[Krisa (OP)]

[] Hi friends. Well, I know that the question about infinity of the Universe is quite hard and maybe unanswerable, but here it is. My own opinion is that the Cosmos is NOT infinite in time or dimensions. Let's start discussion.
You're welcome.

[qpan]

Well, i agree- the universe is not infinite in dimension (according to currenty accepted theories). If the big bang theory holds true, then the universe is currently a finite size and still expanding (as it started as a singularity at the time of the big bang).
Whether or not time is infinite depends on a number of factors- one is the value to omega - the ratio of the universe's mass to the critical mass of the universe. This factor accounts for whether the universe will continue expanding forever or whether the mass is large enough for gravity to pull the universe into a "big crunch." If the latter scenario occurs, them time will be finite and will stop at the big crunch. I could, of course be drastically wrong - but it depends on your definition of time.If another big bang occurs after the big crunch, then time will continue, but that could be classed as a "new" time as it may or may not happen in this dimension (due to our universe disappearing into a singularity at the big crunch and a new singularity forming at the beginning of the next big bang). Maybe.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[MayoFlyFarmer]

I'd like to reemphisize qpan's point taht it depends on your definition of time. (when it stops, and when it ends)  even if you believe in the big bang... what was before it.  The same could be said for space, whats your definition of space? even if you believe in a finite size of the universe, which there IS pretty strong evidence for, whats beyond THAT?
Remeber that for something to be infinate it must not only have no end, but no beginning.

When 900 years you reach look as good you will not, hmm??

[Krisa (OP)]

The teory of the big bang is probably true. Some people think that that is a reason for finite size of the universe. But mathematicians find out that there is an another probabiliy. The universe could begin his life with big bang, but in the moment of its "birth" it was already infinite.
Check it out.
KRISA

[qpan]

Well, people always ask what lies beyond the finite universe, and thats one of the justifications they use for saying that the universe must be infinite. They usually see it as some sort of barrier which cannot be traversed (such as a brick wall encasing our whole universe).

What about looking at the universe differently? We are currently living in a 3D world (lets ignore time for this argument). To simplify the problem so that we can visualise it, lets reduce the number of dimensions to 2, so that we are now completely flat and live on a plane, much like a large piece of paper. What happens if the plane (large pice of paper) is now taken by a 3d person and made into a curve? Its actually very hard for us 2D people to tell- just as it took a long time for people to discover that the earth was not flat. People had initially pondered what was beyond the edge of the earth. But we all know that there is no edge to the earth - it is a sphere.

Many scientists consider the universe to be "spherical" 4(+) dimensional bubble. Consider once again for a 2D person living on the surface of a 3d sphere. If they travel in any direction far enough, they will return to the same point. If the sphere was a balloon, and a 3d person blew it up, the whole 2d universe would expand. So if we all lived on the surface of an expanding 4D hypershere, then theoretically, there is nothing beyond the edge of the universe, as there is no edge of the universe (you simply reappear at the other end, so to speak). This is of course assuming that this dimension is curved, which would actually be extremely hard for us to tell due to the shear size of the universe (just as it was hard for our ancestors to tell that the earth was curved, but on a FAR larger scale!).

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[Krisa (OP)]

Yes you're right, if we want to have a right look about universe, we must for the first talk about geometry of the universe. We don't know exactly that universe has spherical geometry so here is first problem. The question is, if there is any coincidence between geometry and infinity or finity.
Think about this - if the universe is infinite there must be infinite stars, infinite solar systems, infinite solar systems same as ours, infinite Earths, infinite people, infinite myselfs, and so on...
Strange, I dare say.

KRISA

"Quod scripsi, scripsi"

[qpan]

There is one way to prove that space is curved, however, although it is rather difficult due to the large size of the universe and relatively small curvature.
If you draw a triangle on a flat piece of paper, the sum of the angles must add up to 180 degrees. However, if you draw a triangle on a sphere, its angles will add up to be greater than 180 degrees. For example, you stand at the north pole. You travel down due south from the north pole (in any direction as long as it is straight) until you hit the equator. You then turn 90 degrees and travel due west until you travel 1/4 of the way around the world. You then turn 90 dgrees again and travel due north to the north pole. The triangle you just navigated contains 3 right angles!



Now, if we could just draw a big enough triangle...

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[MayoFlyFarmer]

Yes but regardless of the geometrical shape of the universe (or anything for that matter, there must be (at least to my minds bounds) be something beyond it.  The earth is shperical, yet we can escape it.  We just have to travel perpendicular to its plane.

When 900 years you reach look as good you will not, hmm??

[Donnah]

Perhaps infinity is the natural state and things that are seen as finite are merely at the "edge" of our current perception.

[roberth]

I think wormholes were developed in the imagination of Gene Roddenberry. I also think that space is nothing, so when it ends, it's still nothing, so it doesn't end. It's neither finite nor infinite.

[tweener]

There is other evidence that the universe is not infinite.  If there were an infinite number of stars distributed throughout an infinite sized universe, the whole night sky should be as bright as the sun.  This is because any direction you looked would be looking at the surface of a star, and the light would have had an infinite amount of time to reach your eye.  Because the sky is dark, we know that this "infinite" and "static" universe cannot exist.

String theory postulates that the universe is comprised of 11 dimensions, three of which are large, one of which is time, and the rest are extremely small.  All the particles are formed by "strings" vibrating around and in these small extra dimensions.  It's an interesting concept, but has no experimental evidence yet.

----
John - The Eternal Pessimist.

[roberth]

If you've ever looked at the night sky when there is no surface light, it does appear to be covered in stars. Maybe not as bright as the day sky, but the stars are considerably further away than the sun. Look at the amount of light from the sun that reaches Pluto, for example. The sun is a mere speck in the sky. If the universe is finite, what's at the end? Nothing? Space? I don't believe our definitions of finite or infinite cover space.

[chris]

quote:Originally posted by qpan
...the triangle you just navigated contains 3 right angles!

Wonderful thought, but this isn't really a triangle is it ?

Chris

"I never forget a face, but in your case I'll make an exception"
 - Groucho Marx

[qpan]

Well the shape is called a spherical triange - its consists of you making a shape by going in 3 straight lines (all beit on a curved surface) and does contain 3 angles, not sure whether it is truely classed as a triangle though.

quote:Originally posted by MayoFlyFarmer

Yes but regardless of the geometrical shape of the universe (or anything for that matter, there must be (at least to my minds bounds) be something beyond it.  The earth is shperical, yet we can escape it.  We just have to travel perpendicular to its plane.

When 900 years you reach look as good you will not, hmm??

Mayofarmer- you say that we can escape the earth - that is because the surface of the earth is 2d while we are 3d beings and so are able to travel perpendicular to the plane.
To travel in a plane perpendicular to the surface of a 4d hypershere would require that you yourself are a 4d entity!!!

Geometry does matter when talking about what is beyond the edge of the universe, as if you travelled in a straight line forever and the universe is indeed in the shape of a 4d hypersphere, then rather than meeting the edge of the universe at some point in time, you will return to the same point even though you have not reversed direction!

quote:Originally posted by tweener

There is other evidence that the universe is not infinite.  If there were an infinite number of stars distributed throughout an infinite sized universe, the whole night sky should be as bright as the sun.  This is because any direction you looked would be looking at the surface of a star, and the light would have had an infinite amount of time to reach your eye.  Because the sky is dark, we know that this "infinite" and "static" universe cannot exist.

----
John - The Eternal Pessimist.

I'm afraid i don't think this can be used as proof that the universe is not infinite.

Even if the universe is not infinite, there would still be enough stars to fill the night sky without leaving even a patch of darkeness.

However, (i did not postulate this reasoning - saw it on the christmas lectures a while back) space is not a complete vacuum - there is space dust and interstellar hydrogen, amongst other things in between. Light from stars which are extremely far away need to travel vast distances, and there is usually enough interstellar hydrogen or space dust in between to completely absorb the light.

If you think about it, how many stars are there in our galaxy? Many billion billions (i think). And how many can we see in the sky at night? (i haven't counted, but not as many - and thats counting many of the "stars" which are actually galaxies)

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[MayoFlyFarmer]

regardless of the shap, and how many dimensions it has, every shape/structure has bounds, or else it is NOT a shpe/structure.  Therefore there must be SOMETHING beyond it.  I'm not saying that our "universe" is infinite.  But there must be an infinite "something" beyond it.  And I still thing you can escape it.  you can escape our 2D surface by traveling in a 3rd dimension.  If you need to escape a 4D universe, you just need to figure out a way to travel in a 5th dimension.  We jus (obviously) don't know how yet.

BOW DOWN TO THE LORD OF THE FLIES!!!!

[Kryptid]

Here are some things to consider:

*If the Big Bang happened, then the universe could not possibly be infinite in expanse, unless it expanded at infinite speed from the time of the Big Bang. From our observations, the universe is expanding at a FINITE speed. Therefore, the universe MUST be finite if the Big Bang ever happened.

*If the Big Bang DIDN'T happen, then it COULD be infinite. However, it could also be finite.

*The universe could not have always existed. If the universe were infinitely old, then everything in the universe would be at maximum entropy right now. Yet, entropy is NOT at a maximum yet, so the universe has a finite age.

[qpan]

Mayo- the surface of a 4d hypersphere is 3d, just as the surface of a 3d sphere is 2d, so we would need to be able to travel in the 4th dimension to escape from the surface of a 4d hypersphere.

Its not a matter of finding out how to travel in the 4th dimension - its not actually possible to travel in a 4th spatial dimension.

quote:Originally posted by MayoFlyFarmer

regardless of the shap, and how many dimensions it has, every shape/structure has bounds, or else it is NOT a shpe/structure.

I disagree. I don't think you see my point. Something can be finite and not have a boundary - take the surface of a sphere - try and find the boundary of that for me. If the universe is the surface of a 4d hypershere, then it too will have no boundaries. No boundaries means there doen't need to be something beyond the boundary.

"I have great faith in fools; self-confidence my friends call it."
-Edgar Allan Poe

[MayoFlyFarmer]

the SURFACE of the sphere has no boundary, but the SPHERE itself has boundaries or else it would be an infinately big shapeless object.
Also, if a 4th dimension exists, I believe there must be a way to travel in it, why else would we be able to travel in the other 3?  One dimension in which we can't travel out of 4 is not a very good patern, and nature tends to follow patterns

BOW DOWN TO THE LORD OF THE FLIES!!!!

[OldMan]

quote:Originally posted by Supercryptid

Here are some things to consider:

*If the Big Bang happened, then the universe could not possibly be infinite in expanse, unless it expanded at infinite speed from the time of the Big Bang. From our observations, the universe is expanding at a FINITE speed. Therefore, the universe MUST be finite if the Big Bang ever happened.

*If the Big Bang DIDN'T happen, then it COULD be infinite. However, it could also be finite.

*The universe could not have always existed. If the universe were infinitely old, then everything in the universe would be at maximum entropy right now. Yet, entropy is NOT at a maximum yet, so the universe has a finite age.

Isn't Dark Matter what is theorised to be outside the universe? And in it for that matter?

[tweener]

qpan, I agree that what I posted is not "proof" that the universe is finite.  It is a sticky question if one it trying to argue that the universe is infinite and static.  I agree with you fully that the universe may be finite and unbounded.

If a 2D being looks at a circle, they see an entity that they cannot see into from any angle.  It is completely closed to them.  We, as 3D entities can see the whole inside of the circle because we see it from another dimension that is not available to the 2D being.  When we look at a sphere, we see an object that we cannot see into from any angle - it is completely closed to us.  A 4D entity can look at a sphere and see the whole inside at once because they can look into the sphere from another dimension not available to us.  The 4D being can construct a 4D hypersphere that we would perceive as what? The universe?

----
John - The Eternal Pessimist.