"It all started with a big bang!" At least, that's how the "Barenaked Ladies" and "The Big Bang Theory" producers would have you believe it. The Big Bang theory has been the leading explanation for the origin of our universe for decades, one that's supported by a proverbial mountain of evidence.
First of all, we can see that the universe is still expanding in all directions. In fact, recent research suggests it's expanding even faster than we would expect it to. Second, there's a cosmic microwave background (CMB) – what scientists believe is the radiation afterglow of the Big Bang – detectable from every direction.
There are other theories, for example the Oscillating Universe Theory, that supposes the universe sways back and forth, but the vast majority of astronomers ascribe to the Big Bang.
Juliano Cesar Silva Neves, a physicist from the University of Campinas in Brazil, however, is not one of them. In a paper published in General Relativity and Gravitation, he puts forward a different theory – the singularity that led to the Big Bang never existed.
Instead, he proposes that there was a period of contraction that preceded the present period of expansion.
"Eliminating the singularity or Big Bang brings back the bouncing Universe on to the theoretical stage of cosmology," Neves explained in a statement. "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."
To explain his theory, Neves turns to black holes and a mathematical trick first put forward by US physicist James Bardeen in 1968. Bardeen came up with a formula that made it possible to have a black hole without a singularity, while still keeping to the laws of general relativity – he named these "regular black holes". To do this, Bardeen reasoned that the mass of a black hole could be seen as a function depending on the distance to the black hole's center rather than as a constant, as previously assumed.
Neves simply took this idea and applied it to another singularity – the initial singularity, which foreshadowed the Big Bang.
Theoretically at least, this means that the Big Bounce theory could be back in the cards. Instead of the universe inflating from an infinitely dense point (the Big Bang theory), this means the universe continuously expands and contracts, each expansion and contraction lasting billions of years.
While it's a lovely idea, there is, of yet, not a lot of physical proof to back it up, though Neves suggests we start looking at black holes.
"[R]emnants of black holes from a previous phase of universal contraction... may have survived the bounce," he added.