What if the speed of light is NOT constant?

New research suggests it isn't:

So what would this mean for physics if true? Would the theory of relativity have to be changed? The size of the universe? The time it takes the refrigerator light to turn on when opening the door?

 

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Like the inferences in many scientific papers everyday, they are hypothesising on different concepts including totally "speculatively theoretical"concepts.
Not so long ago we had another paper re Hawking claiming BH's do not exist...At least that's what the sensational journalistic type headlines would like to excite you with.
Over time and peer review, I would reckon that nothing will come of this either.

But yes, most certainly, if it did happen to be true, many things including SR/GR would need to be rehashed. But don't hold your breath.

 

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Here's the more recent article on this. The writer assures us all that the laws of physics are unaffected.

http://www.livescience.com/49555-speed-of-light-loophole.html

 

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http://newt.phys.unsw.edu.au/einsteinlight/jw/module6_constant.htm

 

No it doesn't:

The speed of light is constant in a vacuum, so a calculation that finds a speed of light that is different in a non-vacuum doesn't contradict existing theory and isn't even the least bit unusual given that its been known for about four hundred years.

If it were found that the speed of light were different in a vacuum than is currently thought, many things could change depending on the nature of the finding. Some of those are possibilities. But, as I said, such speculation has nothing to do with that article.

Sorry, but you just fell for a provocative title.

 

If space isn't a vacuum, then there's no such thing as the speed of light in a vacuum. There's only the speed of light in particle-filled space, which is different now. So yes, that would definitely change some things for us. It would mean the speed of light is not constant even in space, which is not a vacuum to begin with.

Then there's this quote from another article:

"Light doesn’t always travel at the speed of light. A new experiment reveals that focusing or manipulating the structure of light pulses reduces their speed, even in vacuum conditions.

A paper reporting the research, posted online at arXiv.org and accepted for publication, describes hard experimental evidence that the speed of light, one of the most important constants in physics, should be thought of as a limit rather than an invariable rate for light zipping through a vacuum."===https://www.sciencenews.org/article/speed-light-not-so-constant-after-all

 

For someone who doesn't find any meaning in science you sure spend a lot of time reading about it.

 

http://arxiv.org/ftp/arxiv/papers/1411/1411.3987.pdf

One sentence summary: The group velocity of light in free space is reduced by
controlling the transverse spatial structure of the light beam

The slowing down of light that we observe in free space should also not be confused with slow, or indeed fast, light associated with propagation in highly nonlinear or structured materials
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I think we can still safely say that the speed of light in a vacuum "c " is a constant.
But I'll welcome more expert opinions than MR or mine on this subject.

 

They appear to assert that the speed of light in a vacuum can be varied, by varying the structure, or pulsing of the light. c remains an upper bound on the speed. There is no apparent need to change GR or SR to account for this.

 

Thanks for this. They seem to have managed to create photons in which the wave front is conical (?!) and thus the wave vector has a radial component, i.e. is not fully aligned with the direction of travel of the beam, so the light (I think) is effectively following a longer path in space and thus takes longer to arrive than a plane wave would. I do not understand really how this works, especially how one creates this thing called a "Bessel beam" and what its properties are. They make an analogy with what happens to microwaves in a waveguide, where they say the fact the fields are confined within the guide alters the group velocity. I can sort of see how this might arise but I'm damned if I can see how they get a beam to hang together in free space while exhibiting the same sorts of confinement effect. Maybe a physicist can help here………...

One other thing I suspect we all need to be careful with is their mention of "group velocity". As I understand it, in a dispersive medium, phase, group and front velocities will all be different and only the front velocity (I think, though I may have got this wrong, as it's fairly tricky stuff) travels at c. Free space, of course, is not supposed to be dispersive, but to me the mention of group velocity sets off warning bells.

Journos, of course, will gloss over all this sort of thing in the search for a sensational headline. Beware!

 

I did not read paper, and don't plan to, but suspect what is happening is much like the convergent conical beam an ordinary convex lens forms:

I. e. A very brief flash of light 2 focal lengths away from the lens will come back together as a converging conical wave front 2 focal lengths on the other side of the lens. If one only pays attention to the converging cone of light, the photons that passed thru the lens near its edge traveled farther to arrive simultaneously at the image point with the photons that traveled along the optical axis. Ergo speed of light in conical beam is not constant. - If you buy that logic, I have a bridge I'll sell you cheap.

Without reading their paper, I am not sure this is essentially what they did, but bet it is.

 

No, what it means is that "the speed of light in a vacuum" is a theoretical value only, never quite observed in nature. That's fine - it doesn't alter the theory at all.

Right. "The speed of light" refers to the speed of light in a vacuum. It's been known for about four hundred years that light doesn't always travel at that speed -- it was known long before it was even known what that speed was!

That's sloppy, since the point of the article is that space isn't quite a vacuum.

Exactly right, and exactly in-line with existing theory.

Given that the vacuum of space is very nearly a perfect vacuum, I'd be curiosu to know what value they calculate for "the speed of light in space" and how far that is from the accepted value "in a vacuum". Given that space is very nearly a perfect vacuum, I suspect not much -- probably not enough to be measurable.

 

What's even more interesting is that in some threads he is clearly interested in learning science and those threads go much better than his trolling threads because of it. In his recent thread on jet propulsion, for example, he seemed legitimately interested in learning about it, so that thread went fine.

In this thread, he is about half sincere: he wants to learn about the paper but only insofar as he thinks it points to a need for a major upheaval in science, a prospect he'd like. On learning that it's a yawn-er, he'll stop now.

 

The speed of light isn't constant. Only the "locally measured" speed of light is constant. When light slows down so do you, because of your electromagnetic nature, so it looks like the speed hasn't changed. The actual speed of light varies with gravitational potential. See Einstein talking about it at the Einstein digital archive:

"Second, this consequence shows that the law of the constancy of the speed of light no longer holds, according to the general theory of relativity, in spaces that have gravitational fields. As a simple geometric consideration shows, the curvature of light rays occurs only in spaces where the speed of light is spatially variable."

The work by Miles Padgett et al is nice because it chips away at the dreadful cargo-cult myth that the speed of light is absolutely constant.

 

Yes, and your work is horrible because you replace the real science with your religion about Einstein. The change in the speed of light in this case is unrelated to any change due to gravity, a change that only occurs over finite distances and that is a result of the change in geometry rather than the cause.

Farsight, you need to learn how to do some physics, so that you can actually understand the relevant physics. Until you learn how to do a simple physics problem, then you're simply lost at sea. Without the ability for your ideas to produce the ability to be compared, in detail, with observations, you have nothing that can be considered physics.

 

These remarks have no bearing on the subject of this thread.

 

The speed of light is a constant unless by interference. Namely the interference of science, all your actions and experiments are the change of nothing, you do not effect the constant the stars emit.
You are the interference that makes any change, the change is not a change it is interference of the constant.

Facts not fiction.

 

Uh...

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My cats breath smells like cat food.

 

Yawn. Even if your drivel were true, it wouldn't be relevant here because we are talking about the locally measured speed of light. No need to hijack the thread (Hey everybody, look at me!!!!!) for this off topic distraction.

 

That's almost a Haiku and just as meaningful.