Hi Charlie,

The remaining redshifted light comes from purely from the zero point motion of the mirror itself as it is moving away from the laser beam. At zero Kelvin (or close to it in the real world), the mirror still moves forward and backwards (that is towards the laser source, and away from the laser source). Normally as the mirror moves away from the laser source, the reflected light will be red-shifted and as it moves towards the source teh reflected light will be blue shifted. However at zero kelvin, the mirror will be in its ground state (i.e. its lowest possible energy state), and hence in order to blue shift the reflected light, energy would have to be taken from the mirror to the photons. Since energy states below the ground state (or zero point energy) are forbidden, then there can be no blue-shifted reflected light. What this shows is that one cannot extract useful energy from the zero-point energy.

With the red-shift though, the photons are loosing energy, which presumably is being absorbed by the mirror. This will have the effect of increasing the temperature of the mirror, and the energy of the system, which explains why you will still get some blue-shifted light since the laser is in some way pushing the mirror a little. That is, that there is a small contribution to the blue shifted band due to absorbed photons from the laser itself. So in a way, its not the remaining red-shift that is from pushing the mirror, but rather the blue-shift. Of course in the experiment, because of the non-zero temperature, there is still blue shift which is from the thermal motions since not all atoms in the material would be in the ground state. So the blue-shift from the photons absorbed by the ground state atoms would contribute to the experiment, but are likely swamped by the background thermal motions.

At least that's my understanding of it. I will likely be having dinner with a bunch of quantum physicists this week, so if the topic comes up, and if my brain doesnt melt, I might be able to know more about this.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup