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BlueTommyD t1_iuf2hqu wrote

When the last star dies, we will eventually get a "last" black hole, but not because they will merge.

Black holes give off radiation which actually reduces their mass over time called Hawking radiation.

So, eons after the last star dies, the last black hole will fade from existence.

What happens after that, is really anyones guess. But we have zero evidence that points to anything other than stable equilibrium for eternity (not that time would really have any meaning at that point.)

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tvalvi001 t1_iuf5nx0 wrote

That’s one heck of thoughts there too. Mind boggling stuff

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mschurma t1_iuf85ez wrote

Layman question and it’s been awhile since physics class lol, what happens to the mass let off by all the Hawking radiation at that point? Is there any mechanism that converts radiation back to mass? I get E=mc2, that energy would still exist right? Is there any mechanism that could start turning that back into matter, and given time/gravity, start forming stars again?

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3Dbpb t1_iugetpw wrote

Not a theoretical physicist but I believe the theorized mechanism involves virtual particles. They are pairs of particles that pop up everywhere in particle antiparticle pairs. Normally they recombine nearly instantly but at the event horizon it may be that one of the paired particles falls into the black hole and the other escapes.

The issue with reforming stars is the universe is expanding at an accelerating rate. Which means while there will still be particles they will be isolated and too far away to combine into stars.

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carbonqubit t1_iuggct6 wrote

Virtual particles are a bit of a misnomer, as they're actually mathematical constructs that arise from perturbation theory and used to resolve certain complexities in quantum mechanics. Said another way, theoreticians use them to help better estimate particle interactions like those between say two electrons.

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BlueTommyD t1_iufbhhb wrote

Right. There is no ELI5 for Hawking Radiation - it's too weird. And I am not a Quantum Physicist.

Hawking Radiation is a particular kind of Thermal Radiation that "leaks" from the tiny distance around the Event Horizon of a Black Hole. The radiation never actuallty comes from "inside" the Event Horison, yet it steals energy from the Black Hole - and in a Black Hole, mass and energy are essentially the same thing.

Hawking Radiation itself isn't perfect - and could to the Black Hole Information Paradox - where Black Holes *are* actually deleting information from the universe - although this is up for debate and there are theories which correct for this.

As far as I am aware, you can't turn the energy emitted back in to mass - without just throwing it in to another black hole.

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Other_Evidence8818 t1_iuglcnz wrote

Fusion and fission are mechanisms for turning energy into matter. But after heat death, on average these processes won't be occurring as there are no gradients.

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Ok-Expression7533 t1_iuhbt2i wrote

This also goes into the issue of the nature of infinity time. Like, before all of spacetime happened, time was irrelevant. Equilibrium should have just been forever and ever. Whether it was created or accidental or whatever. It's such a ridiculous, non-intuituve landscape to navigate. We know that spacetime as we know it has had a non-zero chance of occurring, because it is occurring. So rationally it is not unreal to assume that it could be happening infinity times in the past and infinity times in the future and infinity times concurrently. The nature of reality is fucking insane.

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shydude92 t1_iuhj3kd wrote

I was thinking about this too. There's actually something called the Poincare recurrence time, which is the approximate amount of time it would take for a region of spacetime the size of our observable universe to just pop into existence based solely on quantum effects. Unsurprisingly, it's extremely long, involving a power tower of about 5 tens, with a 1.1 at the end. At this length, units don't matter, because whether you use Planck times or years, the difference doesn't really affect the exponent.

Of course, that's nothing compared to infinity, literally; however, there are several problems. First, it's not known if time would still exist in any meaningful sense at this point, since all that would exist would be distended and scattered particles. Owing to the rapid expansion of space, these particles would eventually get so far apart that no particle would be in any other's observable universe and thus no causal contact could be made, and hence you might argue that no time could exist because no longer would there be any way of measuring or observing it. Also, the Poincare recurrence would be much shorter for a region of spacetime much smaller, like the solar system, which would be all we need to exist, hence the question of why our own universe is so large if this presumably wouldn't be the first cycle. One possibility is that there are no cycles, because the PRT does not exist; or, potentially we may live in a multiverse with new regions emerging all the time so the bulk of matter ends up existing in "young" universes, while older ones that have achieved maximum entropy or heat death occasionally experience small spontaneous entropy decreases that amount to only tiny fragments of all matter present.

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DonOctavioDelFlores t1_iufew0l wrote

And what about proton decay?

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sasquatchical t1_iufhrls wrote

Because no real particles with a positive energy can escape the curvature of the black hole, we wouldn’t necessarily be able to detect this occurring from the event horizon. The only “easy” way to explain black hole evaporation is through Hawking radiation.

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