262 research outputs found
A Cyclic Model of the Universe
We propose a cosmological model in which the universe undergoes an endless
sequence of cosmic epochs each beginning with a `bang' and ending in a
`crunch.' The temperature and density are finite at each transition from crunch
to bang. Instead of having an inflationary epoch, each cycle includes a period
of slow accelerated expansion (as recently observed) followed by slow
contraction. The combination produces the homogeneity, flatness, density
fluctuations and energy needed to begin the next cycle.Comment: 15 pages, 1 figure, revisions as publishe
The anamorphic universe
We introduce "anamorphic" cosmology, an approach for explaining the
smoothness and flatness of the universe on large scales and the generation of a
nearly scale-invariant spectrum of adiabatic density perturbations. The
defining feature is a smoothing phase that acts like a contracting universe
based on some Weyl frame-invariant criteria and an expanding universe based on
other frame-invariant criteria. An advantage of the contracting aspects is that
it is possible to avoid the multiverse and measure problems that arise in
inflationary models. Unlike ekpyrotic models, anamorphic models can be
constructed using only a single field and can generate a nearly scale-invariant
spectrum of tensor perturbations. Anamorphic models also differ from pre-big
bang and matter bounce models that do not explain the smoothness. We present
some examples of cosmological models that incorporate an anamorphic smoothing
phase.Comment: 35 pages, 3 figures, 1 tabl
A new kind of cyclic universe
Combining intervals of ekpyrotic (ultra-slow) contraction with a
(non-singular) classical bounce naturally leads to a novel cyclic theory of the
universe in which the Hubble parameter, energy density and temperature
oscillate periodically, but the scale factor grows by an exponential factor
from one cycle to the next. The resulting cosmology not only resolves the
homogeneity, isotropy, flatness and monopole problems and generates a nearly
scale invariant spectrum of density perturbations, but it also addresses a
number of age-old cosmological issues that big bang inflationary cosmology does
not. There may also be wider-ranging implications for fundamental physics,
black holes and quantum measurement.Comment: 7 pages, 3 figure
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