# Homework Help: Redshift question

1. Jan 15, 2009

1. The problem statement, all variables and given/known data
The question:
Explain why pair creation is expected to occur in the early universe, and estimate the redshift at which proton-antiproton pairs are created.

2. Relevant equations

3. The attempt at a solution
My logic for the reason is that the process requires high energy gamma photons to create the proton-antiproton pair. As for the second part, I don't really have a clue, although this is my guess:

For the process to occur, u need a photon to have around $2m_p c^2$ of energy, so:
$$2m_pc^2 = \frac{hc}{\lambda_e} [/itex] where the mass is the rest mass of the proton and the lambda is the wavelength of the original photon which made the pair. Since [tex] 1+Z = \frac{\delta \lambda}{\lambda_e}$$
$$Z = \frac{2 \delta \lambda m_p c}{h} - 1$$

But I don't have any values, so where am I suppose to go from here?