The Big Bang is not the Beginning of TIme......The latest non-linearcosmology.

Jonathan wrote:



In this context, a new paradigm has been recently proposed by Paul Steinhardt
(Princeton) and Neil Turok (Cambridge) - the cyclic universe - that turns the
conventional picture topsy-turvy. (Perhaps the model should be called an old paradigm
since it reinvigorates ancient cosmic mythologies and philosophies, albeit using the
tools of 21st century physics.) In this picture, space and time exist forever. The big
bang is not the beginning of time. Rather, it is a bridge to a pre-existing
contracting era. The Universe undergoes an endless sequence of cycles in which it
contracts in a big crunch and re-emerges in an expanding big bang, with trillions of
years of evolution in between. The temperature and density of the universe do not
become infinite at any point in the cycle; indeed, they never exceed a finite bound
(about a trillion trillion degrees). No inflation has taken place since the big bang.
The current homogeneity and flatness were created by events that occurred before the
most recent big bang. The seeds for galaxy formation were created by instabilities
arising as the Universe was collapsing towards a big crunch, prior to our big bang.

So if the universe is an infinite cycle of big bangs, meaning that with
infinite big bangs, all combinations of universes that can exist will be
created over and over, an infinite number of times. Meaning that the
current universe has existed before and will exist again in the future
an infinite number of times. Meaning that this earth and everything on
this earth that has gone on in the past and is going on at this very
moment has existed and will exist again, an infinite number of times.
Now that's a scary thought.

Ever wonder whether the Big Bang isn't a trendy or paradigmatic
cosmology? After all, many physicists in the first half of the 20th
century were occupied with building big bangs of a different sort.

Is it possible that we have multiple big bangs, at perhaps the galactic
level but not generally beyond this (never involving all available
matter/energy), and no singular beginning or end to all matter/energy,
but just a bunch of localized recycling?


Jonathan wrote:

The universe as an attractor solution.

s





The Endless Universe:
A Brief Introduction to the Cyclic Universe

Paul J. Steinhardt
Joseph Henry Laboratories, Princeton University, Princeton, NJ 08544, USA

http://wwwphy.princeton.edu/~steinh/cyclintro/

http://wwwphy.princeton.edu/~steinh/


Over the last century, cosmologists have converged on a highly successful theory of
the evolution of the Universe - the big bang/inflationary picture.[1] According to
this picture, space and time sprung into being 15 billion years ago in a `big bang.'
When the Universe emerged, it was filled with particles and radiation of nearly
infinite temperature and density. Instants later, the Universe underwent a period of
extraordinarily rapid, superluminal expansion (`inflation') which made the Universe
homogeneous and flat and which created fluctuations that seeded the formation of
galaxies and large-scale structure.

In the last decades, cosmological observations have supported the predictions of the
big bang and inflationary theory in exquisite detail.[1,5] They have also provided one
major surprise. It appears that, billions of years after the big bang, following the
formation of galaxies, the Universe was overtaken by some form of dark energy that is
causing the expansion rate to accelerate. Although dark energy was unanticipated and
has no particular role in the big bang/inflationary picture, the general view has been
that it can simply be added by fiat to the initial make-up of the Universe. There is
no compelling reason for a new theoretical approach. Quite the contrary, many
cosmologists regard the basic cosmic story as being settled.

In this context, a new paradigm has been recently proposed by Paul Steinhardt
(Princeton) and Neil Turok (Cambridge) - the cyclic universe - that turns the
conventional picture topsy-turvy. (Perhaps the model should be called an old paradigm
since it reinvigorates ancient cosmic mythologies and philosophies, albeit using the
tools of 21st century physics.) In this picture, space and time exist forever. The big
bang is not the beginning of time. Rather, it is a bridge to a pre-existing
contracting era. The Universe undergoes an endless sequence of cycles in which it
contracts in a big crunch and re-emerges in an expanding big bang, with trillions of
years of evolution in between. The temperature and density of the universe do not
become infinite at any point in the cycle; indeed, they never exceed a finite bound
(about a trillion trillion degrees). No inflation has taken place since the big bang.
The current homogeneity and flatness were created by events that occurred before the
most recent big bang. The seeds for galaxy formation were created by instabilities
arising as the Universe was collapsing towards a big crunch, prior to our big bang.

The prospects for an alternative cosmology that is so different from the
well-established convention would seem extremely dim. Yet, the cyclic model recoups
all of the successful predictions of the big bang/inflationary theory and has
sufficient additional predictive power to address many questions which the big
bang/inflationary model does not address at all: What occurred at the initial
singularity? What is the ultimate fate of the Universe? What is the role of dark
energy and the recently observed cosmic acceleration? Does time, and the arrow of
time, exist before the big bang? or after the big crunch?

In the new paradigm, each cycle proceeds through a period of radiation and matter
domination consistent with standard cosmology, producing the observed primordial
abundance of elements, the cosmic microwave background, the expansion of galaxies,
etc. For the next trillion years or more, the Universe undergoes a period of slow
cosmic acceleration (as detected in recent observations[1]) which ultimately empties
the Universe of all of the entropy and black holes produced in the preceding cycle and
triggers the events that lead to contraction and a big crunch. Note that dark energy
is not simply added on - it plays an essential role. The transition from big crunch to
big bang automatically replenishes the Universe by creating new matter and radiation.
Gravity and the transition from big crunch to big bang keep the cycles going forever.
In fact, as will be discussed, the cyclic behavior is a strong attractor. That is,
even if the Universe were disrupted from its periodic behavior, it would rapidly
reconverge to the cyclic solution.

The linchpin to the new paradigm is the transition from big crunch to big bang. The
transition was thought to be an impossible passage in which the laws of physics blow
up. However, recent developments in superstring theory suggest that the cosmic
singularity is otherwise, as the two authors have argued in a recent paper with Justin
Khoury (Princeton), Burt Ovrut (Penn) and Nathan Seiberg (IAS). Superstring theory
relies on the idea that the Universe contains nine or ten spatial dimensions,
depending on the formulation, all but three of which are curled up in a compact
manifold of microscopic size. In this framework, the big bang and big crunch may be an
illusion. Expressed in the usual variables of general relativity, it may appear that
our usual space and time are disappearing. However, viewed with the proper variables,
our usual space dimensions actually remain infinite and time runs continuously. The
transition from big crunch to big bang is due, instead, to the collapse, bounce and
re-expansion of one of the extra dimensions. For example, in a variant known as M
theory, the Universe consists of two branes (surfaces) bounding an extra dimension,
and the singularity corresponds to a collision and bounce of the two branes. The
temperature and density of ordinary radiation and matter remain finite at the bounce,
and particles move continuously in a natural and intuitive way. By dispelling the myth
that the big bang is a beginning of space and time, superstring theory opens up new
possibilities for the cosmological history of the Universe. Six months ago, the
``ekpyrotic model"[4] was proposed by Khoury, Ovrut, Steinhardt and Turok as one new
possibility based on the idea of making a universe from a single collapse of the extra
dimension. The cyclic model builds on lessons learned from the ekpyrotic example to
produce a picture with remarkable predictive and explanatory power.

"Paul Bramscher" wrote in message
...
...
Is it possible that we have multiple big bangs, at perhaps the galactic
level

The phrase "Big Bang" refers specifically to the theory
describing the expansion of the space in which those
galaxies exist and shouldn't be confused with normal
explosions. It is possible to have multiple big bangs
but we are constrained to observing only one since we
are inside it. This paper talks about the possibility,
see in particular the simple diagram on page 11:

http://arxiv.org/abs/astro-ph/0301199

but not generally beyond this (never involving all available
matter/energy), and no singular beginning or end to all matter/energy,
but just a bunch of localized recycling?

That description would fit a supernovae, localised
recycling of a limited amount of matter and energy.
I'm sure you can think of other examples.

George

George Dishman wrote:
Note: follow-ups to sci.astro only, this seems off-topic
for the other groups.

"Bjoern Feuerbacher" wrote in message
...

George Dishman wrote:

"Val Rogers" wrote in message
...


The idea of the universe collapsing and then exploding out again is old
(by your definintion of "old"). It's just a little too much deja'vu when
I hear essentially the same thing all over again.


Bjoern has covered most of your post but I think you may still
not be seeing the key difference in Steinhardt's proposal. I
also missed it from the abstract. In his case the universe
doesn't collapse, it continues to expand. Measurements a few
years ago showed the expansion is accelerating and if that
continues it will become exponential just as early inflation
proposed by Guth many years ago. Steinhardt's proposal is that
the brane collisions of string theory may recur and inject new
energy into the expanding universe. There is no cycle of
expansion/collapse as in the QSSC but continuous expansion at
a cyclically varying rate.

Sorry, but that is *not* a difference. Reading the page
http://wwwphy.princeton.edu/~steinh/npr/, I also thought, like you,
that there is no contraction in Steinhardt's model. But on another page,
http://wwwphy.princeton.edu/~steinh/cyclintro/
he clearly says that there *is* indeed a contraction in his model.


I may be wrong, I skimmed through the "Simplified" paper
http://wwwphy.princeton.edu/~steinh/dm2004.pdf
and though he talks of contraction I got the impression
it was significantly different from QSSC.

Yes, his idea is indeed significantly different from QSSC. I did
not dispute that above. I only disputed your assertion that in his
model, there is only expansion, but no contraction.


The first page also says that the ekpyrotic model is the precursor to
the cyclic model, so apparently they are not the same - but from these
popular-science articles, it is not clear to me if there is contraction
in the ekpyrotic model or not, and if, according to Steinhardt, a cyclic
universe could work without contraction or not.


From the abstract:

"In particular, we show that the contraction phase has equation
of state w 1 and that contraction with w 1 has a surprisingly
similar properties to inflation with w -1/3."

Half way down the second page:

".. we find that there are remarkable, unanticipated parallels
between inflationary expansion and the contracting and bounce
phases of the Cyclic Model."

And in the last paragraph of Section I:

"We focus on the two key ingredients needed to understand the
contracting phase: branes and the equation of state w 1."

Section II starts:

"The Cyclic Model was developed based on the three intuitive
notions:

* the big bang is not a beginning of time, but rather a transition
to an earlier phase of evolution;

* the evolution of the universe is cyclic;

* the key events that shaped the large scale structure of the
universe occurred during a phase of slow contraction before
the bang, rather than a period of rapid expansion (inflation)
after the bang."

So clearly he is describing a period of contraction, but
starting on the second line of page 4 he goes into more
detail and seems to describe something significantly
different from the usual understanding of contraction:

"The universe switches from expansion to contraction. The
branes themselves do not contract or stretch significantly.
Rather, the distance between them shrinks as the two branes
crash together. That is, the contraction only occurs in the
extra dimension between the branes. ...
During the contraction phase, the branes stop stretching
and quantum fluctuations naturally cause the branes to
wrinkle."

I understood that to mean that while the distance betwen
the branes is reducing the scale factor of our universe
(which is one of the branes) remains roughly constant
hence the hypervolume(?) product of separation and volume
would decrease, hence the term 'contraction'.

That seems borne out by his summary in the last sentence
of the third paragraph on the page regarding entropy:

"The simple reason is that the branes themselves do not
contract. Only the extra dimensions contract."

This stuff is really over my head but have I got the gist
or have I misunderstood his model?

Yes, I think you have indeed got the gist. I can't say for sure, since I
did not invest much time so far in studying his ideas, but what
you said above looks consistent with my understanding.


Bye,
Bjoern

"Bjoern Feuerbacher" wrote in message
...
George Dishman wrote:
...
This stuff is really over my head but have I got the gist
or have I misunderstood his model?

Yes, I think you have indeed got the gist. I can't say for sure, since I
did not invest much time so far in studying his ideas, but what
you said above looks consistent with my understanding.

Thanks Bjoern, I'll read the paper a few
more times and see how much I can glean.

best regards
George