Is the Universe infinite or finite?

[Wikiy]

I have no idea. On the one hand, the geometry of space suggests space itself is infinite. On the other hand, i find that slightly mind-boggling seeing as space itself began with the Big Bang along with energy. So i have a bit of a hard time imagining how something that began with a confined 3-dimensial volume and continued on expanding at extra-ordinary (yet not infinite) speeds can be infinite in volume.

Also, assuming space really is infinite, this would also mean energy is infinite. I also find this a bit confusing as seeing as when you look at a particular part of the universe, you wont find the amount of energy there to be infinite. Otherwise, the temperature would be infinite, and, well, the implications are something that's kind of unimaginable in physics. I don't really know, apparently, according to mathematics, there is such a thing as a bigger infinity than the next, i.e., 2 hypothetical universes can both have infinite energy yet one of them could have a higher energy density, implying that universe's energy is a bigger infinity than the other universe's infinity.

Personally, i find the image of a finite universe far more appealing, but as Lawrence Krauss would say, the universe doesn't give a damn about our feelings. So I'll hold as the truth whatever it is that scientists hold as the truth. At the moment, that's nothing.

[semaphore]

How are we sure the the solar system isn't the entire universe and the observable universe is just a projection, an illusion, made by the quantum computer that computes and simulates the universe?

We aren't sure! That's why science never claims to have the absolute truth. All we have is the best explanation for our observations, not the ultimate answer. For all we know we could be part of the Matrix

But then, this is holding science to an impossible standard of proof, so while interesting in a sense, it's also entirely useless.

---------- Post added 2012-12-22 at 03:12 PM ----------

according to mathematics, there is such a thing as a bigger infinity than the next

Can you elaborate?

[Deleted]

We aren't sure! That's why science never claims to have the absolute truth. All we have is the best explanation for our observations, not the ultimate answer. For all we know we could be part of the Matrix

Morgan Freeman made a tvshow on this and since that man is basicly god, we can be pretty sure

I'm trying to plug a USB-port in my body to learn Kung-fu (and all my bloody courses for my finals), but I must suggest to not try this yourselves, its very painfull and it makes going to the toilet very akward

[Deleted]

Really, Lizbeth? Not really even that hard to understand?

Well then...

What's beyond the Universe?

There is no "beyond", it's like asking what's after the Earth ends if you go far enough north or some other direction. There is no end or edge. The universe is like an expanding bubble and the space with all the galaxies in it is the skin of that bubble. You can't get off that skin and even if you could, there is no 3d space or rules of physics there. There may be other universes or parallel dimensions or whatever you choose to call them but you cant physically get there.

[Deleted]

After all we've never left the solar system.

Voyager 1?

---------- Post added 2012-12-22 at 05:53 PM ----------

There is no "beyond", it's like asking what's after the Earth ends if you go far enough north or some other direction. There is no end or edge. The universe is like an expanding bubble and the space with all the galaxies in it is the skin of that bubble. You can't get off that skin and even if you could, there is no 3d space or rules of physics there. There may be other universes or parallel dimensions or whatever you choose to call them but you cant physically get there.

That doesn't work in 3 dimensions dude.

[Wikiy]

Can you elaborate?

Well, as an example, you could have an infinity that includes all odd numbers, so; 1, 3, 5, 7, etc. You can also have an infinity that includes all natural numbers; 1, 2, 3, 4, 5, 6, 7, etc. The latter is a bigger infinity.

I'm not really sure about it, to be honest, I've just been under the impression that there is such a thing as a larger infinity than the next.

[Deleted]

such a thing as a larger infinity than the next.

Infinite is infinite. If you divide infinite by 2, it will still be infinite. Infinite is always infinite.

[Deleted]

Voyager 1?

---------- Post added 2012-12-22 at 05:53 PM ----------



That doesn't work in 3 dimensions dude.

The Universe isn't 3 dimensional, we just experience it that way, in fact its 10 or 11 dimensional. But if you want to understand the spacetime (Space and Time are the same entity) its easier if you see the Universe as being 2D, we can't get out of the universe just like a computer caracter can't jump out of the screen onto your desk.

Also, the Voyager hasn't left the solar system quite yet, its not even past the Heliopause, we don't even know how far the edge of the solar system is.

[Deleted]

That doesn't work in 3 dimensions dude.

Dude? Why wouldn't it work 3d though? It works from 1d to 2d, it works from 2d to 3d, theres no reason why it wouldn't work from 3d to 4d..

[semaphore]

Well, as an example, you could have an infinity that includes all odd numbers, so; 1, 3, 5, 7, etc. You can also have an infinity that includes all natural numbers; 1, 2, 3, 4, 5, 6, 7, etc. The latter is a bigger infinity.

I'm not really sure about it, to be honest, I've just been under the impression that there is such a thing as a larger infinity than the next.

I don't think that's how it works. There is no limit to the number of odd numbers, therefore it's an infinity. It's not any smaller than the number of natural numbers, which is also infinite.

[Wikiy]

I don't think that's how it works. There is no limit to the number of odd numbers, therefore it's an infinity. It's not any smaller than the number of natural numbers, which is also infinite.

Just using Krauss' example.

Forget that though. Imagine two universes, both equal (and infinite) in size, with one of them having one extra J of energy. The energy of one is ∞ J while the other is (∞+1) J. This is, of course, assuming the energy density of the first universe isn't ∞ itself (if it were, this universe would not only be infinite energy-wise because of its infinite volume, but also because of the fact that its energy is at every point of space infinite as well).

While in the case of our universe, if it is indeed infinite (in volume), you can't say that the amount of energy would be equal to a universe whose energy is ∞ at every point of space because in our universe, the energy density in most of its volume is just 10^-9 J/m^3 (which is the energy density of empty space) while the energy density of the other universe would be ∞ J/m^3 for every single cubic metre of space.

This is, i think, where the concept of a larger infinity comes in. Meh, it's all so mind-boggling. It's why I'd prefer the universe to be finite. This is more like philosophy than physics.

[semaphore]

Just using Krauss' example.

Forget that though. Imagine two universes, both equal (and infinite) in size, with one of them having one extra J of energy. The energy of one is ∞ J while the other is (∞+1) J.

Didn't Krauss talk about how adding 1 to infinity is still infinity? The energy of both such universes would be ∞

[Deleted]

Dude? Why wouldn't it work 3d though? It works from 1d to 2d, it works from 2d to 3d, theres no reason why it wouldn't work from 3d to 4d..

You liken the Universe to a bubble, a ball-like shape, like the Earth is. You say the Universe exists on the "skin" of that ball. Well, you're thinking in 3D, when you're giving us that description. A ball shape is 3D. In 3D then, what's inside that ball? What's outside that ball? How thick is that skin?

Yeah, it doesn't work like that. You're thinking of extra dimensions by using the three dimensions we can imagine. The thing about extra dimensions is, we can't describe them.

Also, the Universe existing as the skin of a ball would make it finite, whether it was expanding or not.

[Deleted]

Hm, I remember reading this thread before :P

Didn't Krauss talk about how adding 1 to infinity is still infinity? The energy of both such universes would be ∞

Well, there are different "sizes" of infinity in mathematics, Cantor's set theory. The "smallest" is the size of natural numbers, 1,2,3... so it's called countable infinite. Real numbers are uncountable, an infinity called "continuum"... but none of that really matters in current physics.

[Deleted]

I was taught, and my very simple logic still states, that infinity times anything, or infinity minus anything, or infinity plus anything, is still, and always, infinity.

Not right?

[Deleted]

You liken the Universe to a bubble, a ball-like shape, like the Earth is. You say the Universe exists on the "skin" of that ball. Well, you're thinking in 3D, when you're giving us that description. A ball shape is 3D. In 3D then, what's inside that ball? What's outside that ball? How thick is that skin?

Yeah, it doesn't work like that. You're thinking of extra dimensions by using the three dimensions we can imagine. The thing about extra dimensions is, we can't describe them.

Also, the Universe existing as the skin of a ball would make it finite, whether it was expanding or not.

Actually we don't know what infinite is, because we where never able to measure it. Infinite might as well be a circle, because you can keep going round it withouth ever reaching the end

[Deleted]

Infinite might as well be a circle, because you can keep going round it withouth ever reaching the end

Yeah and what happens when you go up?

[Deleted]

Yeah and what happens when you go up?

Thats irrelevant, imagine an infinite straight line that you keep following, what happens when you go left or right instead of forward/backward?

You think of the universe as a 3 dimensional place, when infact it isn't, we just percieve it that way. Keep in mind that everything you touch,see,taste,smell,hear isn't the actual structure/reality of the object you percieve, it is what your brain tells you it is. And the universe does not has to follow the rules your brain dictates. Our brain tells us the universe is 3D (4D if you count in time) but that doesn't have to be the actual structure of spacetime.

It is something ourminds cannot percieve or comprehend, we can only try to explain it by using objects we can understand, like the balloon example, the balloon is all there is, there is no inside/outside of the balloon, only the surface of the balloon.

[Deleted]

Thats irrelevant, imagine an infinite straight line that you keep following, what happens when you go left or right instead of forward/backward?

You think of the universe as a 3 dimensional place, when infact it isn't, we just percieve it that way. Keep in mind that everything you touch,see,taste,smell,hear isn't the actual structure/reality of the object you percieve, it is what your brain tells you it is. And the universe does not has to follow the rules your brain dictates. Our brain tells us the universe is 3D (4D if you count in time) but that doesn't have to be the actual structure of spacetime.

It is something ourminds cannot percieve or comprehend, we can only try to explain it by using objects we can understand, like the balloon example, the balloon is all there is, there is no inside/outside of the balloon, only the surface of the balloon.

If you describe a balloon, on the skin of which the Universe exists, then that's 3D. You can't "explain" non-3D using our language, and if you do, it will be 3D. In fact, most likely, you don't even understand non-3D, so whatever you think you're explaining, isn't anywhere near accurate anyway.

[This name sucks]

It is finite but in all practicality it might as well be infinite in terms of size.

The universe is expanding faster than light travels so we will NEVER be able to hit the limit of a finitely large universe (distance, not matter).

but even though the universe does exist it can't be interacted with at all because light is slower than it.