A group of cosmologists at Penn State University have applied a quantum theory of spacetime to the question of the Big Bang, and discovered that a previous universe may have existed before ours blossomed into existence 13 billion years ago.
The results suggest that the Big Bang was in fact a Big Bounce. As the previous universe collapsed upon itself, it rebounded, creating in the process the universe in which we now live. Such a scenario has been previously suggested, but the Penn State group may have the first solid data verifying the hypothesis.
Cosmology, or the study of the origin and evolution of the universe, depends of two disparate branches of physics: general relativity and quantum physics.
General relativity is Albert Einstein’s theory of gravitation, which in fact predicted the occurrence of a Big Bang a decade before there was any observational evidence supporting the event. The theory enables astrophysicists and cosmologists to understand in part what the early universe, with its densely packed matter and energy, may have looked like.
Quantum physics deals with the subatomic world. As it turns out, the extreme density and temperature of the early universe would have had profound consequences for the behavior of matter and the four forces known to influence matter.
Quantum physics states that many physical quantities are actually whole-number multiples of fundamental constants. For example, matter is composed of atoms, which are indivisible as far as chemistry is concerned. Electric charge is also quantized, since under normal circumstances the smallest electric charge is that of the electron. The energy and angular momentum of atomic electrons are also quantized.
Relativity, however, assumes that spacetime — the four dimensions in which we live — is not quantized. This dichotomy has made it difficult to reconcile the predictions of relativity and quantum physics make for the conditions of the early universe.
“General relativity can be used to describe the universe back to a point at which matter becomes so dense that its equations don’t hold up,” said Abhay Ashtekar, director of the Institute for Gravitational Physics and Geometry at Penn State University in University Park, Penn.
The Penn State group applied a quantum conception of spacetime and used this assumption to run the movie of the universe backward, in a sense, to see what results they would get.
Rather than ending up at the moment of creation, the equations “jumped the track” to indicate there was an earlier universe in the process of contracting before the Big Bang occurred.
“In place of a classical Big Bang there is in fact a quantum bounce,” said Ashtekar. “We were so surprised by the finding,” he added, that the team repeated the calculations for months to include different different possible values of some numbers representing the current universe. But the results kept pointing to a bounce.
The group employed a concept called loop quantum gravity. Under normal conditions, spacetime is made of one-dimensional “threads” held together by these loops. When ambient energies are extreme, such as in a densely packed universe, the threads fall apart into discrete loops, and the quantum nature of gravitation takes over.
The theory predicts that this quantized gravity actually repels matter, creating a Big Bounce. It’s possible that the cosmos has undergone such cyclical rebirths many times.
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