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[Virex]

To toss a completely different but also related ball into the ballpark:

Newton's laws acceleration and gravity appear when thermodynamics, holographic theory and information theory are combined:
http://motls.blogspot.com/2010/01/erik-verlinde-comments-about-entropic.html

This means that gravity could very wel be an entropic force that only exists on the macroscopic scale, and has at least a very different meaning on the quantum scale.

Don't you mean entropic on the quantum scale, but averaging as gravity on the full-scale?

What I mean is that it acts like pressure. Pressure doesn't exist at the microscopic scale, but only as an average over the movement and interactions of many molecules. This is the average over the interactions of lots of information. It also explains why there is no quantum gravity; because gravity is an emergent force and not a fundamental one.

[Realmfighter]

If i wrapped a fiber optic cable around the earth X amount of times and then shown a light in one end, the light coming out of the other end would be delayed if it went around enough times, right?

So what would happen if i connected one end to the other?

[Sean Mirrsen]

Theoretically, it'd keep circulating until you opened the loop. Practically, it'd eventually lose energy and disappear. That's what I think, at least.

edit: Back to space vs the Universe. I think that the Space, like any good coordinate system or what-have-you, is infinite. As in, already infinite, it doesn't need to expand beyond that. The Universe, on the other hand, is just freakishly huginormous. It expands, attempting to fill in the infinite space, like the metaphorical air in an infinite balloon. For a good while, there's enough energy to go around forming matter and things, but eventually the energy will leak into the void. And the Universe will not tolerate a void. Matter will rapidly degrade into energy to fill the void, eventually resulting in a fine "bubble" of stationary energy medium.

Now, whether or not the above actually happens depends on whether the Space is just infinite, or a finite closed loop, or simply some bizarre finite occurence. If it's finite, and small enough to contain the Universe before it overexpands, the system will eventually stabilize. All of Space will be filled with energy, allowing mass and gravity to do its work and eventually reassemble into this gigantic ball of degenerate matter, and eventually raw energy, that will go critical, suck all energy back into itself, then go supercritical and blow the stuff all over the place again, repeating the cycle. It's a fairly simplistic approach to The Universe As We Know It, but it works for me, and for the Multiverse.

[DreamThorn]

@Sean:

You assume that space and time can exist outside the universe, while modern theories sees space and time as parts of the universe.

So, when they say "the universe expands", that means that the total amount of space increases along all inertial reference frames' time axes.

Also, certain measurements done on the background microwave radiation strongly confirms that space is indeed a finite closed loop. (a.k.a. hypersphere)  Combining this with the fact that space expands leads to the so called 'trumpet' shape of the universe.

[Sean Mirrsen]

I guess the 'space is the universe' approach would make sense to people, however 'expanding space' makes no sense. It presumes that space is finite, and then somehow increases in size, which is just plane wrong. For one, if space is expanding while affecting matter (like just scaling the coordinate grid without changing boundary values), we wouldn't be able to detect it, just like a person experiencing relativistic length contraction wouldn't notice it. And if it seems to expand without affecting matter, then how'd we even know it does without knowing what the space border is like?

[Neruz]

We can detect it's expansion because everything in the entire universe is very slowly getting further and further apart from everything else. Furthermore, distant galaxies are accelerating away from us.

When we say space is expanding, we mean it quite literally; space is expanding. It's not growing bigger or taking over outside borders or something, the actual physical space itself is expanding.

[Sean Mirrsen]

Maybe just the universe is? If the fabric of space was expanding, then it'd affect the entirety of matter, not just distant galaxies. The moon would move away from Earth, the Earth would move away from the sun, your left foot would move away from your head. Except every ruler and distance measuring device would tell you nothing is happening. Because if it's an expansion of space, all possible measuring devices will expand with it.

Now, if it was just the universe expanding, it'd make sense. Moreover, it'd make sense if the universe was finite, and the space is larger, or infinite. Since infinite space is kinda depressing for a finite universe (leading to a heat death scenario, as described previously), we'll optimistically assume that space is finite and looped. Now, what ambient energy says on the matter is that the Universe is pushing itself apart like a cloud of gas, except that gas is energy. As long as there is some void to fill, ambient energy will throw itself at it, pulling galaxies apart with a constant, directed flow. As a double-whammy, this brings back the Big Bang and the Center of the Universe as viable points, because this sort of expansion will be radial, and centered on the origin of all energy in the Universe. This is, of course, just my crazy little theory, you're free to stand by whatever you were taught.

[Frelock]

Sean, the problem with the whole "universe is expanding into something" idea is that, we would just so happen to be at the exact center of where it all started.  Everything is moving away from us.  But it's not just that.  Everything is moving away from us in such a way that, were you an observer at any other point, everything would be moving away from you in exactly the same manner.  All points see the separation in the same way, which could in theory be done with a universe expanding into something, but it's highly unlikely. 

There's also other proof; like cosmic background radiation.  Originally, when that stuff was produced from the mess of particles that were left over after the big bang, it was extremely high-frequency radiation.  However, over time, the space expanding out beneath it has lengthened the waves.  So where we originally had X-rays and gamma rays, we now have microwaves.  Not because the waves lost any of their energy, but because of the space being pulled out from under their feet.

As to why our rulers do actually stay the same length, allowing us to notice the expansion, it's because of gravity.  Gravity has the power to warp space, or in our case hold it together; at least locally.  So our galaxy isn't expanding, because the massive gravity of all the stars is roughly keeping the space together.  Actually, the space in our local galactic supercluster isn't expanding much either; the combined mass is enough to hold the "local" space together, as it were.

However, the distances between galactic superclusters is so incredibly immense that gravity(which drops off at a crazy rate as distance increases) just can't hold it all together.  So, superclusters spread apart, as the space between them stretches.  The relative motion of the galaxies in the superclusters is nothing compared to the motion of the superclusters themselves, so they appear to move as one.  Eventually, some of the most distance superclusters will accelerate beyond the speed of light (possible only due to space-stretching effects) and be lost from the visible universe.  On the order of hundreds of billions of years from now, all we'll be able to see is our local galactic supercluster.

[Sean Mirrsen]

Personally, I find gravity being "a power to warp space" slightly ridiculous, but alright.

In ambient energy terms, this may just well mean that the "energy medium" is "running thin", but I have no thoughts on it at this point - meaning that so far, effects of lowering the density of ambient energy on propagating waves haven't occured to me yet.

Also, in your view's case space doesn't "stretch", it "thickens". If it "stretched", there wouldn't be more of it between any given point. If you see it as a coordinate system, you have to pack more gridlines between things if you want to make them seem further. As for background radiation flatting out, wouldn't our almighty space-warping gravity pull them back into shape as they entered our space?

If you think of gravity as this kinda bubble that holds together "warped" air, thinning or thickening the air between the bubbles will do nothing but muffle a sound from one bubble sent to another, if even that.

There'd also be the case that different amounts of gravity warp space differently, creating a large amount of off-hue galaxies.

There's also the possibility that different waves travel at different speeds. I'm not sure if that would make sense (since space-ray should probably be fastest, not slowest), but it's a partially plausible explanation. The initial pulse of radiation would have separated into a gradient of progressively changing wavelengths over time, and we could detect it as such.

tl;dr: I don't have a definite answer from my standpoint yet.

[Neruz]

Personally, I find gravity being "a power to warp space" slightly ridiculous, but alright.

Then you have not been introduced to supermassive singularities (Black holes), or any of their near cousins, like Neutron Stars.

[Sean Mirrsen]

I haven't met one personally, yeah, or I wouldn't be sitting here, would I?

Yes, they have tremendous gravity (actually, perfectly normal gravity, just packed into such a space that its magnitude near the surface is ludicrous). They play with laws of relativity, which led to the concept that they "warp space". I'm not constraining myself with relativity, and treat them like giant gravity wells that they are.

[Il Palazzo]

This is actually an observationally confirmed fact:
http://en.wikipedia.org/wiki/Tests_of_general_relativity#Deflection_of_light_by_the_Sun
first observed by Eddington in 1919 during the solar eclipse.

[Sean Mirrsen]

I see that gravity warps EM emissions. Which makes sense, as gravity is itself (possibly) an EM emission or similar phenomenon. But 'warping space'...

Gravity acting as a 'sink for space' will mean that it should pull stuff together. Unless space has a quantifiable elasticity, resistance or friction, there's no explanation for why distant galaxies would move away from us.

If you look at an average explosion, you'll see that for any given particle that's not on the outermost or innermost extreme, all other particles are moving away from it, either due to the 'sphere layer' of objects with similar velocity expanding, or due to difference of initial impulse between such 'layers' resulting in different speed.

Sorry if the post makes no overall sense, I'm typing on the go and my fingers are getting numb.

[Neruz]

I see that gravity warps EM emissions. Which makes sense, as gravity is itself (possibly) an EM emission or similar phenomenon. But 'warping space'...

In a word; no. That's not what is happening at all. What is happening is the space around the start is being warped. The light is travelling in a perfectly straight line, it's just that around massive objects, straight lines aren't so straight anymore.

Gravity can't affect light directly; light has no mass remember?

Gravity acting as a 'sink for space' will mean that it should pull stuff together. Unless space has a quantifiable elasticity, resistance or friction, there's no explanation for why distant galaxies would move away from us.

Gravity has a limited range, while it affects a far greater area than the other forces, it is still limited. The gravity of a galactic cluster is sufficient to keep the whole thing more or less together, but the distances between clusters are so great that gravity has no real effect whatsoever on other galactic clusters, unless they're real close (at which point they run into each other and make a spiral galaxy!)

If you look at an average explosion, you'll see that for any given particle that's not on the outermost or innermost extreme, all other particles are moving away from it, either due to the 'sphere layer' of objects with similar velocity expanding, or due to difference of initial impulse between such 'layers' resulting in different speed.

No clue what point you're trying to make here.

[Shades]

Gravity acting as a 'sink for space' will mean that it should pull stuff together. Unless space has a quantifiable elasticity, resistance or friction, there's no explanation for why distant galaxies would move away from us.

The movement away is their current velocity, either a residual velocity or an expansion of spacetime, the observed result for our discussion is the same.

The warping of space changes the path of a 'straight line through space'.

These are not related in a way that the existence of one denies the other, either you haven't got what people mean by warping space or I have completely miss-understood your complain against the movement away?