What do they mean when they say the Universe is expanding?

Can you actually say the universe is expanding? I'm not too sure but I think when we say universe we mean everything that exists anywhere. So for the universe to expand there needs to be space (or something) somewhere.

But then isn't this space supposed to be part of the universe?

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I find it funny how we can say "this is what's happening" so authoritatively. Reality's so dodgy.

 

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If the Earth (Universe) is stretching doesn't it need space (or something) outside of it's "boundaries" and isn't whatever it is that is outside this "boundary" part of the universe too?

 

Someone correct me if i'm wrong. We don't know what's outside of 'space', but we do everything is moving away from each other. In billions of years there will be no more stars in our sky, well in theory.

 

that's exactly how it is. once you get the idea of a sphere in your head, just imagine adding another dimension. you could say the surface of the sphere is the present, inside the sphere is the past, and outside the sphere is the future. the sphere is expanding, so the surface area is getting larger (the space between objects in the universe is increasing) but then that would make the spacial universe 2 dimensions. so to make it accurate to our universe, you just add another dimension. its just really hard to visualize it because we have only ever conceived of 3 dimensions on a normal basis.

 

JamesR and RoyLennigan, I think I see what you mean. It's stretching in hyperspace.

Would I be correct if I deduce that the universe is actually infinite but space is stretching thus causing galaxies to move away from each other?

 

Thanks for clearing that up.

 

Ok, wait...

If the universe is infinite, and we're just a part of an expanding 3-D type sphere of space within that infinite universe, then it's possible that there are other (perhaps even an infinite amount of!) expanding 3-D type spheres of space like our own, yes?


(I would have started a new thread with this question, but it's so dependent on this one that I decided against it...)

 

The Bubbles Universes theory doesn't work in my mind. What would be between the Universes? Am I correct in saying that space-time does not exist between the Universes.

 

Yes, as far as I understand it (basically from what I've read in this thread), space-time would not exist between multiple universes. They would coexist in the 4 dimensional space, right?

 

In response to the thread question-

When scientists say that "the universe is expanding" they are reffering to the big bang theory.

When the big bang occured there was an immense expolsion (obviously), and, as everyone knows when an explosion occurs, the fragments/matter are blow outwards i.e. when a frag grenade explodes.

The same happend in our solar system, and i suppose in others, the force of the big bang is still pushing the universe outwards, making the universe 'expand'. Thats what i picked up in Gcse physics anyways.

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I invite anyone to correct me if im wrong, which admittedly is a fairly high possibility!

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:m:

 

Does matter displace space? Each and every particle needs room. Matter must occupy an equivalent volume of space. The introduction of matter into spacetime resulted in a less dense spacetime making room for it. Perhaps the expansion is merely matter making room for itself. Something has to give way. If there is finite matter then expansion will stop eventually, no? In the beginning it may have been very difficult to move space but over the years space gradually weakens its position allowing matter to speed up the settling in. Spacetime and matter are like oil and water.

Nobody knows but I think it important to put stuff out there that others can read, laugh at or take seriously and run with. Sometimes innocent remarks stimulate the genius of fellow human beings. Not that mine will.

 

If matter were to displace spacetime would that mean that time doesn't exist within matter. Can't think logically how that would work?
But I guess one can view Einsteins classic theory of relativity as matter displacing/bending spacetime directly proportional to its mass.
Am I wrong in saying so?

 

Sorry to dredge up an old thread, but I just have a question regarding this:

As space-time expands, do the objects on it's surface (ie, in your analogue, the objects on the earth) stretch and get bigger too? Like, if you draw a dot on a piece of rubber then stretch it, the dot too gets bigger.

 

They mean that distance scales increase over time (in the reference frame of the universe). Forget all those analogies about balloons and rubber sheets; you don't need them when you consider length contraction in different reference frames in special relativity, you shouldn't need them here.