- Big Bounce
The Big Bounce is a theorized
scientific modelrelated to the creation of the known Universe. It derives from the " cyclic model" or " oscillatory universe" interpretation of the Big Bangwhere the first cosmological event was the result of the collapse of a previous universe. [cite news |first= |last= |authorlink= |coauthors= |title=Penn State Researchers Look Beyond The Birth Of The Universe |url=http://www.sciencedaily.com/releases/2006/05/060515232747.htm |work=Science Daily |publisher= |date=May 17, 2006 |accessdate= Refering to cite journal |last=Ashtekar |first=Abhay |authorlink= |coauthors=Pawlowski, Tomasz; Singh, Parmpreet |year=2006 |month= |title=Quantum Nature of the Big Bang |journal=Physical Review Letters |volume=96 |issue= |pages=141301 |doi= |url=http://link.aps.org/abstract/PRL/v96/e141301 |accessdate= |quote= ]
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 mechanicsand its uncertainty principle.Fact|date=July 2007 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. The problem of "failed universes" (those that fail to produce carbon-based life forms) is also resolvedVague|date=September 2008.
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 gravitythat claimed to mathematically solve the time before the Big Bang, which would give new weight to the oscillatory universe and Big Bounce theories.cite journal |last=Bojowald |first=Martin |authorlink= |coauthors= |year=2007 |month= |title=What happened before the Big Bang? |journal=Nature Physics |volume=3 |issue=8 |pages=523–525 |doi=10.1038/nphys654 |url= |accessdate= |quote= ]
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 cosmologypurported to show that a previously existing universecollapsed, not to the point of singularity, but to a point before that where the quantum effects of gravitybecome 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 has yet to be verified by other researchers. In particular, within the loop quantum cosmology, Bojowald's claims have been challenged based on a model that is closer to the full theory and that is in a precise sense exactly solvable. However, the jury is still out in terms of what predictions will survive more detailed considerations, but the results so far found give this cyclic model greater visibility as a possible explanation of the beginning of the Universe.
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 Freezeor heat death rather than a Big CrunchFact|date=September 2008 (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.
Furthermore, it remains a possibility that a better understanding of
quantum foammay result in a re-interpretation of the evidence regarding the fate of our universe.
In 2008 the "Physical Review Letters" published what seems to be the confirmatory evidence of the Big Bounce theory after the works of Alejandro Corichi in the Mathematics Institute of the Universidad Nacional Autónoma de México in collaboration with the Parampreet Singh. [cite journal |last=Ashtekar |first=Abhay |authorlink= |coauthors=Corichi, Alejandro; Singh, Parampreet |year=2008 |month= |title=Robustness of key features of loop quantum cosmology |journal=Physical Review D |volume=77 |issue= |pages=024046 |doi=10.1103/PhysRevD.77.024046 |url= |accessdate= |quote= ]
Loop quantum gravity
John Archibald Wheeler
*cite book |title=Faster than the Speed of Light: the Story of a Scientific Speculation |last=Magueijo |first=João |authorlink= |coauthors= |year=2003 |publisher=Perseus Publishing |location=Cambridge, MA |isbn=0738205257 |pages=
* [http://www.science.psu.edu/alert/Ashtekar5-2006.htm Penn State Researchers Look Beyond The Birth Of The Universe] (Penn State) May 12, 2006
* [http://www.science.psu.edu/alert/Bojowald6-2007.htm What Happened Before the Big Bang?] (Penn State) July 1, 2007
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