2) Inflationary Big Bang and Quantum Cosmologies
Since the 1970s, a variety of problems in the standard Big
Bang model have led scientists to pursue inflationary Big Bang and beyond
that quantum cosmology. These included technical problems as well as the need
to introduce quantum physics into the conversation, both because the universe
at its earliest epochs was arbitrarily small (and thus subject as a whole to
quantum physics) and because physicists were searching to unify gravity
theoretically with the other physical forces (i.e., the electroweak and strong
nuclear forces).
Science minisummary: Inflationary Big Bang and quantum
cosmologies. 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
dont 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: Dr. Robert Russell
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