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Background

As seen on this picture of the cosmic microwave background (take from the Wikipedia entry on the very same topic) there exists irregularities in the distribution of matter: Cosmic microwave background. Boom baby!

To my knowledge, this is because the Universe wasn't formed with all the matter (or whatever you should call whatever existed right after the big bang) in a completely regular pattern (or if it was the case that anti-matter had this big fight with ordinary matter after the Big Bang, it's really not that important I guess), and I guess this is the reason why we have a highly diverse universe today, inhabited by galaxies, black holes, and Justin Bieber.

Question

What would the Universe look like if there were no irregularities in it from the get-go? Would we have a big massive black hole in the middle (if one even can talk about a middle), would the Big Bang never happen, or have I just misunderstood the whole thing, making my question completely nonsensical?

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Note that what we see now is how the universe looks if it started with remarkable few and small irregularities. –  dmckee Nov 20 '11 at 20:59
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up vote 5 down vote accepted

If the uniformity were somehow perfectly smooth, all we would have is a very tenuous nebula of mostly Hydrogen, with some Helium and a little bit of Lithium. Without the irregularities to start off star formation or any of those activities, that's all we'd have. I'm not about to run a back of the envelope calculation, but I would think that the overall density wouldn't be much greater than current interstellar space.

Going further back, we would possibly be in a state of having no baryonic matter at all. While delving into areas we don't really know that much about (but we are exploring), one school of thought says that because of the irregularities, somehow regular matter won out over anti-matter.

As to the massive black hole idea, it would most likely not be the case because of cosmic inflation. The space would still be expanding so that a collapse wouldn't be feasible in that epoch of the universe. And the question is pretty nonsensical in that nothing is perfect. An irregularity is pretty much a certainty given we are dealing with particles that have mass.

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So the density would be greater than what you quote in this answer: physics.stackexchange.com/q/25378 but borbably not by much? –  Brightblades Nov 21 '11 at 14:10
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