# Photon off a mirror ?

1. Feb 10, 2010

### cragar

I was told today that when a photon hits the mirror it is absorbed by the atoms in the glass then reemitted by the matter , then I was told that the photon that is remitted can emit before the initial photon gets their . How does this work , Is it possible that the photon has magnetic field and this is what is causing it . The photon has spin so then does it have a b field.

2. Feb 11, 2010

### PhilDSP

I'm not 100% clear what you mean based on what you said. But I think it's possible to visualize the case by imagining we have a foam ball that is hung from a string. On its equator is a bee-bee pressed into the foam.

The ball is set spinning at a speed which is just slightly less than that which would generate enough centrifugal force to dislodge the bee-bee. If we shoot another bee-bee into the ball where it hits the equator just narrowly missing the other bee-bee then the other bee-bee would likely be dislodged and fly back at us.

However since the bee-bee that was fired is also near the threshold of becoming dislodged, it sticks to the ball for an entire revolution before centrifugal force overcomes friction and the fired bee-bee now is ejected toward us too.

3. Feb 11, 2010

### DrChinese

Absorption and re-emission is not the best model for reflection. ZapperZ has posted a FAQ on a similar issue - light transport through a solid - in the General Physics section which I quote partially below:

The process of describing light transport via the quantum mechanical description isn't trivial. The use of photons to explain such process involves the understanding of not just the properties of photons, but also the quantum mechanical properties of the material itself (something one learns in Solid State Physics). So this explanation will attempt to only provide a very general and rough idea of the process.

A common explanation that has been provided is that a photon moving through the material still moves at the speed of c, but when it encounters the atom of the material, it is absorbed by the atom via an atomic transition. After a very slight delay, a photon is then re-emitted. This explanation is incorrect and inconsistent with empirical observations. If this is what actually occurs, then the absorption spectrum will be discrete because atoms have only discrete energy states. Yet, in glass for example, we see almost the whole visible spectrum being transmitted with no discrete disruption in the measured speed. In fact, the index of refraction (which reflects the speed of light through that medium) varies continuously, rather than abruptly, with the frequency of light.

Secondly, if that assertion is true, then the index of refraction would ONLY depend on the type of atom in the material, and nothing else, since the atom is responsible for the absorption of the photon. Again, if this is true, then we see a problem when we apply this to carbon, let's say. The index of refraction of graphite and diamond are different from each other. Yet, both are made up of carbon atoms. In fact, if we look at graphite alone, the index of refraction is different along different crystal directions. Obviously, materials with identical atoms can have different index of refraction. So it points to the evidence that it may have nothing to do with an "atomic transition".

When atoms and molecules form a solid, they start to lose most of their individual identity and form a "collective behavior" with other atoms. It is as the result of this collective behavior that one obtains a metal, insulator, semiconductor, etc. Almost all of the properties of solids that we are familiar with are the results of the collective properties of the solid as a whole, not the properties of the individual atoms. The same applies to how a photon moves through a solid.

I am sure some of the others here can provide more on this as well.

4. Feb 11, 2010

### jnorman

QED by feynman is a good place to start reading about photons interacting with glass and mirrors.

5. Feb 11, 2010

### cragar

thanks for the responses .