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Re:Strangeness of Black Holes by dr_dshiv on Friday January 18, 2019 @06:42AM (#18938617)
I'm curious about the description of a black hole as a singularity. I'm going to resort to Neoplatonist philosophy to try to understand this.

In the formation of the universe, the notion of a singularity points at an old idea, argued by Plotinus, that everything started with "The One". This is commensurable with the statement that the boltzmann entropy of the start of the universe, prior to inflation, would be equal to "1" -- because that is the total volume of possible phase space. That, to me, is very elegant -- although it is unclear whether there are predictions about how the 1 becomes 2 ("the indefinite dyad"), 3 and then the inflationary myriad. But still, I'm impressed that the logic of ancient philosophy could correspond reasonably with modern physics.

From this perspective, I'm interpreting big bang's "singularity" as =1. What is the nature of the singularity of a blackhole? Is the event horizon itself the singularity, or does it just an effect of a singularity at the center of the blackhole? Is there a "One" at the center of the blackhole?

Re:Strangeness of Black Holes by whatshisface on Friday January 18, 2019 @08:12AM (#18939044)
If one doesn't understand a scientific theory then their understanding of it contains no information. Ancient philosophy rarely contains information. As a result the two often appear to line up.
Re:Strangeness of Black Holes by yesenadam on Friday January 18, 2019 @08:28AM (#18939115)
>Ancient philosophy rarely contains information.

Sounds like you haven't read much, gee. What a strange comment. It has a far higher signal/noise ratio than modern philosophy, I'd say, maybe because usually only the best has survived.

Re:Strangeness of Black Holes by whatshisface on Friday January 18, 2019 @09:34AM (#18939523)
>It has a far higher signal/noise ratio than modern philosophy

You can look at it this way: every possible statement seems to have been made by at least one ancient philosopher, especially once you include the non-western traditions. There were atom-ists, and continuum-ists, and so on. If you view ancient philosophy as one big bucket of sentences, it will fill up sentence space fairly uniformly. You could reconstruct ancient philosophy just by coming up with reasonable-sounding claims about things they were aware of back then until you ran out of possibilities, although that wouldn't produce the historical association of certain views with certain people.

A distribution that uniformly fills space is, in the technical sense of the word, "no information." If you trim it down (for example by doing experiments and discarding whatever doesn't match your newfound knowledge of reality), you get a distribution that "has information."

To put it concretely, finding out that an ancient philosopher said something doesn't help, because ancient philosophers said everything they could think of. Whether that is better or worse than what philosophers are doing now is up to philosophers to decide, I guess.

Re:Strangeness of Black Holes by teolandon on Friday January 18, 2019 @10:59AM (#18940156)
I haven't actually taken every single statement said by ancient philosophers (if you can even clearly classify philosophers as 'ancient' -- what's the date cutoff?), and put them in a bucket, and checked that the sentence space in that bucket is filled up uniformly.

However, new sentences are made every day, new words made very often. Nobody cares about the technical sense of the words "no information". If your argument was extended from 'ancient philosophy' to 'anything ever said by humans', then anything ever said by humans would fill the sentence space fairly uniformly, so finding out that anyone has said anything doesn't help.

A single human has not considered and thought about every sentence possible. They have their own beliefs and knowledges, and by reading ancient philosophy, they can expand that knowledge base, change those beliefs. Ancient philosophy is not inconsequential, and it certainly contains "information".

Re:Strangeness of Black Holes by dpark on Friday January 18, 2019 @11:08AM (#18940220)
I think whatshisface is being overly dismissive of the value/information in ancient philosophy. But the heart of his comment is that you can cherry pick pretty much whatever you want from ancient philosophy because the corpus is so large. If you, e.g., selectively choose statements that vaguely line up with quantum mechanics, you haven’t proven that Ancient Greeks knew quantum mechanics or had some unexpectedly deep understanding of the universe. You did something equivalent to P-hacking to dig meaningless correlations out of the noise.
Re:Strangeness of Black Holes by dr_dshiv on Friday January 18, 2019 @11:27AM (#18940397)
Right, it would be inappropriate to claim that Plato predicted the big bang!

He did arguably explicitly predict that basic mathematical/geometric forms underlie the structure of the universe. E.g., that atoms would be composed of pyramids, cubes, dodecahedrons and that the behaviour of atoms would be based upon the different geometric properties of basic forms.

That idea is only partially correct, however. Atoms are based on the basic mathematical forms -- but on the spherical harmonics of electron clouds, not point geometries. Whoops! Otherwise, the idea is commensurable with modern atomic understanding.

Earth, water, air and fire correspond not to elements (ice can melt, obviously) but to phases of matter. (Solid, liquid, gas, plasma).

There is a reason Classical Greek philosophy underlies western civilization. They were not dummies and there is still a lot we can learn from them. It's not like all their ideas were examined in the 1800s and we took all the good ones, leaving the classics as a sort of intellectual skin worth shedding. Instead, it is the core we build on. It's worth understanding the core -- and giving them the benefit of the doubt to identify interesting ideas.

Like that the universe begins with "the one" :)

Re:Strangeness of Black Holes by dpark on Friday January 18, 2019 @01:30PM (#18941525)
That is some impressively hand-wavy equivalency. Plato predicted something pretty much entirely wrong and you're pretending he was generally correct. Plato believed, without evidence, that there were some indivisible units of matter. That's all he got right (and even that was arguably incorrect given subatomic particles).
Re:Strangeness of Black Holes by whatshisface on Friday January 18, 2019 @03:16PM (#18942618)
>If your argument was extended from 'ancient philosophy' to 'anything ever said by humans', then anything ever said by humans would fill the sentence space fairly uniformly, so finding out that anyone has said anything doesn't help.

That's accurate, though. If I told you a statement and backed it up with the claim that "at some point in history, a human said it" then you really haven't learned very much. Likewise, if a statement is tagged with "and by the way, an ancient philosopher believed it," you may have learned something about history, but the statement itself hasn't gotten any more believable.

Re:Strangeness of Black Holes by ta1234567890 on Friday January 18, 2019 @11:17AM (#18940308)
This argument could be used pretty much for any field and it's just BS.

If you apply the same principle to all of language then you could say language has no information. Try it with a dictionary, the words are distributed pretty uniformly, does the dictionary have no information?

Same for the whole universe.

So are you saying that "information" only exists when some arbitrary observer (in this case you), applies some sort of filter or boundary to what they are looking at?

Re:Strangeness of Black Holes by whatshisface on Friday January 18, 2019 @11:51AM (#18940579)
>Try it with a dictionary, the words are distributed pretty uniformly, does the dictionary have no information?

That is not true at all: the dictionary is highly concentrated in correctly-spelled English words. If the dictionary was evenly spread over the space of sequences of letters A-Z it would not be useful at all, because next to Cat would be Cas and Cau.

Re:Strangeness of Black Holes by Retra on Friday January 18, 2019 @12:32PM (#18940994)
Words are not distributed uniformly in a dictionary at all. They are distributed according to the grammatical structure of the text.
Re:Strangeness of Black Holes by perfmode on Friday January 18, 2019 @07:20AM (#18938778)
I think you’re reading tea leaves here
Re:Strangeness of Black Holes by lucozade on Friday January 18, 2019 @08:22AM (#18939092)
Probably just the One tea leaf
Re:Strangeness of Black Holes by pc86 on Friday January 18, 2019 @10:51AM (#18940087)
Probably a piece of toilet paper they think is a tea leaf.
Re:Strangeness of Black Holes by robin_reala on Friday January 18, 2019 @07:16AM (#18938759)
I think your assumptions are off. Anyway, the event horizon isn’t the singularity itself, it’s the point of no return that surrounds the singularity.
Re:Strangeness of Black Holes by platz on Friday January 18, 2019 @08:44AM (#18939216)
Maybe there is a One. Some physicists think that inside a black hole is a white hole, which would look like expansion. Our cosmological horizon could match up with this
Re:Strangeness of Black Holes by perfmode on Friday January 18, 2019 @08:48AM (#18939233)
Is this the idea that our observable universe is actually inside of a larger black hole?
Re:Strangeness of Black Holes by platz on Friday January 18, 2019 @09:00AM (#18939307)
That's right
Re:Strangeness of Black Holes by pvinis on Friday January 18, 2019 @09:11AM (#18939377)
I've never heard of this. Any suggestions on where to read about these theories?
Re:Strangeness of Black Holes by dpark on Friday January 18, 2019 @10:45AM (#18940032)
I think you just read everything there is to read about this. To my understanding, the idea that our universe is actually inside a black hole is not a “theory” in the sense that, say, relativity is a theory. It’s pure conjecture, and essentially not falsifiable. It’s more akin to the “theory” that our universe is a computer simulation.
Re:Strangeness of Black Holes by michaelmrose on Friday January 18, 2019 @11:25AM (#18940384)
So what happens to stuff falling into the outside black hole?
Re:Strangeness of Black Holes by platz on Friday January 18, 2019 @11:58AM (#18940642)
you probably still hit what looks like a singularity from your perspective and get spagettified
Re:Strangeness of Black Holes by michaelmrose on Friday January 18, 2019 @02:13PM (#18941998)
Wouldn't that be additional mass appearing from nothing from the perspective of this universe
Re:Strangeness of Black Holes by matt_kantor on Sunday January 20, 2019 @09:47PM (#18957232)
Maybe this could be dark energy?

WARNING: This comment contains zero science. I didn't even Google it.

Re:Strangeness of Black Holes by perfmode on Friday January 18, 2019 @09:48AM (#18939619)
It’s the most intuitive explanation I’ve encountered for why we don’t see other life. (They might be inside of black holes.)
Re:Strangeness of Black Holes by matt_kantor on Sunday January 20, 2019 @09:51PM (#18957253)
This is not intuitive to me. Why would they be inside black holes and not outside them?
Re:Strangeness of Black Holes by andrepd on Friday January 18, 2019 @08:50AM (#18939249)
>I'm curious about the description of a black hole as a singularity. I'm going to resort to Neoplatonist philosophy to try to understand this.

Modern physics (with its successful predictions) require complicated mathematics to understand. What makes you think that neoplatonist thought can help you understand a modern scientific theory?

Re:Strangeness of Black Holes by dr_dshiv on Friday January 18, 2019 @05:31PM (#18943732)
Complicated mathematics doesn't make the singularity more understandable. It just makes more people give up trying to understand. I don't think any physicist would claim that modern physics understands time=1.

Neoplatonist thought holds the belief that the structure of the physical world is based on fundamentally basic mathematical patterns -- which is completely commensurable with modern physics. That they viewed the one as the origin of reality seems to provide a reasonable and human-readable perspective on how the entire universe of 100B+ galaxies could once exist in a volume smaller than the nucleus of an atom.

Math =! understanding. I have faith that the world is fundamentally reasonable and understandable. All models are Wong, some are useful, that sort of thing. So I appreciate the perspective of very smart ancient philosophers on this origin issue.

Re:Strangeness of Black Holes by lostmsu on Friday January 18, 2019 @07:43PM (#18944491)
> Complicated mathematics doesn't make the singularity more understandable.

What do you mean it does not? Limit theory does that in great depths. Some cases are unaccounted for, but that might actually be due to the incompleteness theorem.

Re:Strangeness of Black Holes by dr_dshiv on Saturday January 19, 2019 @06:32AM (#18946484)
I don't mean to be dismissive of complex math, but it can be seen as an excuse by people who expect the universe to NOT make intuitive sense. Usually, powerful mathematical explanations are quite simple (Maxwell's equations, Boltzmann's, etc)
Re:Strangeness of Black Holes by lostmsu on Monday January 21, 2019 @04:52AM (#18959132)
I, for one, don't expect the universe not to make intuitive sense. I just think average folk intuition is waaay to weak for that. Actually, I think the same applies to nearly all people, mathematicians the least of all.
Re:Strangeness of Black Holes by danbruc on Friday January 18, 2019 @09:24AM (#18939456)
Most physicist probably don't think that black holes actually have a singularity and attribute singularities predicted by general relativity to the fact that the theory is only approximate and breaks down under the conditions at the center of a black hole. Just because the equations say there is a singularity does not mean that there is a real singularity.
Re:Strangeness of Black Holes by Retra on Friday January 18, 2019 @12:39PM (#18941050)
Ideally, we'd understand space completely in terms of the relationships between things, and our coordinate geometry would not ascribe any "positions" to events, but only "relations" between events. Singularities are places where our improperly-formed coordinate maps break down. Which means we'd rather like to look at black holes as holes in the coordinate mapping, rather than as singularities, but we don't have the mathematical prowess to do that. Or good enough scientific understanding of the phenomena to know that we've done it correctly.
Re:Strangeness of Black Holes by danbruc on Friday January 18, 2019 @03:13PM (#18942587)
Coordinate systems are not the primary issue. It's true that coordinates can be problematic but the laws of physics are independent of coordinates because those are of course only a tool we use to perform calculations. But take for example the classical law of gravitation which requires dividing by the square of the distance between the two bodies. The distance is independent of the coordinates you use to describe the positions of the bodies but you still get a divergent force as the distance approaches zero. So the breakdown of the law is not due to a bad choice of coordinates but inherent in the equation and a strong indication that the law is probably only approximate for short distances.
Re:Strangeness of Black Holes by Retra on Friday January 18, 2019 @03:59PM (#18943018)
I believe you're just saying the same thing I am in different terms. The fact that zero is even a 'distance' you can divide by is consequence of the fact that you're deriving distance from the coordinates of the bodies. If distance was instead fundamental (and not a function of coordinates), you'd not even have a zero distance, and you'd have no inclination to attempt dividing by it. (But the math for doing that is basically to always account for every part of every body, and that's just entirely intractable.)

This is assuming mostly Newtonian physics, of course. Once you start dealing with fields and quantum mechanics, none of this makes as much sense.

Re:Strangeness of Black Holes by danbruc on Friday January 18, 2019 @04:39PM (#18943363)
Coordinates and distances are independent concepts. They are function from the space you are working with into the reals assigning each respectively each pair of elements a real number for each coordinate respectively one real number for the distance. You can for various reasons choose coordinates and distances in a way such that they have simple mathematical relationships but that is just an arbitrary choice. The classical law of gravity is only dependent on distances, which is a physical meaningful concept, but not on coordinates, which are not physically meaningful. In that sense distances are fundamental in a way in which coordinates are not and a distance of zero is a meaningful thing, namely two things are at the very same place.
Re:Strangeness of Black Holes by raattgift on Saturday January 19, 2019 @04:06PM (#18949171)
I think what you're aiming for here is the statement: somewhere in a black hole spacetime the Kretschmann scalar goes to infinity.

The Kretschmann scalar is the square of the Riemann tensor, or in notation R_{\alpha\beta\gamma\delta}R^{\alpha\beta\gamma\delta}.

There are no forces or coordinates or anything like that to even consider; it's a curvature invariant. ( https://en.wikipedia.org/wiki/Curvature_invariant_(general_r... )

If the Kretschmann scalar is non-infinite at a point then there is no gravitational singularity there.

If you really want to think about a black hole spacetime in a coordinate system, then in Schwarzschild coordinates for a Schwarzschild black hole, K = \frac{48M^2}{r^6} where K is the Kretschmann scalar. You can see that when r=0, K is undefined.

Other coordinate systems and black hole spacetimes are available.

However, generically, one can distinguish between a coordinate singularity and a gravitational singularity by calculating the Kretschmann scalar at a point. If the Kretschmann scalar is non-infinite then it cannot be the latter, whatever the coordinate basis is.

Continuing to think generically and without choosing coordinates:

"distance" -> it's still interesting for considering non-gravitational body forces of objects as we take the Kretschmann scalar around the objects towards infinity.

Essentially, tossing in one test particle just causes it to free-fall forever; tossing in two classical objects simultaneously (in Schwarzschild coordinates on Schwarzschild black hole spacetime)[1] means at some object- proper-time each object will collide with the other. They will still free-fall forever; there is a notional "down" if we have a gradient in the Kretschmann scalar field. However, the free-falling trajectories available narrow even after contact. For classical objects that are mutually repulsive, pressure[2] builds as they continue on converging free-falling trajectories and eventually classical forces cannot keep the two objects separated; they are forced into each other. The resulting compacted matter, whatever its nature, continues to free-fall forever.

Quantum-mechanically, who knows? Firstly we're way into the ultraviolet completion of the Standard Model, and secondly there's no reason to expect quantum mechanical effects to contribute to the stress-energy tensor in ways that do not look sufficiently classical under averaging or other tricks that let one continue using the geodesics of the black hole background metric or make only small perturbations to them. And we're ignoring quantum-mechanical effects outside the black hole, like Hawking radiation.

- --

[1] The simultaneity condition is a handwavy way of absorbing messy behaviour as we drop two identical charges into a black hole. See Cohen & Wald (1971), http://adsabs.harvard.edu/abs/1971JMP....12.1845C

[2] Pressure here is encoded in the stress-energy tensor T as T^{ii}, i \neq 0. Since the Einstein Field Equations say essentially G = T, we have to deal with pressure as it becomes non-negligible, because as a component of T it must be reflected in the curvature represented here as the Einstein tensor G. This is a practical example of where General Relativity is a dynamical non-linear theory. Two classical objects with identical electric charge within the horizon of a black hole makes a surprising bookkeeping mess! (compare the Schwarzschild metric with the https://en.wikipedia.org/wiki/Reissner%E2%80%93Nordstr%C3%B6... and there we are talking about what's outside the black hole and ignoring quantum mechanical effects altogether).

Re:Strangeness of Black Holes by ben_w on Friday January 18, 2019 @09:15AM (#18939398)
The ancient Greeks put the “Euclid” into “Euclidian geometry”. It took until about 1813 for that to be replaced with non-Euclidian geometry, and everything that makes General relativity really interesting is non-Euclidian.
Re:Strangeness of Black Holes by dr_dshiv on Friday January 18, 2019 @05:41PM (#18943815)
Keep in mind that the first 28 postulates of Euclid remain valid even in non Euclidean geometry. Even Euclid had to invoke another principle to clarify the 29th, which is now seen as an optional principle.

http://mathworld.wolfram.com/EuclidsPostulates.html

Re:Strangeness of Black Holes by dr_dshiv on Friday January 18, 2019 @11:14AM (#18940275)
Keep in mind that this idea of oneness wasn't just some idea of some philosopher -- it was the central idea of Platonic philosophy. Obviously, I disagree with a knee jerk rejection.