- #36
Adrian Baker
- 378
- 2
Originally posted by Thallium
Sorry. Here comes another unintelligent question: What is the "inverse square law"?
Light diminishes inversely proportional to the square of its distance from the source.
Originally posted by Thallium
Sorry. Here comes another unintelligent question: What is the "inverse square law"?
You must understand that the energy of a photon is given by its frequency (E=hf) not by its speed. I presume you know that, else your overall question would not make sense. Due to the Doppler effect, the frequency/energy of a photon is observer dependent. To understand where the energy "went", look up the relativistic doppler effect. Bottom line: the energy doesn't "go" anywhere, it's just measured to be different in different reference frames.Originally posted by Adrian Baker
I'm not sure that this is correct Doc Al. If c is the same for all observers, then the energy of a photon must be fixed for all observers surely? I really don't understand this energy loss with redshift, perhaps you could expand your reply to show me how this could be so?
To get into the details of Doppler and cosmological redshift, I would suggest the Relativity & Cosmology forum.Perhaps it should be on another thread though?
Originally posted by Adrian Baker
Thanks for the ideas here, and I understand the stretching idea of a photon as the universe expands and this gives a good mental picture of what is happening. But I still have a problem with this. For an observer, the energy of a photon is given by E=hf Where is the time factor in this then? Mathematically, Energy is lost. Is the Maths wrong, or is there a correction factor to E=hf that I am unaware of?
I can't see how Relativty helps either, although that maybe because my Maths isn't good enough.
Originally posted by Adrian Baker
Light diminishes inversely proportional to the square of its distance from the source.