# Thread: The Universe Must Be Infinite

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## The Universe Must Be Infinite

The universe must be infinitely large, or there must be something everywhere:

Any given object's gravity will have a pulll on everything else on the universe, eg. the earth's gravity will (in a very small way) pull at a star millions of light years away. This is because gravity acts over an infinite distance, although it may grow weaker with distance. If the universe is finite then it must have a boundary, and supposedly there would be NOTHING outside this boundary. However, gravity acts over an infinite distance, and no matter where you are there must be some manifestation of this gravity, whether it be gravity waves or something else. This manifestation of gravity IS SOMETHING, and this "somethingness" is everywhere, because (as i keep repeating) gravity's effect covers infinite distances.

Right, well that is my theory, your thoughts?

P.S. I don't think that the universe is infinite, i just want this idea to be disproved! Many thanks.

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Originally Posted by alex.blakes
The universe must be infinitely large, or there must be something everywhere:

Any given object's gravity will have a pulll on everything else on the universe, eg. the earth's gravity will (in a very small way) pull at a star millions of light years away. This is because gravity acts over an infinite distance, although it may grow weaker with distance. If the universe is finite then it must have a boundary, and supposedly there would be NOTHING outside this boundary. However, gravity acts over an infinite distance, and no matter where you are there must be some manifestation of this gravity, whether it be gravity waves or something else. This manifestation of gravity IS SOMETHING, and this "somethingness" is everywhere, because (as i keep repeating) gravity's effect covers infinite distances.

Right, well that is my theory, your thoughts?

P.S. I don't think that the universe is infinite, i just want this idea to be disproved! Many thanks.
Your 'theory' (speculation) is based on the assumption that gravity does cover infinite distances.
Even if it can cover infinite distances, doesn't mean that it does.
I can smoke crack, but I don't.

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I'm willing to bet that gravity (does it have a speed?) can't travel fast enough to keep up with the expansion of the universe. Also, most of the universe is empty so what will it have an effect on? It can't effect nothing so its as though its not there?

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Originally Posted by Sovieto
I'm willing to bet that gravity (does it have a speed?) can't travel fast enough to keep up with the expansion of the universe. Also, most of the universe is empty so what will it have an effect on? It can't effect nothing so its as though its not there?
True too...

The current consensus is that it propagates at the speed of light. Which means that it can keep up with the expansion, locally.

One more thing, our description of gravity stretching into "infinity" is just a mathematical concept.

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6. If the universe isn't infinite, it still doesn't have a boundary, any more than the Earth has an edge for sailors to fall over. The universe would curve over onto itself if it is finite, so you would simply wrap over to the other "side" of the "map" without crossing an edge at all. Or, the universe might be infinite. We, as a species, don't know yet whether the universe is infinite, and we will probably never know.

Fraser and Pamela did some episodes about the size and shape of the universe.

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Originally Posted by Empyre
If the universe isn't infinite, it still doesn't have a boundary, any more than the Earth has an edge for sailors to fall over. The universe would curve over onto itself if it is finite, so you would simply wrap over to the other "side" of the "map" without crossing an edge at all. Or, the universe might be infinite. We, as a species, don't know yet whether the universe is infinite, and we will probably never know.

Fraser and Pamela did some episodes about the size and shape of the universe.
The Earth really is a bad analogy for this one, because the Earth does have boundaries. At its center and at the surface. The difference between the Earth and universe would be that the Earth is infinite but unbounded in certain directions, the Universe in All directions.

8. OK, I worded it incorrectly. I mean that the 2D surface of the Earth has no edge, finite but unbounded. Likewise, a finite, flat universe would be the 3D "surface" of a hyper-toroid, finite but unbounded. It would be flat in the sense that parallel lines would always remain parallel. This is as they discussed in episodes 77 - 79. All this doesn't mean that the universe must be finite, just that it can be finite.

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Originally Posted by Neverfly
True too...

The current consensus is that it propagates at the speed of light. Which means that it can keep up with the expansion, locally.
Would gravity's effect be weakened by the expansion of the universe, just as light is red shifted?

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Originally Posted by abo999
Would gravity's effect be weakened by the expansion of the universe, just as light is red shifted?
I wouldn't choose that particular wording- But I think I understand what you mean...

With the expansion moving ahead of gravity, it would need to play a bit of catch- up. Over great distances, the effect of gravity would be too weak to measure anyway. But yes, you would notice less of it's effect at that distance due to the expansion.
I would not say that expansion weakens gravity, however.

11. 1st post, 1st hack:

that which exists as a physical entity has limits

therefore, somewhere, way the heck out there, is a limit.

12. I've read a book called the constants of the universe by james barrow, in it he talks about a theory where the gravitational constant is (or wasn't) always actually constant. Just a thought. great read by the way. And wouldn't light travel faster than the force of gravity or something. so maybe light is what's exploring new frontiers in the universe and the force of gravity is a little behind