[HN Gopher] The quantum mysteries of black holes
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The quantum mysteries of black holes
Author : wjSgoWPm5bWAhXB
Score : 30 points
Date : 2022-11-01 10:09 UTC (12 hours ago)
(HTM) web link (science.uq.edu.au)
(TXT) w3m dump (science.uq.edu.au)
| denton-scratch wrote:
| The article is annoyingly superficial.
|
| It says: "This [superposition] is most commonly illustrated by
| Schrodinger's cat, which can be both dead and alive
| simultaneously."
|
| Schroedinger used the cat example to illustrate his view that a
| particle being in two mutually-exclusive states at the same time
| was absurd. He thought it was obvious that the cat _cannot_ be
| both dead and alive simultaneously.
| blueprint wrote:
| it's absurd because pretty much every particle of the cat is
| measured and thus decohered by other particles in the cat
| jerf wrote:
| In the cat thought experiment, the "box" needs to be
| conceived of as something that totally isolates you from the
| cat. No "quantum influences" travel across it. Otherwise it
| has no point.
|
| This is obviously impossible... hence, "thought experiment".
|
| If you want to make the argument this makes it ultimately
| harder to understand rather than easier, well, I'd say the
| evidence overall would favor that. It seems to confuse more
| than it casts light on anything.
|
| But if we _did_ have such a box, then the cat could be alive
| and dead simultaneously. The dead portion of the cat
| superposition would consistently see the cat as dead, the
| living portion would consistently see the cat as alive. From
| within the box nothing could collapse the superposition any
| further. Once opened you would see only one of them. People
| are bothered by the macroscopic implications of this
| violation of our intuition of how the universe works. It is
| not entirely clear to me that such a violation could ever
| manifest in reality, though; that is one heck of a box, in a
| universe with gravity, neutrinos, dark matter, etc.
| awb wrote:
| > In the cat thought experiment, the "box" needs to be
| conceived of as something that totally isolates you from
| the cat. No "quantum influences" travel across it.
|
| Is that true? I've seen references to observed macro
| superpositions without such a box:
| https://en.m.wikipedia.org/wiki/Quantum_superposition
|
| > A double slit experiment has been performed with
| molecules as large as buckyballs and functionalized
| oligoporphyrins with up to 2000 atoms.
|
| > An experiment involving a superconducting quantum
| interference device ("SQUID") has been linked to the theme
| of the "cat state" thought experiment.
|
| > A piezoelectric "tuning fork" has been constructed, which
| can be placed into a superposition of vibrating and non-
| vibrating states. The resonator comprises about 10 trillion
| atoms.
| blueprint wrote:
| It was not a gedanken experiment, though; it was a joke.
| The box is totally irrelevant, because a cat in a box is
| _not in a box_ , because the cat is not isolated, because
| the cat is actually a compound system _already_. If you had
| a single particle in a box, okay, yes, that 's valid.
|
| The cat would not be alive and dead simultaneously
| regardless of the box because it's totally entangled with
| and decohered / observed by the other elements in the box.
|
| A single particle, or a coherent system, _can_ be thought
| of as being isolated though. Do you see what I mean
| blueprint wrote:
| maybe you edited your post but thought experiments are not
| supposed to be impossible at all. they're supposed to be
| realistic. that's why we consider them "experiments".
| Einstein's photon in a moving box counting time gedanken
| experiment was used to illustrate _very_ real physics
| nathan_compton wrote:
| gee wilikers, you solved it!
| blueprint wrote:
| you act like I wasn't just talking with someone here on HN
| who was convinced we "live in a classical world" when in
| reality everything is governed by the same quantum physics
| on every scale.
| denton-scratch wrote:
| > you act like I wasn't just talking with someone here on
| HN who was convinced we "live in a classical world"
|
| I didn't understand your original reply to my comment;
| now I understand why, I think.
|
| Perhaps I failed to express myself clearly? I didn't say
| anything about quantum vs. classical worlds; I made a
| remark about the purpose for which Herr Schroedinger
| devised his cat story. His purpose was the opposite of
| the purpose implied by the article. He thought that the
| absurdity of a cat being both alive and dead demonstrated
| the absurdity of a particle being in two states at the
| same time.
|
| That is, I was talking about Herr Schroedinger's
| opinions, not my own. IANAPP, but FWIW I'm convinced that
| quantum theory in the sense of evolution of the wave
| function is correct. I don't know of any convincing
| explanation of wave-function collapse as a result of
| "observation". I don't buy many-worlds, and "just shut up
| and solve the equations" doesn't cut it for me.
|
| So in fact I'm convinced that we _don 't_ live in a
| classical world.
| blueprint wrote:
| no, no! it was an entirely different person here almost 2
| wks ago who was arguing with me about whether quantum
| mechanics can be understood without the math, all while
| making claims that showed how little he knew of the
| topic. he might have been trolling anyway. In my reply to
| you I was merely agreeing, herr denton-scratch. many
| worlds doesnt (afaict) posit why/how branch selection
| even occurs so it's sort of incomplete IMO. wavefunction
| collapse doesn't seem to exist either, but rather is a
| result of entanglement with the observer. my personal
| guess is something like superdeterminism in principle but
| I keep an open mind. I suspect that there are some basic
| consequences/meanings of the existence of
| state/information and entanglement themselves which have
| been too subtle to have been seen as assumptions in the
| past, and I am slowly working on formalizing them.
| SuoDuanDao wrote:
| I really like the interpretation that if the cat is dead, it
| can't measure anything and is therefore reliably alive
| (quantum immortality). Of course, that doesn't change that
| someone else can observe the cat being dead after opening the
| box.
| nathan_compton wrote:
| At this stage I don't think very many philosophers consider
| measurement as it takes meaning in quantum mechanics to
| have anything in particular to do with living creatures or
| brains or consciousness or anything.
| snarfy wrote:
| What is the gravitational force at the singularity? How does that
| reconcile with the maximum force? c^4/4G
|
| It seems like there is a contradiction there.
|
| https://www.motionmountain.net/maximumforce.html
| pdonis wrote:
| Gravity is not a force in GR; it's spacetime curvature.
|
| I don't know where this "maximum force" thing is coming from,
| but it isn't from actual physics.
| Rexxar wrote:
| The force at this point is mathematically undefined except if
| it is 0: What could be the direction of the force ?
| est wrote:
| I would assume we are like living pixels on a computer
| monitor, and black holes are the boundaries of the display
| viewport.
| t8sr wrote:
| Huh? What are you saying: you don't think there are black
| holes?
|
| Edit: the page you linked is a random dude who keeps publishing
| on a single topic that mainstream physics has been mostly
| ignoring. I wouldn't go as far as call him a crackpot, but he's
| definitely in the fringes. After scanning the site I still have
| no idea what he's on about, and a cursory check of published
| literature seems to support this is at least not an idea most
| people in mainstream physics would recognize.
| snarfy wrote:
| Oh there are black holes. We even have videos [1]. But are
| they infinitely dense at the singularity or is there a limit?
|
| [1] - https://www.eso.org/public/videos/eso1825e/
| philipov wrote:
| Our theories break down at the singularity and we don't
| know what happens there. That's part of why quantum gravity
| is such a big topic of research.
| SAI_Peregrinus wrote:
| AFAIK, most mainstream physicists assume the singularities
| are an artifact of the incompleteness of General
| Relativity, and that they won't exist in a theory of
| Quantum Gravity. Singularities and infinities in physics
| tend to indicate problems with a theory, they're the reason
| it's common to say that physics "breaks down" inside black
| holes.
| t8sr wrote:
| I mean, look - arguing about what happens inside the even
| horizon is kind of fun but ultimately pointless. Just FYI,
| the site you linked in the parent comment does not
| represent anything I'd call mainstream physics.
| snarfy wrote:
| this is better [1]
|
| [1] - https://arxiv.org/abs/physics/0309118
| t8sr wrote:
| Not really, that's just the same guy writing a PDF. It's
| not cited, peer reviewed or published in a journal. It's
| literally just a dude writing stuff on the internet -
| that's not necessarily a problem, but there are literally
| tens of thousands of people with "great ideas" that marry
| GR and QM, and none of their theories go anywhere, or
| make any testable predictions.
|
| He makes some bold claims, no predictions and doesn't
| seem to get published, which strongly indicates he can't
| get past peer review.
| t8sr wrote:
| The actual paper is here:
| https://link.aps.org/doi/10.1103/PhysRevLett.129.181301
|
| The summary says almost nothing, so here's what I got from the
| abstract. First some context: we currently don't have any physics
| theory that predicts the gravitational field of a particle in a
| superposition. This isn't due to a lack of ideas for theories,
| but in large part because the predicted effects are much too
| small to run experiments, for at least a few more decades.
|
| The paper is about a simulation based one candidate theory for
| such a gravitational field. The interesting result is that the
| simulation yields a range of black hole masses predicted by the
| theory, even though the authors didn't specifically plug that
| assumption in. This could be an argument in support of the
| theory. (But could also be a coincidence, or stem from some
| underlying math that the researchers didn't think about, that
| also underlies the mass prediction, which would mean the result
| is a tautology.)
| zmgsabst wrote:
| I've heard black holes described as "more diameter than the
| circumference suggests" -- to paraphrase Kip Thorne.
|
| Is there a point where you're at "quantum scale" around the
| singularity but not across the singularity? -- like a quantum
| Einstein ring?
| BoGoToTo wrote:
| Are you sure that quote isn't referring to the length dilation
| that occurs in a gravity well? Space is non-Euclidean so you
| can have a sphere with a radius larger than the circumference
| would allow.
| zmgsabst wrote:
| His quote is exactly referring to that: but my question is,
| are black holes curved enough that you can have a
| circumference at quantum scale with a diameter above that
| scale? -- ie, at which quantum effects would happen around
| but not across the singularity.
| pdonis wrote:
| _> I've heard black holes described as "more diameter than the
| circumference suggests" -- to paraphrase Kip Thorne._
|
| I'm not sure where Thorne said whatever you are paraphrasing,
| but this description does _not_ apply to black holes. It
| applies to ordinary gravitating bodies like stars and planets,
| but unlike them, black holes do not have a well-defined
| "diameter". The singularity inside the hole at r = 0 is not a
| place in space, it's a moment of time. So there is no well-
| defined "spatial distance from the singularity"; that would be
| like having a well-defined "spatial distance from tomorrow",
| which makes no sense.
| karmakaze wrote:
| Seems a point in space-time, like a point in (longitude,
| latitude) where at latitude 90, longitude loses meaning.
| fartsucker69 wrote:
| What do you mean by "across the singularity"? The singularity
| is a single point in the center. There's no being across it
| really.
| actionfromafar wrote:
| I'm sure that's right, but on the other hand space itself is
| getting "denser" nearer to the singularity. I don't know what
| to make of that.
| pdonis wrote:
| _> space itself is getting "denser" nearer to the
| singularity_
|
| Where are you getting this from? It makes no sense.
| pdonis wrote:
| _> The singularity is a single point in the center._
|
| No, it isn't. It's a spacelike line that is to the future of
| every event inside the hole. It's a moment of time, not a
| place in space.
| zmgsabst wrote:
| When the shortest path lies on some sphere around the
| singularity where the circumference of that sphere is
| "quantum scale" but chords passing near the center are not.
|
| In the 2D example, is there some area where quantum effects
| happen in an annulus rather than in a disc because that
| central stretched region is "too big".
| pdonis wrote:
| _> some sphere around the singularity_
|
| There is no such thing. The singularity is a moment of
| time, not a place in space.
| zmgsabst wrote:
| The event horizon is an example of a sphere around the
| singularity. So is the photon sphere.
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