24 Mar '16 12:05>
http://phys.org/news/2016-03-optical-slower.html
Originally posted by apathisthttps://en.wikipedia.org/wiki/Refractive_index
[b]"Although light does slow down when traveling through clear dense materials such glass or water,..."
I thought no it doesn't,....[/b]
Originally posted by humy...http://www.askamathematician.com/2011/08/q-if-light-slows-down-in-different-materials-then-how-can-it-be-a-universal-speed/
"... light travels 1.333 times faster in a vacuum than it does in water...."
implying that light does slow down when traveling through water. ...
Originally posted by apathistThat's what I read into it. The twisting is forcing the photons to take a path length longer than a straight path, sort of a drunkard's walk.
http://www.askamathematician.com/2011/08/q-if-light-slows-down-in-different-materials-then-how-can-it-be-a-universal-speed/
"Here’s the idea: a medium, whatever it is, is made up of molecules. When a photon (light particle) hits a molecule it is sometimes absorbed. Its energy is turned into raised electron-energy-levels, or vibrations and flexing, or m ...[text shortened]... merely traveling a farther distance, so of course they take longer. I think it said 0.1% longer.
Originally posted by apathistThat's right. Light is continually stopping and starting when traveling through material, and this is what causes the appearance of traveling slower. But whenever light is traveling it always travels through a vacuum, and it always travels at c.
http://www.askamathematician.com/2011/08/q-if-light-slows-down-in-different-materials-then-how-can-it-be-a-universal-speed/
"Here’s the idea: a medium, whatever it is, is made up of molecules. When a photon (light particle) hits a molecule it is sometimes absorbed. Its energy is turned into raised electron-energy-levels, or vibrations and flexing, or m ...[text shortened]... merely traveling a farther distance, so of course they take longer. I think it said 0.1% longer.
Originally posted by apathistActually this is quantum mechanics so its all a little bit more complicated than that.
When a photon exists, it always moves at c. When it is absorbed by a molecule, the energy state of the electrons in that molecule is increased [b]and the photon doesn't exist anymore. After a while, the energy level of the electrons in that molecule drop, and photon is emitted. That delay is why light propagates slower through a medium than in a ...[text shortened]... merely traveling a farther distance, so of course they take longer. I think it said 0.1% longer.[/b]
Originally posted by lemon limeActually, if I understand this correctly, that isn't right and what that link says contradicts modern quantum physics.
That's right. Light is continually stopping and starting when traveling through material, and this is what causes the appearance of traveling slower. ...
Originally posted by apathistThe link says
http://www.askamathematician.com/2011/08/q-if-light-slows-down-in-different-materials-then-how-can-it-be-a-universal-speed/
"Here’s the idea: a medium, whatever it is, is made up of molecules. When a photon (light particle) hits a molecule it is sometimes absorbed. Its energy is turned into raised electron-energy-levels, or vibrations and flexing, or m ...[text shortened]... merely traveling a farther distance, so of course they take longer. I think it said 0.1% longer.
Originally posted by humyIf there were 'stop and start' kind of motions, wouldn't that lead to Cherenkov radiation due to deceleration and acceleration effects? If so, the lack of such radiation would indicate there was no such start and stop motion.
The link says
1) The speed of light is an absolute.
2) Light slows down when it passes through a medium (like water, glass, air, &hellip😉.
and falsely makes out 1) and 2) contradict, which they don't because they have been misrepresented. It fails to mention that when we say "The speed of light is an absolute" as in 1) , we mean "The speed of light is an ab ...[text shortened]... what is going on is made too simplistic and contradicts modern understanding of quantum physics.
Originally posted by sonhouseLight doesn't decelerate or accelerate, whether there is start/stop activity or not.
If there were 'stop and start' kind of motions, wouldn't that lead to Cherenkov radiation due to deceleration and acceleration effects? If so, the lack of such radiation would indicate there was no such start and stop motion.
Originally posted by humymisedit:
The link says
1) The speed of light is an absolute.
2) Light slows down when it passes through a medium (like water, glass, air, &hellip😉.
and falsely makes out 1) and 2) contradict, which they don't because they have been misrepresented. It fails to mention that when we say "The speed of light is an absolute" as in 1) , we mean "The speed of light is an ab ...[text shortened]... what is going on is made too simplistic and contradicts modern understanding of quantum physics.