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From: Hal Finney <hal.domain.name.hidden>

Date: Wed, 8 Jan 2003 16:07:47 -0800

Paul Steinhardt, one of the original cosmic-inflation theorists and the

man who coined the term "quintessence" has a new theory of cosmology

which is described at http://arxiv.org/abs/astro-ph/020447. The abstract

reads,

The Cyclic Model is a radical, new cosmological scenario which

proposes that the Universe undergoes an endless sequence of epochs

which begin with a `big bang' and end in a `big crunch.' When the

Universe bounces from contraction to re-expansion, the temperature

and density remain finite. The model does not include a period of

rapid inflation, yet it reproduces all of the successful predictions

of standard big bang and inflationary cosmology. We point out

numerous novel elements that have not been used previously which

may open the door to further alternative cosmologies. Although

the model is motivated by M-theory, branes and extra-dimensions,

here we show that the scenario can be described almost entirely in

terms of conventional 4d field theory and 4d cosmology.

The theory does not actually have a "big crunch" in the traditional sense;

rather, after a long period of expansion so that there is less than one

particle in each visible segment of the universe, a hidden dimension

contracts and suddenly the universe is full of light and energy, and it

starts expanding again. There is no inflation as in the regular model,

instead the long period of expansion from the previous cycle is what is

responsible for the remarkable uniformity that is observed.

The interesting aspect from this list's perspective is how to regard

infinite-time cosmologies. Does it make sense to imagine a universe

which has had an infinite past? How could we simulate that on a computer,

if there were no starting point?

I think Steinhardt's model also allows for a spatially infinite, flat

universe as well. So we have infinities in all directions, temporal as

well as spatial.

We could avoid the problem by postulating that every cycle in Steinhardt's

model is identical, giving the effect of a single universe, but I don't

think there is any reason in the theory to suppose that would happen.

Rather, each crunch is slightly different, and these small perturbations

carry over into unique initial conditions for the next big bang.

How could we go about modelling a universe like this? Can we rule out

Steinhardt's cosmology on fundamental principles? Are infinite-time

universes of zero measure compared to ones with a fixed beginning?

It would be interesting if the everything-exists model could be used to

constrain cosmological theorizing in this way.

Hal Finney

Received on Wed Jan 08 2003 - 19:16:08 PST

Date: Wed, 8 Jan 2003 16:07:47 -0800

Paul Steinhardt, one of the original cosmic-inflation theorists and the

man who coined the term "quintessence" has a new theory of cosmology

which is described at http://arxiv.org/abs/astro-ph/020447. The abstract

reads,

The Cyclic Model is a radical, new cosmological scenario which

proposes that the Universe undergoes an endless sequence of epochs

which begin with a `big bang' and end in a `big crunch.' When the

Universe bounces from contraction to re-expansion, the temperature

and density remain finite. The model does not include a period of

rapid inflation, yet it reproduces all of the successful predictions

of standard big bang and inflationary cosmology. We point out

numerous novel elements that have not been used previously which

may open the door to further alternative cosmologies. Although

the model is motivated by M-theory, branes and extra-dimensions,

here we show that the scenario can be described almost entirely in

terms of conventional 4d field theory and 4d cosmology.

The theory does not actually have a "big crunch" in the traditional sense;

rather, after a long period of expansion so that there is less than one

particle in each visible segment of the universe, a hidden dimension

contracts and suddenly the universe is full of light and energy, and it

starts expanding again. There is no inflation as in the regular model,

instead the long period of expansion from the previous cycle is what is

responsible for the remarkable uniformity that is observed.

The interesting aspect from this list's perspective is how to regard

infinite-time cosmologies. Does it make sense to imagine a universe

which has had an infinite past? How could we simulate that on a computer,

if there were no starting point?

I think Steinhardt's model also allows for a spatially infinite, flat

universe as well. So we have infinities in all directions, temporal as

well as spatial.

We could avoid the problem by postulating that every cycle in Steinhardt's

model is identical, giving the effect of a single universe, but I don't

think there is any reason in the theory to suppose that would happen.

Rather, each crunch is slightly different, and these small perturbations

carry over into unique initial conditions for the next big bang.

How could we go about modelling a universe like this? Can we rule out

Steinhardt's cosmology on fundamental principles? Are infinite-time

universes of zero measure compared to ones with a fixed beginning?

It would be interesting if the everything-exists model could be used to

constrain cosmological theorizing in this way.

Hal Finney

Received on Wed Jan 08 2003 - 19:16:08 PST

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