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Black holes as the source of dark energy

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Re: Black holes as the source of dark energy

#41

Post by bArray »

> In one such model, black holes do not contain a singularity, but are instead filled with vacuum energy. These vacuum-energy black holes are intriguing because their growth is coupled to the expansion of the universe: as the universe expands, these black holes gain mass.

I would think about this differently. What if the actual space inside these black holes does not stretch as the Universe itself does? The density relative to that of the Universe would increase, but they just maintained the density they originally had.

Thinking about a piece of fabric stretched with a mass on, as you drag the corners out, the curve (gravity) on the fabric (space) caused by the mass increases. If you locked the mass depth, it would look like it has gotten heavier.

Re: Black holes as the source of dark energy

#42

Post by elorant »

hn_throwaway_99 wrote: post #38
ketralnis wrote: post #25

Earlier quoted context omitted.

She's generally good but in addition to the clickbait she also has a habit of "it's so easy, it's just [controversial pet theory] and the rest of science disagrees because they are wrong". I find that most physicists in educational roles shy away from interjecting with opinions and even mild speculation more than they should but she tends to overcorrect in the other direction. This tends to attract a particular type…

> "it's so easy, it's just [controversial pet theory] and the rest of science disagrees because they are wrong". That's probably the best description of her style of argument I've read, and it's honestly why I can't stand reading/watching her anymore. Much too much of it comes off to me as "What the physics establishment doesn't want you to know!!" type of stuff, so it then attracts the "yeah, she's speaking truth to…

You should read her book where she goes into greater detail about the shortcomings of modern science. While I also don't generally enjoy her style, there's a lot of valid points in her arguments.

Re: Black holes as the source of dark energy

#43

Post by justinpombrio »

pdonis wrote: post #8
bmitc wrote: post #5

Earlier quoted context omitted.

It is my understanding that, from a gravity-only standpoint, you are right. But I actually thought that black holes slowly evaporate, i.e., lose mass, from emitting Hawking radiation. It isn't clear from the article whether the vacuum energy black holes still have that property. The article confuses me on something else. It mentions a link between black hole mass and the expansion of the universe, but then it seems t…

> I actually thought that black holes slowly evaporate This is believed to be true, but the time scale is something like 60 or more orders of magnitude longer than the age of the universe, so (a) no evidence for this effect exists or is likely to be found any time soon, and (b) it's irrelevant for the dynamics of our current universe anyway.

I thought we had evidence that black holes evaporate in that Earth hasn't been swallowed up yet.

A while back there were concerns (notably not from physicists) about the LHC forming black holes. I remember the response being that tiny black holes frequently form in the upper atmosphere due to high energy particle collisions, but black holes emit more radiation the smaller they are(!), so these tiny black holes evaporate nearly instantly. (Thus the same would happen if the LHC made any.) A tiny black hole that didn't evaporate would be scary because it could grow larger but not smaller.

Re: Black holes as the source of dark energy

#44

Post by btilly »

DiogenesKynikos wrote: post #32
btilly wrote: post #27

Earlier quoted context omitted.

The "no hair theorem" is a theorem of classical general relativity. Attempts to try to model it with some quantum mechanics thrown in show a tremendous amount of additional state that scales with the surface area of the black hole. This work suggests even more complications to that picture. That it looks very different from the classical theory. All of this should come with disclaimers and fudge factors because of ou…

Black holes probably have additional state in a full quantum theory, such as lepton number. However, to an extremely good approximation, they'll still look like objects with just three properties.

Current thinking is that black holes have a LOT of state, not just a little. Anything else would result in loss of entropy.

See https://physics.stackexchange.com/a/163046/6796.

Re: Black holes as the source of dark energy

#45

Post by andrewflnr »

justinpombrio wrote: post #43
pdonis wrote: post #8

Earlier quoted context omitted.

> I actually thought that black holes slowly evaporate This is believed to be true, but the time scale is something like 60 or more orders of magnitude longer than the age of the universe, so (a) no evidence for this effect exists or is likely to be found any time soon, and (b) it's irrelevant for the dynamics of our current universe anyway.

I thought we had evidence that black holes evaporate in that Earth hasn't been swallowed up yet. A while back there were concerns (notably not from physicists) about the LHC forming black holes. I remember the response being that tiny black holes frequently form in the upper atmosphere due to high energy particle collisions, but black holes emit more radiation the smaller they are(!), so these tiny black holes evapor…

To be more precise, if LHC was capable of forming black holes, then they would also be regularly formed in the upper atmosphere by cosmic rays... but more likely neither of those is the case. I don't think many serious physicists actually think particle collisions create black holes.

Re: Black holes as the source of dark energy

#47

Post by andrewflnr »

smath wrote: post #7
2bitencryption wrote: post #4

In my imagination, I always thought we could put a black box around a black hole, and it would be indistinguishable from any other mass - that is, any other mass that can be treated as a point mass. I.e. put a black hole with solar mass 1 in a black box. Put a star with solar mass 1 in another black box. From a gravitational point of view, you couldn't tell the difference, yes? But this result implies that the black…

You mention point mass. Yes, the volume also matters. If your second black box contains the same mass but over a bigger volume, then the spacetime curvature it will cause will be less extreme than the black hole in the first box. The book I most like on this topic is Kip Thorne's Black Holes and Time Warps. IMO Thorne is a better explainer than Hawking.

I'm pretty sure by the time you're outside the box, assuming it's the same size for both, you can't tell anymore. I'm quite confident this is the case for classical gravity and a spherically symmetric "box", and I don't think tides or relativistic corrections are noticeably different far away from the horizon. (Yeah, you'll feel the black hole's tides, but stars have tides too.)

Re: Black holes as the source of dark energy

#48

Post by dtgriscom »

pmontra wrote: post #20
pdonis wrote: post #6

Earlier quoted context omitted.

> I always thought we could put a black box around a black hole, and it would be indistinguishable from any other mass - that is, any other mass that can be treated as a point mass. Yes, that's what the standard theory of black holes says. > this result implies that the black box with the black hole will gain mass over time, even without adding any mass into the black box? Sort of. First, it's important to note that…

If I understood the paper [1] correctly, the idea is that all black holes don't contain a singularity. They have vacuum energy instead and that leads to the increase of mass and dark energy. [1] https://iopscience.iop.org/article/10.3847/2041-8213/acb704/...

> all black holes don't contain a singularity.

Do you mean "not all black holes contain a singularity"?

Re: Black holes as the source of dark energy

#49

Post by piyh »

vl wrote: post #35
thricegr8 wrote: post #12

Cross-posting /r/bestof ( https://www.reddit.com/r/worldnews/comments/113casc/scientis... ) because it really does a nice job with history and breaking down the highlights (to me at least:) -------- Reading the paper, this is the best summary I can make. Note that I'm an engineer, not an astrophysicist. The basic thought is that in 1963, a guy named Kerr seems to have come up with the best approximation of black hole…

> In 2019, 2 guys named Kevin Croker and Joel Weiner demonstrated that the universe's expansion rate varies based how heavy the space next to it is. Does it expand faster next to heavy object or slower?

Slower if I'm remembering SpaceTime correctly

https://m.youtube.com/watch?v=bUHZ2k9DYHY

Re: Black holes as the source of dark energy

#50

Post by ISL »

andrewflnr wrote: post #45
justinpombrio wrote: post #43

Earlier quoted context omitted.

I thought we had evidence that black holes evaporate in that Earth hasn't been swallowed up yet. A while back there were concerns (notably not from physicists) about the LHC forming black holes. I remember the response being that tiny black holes frequently form in the upper atmosphere due to high energy particle collisions, but black holes emit more radiation the smaller they are(!), so these tiny black holes evapor…

To be more precise, if LHC was capable of forming black holes, then they would also be regularly formed in the upper atmosphere by cosmic rays... but more likely neither of those is the case. I don't think many serious physicists actually think particle collisions create black holes.

Collisions of sufficient energy could potentially create tiny black holes. GP has the right idea though -- evaporation goes power-law faster the smaller the black hole.

No matter what the mechanism for protection from cosmogenic-collision black holes, if they were problematic, the Sun would have been destroyed long ago through a black-hole creation, black-hole capture, solar-collapse process with cosmic rays much higher in energy than anything humans will ever generate. So, as long as you can look outside and see the sun, you need not ever sweat the particle-collision destroys the world hypothesis, no matter whence the particles are generated.

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