The current cosmological consensus is that the universe began 13.7 billion years ago with the Big Bang. But a legendary physicist says he’s found the first evidence of an eternal, cyclic cosmos.
The Big Bang model holds that everything that now comprises the universe was once concentrated in a single point of near-infinite density. Before this singularity exploded and the universe began, there was absolutely nothing - indeed, it’s not clear whether one can even use the term “before” in reference to a pre-Big-Bang cosmos, as time itself may not have existed yet. In the current model, the universe began with the Big Bang, underwent cosmic inflation for a fraction of a second, then settled into the much more gradual expansion that is still going on, and likely will end with the universe as an infinitely expanded, featureless cosmos.
Sir Roger Penrose, one of the most renowned physicists of the last fifty years, takes issue with this view. He points out that the universe was apparently born in a very low state of entropy, meaning a very high degree of order initially existed, and this is what made the complex matter we see all around us (and are composed of) possible in the first place. His objection is that the Big Bang model can’t explain why such a low entropy state existed, and he believes he has a solution - that the universe is just one of many in a cyclical chain, with each Big Bang starting up a new universe in place of the one before.