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.For a non-technical introduction see Goldsmith, Einstein's Greatest Blunder? Chs 10 on, Trefil, The Moment of Creation, Chs. 10 on, Drees, Beyond the big bang, Appendices 3, 4. For a more technical introduction...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.These include the absence of antimatter in our universe, the formation of galaxies, the uniformity of the background radiation, and the flatness of the universe. See Trefil, The Moment of Creation, Chs....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.John D. Barrow, Impossibility: The Limits of Science and the Science of Limits (Oxford: Oxford University Press, 1998), Ch. 6, esp. p. 181.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.Some of the original papers include J. B. Hartle and S. W. Hawking, "Wave Function of the Universe," Phys. Rev. D 28:2960-2975, and A. D. Linde, "Particle Physics and Inflationary Cosmology,"... 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’.

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a) t=0 revisited

Contributed by: Dr. Robert Russell