Energy of a photon is given by planks constant x frequency; E=hf

With the doppler effect reducing the frequency (shifting a photon to the red side of the spectrum) if the light source is moving away relative to your position the energy would be less. But where is this loss of energy going to?

Similarly if the photon is blue shifted by the source moving towards you relative to your position where does this gain in energy come from?

Does this means if you are in a solar powered rocket and move towards a light source and harness the energy of its photons to speed your rocket, it would accelerate (unsure if the acceleration would increase as it gets harder to accelerate as you get faster) as the photons would have increasingly greater energy as you move quicker towards the source. So surely this makes speeds close to light speed possible just using a light source?

Open for discussion.

The speed of light relative to you would be the same regardless of how fast you were traveling. For example, if you stand and shine a flashlight at a wall, the photons hit the wall at the speed of light. If you run towards the wall at 20 mph and shine the flashlight, the photons do not hit the wall at the speed of light + 20 mph. They still hit at the speed of light.

Im fully aware of that thank you. Please read my post properly.

The photons haven't lost energy. There are fewer photons hitting the solar panel per time unit in a red shift, but the energy of the photons is the same.

This post was edited by bergmann on Feb 24 2009 11:49pm

theoretically it is possible if you could catch all of the photons and harness them for energy as you progressed.