Expert: Tom Whiting - 8/21/2008

Question
I was reading a book yesterday and it was talking about how space is
expanding and we can tell that it is still expanding because we measure the
redshifts. It also talked about the three different end of the universe models,
how one is flat, one is that the universe collapses backward onto itself and
the other was that it expands until every star dies. What I don't understand
is, if space is expanding.. what is it expanding into? Is there another layer of
space where there is room for it to grow? I mean if you put a sponge into a
glass of water, it will only expand as far as the limits of the glass allow it to.
Is there a limit to space expansion? I mean we can't expand into nothing? We
have to be expanding into some alloted space or are we stealing area from
other universes with our expansion? Is the area available for our expansion
infinite?

Answer
Hi Raechel,
Well, you're combining some real science (stuff that's testable,
observable, we can develop hypotheses, draw conclusions, etc.)
with some items that are only philosophical (NOT testable, not
observable, etc) where I can only offer my humble opinion,
and you've also mixed in a little fantasy or science fiction too,
or what is thought by many to be pure fiction.

So let's get started.  Yes, our Universe is expanding, not because
of redshift, but since it is expanding, we can use a redshift
measurement as a measurement of distance (the highest rung on
the astronomical distance ladder, therefore the least accurate,
percentage-wise).  But your book is behind the times; a recent
study of Type Ia supernova indicates that our current Universe is
not only expanding, it's accelerating it's spacial expansion as time
goes by.  (And appears to be doing so, forever onward). See
http://flux.aps.org/meetings/YR03/APR03/baps/abs/S2290.html

Realize it's just the space expanding, or more accurately the
space-time continuum (Einstein's Relativity, circa 1917)
and not the matter. Kind of like an empty canoe going down a fast
flowing mountain stream, faster and faster, that's how to look
at the distant galaxy clusters and how they are receding from us and from each other.


What's it expanding into?  {An identical question would be, what
existed just prior to the Big Bang?}  Honest answer is...we don't
know. Maybe we never can know. (Even science cannot know the unknown, as Mr. Spock stated on a past TV Startrek show).
Currently, this is a philosophical question asked by many,
but it's not scientific because no data, no observations, can be made.)
But your expanding sponge in water in a container like a glass is not
an applicable analogy.  A better analogy perhaps....our recent
ancestors of the 19th century believed that light just HAD to have a
medium to travel on, because how could something travel...on nothing?  For a while, they even "invented" a medium in space called "ether" in all of space, because light just HAD to have something to travel on. Today of course, we know that light needs nothing to travel on, in fact it goes it's fastest in space where there is no resistance, like in air and water. In a similar fashion, who says that our Universe has to be expanding into 'something'?

Like light, there is no requirement for that 'something' to exist.  How do I picture it?  Prior to the Big Bang, in my mind there existed the "Primordial Void"...(or Primeval Void)...no space, no time, no matter, no energy, no nothing....and that's the same "thing" or more appropriately, the same 'nothing'.....that our Universe is expanding into. It's just a large undefined 'volume' that contains no space, no time, no matter, and no energy, no dark matter, and no dark energy, in effect, absolutely nothing. And probably extends forever, or so far out exponentially, that for us, it may as well be....to infinity. So yes, we can, and probably are,
expanding with greater and greater acceleration, into nothing.
Just my opinion of course, I cannot subtantiate it...it just keeps
me from lying awake at nights... ;-)

The idea and suggestion that 'other' Universes exist, is pure
speculation and fantasy.  Most of us feel that it is in the realm
of science fiction. In any event, that's another proposal that there
is no data, no observations, available to test, so in any event,
it's a philosophical question and has no basis in science.
(People get that idea from watching too many Sci-fi programs on TV).

So going back to your book, that's old information that the Universal
expansion will eventually come to a halt, and collapse on itself. That ain't gonna happen now....ie, the Big Crunch...is out.

So there are only 2 models remaining...the Universe eventually suffers a "heat" death after all the stars use up their available
hydrogen fuel some trillions of years from now, and be a huge distance apart, or
The Big Rip...spacial expansion accelerates to the point of eventually ripping whole galaxy clusters apart (the expansion component force eventually over-rides weak gravity force more and more), eventually ripping singular galaxies apart, and finally ripping whole Solar systems apart, and finally molecules and even atoms apart. But this event is also trillions of years from now.
Looks like it will be either one or the other, or both.
{Another outside theory is that the proton is unstable, with a half-life of something like 10 to the 32 power years, but that is
much farther out than hundreds of trillions of years, so it's doubtful that we can progress out to that many years.}
Hope this helps,
Clear Skies,
Tom Whiting
Erie, PA