🚀 go-pugleaf

> The article in yesterdays Oregonian (from the Chicago Tribune News Service)
> about Stephen Hawking's talks in Chicago, left me with several questions.
> 
> 	1)    "One of the revolutionary consequences of the
> 		inflationary universe model is that there may be
> 		more than one universe; there may be an infinite
> 		number of universes."
> 
> I take it that the inflationary universe is the balloon example that was
> given here within the last couple of months.  

No, that was a two-dimensional analogy of the "current" (Hot Big Bang) model.

> But why and how can there
> be more than one universe?

Well, on the other hand, why not?  None of the current speculations (oops --
I mean, theories) provides any way to detect their existence, or allow
communication, or whatever.  A really *neat* theory, in the view of modern
cosmologists, in one that CAN NEVER BE TESTED by observation; as such, it is
immune to disproof.  Of such things is tenure made ...

> 	2)	 "Some funny things will happen when the universe
> 		begins to collapse.  The direction of time will be
> 		reversed and the past will become the future..."

Hardly.  The "past" is fixed in concrete, while the future is probabilistic,
according to current physics.  That's unlikely to change -- unless we were
to go from an uncertain past into a pre-determined future ... ulp ... maybe
we should leave it alone ...

> 		  "An observer on a space ship in the recollapsing
> 		would see things going in reverse, from disorder to
> 		order..."
> 
> Somehow it seems that even if/when the universe begins to collapse, we
> will still be going "forward" in time, regardless of whether things are
> going from order to disorder or disorder to order.??
> Max Guernsey

I'm sure you're right.  The whole business of the "laws of thermodynamics"
is in interpretive quicksand, in my view.  The "laws" were derived from a
tiny time-slice of a vast, evolving universe, and are expected to be valid
under all possible evolutions.  Maybe, but I doubt it.  Like the inverse
square law of gravity, which breaks down at very tiny distances (the nifty
"singularity" of mathematical description) we're likely to find the "laws
of thermodynamics" become invalid, and need "correction" when we get too
far from the environment in which they were derived.

The sky *will* get bright at night, though, just before the end ...

-- 
Ed Nather
Astronony Dept, U of Texas @ Austin
{allegra,ihnp4}!{noao,ut-sally}!utastro!nather
nather%utastro.UTEXAS@ut-sally.ARPA

In article <2649@tekig.UUCP> maxg@tekig.UUCP (Max Guernsey) writes:
>The article in yesterdays Oregonian (from the Chicago Tribune News Service)
>about Stephen Hawkings talks in Chicago, left me with several questions.

(The remaining text of his article appears at the end of this one.)

I was at the talk Hawking gave here on campus.  I will try to clarify
some things that were skipped over in the news story you read.  I am
putting his talk a little bit out of order here, but I still have the
outline correct, I believe.

The inflationary universe model allows for multiple universes in
the sense that there can be disjoint sections of the universe
which are still separated by regions in the "false vacuum" state.
The false vacuum, you will recall, expands exponentially with time.
Thus *if* the universe still consists of "bubbles" of the true
vacuum surrounded by false vacuum, then the bubbles can be thought
of as separate universes, although each would have a boundary.
Most workers in the field would prefer a situation in which new
bubbles of true vacuum are formed early enough and fast enough
that the bubbles all merge together and the entire universe enters
the "true vacuum" state.

The remainder of your question is more difficult and Hawking's
exposition left me unconvinced (or, if you prefer, baffled).
His first point was that there are three "arrows of time".

	1. The thermodynamic arrow - closed systems change
	   from states of more order to states of less order.

	2. The psychological arrow - what we remember is the
	   past and what we do not remember is the future.

	3. The cosmological arrow - the universe was smaller
	   in the past and is getting larger.

He asserted without proof that the thermodynamic arrow determines
the psychological arrow.  I can believe this but I couldn't prove
it.  Then he went into a discussion about boundary conditions and
their relation to the thermodynamic arrow of time.  His point seemed
to be that when we start our laboratory systems off in an ordered
state we are in effect imposing an initial condition but no final
condition on the evolution of the system, thus imposing our arrow
of time on the system beforehand.  In principle we could ask ques-
tions about systems which ended in an ordered state, or ones which
both began and ended in ordered states.

He then went on to discuss closed cosmological models -- models in
which the universe will eventually recollapse.  He proposed that
the most elegant boundary conditions for such a universe are that
it should have no boundary at all.  This requires that spacetime
should be "smooth" at the beginning AND AT THE END.  To have low
entropy at the end means that the universe, which is disordered now,
will have to later become more ordered.  In this way he ties together
the cosmological and the thermodynamic arrows of time.  By the
connection with the psychological arrow it would follow that our
subjective flow of time would turn backwards to correspond with the
reversed thermodynamic arrow.

If you understand what that would be like, please explain it to me!

-------------------------------------------------------------------
>	1)    "One of the revolutionary consequences of the
>		inflationary universe model is that there may be
>		more than one universe; there may be an infinite
>		number of universes."
>
>I take it that the inflationary universe is the balloon example that was
>given here within the last couple of months.  But why and how can there
>be more than one universe?
>
>	2)	 "Some funny things will happen when the universe
>		begins to collapse.  The direction of time will be
>		reversed and the past will become the future..."
>
>		  "The reason, again, is the second law of
>		thermodynamics..."
>
>		  "An observer on a space ship in the recollapsing
>		would see things going in reverse, from disorder to
>		order..."
>
>Somehow it seems that even if/when the universe begins to collapse, we
>will still be going "forward" in time, regardless of whether things are
>going from order to disorder or disorder to order.??
>
>
>Max Guernsey
>maxg@tekig4
_____________________________________________________
Matt		University	crawford@anl-mcs.arpa
Crawford	of Chicago	ihnp4!oddjob!matt