Why did inflation start, and then, once the universe was inflating, why did it stop again?
It began at the big bang, and it’s generally believed that it still is (expanding).
The “blast” from the big bang imparting initial velocities* is the force for expansion, the gravity of the matter in the universe is the counter-force pulling it back.
Which will win in the long run is an open question.
- Yes, I know this is at best incomplete and at worse misleading, but I think it approximates the effect in an understandable way.
Uh … no … I’m not asking about the Big Bang itself. I’m asking about the inflationary epoch that occured a tiny fraction of a second after the big bang when the space-time fabric was expanding at super-luminal speeds.
What drove this inflation and why did it stop?
IANAAP, but my impression is that the idea of inflation is a fudge factor thrown in to account for the uniformity of the background radiation, but other than that there’s not really a good explanation of it. If there’s more to it, I’d like to know, so please educate me.
Quite aside from which, I thought recent evidence indicates that the universe’s rate of expansion is increasing.
For other novices like me: Cosmic Inflation vs. Cosmic Expansion.
(I think.)
Ah, never mind me, then. Carry on.
Excellent question.
Unfortunately, the thing that’s so excellent about it is that nobody knows the answer. There’s hand-waving about the Universe undergoing a phase change, presumably as the temperature decreased, and presumably the energy in the inflation field decayed into more familiar sorts of particles at the end, but that’s about all anyone knows or can guess.
Ah. So the answer is “we don’t know for sure”?
I’ve been Googling. What about this explanation by Guth (the guy who came up with inflation in the first place).
He seems to be saying that early in the history of the universe a chance fluctuation led to a localized area in a false vacuum state. This false vacuum state possessed negative gravitational energy which rapidly inflated that small area at super-luminal velocities to be many, many orders of magnitude larger. The inflation died out as a result of the natural decay of the false vacuum state.
Are their other models for inflation besides Guth’s?
He also states that the energy density of the universe remained constant throughout the expansion because of the metastability of the false vacuum. Energy was conserved by the gravitional field becoming much more negative. This leads to a few follow-on questions:
Was most of the energy (and matter) in the current universe created during the inflationary epoch and not in the Big Bang itself?
What does it mean for the gravitational field to become more negative? Does this just mean that a tremendous amount of potential energy is being stored in it?