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With the introduction of the “inflationary Big Bang”
scenario by Alan Guth and colleagues in the 1970s and further developments in
this direction in the 1980s, these problems were basically solved. According to
inflation, the extremely early universe (roughly the Planck time 10-43
seconds) expands extremely rapidly, then quickly settles down to the expansion
rates of the standard Big Bang model. During inflation, countless domains may
arise, separating the overall universe into huge portions of spacetime in which
the natural constants and even the specific laws of physics can vary. The effect
of inflation on the problem of t=0, however, is fascinating. In some
inflationary cosmologies, the Hawking-Penrose theorems don’t apply during the
inflationary epoch. In these cosmologies we may never know whether or not an
essential singularity exists, even if it does. Recently, attempts have been made
to unify quantum physics and gravity and apply the results to cosmology.
Proposals by Hawking and Hartle, Linde, Isham, Guth, Hawking and Turek, and
others, are still in a speculative stage, but there are already some indications
of what different quantum cosmologies might look like, including models with or
without an initial singularity (‘eternal inflation’), with open or closed
domains embedded in an open or a closed mega-universe, and so on. In most
quantum cosmologies, our universe is just a part of an eternally expanding,
infinitely complex megauniverse. Quantum cosmology, however, is a highly
speculative field. Theories involving quantum gravity, which underlie quantum
cosmology, are notoriously hard to test empirically, and they lift the
philosophical issues already associated with quantum mechanics to a much more
complex level since the domain is now ‘the universe’.
Contributed
by: Robert Russell
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