## Wednesday, October 15, 2014

### Boltzmann-tail of the Planck-spectrum

can you estimate the time how long would you have to wait until
1. the Hubble space telescope would see a CMB photon at visible energies?
2. XMM-Newton registers a CMB photon at $X$-ray energies?
3. Fermi-LAT would register a CMB photon at MeV-energies?