We are the outcome of a process which took nearly 14 billion years during which atoms, stars, planets and biospheres emerged from a hot and dense big bang. The details of this process are sensitive to a few important numbers — the so-called constants of physics.

Martin Rees, the Astronomer Royal, discussed the key stages in this process in the lecture below, given on 17 March 2014 as a public event during the Cambridge Science Festival, and linked to a conference on the philosophy of cosmology. The talk also addressed two questions: What would our cosmos be like if the key numbers were different? And could a huge variety of other universes exist as part of physical reality, each the aftermath of a different big bang?

Physicists are hard at work on these questions. In fact, just a couple of hours before Lord Rees gave this talk, US researchers announced a result that could signal a major breakthrough in our understanding of how our Universe evolved (see this Plus article). Watch out for the references to this in the lecture — good timing!