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Originally Posted by T@T
I do understand the power of gravity and even the possibilty that it can force matter to go faster than the speed of light (black holes)
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As far as we know it doesn't force matter to go faster than the speed of light, if only because that would require infinite energy.. as something approaches the speed of light, its mass increases so to move it faster requires more energy to overcome that increased inertia.. more and more and more until it would take an infinite amount of energy to accelerate even 1 molecule to exactly the speed of light.
Quote:
Originally Posted by T@T
But that balloon theory doesn't really do it for me as they left out gravity and the effects it has on galaxies.
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They don't leave it out of their theories and calculations though. The short video doesn't mention it simply because it was trying to explain why there's no "center" of the big bang. Gravity keeps small clusters of galaxies together, but the expansion of the universe pushes those clusters apart.
Plus the expansion is accelerating, so eventually there could come a point where even the gravity of galaxy clusters isn't sufficient to keep them together and they'll be pulled apart.
The balloon thing isn't really a theory, it's just an analogy to try and take something very complex and render it at a level we can grasp visually. Remember in the balloon illustration, the surface of the balloon represents all dimensions of space. And in reality the shape isn't a sphere like the balloon, but a "3-manifold", something analogous to a sphere in more dimensions.
But for what it is the balloon analogy is apt, at the scale that matters for the universe, it behaves like the surface of the balloon does.. it stretches away from everything else, moving everything apart from everything else, because that's exactly what we observe; beyond a few exceptions, everything is moving away from us, and the further away it is, the faster it is moving away.
The other alternative is that the earth just happens to be at the exact middle of the universe.
Quote:
Originally Posted by T@T
I think a theory that gravity and massive black holes are pulling galaxies apart is better than the total unexplained balloon theory.
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Gravity is weak though, weaker than the force that's driving the expansion of the universe. And what you are proposing doesn't really work, if there are massive black holes pulling galaxies apart, then they'd have to be pulling galaxies together from another point of view.
Unless you're saying there's all the galaxies in a huge cluster surrounded by black holes, but that just puts us back into a universe where the earth is the center of the universe (who put us there, god?
). And you need to explain how everything got that way. PLUS if you work out the math, it actually doesn't work. If you had evenly distributed black holes all around the known universe, the gravitational effect from all those black holes inside their perimeter is exactly zero
And that also implies a universe where there's stuff in the middle, and empty space if you go out far enough, but that's not what the universe is like. The universe is self contained, if you go out far enough, you either eventually get back to where you started, or you go on forever. And space is flat to the limits of our ability to measure, so it's infinite.
Dark energy is responsible for the expansion of the universe, and even right now dark energy makes up 72% of the mass-energy density of the universe, and as it expands that'll keep going up, so gravity due to mass (normal matter makes up 5%, dark matter 23%) is getting less and less significant all the time, while the expansion is getting faster and faster.
