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Ognik
2010-Apr-07, 02:39 AM
Question of infinity always get me thinking in circles.....

Assuming an open/infinite universe with an average density, this surely implies an infinite mass? IE an infinite number of atoms. However can we then have an infinite number of compounds, given that one of the possible combinations would be all atoms combined.......

I suspect I have some holes in my understanding :-) - any ideas out there?

grapes
2010-Apr-07, 03:33 AM
Assuming an open/infinite universe with an average density, this surely implies an infinite mass? IE an infinite number of atoms. However can we then have an infinite number of compounds, given that one of the possible combinations would be all atoms combined.......So by the combination, you mean all atoms in the universe in a single molecule?

Even if you had a finite number of atoms, you could still end up with an infinite number of combinations--you just couldn't make them all. :)

WayneFrancis
2010-Apr-07, 06:34 AM
yup, in an infinite universe with infinite mass you could have an infinite number of different compounds technically but I'm unsure what the issue you are having is?

I mean I understand some people being confused that in a infinitely large universe there a very high probability that there are an infinite number of you running around. Heck in an infinite universe there is a non zero chance that a dead adult you might form from a individual atoms in cosmic cloud of material. I say dead because I'm not sure that a live you could form.

In an infinite universe anything that can happen does happen.

grapes
2010-Apr-07, 02:25 PM
In an infinite universe anything that can happen does happen.Well, there still might be limits.

For instance, in an infinite universe of Just Iron, you're kind of limited to the possibilities. The same may apply here, or in any infinite universe, in principle.

WayneFrancis
2010-Apr-07, 03:23 PM
Well, there still might be limits.

For instance, in an infinite universe of Just Iron, you're kind of limited to the possibilities. The same may apply here, or in any infinite universe, in principle.

But that is it. In an infinite universe of just Iron anything can happen in a universe of Iron will happen.

I'm not saying in an infinite universe of nothing something will happen that requires something of the universe that it can not provide. I'm saying in a infinite universe what ever can happen in that universe will happen.

For example if the universe was infinite and there was only 2 helium atom in the whole universe then the universe will only allow certain things to happen. I agree there are limits but it is only dicated by what that universe can do. Not saying something like "If our universe is infinite then the entire universe will turn to solid gold" that isn't something our universe can do as far as we know.

Shaula
2010-Apr-07, 04:04 PM
The universe has unpleasant things like stars and hot gas that tend to ionise and bust up complex molecules. There is a sort of sweet spot where complex molecules form - the gas must be dense enough to give atoms a good chance of meeting, there must be enough UV/IR around to generate free radicals or give the atoms enough KE to overcome the activation energy barrier, the cloud must be fairly stable to allow time for the right collisions to happen and so on. Complex molecules tend to grow by addition IIRC, so you have a dynamic equilibrium where they are forming and being broken up all the time. The practical upshot is the the probability of two huge molecules forming is low, as is the probability of them meeting in the right condition to react to form a larger molecule. The odds of this happening twice and then the two products meeting to make an even larger molecule are tiny - and so on, and so on.

So while in theory you could have an infinite number of compounds the odds of this happening are so tiny (and negative feedback mechanisms like stars don't help) that it would probably take infinite time to happen. And the problem there is that we are not 100% sure the bound proton is stable over infinite time (some GUTs propose that it decays). So it is possible that by the time all combinations could have been made there aren't any protons left...

grapes
2010-Apr-07, 11:46 PM
But that is it. In an infinite universe of just Iron anything can happen in a universe of Iron will happen.

I'm not saying in an infinite universe of nothing something will happen that requires something of the universe that it can not provide. I'm saying in a infinite universe what ever can happen in that universe will happen.

For example if the universe was infinite and there was only 2 helium atom in the whole universe then the universe will only allow certain things to happen. I agree there are limits but it is only dicated by what that universe can do. Not saying something like "If our universe is infinite then the entire universe will turn to solid gold" that isn't something our universe can do as far as we know.I wasn't trying to make something non-iron occur in the iron universe. :)

I was just pointing out the limit of the logic. In your 2 helium atom universe, you could say "the two atoms will meet" but if the two atoms are headed in opposite directions (at greater than atom escape velocity of course) they will never meet. Just the ability to describe an occurence doesn't guarantee it will occur. Even in an infinite universe, the parameters have to be set right.

I mean I understand some people being confused that in a infinitely large universe there a very high probability that there are an infinite number of you running around. Heck in an infinite universe there is a non zero chance that a dead adult you might form from a individual atoms in cosmic cloud of material. I say dead because I'm not sure that a live you could form.

In an infinite universe anything that can happen does happen.See, how do we know what can happen in an infinite universe? These things are complicated.

violentquaker
2010-Apr-08, 01:21 AM
I wasn't trying to make something non-iron occur in the iron universe. :)

Would that be... ironic? :dance:

01101001
2010-Apr-08, 04:29 AM
At some point, some monster molecules are going to face up to their own gravity and stop having the ability to have an arbitrary chemical structure.

violentquaker
2010-Apr-08, 04:39 AM
At some point, some monster molecules are going to face up to their own gravity and stop having the ability to have an arbitrary chemical structure.

I would need to look at the math on this one before I believed you... wouldn't it be possible for a molecule of sufficiently low density to grow infinitely large without the force between any given constituent atoms growing without bound?