how big is the universe?

I'm having trouble understanding just how big the universe is.

Many people I talk to seem to think (assuming, for example, that the
universe is 13 billion years old)- that it's 13 billion light years in
radius- that we can almost see back to the edge- of course there is no edge
and that's all about lookback time and the "observable universe", not
current reality and distances.

Assuming that Guth's theory of inflation is more or less true- I vaguely
remember reading in some "popular" astronomy book that the universe inflated
to a size much bigger than the observable universe- so that the O.U. is a
tiny little part of the total universe. If this is the case, how could we
know how big it is? And, I've seen some recent cosmology writing implying
that it is infinite. I can understand the suggestion that if space will
continue to get bigger forever- that it is "open"- but I can't equate open
with infinite. I think when some astronomers say infinite, they don't mean
to imply infinite as we non scientists think of it.

Anyways, I find this all very fascinating. It's tough enough to imagine that
the universe may be 10-15 billion light years to the "edge"- but to ponder
that this observable universe may only be a tiny part of a much bigger
inflated universe really pushes me over the edge. G

But, I'm rambling- if the universe is much bigger than the observable
universe- how could we ever know how big it is? And, when astronomers try to
determine the total mass- do they mean the total mass of the observable
universe or the total universe, and does it make a difference?

One last bit of rambling- I have this crazy idea that if we can ever figure
out what dark matter and dark energy is- not only will all of that contain a
vast amount of information- similar to the way that electromagnetic energy
contains info- but that such discoveries will cause a quantum level advance
in the physical sciences- so important that it will be a milestone in human
evolution.

JZ

There was a nice piece of work that hit the news recently (I don't
have a link to the paper right now) that analyzed the scale of
background fluctuations in the CMB to try to set a limit on the size
of the universe.

The reasoning was that if we see fluctuations at all scales, the
universe should be infinite or very, very large. The fluctuations
were caused by what were essentially sound waves echoing back and
forth across the early universe before it inflated (I think that is
right) when all regions were communicating with all others. Like
sound in an organ pipe, if the universe had a particular size then
some vibration modes would be preferred over others, leaving a
characteristic fingerprint. On the other hand, if the univers was
infinite there would be no preferred mode and all frequencies would be
present.

The answer they got was surprising to me. The fluctuations cut off
above a certain scale, which they calculated implied a current size of
around 70 billion light years. So according to their results the full
universe is bigger than the observable universe, but not a whole lot
bigger. The observable universe is a sizable fraction of the whole,
which I find surprising.

This is new work and it may not hold up, but it was nicely done and if
it stands it will have deep implications for inflation and a host of
other theories that want the universe to be orders of magnitude larger
than the observable universe.

Ed Gibbs

There was a nice piece of work that hit the news recently (I don't
have a link to the paper right now) that analyzed the scale of
background fluctuations in the CMB to try to set a limit on the size
of the universe.

The reasoning was that if we see fluctuations at all scales, the
universe should be infinite or very, very large. The fluctuations
were caused by what were essentially sound waves echoing back and
forth across the early universe before it inflated (I think that is
right) when all regions were communicating with all others. Like
sound in an organ pipe, if the universe had a particular size then
some vibration modes would be preferred over others, leaving a
characteristic fingerprint. On the other hand, if the univers was
infinite there would be no preferred mode and all frequencies would be
present.

The answer they got was surprising to me. The fluctuations cut off
above a certain scale, which they calculated implied a current size of
around 70 billion light years. So according to their results the full
universe is bigger than the observable universe, but not a whole lot
bigger. The observable universe is a sizable fraction of the whole,
which I find surprising.

This is new work and it may not hold up, but it was nicely done and if
it stands it will have deep implications for inflation and a host of
other theories that want the universe to be orders of magnitude larger
than the observable universe.

Ed Gibbs

"Ed Gibbs" wrote in message
...
There was a nice piece of work that hit the news recently (I don't
have a link to the paper right now) that analyzed the scale of
background fluctuations in the CMB to try to set a limit on the size
of the universe.

The reasoning was that if we see fluctuations at all scales, the
universe should be infinite or very, very large.


When astronomers use the term "infinite" in this context, what do they mean?

"Ed Gibbs" wrote in message
...
There was a nice piece of work that hit the news recently (I don't
have a link to the paper right now) that analyzed the scale of
background fluctuations in the CMB to try to set a limit on the size
of the universe.

The reasoning was that if we see fluctuations at all scales, the
universe should be infinite or very, very large.


When astronomers use the term "infinite" in this context, what do they mean?

I think when they say "infinite" they mean just that - goes on forever
and ever without end.

That is distinctly different from very, very large - which implies
that it is finite, though possibly so large that it appears for all
intents and purposes to be infinite.

There are also finite but unbounded - a universe that could be very,
very large (not infinite) but has no edge - say a 4 dimensional sphere
that you can go around to come back to where you started, as you can
on the surface of the earth.

Then there are things like perpetual inflation, which posits that our
very, very large big bang universe is one of an enormous and
constantly growing (though quite possibly finite) number of big bang
universes.

And then there are the really crazy theories...;-)

Ed Gibbs

Joe Zorzin wrote in message ...
When astronomers use the term "infinite" in this context, what do they mean?

I think when they say "infinite" they mean just that - goes on forever
and ever without end.

That is distinctly different from very, very large - which implies
that it is finite, though possibly so large that it appears for all
intents and purposes to be infinite.

There are also finite but unbounded - a universe that could be very,
very large (not infinite) but has no edge - say a 4 dimensional sphere
that you can go around to come back to where you started, as you can
on the surface of the earth.

Then there are things like perpetual inflation, which posits that our
very, very large big bang universe is one of an enormous and
constantly growing (though quite possibly finite) number of big bang
universes.

And then there are the really crazy theories...;-)

Ed Gibbs

Joe Zorzin wrote in message ...
When astronomers use the term "infinite" in this context, what do they mean?

http://www.forestmeister.com

"Ed Gibbs" wrote in message
...
I think when they say "infinite" they mean just that - goes on forever
and ever without end.

And there is actually some logic to this, that the universe may be infinite
in the common sense? I can see it as a philosophical speculation, but can it
be derived from a scientific model? I'm non scientist, so I'm not arguing
against- actually, I find the idea fascinating- but I'm trying to get a
grasp on what it means, scientifically. Since the universe was once very
small, and as it grew, it must have been finite- how does something go from
being finite to infinite? Or, does the model say that it was infinite from
the beginning, and what does that really mean? I've read some speculation
that our big bang was something that occured withing some bigger framework,
which perhaps is infinite, so in that sense, I can sort of "get it".




That is distinctly different from very, very large - which implies
that it is finite, though possibly so large that it appears for all
intents and purposes to be infinite.

Either way, it's mind blowing- to think of all the stuff out there, that if
knew about it we'd be shocked. We need to somehow, eventually, learn about
what's out there, otherwise we are very provincial indeed. (I don't like the
word "indeed", but sometimes I use it when I'm in awe. G)



There are also finite but unbounded - a universe that could be very,
very large (not infinite) but has no edge - say a 4 dimensional sphere
that you can go around to come back to where you started, as you can
on the surface of the earth.

OK, I can get that one- that's easy by comparison.




Then there are things like perpetual inflation, which posits that our
very, very large big bang universe is one of an enormous and
constantly growing (though quite possibly finite) number of big bang
universes.

And then there are the really crazy theories...;-)

No doubt if our civilization continues for centuries, each generation will
push the envelope, each discovering more amazing stuff than the last. I find
this to be wonderful, the bigger and more outrageous the better- from a
philosophical point of view.

Now, if only somewhere out there is some civilization that has been around
for millions of years, which has done a "Comparative Study of Evolution on a
Galactic Scale" and the follow up "Compartive Study of Civilizations on a
Galactic Scale". Then of course, an even more advanced civilization will do
a compartive study across galaxies. And, somewhere out there is the most
advanced, the smartest, of all that may have a deep understanding of the
universe on a scale larger than their respective "visible universe". My
theory, from a dummy's point of view, is that when we have a better
understanding of dark matter and dark energy, somehow there is a lot of
infomation contained therein, that could tell us a lot about a big chunk of
the universe, maybe beyond "the edge" of the visible universe- such as the
"large scale structure" too big for us to see- structures so big that from
within any given "visible universe" you could see only a small part of it.



Ed Gibbs

Joe Zorzin wrote in message
...
When astronomers use the term "infinite" in this context, what do they
mean?

http://www.forestmeister.com

"Ed Gibbs" wrote in message
...
I think when they say "infinite" they mean just that - goes on forever
and ever without end.

And there is actually some logic to this, that the universe may be infinite
in the common sense? I can see it as a philosophical speculation, but can it
be derived from a scientific model? I'm non scientist, so I'm not arguing
against- actually, I find the idea fascinating- but I'm trying to get a
grasp on what it means, scientifically. Since the universe was once very
small, and as it grew, it must have been finite- how does something go from
being finite to infinite? Or, does the model say that it was infinite from
the beginning, and what does that really mean? I've read some speculation
that our big bang was something that occured withing some bigger framework,
which perhaps is infinite, so in that sense, I can sort of "get it".




That is distinctly different from very, very large - which implies
that it is finite, though possibly so large that it appears for all
intents and purposes to be infinite.

Either way, it's mind blowing- to think of all the stuff out there, that if
knew about it we'd be shocked. We need to somehow, eventually, learn about
what's out there, otherwise we are very provincial indeed. (I don't like the
word "indeed", but sometimes I use it when I'm in awe. G)



There are also finite but unbounded - a universe that could be very,
very large (not infinite) but has no edge - say a 4 dimensional sphere
that you can go around to come back to where you started, as you can
on the surface of the earth.

OK, I can get that one- that's easy by comparison.




Then there are things like perpetual inflation, which posits that our
very, very large big bang universe is one of an enormous and
constantly growing (though quite possibly finite) number of big bang
universes.

And then there are the really crazy theories...;-)

No doubt if our civilization continues for centuries, each generation will
push the envelope, each discovering more amazing stuff than the last. I find
this to be wonderful, the bigger and more outrageous the better- from a
philosophical point of view.

Now, if only somewhere out there is some civilization that has been around
for millions of years, which has done a "Comparative Study of Evolution on a
Galactic Scale" and the follow up "Compartive Study of Civilizations on a
Galactic Scale". Then of course, an even more advanced civilization will do
a compartive study across galaxies. And, somewhere out there is the most
advanced, the smartest, of all that may have a deep understanding of the
universe on a scale larger than their respective "visible universe". My
theory, from a dummy's point of view, is that when we have a better
understanding of dark matter and dark energy, somehow there is a lot of
infomation contained therein, that could tell us a lot about a big chunk of
the universe, maybe beyond "the edge" of the visible universe- such as the
"large scale structure" too big for us to see- structures so big that from
within any given "visible universe" you could see only a small part of it.



Ed Gibbs

Joe Zorzin wrote in message
...
When astronomers use the term "infinite" in this context, what do they
mean?

Joe Zorzin writes:

http://www.forestmeister.com

"Ed Gibbs" wrote in message
...
I think when they say "infinite" they mean just that - goes on forever
and ever without end.
[...]
Since the universe was once very small, and as it grew, it must have been
finite- how does something go from being finite to infinite?

It can't, and it doesn't.


Or, does the model say that it was infinite from the beginning, and what
does that really mean?

See http://www.astro.ucla.edu/~wright/infpoint.html.


-- Gordon D. Pusch

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