# Gamma photon wavelength: Is there a limit?

1. Oct 30, 2014

### jerromyjon

Is there any known limit to the energy of a photon? I've seen a reference to pair production in the highest bracket over 1.02 MeV and I've seen references to energies from cosmic sources in the TeV range which aren't very well understood but is there any theoretical limit?

2. Oct 30, 2014

### Staff: Mentor

At least with current physics, such a limit is impossible. Imagine a photon would have a "maximal energy" in our lab frame. Then another observer, moving in the opposite direction, would observe a higher than maximal energy.

3. Oct 30, 2014

### jerromyjon

Thank you for your reply! I don't see how that makes a difference though, observation doesn't affect its maximal velocity. I am trying to grasp wavelength relevance which is exactly proportional to energy if I am not mistaken. I've read that the wavelength ranges overlap to some degree but generally gamma rays originate in the nucleus of atoms and x-rays originate from electrons in the shell. The wavelengths are roughly the scale of an atom and shorter for gamma, longer for hard x-rays. I'm just trying to get it into a reasonable perspective...;)

4. Oct 30, 2014

### Staff: Mentor

The velocity is always the speed of light.
The frequency and therefore the energy (yes, they are exactly proportional) depends on the observer.

Well that is just a naming convention.

5. Oct 30, 2014

### jerromyjon

Is that exclusively due to frequency shift from gravitational, doppler and cosmological differences or are there other factors?

6. Oct 31, 2014

### Staff: Mentor

In the setup I described (as an example), just doppler effect.

7. Oct 31, 2014

### jerromyjon

Thank you very much, I get your point. Velocity is a constant because it is the same for all observers, but energy varies with respect to the observer.