[neilep (OP)]

Hello,

If the Universe is infinite then I suppose I kinda accept that 'infinity' exists, but if the Universe is expanding and contracting to the point where time stops and starts again then surely the term 'infinite' has no meaning eh ?

So, does 'INFINITY' have any meaning at all in a non infinite Universe ?

You non-infinte answer/comments would be temporarily welcomed.

'Men are the same as women...just inside out !'

[gsmollin]

It should be perfectly obvious that there are no examples of infinity in a finite universe- it's an oxymoron.

Infinities exist in mathematics, and they even come in orders. Outside of that, I can't show you any infinities.

[neilep (OP)]

Well there you go...the obvious was staring me in the face after all...ta

'Men are the same as women...just inside out !'

[OldMan]

You could say the Universe has to expand into something and that something is the infinite.

Tim

[gsmollin]

Well that's the diffculty of it all. When we say "universe" we are encompassing all space. The universe doesn't expand into something, because that something would be part of the universe. We can't talk sense about outside the universe, since if we could, we have just defined another region of the universe.

[OldMan]

Call me evil but I'm going to mess with that idea. [}:)]

What about a multi-verse? Such as a parallel universe, which lets just say exists. If the universe encompasses everything but there is a parallel universe how can it fit into the picture of the universe if it already contains everything?

Sorry just playing devil's advocate. If you hadn't already I'[m sure you'll now realise I don't know squat.

The real problem exists up here in our heads. We need boundaries to measure things and can't work outside them.

Tim

[Quantumcat]

Well, if the universe encompasses everything, why do we talk about it expanding or decreasing?? Surely that can't happen, since there's nothing greater than the universe to compare its expansion to, and if it expands then everything else will expand and we won't be able to see the difference.

So what do they mean about expanding if that can't really happen?

Or can it and I'm just dumb and confused?

Am I dead? Am I alive? I'm both!

[jai]

we talk about infinite things all the time, like numbers. so these are just abstract ideas eh? but then for all the physical proof that we have, surely the universe is just an abstract idea. maybe dragons and fairies really did exist before and we just wiped them out with a new 'idea' (science) about the way things work. maybe we are gods and if we can imagine it it exists? []

all good thoughts, but where does it get us except into a smaller and smaller box? and we all live in a box.

anyne like 'Johnathon Livingston Seagull'?

yes, but.........

[neilep (OP)]

.... Jai are you saying that fairies don't exist ?...tch.!!..next thing you'll be saying is that Santa Claus is a myth too .....presumably 'Johnathon Livingston Seagull' is a book eh ?...is it a recommended read ?.....(3 mins later)...yep checked it out on Amazon...Jai, I'm gonna have to buy that now aren't I ?

'Men are the same as women...just inside out !'

[jai]

yup, very cool, read it when i was 18 and recommended by my father. dont blame me if you dont like it though!!![]

yes, but.........

[TECHFACTOR]

TECHFACTOR: Until someone can prove that Infinity does not exist it Exists;"period".

[lightarrow]

So, does 'INFINITY' have any meaning at all in a non infinite Universe ?

Yes, infinite time of existence.

[lyner]

Surely, 'infinity' is just a construct.
Nothing (no 'thing') can be infinite because you could just add a bit to it.
Why should we want infinity to exist or not? Only a few Mathematicians have got their heads around what is meant by the term. It's bandied about in ignorance, in the same way that  absolute zero, the speed of light and a dozen other terms are used.
It's fair enough to use the term but, if you do, you can't rely on the outcome of any argument involving it if you don't use all the necessary rigour.

[Soul Surfer]

Infinity is a mathematical concept and I do not like using it in physical situations I prefer to use the term indefinite to mean that there is no practical limit to something.  Consider for example a closed, transparent smallish finite universe like the inside of a black hole if you look far enough away you will see again the bit of space that is currently occupied by the back of your head in the remote distance and assuming that millions of years ago your head was not there you could see a lot further beyond that. This is like looking into the space between two parallel flat mirrors where you see many reflections of yourself going of into the distance. eventually what you see will fade into darkness or you will look so far back in time you will get to the cosmic microwave background when the evolving universe was no longer transparent. It is a definite possibility that our universe is in fact smaller than the distance to the CMB but it is quite difficult to detect and prove because things will have changed greatly if (for example) the circular oath round the universe was a few billion years. people are looking to see if it is and there have been some hints that it may be.

[socratus]

Does infinity have any physical parameters?
==========..
The Universe is Infinite Vacuum in the state of T=0K,
 at first of everything. Why? Because it is visual fact.

The Universe as whole is Kingdom of Coldness.
Now the physicists think that this Kingdom of Coldness
in a state of T=2,7K ( after big bang). But if somebody
 belief in “ big bang”, he must take in calculation
that T=2,7K expands and therefore T=2,7K is temporary
parameter and with time it will go to T=0K.
 #
Last August (2007), ground and satellite observations revealed what
appeared to be an enormous "hole in the universe," a mostly empty
region of the sky, 900 million light-years wide - about 5 billion trillion
miles –  http://www.physorg.com/news141317146.html
Where is gravity there? The "hole in the universe " must have zero gravity.
It means these spaces must be in state T=0K.
Only  mass and energy  can warm up the Kingdom of Coldness.
 But the detected material mass of the  matter in the Universe is so small
(the average density of all substance in the Universe is approximately
  p=10^-30 g/sm^3) that it  cannot “ close “ the Universe and therefore
 the Universe  is “ open”, endless and this small mass can warm up the
Kingdom of Coldness only in it some limited and local points.
Therefore astrophysicists  search for “ dark matter” because it will save the
“ law of gravitation “ as a first law of the Universe and it will
warm up the Kingdom of Coldness.
#
The cosmological constant of Universe is  zero or near to it.
This physical quantity cannot “ close” the Universe therefore
 the Universe is endless.
http://en.wikipedia.org/wiki/Cosmological_constant
#
Sakharov's induced gravity: a modern perspective
Authors: Matt Visser (Washington University in Saint Louis)
(Submitted on 19 Apr 2002)
Abstract: Sakharov's 1967 notion of ``induced gravity'' is currently
 enjoying a significant resurgence. The basic idea, originally presented
 in a very brief 3-page paper with a total of 4 formulas, is that gravit
 is not ``fundamental'' in the sense of particle physics. Instead it was
 argued that gravity (general relativity) emerges from quantum field
 theory in roughly the same sense that hydrodynamics or continuum
elasticity theory emerges from molecular physics. In this article I will
translate the key ideas into modern language, and explain the various
versions of Sakharov's idea currently on the market.

Sakharov's induced gravity: a modern perspective
--Matt Visser
http://arxiv.org/abs/gr-qc/0204062
#
The Universe Is Not Expanding Uniformly
A few weeks ago, researchers announced the discovery of a "dark flow"
of invisible matter tugging at distant galaxy clusters at the edge of the
 universe. Now comes more evidence of unseen and unknown forces in
 the cosmos, but this time its closer to home. A group of researchers have
 discovered that our particular part of the Universe — out to a distance
 of 400 million light years — is not expanding uniformly in all directions
 as expected. To be exact, the expansion is faster in one half of the sky than
 in the other. "It's as if, in addition to the expansion, our 'neighbourhood' in
 the Universe has an extra kick in a certain direction," says Mike Hudson
from  the University of Waterloo in Ontario, Canada. "We expected the
expansion to become more uniform on increasingly larger scales, but that's
 not what we found.
" If confirmed, their findings will result in a new understanding of the
 Origin  of structure in the universe and possible revisions to the standard
cosmological  model.    (...)
Read the rest of The Universe Is Not Expanding Uniformly (268 words)
 Source:
http://www.universetoday.com/2008/10/11/the-universe-is-not-expanding-uniformly/
 #
When the next revolution rocks physics,
chances are it will be about nothing—the vacuum, that endless
infinite void.
http://discovermagazine.com/2008/aug/18-nothingness-of-space-theory-of-everything

http://discovermagazine.com/topics/space

#
" The problem of the exact description of vacuum, in my opinion, 
 is the basic problem now before physics. Really, if you can’t correctly
describe the vacuum, how it is possible to expect a correct description
of something more complex? "

  / Paul Dirac ./
#
"Now we know that the vacuum can have all sorts of wonderful effects
over an enormous range of scales, from the microscopic to the cosmic,"

 / Peter Milonni.
from the Los Alamos National Laboratory in New Mexico./
=================…
Best wishes.
Israel Sadovnik. / Socratus.
http://www.socratus.com
http://www.wbabin.net
http://www.wbabin.net/comments/sadovnik.htm
http://www.wbabin.net/physics/sadovnik.pdf

[JP]

The concept of infinity is extremely useful in physics, however.  It often shows up in calculations where the size of what you're looking at is very small compared to something else.  You can often call that something else "infinitely big" without introducing a lot of error. 

At other times infinities show up and signal a place where the theory has a problem.  For example, a classical electron is a point, and the electric field around it goes like 1/r^2.  If you're on the surface of the electron the force becomes infinite.  Quantum theory cleans this problem up a bit.  Likewise, according to general relativity, the center of a black hole is infinitely dense.  I think most physicists assume that a good theory of quantum gravity will somehow explain this in terms of non-infinite things.

[lyner]

Yebbut the Physicist's / Engineer's view may well be too sloppy when the going gets tough. For instance, when two quantities each 'go to infinity', their ratio may well go to zero, another infinity or unity. Treat with care.

[yor_on]

'Men are the same as women...just inside out !'
Neil you are a man of true vision and depth.

[Mr. Scientist]

<font color="blue">Hello,

If the Universe is infinite then I suppose I kinda accept that 'infinity' exists, but if the Universe is expanding and contracting to the point where time stops and starts again then surely the term 'infinite' has no meaning eh ?

So, does 'INFINITY' have any meaning at all in a non infinite Universe ?

You non-infinte answer/comments would be temporarily welcomed.</font id="blue">

<font color="blue">'Men are the same as women...just inside out !'</font id="blue"> [/IMG]

If there is a symmetry in time, (such as a big crunch), then the universe isn't really infinite. If the universe continues to expand, (as it seems to be accelerating now), would mean it would continue to expand for an eternity, unless a big rip occurs in the fabric of spacetime.

[yor_on]

Everything can be infinite.
Take a distance, any distance, half it, half it again and then..
until you run out of breath or numbers.


We do have the Planck size though.

"Max Planck was the first to propose the Planck length, a base unit in a system of measurement he called natural units.
By design, the Planck length, Planck time, and Planck mass are such that the physical constants c, G, and \hbar \  all equal 1 and thus disappear from the equations of physics.

Although quantum mechanics and general relativity were unknown when Planck proposed his natural units, it later became clear that at a distance equal to the Planck length, gravity begins to display quantum effects, whose understanding would seem to require a theory of quantum gravity. Note that at such a distance scale, the uncertainty principle begins to intrude on one's ability to make any useful statements about what is actually happening. "

That seems to draw some kind of border physically in spacetime but, who knows?
http://www.answers.com/topic/planck-length