What we call the speed of light is exactly that-- it is the upper limit on the speed at which conventional matter or energy can travel through space, and, therefore, it's the upper limit on the speed of propagation of information as well. What we refer to as c is, as we currently understand it, the speed of causality-- if object X does something that has an effect on object Y, that effect will travel at <= c.
Light Years and Time
- Thread starter KaguyaLady
- Start date
The GPS chip in every damn smartphone on the entire planet measures the speed of light, one way, from multiple satellites, several times per second. If there was a variance of more than a tiny fraction of a percent they probably error out immediately and if they didn't error out, you would be directed into the wrong driveway or a boat ramp stuff like that.
I'm sure his IQ is 20 points higher than mine, but the last thing I would do is trust his analysis of anything. His video about electrical signals traveling outside of a wire was refuted by...pretty much every physics and EE channel on youtube. The main thing he is smart about is getting lots of views and adsense revenue from putting out half-truths.
Except that he wasn't wrong (although his initial formulation of the problem was a little too ambiguous); there's just some really counterintuitive stuff going on related to how electric fields interact with the wire, at least if the extent of your mental model of electric current is "balls in a tube".
(This is something that can be and has been experimentally verified; it's not just a hypothetical thought experiment and the physics behind why it works the way it does are actually kind of important in some fields-- transmission lines are weird.)
If you et al had watched the video you would know he was talking about the one way direction of the speed of light
When there is a combination of an electric field and magnetic field at 90 degrees to each other, energy is transmitted through the fields along and outside the wire. These electromagnetic fields conducting energy is the electricity.
When there is a combination of an electric field and magnetic field at 90 degrees to each other, energy is transmitted through the fields along and outside the wire. These electromagnetic fields conducting energy is the electricity.
He did a terrible job explaining it, which would not be a big deal, but it’s his job to explain things.
My main concern was with the guy I mentioned saying how since light years are like that then everything is illusory and our perception of reality is unreal. I think it's safe to say he's wrong about that. weird how bad conclusions come from facts.
No, you just don't understand what I'm saying.
If the speed of light going right to left were different going left to right, the number of wavelengths between two objects would be different for the right-going and the left-going waves for the same frequency. The geometry of an interference pattern is a function of how many wavelengths there are between objects along the direction of travel. The only way to make it turn out the way it does is if the distance measured from right to left divided by the time it takes to go from right to left is the same as the distance it takes to go from left to right divided by the time it takes to go that distance. So if the distance is the same, the speed of light is the same because we can count the wavelengths and measure the distance with either a right to left ruler or a left to right ruler and that's the same too.
It's utter nonsense to say anything different. You might as well say your ruler is two feet long from right to left and no distance at all from left to right and everybody would regard that as the height of stupidity, but dress it up in enough awe and wonder and you can make people think you might be on to something when you're spouting bullshit.
Mr. Muller either knows better and he's gaslighting you or he doesn't know better and he has no business trying to tell people about physics.
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Yes, since we use the speed of light to calibrate all other speeds, if the speed of light is anisotropic, all kinds of other things we think are isotropic couldn't be, including crystals (some of which really are anisotropic, and we can measure that).
My first thought when I saw that video on the speed of electrical energy a while ago was "what a confusing way to explain transmission lines".
This still wouldn't cause different optical phenomena. Here's why:
1. in a vacuum, there is no interaction between photons that move in different directions. When there is, that interation is entirely energy-dependent, not speed-dependent, so scattering, absorption, etc. still function exactly the same way. Things still have the same proportional momentum and energy.
2. In a medium, you'd say that e.g. because of E=hc/lambda you'd immediately see a difference in wavelength of light going into or out of a different phase, causing slower light to bend more. However, for the same reason as before, the refractive index is simply proportionally lower for lower light speeds, preserving angles in refractive media. Length contraction preserves number of wavelengths per distance.
3. At a distance when e.g. looking at the angles of light coming at you, sure the lower-speed dimension will appear to have smaller angles of light, but you'll also be contracted in that dimension, preserving angles anyway.
Since the speed of light is also the speed of causality, all of this works the same for any matter system interaction. Anisotropy of light is very hard to measure accurately.
In a world with such large anisotropies, matter would actively contract and lengthen when rotated, yes. That's a big consequence of anisotropic light speed, and again - that's why this is one of those hypotheses still open to explain dark energy, at least partially. After all, it seems like dark energy somehow actively expands and gravity actively contracts light without an obvious place for that energy to go. It seems to be an elastic feature of the universe.
This is actually something i learned in a university physics course. Because anisotropic light speed is already a thing and very relevant to e.g. electricity and thermal flow within certain materials. For a lot of this, you have to go through the math to untangle the actual effects.
To be clear, science has long ruled out large anisotropies. Just going by the wikipedia article, it's going to be smaller than 10^-9. (https://en.wikipedia.org/wiki/One-way_speed_of_light)
You're taking the angry incredulous approach to hammering physics into a shape that fits your worldview, but like with many other science topics, this stuff just isn't immediately obvious and intuitive. I'm also, to be absolutely clear on this, not saying that light speed is anisotropic or that I believe in these alternative models of the universe, I'm just explaining the actual theory behind it so you get an accurate idea of what it's actually saying.
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I didn't make up the super extreme anisotropy. It's right there in the video. He claims scientists haven't ruled out that the anisotropy could c*2 in one direction and infinite speed in the other. Which they have.
I say, if you have evidence, bring it. If you don't and you're making claims that are at odds with a theory so well established as general relativity, you're just wasting people's time and sowing doubt where there really isn't any.
I... don't have evidence for anisotropy. But if light speed were anisotropic, it'd be pretty hard to detect and wouldn't change much about most of our big theories of physics. It would do basically nothing to general relativity, as (again) mentioned in the wikipedia article and any other explanation you'll find.
The Veritasium video mentioning large anisotropy is by example. It's not a mainstream hypothesis held in the larger cosmology world, and moreover entirely inconsistent with observations. The types of anisotropies that would e.g. explain dark energy are exceedingly small, much less than 1e-9, and to be absolutely clear about the nature of that type of anisotropy: it's not based on cardinal directions. That, too, is just an example of what anisotropic light speeds would look like. What cosmologists consider a still open possibility is e.g. light speed anisotropic across gravitational gradients.
And I'm not sure why you're mentioning wasting people's time? You brought up things that were clearly misunderstanding the theory, I took the time to explain them. All the time we've wasted is yours and mine.
The Veritasium video mentioning large anisotropy is by example. It's not a mainstream hypothesis held in the larger cosmology world, and moreover entirely inconsistent with observations. The types of anisotropies that would e.g. explain dark energy are exceedingly small, much less than 1e-9, and to be absolutely clear about the nature of that type of anisotropy: it's not based on cardinal directions. That, too, is just an example of what anisotropic light speeds would look like. What cosmologists consider a still open possibility is e.g. light speed anisotropic across gravitational gradients.
And I'm not sure why you're mentioning wasting people's time? You brought up things that were clearly misunderstanding the theory, I took the time to explain them. All the time we've wasted is yours and mine.
I don't know what "proof" means in this context.
I am nothing like an expert in these fields, but a simple question occurs to me: "What is direction"? Or, put another way, who decides, on a cosmic scale, what "north", "east," or "up" even mean?
When I look into the heavens with my very amateur telescope, I see a jumbled mess of galaxies and stars. It is clear to anyone who does so that galaxies have every imaginable orientation compared to the Milky Way we live upon. For the many galaxies organized as discs, and there are ample numbers of them, we do not have any kind of consistent organization and orientation compared to us or each other.
So, how would the light in those galaxies ,or ours, know what "direction" even was? What does "directionality" even mean to a photon in any given galaxy? How would anyone or anything establish this knowledge for a particle? It sound awfully close to claiming one has an inertial frame of reference. Or, at any rate, some other privileged frame of reference that I would suspect would be very difficult to establish and demonstrate that distant inanimate objects know about it and agree about it.
I would say that the burden of proof is on those claiming light has speed directionality, because appearances are all against it. It requires, surely, some sort of mechanism to account for the jumbled orientation of everything on the one hand, and yet some sort of detectable orientation that affects light speed on the other.
I assumed someone mentioned this already but maybe not
en.wikipedia.org
The basic question was settled in 1887 and confirmed many times thereafter.
Michelson–Morley experiment - Wikipedia
en.wikipedia.org
The basic question was settled in 1887 and confirmed many times thereafter.
Actually, while Michelson-Morley is justly famous, we've been measuring the speed of light with some degree of accuracy for centuries. In my scattershot rummaging around, the speed of light never seems to be the thing actually of interest, but brilliant people reconciled the observations they had by deducing a finite speed of light.
This is the earliest I could find (1676):
This is the earliest I could find (1676):
So consider a U shaped particle accelerator. What would happen if a charged particle was accelerated close to the speed of light up the side where the one way c is faster than c and then turns to come back along the side where the one way c is slower than the speed of light and the particle speed exceeds it?
Here's what I'm talking about since some of you can't understand text explanations. Below is an illustration of the forward (orange) and reverse (blue) wave of the same strength and frequency, along with their interference field strength (gray). The forward and reverse wave having the same frequency is arranged in interference experiments by putting mirror on the right of the graph, at x = 3*pi. This is what we all assume happens. It is also what actually happens. You can measure this; many people have done so, including me.
Pay attention to the shape of that gray line that represents the standing wave field intensity - it's a perfect sinusoid with only one spatial frequency.
It's well established that spatial frequency is proportional to the speed of propagation.
Now if you make the right to left slower than the left to right, the pattern of the interference changes:
As you can see in this (very anisotropic) case, the spacing and the strength of the standing waves, represented by the gray line, become irregular, because you are summing two waves with different spatial frequencies.
If there were significant anisotropy, we would have noticed it ages ago. It would affect the diffraction of everything. Now I'll grant that there could be some kind of anisotropy, but it would have to be below the resolution of an interferometer or it would have been noticed, and somebody would have gotten a major physics prize for it.
If the constant c weren't true, every one of Einstein's equations would need a correction factor built in to account for the difference, but unless there's evidence that's really happening, it's not worth complicating the math and throwing unmerited doubt on the certainty with which physicists carry out calculations.
Pay attention to the shape of that gray line that represents the standing wave field intensity - it's a perfect sinusoid with only one spatial frequency.
It's well established that spatial frequency is proportional to the speed of propagation.
Now if you make the right to left slower than the left to right, the pattern of the interference changes:
As you can see in this (very anisotropic) case, the spacing and the strength of the standing waves, represented by the gray line, become irregular, because you are summing two waves with different spatial frequencies.
If there were significant anisotropy, we would have noticed it ages ago. It would affect the diffraction of everything. Now I'll grant that there could be some kind of anisotropy, but it would have to be below the resolution of an interferometer or it would have been noticed, and somebody would have gotten a major physics prize for it.
If the constant c weren't true, every one of Einstein's equations would need a correction factor built in to account for the difference, but unless there's evidence that's really happening, it's not worth complicating the math and throwing unmerited doubt on the certainty with which physicists carry out calculations.
To clarify, M-M were looking for influence of "Aether" in light propagation, not the specific speed of light.
I have conflated lack of detection of aether with lack of detection of anisotrophy (which was one of the topics under discussion). I can't imagine that a universe could have anisotrophic light speed without triggering M-M or one its many later confirmations, but I should acknowledge the difference, i.e. light speed could vary in some way not related to the direction of an underlying fluid or orientation of the experimental device.
This also misunderstands how the anisotropy works. You can't accelerate a particle beyond the speed of light in a vacuum. It would simply move at the energy-equivalent speed of light all the way. This is true for any relativistic system by the way, including real-life closed paths that move through gravity gradients. That is, for instance, how you get the gravitational doppler effect from GPS signals.
Alright, you keep saying this thing and hammering on it and basically not listening to the reason it's not true. But I can use your graphs as a jumping-off point.
Imagine that graph looking wider when the wave moves rightward and looking narrower when the wave moves leftward. Smaller wavelength, smaller c going back, but the wavelength and amplitude end up matching the other way.
THAT's langangian-variant anisotropic c.
If you could explain how that's different from not being anisotropic at all, that would help. What does it mean for the wave to travel faster in one direction than the other in that hypothetical universe? How is it different than the one Einstein assumed and how would one measure the difference if it were so? If it's impossible to measure the difference, there is no difference, and you're just describing the same situation with more complicated math.
The problem here is that c isn't the speed of light, it's the speed of causality. All interactions in particle physics depend on it, so changing c doesn't just change the speed of light, it also changes the range of interactions, all kinds of stuff. One of the ways you can 'summarize' all of those changes is to proportionally change the scale factor of the universe, squishing everything proportional to changes in c. That's an oversimplification of course.
And again, Einstein didn't say anything about c being isotropic - he said transported clocks should synchronize when they come together along a closed path as clock transport speed tends to 0. One of the fitting solutions to that is a lagrange invariant timespace, but it's not the only thing that fits.
The only way to measure this, is to consider effects that are scale dependent, i.e. things that will behave differently if the universe has different behavior in one direction compared to the other. A good example of things that will respond to an anisotropic universe is things like spin directions, chirality, etc.. As it turns out, chirality is somewhat mysteriously different for left and right chirality of leptons (electron and muon). One of the ways you can explain that is with an anisotropic universe. Although to be clear: only lepton chirality seems to be asymmetric, other things that would point towards anisotropic c are, as far as we can measure, fully symmetric.
And, well, situations don't have to be described by simple math? That's the beauty argument all over again, and that has only led to utter failures like string theory.
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Edit: actually just thought of another analogy that could make this more understandable if you've watched enough pop science about spacetime curvature. Are you familiar with the concept that light travels along geodesics? i.e. the 'bending' of light around massive objects happens not because light has gravity and is accelerated towards the object, but because spacetime is locally curved and light just follows the same straight path it always does, only that path now has a bend in it. That's a geodesic.
In a universe where light speed is, say, different in two orthogonal directions, consider a light ray in orbit around a black hole. If in the X-direction the light is slower than in the Y-direction, to orbit in the same amount of time, the path in the X-direction has to be shorter. The only way to make this happen is to squish local space in the X-direction. From an isotropic point of view, the light now orbits in an ellipse, but in the universe itself this would be unmeasurable as everything is squished, including rulers.
And again, Einstein didn't say anything about c being isotropic - he said transported clocks should synchronize when they come together along a closed path as clock transport speed tends to 0. One of the fitting solutions to that is a lagrange invariant timespace, but it's not the only thing that fits.
The only way to measure this, is to consider effects that are scale dependent, i.e. things that will behave differently if the universe has different behavior in one direction compared to the other. A good example of things that will respond to an anisotropic universe is things like spin directions, chirality, etc.. As it turns out, chirality is somewhat mysteriously different for left and right chirality of leptons (electron and muon). One of the ways you can explain that is with an anisotropic universe. Although to be clear: only lepton chirality seems to be asymmetric, other things that would point towards anisotropic c are, as far as we can measure, fully symmetric.
And, well, situations don't have to be described by simple math? That's the beauty argument all over again, and that has only led to utter failures like string theory.
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Edit: actually just thought of another analogy that could make this more understandable if you've watched enough pop science about spacetime curvature. Are you familiar with the concept that light travels along geodesics? i.e. the 'bending' of light around massive objects happens not because light has gravity and is accelerated towards the object, but because spacetime is locally curved and light just follows the same straight path it always does, only that path now has a bend in it. That's a geodesic.
In a universe where light speed is, say, different in two orthogonal directions, consider a light ray in orbit around a black hole. If in the X-direction the light is slower than in the Y-direction, to orbit in the same amount of time, the path in the X-direction has to be shorter. The only way to make this happen is to squish local space in the X-direction. From an isotropic point of view, the light now orbits in an ellipse, but in the universe itself this would be unmeasurable as everything is squished, including rulers.
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No, it's rationalization for saying the speed of light can be different without making any difference in which case it begs the question.
What do you mean by different? It appears to be what any normal physicist would call the same. Likewise you appear to mean by anisotropic, what most physicists would describe as isotropic.
He assumed based on evidence he was aware of, that it was isotropic, and he baked that into all his formulas.
Asymmetry of a particle isn't the same thing as anisotropy of space. I'm open to the idea there's something weird going on with leptons. In fact, there's a number of weird things going on with leptons, including neutrino oscillation.
Nevertheless, this theory needs a nice shave with Occam's Razor. Direction anisotropy in the speed of light is one of those entities Occam said should bring receipts.
yeah, quite aware of that, not that I'd say I have a solid understanding of general relativity.
In other words, just the same as it would be if the speed of light were the same in every direction. I feel like you're working too hard to make my argument for me.
Not only are you now assuming that maybe the speed of light anisotropic, you're also saying everything else has to be anisotropic in just the right way so everything works out exactly as it would if it were isotropic.
Well wouldn't that be a coincidence? /s
So does the particle automagically decelerate to the new speed without a force to decelerate it. If the particle is charged there is also the matter of radiating while it decelerates. Does it change to the new speed without radiating? The link you provided about only dealt with light. Is there any information about how it is handled for particles with mass and charge that are also a big part of special relativity?
Alright I'm giving up on you Shavano, I've tried to be nice and just explain physics but you continue being a jackass about this. I'm not arguing or doing any kind of weird rationalization, I'm trying to explain what langangians and symmetry mean and you're just unwilling to follow anything through. We're not even progressing past the simplest conceptual ideas, so I don't see us ever getting to the actual math.
What seems to be by far the hardest for y'all to understand is that c is an innate feature of the universe, it's not separate from spacetime. Anything that changes c will change everything about spacetime in unintuitive ways.
As far as the universe is concerned, everything still travels on a geodesic so nothing accelerates. It's just that geodesics aren't symmetric anymore.
What seems to be by far the hardest for y'all to understand is that c is an innate feature of the universe, it's not separate from spacetime. Anything that changes c will change everything about spacetime in unintuitive ways.
Also why I despair of humanity (or anyone) ever creating a method of FTL travel. c is the clock speed of the chip that runs the universe. The limit of the simulation, if you like simulation theory. How fast God thinks if you're religious. Etc, etc.
It's impossible to travel at c in our universe if you have mass (it would require infinite energy), but you can theoretically get very close. The universe would look very strange if you could get to .99 c - you would arrive at destinations many light years away in just a few weeks/days, due to the universe ahead of you shrinking. I used to think the high-speed traveler would to themselves appear to go much faster than light, but they never do - every instrument would tell them they're going .99 c, and yet by trading time for velocity their destination measures much closer. Conceptually that's hard for me to envision. c itself would be even weirder - the entire universe would appear to have no depth, and traversing any distance would, to you, be instantaneous.
Yes, the universe would look very strange if you were traveling at .99c (relative to us, who are not moving at approximately zero speed with respect to the nearby objects in the universe). But from your perspective, you wouldn't be traveling to destinations light years away in little time. You'd be traveling to things that appear from your perspective quite nearby, and anything you see as light years away would take you years to get to.
...yes, which is what I posted.
"...due to the universe ahead of you shrinking." "..their destination measures much closer."The state of c itself is more conceptually interesting, as the universe would have no depth at all.
Given the immense scale of the known universe, c (as the propagation rate of causality) seems profoundly slow.
Only to those that live fast. It doesn't seem that way to red dwarf stars....yes, which is what I posted.
The state of c itself is more conceptually interesting, as the universe would have no depth at all.
Given the immense scale of the known universe, c (as the propagation rate of causality) seems profoundly slow.
Kind of a side note at this point since the rest of the thread has gone on to discuss other things, but:
You're probably very familiar with the fact that your observation is delayed from the event in the context of a different sense: sound propagates much more slowly than light, so you can easily observe the delay between light and sound reaching you at even short distances (sound takes ~5 seconds to travel 1 mile in atmosphere). Think about fireworks, or lightning/thunder, or any number of other similar things where there is an easily observable delay between seeing something and hearing it.
Re one way speed of light, I ranted about it here
So basically, there's two things. The speed of light, one and only, is easily measurable in an one way experiment. You just slowly transport the clock. That's how the speed of light was first measured, one way time it takes the light coming from Jupiter to travel across Earth's orbit.
However, a somewhat esoteric variation on the theory of relativity exists, where in addition to the speed of light we all know and love, there is "a speed of light" in particular direction, which can be anisotropic and comes with an extra, likewise anisotropic, transformation for time, chosen such that the outcome of any experiment would be exactly the same, as it precisely cancels out anisotropy of the speed of light.
Any experiment measuring the speed of light, in the esoteric variation, would measure the speed of light (and not "a speed of light" in that direction).
Furthermore, in that esoteric variation, it would make sense to define "speed" differently, using dt from a slowly transported clock for the divisor.
Near as I can tell this is just an extra obnoxious way to calculate the same predictions, a lot like I dunno applying a rotation like
t' = cos(alpha)*t + sin(alpha) * x and x' = cos(alpha)*x - sin(alpha) * t
prior to every calculation, and then applying an opposite rotation to the results.
edit: also, a shameless plug: relativistic spaceflight visualizer (that also does time dilation, and will even show you the cosmic background radiation):
https://dmytry.github.io/space/
So basically, there's two things. The speed of light, one and only, is easily measurable in an one way experiment. You just slowly transport the clock. That's how the speed of light was first measured, one way time it takes the light coming from Jupiter to travel across Earth's orbit.
However, a somewhat esoteric variation on the theory of relativity exists, where in addition to the speed of light we all know and love, there is "a speed of light" in particular direction, which can be anisotropic and comes with an extra, likewise anisotropic, transformation for time, chosen such that the outcome of any experiment would be exactly the same, as it precisely cancels out anisotropy of the speed of light.
Any experiment measuring the speed of light, in the esoteric variation, would measure the speed of light (and not "a speed of light" in that direction).
Furthermore, in that esoteric variation, it would make sense to define "speed" differently, using dt from a slowly transported clock for the divisor.
Near as I can tell this is just an extra obnoxious way to calculate the same predictions, a lot like I dunno applying a rotation like
t' = cos(alpha)*t + sin(alpha) * x and x' = cos(alpha)*x - sin(alpha) * t
prior to every calculation, and then applying an opposite rotation to the results.
edit: also, a shameless plug: relativistic spaceflight visualizer (that also does time dilation, and will even show you the cosmic background radiation):
https://dmytry.github.io/space/
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Yeah, I never liked the modified Lorentz equation ‘theories’ (quotes for unobservability).
I haven’t followed any of the various YouTube links, because my time is worth more than pumping up random videographers’ ad revenues, but as someone who used to work in the field, anisotropies in the speed of light (defined as the propagation speed of electromagnetic waves) are definitely a thing, in the sense that you can construct a predictive theory that includes it and in which it is observable.
It’s important to maintain a distinction between the speed that electromagnetic waves travel in vacuum, and the constant ‘c’ used to define the set of coordinate transforms that the laws of physics appear to be invariant under. As far as we know, these two quantities are the same, but that’s just a consequence of light having no mass and the absence of interactions between light in a vacuum and something in (or defining) a specific frame.
The best way to understand it is to imagine that there’s a background field (note: not the same as the aether, which was supposed to be the thing that electromagnetic waves were oscillations of) that for some reason has undergone some spontaneous symmetry breaking that also weakly couples to light. If this coupling is different for light than it is for, say massive particles, then the result is that the propagation of light through a vacuum looks a lot like the propagation of light through an anisotropic medium.
You can put these kinds of interactions into the Standard Model by adding new terms, and if their coupling coefficients are weak enough, they could be there and we just haven’t noticed their effects yet. Note that because these terms act like a background medium through which light moves, they break Lorentz Invariance —at least until you account for whatever might have generated the effective term: you could have this kind of anisotropic speed of light even though the underlying physics might retain Lorentz Invariance, in the same way that light moves through glass at different speeds than it does through vacuum even though the fundamental theory governing light and glass is as far as we know Lorentz Invariant.
The Standard Model Extension is one framework that tries to catalog all possible ways the Standard Model might seem to break (or definitively break) Lorentz Invariance in observable ways. It’s the one I used to work with. You can extend the discussion above to define terms that describe how different elementary particles might differentially couple to a background field, and you can throw in all kinds of other terms into the Standard Model to get a field theory that breaks Lorentz Invariance.
So far, experiments have shown that the coupling coefficients for these terms must be extremely close to zero. This might seem meaningless, but it has occasionally been used to rule out some versions of supersymmetry theory. That’s gotta be some kind of a win.
Edit: typos and (some) clarity
I haven’t followed any of the various YouTube links, because my time is worth more than pumping up random videographers’ ad revenues, but as someone who used to work in the field, anisotropies in the speed of light (defined as the propagation speed of electromagnetic waves) are definitely a thing, in the sense that you can construct a predictive theory that includes it and in which it is observable.
It’s important to maintain a distinction between the speed that electromagnetic waves travel in vacuum, and the constant ‘c’ used to define the set of coordinate transforms that the laws of physics appear to be invariant under. As far as we know, these two quantities are the same, but that’s just a consequence of light having no mass and the absence of interactions between light in a vacuum and something in (or defining) a specific frame.
The best way to understand it is to imagine that there’s a background field (note: not the same as the aether, which was supposed to be the thing that electromagnetic waves were oscillations of) that for some reason has undergone some spontaneous symmetry breaking that also weakly couples to light. If this coupling is different for light than it is for, say massive particles, then the result is that the propagation of light through a vacuum looks a lot like the propagation of light through an anisotropic medium.
You can put these kinds of interactions into the Standard Model by adding new terms, and if their coupling coefficients are weak enough, they could be there and we just haven’t noticed their effects yet. Note that because these terms act like a background medium through which light moves, they break Lorentz Invariance —at least until you account for whatever might have generated the effective term: you could have this kind of anisotropic speed of light even though the underlying physics might retain Lorentz Invariance, in the same way that light moves through glass at different speeds than it does through vacuum even though the fundamental theory governing light and glass is as far as we know Lorentz Invariant.
The Standard Model Extension is one framework that tries to catalog all possible ways the Standard Model might seem to break (or definitively break) Lorentz Invariance in observable ways. It’s the one I used to work with. You can extend the discussion above to define terms that describe how different elementary particles might differentially couple to a background field, and you can throw in all kinds of other terms into the Standard Model to get a field theory that breaks Lorentz Invariance.
So far, experiments have shown that the coupling coefficients for these terms must be extremely close to zero. This might seem meaningless, but it has occasionally been used to rule out some versions of supersymmetry theory. That’s gotta be some kind of a win.
Edit: typos and (some) clarity
I think the issue with his videos is that while not necessarily factually false, they're often in a sense opposite of educational.
E.g. if you are trying to educate people about electricity and wires you'd come up with some simple approximation like water-in-hose model, that allows people to correctly predict when the lightbulb in this experiment will actually fucking turn on as in will attain some reasonable fraction of rated brightness, like, enough to be seen.
edit: in fact come to think about it, a LED lightbulb got forward voltage below which it won't turn on at all, while an incandescent bulb may be too cold to emit even a single photon of visible light, so what ever the bulb type you can't call an arbitrarily small fraction of rated voltage "on".
Then you may teach people about transmission lines and antennas and so on, so they can predict when the lightbulb will first get a tiny current flowing through it.
But there comes this guy, who has zero interest in actually educating anyone about that, and makes a clickbait video after which the intended audience wouldn't be able to get anything right at all. The worse part is that he obviously knows what he's doing, since he sets himself up a caveat that the lightbulb turns on once there's any current through it at all.
I did love how Mendhi the eyebrows self shocking guy one upped him on technicalities by pointing out that there's always a little bit of thermal noise current.
E.g. if you are trying to educate people about electricity and wires you'd come up with some simple approximation like water-in-hose model, that allows people to correctly predict when the lightbulb in this experiment will actually fucking turn on as in will attain some reasonable fraction of rated brightness, like, enough to be seen.
edit: in fact come to think about it, a LED lightbulb got forward voltage below which it won't turn on at all, while an incandescent bulb may be too cold to emit even a single photon of visible light, so what ever the bulb type you can't call an arbitrarily small fraction of rated voltage "on".
Then you may teach people about transmission lines and antennas and so on, so they can predict when the lightbulb will first get a tiny current flowing through it.
But there comes this guy, who has zero interest in actually educating anyone about that, and makes a clickbait video after which the intended audience wouldn't be able to get anything right at all. The worse part is that he obviously knows what he's doing, since he sets himself up a caveat that the lightbulb turns on once there's any current through it at all.
I did love how Mendhi the eyebrows self shocking guy one upped him on technicalities by pointing out that there's always a little bit of thermal noise current.
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Nah, I think that's underselling veritasium a lot. A LOT. Veritasium isn't trying to run through a standard curriculum, he's trying to get into some more involved physics that shows the e-field nature of electricity, and one of the most spectacular ways to do that is to show this experiment.
As the recent interactions with Shavano show, it's really hard to dislodge an ingrained belief once you have it, but that's really the only fundamental criticism of the video: that it goes against something you already believed. More specifically: it goes against a strongly held belief, not a weakly held one.
Because that's rule #1 of educational videos, right? They're entertaining and engaging when it subverts a weakly held belief, but gets dunked on when it goes against strongly held beliefs. Judging the educational value of the video on that aspect is misunderstanding educational videos.
As the recent interactions with Shavano show, it's really hard to dislodge an ingrained belief once you have it, but that's really the only fundamental criticism of the video: that it goes against something you already believed. More specifically: it goes against a strongly held belief, not a weakly held one.
Because that's rule #1 of educational videos, right? They're entertaining and engaging when it subverts a weakly held belief, but gets dunked on when it goes against strongly held beliefs. Judging the educational value of the video on that aspect is misunderstanding educational videos.
Did he even do any actual experiment? A bunch of actually educational (and less successful youtubers) did, showing the millivolts that get induced in the wires at the lightbulb after the nanoseconds and then the ramp up that happens after full speed of light delay for the wire.
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edit: basically, I think the issue is that he is trying to get into some more involved physics, while maintaining it at water-in-a-hose level of detail (the bulb is either turned on or not etc etc). That just doesn't work. If you want to get into what happens between the wires, then you also have to have a bit more than binary depiction of the bulb state.
With regards to special relativity, I honestly don't see what his video teaches anyone, since of course the speed of light can be measured with either a mirror (light travels two ways) or with slow clock transport (light travels one way), and that those two numbers correspond to each other, does rule out a number of actually distinct theories of physics.
In a certain sense, nothing at all is measurable, because you can always modify any theory which involves some quantity q to a mathematically equivalent theory with some q' such that f(q', x) = q and neither q' nor x are measurable plus you can just ditch ' for extra confusion.
edit: on another note there's a lot of rather annoying algebra of that nature I had to do to make my relativistic visualizer work at speeds that are less than floating point precision away from c. I even had to add a little bit of gray to the sky and subtract it back out, to avoid ugly artifacts that resulted from denormal numbers getting treated as zeroes.
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That's certainly overselling it. In this video, he doesn't actually do the experiment, he just does a bunch of CGI drawings that he appears to have rather thoroughly confused himself with. He also illustrates it with a prop, a physical lightbulb, whereby he doesn't actually bother to illustrate the "turn on dimly instantaneously, turn on full brightness after a while" phenomenon.
edit: basically, I think the issue is that he is trying to get into some more involved physics, while maintaining it at water-in-a-hose level of detail (the bulb is either turned on or not etc etc). That just doesn't work. If you want to get into what happens between the wires, then you also have to have a bit more than binary depiction of the bulb state.
With regards to special relativity, I honestly don't see what his video teaches anyone, since of course the speed of light can be measured with either a mirror (light travels two ways) or with slow clock transport (light travels one way), and that those two numbers correspond to each other, does rule out a number of actually distinct theories of physics.
In a certain sense, nothing at all is measurable, because you can always modify any theory which involves some quantity q to a mathematically equivalent theory with some q' such that f(q', x) = q and neither q' nor x are measurable plus you can just ditch ' for extra confusion.
edit: on another note there's a lot of rather annoying algebra of that nature I had to do to make my relativistic visualizer work at speeds that are less than floating point precision away from c. I even had to add a little bit of gray to the sky and subtract it back out, to avoid ugly artifacts that resulted from denormal numbers getting treated as zeroes.
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I'm surprised by the responses to the video! All he asks in the first of the video is Can You Measure Light in One Direction?
And you can't. You just cannot measure the speed of light in one direction because relativity prevents us from maintaining synchronized clocks. The result is that the speed of light c is really the average speed over a round-trip journey, and that we cannot be certain that the speed is the same in both directions.
And you can't. You just cannot measure the speed of light in one direction because relativity prevents us from maintaining synchronized clocks. The result is that the speed of light c is really the average speed over a round-trip journey, and that we cannot be certain that the speed is the same in both directions.
And the answer is, yes you can, using slow clock transport. You move one of the clocks slowly. Under conventional theory of relativity, the time dilation can be made arbitrarily small by transporting the clock slower. Matter of fact, the speed of light was first measured in one direction (from Jupiter, across Earth's orbit, on one way trip) using slow clock transport (the slow clock was Earth).
The light travels in one direction, and its speed is measured in that one direction. If you were measuring the speed of light in flowing water, for example, you would have measured the one way speed of light in water, which wouldn't be equal to the speed measured the other way.
Under modified special relativity with non isotropic speed of light (which is now somewhat esoteric), you indeed can not measure one way speed of light, because under that theory there is an additional time dilation term which does not go away when you move the clock slowly. That theory, however, is mathematically equivalent to the special relativity you would normally learn, in the sense of always yielding identical predictions for any experiments.
This isn't some special property of light; any theory can be modified in such a manner. We routinely make all sorts of modifications like this just to fix numerical issues with floating point numbers. For example, we frequently represent 3D object orientations with 4 numbers (even though 3D rotations only got 3 degrees of freedom), but that doesn't mean there really is some aspect of how the object is rotated, that is forever unobservable; it doesn't mean that nobody has ever measured the heading of a ship.
The same applies to special relativity - you can introduce 3 superfluous degrees of freedom for speed of light's anisotropy, which cancel out exactly at the end when you arrive at any prediction (e.g. a prediction of what the clock will read when the light gets to it).
edit: I can think of even worse modifications, too. If implementing a relativistic videogame, I can imagine wanting to have "one way speed of light" be c/2 away from the player and infinity towards the player, for the purpose of shoehorning relativity into an existing non relativistic game engine. You could also imagine some alien interstellar empire which has the capital in some star system, and adopts some modified relativity as a date and time standard across the empire. The point being, you can represent the same physical phenomena in all sorts of ways that, if you don't screw up the math, are exactly identical at the end of a calculation.
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Two questions:
1. What about that result is interesting?
2. What about the responses to the video surprises you?
OK, can anyone just read and internalize the fucking wikipedia page on this? No, slow clock transport isn't a watertight measurement of one-way speed of light. It is still inherently undefined and a matter of definition or convention to consider the one-way speed of light to be equal to the average two-way speed. Even arbitrarily slow clock transport does not in practice measure anisotropy to an arbitrary level of precision.