There are probably more theories floating around to explain the birth, life and death of the universe than for any other scientific concept. Some scientists champion the idea of the Big Bang that created everything around us, others postulate that that we live in a steady state universe with no beginning or end. Now, math has set one thing straight: our universe definitely had a start.
Two cosmologists, Audrey Mithani and Alexander Vilenkin both from Tufts University in Massachusetts, have stuck their necks out with a new mathematical paper that considers the mathematics of eternity. In it, they take a close look at the concept of a universe that has no beginning or end.
Currently, there are two main descriptions of the universe's existence that suggest that the universe is eternally old—without a Big Bang. The first is the eternal inflation model, in which different parts of the universe expand and contract at different rates. Then, there's the idea of an emergent universe—one which exists as a kind of seed for eternity and then suddenly expands into life.
Thing is, it turns out that the idea of an eternal universes can only allow certain types of universe expansion to occur—and then they go on to show that the current inflation models that have been suggested have to have a begining. Needles to say, some of the math in their paper is pretty complex—you can read it here, though, if you'd like—but they manage to sum the whole thing up rather neatly:
"Although inflation may be eternal in the future, it cannot be extended indefinitely to the past."
They also manage to scupper the idea that an emergent model of the universe can't stretch back eternally—but they choose to do that using quantum mechanics. Agains, neatly summing it up, they say:
"A simple emergent universe model...cannot escape quantum collapse."
Basically, they've taken aim at the two current models of the universe that asume it's eternally old, and conclude that "none of these scenarios can actually be past-eternal." Which means the universe definitely had a beginning. [arXiv via Technology Review]