The Big Bounce: The big bang may not have been the beginning of the universe, but merely the beginning of one of an infinite series of universes. Yeah, wrap your mind around that!Courtesy Pat Rawlings/SAICThe Big Bang and the new kid - the Big Bounce - are facing off and it looks as if the Big Bounce is pulling ahead in the polls. Big bounce theory, proposed by Martin Bojowald, is based on loop quantum gravity. And what, you may ask, is loop quantum gravity??
Well, since you asked so nicely...loop quantum gravity - or loop gravity - is a theory of spacetime that attempts to reconcile quantum mechanics and general relativity, according to Wikipedia. Basically, loop gravity tries to prove that gravity is quantized (or broken down into discrete steps). Read more here.
So now that you know a little bit about loop gravity, we can move on to the theory at hand. The big bounce says that the universe is like a bouncy ball. When the ball hits the ground, the universe is at its smallest; as the ball rises above the ground, the universe expands; as the ball moves back towards the ground, the universe begins to implode; when the ball starts to rise after hitting the ground, the universe expands again... You get the idea.
Where the big bounce differs from the big bang is that it resolves the issue of the big bang singularity. And again, you may ask, what in the world is the big bang singularity? Well, for those of you not in the know: the big bang singularity is the single point from which the entire universe is supposed to have sprung. It is, in fact, the major sticking point in the big bang theory; the calculations just can't account for such a singularity.
"Without any evidence associated with the earliest instant of the expansion, the Big Bang theory cannot and does not provide any explanation for such an initial condition." - Big Bang Wikipedia page
So for years, this singularity has been an assumption inherent in the theory. And you know what the problem with assuming is...
This is where the big bounce starts to look mighty good! The big bounce suggests that, as the universe implodes, the energy density of space increases to a point that gravity ceases to be attractive and repulses instead. When gravity becomes repulsive, the universe stops shrinking and begins to expand. Once the density moderates, gravity switches back to being attractive. This explains the explosive expansion seen and accounted for in the big bang theory.Big Bounce: The universe implodes until gravity becomes repulsive and a new universe explodes from the ashes, so to speak.Courtesy Relativity 4 Engineers
Now here is where the big bounce gets really cool! The idea that the universe implodes and explodes like a ball bouncing leads Bojowald to believe that there have been an infinite number of universes before ours and an infinite number of universes to come. Each universe expands, increasing in inertia (or disorder) until it implodes, thus clearing the slate for the new universe.
“If order has been decreasing for an infinite span of time, the universe should by now be so disorganized that structures we see in galaxies as well as on Earth would be all but impossible. The right amount of cosmic forgetfulness may come to the rescue by presenting the young, growing universe with a clean slate irrespective of all the mess that may have built up before.” - Bojowald, Scientific American
No slate can be completely cleared, so Bojowald is now focusing on trying to learn about the universe that came before ours by studying gravitational waves and neutrinos.
To get the full story check out Bojowald’s article in the October issue of Scientific American.
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