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# aha
that was implicitly contained in the 'standard model of the universe' bit. for that to happen, the standard model of cosmology has to be more or less accurate. (it probably is, to be honest, but there are plenty of loopholes and things that simply don't seem to make total sense.) basically the idea is that everything will end up with radiation - in the end stars will have processed almost everything that can be processed and black holes swallowed everything else and the few things left over will have decayed, and then eventually the black holes themselves will decay in hawking radiation. it seems very possible that every fundamental particle is unstable, and most if not all theories that combine the strong and electroweak forces predict that; i'm willing to believe it, to be honest, although the half-lives may be of the order of tens of billions of years, or more. given a standard cosmology, and all of that, the 'heat death' seems inevitable. unless you can find a way of changing the laws of thermodynamics, and of gravity, it's hard to avoid.

except that the standard model of cosmology may be quite wrong. we may not even understand hawking radiation, although we may observe an analogue of it in the next year or two. (any quantum radiation from any kind of horizon will go a long way to justifying the argument for hawking radiation - although naturally it won't prove it. there are groups have now made acoustic black holes, which are like real black holes but for sound waves, and in a couple of years we should be in a position to measure the hawking radiation, if it exists. i'll be stunned if it doesn't.) fundamental particles may not decay. like you say, proton decay has never been observed. the universe might collapse on itself. physics we have absolutely no idea about could come into force when the universe grows too big - or if it contracts to too small a scale. the whole thing could be based on physics that is accurate on local scales but applied very badly on cosmological scales.

my view is that all bets are off in cosmology right now. at the heart of it, we don't understand what's going on - just how it looks when we interpret it using a particular model. there's a fuckload of observational support for that model, but even so... it's just a model. phenomenology, to use the jargon.
(I helped save b3ta! boris the spider, Fri 23 Sep 2011, 23:41, archived)
# also
in case anyone wanted MORE walls of text from me tonight (i think i'm now on a dozen ignore lists), this is where penrose's recent news stories have come from. penrose has a theory, which hasn't been satisfactorily published but which actually is quite elegant in principle, where you map the heat death of the universe onto the start of another. the details are a bit... detailed, but it boils down to looping future infinity onto past infinity, and being able to do so because the only things left in the universe are photons which for some reason i've never understood because he's not written a proper paper about this that i've ever seen means that there's no firm definitions of distance. so the massive distances at the end of the universe apparently can be mapped onto tiny distances in the very early universe. the heat death leads to a new big bang, new universes, and yet more physicists to evolve and ask WHAT THE FUCK HAPPENED TO THE ENTROPY?

oh, and also for respected physicists to work it out and then put out ill-advised papers based on statistics they readily admit they don't understand, which promptly get rubbished by the rest of the community.
(I helped save b3ta! boris the spider, Fri 23 Sep 2011, 23:47, archived)
# actually i think i'm being as clear as mud
i could probably explain all this a bit more comprehensibly
(I helped save b3ta! boris the spider, Fri 23 Sep 2011, 23:49, archived)
# is that where suggested the concentric rings on the wmap image were left over gravitational waves?
(I helped save b3ta! Rebel biscuit stercore sumus et nos esse novimus, Fri 23 Sep 2011, 23:50, archived)
# Yep
They never actually explained where the concentric rings were meant to have come from, and they used some really weird statistics where they compared everything with white noise rather than with simulated maps. That's like looking for discrepancies in a recording of a Beatles track by comparing it with white noise rather than a reasonably precise cover version. Or like looking for yellow blocks in a field of blue instead of a field of random colour. The papers were not well received - which isn't entirely Penrose's fault; he's never pretended to be an observational cosmologist nor a statistician.
(I helped save b3ta! boris the spider, Fri 23 Sep 2011, 23:54, archived)
# what if the universe is not a closed system and entropy could be leaked in?
if that makes sense
i drew a horse
(I helped save b3ta! Rebel biscuit stercore sumus et nos esse novimus, Fri 23 Sep 2011, 23:48, archived)
# Then all bets are off, depending on how you define "universe"
For us, it basically just means "everything", so by definition entropy can't come into it from outside, and neither can heat nor anything else. What we see might just be a tiny patch of it, but what we attempt to describe is everything. (We'd term something we can't see as "superhorizon" - our metaphors are still kind of stuck in the 15th century.) Cosmology depends on superhorizon scales, but you can get some seriously interesting stuff going on if you play around. Topology is a nice example. General relativity is lovely and all, but it says *nothing* about how the world looks as a whole; it's entirely possible that's doughnut shaped, or like a football, or like any crazy shape you can imagine, perhaps like a loaf of bread that someone drilled repeated holes into. Each model can easily describe our actual universe and all our observations, but each have extremely different behaviour.

So basically if you start taking stuff outside the observational universe seriously, a lot of things can happen.

Plus, I've never been able to draw horses :( I basically can't even draw :(
(I helped save b3ta! boris the spider, Fri 23 Sep 2011, 23:58, archived)
# I have enjoyed reading this.
informative informed opinions.
(I helped save b3ta! arrangedletters, Sat 24 Sep 2011, 0:13, archived)
# I would quite like to have a physicist on speedial
(I helped save b3ta! Rebel biscuit stercore sumus et nos esse novimus, Sat 24 Sep 2011, 0:17, archived)
# i'm not quite on speeddial
but i'm on b3ta quite a bit and normally willing to offer my opinionated opinions

edit: i also enjoy this kind of thing :)
(I helped save b3ta! boris the spider, Sat 24 Sep 2011, 0:19, archived)
# hah excellent can't beat a good chat about physics
Edit: i do have some questions about dark energy, but its too late
(I helped save b3ta! Rebel biscuit stercore sumus et nos esse novimus, Sat 24 Sep 2011, 0:30, archived)