if the universe is infinite how can it expand or decrease in size,?

Question

Ive also read that the universe is the shape of a doughnut,how is that "infinite" and if it is getting bigger or smaller whats it getting bigger in

Answer 1

You have to be a bit careful using words such as 'size' when you talk about 'infinity'. The simplest definititon of 'infinity' is that it's 'large without bound'. The set of all integers, for example, is infinite because no matter how big an integer you write down, I can always add 1 to it to get a still bigger integer.

Since the observable Universe is currently believed to have begun about 12 to 14 billion years ago in what is called the 'Big Bang' the real question (in cosmology) is simply, "What was there -before- the Big bang?" And this is really equivalent to your question about how the Universe can expand if it's already infinite. The answer is that the 'observable' Universe is finite, but it is expanding and will continue to expand (so far as we know) without limit. And nobody really knows anything about what it is expanding *in*. There are some interesting theorys and suspicions, but nothing is known with anything like scientific certainty.

As for the Universe being 'doughnut shaped', there are (when last I heard) 12 dimensions to physical reality and it's entirely possible that, in a 12-D space, a 4-D projection of some 'doughnut like' shape might look like a sphere. Certainly the shadow (projection) of a 3-D doughnut onto a 2-D surface 'looks like' a sphere if the doughnut is thick enough and held so that it's edge on to the light source.


Doug

Answer 2

That's actually not 'unanswerable' as some people have put. Its always the non-scientific types who rush to say that something is unknowable - why? Go to the philosophy room to babble such nonsense!

To answer your question, the universe is not infinite, if it was, then obviously it could not expand or even decrease in size because infinity cannot shrink to a finite size - if you think of it logically it will make sense. Standard theory is that the universe is about 13.8 billion light years across. Now if it were expanding 'in to' anything - (generally thought that its not) but if it was, imagine a higher dimensional space that WAS infinite, it would only be our local spacetime bubble (a bubble 13.8 billion light years across) that was getting bigger.

As for the doughnut shaped universe what that really means is what happens at the edge. If you have a piece of paper and you call that the universe imagine flying off the edge, many scientists suggest rather than meeting a white fence saying 'EDGE OF UNIVERSE' you might end up on the other side. To visualise that effect you could stick that end of the paper with the opposite side. What if you go off the paper the other way? To visualise that you'd have to stick the 2 ends of the cylinder together - If you can imagine it what you have with your piece of paper is the shape of a doughnut. You're right that you cant have an infinite 3-torus (what scientists call the shape) though because if the universe was infinite there'd be no edge to cross.

regards!

Answer 3

You're right; both things can't be true.

But it depends on what you mean by 'the universe', and on what you mean by 'infinite'.

Mathematicians and Philosophers use these terms differently, and Physicists are deliberately vague about which definition they are using (in order to make their discoveries seem more exciting)

The 'infinity' that mathematicians use just means 'incalculably large' (because if you can't see the end of a number, then it might as well go on forever). In Maths, you can divide 1 by infinity, and end up with an infinite number of infinitely small divisions between 0 and 1.

But for Philosophers, 'infinity' really IS endless. Infinity, by definition, CANNOT fit between 0 and 1; even infinitely small things would go on FOREVER if there were to be an infinite number of them.

No 'thing' can go on forever, so outside anything in the universe there MUST be an endless amount of NOTHING (because nothing else can be truly endless, and everything else is finite).

However, this would lead to a boringly ambiguous universe without any 'big bang', nor any 'time dilation', and where mathematics can't provide any 'grand unified theory', because we don't have enough information, and we can't tell how much of our information is UNRELIABLE.

Answer 4

Cosmologists do no longer think of the universe is going on "perpetually." modern-day questioning is that the universe is finite yet unbounded. IE the Universe has no edges or obstacles, yet there's a maximum distance aside 2 gadgets could be in the Universe. So in case you travelled in a as we communicate line, you will possibly in no way hit an edge, yet you may at last get returned to the place of the place you began. there is not any "outdoors" the Universe. And, for besides the fact that reason, the area between each element in the Universe is slowly growing to be extra desirable. How it quite is occurring is every person's wager, inspite of the undeniable fact that it skill that throughout the time of approximately a hundred billion years our Galaxy would be crusing on my own by an interestingly empty cosmos, the different galaxies having receded into the area so far that they are going to be invisible. None of it "is clever," however the Universe is under no criminal duty to conform with our concept of what's clever. And all of this continues to be debatable, cosmology by no skill claims to have all of it found out. A destiny Einstein may be able to come alongside and %. up the place he left off.

Answer 5

We know that the universe is expanding due to red shift which proves that the distance between galaxies are expanding.
What it is expanding into; nobody knows, its just 'nothing' or dark matter...
there is also a theory that rather than the universe having an end it just joins up with itself into a sort of ring shape; or doughnut shape.
you want something that will really give you a headache though: the universe is 11 dimensiontional all 90 degrees to each other - I garentee you wont b able to visulise more than 3 dimensions

Answer 6

If the universe is infinite, it can be infinite in any imaginable shape,
the universe could just be a neutron of an atom of a living dustbin, and the universe in which that dustbin is in is just a neutron of an atom of a remote control, and the universe in which
that remote control is in just an electron of an atom on a Unicorns hoof and so on for ever. bigger and bigger universes, but they are all the same universe.
A pebble on the beach is in the universe, the universe is in the pebble. The pebble is nothing, the pebble is all that there is.
Infinity is just 5 inches square.

Anything you can imagine is true, though you may not be able to understand that because you have yet to see the nothing which is everything.

Answer 7

There is a difference between infinite and static.

The universe is a living thing and like all living things it changes as it gets older. There is some doubt that the universe is infinite. Common beliefs suggest that the universe will expand untill it can no longer be held together by interstellar gravity and then it will collapse into a microstar and explode (The big bang therory)
Will this result in the rebirth of our universe (making it infinite) or will a new, different universe be formed. (making it finite)?

Answer 8

I think everyone here has missed the point of special relativity.

You can define the universe as being infinite (i.e. limitless) because the dimensions in which the universe sit are defined by the very matter that sits in them. Remember, the speed of light is the constant of the universe. Fundamental bosons travel at the speed of light. Distance and time are totally dynamic around this speed of light, so the dimensions of space and time are also totally dynamic around this speed of light.

You don't have to think of the universe expanding as being a collection of mass spreading into some defined grid of dimensions. Instead, think about the universe as being that collection of mass and the dimensions contracting within them (at the speed of light). This model is equally as valid and still holds true under all the laws of relativity (general and special).

In this sense, the dimensions of space time are in fact not some infinite field into which matter can spread but a bi product of the existence of matter itself.

From your frame of reference, the universe is expanding. It's not quite as simple as that.

Answer 9

I saw a show recently about the doughnut shape theory. The show also said that there may be other universes in the doughnut shape around our universe and that they may be like other dimensions. As for what all of those doughnut universes may be expanding in....well my guess is the glass of milk of a huge giant.

Answer 10

The universe is not infinite, never has been, never will be. People use that word wrongly, never really understanding the full meaning of it.

However, our universe is boundless. You cannot go to the edge of it, due to the curvature of space-time. And since time only exists within the universe, not outside of it, to all intents and purposes it goes on forever - it goes on until the end of time. Which is not the same as being infinite.