Physics of refraction question

[dlwalke]

I'm reading through Chapter 1 (The Chemistry and Physics of Diving) of PADI's "Encylopedia of Recreational Diving". I'm going through this section where it explains refraction and it indicates that "refraction results when light travels at different speeds through various substances due to different densities." This can't be right can it? Isn't the speed of light the one thing in the universe that is immutable (186,000 miles/sec)?

Dave

 

[neil]

As I understand it, light traveling unimpeded through vacuum travels at 183,310 miles per second. In air it slows by 0.03%, in water 25% and glass 35%.
Neil

 

[dlwalke]

OK. I see the light.

I wonder though if the speed of light really slows down in a non-vacuum or if the photons are forced to take curvy paths (i.e., past atoms and such) and therefore the apparent speed in the overall direction of travel is slower even though the photons themselves are still traveling at 183,310 miles/sec?

There was an interesting experiment not too long ago in which researchers were actually able to make light travel so fast that it exited the tube through which it was traveling before it even entered. For reasons that are explained in this article http://news.bbc.co.uk/hi/english/sci/tech/newsid_841000/841690.stm but that I can't say I understand, this doesn't violate any Einsteinian principles.

Dave

 

[Diver0001]

dlwalke once bubbled...
OK. I see the light.

I wonder though if the speed of light really slows down in a non-vacuum or if the photons are forced to take curvy paths (i.e., past atoms and such) and therefore the apparent speed in the overall direction of travel is slower even though the photons themselves are still traveling at 183,310 miles/sec?

<snip>

Dave

I think what you're describing is what actually happens. In quantum physics it's known that the act of observing something can change the results. The energy (photons or whatever you use) required to make something observable something can actually "bounce" small particles around.

R..

 

[Walter]

The speed of light is not absolute. When refferring to "the speed of light," it is the speed of light in a vacuum to which is being referred. Light slows down in mediums of different densities.

 

[SDAnderson]

This gets complicated very quickly, but here's an excellent primer, replete with illustrations: Refraction of Light

Walter is correct. The speed of light, (c), is not a constant. The measure by which a wave of light changes speed as it passes through a medium is called the refractive index. And yes, the refractive index works both ways: light waves entering a denser medium will slow, light waves entering a less dense medium will accelerate. Neat trick, huh? It has something to do with the photons which comprise a light wave and the boundaries between energy and matter and I told you this gets complicated really quickly.

What's really interesting is that light waves can be accelerated to faster than the "speed of time," literally arriving at one point before they leave another. If this doesn't give you a brain cramp, I don't know what will.

The most common example of the refraction of light is a rainbow. For those being picky, rainbows also involve the dispersion and reflection of light waves, but who wants a handful of nits?

Steven

 

[Cave Diver]

dlwalke once bubbled...
There was an interesting experiment not too long ago in which researchers were actually able to make light travel so fast that it exited the tube through which it was traveling before it even entered. For reasons that are explained in this article http://news.bbc.co.uk/hi/english/sci/tech/newsid_841000/841690.stm but that I can't say I understand, this doesn't violate any Einsteinian principles.

Dave

I read something else regarding this lately, if I can find it I will post it. It was extremely interesting.