What is the universe?

Question

If the universe is an expanding sphere than in what space is it expanding? Is there space beyond the universe? Is it more logical to think the entirety of existence is in our universe or that there are more expanding spheres out in the same space? Am I using an extreme over-simplification in referring to the universe as simply an expanding sphere?

Answer 1

It is probably an over-simplification to think of the universe as an expanding sphere, but I don't know how else to think of it.

Often used is the analogy of a surface of a balloon, in which the universe has therefore been reduced to two space dimensions. As the balloon expands, the 'size of the universe' (the surface area) expands. I shall call it the 'ballooniverse'.

Note that the 'big bang' sounds like the end rather than the beginning of a ballooniverse, so I think it must started by a 'big blow'.


Every point we see seems to be receding from us. That doesn't mean we are in the 'center' - in fact there is no centre. Every point in the ballooniverse has the same view, of things rushing away from it. This matches our experience of the real universe.

The fact that there actually is no center within the ballooniverse; that also matches what they say about the real universe.

If the balloon has expanded fast enough, light from the far side of the ballooniverse has not had time to reach us, and so it is presently invisible to us. We believe that this also matches the real universe.

If we travel in a straight line in any direction, the shape of the ballooniverse leads us back to our starting point. I don't know if this is supposed to be true for our real universe!, but I know that it has been postulated.

Even though the balloon has only two dimensions, it is expanding in three dimensions. You can imagine that our own universe might therefore be expanding in four dimensions, but I have no idea what that might mean.

The success of the analogy in so many areas leads me to believe that it is a good one. That doesn't make four-space-dimensional thinking any easier for me, however!

With regard to your other questions, you can see that there might be other ballooniverses that are either separate to our own, are enclosed by it or are enclosing ours. It boggles the mind to extend those different concepts to our own universe. Needless to say, we can have no contact with these other universes. Unless...the universes actually intersect in a plane (or a line ,for a ballooniverse). Who could have thought that cosmology could be so interesting? Oh well - lots of people, I guess :)

Answer 2

An expanding sphere is a good analogy. I'll continue with it if you don't mind.

The expanding sphere analogy is 'correct' in the sense that the universe is expanding. However you have to think of our universe not as the sphere itself but analogous to the surface of the sphere.

A two dimensional being who's universe is the surface of an expanding sphere would say - I can tell the universe is expanding, but where is it expanding to? We as three dimensional beings would answer into the third dimension. The two dimensional beings would say - what's that? I understand mathematically, but come on, that's just a numerical trick....

Same thing. We are the three dimensional surface of a 4 dimensional hypersphere. Our universe is expanding "into" the fourth dimension in the same way the surface of the sphere expands into the third.

The mistake in your analogy was thinking our universe is the sphere itself rather than the surface of the sphere. "Where" is not someplace you can point to or reference using only three spacial dimensions.

Here's the really trippy part - according to general relativity, the 4th dimension that our universe is expanding into is time. Yep, the math works whether the fourth dimension is physical or temporal.

Answer 3

In order to understand, stop thinking about a sphere. Universe is not an expanding sphere. That it expands means that everything is getting more distanced. Instead, think of an elastic band that is stretching in all 4 dimensions.
As your life is expanding day after day (so is time, being created day by day), so is space.

To answer your question: space is the same as time.

Answer 4

Are you over-simplifying... yes... but to even come close to understanding, we need to over-simplify. First of all... the distances we are talking about boggle the mind, farther than even light travels in a billion years, so we can forgive the over-simplification.

Current theories hold that the universe is expanding. They also theorize that if you traveled in one direction far enough, you'd eventually get back to where you started... think of the universe being stretched on the surface of a balloon...

As for other universes... no one knows. There are theories abounding, but unfortunately there is no known way to test the theories.

cheers! Any further questions let me know!

Answer 5

Actually, i think it's more conceptual than anything. And since i don't think we will ever be able to measure the universe and end our curiosity, i wouldn't lose any sleep over that. If it is forever expanding, even if we did develope a tool to measure it(highly unlikely), we would never get an accurate measure. Maybe it is everything, and everything is within it. And as it grows, it creates more space that was previously nonexistent. It's mindboggling if you really try to analyze it, but I view it as an Idea moreso than a physical and tangible entity.

Answer 6

First stop thinking of the universe as a sphere.The universe is expanding into time.Time and universe coexist. Time started when the universe was born. There is no space beyond the universe. Universe includes all matter and energy.

Answer 7

I don't think anyone is really qualified to answer this. lol. But then again, our universe may also be contracting. Objects large in mass and close to each other are attracted to each other. (centripetal force). So maybe we are collapsing. As much as I would like to imagine other Universes out there. I don't think we will ever meet someone/thing from over there since technology (nor humans) will ever reach such a great invention. Then there will be non-believers who won't want it. It's easier just to believe what the bible says.

Answer 8

# everything that exists anywhere; "they study the evolution of the universe"; "the biggest tree in existence"
# population: (statistics) the entire aggregation of items from which samples can be drawn; "it is an estimate of the mean of the population"
# everything stated or assumed in a given discussion