High-Energy Doppler Shift & Pair Production

[Albertgauss]

Hi all,

Let's say you are at rest with respect to the galaxy, and you have low energy photons all around you. Now, if I crank my energies up relatvisitcally, the frequency and thus E = hf of those photons will increase. Red Light becomes Blue Light, Blue Light becomes UV, UV to X-ray, and finally X-ray to Gamma Ray. But the limit of not finding photons of higher energy than Gamma is pair production. Could I ever move with high enough energy through the universe that all photons will look like pair-produced particles, first electrons and anti-electrons, then maybe something heavier like protons and anti-protons? That is to say, if I moved with high enough energy, would I not actually see anymore light, but particles where light used to be? I know that you need a recoil atom for pair-production, but let's say these are mostly available.

As a side-note: If there are not recoil atoms for pair production, what kind of photon would I have at such extreme, relatvistic energies?

 

[PeterDonis]

I know that you need a recoil atom for pair-production, but let's say these are mostly available.

It's not enough for recoil atoms to be available: they have to be at rest relative to *you*, not the photons that are supposed to pair produce. In other words, the critical parameter for pair production is not the photons' energy relative to you, but the photons' energy relative to the recoil atoms.

Of course, one way to ensure that would be to have the recoil atoms be the ones making up you and your rocket ship; but that might not be very pleasant for you.

If there are not recoil atoms for pair production, what kind of photon would I have at such extreme, relatvistic energies?

Um, a very, very energetic one? Classically, there is no limit to how much energy a photon can have.

Quantum mechanically, one could argue for limits to the energy that can be packed into a single particle, but any such limit is going to apply to you, traveling at ultra-relativistic velocity relative to the rest of the universe, not the photons that have low energy relative to the rest of the universe.