Light travels slower in water than in air. If light travels at different speeds in different mediums....?

Question

is there any known medium in which light travels at a velocity greater than 186,000 mi/sec? If not, is there, in theory, any reason why such a medium could not exist?

In the future could a medium with an index of refraction less than 1 be discovered? Would this defy Einstein's theory of relativity or any other law of physics? And were not laws meant to be broken (in the scientific world as well as in the human world)? Many previously accepted scientific "laws" have been invalidated over the centuries. Einsteins theories have largely superseded Newton"s. So why could a medium with n less than 1 be discovered in the future. Because it would be inconsistent with Einstein's beliefs? Because it might invalidate them? What about your cherished tachyons zooming by at warp speed? What medium are they traveling in (according to theory, of course)?

Typos above - "Einstein's" not "Einsteins" and "couldn't" not "could"

I love the idea of "quantum entanglement." It makes it sound as though God is not only "playing dice" but playing Pac-Man too.

Answer 1

the speed of light, c, is measured to be the speed in vacuum......
all other mediums (or media?) have greater index of refraction n, (for all other meduims n>1), thus, slower speed of light...
(for vacuum n=1, for air n=1.003, for water n=1.33 )
there can not be a medium where n<1....

if, however, there is a discovered medium such that n of the medium is less than the n of vacuum, the speed of light known to be c is not anymore valid...there will be a new speed of light measured....

Answer 2

Not really.

There's a way around the speed of lights upper limit, but it involves the light not actually traveling the distance between two points.

It involves two phenomena called quantum entanglement and 'spooky action at a distance'(Einsteins own description). A mass of atoms are supercooled to form an Einstein-Bose condensate. That means all the atoms act as one big particle. Light hitting one side of the cloud of entangled particles exits the other side without passing through the gap between the point of absorption and re-emission.

There are limitations in the uses for this though the condensate is difficult to maintain in a single cloud. Dividing the cloud physically without breaking the entanglement is technically infeasible, and bombarding it with enough light to be useful for data transmission would break down the state of entanglement before any useful data could be sent.

The light speed barrier isn't really broken by though because the light doesn't travel through physical space. It becomes a temporary property of the cloud between absorption and emission.

Answer 3

The idea of an "index of refraction", where light travels slower than the speed of light, is really just an engineering approximation. What "really" happens is that the photons are coherently absorbed and re-emitted by the atoms in the medium in just such a way that it is exactly as if they were travelling more slowly.

That being said, a short piece of waveguide or lightguide can act as a medium where the light travels "faster than light". For example, if you make a metal object by:
1) sawing up pieces of 15 cm square aluminum tubing into 15 cm lengths
2) placing them tightly-packed on a flat surface with their open faces upward and
3) welding them all together,
you will make an object where 20 cm radio waves travel through it "faster than light". This trick is often used when making lenses for radio waves: an inner, lenticular lens with index of refraction greater than one is surrounded by a ring of short waveguide that has index less than one.

This "faster than light", however, refers to the phase velocity of the signal, not the group velocity. It is therefore impossible to send signals faster than light by this method, and in fact on a quantum level no photons are actually travelling faster than light.

Answer 4

Such a medium can't exist bcoz Light is independent of any medium. That is why Light can travel in Space which is actually a vacuum.

The Light wave is different from Sound waves which is dependent on medium. Sound travels in different speeds in different mediums. Sound can't travel through vacuum.

Answer 5

Yes, light travels at different speeds in different mediums. However, no medium cause the speed of light to increase over the value you stated (which is the speed of light in a vacuum). Other mediums will only cause it to slow, not increase.

Answer 6

Light travels faster in air than in glass for example because of the density it is simply blocked by some of the particles therefore slowing it down.

Answer 7

No.
Yes, it will contradict Einstein relativity theory.

Answer 8

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Answer 9

“*” General Remakes Vis-à-vis Your Science-related Questions: I must say I am utterly tickled and tremendously impressed by your genuine and demonstrated interest in popular physics, mathematics, and philosophy of science related topics. Frankly, I would have loved nothing more than to have been able to “satisfactorily” (at least according to my own benchmarks) address some of your ongoing scientific inquiries. Lamentably, the technical confines and the inherently limiting nature of this forum – not to mention perhaps ultimately my own inability to serve as a science expositor – are among the principal reasons that make such an objective/undertaking all but an entirely impractical aspiration. Y!A’s intrinsically entertaining format is simply not conducive to, or accommodating of, “conscientious” rejoins about cutting edge research. How can anyone, for instance, offer a science enthusiast a site where s/he could become privy to the continuing findings of research in progress. And even if such a site existed, there is always the issue of incomprehensibility of the underlying language (mathematical or otherwise) - a truly daunting snag for the layperson to overcome. I assure you; it is NEVER about acting: evasive, pretentious, intellectually cute, maliciously ambiguous, or otherwise “hard to get”. It is about the reality of a highly technical and specialized field of study with a nearly impenetrable language of its own that many a times is dolefully inaccessible to all (professionals included) but the very few who happen to have dedicated their entire lives to the endeavor. … Though the overlap/interplay between philosophy and science is patently evident to everyone (and perhaps that being part of the problem), in reality, their “marriage” is not always a comfortable or even a compatible arrangement - at least not without a more operative linguistic base for dialogue. That said, I am not one to subscribe to a derisory strategy of offering half-truths and misinformation and promptly passing them as “answers” to reflective scientific inquiries with embedded, and at times highly controversial, philosophical substance/charge. Admittedly, some of the questions here (e.g. the falling over optical illusion effect of an overflowing round glass cup) are rudimentary enough to lend themselves to persuasive/straightforward replies. Whereas others are by far more convoluted and complex than even the questioner him-/herself might have initially recognized. In other words, some questions are so elementary, in fact, that one should not feel obliged to regurgitate/reproduce the already adequate answers allover again, whilst the fair treatment of others is so utterly beyond the limited scope of this medium that any attempt at providing a diligent answer becomes almost an exercise in futility. In all, the best anyone can offer on those intricate questions, is NOT per se an “answer” but perhaps valuable pointers to assist the questioner with his/her own further investigations. Anyway, at least, that’s what I’ll hope to do in such cases.



With respect to the question at hand:

1- Look into “Cherenkov radiation” as well as the difference between the Phase Velocity and the Group Velocity of a wave. A great part of the conventional answer is there.
2- Try to always imagine alternatives, and equivalent treatments. Many a times in physics it is more convenient, for instance, to change coordinate systems. Or instead of a non-moving coordinate system and a moving object in it, you can alternatively treat the object as stationary and the coordinate system as moving. Be open to look for solutions out of the box.
3- Consider examining the spacetime backdrop (dimensionality) against which physics is ultimately formulated.
4- Try to do an off-the-wall Gedunken experiment where you “assume” the vacuum to be a medium of quantized (or otherwise) spacetime (not luminiferous aether, btw) in which a photon travels. Consider the coupling effects of such a spacetime vacuum medium on a photon. (Technically a whole lot trickier task).


Start there, and good luck!




P.S. "*" I answer a light-hearted question with a light-hearted response, but when it comes to more serious questions:

1- I always consider the best interests of the questioner first and foremost.
2- I will not answer open-ended/controversial/evolv... questions by shoving my personal opinions down the questioner’s ears.
3- I will provide enough objective tips and pointers for the asker to embark on a journey of his/her own without being necessarily misled by biased opinions (my own included).
4- I recognize the space and technical limitations of this site (e.g. helping someone with a computer virus problem – as important and useful as in fact that maybe – is one thing, considering the philosophical implications of basic quantum mechanical principals in even a remotely satisfactory fashion on Y!A is a whole different issue.) ... Not to mention, here one has to always watch out for not being accused of “Chatty” (and loose interpretations thereof) conduct.
5- Not everything in science (e.g. certain mathematical constructs and objects, conclusions, etc.) is always so easily reducible to “words”. And even when they are the “jargon” is usually alien to most people and hence could serve as a source of additional confusion.
6- It is utterly unrealistic to assume that a forum like Y!A is the suitable place for highly technical scientific considerations, and in non-mathematical language no less.
7- As a case in point: Consider my honorable intentions in providing a conscientious justification for my herein mentioned stance. Even at that, if I understood your comments correctly, I seem to have miserably failed, imagine the rest!

Answer 10

i'm not qualified to answer this one. i just wanted to do a loving sigh over your comment about quantum entanglement......sigh