Friam

Physics question

Classic

List

Threaded

4 messages Options

Mike Oliker

Physics question

Physics Question: How did the early universe avoid collapsing into a single
black hole? The gravity must have been immense. Why, in fact, wasn't the
initial particle the ultimate black hole?

-Mike Oliker

Douglas Roberts-2

Physics question

I recommend this

*The First Three Minutes: A Modern View of the Origin of the Universe*
http://www.amazon.com/gp/product/0465024378/103-6054335-2612634?v=glance&n=283155

as an excellent lay-level introduction to cosmology for answers to questions
like that.

--Doug

On 12/11/05, Mike Oliker <mike.oliker at comcast.net> wrote:

>
> Physics Question: How did the early universe avoid collapsing into a
> single
> black hole? The gravity must have been immense. Why, in fact, wasn't the
> initial particle the ultimate black hole?
>
> -Mike Oliker
>
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at Mission Cafe
> lectures, archives, unsubscribe, maps at http://www.friam.org
>

--
Doug Roberts
505-455-7333 - Office
505-670-8195 - Cell
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://redfish.com/pipermail/friam_redfish.com/attachments/20051211/d91a69cd/attachment.htm

Martin C. Martin

Physics question

In reply to this post by Mike Oliker

It's been a long time since I looked at physics, and I never really
studied cosmology. But my interpretation is that it was basically taken
as a premise of the big bang theory that the universe starts out as a
point (or at least really, really small) with a large "explosion" velocity.

So: just as a projectile can leave the earth if it moves fast enough, so
the universe doesn't collapse into a black hole because it was expanding
fast enough.

Of course, this doesn't take into account the relativistic effect that
time differences and distance differences can be different for different
observers, and that velocities are relative, which was only exacerbated
by extreme gravity in the early universe. But I think it's still
basically true.

- Martin

Mike Oliker wrote:

> Physics Question: How did the early universe avoid collapsing into a single
> black hole? The gravity must have been immense. Why, in fact, wasn't the
> initial particle the ultimate black hole?
>
> -Mike Oliker
>
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at Mission Cafe
> lectures, archives, unsubscribe, maps at http://www.friam.org

Russell Standish

Physics question

Your explanation, whilst poetic and stimulating, is not really
correct, and probably misleading. The problem is thinking of the big
bang as occuring at a point in space, and of the universe's particles
having an escape velocity. The escape velocity of the universe is
greater than the speed of light (nothing can escape the universe by
definition), and I'm not sure that it can be meaningfull to talk about
escape velocity of the initial singularity, as it is not a point in
space, but a point in spacetime (aka event).

The simplest way of understanding the universe's evolution from
General Relativity (our current best theoretical description) is
through the Friedman model. The Friedman model has constant curvature,
which is related to a parameter known as the fraction of critical
density, written \Omega.

\Omega < 1 corresponds to a universe that expands forever.
\Omega=1 corresponds to a universe that expands forever, but
asymptotically approaches a static solution with everything at
infinity from everything else. \Omega > 1 implies that gravity
overwhelms the universes expansion, leading to the "Big Crunch". How
long this takes, depends on how large \Omega is. Mike Oliker's
scenario can only happen if \Omega >> 1.

Astronomical measurements indicate that \Omega is very close to 1 for
our universe. However, the most recent results show the universe's
expansion to have started accelerating around 1 billion years ago, a
fact that's in contradiction with the Friedman model, and requires an
additional term \Lambda (the Cosmological constant) that Einstein
originally added to GR to make a static solution possible, to be
regretted by him as his "greatest blunder" later on. Somewhat ironic,
don't you think.

Cheers

On Sun, Dec 11, 2005 at 07:45:31PM -0500, Martin C. Martin wrote:

> It's been a long time since I looked at physics, and I never really
> studied cosmology. But my interpretation is that it was basically taken
> as a premise of the big bang theory that the universe starts out as a
> point (or at least really, really small) with a large "explosion" velocity.
>
> So: just as a projectile can leave the earth if it moves fast enough, so
> the universe doesn't collapse into a black hole because it was expanding
> fast enough.
>
> Of course, this doesn't take into account the relativistic effect that
> time differences and distance differences can be different for different
> observers, and that velocities are relative, which was only exacerbated
> by extreme gravity in the early universe. But I think it's still
> basically true.
>
> - Martin
>
> Mike Oliker wrote:
> > Physics Question: How did the early universe avoid collapsing into a single
> > black hole? The gravity must have been immense. Why, in fact, wasn't the
> > initial particle the ultimate black hole?
> >
> > -Mike Oliker
> >
> >
> > ============================================================
> > FRIAM Applied Complexity Group listserv
> > Meets Fridays 9a-11:30 at Mission Cafe
> > lectures, archives, unsubscribe, maps at http://www.friam.org
>
> ============================================================
> FRIAM Applied Complexity Group listserv
> Meets Fridays 9a-11:30 at Mission Cafe
> lectures, archives, unsubscribe, maps at http://www.friam.org

--
*PS: A number of people ask me about the attachment to my email, which
is of type "application/pgp-signature". Don't worry, it is not a
virus. It is an electronic signature, that may be used to verify this
email came from me if you have PGP or GPG installed. Otherwise, you
may safely ignore this attachment.

----------------------------------------------------------------------------
A/Prof Russell Standish Phone 8308 3119 (mobile)
Mathematics 0425 253119 (")
UNSW SYDNEY 2052 R.Standish at unsw.edu.au
Australia http://parallel.hpc.unsw.edu.au/rks
International prefix +612, Interstate prefix 02
----------------------------------------------------------------------------