A physicist from the University of Campinas in Brazil isn't a big fan of the idea that time started with a so-called Big Bang. Instead, Juliano CÃ©sar Silva Neves imagines a collapse followed by an expansion, one that could even still carry the scars of a previous timeline.

The idea itself isn't new, but Neves has used a fifty-year-old mathematical trick describing black holes to show how our Universe needn't have had such a compact start to existence. At first glance, our Universe doesn't seem to have a lot in common with black holes. One is expanding space full of clumpy bits;

The other is
mass pulling at space so hard that even light has no hope of escape. But at the
heart of both lies a concept known as a singularity – a volume of energy so
infinitely dense, we can't even begin to explain what's going on inside it.

Neves says, "There are two kinds of singularity in the Universe. One is the alleged cosmological singularity, or Big Bang. The other hides behind the event horizon of a black hole."

Taken a step
further, some propose the Universe itself formed from a black hole in some
other bubble of space-time. No matter which kind we're talking about,
singularities are zones where Einstein's general relativity goes blind and
quantum mechanics struggles to take over. Sci-fi writers might love them, but
the impossible nature of singularities makes them a frustrating point of
contention among physicists. The problem is, if we rewind the expanding
Universe, we get to a point where all of that mass and energy was concentrated
in an infinitely dense point. And if we crunch the numbers on collapsing
massive objects, we get the same kind of thing. Singularities might break
physics, but so far we haven't been able to rule them out. On the other hand,
some physicists think there's some wiggle room. Theoretically speaking, not all
models of a black hole need a singularity to exist.

"There are no singularities in so-called regular black holes," says Neves.

In 1968, a
physicist by the name of James Bardeen came up with a solution to the
singularity problem. He devised a way of mathematically describing black holes
that did away with the need for a singularity somewhere beyond its event
horizon, calling them 'regular black holes'. The history and reasoning behind
Bardeen's model is, well, super dense; but for a tl;dr version – he assumed
that the mass at the heart of a black hole needn't be constant, but could be
described using a function that depended on how far from its center you were.

That means
we can dust our hands of any stupid singularities, as mass still behaves as if
it has volume. Even as it is still squeezed into a tight space.

Neves
suggest we take Bardeen's work even further and apply it to that other annoying
singularity – the cosmological variety that preceded the Big Bang. By assuming
the rate of the Universe's expansion depended not just on time, but its scale
as well, he showed there was no need for a quantum leap out of a singularity
into a dense, voluminous space 13.82 billion years ago.

So what
happened instead?

"Eliminating the singularity or Big Bang brings back the bouncing Universe on to the theoretical stage of cosmology," says Neves.

This
'bouncing Universe' is actually a century-old idea that the expanding Universe
as we experience it today is space bouncing back outwards after a previous
contraction. Though it's currently somewhat of a fringe concept in cosmology,
Neves supports the view that traces of the pre-collapse Universe might have
survived the Big Crunch. If so, finding those scars might help validate the
hypothesis.

"This image of an eternal succession of universes with alternating expansion and contraction phases was called the cyclical Universe, which derives from bouncing cosmologies," says Neves.

Until we
have solid observations, the bouncing Universe model will no doubt stay in the
'nice idea' basket. Still, anything that solves the singularity problem
deserves investigating. Neves's work is just one of a number of possible
solutions that swaps around assumptions to eliminate the need for
physics-breaking impossibilities.

It's a
sticking point we'll need to solve sooner or later.

This
research was published in General Relativity and Gravitation.

## Comments

## Post a Comment