to the same curve for each direction, then the one way speed of light is the same. "_ - they will always fit the same curve for each direction, independent of what the one-way speed of light really is.
_"in either case you'd need to adjust the timing or strength of the magnets"_ - you wouldn't need to, because the timing and current in the electromagnets would be subject to the same isotropic speed of the light.
The one-way speed of light is theoretically impossible to measure. Trying to come up with mechanisms that could measure it, is like coming up with mechanisms for a perpetuum mobile. It is just a matter of determining why it fails.
@@renedekker9806 Romer's experiment!
@@rogerphelps9939 :"Romer's experiment!"_ - That's a difficult one.
The mathematics for why Rømer's experiment is not a one-way speed of light measurement is described by L. Karlov in “Does Roemer's method yield a unidirectional speed of light?” Australian Journal of Physics 23, 243-258 (1970)
I have a hard time interpreting what the correct interpretation of the math is, but I think it may be the following:
Rømer's experiment measured the time between eclipses of Jupiter's moon Io. When the Earth in its orbit is moving away from Jupiter, there should be more time between those eclipses than when the Earth is moving towards Jupiter. Assuming the speed of the Earth wrt. Jupiter is the same in both case (but in opposite direction), you can calculate the (one-way) speed of the light from that difference.
But how do we know that those speeds are the same? We measure that by measuring angles towards the Sun. Those measurements are based on the lines of sight to the Sun and Jupiter, that is, based on the (one-way) speed of light from the Sun to the Earth.
Due to that, with an anisotropic speed of light, the Earth's speed would appear to be larger on one side of the Earth's orbit than on the other. That is, the orbit of Earth would appear to be more elliptical. The difference in travel time of the light between both side of the Earth's orbit would be attributed to that difference, rather than to the lower/higher speed of light.
@@rogerphelps9939 That is a difficult one. The mathematics for why Rømer's experiment is not a one-way speed of light measurement is described by L. Karlov, in “Does Roemer's method yield a unidirectional speed of light?” Australian Journal of Physics 23, 243-258 (1970)
I have a hard time interpreting the math, but I think it may be the following.
Rømer's experiment measures the apparent time between eclipses of the moon Io of Jupiter. It then compares those times at a part of the orbit of Earth when it is moving away from Jupiter, with the part where Earth is moving towards Jupiter.
Effectively, it is a comparison of the Doppler shift in two directions.
But the calculations assume the speed of the Earth wrt Jupiter is the same for both directions. The result depends on that, but that is merely a convention. To measure the "real" speed of the Earth, you would need to measure the distance Earth travels between two points in time. But how much you measure for that speed, depends on the one-way speed of light again. That is, you are measuring the one-way speed of light in relation to the one-way speed of light.
A couple points: 1) the expansion of space has the effect of slowing light in that the frequency is reduced and energy isn’t conserved. 2) the moving mass you mentioned in the end of the video you say we would not be able to detect, we do detect with LIGO. You are describing gravitational waves. I must say, I thoroughly enjoy your videos sir. Thank you and I always look forward to seeing the next! 👍🏻👍🏻
Does a mass at constant velocity produce gravitational waves? I thought it was only masses in orbits with angular acceleration
@@Holobrine You are correct, only accelerated masses in an asymmetric configuration (like two orbiting masses, but not one spinning mass) cause gravitational waves. But while a mass moving linearly with constant speed wouldn't radiate waves, it would still have a varying field that could in theory be detected locally with a LIGO-like system.
In practice this particular case (e.g. caused by the sun moving relative to the earth) is absolutely impossible to detect with current designs, because the gradients in the field would be much lower, and several sources of noise like seismic noise and thermal noise, that are small in the region of interest for gravitational waves, explode in the low-frequency limit.
@@entcraft44 It would be a 'wave' but it would just have an extremely low 'frequency' If a large black hole zipped right past the earth you would probably be able to see it with ligo, lol. (and the 'frequency' would be higher if it were closer as well, if you think about it)
LIGO measures the 2-way length of a laser bouncing multiple times between two mirrors, it's the 2-way speed of light that determines the result. It uses interferometry so the laser has to go out and come back in order to work. So LIGO wouldn't be able to detect changes in the one-way thing.
@@takanara7 you are mistaken
Yeah, the final counter-example of a mass passing by during your measurement is just bad science. You are expected to keep black holes off your optical table and locked in a separate cabinet.
But how do you prevent your black hole from eating the cabinet?
feed it some negatively charged hot noodles and keep it contained in a spaghettic field.
@@theterribleanimator1793 That does work, since the mass is pre-spaghettified but the BH can't have any angular momentum otherwise the noodles bunch up around the equator. Good luck finding a non-spinning black hole.
Also, you'll have to remove the noodles to use the BH later.
@@raulkaap damn, didnt think that far ahead.
forcing me to keep my blackholes in a separate cabinet is just another example of regulation overreach!
The moment you said a spring with a different constant on one side than the other, I instantly realized as it vibrated, it would grow in vibration in a single direction and I was like:
“Free energy machine!!!” 😂
babe wake up, huygens optics uploaded!
This same AI bot comment on all "aether" videos is suspicious
@@ExistenceUniversity ai bot lol. it's a meme and i'm excited
@@screambmachine Sorry, I meant NPC mindless comment
Babe, wake up, the NPCs are fighting.
Jeez time for an update guys the jokes are stale.
It is hilarious to me that you think you are being cool by "joining in on the memes" when in reality you are repeating bot comments because you saw them and thought "this is how I can be cool and popular".
This is the NPC mindset. Sees bot comment, thinks "popular meme, me be popular too if I mindlessly repeat comment everywhere."
"All the cool bots are doing it"
It seems like this is just the simultaneity paradox in disguise. Alice and Bob meet up, get two clocks, and synchronize them. Alice moves a distance D left, Bob moves a distance D right, and they both stand still (relative to each other). Every second on the second, Alice flashes a light. Bob sees these flashes happening periodically, with a 1-second interval between each, and thus infers Alice experiences the same rate of time as he does. Moreover, Bob sees these flashes come slightly *after* each tick of his clock, with the delay given by dt=2D/c. When Bob also flashes a light every second on the second, Alice observes the exact same period of 1 second, and the exact same delay of 2D/c.
If the clocks are still synchronized after having been moved, then the one-way speed of light necessarily equals the two-way speed. The only way for the one-way speed to differ is if the clocks are *not* synchronized. But, there is already a reference frame in which the clocks are not synchronized! Consider Charlie, who is on a rocket ship moving 0.5c to the right, relative to Alice and Bob. Charlie sees light take longer to get from Bob to Alice, than it does going the other direction, simply because both Bob and Alice are moving fast left from Charlie's perspective. Relatedly, Charlie *also* sees Bob's clock being ahead of Alice's clock, i.e. the clocks are desynchronized to account for the differing times required to cross the distance in either direction.
The definition of "simultaneous events" is entirely dependent on your reference frame; simultaneity only makes sense for events at the same location. When events are at different locations, "simultaneous" depends on the observer. Measuring the one-way speed requires some notion of simultaneity across distances, which makes it inherently ambiguous. Even if the one-way speed were different than the two-way speed, then there would be some speed at which Charlie could move that results in the clocks being synchronized in his reference frame. We can simply redefine "simultaneous events" to be events which are simultaneous from Charlie's reference frame, which results in the one-way speed equaling the two way speed. This is a simple change of coordinates. The "one-way speed" is not unknowable in the same sense as Russel's Teapot. Rather, it's unknowable in the same sense that "which way's left?" is unknowable. It's an entirely semantic paradox, a simple matter of definition and choosing a coordinate scheme. It doesn't even qualify as a mystery.
Veritasium can be good sometimes, but he also pushes pseudoscience and click-bait like "Parallel Worlds Probably Exist", "Most People Don't Know ...", "The Big Misconception About Electricity", ...
I'll stick to Huygens Optics 💖
Electromagnetic waves do not need a medium to propagate while mechanical waves need a medium of propagation. That is why this analogy is not valid.
EM waves propagate in the EM field. You might not want to call it a medium, but the math is exactly the same.
@@TheOneMaddin EM waves always travel at maximum speed of propagation. Sound waves travel relative to the maximum speed of mechanical wave propagation in air.
Maximum speed of propagation does not imply there is a medium. It just suggests waves can travel relative to maximum speed of wave propagation.
The notion that light slows down in the medium is false. Light never slows down in a medium. Photons just takes longer path while travelling through medium at the same speed as outside of the medium.
Or ... one can actually trace the evolution of the constant evolved for denoting the speed of electromagnetic propagation, in a given medium, called "the speed of light" to Wilhelm Weber, read the old scientific publications, and literally understand that the speed depends on the inverse product of the magnetic and dielectric (permeability) constants in a give medium. Ones armed with such an "archaic" (and seems now days unconventional) knowledge one can ask the simple question, does any medium show dependency of the magnetic or the dielectric constants on its geometrical structure ( different properties based on the material spacial orientation). If that were to be the case, then it seems that either the magnetic or the dielectric permeability will have different values when an electromagnetic vibration propagates in space so the "speed" of ( light ) that wave propagation will be different in the different dimensions, if not, then clearly there will be no difference, exactly based on the physical (and formulated) definition of what the speed of light is.
The equivalence principal tells us if we do these experiments while in freefall we will always get the same results. This is even true if the experiment is done in free fall towards the event horizon of a black hole (one large enough to ignore tidal effects).
However, observers in different reference frames may see things very differently. Light will always move at the same velocity, but clocks in different reference frames won't agree. Since the velocity is constant, the wavelength will appear different.
Best time resolution in a time-of-flight experiment with electronic triggers may be around 50 picoseconds. A 1 ppm error of c consequently can be achieved at a measuring distance of the light path of more than 15 km. Getting a stable signal transport over e.g. a coax cable of the same length looks almost impossible.
However, if it may be feasible, rotating the whole setup 180 degrees might answer the question of whether the vacuum in space is anisotropic, of course only at the precision level of 1 ppm..
gps satellites can give a unique one-way predictable source of future information that could reduce need for timing data / start cues / synchronizing, right? and will be below margin of error, else you use a signal like the upcoming weird nova we expect, the arc difference will be minimal, but gps can be timed in midpoint, and as they are timestamped, reading the data means nothing then (but you can say speed of causality slows the clock?)
Derek makes excellent videos in general imho, though I maintain critique of his "impossible to know" video as mostly or pure notoriety rooted in unfalsifiable rhetoric - as well critique his rhetoric around defending clickbait "because giraffes," sigh
Aren’t the conservation of energy and momentum downstream of Noether’s theorems, which take symmetry as an assumption? Saying c must then be symmetrical is a circular argument.
Just had another thought albeit somewhat impractical. You could measure the one way speed of light if it was traveling around the circumference of a black hole such that its path was that of a closed circle. Who knows, maybe some super advanced aliens have done that :)
You don’t make mention of length contraction/time dilation in your proposal which depends on the speed of light in a given direction.
Given that these depend on c, it’s likely that these effects would cancel out the infinite energy and there would be no observable difference if the speed of light was different in different directions. It would be interesting to see a follow up taking these into account.
Honestly I think that it doesn't feel like that's possible, because if it were, then wouldn't we see a little bit of redshifting if we look at something in one direction vs a different direction? Since, if the speed of light is different, that would mean the waves would get a little doppler shift if you look at them from a different direction.
*3 way*
Could you just set up a “triangle”? So if the three-way speed is that same as the two-way speed, then each way is almost certainly the same speed.
every time I hear Huygens Optics talk I feel how much smarter than me he is, and even these long form videos can't fit all the knowledge he has to share
Now i might be missing something but we know the speed of sound is constant in air so could one not use spund to trigger the clock and the delay is the distance divided by speed of sound. Thus avoiding measuing the two way speed of light.
Why isn't it setup so the sensor detects the light twice? First the light directly from the source and second the light off the mirror? Distances and time between sensor detections are known
Well, you convinced me.
But there again I'm more content to accept "common sense" explanations than any mathematician, or most scientists, would. So, for now, I'm going to ignore any "special pleading" attempt to introduce a possibility of there being a difference in light speed with a change of direction, while in a vacuum.
my simple mins alwas was like ligt cant change speed becos than my camera les woud work difrently depending on wich way im facing
Now I am imagining that little green fempto-pulsed laser blip surfing a gravity wave and I am very happy with that.
Thank you for the spring mass analogy. Love when EE concepts match up pretty well to mechanical concepts. Gives more intuition about the more abstract concepts which can be powerful.
Love your videos by the way. Optics was one of my favorite courses in college and these videos solidify fundamental teaching while at the same time not shying away from more advanced concepts and topics. At the end of our course, our professor talked some about non-linear optics but treated it as dark magic. Would be awesome to explore some experiments or topics in that realm if your equipment would allow.
wait isnt this difference in propagation speed caused by local gravitational fluctuations the working principe behind a gravitational wave detector?
I might be misunderstood but that sounds to me like we can measure it
Yes but because it is based on interference, always in a two-way way.
If in a Frame of Reference there is a shift in time as a function of shift in space, then light would effectively travel at different speeds depending on the direction it travels. This is exactly what happens in the equation t’ = gamma(t-vx/cc). In a moving Frame of Reference, time is shifted proportional to distance. It’s the x in the special relativity time dilation equation. Therefore the speed of light is different in the 2 directions depending on the Frame of Reference.
Does that mean we could trick conservation of energy with a clever application of relativity?
@@mikelord93no. From a moving Frame of Reference perspective, the distance is identically contracted in both directions of the round trip journey, and time is similarly dilated. But in one direction time is also shifted forward proportional to distance and then shifted backwards in the opposite direction proportional to distance. This means in effect from the moving Frame of Reference, light seems to travel at a different speeds in the two directions to compensate for this shifting of time as a function of distance.
Light can have different speeds in two opposite directions with respect to a moving frame of reference. The law of conservation of energy is still preserved.
The only issue with the conclusion is if we take the reference of an object in motion, let’s say traveling at say 1/2C then the speed of light forward of the object should appear to be slower (1/2C) while the speed of light aft of the object should appear to be faster (3/2C). This simple thought experiment seems to suggest that there MUST be a difference in 1 way speed of light for any object in motion.
A traveler moving at any speed would always measure the speed of light to be c in any direction, that's the fundamental observation that SR is based on.
Wait, I'm afraid that the definition of 'direction' was assumed, and never discussed or mentioned here. What exactly is a DIRECTION? Does the location of the observer (perspective) come into play with the definition of direction?
4:30 He mentions 'from the left' and 'from the right' to differentiate directions. Are these directions universal around some coordinate system? Or are they relative to the observer (in this case, the clock in the middle)?
Huygens Optics there is a channel called Dialect - do you know them? They are talking the same problem that you do - but they don't take for granted that the one way speed is 1/2 the 2 way speed... They allow it to be any value - even the one way being faster than the 2nd way... Thus they are trying to explain a different interpretation of relativity! I wish you could watch their videos and tell us what you think of them!
I don't think your asymmetric spring reasoning is correct. What you describe is a type of spring that generates different forces at its two end points for a given elongation, which as you point out violates conservation of momentum (and the action reaction principle).
What I imagine as a (legal) two constant spring, for example, would be one that has k1 under compression and k2 under elongation (which isn't hard to achieve) but this would still result in isotropic propagation, so I'll come up with another spring.
This third spring "detects" which of its ends is the first one to move (left or right) and "decides" if it will act as a k1 or k2 spring. A wave propagating from the left will encounter a medium with an elasticity given by k1, different from a wave approaching from the right (k2), resulting in two different wave speeds while conservation of momentum is preserved.
Some possible issues with a system like this would be how the spring could "detect" and "decide" fast enough, intuitively this seems to require information to reach the spring's "decision" system faster than light travels in order to adapt to a traveling wave of light so as to slow it down.
To be honest I also didn't find the last part of the video very convincing. It seems that reflecting light would violate conservation of energy but that is because we use formulas derived assuming C1 = C1' to start with, maybe we can come up with better ones. To be actually convincing I think you'd have to show how exactly that "illegally" obtained free energy could be turned into profit, but I can't really come up with any ideas about how. For example you could argue that these extra energy photons could be used to excite an atom, which will then emit a higher energy photon, which gets reflected for an even higher boost of energy, and so on. But then who is to say that atoms themselves would be excited isotropically?
Thanks for reading so far down lol.
The arguments in the video cannot prove that c1 = c1' in the general case. Rather, they hint that such an effect would require a significant remodeling of our theories rather than just a small correction.
@@entcraft44 Absolutely agree with this interpretation. I just wanted to point out that you could imagine a sort of medium which propagates waves anisotropically without violating newton's principles. That being said, I'm pretty sure our whole current model of physics does assume that empty space is symmetrical or isotropic (I don't know which word fits here better). The fact that a model with this "extra" assumption that c1 = c1' doesn't fail experimentally is proof enough for me otherwise.
an anisotropy you forgot to consider was if the grid of springs was moving in some particular direction with respect to the observer
Indeed all examples assume the setup and observer are within the same inertial frame of reference.
Yes, light propagating through space will be the same in any direction; but while the light is travelling, the receiver can move, which makes the detection at the detectors register different speeds. Your initial setup is indeed a two-way experiment... but you can change the setup: 1) 2 detectors in close vicinity, in the center, with a high precision clock that records the time when the detectors on left and right are triggered. 2) Put two emitters that have a stable clock, that will always tick at the same rate (more detail later). Each emitter will fire a short pulse (milliseconds are fine, you just mark the leading edge detection). Amazon has lasers that are good for up to 2 miles (10,000ft)... (light is approximately 1 foot per nanosecond, so over 10000ft is 10000ns or 10us.) Over the 10us, because of our motion through the universe towards VIrgo according to the redshift in the CMB, we move 370km/s or .0012 ft/ns... so it will move 12ft over 10us, and register a different speed from one side vs the other of +/-12ns... or a total difference in the speed of light of 24ns. (in the perfect arrangement).... so this would need to be aligned with the constellation virgo/cetus(opposite side constellation), so that there is a best-case... it's aligned to approximately +9degrees north; can't really just make this go any direction, or you can end up with a near null result, the orbit around the sun is 10% of the speed through the universe, and the rotation of earth is 1% of that... so +/-1.2ft or +/-0.012ft from those effects... the motion through the universe is much more on point.
Mind you - the speed of light does not change based on the speed of the emitter... just the speed of the receiver - such speed is then c+v and c-v..... There may be additional skews to the stable clocks.... that once deployed they are not in exactly the same gravitational field... but this will be a constant effect, and the constant drift can be factored out. Air pressure is an insignificant factor; and since it's likely that the 4 miles the experiment covers (2 miles from one side of center and 2 miles from the other side) will likely be the same it ends up being non-measurable... and any change under like 100,000atm is barely notable... a few millibar is not going to change the experiment...same with humidity - the same amount of humidity is likely experienced across the apparatus.
Another way to consider this is say you're playing catch with someone else, and every second they throw a ball at you at the same speed, if you move towards them, then the throw that happens while you are moving will be caught by you in a slightly shorter time. If you continue to stand in place, at this new distance per second, the ball will be registered as every 1 second. If you walk away during a throw, then the time it takes to catch the ball is slightly longer, again, until you stop. If the experimental apparatus is perpendicular to the velocity, that's basically initial conditions - and every pulse is received at 1 second intervals from both sides... as the apparatus aligns with the direction of motion, it's like the center detector is able to take a few steps forward, and pulses from one side will arrive in slightly shorter time or slightly longer time, whether the detector is moving towards or away from the emitters respectively. Once it reaches the maximum alignment, the pulses will still be every 1 second, but will be skewed from each other compared to where they started... if they start on every integer second, then it would be at +12ns and -12ns from the original state along a timeline. The times between each impulse registered from each side are subtracted from each subsequent sample, leaving a small delta change between each received pulse... at the end you'll have a net bias (probably) from clock skew, this can be removed by subtracting the final value from the initial value, and subtracting that sloped line from the result, biasing the beginning and and to 0. (This would mean a complete 24 hour cycle should be run... it would be less meaningful to do only 6 hours or even 12 hours - because at the 12 hour mark you're not necessarily in the same arrangement, since the apparatus is aligned with a specific point on the horizon, at 180 degrees of earths rotation, then the device is no longer in the same alignment as it started, but is tipped in a counter direction (that's not the right word but maybe you get the idea).
I have been working on setting up this experiment, and if I can get the apparatus built, I would take it to the great salt lake, there are very few areas where there are 4 miles in an arbitrary direction that are entirely clear and flat, and wouldn't interfere with the line of site - could built something in the ocean maybe, but it would have to be tied to the ground. The two emitters and the center detector MUST be rigidly arranged - floating them, or launching them into space will not help. Anyway - I did setup a program for an FPGA that has a high speed clock, and two registers internally that can be latched when a signal from a light detector is received... the latched clocks can be read more slowly and stored in a computer over the next second between each pulse. The FPGA though is actually pretty slow, and although I'm almost able to get a 600ps clock, it's unstable, and a temperature corrected crystal oscillator that is more than a Ghz is expensive... That, and I don't know how many photons the photodetectors have to see, or how bright the intensity is - but I would expect actually quite a bit of noise from that receiver - plus, I don't know a good way to gate a laser pulse - for the same reason, propagation of all the voltage regulators, plus time to build up a signal to transmit are likely going to cause more noise in the experiment than +/-12ns. I've somewhat settled on using a synchronous AC motor that rotates 60RPM (once per second) and put a wheel with a 1mm slot on it - but even then, as that is actually pretty slow, it's going to uncover a fraction of the beam, and then the whole beam, and then start covering a fraction of the bean as it passes... which makes the signal leading edge not very concise... and is another point of noise. There are high precision frequency generators/counters but I find they are $16,000+ to be within a range of desired resolution, and then that is a bulky external thing, which introduces nanoseconds of delay with propagation of those signals... I just don't see it being done with off-the-shelf components. Probably have to make an ASIC with dedicated silicon for the clock and 2 latch registers (a super simple thing, though you do need about 52 bits of precision, which is quite a lot of bits, and a long chain to update.... which potentially makes the clock have grey bits in the middle while it's still counting a clock tick... the clock edge at one end will change even while the middle of the counter is still updating from the previous tick. That and the light detectors need to be pretty precise, and the module I got, the sensor is actually not JUST the sensor but has a transisitor the detector is attached to - which, again, signal jitter/noise. I don't know if maybe I got a DLP(?) sort of chip used in projectors that could gate small mirrors in two directions pretty fast... I would think those are still on the scale of 100s of microseconds... and far from the nano/picosecond gating I would want.
Speaking of space, changes in space of the gravitational field only propagate at the speed of light also, which means ahead of our planet the field is somewhat compressed, and slightly more dense and is slightly weaker, so satellites will orbit just slightly further away (1 meter per kilometer roughly), and on the trailing side, the field will be elongated, and have slightly greater effect, making satellites on that side orbit slightly closer... This makes GPS signals always take the same amount of time to arrive. There is a thing in the solar system the 'Axis of evil' which is an overall alignment of the elliptical orbits of things that is always in the same direction. One could argue that GPS (multiple emitters some fixed distance away from a central detector that registers the time in the same location with 0 propagation time of the clocks signal) is the same as the above; that is, the same, except for the specification of being rigidly attached.
On my channel the last few videos I did were on simulations I built (open source, links in descriptions to the demos and/or more information documents in the github repo) that are based on the one-way constant speed of light... and indeed, any two-way measurement will always be a constant time for a distance, in any frame, moving in any direction, while the individual one-way paths are neither the speed of light (as registered by a moving receiver). Light, once emitted no longer has anything to do with the source that emitted it, and it propagates in space regardless of what the source does afterward... Though the net combined effect does result in light aberration, both on transmission, and on reception of signals (see synchrotron radiation beaming effect for more about this aberration for electrons travelling close to the speed of light - the direction the light is detected is mostly all directed forward.
Mind you this does not measure the one-way speed of light. It only measures the differences in the one way speed of light
If the speed of light varied based on direction, then the observable universe would not be spherical and we would not be at its center. We'd see farther in some directions than others and thus see more stuff in those directions. We could (roughly) measure the relative speeds of light coming from different directions by counting the number of galaxies visible in those patches of the sky. I think it would also show up as an anisotropy in the size of the temperature fluctuations in the CMB. The relation between redshift and distance would be anisotropic. And probably other stuff too that I can't think of at 3 in the morning.
I thought of similar things. If there are enough stars with redshift to measure the expansion of the universe it should be possible to see a different speed of expansion in different directions if rhe speed of light would be direction dependent. The point of seeing more galaxies is brilliant as well (If mine has any merit & independent of that)
As someone who studies physics and electronics my brain got constant error 404 with the spring. It's a spring not a resistor, It's a spring not a resistor, It's a spring not a resistor...
Armand Hyppolyte Fizeau is one of the best names I've ever heard, holy crap
P.S. how do you pronounce "Huygens"? Is part of that silent like the Vietnamese Nguyen (or are my white eyes just seeing the same letters and assuming a connection lol)?
kind of like HOY-guns
Your mom is so big she can measure the one way speed of light with how far her eyes are apart
Хаха, спасибо, за информацию, никогда не думал, что буду учиться оптике на Ютубе!
LIGO Proves light travels at the same speed both ways. These videos are pointless, fun, but honestly pointless.
It really doesn't prove any such thing.
And this, ladies and gentlemen, is how you explain in a easy way something hard to understand. What a great video!!!
Fantastic video, I'm glad TH-cam recommended your channel!
If you were flowing with a river (but didn't know it), could you measure the one-way speed of sound in the water? Is this a valid analogy?
21:00 That's how free energy devices is made scientific way.
I don't see why the "one way" speed of light is an issue of such concern to so many people. We fundamentally do not believe that there is any such thing as a "special direction" in space. Why WOULD the speed of light a long a path depend on which way it's going? The natural, obvious Occam's Razor assumption is that it travels the same speed both ways. And by the way - even if it didn't, it WOULDN'T MATTER, because if it did, then we could use that as a way to MEASURE the one-way speed of light. There very fact that we can't measure it means it's entirely irrelevant to us.
People just like to "pick at things."
Exactly. Considering there is no way to say whether it is different or not, just assume that it is the same and move on. I guess people just can't understand that this doesn't change anything at all for us
they want to pretend they know more, but it is really to make up a hundred hidden variable, as long as they stay hidden....
that saying goes, part of one way speed of light is actually easy to disprove, specifically "directionally/opposing anisotropy" speed of light in 16:13/18:30
because they easily violate snell's law
however snell's law can only only experiment locally
19:24 What is that on the bottom right supposed to be?
slip of the tongue: replace string by spring
@@HuygensOptics Oh I see, a spring string bottom, I’m not native and had to look that up. 😅
What a prank! 🤣🤣🤣 "This is the end of the video"
This scared me a lot😬
I think the speed of light is the same in both directions. Because if speed of light in one way was different even by a tiny amount, the universe would look completely different in different directions.
Also, if speed of light was different in different directions, things like GPS would break because the time dilation would be different than expected.
13:06 well, properties of SI system of units
If light was biased, half the galaxies on one side of the sky would looker younger and closer than the other half. Otherwise the question becomes "...within a sphere small enough to ruin your experiment idea"
No one actually thinks light moves at different speeds in different directions. That's not the point. The point is that no matter how obvious that we think that it MUST be that this is true, the universe appears to have conspired to make it so that we can never prove it to be true. So it may be obviously true, but it appears that even Einstein could not rigorously prove it so. And that's the point
no, if light was biased, then every interaction with light would cause a change in momentum, on average against the direction of the fastest emission of light.
so things would move against light, and the doppler effect would appear to cancel the asymmetry
The speed of light being different in different directions breaking the conservation of energy explains why a lot of people very desperately want this to be the case since it would allow for infinite energy devices.
*Advanced Tinkering* channel just mentioned you in an absolutely lovely way in the video "Creating Ultra-Fine Details in Titanium - 20 Micron Resolution" ! 🤗
Well, if we did measure different times for different directions than it would mean that there was some additional moving gravitational potential somewhere in the vicinity of the light's trajectory and in fact we do use it cosmology when we measure the mass of black holes in a galaxy using long term gravitational lensing observations - recently covered by Anton Petrov on his channel discussing results from a Warsaw, Poland study on this exact subject.
There's really no good reason to assume that light travels with different speeds in opposite directions when there's no change with respect to time in gravitational potential.
If there was a difference we would not be able to infer anything about masses from any measurements, which would be contrary to experiments and day to day perception.
Good video.
You compare the situation with an elastic medium that has different spring constants for the two directions, which leads to violation of conservation laws. But that is not the only way to achieve anisotropic propagation speed. The medium itself could be isotropic, but simply have a velocity in one direction. That would not lead to violation of conservation laws.
I think the more profound observation is that there is a delicate link between the one-way speed of light, and how simultaneity of distant events is defined. The definition of simultaneity makes it theoretically impossible to measure the one way speed of light. You might want to do another video on that.
Ever since I discovered this myself, I have marvelled at the following simple sentence in the introduction of Einstein's 1905 SR paper:
_"We have not defined a common “time” for A and B, for the latter cannot be defined at all unless we establish _*_by definition_*_ that the “time” required by light to travel from A to B equals the “time” it requires to travel from B to A"_
Einstein already knew that what you have discovered as well: that the one-way speed of light is a matter of definition, not of measurement.
' is pronounced 'prime' in math.
wow i’m so glad i didn’t click away after the first half lmao
first half was amazing (for the viewer that’s not familiar w the conclusion)
just excellent motivational context-building
but the second half was an amazing next layer deeper of thought experiment / pre-analysis
There's an experiment that came to me today, just before this video came out, that I would love to see, but don't have the means to perform. I just recently learned that Neodymium-doped Lithium Niobate can be used as a lasing medium. I am incredibly interested in the interference and diffraction patterns produced by it, specifically when it is being used as a laser medium while also piezoelectrically oscillating. Lazing Lithium Niobate, even when not doped, is a parametric down conversion process too, producing more than typical entangled photon pairs! If you're interested at all I can link you to a few papers, and a source for Neodymium-doped Lithium Niobate on substrate.
Love you so much!!
I love this approach! Finding contradictions in conservation laws and the inconsistent consequences if one assumes anisotropic speed of light.
If the clock and the sensor is the same, i.e. a quickly rotating disc of photosensitive material, and the disc at both ends of the race track is coupled with a long axle that spins at a constant rotational speed, will this device show a different speed of light one way (angle between dots) if it is oriented horizontally and vertically in a deep shaft? I suppose the measured rotating speed of the disc at the bottom of the shaft will be higher than that of the top one, even if they sit on the same axle.
Force is propagated through material at the speed of sound of the material
read Alberto Martinez' book Kinematics: The Lost Origins of Einstein's Relativity - he goes into how speed and velocity were confused in relativity. thanks
Was just writing a comment about the AlphaPhoenix video when you mentioned it. Another under-rated channel.
Would the difference in c result in different wavelengths for the same frequency propagating in opposing directions? Those quantities feel tractable to measure, and are a lot more local of a measurement, avoiding the whole loop problem.
It felt like the video was about to go there a couple of times, so maybe I missed where the idea was dismissed as not even wrong 😅
@@joshmyer9 And how would you measure it? Since you have the same frequency, you can assume that the speed is the same.
Wow! I love hove how concise yet clearly and detailed you describe such complex topics. You are great educator.
You can't. When you have two detectors separated at a distance from each other, you won't be able to connect them to the "same" time measurement, because they are already in their own reference of time. Ponder on what "time-space" means. If you don't understand what I am saying, just go back to read the "train going through a tunnel" example again.
Because if you want to compare the time of the two separated detectors, you have to bring them together, meaning at least one of them has to go through acceleration and deceleration, during which process their time reference is already changed.
Well you can always modulate a timestamp on a light pulse
And then decode it to get the speed relative to the receiver you point a "laser" at tx an rx both have atomic clock, and you can synchronize both using a 3rd atomic clock half the distance between Rx and tx to average out any time dilation effect...
How long does the second pulse take on average from the previous detected pulse, knowing the distance traveled and the time encoded on the radio signals
Sometimes I think that our universe is built this way because others have collapsed one way or another due to catastrophes from things like the mentioned "opposing anisotropy".
There are similar issues arise with, for example, negative mass, infinite speed of light, time loopholes, perfect portals and so on.
In other words, a world with free energy or an energy sinkhole will always destroy itself.
The graphics in the first half of this video are terrible! I seriously can't follow anything this guy is trying to explain. However, I was able to follow the Veritasium video perfectly even though I don't agree with it.
I thought the LIGO gravitational wave detector measures exactly this. I thought it worked because the speed of light is changing through the detector. but maybe my high-school education is failing me 🤔
This must be a mirror universe where port and starboard are flipped... 😂
And what if you pass the light beam through glass in both direction, same refraction angles, same diffraction angles, sam wave propagation speed, issue solved ?
Formulae assuming c to be constant would make predictions differing from observations in proportion to the specifoc error in c at time of the observation.
We don't see this...
C must be universal, no?
T. Folse. That guy just rips off content under fair use. It wouldn't be so bad if he made at least SOME original content.
Only 400 views in 15 minutes?
So, can you show a demo of speed of light vs speed of stick ringing a bell on the moon? Let the stick be stretched from earth to moon and the laser be located on earth. Now switch on the laser and push the stick at the same time. Which one will hit/ring the bell on the moon first? No need to search for an Internet answer; there is no response to this question.
Ok... so we put this clock on a train going thisaway, and we put that clock on this train going thataway and then we go choo choo real fast and then we put both clocks in the mail (DHL) back to the train station and THEN WE READ BOTH CLOCKS ON THE SAME DESK AT THE SAME TIME TO FIND HOW FAR AWAY THE CLOCKS ARE FROM EACH OTHER IN TIME or however you want to say the clocks experienced different rates of time... I am so fucking confused by how they managed to get both clocks into the same spot, doesn't that literally mean they're in the same frame of reference? (obviously we're not really talking about clocks here.) If you put them 'clocks' right next to each other, i mean straight up zero distance between them, how the fug can you say they're not in the same frame... so... there's no time dilation... wait what!? 😮
Aren't conservation laws written in their well-known form assuming isotropic speed of light? In other words, you would need a skew factor between conserved "to the right" energy and "to the left" energy if speed of light wasn't isotropic (same for momentum) (*). I'm just trying to think in terms of mass as photon boxes, then your mass on a k1,k2-spring scenario doesn't really violate the conservation laws (I think). So I don't buy the last argument. But I like the analogy, it does make it seem intuitive. But I think in this extreme example, the analogy does not apply, or at least you need one more assumption or piece of evidence to make it applicable.
*) to clarify, conservation of energy and momentum are a consequence of Noether's theroem, they're a consequence of time and translation symmetry. But speed of light not being isotropic is no longer time and translation symmetric so you can't apply those conservation laws.
12:40
HEAVISIDE EQUATIONS!
Also!
Do you do podcasts!?
I'd love to see you interviewed by DemystifySci if you would honor us with your presence!
I will repost my comment from Veritasium's video
HOW TO MEASURE SPEED OF LIGHT
We can measure the time it takes light to go from point A to B in vaccum, bounce of the mirror and go back from B to A, BUT inside a glass
Then repeat the experiment but in the opposite way. If the speed of light decreases by the same % going from vacuum to glass regardless of the direction, we should be able to see the difference in travel time.
Furthermore, we can make 2 additional experiments (both ways in vaccum and both ways in glass), so that we have 4 measurements of time and 4 unknown velocities - easy to solve equations
Great video btw :D
At 2:33 onward, you talk about seeking to prove C1 = C1' and therefore get C2 = C1 + C1' but my question is: Does a mirror reflect instantaneously (Tm = 0) or is there a delay (Tm > 0)? If Tm > 0, it must still be very small, but when you're talking about the speed of light, small is not zero.
I'm no physicist so I'm not sure if this is important or irrelevant, but, at the very least, C2 = C1 + C1' + Tm and so inferring the one-way speed of light by halving the two-way speed of light would still not be correct.
you're never going to measure the one-way speed of light with a single clock, that I think is the fundamental problem with both this video and veritasium video. In order to measure the one-way speed of light you'll need two clocks, one at each end of a distance D, and those can be atomic clocks that are synchronized by GPS (signals that are perpendicular to D). The problem veritasium made is thinking that just because he wasn't able to think through how to do it he concluded that it was impossible, that's hubris. QED. anyone disagree ???
There is a miscalculation at 8:04 and it appears to be important. You accidentally have Δtr_31 = D/c_1 when it should be D(1/2c_1 + 1/2c'_1), you also committed this same mistake for Δtr_42. It is not an important mistake though, because you fix it immediately.
2:57 you say that C_2=(C_1+C_1’)/2 but this is completely false. You cannot just take the arithmetic mean.
You have to use the harmonic mean when working with speeds. The right formula is
C_2 = 2/(1/C_1 + 1/C_1’)
Wave propagation is instant difficulty in the emitter-receiver aspect of amplitude-frequency density-intensity in a holographic time-timing ratio-rates Perspective Principle of what is used in heterodyne radio and is a ubiquitous property of holography-quantization, eg the constants provided, such as permittivity are prime-cofactor products of collapsed Superspin/Epicyclic superposition identification in the general context of numberness probability differentiates dominance sequences, (have to draw the 0-1-2-ness in 3-ness -> 3D-T Physics drawing the picture of condensed form following functional concepts.., every possible movement is a potential focus of temporal thermodynamical superposition focus of reciprocation-recirculation relative-timing ratio-rates, and the speed of light is a 2-ness propagation of a differentiates rate of rate wave-packaging.
Navigators must be living and breathing this duality of heterodyne transmission in Doppler shape shifting circumstances, but it takes time to accumulate a skill very similar to Euler's e-Pi-i superimposed fields sense.
Of course the recognition of Euler's e-Pi-i Entanglement and 1-0-infinity instantaneous probability range according to wave frequency-amplitudes alignments is a Radar/Navigation Operator person's task, and you qualify for the tinfoil hat if you solve the orientation of Entanglement Fusion-Fission Function Fields positioning, and make the speed of light a trivial fantasy.
Holographic Principle nucleation ensures..
We can't measure nothing in No-thing, only deny it's some thing else, which is trivial non sense putting some distance between POV.
To define a one-way speed of light between two different points, you must have a concept of simultaneity at those two points. According to special relativity, this is meaningless; you can pick a velocity v in any direction and define (x_1,t_1) to be simultaneous with (x_2,t_2) if (t_1-t_2) = (x_1-x_2) dot v. This gives you different speeds of light along the direction of v. Of course, this is not measurable by any experiment, which is why you can assume that the speed of light is the same in opposing directions as a matter of convention (although there is something more to be said about diagonal directions).
An interesting conundrum. But, the difference in speed is purely theoretical as the one way speed of light has no practical use in observation.
Unless, of course you want to observe an observer, in which case ???
There is also the effect of gravitational lensing, the effect of gravity on light, there is an effect of bending the light and even Newton understood that things continues, at the same speed and direction unless forced not to, by a force.
So, if you were on the edge of a supermassive black hole and shot a laser beam at the dearest dark object and measured the reflection time, it would seem obvious that the speed of light in both directions would not be the same, but the average speed would =C.
And that's it realy.
While I am here I will drop this little puzzle for budding geniuses.
Tn + En = S n
Sn + Tn = E n
En + Sn = T n
Think Fermat's Conjecture. With T= time, S = space E = energy.
Every reflection in the setup changes a direction of a beam
But can't wee use a monochromatic light beam, say using FEL, whose frequency is exactly known. Then measure the wavelength precisely using a defracttion grating and figure out the one way speed by c=frequency X wave length? Won't that be a one way speed measurement?
Yes, we're calculating c here from other stuff. But we do so in every experiment.