http://publish.aps.org/ejnls/prdfetch/abstract/PRD/V58/E023501/
(accessible for subscribers only):
Can the Universe create itself?
J. Richard Gott and III Li-Xin Li
Department of Astrophysical Sciences, Princeton University, Princeton,
New Jersey 08544
15 July 1998
Phys. Rev. D 58, 023501 (1998) (43 pages)
(Received 30 December 1997; published 29 May 1998)
The question of first-cause has troubled philosophers and cosmologists
alike. Now that it is apparent that our universe began in a big bang
explosion, the question of what happened before the big bang
arises. Inflation seems like a very promising answer, but as Borde and
Vilenkin have shown, the inflationary state preceding the big bang
could not have been infinite in duration---it must have had a
beginning also. Where did it come from? Ultimately, the difficult
question seems to be how to make something out of nothing. This paper
explores the idea that this is the wrong question---that that is not
how the Universe got here. Instead, we explore the idea of whether
there is anything in the laws of physics that would prevent the
Universe from creating itself. Because spacetimes can be curved and
multiply connected, general relativity allows for the possibility of
closed timelike curves (CTCs). Thus, tracing backwards in time through
the original inflationary state we may eventually encounter a region
of CTCs---giving no first-cause. This region of CTCs may well be over
by now (being bounded toward the future by a Cauchy horizon). We
illustrate that such models---with CTCs---are not necessarily
inconsistent by demonstrating self-consistent vacuums for Misner space
and a multiply connected de Sitter space in which the renormalized
energy-momentum tensor does not diverge as one approaches the Cauchy
horizon and solves Einstein's equations. Some specific scenarios (out
of many possible ones) for this type of model are described. For
example, a metastable vacuum inflates producing an infinite number of
(big-bang-type) bubble universes. In many of these, either by natural
causes or by action of advanced civilizations, a number of bubbles of
metastable vacuum are created at late times by high energy
events. These bubbles will usually collapse and form black holes, but
occasionally one will tunnel to create an expanding metastable vacuum
(a baby universe) on the other side of the black hole's Einstein-Rosen
bridge as proposed by Farhi, Guth, and Guven. One of the expanding
metastable-vacuum baby universes produced in this way simply turns out
to be the original inflating metastable vacuum we began with. We show
that a Universe with CTCs can be stable against vacuum
polarization. And it can be classically stable and self-consistent if
and only if the potentials in this Universe are retarded---which gives
a natural explanation of the arrow of time in our
universe. Interestingly, the laws of physics may allow the Universe to
be its own mother. [S0556-2821(98)00614-6]
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