Most physicists today subscribe to the theory that our universe began in a spacetime singularity known as the Big Bang, but this isn't the only theory that's around. For instance, some physicists have proposed that our universe is just one among many, that perhaps space and time did not have a beginning at all.

These alternative theories are interesting, but because the other universes that they posit are often conceived of as separate from our own, they're difficult to test. But what if the cosmos was not quite so clean cut? What if bubbles of previous universes were still floating around in our universe, like soap bubbles that didn't quite drain out with the last bath?

That's the idea behind a new theory proposed by Brazilian physicist Juliano Cesar Silva Neves. He has theorized that our universe was never squashed into a Big Bang-like singularity at all. Rather, he believes that the cosmos has undergone a series of expansions and contractions, and that these "bounces" were messy and left behind vestiges of previous universes that we can look for in our universe today, reports Phys.org.

"I believe the Big Bang never happened," said Neves, who works as a researcher at the University of Campinas's Mathematics, Statistics & Scientific Computation Institute (IMECC-UNICAMP) in Sao Paulo State, Brazil.

In a 'bouncing' universe, each bounce leaves something behind

Neves' theory isn't just a fanciful idea; it's based on a modified version of the general relativity equations that describe the geometry of the cosmos. Unlike most of these models, Neves' version introduces an additional mathematical function known as a "scale factor," which takes into account the scale of the universe rather than just its cosmological time. And when this scale factor is added to the equation, the Big Bang itself ceases to be a necessary condition for the cosmos to begin universal expansion.

"Eliminating the singularity or Big Bang brings back the bouncing universe on to the theoretical stage of cosmology. The absence of a singularity at the start of spacetime opens up the possibility that vestiges of a previous contraction phase may have withstood the phase change and may still be with us in the ongoing expansion of the universe," explained Neves.

The idea of a bouncing universe that Neves alludes to here is the notion that our cosmos undergoes a cycle of expansion and contraction. But according to his models, each bounce is imperfect; there are some bubbles from previous universes that don't quite get destroyed by each contraction. If Neves is correct, these bubbles should still be floating around out there, somewhere.

The most likely candidates for these vestiges? Black holes.

"Who knows, there may be remains of black holes in the ongoing expansion that date from the prior contraction phase and passed intact through the bottleneck of the bounce," said Neves.

Of course, researchers will need to find one of these vestiges if Neves' theory is to be vindicated, but the mere possibility that there might be a way to actually observe remnants from a previous universe is a big part of what makes his model so compelling. It's verifiable. We just need to look "for traces of the events in a contraction phase that may have remained in the ongoing expansion phase," implored Neves.

Let the search begin.

The paper was published in the journal General Relativity and Gravitation.