May 23, 2006 — The Big Bang may have been a Big Bounce, say theorists searching for what preceded the birth of our own universe.
If their new mathematical simulations are correct, what came before the Big Bang was a previous universe a lot like our own. It collapsed on itself, then some weird physics caused it to inflate into the universe we have today.
What has blocked the pre-Big Bang view from theoreticians was the mathematical expression of what was happening -- based on certain assumptions about space-time.
The problem was the calculations kept ramming up against infinity. When that happens, equations fail.
"It’s like having an impenetrable wall," said physicist Abhay Ashketar of Pennsylvania State University. "When it comes to infinity we cannot, in physics, go beyond it."
Spacetime is a model that combines three-dimensional space and one-dimensional time into a single unit called the space-time continuum. In this continuum, time is considered the fourth dimension.
What was becoming infinite in scientists' calculations was the curvature of the space-time continuum as you near the time when everything in the universe and all the gravity was concentrated into a single point.
The pre-Big Bang gravity basically shredded the space-time fabric and left only the physics of atoms -- quantum physics -- to work with.
To peer into that unimaginable crush, Ashketar and his colleagues backed up and started over, without assuming that the "fabric" of space-time continuum existed in the earliest moments of the universe. They published their results in the current issue of Physical Review Letters.
"The general belief is that the continuum may be just an approximation," said Ashketar. "This is something even Einstein said."
Instead, the team applied what’s called loop quantum gravity, a strategy that has been developed to join quantum physics with Einstein’s General Relativity. According to loop quantum gravity, the fabric of space is made of discrete and identical one-dimensional quantum threads. At the Big Bang, the fabric is a shredded mess and only these threads can be followed further back.
Using this concept, the researchers concluded that a previous universe collapsed in on itself in a gigantic gravitational Big Crunch. Then, when the density of that crunch reached super astronomical values, gravity flipped into a repulsive force -- another weird outcome of these physics -- and inflated the new universe in which we live.
"It’s long been speculated that as you get to the Big Bang, quantum theory was going to be important," said physicist Jorge Pullin of Louisiana State University. It’s also been speculated that if you could work out the equations, you’d probably see that the Big Bang was a Big Bounce, he said.
But this is the first time that anyone has actually done a thorough job working through the physics back through the Big Bang, he said.
As for what it tells us about the previous universe, it’s not much, said Pullin. "The only thing you can conclude is that the bounce occurs," he said.
That’s not to say we will never learn more about the earlier universe. Astronomers are discovering patterns in the cosmic background radiation that appear to be the inflated remnants of electron-sized irregularities in the first instant of the Big Bang. Could those irregularities, combined with loop quantum gravity, reveal patterns inherited from the earlier universe?
"There may be certain hints left behind," said Pullin.
