One of the most baffling aspects of the Big Bang theory is figuring out how to explain what happened "before" time and space began. The language itself is awkward. How does it make sense to even refer to a time "before" time itself existed?
Physics is of no help either. Our scientific theories are no better at explaining what happens when all of existence is crunched into an infinitely dense point, known as a singularity, where time and space cease to exist, which is what our Big Bang theories suggest must have been the case prior to the bang.
There's a new theory on the block, however, that seems to escape this conundrum while still retaining much of the cosmology of the Big Bang that we're already familiar with. In fact, the theory, casually referred to as "the flipped universe," purports to be a straightforward interpretation of general relativity, and it claims that time didn't begin with the Big Bang — time existed before the Big Bang, according to a University of Oxford press release from David Sloan, postdoctoral research associate at Oxford's Department of Physics.
Unlike other theories that attempt to solve the Big Bang singularity problem by reworking the fundamentals of the Big Bang itself, the theory of the flipped universe keeps the fundamentals. No modifications to Einstein’s theory of general relativity are needed. Rather than dispute the Big Bang, it merely calls into question the Big Bang's position as the beginning of time. It's a matter of interpreting the theory differently, rather than reworking it.
Of course, this change in interpretation isn't quite so simple as it might sound. If the Big Bang isn't the beginning of time, then it changes a lot about how we might conceive of the universe. For instance, if time existed before the Big Bang, then it means that there must exist something on the other side of the Big Bang; another universe. In fact, it's our universe, only flipped back-to-front.
This flipped universe ought to look qualitatively similar to our own, with a few eccentric reversals. For instance, there would be an inversion of “chirality”, meaning that objects that look right-handed in our universe instead emerge left-handed on the other side. Entropy ought to be inverted as well, and for someone living on the other side, time would seem to run in the opposite way from our own. From their perspective our universe would be their past.
It's a mind-bending way of thinking about things, but it's also a theory that doesn't fall into some of the mind-breaking paradoxical traps that singularity physics attempts to grapple with.
And so, perhaps the Big Bang happened, but rather than being a beginning, it was just a transition of sorts, a door to a mirrored existence, a mind-twisting rabbit hole through which time passes but where reality itself is flipped.
It's an Alice-in-Wonderland world, physics. Until we finally do definitively solve these mysteries, it's sure to be a wild ride.