Question of infinite

Great Debates
1

Two questions really in this one…

First, as I understand it, if the density of the Universe is higher than the critical density, the universe will collapse in a Big Crunch some time in the future. If the density of the universe is less or equal to the critical density the universe will continue to expand forever, i.e. the universe is infinite. That brings me to my first question, taking the second option as fact (the universe will expand forever) that means the universe currently has an ‘edge’ which means it is not infinite, but since we know it will expand forever it IS infinite.

So, really the question is, Is the universe infinite now, or will it become so. And how can you become infinite? Either something is or is not without end…if it is becoming infinite, wouldnt that make it infinite now?? a paradox? or am I missing something?

Secondly, assuming an infinite universe, could one then assume that given infinite time, that anything is possible? i.e. say God? would it be possible in an infinite universe that at some time everything came together to create a ‘person’ that is omnioptent and all powerfull? And that, that person created, or will create, others? Or if God is not a good example lets take superheros. A stretch I know, but bear with me.

If in a infinite univers there are infinite possiblites than would it not mean that the chance of someone being born with the ability to say, control the weather be possible? If time continues could not all the right things converge at some point to create somone or something like that??

Any opinions would be welcome!

2

An open universe can be infinite or finite. If it is finite, it will always be finite; if infinite it will always be so.

I don’t think it is reasonable to assume that an infinite universe and infinite time imply that anything is possible.

3

It is not possible that 1 + 1 = 2 and 1 + 1 = 3, no matter how much time and space you have.

4

First, as far as we know, the universe doesn’t have an “edge”. It’s not expanding INTO anything. Everything is just getting farther apart.

Consider the set of all integers ( … -3, -2, -1, 0, 1, 2, 3 … ). It’s infinite, right? Now multiply it by two. The new set ( … -6, -4, -2, 0, 2, 4, 6 … ) is just as infinite as the old one, but everything is twice as far apart.

The expanding universe is like that .

So there’s no “becoming infinite”. It is infinite. It has always been infinite. It will remain infinite.

Consider the volume of the visible universe, about 10 billion light years. Think of this as a bubble. In an infinite universe there will be an infinite number of these “bubbles”. But within any finite volume there can only be a finite number of ways that you can arrange matter and energy. Which means that the universe must necessarily contain some “bubbles” that are identical to each other.

So there’s a very good chance that somewhere an unimaginably far distance away there an exact copy of me typing exactly these same words … .

But the fact that SOME arrangements of matter and energy MUST repeat doesn’t mean that they ALL do. And furthermore, some might never occur at all. Some arrangements are certainly prohibited by the laws of physics, even if we can imagine their existence.

As far as we know, the Theory of Relativity prohibits “faster than light travel”. I suspect that the Second Law of Thermodynamics prohibits the existence of an “omnipotent being”.

While future discoveries might change our understanding of the structure underlying the universe, we do know that SOME rules must exist, and therefore that SOME arrangements of matter are impossible.

So, no, an infinite universe is not a proof for the existence of God … .

5

The most common view of the universe that I’ve come across is that the universe is finite, but unbounded. Basically, this means that if you went far enough in one direction, you’d come back to where you started, due to the curvature of space. Think of it as analogous to the surface of the Earth. There’s a finite surface area on Earth, yet there are no boundaries - traveling in a straight line brings you back to where you started. That’s the 2D case. Now expand that into 3D (don’t try to visualize it - that’s impossible). While the surface of the earth is the 2D surface of a 3D sphere, the expanded case would be the 3D “surface” of a 4D hypersphere. Though to be more accurate, I believe the current leading theory is that the universe is shaped like the surface of a hypertorus, not a hypersphere. So we basically live in a giant, 4D donut. Or something like that.

The point is, finite space doesn’t necessitate an “edge”, or some infinite void into which we’re expanding. The universe doesn’t expand “into” anything, it just expands. The question “what’s outside the universe” is meaningless, because the universe is, by definition, everything.
Jeff

6

Even though I am a believer myself, I think I’ll have to say no to this one; by most definituions, God is also omnipresent, so the universe would not only have to contrive to give rise to him somewhere, it would have to do so everywhere.

7

Just to clairfy my position, I wasnt expounding that a infinite universe = God, but that in an infinite universe would it stand that there are a infinite number of possibilities. So anything would be possible regardless of how it might seem to us.

8

No, in an infinite universe not [everything would be possible], but [everything possible would be expected].

9

Where exactly does the idea of an infinite universe come from? Surely a Big Bang would lead to a finite expanding universe?

10

or to put it another way, in infinite throws of a six-sided dies, it would (probably, I’m not actually sure of the math) be expeced that you would eventually throw a six, but regardless of the number of tries, you would never throw a seven.

11

Probably, although it is important to remember that the big bang (supposedly) happened everywhere at once, rather than at a point in space that already existed, because the big bang is (supposedly) the origin of space itself.

It isn’t that a particle blew up and created matter, it is that space and time came into existence and started expanding.

12
13

bah…the post above should finish with…

I like that quote, puts my question into good context.

thanks!

14

The dice example is a good one to explain the difference btw 6 and 7.

But I think there’s a flaw which means it’s not necessarily applicable to your above statement.

If there the dice has infinitely many sides 1,2,3… you get a situation where the probability of each outcome is 0, though some one must occur.

This can mean that if you throw an infinite number of them, the expected no. of 1s is still 0.

I don’t know if this crops up in the real world, but the maths is definitely valid iirc. (anyone wanting an explanation of measure theory, please ask)

15

The math doesn’t work there, unless you’re willing to assign non-equal probabilities to rolling each number. You can’t have a uniform distribution on a countable set.

16

Ah, but I am willing to assign non-equal probabilities to each number :slight_smile:

Seriously :smack: I wrote too quickly and glossed over too much, and it’s too late at night to explain measure theory from scratch.

In an infinite universe doesn’t necessarily mean everything possible is to be expected, is right, right? Can you explain it, you’ve seen the goof-up I’ve made :slight_smile:

17

In an infinite universe, the probability that a particular possible event doesn’t happen approaches 0 as time keeps going. So in all likelihood, anything that’s possible will happen, but the less likely a particular event is, the less money you’d want to put on its happening in a given timeframe.

18

Since the visible universe is expanding at the speed of light, any particular photon will never reach the edge of the observable universe- this means the visible universe is effectively infinite also.
It doesn’t contain any other versions of you though- not a big enough infinity.

SF worldbuilding at
http://www.orionsarm.com/main.html