Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: flr on 25/03/2013 22:40:34
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Apparently some claims are made that the speed of light is not constant after all, but have small variations:
http://www.natureworldnews.com/articles/1010/20130325/speed-of-light-variable.htm
The first question came into my mind is E0=m_rest*c^2. Which c goes in there? The bigger or the smaller? Is E0 strictly constant (meaning that m_rest fluctuate such that cancel out fluctuations of c and maintain a constant E0)? Or the energy E0 fluctuate? If the frame invariant E0 fluctuate what is left of the energy conservation principle?
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Want to know my view?'
Bs.
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.... Do you have a long version ?
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It fits in well with my own ideas. Although I would put "Over long Distances" in there.
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Sounds plausible. The constant speed of light postulated by SR assumes space is a vacuum, but quantum theory says that it isn't. We know that light traveling in a non-vacuum (through matter, for example) travels at an effective speed of slower than its vacuum speed due to interaction with the matter. It seems plausible that light interacting with virtual particles in a vacuum might be slightly slowed down due to those interactions.
Plausible doesn't necessarily mean it's true, though, especially since we don't really know much about the quantum nature of space-time itself.
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Sounds plausible. The constant speed of light postulated by SR assumes space is a vacuum, but quantum theory says that it isn't. We know that light traveling in a non-vacuum (through matter, for example) travels at an effective speed of slower than its vacuum speed due to interaction with the matter. It seems plausible that light interacting with virtual particles in a vacuum might be slightly slowed down due to those interactions.
Plausible doesn't necessarily mean it's true, though, especially since we don't really know much about the quantum nature of space-time itself.
As far as I can understand it, they don't mean slowed down. It means that the propagation distance is changed. Like a Newton's Cradle with one bigger ball would skip a larger distance across, but with a photon that distance is a point which is the speed of C. So the points are moved further apart, which doesn't mean slowed down, or speeded up, it means travels a greater distance at C.
http://www.sciencedaily.com/releases/2013/03/130325111154.htm (http://www.sciencedaily.com/releases/2013/03/130325111154.htm)
Maybe they don't mean that, but that is what I use in my theory.
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From both those explanations, they don't seem to be talking about distance changing (which would go into general relativity). They're just talking about the interaction between quantum fluctuations in space and light slowing light down.
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That depends on views. The one we can measure is 'c'. The one you seem to refer too JP, is more of a theoretical point of view, not proven by any experiments I know of? Light is at 'c', if one want it differently, give me the experiment to prove it by.
The last one was neutrinos, wasn't it?
And using 'c' it's the interactions with 'densities', as matter, that 'steals time,' as I see it. Not lights speed in a vacuum. We want to go faster? Then we need to look at degrees of freedom, and see if we can 'bend' them. Everything have one defined 'speed', including matters interactions with light/radiation, as far as I can see.
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If you want to think of it as a field with densities, then what 'moves' is communication. The communication can easily be seen as a constant, adapting to densities. If there is a ratio relative density you will be able to see how the constant adapt.
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But, using frames of reference you have no 'preferred frame' to define it from, although our definition of lights speed in a vacuum indeed use one frame only, the one all experiments use. The local one. So we have a preferred frame practically, although using that frame together with a preconception of a 'same common universe' ignoring observer dependencies. Which makes us, really smart?
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And sorry Flr, wasn't meant to you, it was rather me in a bad mood :) The question is indeed valid.
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That depends on views. The one we can measure is 'c'. The one you seem to refer too JP, is more of a theoretical point of view, not proven by any experiments I know of? Light is at 'c', if one want it differently, give me the experiment to prove it by.
If you read the link Pincho posted above, the author mentions that attosecond laser pulses might make this testable.
And using 'c' it's the interactions with 'densities', as matter, that 'steals time,' as I see it. Not lights speed in a vacuum.
Their point is that a quantum vacuum is not a classical vacuum and it has virtual particles which can interact with light. That could plausibly vary it's speed. I don't know the details well enough to comment on any flaws, but the basic idea makes sense. Since it's been approved for publication in a well-regarded, peer-reviewed physics journal, those better qualified than I apparently think so as well.
None of this would chance the constancy of the speed of light in a classical vacuum. It's likely to be hyped by the media to be an overturning of classical relativity, which it certainly isn't.
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'virtual particles' ?
Indeterminacy is more to my taste. And discussing any 'speed' you need to make it measurable. In what way will you prove that 'virtual speed'?
If it is a field the whole concept is meaning less. Then the 'speed' we define is 'real' for us, 'virtual particles' able to take any configuration, energy, and 'speed'. As far as I can see?
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Although, if it is as I expect, 'virtual particles' will tick to the same clock as 'c', which is 'c' by the way. I will now state that this must be true. Or I'm sadly mistaken on the universe :) You can't have virtual fields not obeying the reality we measure, somehow they must fall in line with the constant.
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'virtual particles' ?
Indeterminacy is more to my taste. And discussing any 'speed' you need to make it measurable. In what way will you prove that 'virtual speed'?
By measuring it, in the experiment I mentioned above.
I'm not here to argue over this. I don't think either of us understand the mathematics of their work well enough to critique it (and they haven't been published yet). From my physics training, it's plausible. We know that light interacting with real particles slows down, and we know that light can interact with virtual particles in a vacuum, so it's plausible it could slow down as a result. Once they publish the papers, we can take a look and critique their math (if either of us can understand it).
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Heh :) Spot on JP. And what was it now both Einstein and that other guy Feynman like to say, 'If you can't make it understandable you're probably bicycling in the great blue yonder."
As for virtual particles.
http://www.mat.univie.ac.at/~neum/physfaq/topics/virtual
and how 'real' are they?
http://www.mat.univie.ac.at/~neum/physfaq/topics/virtreal
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I think that it should be noted that this doesn't mean that the speed of light isn't invariant. The value c is the invariant value of the speed of light. Think of it as the speed that light is moving between interacting with virtual photons.
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Someone is skeptical about that reserch on the speed of light:
http://motls.blogspot.it/2013/03/speed-of-light-is-variable-only-in-junk.html
I haven't read the original work, however, so I can't judge.
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Yes, that's how one can see it. What is 'real' can only be so from direct experiments, as soon as you move to 'weak experiments' you are alienating yourself from what we can measure in a direct local experiment for example. I guess you can use a Sigma value for that too :) if you like, defining how far away you've gone depending on how you set the definitions of course. Those believing that this will be a better way will set them as the more indirect measurements you make, validating a propositions, the more probable it will seem. I can set the opposite, the more 'indirect', not measuring directly, you need, the more questionable it becomes to me :) Not the whole truth of course, but it put a light on it. I prefer direct experiments giving as 'real' a outcome as possible. From that I can, and ever so happily will, theorise.
And 'virtual particles' are questionable from the beginning as I see it.
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I like Lubos, he have a flair for presenting his thoughts in a understandable way, even when you don't agree. Therefore he falls under the Einsten/Feynman rule of 'not bicycling' :)
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I think that virtual particles have been made in a lab, so they are considered to be factual. I don't have a problem with them.. I use them.
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I think that virtual particles have been made in a lab, so they are considered to be factual. I don't have a problem with them.. I use them.
Virtual photons cannot b oberved. They're pretty much a mathematical construct anyway. It's not very meaningful to speak of things that can't be observed as if they are real.
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Someone is skeptical about that reserch on the speed of light:
http://motls.blogspot.it/2013/03/speed-of-light-is-variable-only-in-junk.html
I haven't read the original work, however, so I can't judge.
Good find. He does link to the original papers, and after reading the variable speed of light one, I to agree with his (and yor_on's) original assessment that it's garbage. They propose a model out of the blue, ignore the quantum theory of the vacuum, and show that it gives a variable speed of light.