# Refraction of single photons

1. Feb 10, 2014

### Choisai

As a physics student, I was taught that refraction happens because when light approaches a material with a refraction index that is different than the index of the medium it is travelling through at that moment, the light that hits it first, as shown here:

This raises to me two questions:

1) From this explanation it follows that waves that come perpendicular to the surface should not 'bend'. That is however not what I have seen personally. How can that be explained?
(I gather from that that such drawings are merely analogies and should not be taken literally, but that doesn't give me a full explanation)

2) What happens when single photons hit the material? Will they 'bend' as well?

2. Feb 10, 2014

### bhobba

I hate to tell you, but the explanation is your personal experience is wrong - it doesn't bend. Don't feel too bad though - personal experience is notoriously 'imprecise'

Best to have that explained by a master:
https://www.amazon.com/QED-Strange-...s=QED:+The+Strange+Theory+of+Light+and+Matter

But, and this is maddening, even that is a simplification, requiring some hairy solid state physics to fully explain.

Thanks
Bill

3. Feb 10, 2014

### Bill_K

What direction could it bend? If the waves come in perpendicular to the surface, there is no preferred direction, and so the wave must continue to go straight, by symmetry.

Refraction is a collective effect involving many photons and the motion of many atoms in the medium. A single photon will go straight.

Even for a classical wave, refraction only takes place in the steady state after the wave has fully penetrated the medium. When the wave first arrives it will go straight, and this will be followed by a transient period during which the atomic motions come up to speed.