Re: The Big Crunch may be a possibility

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

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

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

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

>
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?
>

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?

>
I'm fairly out of date on this, but before the discovery of dark energy, the consensus was that the universe is either flat, or so close to spherical as to be indistinguishable.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.)
>
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.
>
Fascinating stuff. Thank you for sharing the article!
>

 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.

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 Like I said, I'm somewhat out of date; it has been a very long time since I was a physics student in uni.

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?

That is an excellent question! The answer is "Sort of. It depends."
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.
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. 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).
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.
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.
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.
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.
Cool stuff. I love physics!
--
[The address listed is a spam trap. To reply, take off every zig.]
Kestrel Clayton
"Every normal woman must be tempted, at times, to stoke the fire,
host the black mass, and begin eating hearts." — Rose Bailey