Quote:
Originally Posted by Karls48
Bojan wrote-“Photon is stable and does not decay. We can detect it even if it is coming from near the edge of the visible Universe.
What is happening, thought, wavelength is changed (it becomes longer) because of expansion of the universe (similar to Doppler effect), so the photons from the edge of the visible Universe would have wavelengths infinitely long (frequency would have been zero, energy also zero).”
Is no this just fancy way to say that the photon decayed to nothing? By this definition it would become DC current with zero voltage. Where did the original energy it had go to? What happen to the law of conservation of energy?
|
It's a good question. And there is a simple answer. The laws of physics such as the conservation of energy apply
within frames of references
not across them. In the photon's frame of reference (if it can be called that), the photon doesn't lose energy, as much as it doesn't lose energy in the observer's frame. The observer in his cosmological frame of reference only sees the photon of a particular frequency and doesn't see a change of the photon's energy
in his frame. Energy is therefore conserved in both frames.
Consider relative velocities. Each observer will measure a different velocity in their frame of reference and therefore calculate a different kinetic energy. For kinetic energy to be conserved across frames would imply a baseline common to all the observers (an absolute frame of reference) which of course doesn't exist.
Regards
Steven