Logically why the universe cannot be infinite in size.

**donnydarkoIRL** · 10-04-2007 10:28 AM

My friend a psychologist keeps urgin me to record all my dreams for her studies. But i started to forget and she was able to tell that i was making them up from prvious patternns!

**brucelee** · 10-04-2007 02:25 PM

so I must be making up those dreams. I have read somewhere that when someone dreams about flying, it means he wants to have sex.hehehe.

**donnydarkoIRL** · 10-04-2007 02:27 PM

I don't really no much about it. Sometime id like to get one of those dream interpretation books, but i don't have the inclination at the moment.

**Bomp** · 10-04-2007 09:54 PM

The big bang theory is incompatible with an infinte universe. It is widely accepted nowdays that the universe is not infinite, it was discredited a long time ago by a logical thought experiment.

It was assumed some time ago that the universe was infinite, this was because if it wasn't infinite, then it would collapse in on itself due to gravity. So it was postulated that the universe was infinite (and also almost uniform in distribution to prevent to much variance in mass at different regions, which would also cause many smaller collapses).

However, IF the universe was infinte in size AND unifrom, then the sky as we look at it would be INFINITELY bright. The explanation for this is that if you consider imaginary spherical shells of all different sizes with earth at the centre of them, and the surface area of each of these shells is determined by 4*pi*radius(squared) (radius being the unifrom distance of the shell fromthe earth) : Then, since the universe must be uniform, then the amount of stars on each shell must be proportional to
the distance from earth (i.e. the shells radius) squared.

Following on from this, when you take into account the physical relationship that the intensity of radiation decreases inversely proportional to the distance from the source squared(i.e. once again the radius of the shell squared), then it must be concluded that the amount of radiation coming from each shell must be equal, no matter how far away the shell is. Since the amount of radiation coming from each shell is finite, and that there are an infinite number of shells, then the radiation wacking the earth every second would be infinte.

The big bang theory originally came about to counter this by trying to explain the fact the universe is expanding, and not collapsing in on itself as it would if it were finite.

However, since then, even crazier shit have been hypothesized (but not proved) such as anti-gravity to take into account the expanding universe.

**brucelee** · 10-05-2007 03:38 AM

the question is how finite is the universe?where does it stop? if it is finite then it is improper to call it "universe".

**Punisher136** · 10-05-2007 04:40 AM

Think of the universe as a bunch of marbles (galaxies). Those marbles can move in any direction and there's almost no limit to where they can move. Because of their existance tho, space has to curve around them or the physics aspect would be off and it would be unbearable pressure making life or the moving of anything nearly impossible. It can expand and contract with the movement of galaxies but at any given time it does have a definite size that is too large to be measured by humans. Like I said before, this edge wouldn't physical exist but it is more or less a spot of high gravity where you can't move any further.

**Bomp** · 10-05-2007 09:02 AM

Yeah, there's loads of crazy shit when you look into general relativity and all that. Truth is, the universe doesn't work as simply as we see everyday things happen, when you take into account giant masses and the invariance of the speed of light. Even if the universe is finite, you would never actually be able reach the 'edge' of it, it is thought if you set out in a 'straight' line and kept going indefinitely, you could end up where you started due to curved space and all that.

**Punisher136** · 10-05-2007 09:26 AM

Originally Posted by Bomp

Yeah, there's loads of crazy shit when you look into general relativity and all that. Truth is, the universe doesn't work as simply as we see everyday things happen, when you take into account giant masses and the invariance of the speed of light. Even if the universe is finite, you would never actually be able reach the 'edge' of it, it is thought if you set out in a 'straight' line and kept going indefinitely, you could end up where you started due to curved space and all that.

I'm not a fan of string theory, but I believe einstein was on the right track when he had relativity and most of the space-"time" stuff.