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Eldar Black Holes

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Re: Eldar Black Holes

#151

Post by zmyrgel »

hliyan wrote: post #3

I don't think that's possible. Perhaps the singularity itself will survive a "Big Crunch", but I doubt anything between it and the event horizon will. And without the ability to survive the end of the universe, life is unlikely to emerge inside an orbit within a blackhole. Because of the time dilation, life will evolve there hundreds if not thousands of times slower compared to the rest of the universe. So the lifesp…

But if the black hole can survive the big bang, therefore it can exist longer that rest of the universe so it seems to have plenty of time to evolve anything.

Re: Eldar Black Holes

#152

Post by simonh »

bArray wrote: post #135
simonh wrote: post #85

Earlier quoted context omitted.

Being emitted as undifferentiated Hawking radiation, after the black hole has shrunk to microscopic size, and when it finaly ceases to exist doesn't sound like much of a happy ending.

Wouldn't the black hole's horizon also shrink past a planet orbiting it as it loses mass?

I don’t think it makes physical sense to talk about planets orbiting inside the event horizon. Black holes only shrink due to emitting Hawking radiation from the perspective of our frame of reference at a distance. We can consider the contents of the black hole to be undifferentiated mass/energy. From the perspective of a planet in that situation, that’s kind of meaningless as the process would take infinite subjective time.

Re: Eldar Black Holes

#153

Post by garmaine »

raattgift wrote: post #149
garmaine wrote: post #147

Earlier quoted context omitted.

Yes-ish. There are two reasons we are living inside an event horizon. First the accelerating expansion of the universe means that light emitted from earth now will never reach most of the observable universe. We can look up and see galaxies that are already beyond our cone of influence. That is the primary effect. But a secondary effect is that the mass of the universe (Big Bang remains) is sufficient even though not…

No, respectfully, not unless you radically redefine what you mean by "black hole". If by "black hole" you mean an object sourcing a Kerr-Newman-like metric, then you have the problem that the distribution of matter in the distribution we see is not at all like the interior region of such a metric. The metric one can infer from the bulk distribution of the visible matter is best described by a Robertson-Walker metric.…

I think you did everything but address the point I made...

Re: Eldar Black Holes

#154

Post by yaks_hairbrush »

garmaine wrote: post #146
tigershark wrote: post #134

Earlier quoted context omitted.

Why not? You can’t have a black hole without a singularity. A black hole is formed only when >3 solar masses collapse in a singularity. Maybe the opposite is theoretically possible, the so called naked singularity in which a singularity is not hidden by an event horizon.

A black hole is a region that light cannot gravitationally escape. It has nothing to do with singularities which often but not always exist inside of a black hole. Small black holes often have singularities just to have enough mass density to capture light. It is not required though — imagine a binary system of two neutron stars that are each just below the mass threshold to collapse into a singularity. It would be a…

> More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang

This is true...

> meaning we exist inside of a black hole as big as the observable universe.

This is an unwarranted jump. I'd recommend looking at the reference [0] from Sean Carroll.

[0] http://www.preposterousuniverse.com/blog/2010/04/28/the-univ...

Re: Eldar Black Holes

#155

Post by garmaine »

yaks_hairbrush wrote: post #154
garmaine wrote: post #146

Earlier quoted context omitted.

A black hole is a region that light cannot gravitationally escape. It has nothing to do with singularities which often but not always exist inside of a black hole. Small black holes often have singularities just to have enough mass density to capture light. It is not required though — imagine a binary system of two neutron stars that are each just below the mass threshold to collapse into a singularity. It would be a…

> More oddly still as you approach the size of the observable universe, the required mass density crosses the cosmic mass density, meaning light emitted from Earth cannot gravitationally escape the universe created by the Big Bang This is true... > meaning we exist inside of a black hole as big as the observable universe. This is an unwarranted jump. I'd recommend looking at the reference [0] from Sean Carroll. [0] h…

There is nothing to be learned in that article. He says that the question is nonsense because we don’t know what is outside the observable universe. That’s not a very interesting thought restriction.

Re: Eldar Black Holes

#156

Post by raattgift »

garmaine wrote: post #153
raattgift wrote: post #149

Earlier quoted context omitted.

No, respectfully, not unless you radically redefine what you mean by "black hole". If by "black hole" you mean an object sourcing a Kerr-Newman-like metric, then you have the problem that the distribution of matter in the distribution we see is not at all like the interior region of such a metric. The metric one can infer from the bulk distribution of the visible matter is best described by a Robertson-Walker metric.…

I think you did everything but address the point I made...

Quoting you:

> We are in a black hole.

This is straightforwardly wrong. Solve the null geodesics in the near-horizon for any observer you care to conjecture, and you'll see.

Re: Eldar Black Holes

#157

Post by shullbitt0r »

whatshisface wrote: post #20
wcarss wrote: post #18

Earlier quoted context omitted.

off-topic a bit: does anyone have suggestions for paths for the layperson toward being able to reason and intuit about this stuff at one level beyond pop physics claptrap? I have heard "the theoretical minimum" suggested in the past, but I haven't heard from anyone who has actually used it to go from zero to say, general relativity, only people who think it sounds good. It also seems like a steep investment -- I just…

The only well-traveled path to understanding physics starts at "highschooler with a lot of confidence in their math skills," and it takes four years minimum. Anything else is going to be a long shot, just by virtue of the fact that nobody's doing it (for the most part). Nobody has ever discovered a way to truthfully map physics concepts into English sentences that you can understand without having to have explored th…

Can we talk about how real the perceived mismatch between other "social", "humanitarian" sciences and the "natural" sciences is?

Re: Eldar Black Holes

#158

Post by Terr_ »

Balgair wrote: post #102
jcadam wrote: post #45

Reminds me a bit of the old short story The Crystal Spheres. In that universe, once a civilization had attained a certain level of advancement, they intentionally migrated to a black hole to await the arrival of others (the idea being that all advanced civilizations in the universe were separated by so much time , that they suffered from a sort of loneliness). https://en.wikipedia.org/wiki/The_Crystal_Spheres

The BHs act like cosmic 'eggs', with civilizations acting like the 'sperm' then? Talk about first mover advantage!

"Earth" by David Brin contains a direct "black hole as sperm" metaphor from one character.

Re: Eldar Black Holes

#159

Post by candiodari »

IntronExon wrote: post #66
andrewflnr wrote: post #52

Earlier quoted context omitted.

I never thought of that in the context of strangeness, lepton number, and other conserved quantities. I don't think strangeness is really measurable (and I don't remember if it's technically conserved), but black holes should probably preserve lepton number somehow. Is that a quantum gravity sort of problem?

It might be, in that a Q-ball or something similar could there instead of a singularity, or it could be that there is no interior. Remember that the Holographic Principle implies that the total entropy of the volume of the hole can be encoded in the 2D event horizon of the hole. The singularity is a prediction of GTR, but GTR breaks down there too. This is why black holes are so exciting in the context of new theorie…

I've often wondered why that 2D event horizon is necessary. The space near the event horizon also gets stretched, from the perspective of things falling towards it. That is, if you're falling towards a black hole, the event horizon is a point that's getting closer, but it's infinitely far away (collision with event horizon will happen at a time in the future further than any other event in the future). Sufficiently stretched space would provide more than enough space to contain all the objects falling in and make it look from the perspective of someone falling in like nothing at all is happening.

It even preserves relative motion ! If A and B are both falling towards the event horizon, their relative movement doesn't change : by that I mean that if it was 2 moons, and someone launched a rocket from A towards B, it would take, say 10 hours to get to B. When both fall towards the black hole that time can still lengthen from the perspective of someone standing on A or B. It can shorten. It can stay the same. Depends on how it was changing before they started falling in.

So it could simply be that relativity stretches the space time near the event horizon enough for everything to fit in there, like that tent in Harry Potter. It looks weird from the outside, but if you're falling into the black hole it's the opposite: everything outside of that (very, very large) space near the event horizon is what looks weird. But if the black hole is big enough, it looks weird, but ... not very much.

The entirely weird thing is, you can choose initial conditions where all distances lengthen proportionally, in fact that's the more common scenario. So for all objects that are falling into the black hole, and objects not falling into it, all distances lengthen. Make the black hole big enough and the difference between things falling into it and things orbiting it or even moving away are very very small indeed.

And now you look at our universe, and that's exactly what you see. The value of the cosmological constant (ie. the universe is expanding, but ever slower and it will never actually stop expanding) can be explained by the assumption that we're falling into a very, very large black hole.

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