Re: The Big Crunch may be a possibility

On Sat, 22 Mar 2025 10:53:53 -0400, Kestrel Clayton
<richZIG.e.clayZIGton@gmail.com> wrote:

On 21-Mar-25 10:30, RonO wrote:

On 3/20/2025 5:27 PM, Kestrel Clayton wrote:

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On 20-Mar-25 17:33, RonO wrote:

https://www.nbcnews.com/science/science-news/dark-energy-changing-
understanding-rcna197386
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Dark energy may be waning, and the acceleration of our galaxies may
one day end.

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That's interesting. I couldn't tell from the Berkeley Lab public
release whether this new data suggest the rate of expansion is
dropping, or if the acceleration of the rate of expansion is
decreasing (instead of increasing, which is the current consensus). In
other words, is it slowing down, or just not speeding up quite as fast?
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What would happen after the big crunch?  Would all the matter in the
universe eventually fall into one large black hole?  How much matter
can a black hole contain before something like the Big Bang happens?
There is already "evaporation" from black holes.  Would anything send
the evaporation out of control?  Could anything like a Big Bang occur
within a black hole to create a new universe within the event horizon?

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I'm fairly out of date on this, but before the discovery of dark
energy, the consensus was that the universe is either flat, or so
close to spherical as to be indistinguishable. That would indicate the
expansion of the universe would eventually halt, but the universe
would not really collapse. Instead, given enough time, the stars would
all burn out, all protons would eventually decay, and even the black
holes would evaporate, until all that remains are photons, electrons,
and some other, weirder particles. (However, I know photon decay is
currently considered less certain a prospect than in the 1990s, so YMMV.)
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Everything collapsing into a massive black hole still seems unlikely,
but if it did, that would simply be a different route to the photon
age. Eventually energy states are so low that quantum phenomena become
the biggest movers and shakers in the universe, and after that... we
really don't know. It's simply off the map, as far as modern physics
goes.
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Fascinating stuff. Thank you for sharing the article!
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Google thinks that there might be enough dark matter and regular matter
in the universe so that the collapse would happen if the expansion stops.

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That's very interesting. Like I said, I'm somewhat out of date; it has
been a very long time since I was a physics student in uni.
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One science article that I read recently noted that inflation predicted
that there are parts of the universe that would not be visible to the
Webb telescope.  The fringe of our universe expanded away so fast that
there would be a sort of event horizon past which light has not reached
us inside the visible universe.  Sounds weird, but is all matter further
away than that horizon, part of the calculations about whether the
universe will collapse or not?

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That is an excellent question! The answer is "Sort of. It depends."
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Because space itself is expanding, some things are receding away from us
at what appears, from our local frame of reference, to be faster than
the speed of light. This also implies the existence of matter so far
away that light from it could never reach us, even given infinite time.
This matter is beyond the cosmic event horizon (sometimes called the
Hubble volume, though that's not quite the same thing) and it is, in a
very real sense, in a different universe.
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The really wiggy and cool thing here is it means we have infinite
overlapping universes, since any point in space has a different cosmic
event horizon.

Correct.  This is Max Tegmark's Level I multiverse:
<https://en.wikipedia.org/wiki/Multiverse>

If, for example, the radius of the cosmic event horizon
is 7, that means point 1 and point 10 are in separate universes, but 5
is in BOTH of those universes, and 5's universe includes both points 1
and 10 (although not all of 1's universe or 10's universe).
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If the expansion of space due to dark energy never drops to zero, then
any point that has left your cosmic event horizon is forever beyond your
reach. Even given infinite time, a photon from you can never reach that
point, because the expansion of space is causing it to recede faster
than the photon travels. It is outside your universe.
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On the other hand... if the expansion of the universe will eventually
cease, there is no cosmic event horizon, since any given photon has an
infinite time to get anywhere, and no point can recede from that photon
faster than the photon's speed.
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Thus, to answer your question above: Although things outside our current
cosmic event horizon cannot be affected by gravity HERE, mass between
here and there tugs on both of us, dragging us together. So 1 isn't
pulling on 10, but both are pulling on 5, and 5 is pulling on both.
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Further, if the universe eventually collapses, that means things that
are currently outside our observable universe will eventually re-enter
our bubble, as gravity drags things that left our cosmic event horizon,
or were always outside our cosmic event horizon, back into our universe.
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Cool stuff. I love physics!

One hypothesis about dark energy is that it's an intrinsic effect of
space itself.  If so, then as space expands, so too does the total
amount of dark energy between objects, and so too does the rate at
which they separate.  If that is so, it would mean that once objects
go beyond the Hubble volume, they will forever expand ever faster from
us.

OTOH it's possible that objects within each Hubble volume can still
eventually collapse together.  If so, then each Hubble volume could
eventually become isolated from the larger Cosmos.  It's unclear to me
if this would happen before or after the evaporation of large Black
Holes.

--
To know less than we don't know is the nature of most knowledge