[McQueen]

I'm sorry if my reference to virtual photons offends you. Some people take virtual photons very seriously, in the context of light propagating through media.

Sorry , my bad, I was out of line to make such a statement. Incidentally I do believe that 'virtual photons' exist and play an indispensable part in the working of the world and the Universe. P.S. On re-reading my post I realise that it is even worse than I had originally thought. Once again my apologies.

Please clarify why light waves, ocean waves,  gravitational waves and radio waves cannot carry energy.

Out of  these  "waves" only ocean waves are true waves that disperse their energy across the wave front i.e., the energy is shared in common,  all of the others ( leaving aside gravitational waves) have discrete energies as demonstrated by Max Planck..

Coming back to the topic of light slowing down as it travels through  glass..... Here is another quantum mechanics explanation that also involves absorption and emission of photons by electrons as they travel through glass:

"To make the classical picture quantum, we say that a single photon entering the material will potentially be absorbed and re-emitted by each of the atoms making up the first layer of the material. Since we cannot directly measure which atom did the absorbing, though, we treat the situation mathematically as a superposition of all the possible outcomes, namely, each of the atoms absorbing then re-emitting the photon. Then, when we come to the next layer of the material, we first need to add up all the wave-functions corresponding to all the possible absorptions and re-emissions.

Thus, we more or less reproduce the Huygens’s Principle case, and we find that just as in the classical case, the pieces of the photon wave-function corresponding to each of the different emissions will interfere with one another. This interference will be constructive in the forward direction, and destructive in all the other directions. So, the photon will effectively continue on in the direction it was originally headed. Then we repeat the process for the next layer of atoms in the medium, and so forth.
It’s important to note that when this picture is valid the probability of being absorbed then re-emitted by any individual atom is pretty tiny– when the light frequency is close to a resonance in the material, you would need to do something very different. (But then, if the light was close to a resonant frequency of the material, it wouldn’t be a transparent material…) while the probability of absorption and re-emission is tiny for any individual atom, though, there are vast numbers of atoms in a typical solid, so the odds are that the photon will be absorbed and re-emitted at some point during the passage through the glass are very good. Thus, on average, the photon will be delayed relative to one that passes through an equal length of vacuum, and that gives us the slowing effect that we see for light moving through glass."

[Nicholas Lee (OP)]

Thank you for your help, those explanations really helped.

[evan_au]

A sideline was split off to "What is a wave?", http://www.thenakedscientists.com/forum/index.php?topic=66623.0