1) Calculating the expansion of the Universe

a) The size of astronomical objects is measured in light years - the distance photons of light travel in one year. If the speed of a photon is 3 x 108 m/s, how many meters does a photon travel in one year?

b) Light from objects at the edge of the expanding Universe takes an estimated 13.8 billion years to reach the Earth. Approximately how many meters is this?

c) The radius of the very early Universe is estimated to have been1035 meters. By how many factors of ten has the Universe expanded?

2) Energy of a photon of an early universe photon

a) About 400,000 years after the Big Bang, the universe had cooled to 3,000 K. At this time, what was the energy of a photon in joules? (Useful info: k = 1.38 x 1023 J/Kelvin or k = 8.62 x 105 eV/Kelvin and 1 MeV = 106 eV)

b) What was the energy of a photon in megaelectron volts?