Big Bounce

The Big Bounce is a theorized scientific model related to the formation of the known Universe. It derives from the cyclic model or oscillatory universe interpretation of the Big Bang where the first cosmological event was the result of the collapse of a previous universe.[1]

Expansion and Contraction

According to one version of the Big Bang theory of cosmology, in the beginning the universe had infinite density. Such a description seems to be at odds with everything else in physics, and especially quantum mechanics and its uncertainty principle, because if it were true, it might have collapsed into so much antimatter. It is not surprising, therefore, that quantum mechanics has given rise to an alternative version of the Big Bang theory. Also, if the universe is closed, this theory would predict that once this incarnation of the universe collapses it will spawn another universe in an event similar to the Big Bang after a universal singularity is reached.

According to some oscillatory universe theorists, the Big Bang was merely the beginning of a period of expansion that followed a period of contraction. In this view, one could talk of a Big Crunch followed by a Big Bang, or more simply, a Big Bounce. This suggests that we might be living in the first of all universes, but are equally likely to be living in the 2 billionth universe (or any of an infinite other sequential universes).

The main idea behind the quantum theory of a Big Bounce is that, as density approaches infinity, the behavior of the quantum foam changes. All the so-called fundamental physical constants, including the speed of light in a vacuum, were not so constant during the Big Crunch, especially in the interval stretching 10⁻⁴³ seconds before and after the point of inflection. (One unit of Planck time is about 10⁻⁴³ seconds.)

If the fundamental physical constants were determined in a quantum-mechanical manner during the Big Crunch, then their apparently inexplicable values in this universe would not be so surprising, it being understood here that a universe is that which exists between a Big Bang and its Big Crunch.

Recent developments in the theory

Martin Bojowald, an assistant professor of physics at Pennsylvania State University, published a study in July 2007 detailing work somewhat related to loop quantum gravity that claimed to mathematically solve the time before the Big Bang, which would give new weight to the oscillatory universe and Big Bounce theories.[2]

One of the main problems with the Big Bang theory is that at the moment of the Big Bang, there is a singularity of zero volume and infinite energy. This is normally interpreted as the end of the physics as we know it; in this case, of the theory of general relativity. This is why one expects quantum effects to become important and avoid the singularity.

However, research in loop quantum cosmology purported to show that a previously existing universe collapsed, not to the point of singularity, but to a point before that where the quantum effects of gravity become so strongly repulsive that the universe rebounds back out, forming a new branch. Throughout this collapse and bounce, the evolution is unitary.

Bojowald also claims that some properties of the universe that collapsed to form ours can also be determined. Some properties of the prior universe are not determinable however due to some kind of uncertainty principle.

This work is still in its early stages and very speculative. Some extensions by further scientists have been published in Physical Review Letters.[3]

Objections

One of the main objections to the Big Bounce view is the evidence that has been accumulating that our universe is destined for a Big Freeze or heat death rather than a Big Crunch[citation needed] (see Accelerating universe). However, this evidence does not exclude the possibility that our Big Bang was preceded by the very last Big Crunch, at least the very last one in our vicinity.

Another main objection is that a Big Bounce would reverse entropy by resetting the state of the universe, violating the second law of thermodynamics. Also, the collapse into a singularity would destroy most of the information in the previous universe.

Furthermore, it remains a possibility that a better understanding of quantum foam may result in a re-interpretation of the evidence regarding the fate of our universe.