### Is There a Place Outside the Universe? If So, What Is It?

*Question posed by Lain*.

This is one of those questions that brings up untold numbers of other questions. First of all, you might want to ask how big is our universe? A lot of people think that our universe is infinite in extent, so if that's the case how can there be anything outside it?

It's kind of tricky to think about these things, so a good trick* is to bring things down a level or two. Now, you know that the universe we can wander around in is three- dimensional; that is, it has three directions we can head in. These are left/right, up/down and forwards/backwards**.

Let's make it simpler by imagining a two-dimensional universe. The best way to do this, I think, is to imagine (or actually grab) a sheet of paper. The surface of this sheet of paper is two-dimensional: stickpeople in this two dimensional world can only travel forwards/backwards or left/right. Up/down is completely lost on them, and they can't even tell it exists. If you had an infinite sheet of paper, it'd spread out in all directions in the two dimensions of the paper, and as far as the stickpeople were concerned, it's never ending, so how can there be anything outside it?

We know, though, that there's a third dimension we can play with. We can stack sheets of paper in the up/down direction too, but each of these two-dimensional paper universes can have no idea that any of the others are there at all, because they're stuck in two dimensions. We're stuck in three dimensions. Maybe there's another direction that we don't know about, that we can't see or even comprehend.

There's another possibility, too: we know that the normal laws of our universe break down when the kinds of forces that are found in a black hole come into play. Some scientists have suggested that the centres of black holes could be birthing places for entirely new universes, with these 'baby' universes taking on some of the characteristics of our own universe, with slight, random differences. A sort of 'natural selection' with universes rather than monkeys.

It's also possible that our infinite universe contains within itself other infinite universes. Sounds weird, doesn't it? How could something, even an infinite something, contain other infinite things? Try thinking about it like this:

- There are an infinite number of counting numbers, right? 1, 2, 3, 4, ... , eighty billion, ... , fourteen googol, ... Whatever number I give you, you can always add one on to that.
- What about odd numbers? 1, 3, 5, 7, 9 and so on... If I give you an odd number, you can always find another, bigger one by adding on 2. So there's an infinite number of odd numbers. But this is itself contained within the 'universe' of whole numbers.
- There's another infinity contained inside the infinity of whole numbers: the even numbers.
- There's also the infinite set of square numbers, of prime numbers...

I'm waffling a bit. The real answer to your question is that we don't know: we don't know if there's anything out there***, and if there is, we don't know what it is. One of the most captivating ideas is that of other universes: some may be similar to ours, but others may have wildly different physical laws! Gravity and electromagnetism may be stronger, or weaker, or entirely absent; protons and neutrons may have entirely different properties; some may be indistinguishable from our own except that you had your eggs scrambled last Thursday morning, rather than fried.

Here's an idea to keep you awake tonight: There are four fundamental forces of nature: the strong force; the weak force; the electromagnetic force; and the gravitational force. The gravitational force plays a central role in the way the universe works due to it's long range, but it is relatively weak. One reason that has been put forward for this is that the gravity we experience does not originate in our universe, but is leaking through from other universes that are nearby in some other dimension.

And lastly, another fantastic thought experiment:

If the universe is infinite in extent, and the amount of matter in it is also infinite, but (and this is the crucial bit) the number of different types of things that the matter is made out of**** is

*finite*, this has an interesting consequence: If you define a section of the universe, you only have a finite amount of matter in it. If you look at other sections of the universe that are the same size, you might find that you have roughly the same amount of matter in it, and the general make-up of that matter is pretty similar, but it's all put together in different ways. There are*lots*of ways of putting this matter together, but not an*infinite*number. If the universe*is*infinite, eventually you're going to have to reuse the same pattern. This means that, if our universe*is*infinite, and the amount of matter in it*is*infinite, and the number of types of building block is*finite******, then if you travel far enough (in any direction) you will eventually come across an*exact copy*of our section of the universe. An*exact copy*of our solar system. An*exact copy*of Earth.
And an

*exact copy*of you.* And by 'trick' I mean 'useful simplification'. There are certain anti-science types who'll leap on words like that because they don't really understand what they mean.

** Given a sensible frame of reference. Such as sitting where you are right now.

*** I've just surprised myself by discovering that I don't appear to have written anything about the Great Attractor, which sort of fits in with this post in that it may have relevance to ways of discovering things that exist outside our universe. Remind me about it some time. Oooh, there's also something I read about the possibility of detecting 'scars' in the cosmic microwave background radiation of the universe. Scars that may be evidence of collisions with other universes...

**** e.g. atoms: If there's only a finite number of possible

*types*of atoms, but an infinite number of each type.

***** This all seems like it might be true for our universe, by the way.

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