The quantum mysteries of black holes
science.uq.edu.au
science.uq.edu.au
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.)
It says: "This [superposition] is most commonly illustrated by Schrödinger’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.
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.
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.
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
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.
It seems like a four way black hole merger could possibly leave a space in the middle.
Is there a point where you’re at “quantum scale” around the singularity but not across the singularity? — like a quantum Einstein ring?
Where are you getting this from? It makes no sense.
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”.
There is no such thing. The singularity is a moment of time, not a place in space.
Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either.
What facts specifically are you trying to articulate about spacetime geometry around a black hole?
I already have: the singularity is a moment of time, not a place in space.
> Saying that an event horizon or photon sphere isn’t around the singularity of a black hole doesn’t make sense, either.
Yes, it does, for the reason I've already given: because there is no such thing as a sphere around a moment of time.
> What facts specifically are you trying to articulate about spacetime geometry around a black hole?
The fact that the singularity is not a place in space, it's a moment of time.
What fact about spacetime geometries are you trying to convey?
You should try explaining the relevance of what you’re repeating in terms of spacetime geometries rather than just repeating the same statement over and over — which isn’t a constructive reply.
No, it isn't. At least not in GR (perhaps your definition is valid in some other context).
In GR, a singularity is present in a spacetime if the spacetime has non-extendable geodesics. Strictly speaking, the singularity itself is not even part of the spacetime manifold; but if we attach it to the spacetime manifold as a sort of boundary, it does not have to be a point. In the case of the singularity at r = 0 in Schwarzschild spacetime, the singularity is a spacelike line which is to the future of all events inside the hole. No geodesics can be extended past that line because spacetime curvature increases without bound as it is approached (and curvature is "infinite" on the line itself, which is why the line itself is not and cannot be part of the spacetime manifold, since curvature invariants must be finite everywhere on the manifold).
> You should try explaining the relevance of what you’re repeating in terms of spacetime geometries
What I am saying is a well known property of a well known solution in GR. I am describing it in as non-technical language as I can. Perhaps what I said above will help.
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.
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.
In the case of the Earth, the coordinate singularity in longitude at the poles is an artifact of the coordinates: the Earth's poles are perfectly good parts of the Earth's surface and nothing physically goes wrong there. You just need to pick different coordinates if you want to cover the poles.
The case of the horizon of a black hole in Schwarzschild coordinates is similar: there is a coordinate singularity, but it's an artifact of the coordinates. You can find other coordinate charts that have no coordinate singularity at the horizon.
The black hole singularity at r = 0, however, is not an artifact of coordinates. It is a genuine physical singularity, where the spacetime curvature goes to infinity.
To be fair we don't know the physical curvature goes to infinity--the math says it does.
More precisely, the math of the theory that works everywhere we can test it, when extrapolated to r = 0 inside a black hole, where we cannot directly test it, says the curvature increases without bound as r = 0 is approached. The mathematical process of extrapolating a well tested theory into a domain where we cannot directly test it is used all the time in science; there's nothing inherently questionable or unreliable about it.
The issue in this particular case is that the extrapolation gives us an answer that has a problem: it doesn't seem physically reasonable to have curvature increasing without bound in a finite time, along a finite arc length on the worldline of some observer, at which point spacetime just ends and the observer is destroyed. So most physicists believe that GR, the theory, will actually break down somewhere before this point is reached, and we will need a new theory, which most physicists believe will be a theory of quantum gravity, to tell us what actually happens in this regime.
But you're correct that we won't know for sure unless and until we have some way of testing what happens in this regime.
c^4/4G
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.
He makes some bold claims, no predictions and doesn’t seem to get published, which strongly indicates he can’t get past peer review.
I read this maybe a couple years ago and it seemed legit, but I'm not a physics guy and didn't really research it more or notice it's just one guy. The idea of a maximum force is interesting in that it would put limits on some theories.
I don't know where this "maximum force" thing is coming from, but it isn't from actual physics.