Question

At the time of recombination (z = 1100), the largest CMB temperature fluctuations (hot spots and cold spots) were 380,000 lightyears in size. What size (in Mpc) are these CMB fluctuations today (1 Mpc = 3.1 × 10⁶ lightyears)? Write two or three sentences about how this size compares to the sizes of galaxy clusters today (which are around 100-150 Mpc in size) and what the connection is between the CMB fluctuations and galaxy clusters.

Answer 1

at the time of recombination, the density of matter was almst same everywhere. as time went by these fluctuations became more denser and massive under gravity giving rise to stars, galaxies and galaxies clusters.

present size of temperature fluctuation = (1+z) * 380000 ly

                                                         = 1101 * 380000 ly

                                                          = 418380000 ly

                                                           = 134.9 Mpc