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.
How does this help? Well, Penrose posits the end of each universe will involve a return to low entropy. This is because black holes suck in all the matter, energy, and information they encounter, which works to remove entropy from our universe. (Where that entropy might go is another question entirely.) The universe’s continued expansion into eventual nothingness causes the black holes themselves to evaporate, which ultimately leaves the universe in a highly ordered state once again, ready to contract into another singularity and set off the next Big Bang.
As alternative theories go, it’s not without its merits, but there’s no evidence to support it…until now. He says he’s found evidence for his ideas in the cosmic microwave background, the microwave radiation that permeates the universe and was thought to have formed 300,000 years after the Big Bang, providing a record of the universe at that far distant time. Penrose and his colleague Vahe Gurzadyan have discovered clear concentric circles within the data, which suggests regions of the radiation have much smaller temperature ranges than elsewhere.
So what does that mean? Penrose believes these circles are windows into the previous universe, spherical ripples left behind by the gravitational effects of colliding black holes in the previous universe. He also says these circles don’t work well at all in the current inflationary model, which holds all temperature variations in the CMB should be truly random.
Here’s where the fun begins. If the circles are really there and are really doing what Penrose says they’re doing, then he’s managed to overthrow the standard inflationary model. But there’s a long way to go between where we are now and that point, assuming it ever happens.
The inflationary model has become the consensus for a good reason - it’s the best explanation we’ve got for the universe we have now - and so cosmologists will examine any results that appear to disprove it very critically. There are also a couple key assumptions in Penrose’s theory, particularly that all particles will lose their mass towards the end of the universe. Right now, we don’t know whether that will actually happen - in particular, there’s no proof that electrons ever decay.