121 research outputs found
Hurdles for Recent Measures in Eternal Inflation
In recent literature on eternal inflation, a number of measures have been
introduced which attempt to assign probabilities to different pocket universes
by counting the number of each type of pocket according to a specific
procedure. We give an overview of the existing measures, pointing out some
interesting connections and generic predictions. For example, pairs of vacua
that undergo fast transitions between themselves will be strongly favored. The
resultant implications for making predictions in a generic potential landscape
are discussed. We also raise a number of issues concerning the types of
transitions that observers in eternal inflation are able to experience.Comment: 15 PRD-style pages, 5 figures, expanded discussion of measures in
Sec. II, added reference
Cosmic Perturbations Through the Cyclic Ages
We analyze the evolution of cosmological perturbations in the cyclic model,
paying particular attention to their behavior and interplay over multiple
cycles. Our key results are: (1) galaxies and large scale structure present in
one cycle are generated by the quantum fluctuations in the preceding cycle
without interference from perturbations or structure generated in earlier
cycles and without interfering with structure generated in later cycles; (2)
the ekpyrotic phase, an epoch of gentle contraction with equation of state
preceding the hot big bang, makes the universe homogeneous, isotropic
and flat within any given observer's horizon; and, (3) although the universe is
uniform within each observer's horizon, the global structure of the cyclic
universe is more complex, owing to the effects of superhorizon length
perturbations, and cannot be described in a uniform Friedmann-Robertson-Walker
picture. In particular, we show that the ekpyrotic phase is so effective in
smoothing, flattening and isotropizing the universe within the horizon that
this phase alone suffices to solve the horizon and flatness problems even
without an extended period of dark energy domination (a kind of low energy
inflation). Instead, the cyclic model rests on a genuinely novel,
non-inflationary mechanism (ekpyrotic contraction) for resolving the classic
cosmological conundrums.Comment: 28 pages, 5 figures, 1 tabl
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