Everything about The Oscillatory Universe totally explained
The
oscillatory universe is a
cosmological model, originally derived by
Alexander Friedman in 1922, investigated briefly by
Einstein in 1930 and critiqued by
Richard Tolman in 1934, in which the universe undergoes a series of oscillations, each beginning with a
big bang and ending with a
big crunch. After the big bang, the universe
expands for a while before the gravitational attraction of matter causes it to collapse back in and undergo a
bounce.
Scientific Issues
In the simple cases studied by Friedman, containing just
homogeneous matter and possibly a negative
cosmological constant, each "bounce" is a
gravitational singularity with infinite density and zero size. It is then a matter of taste whether to extend the solution through the singularities, giving an infinitely oscillating model, or to assume that only one cycle exists. The oscillating model was once popular among cosmologists who thought that the singularities could be avoided and so each big bang would be connected to an earlier big crunch: the mathematical singularities seen in calculations were supposed to be the result of over-idealizations (for example assuming too much symmetry or neglecting some force), and would be resolved by a more careful treatment, or by an alternative theory of gravity such as
Brans-Dicke theory. In this case, as pointed out by Tolman,
entropy would build up from oscillation to oscillation; according to Tolman this would cause each oscillation to last longer and reach a larger size than the one before, in some sense tending towards a condition of
heat death. However, in the
1960s,
Stephen Hawking,
Roger Penrose and
George Ellis showed that singularities were a universal feature of cosmologies with a big bang and that no feature of
general relativity could prevent them. Since no "memory" of previous cycles would be preserved, the entropy issue was eliminated, but by the same token there was little reason to postulate cycles before or after the present one. Other measurements suggested the universe isn't
closed. These arguments caused most cosmologists to abandon the oscillating universe model.
John Archibald Wheeler, who believed that a closed universe was necessary on general principles, speculated that the
fundamental physical constants could be re-processed to new values at each bounce, providing a mechanism for
anthropic selection.
The theory has been revived in
brane cosmology as the
cyclic model, which evades most of the arguments leveled against the oscillatory universe in the sixties. Despite some success, the theory is still controversial, largely because there's no satisfactory
string theoretic description of the bounce in this model.
Further Information
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