Quentin Cooper is joined by John Barrow of Cambridge University and Jocelyn Bell-Burnell, President of the Institute of Physics, to discuss the work of the early-20th century physicist Enrico Fermi. He finds out how sensible estimations are helping scientists and mathematicians to unravel the magnificent and the mundane, from the amount of matter in the universe to the probability of having the same bank PIN code as your next-door neighbour.