“It is difficult to make predictions,” goes the Danish quip, “especially about the future”.
Fortunately for cosmologists, this isn’t quite the case. They need only make one reasonable assumption – that the fundamental laws of physics don’t change – and with the help of a blackboard the fate of the universe is revealed to them.
To see how this works, let us first understand how physical laws have shaped the universe’s past. For the sake of convenience, we will use a “logarithmic clock” – i.e. 10 raised to some number x, or 10x – to measure the amount of time elapsed in years since the Big Bang.
