Is the universe heading towards a Big Freeze, a Big Rip, a Big Crunch or a Big Bounce? Or is it part of an infinitely recurring cyclic model?
2 Answers
What is the future of our universe?
Like StephenG said, nobody knows for sure. But we do have confidence that the universe is expanding, and we also have confidence that the expansion is speeding up. So extrapolating from that, the future looks cold and lonely and bleak. A bit like life for the older generation!
Is the universe heading towards a Big Freeze, a Big Rip, a Big Crunch or a Big Bounce? Or is it part of an infinitely recurring cyclic model?
I'd say the Big Crunch and the Big Bounce are out. The universe didn't contract when it was small and dense. Instead it expanded, and that expansion is increasing. So it looks like we're in for a Big Freeze. However I wouldn't rule out a Big Rip of sorts. Have a look at page 5 of this paper where Milgrom mentions the strength of space. Then think of the balloon analogy, but make it a bubble-gum balloon, in vacuum.
Image courtesy of the one-minute astronomer.
The skin gets thinner and the balloon expands, then the skin gets even weaker, so the balloon expands even faster, and so on. Bubble-gum bubbles sometimes end badly, and there's something about this article by Phil Plait that strikes a chord.
Or is it part of an infinitely recurring cyclic model?
I don't know. I have no evidence to suggest that there's any kind of recycling going on, and I can't think of mechanism by which this might occur. I have of course read about "conformal cyclic cosmology", but I just don't buy it, along with other stuff from Penrose.
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$\begingroup$ In a recent lecture Neil Toruk argues eloquently for why the universe will contract and become a new big bang. If simplicity is a guide to truth (engineers will disagree). It is up to the dark energy, isn't it? And its properties, especially in the far future, are unknown. $\endgroup$ Jan 13, 2016 at 5:04
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$\begingroup$ @LocalFluff : why don't you ask a question on that? $\endgroup$ Jan 13, 2016 at 8:22
Your guess is as good as any cosmologist's.
We don't know how it came into being, not with any confidence. There are theories, but nothing definitive has emerged to explain where it all came from. This may be hotly disputed by proponents of each theory, but we're not there yet, IMO.
We're not sure yet about what all the relevant forces are ( e.g. dark matter, dark energy ) so any theory about how those affect possible futures is simply a complicated guess at this point. This alone, IMO, makes conjectures about the universe's future pointless, IMO.
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$\begingroup$ Though I totally agree with you, this is not an answer :p $\endgroup$– NicoJan 12, 2016 at 9:52
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2$\begingroup$ In science "I don't know" is, sometimes, the correct answer. I would be writing science fiction if I proposed any other kind of answer. If people want to debate the details of theories in their answers that's fine with me. $\endgroup$ Jan 12, 2016 at 10:14
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1$\begingroup$ You are absolutely right. That was a pun, the only way to answer this question is to explain why it is still unanswered. $\endgroup$– NicoJan 12, 2016 at 10:18
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$\begingroup$ This is good; I would advise maybe fleshing it out a bit, including the evidence that we do have so far. $\endgroup$– HDE 226868 ♦Jan 12, 2016 at 21:37