Re: Article: How Will the Universe End?

From: Mitchell Porter (
Date: Mon Mar 08 2004 - 06:10:14 MST

Tommy McCabe said

>>Eleventh, given the time frame (10^36 years in the future), and given
>>current theories about cosmic expansion, who says there would even be

and I said

>Expansion isn't relevant to whether there's dust.

but I suppose it is, since it's the increase in the volume
of space which prevents all the remnant particles from
meeting up to form complex structures again.

I think Dyson's idea about positronium clouds as an
end-state has something going for it. Positronium is a
bound state of an electron and a positron. Obviously
they're in danger of annihilating, but if they have enough
momentum they can stay apart, while remaining attracted
by their opposite charges. I don't know if Dyson ever
wrote it up, but after his "Life Without End" paper,
when the idea of proton decay became fashionable,
he came up with the idea of positronium clouds rather
than dust clouds. The problem of proton decay comes
about in unified field theories which say that quarks can
become leptons (e.g. electrons), a transition which is
impossible in the Standard Model but which would just
be extremely rare in a unified field theory. This implies
that all atomic nuclei would eventually turn into
electrons and neutrinos, rendering atoms (and
molecules and dust) mortal. But electrons (and positrons)
were still immortal in these scenarios, thus the use of
positronium. I believe Dyson envisages "gravitationally
bound positronium", in which you have an electron
and a positron orbiting each other at great distances;
such a system would have a large number of energy
levels (akin to the electron orbitals in an atom, but
far more numerous). The positronium "atoms" would
interact with each other gravitationally and
electromagnetically. I still have my "no rigid bodies"
problem, but I guess I can also see very long-lived
"gravitational molecules" of positronium, larger than
today's observable universe, in which epochs pass
without any structural change, and in which complicated
orbital resonances meanwhile do the computing.
If you lived in one of those island galaxies I described
in a previous post, your long-range planning might
center on preparations for the positronium era -
setting up the initial conditions of your final, positronium

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