They are singularities in the framework of general relativity, i.e. while ignoring quantum mechanics. I think most people expect the right version of quantum gravity to make the singularities go away, but studying classical GR is worth it on its own, so it's often ignored like in this statement you quoted.
What if gravity is non-linear and thus collapses the wave function? I think Penrose has suggested gravity as an objective collapse interpretation. The measurement problem still hasn't been resolved, but we observe a classical world around us, despite the fact that decoherence simply spreads the superposition of interacting quantum systems to the world. Gravity could be what prevents the linearity of quantum systems from putting the entire universe into superposition.
Gravity is non-linear (as in: the Einstein field equations are non-linear differential equations).
That has nothing to do with the measurement problem. Also, the measurement problem is only a problem of the Copenhagen interpretation. It doesn't exist in the many worlds interpretation.
> Also, the measurement problem is only a problem of the Copenhagen interpretation. It doesn't exist in the many worlds interpretation.
Doesn't many worlds require branching into numbers of branches that would in some cases be irrational numbers? And you have to have some kind of index on the branch to make some of them physically distinguishable enough to still maintain probability. If equivalent branches are in there it's hard to explain how a 75%/25% branch would be distinguishable as a probability to an observer without some kind of extra index like information that has them land in the 75% more often. ( https://en.wikipedia.org/wiki/Many-worlds_interpretation#Pro...)
> That has nothing to do with the measurement problem.
He refered to I think the Diósi-Penrose model, where it would:
In that link that says that was Everett's initial attempt to solve but it has been debated and extended. I only have a podcast understanding of it, and have heard the popular proponents of many worlds like Sean Carrol say that is the biggest problem that needs more development, he has his own self-locating thing but there are many other approaches.
But on the other point, how can there be an irrational number of branches to sample these statistics from? I just can't visualize the type of structure that would have that but I'm sure it is more subtle. I've heard the branches aren't branches under MWI but instead are something more continuous and I guess I don't understand it at that point.
Wikipdeia references https://arxiv.org/abs/0905.0624 and first thing I noticed in section IV the author incorrectly calculates copenhagen prediction (because probabilities are counterintuitive), but correctly everettian prediction (because marginal outcomes are obvious there) and claims this discrepancy disproves MWI, he conveniently forgets about empirical equivalence of interpretations, so that it's easier to make an error and get different predictions. Then makes incorrect claim about MWI. Any given observer will probably observe confirmation of Born rule due to the law of large numbers.
The structure of superposition is given by solution of the Schrodinger equation. It's often continuous, e.g. electron's s orbital in atom is a continuum of coordinate eigenstates. In this case a discrete sum is replaced with an integral and Born rule becomes a function on this continuum, but a discrete case can be easier to understand, so I recommend to start with that. The proof follows the law of large numbers https://en.wikipedia.org/wiki/Law_of_large_numbers
Gravity as in the actual force or field, not the current equations. You mentioned quantizing gravity, a few physicists like Penrose doubt it can be done. MWI is not a consensus, and there are more than two interpretations. Objective collapse theories have also been proposed, at least one involves gravity as the mechanism.
The nonlinearity of gravity is obvious even in the solar system - it was discovered because Mercury's orbit, when described with the linear theory of Newton's universal gravitation, behaved as if there were an additional hidden mass between its orbit's periastron point and the sun. Or, if you prefer, summing all the sources of gravitation in the solar system is insufficient for describing all the observed orbits in the solar system. (Indeed, even if you summed all the sources of gravity in the galaxy, you wouldn't get the evolution of the relatively eccentric elliptical orbit of Mercury right.)
Precision measurements by satellites around Earth and spacecraft scattered around the solar system reveal the nonlinearity of gravitation, as do precision measurements of systems like Hulse-Taylor and PSR J2222-0137.
A linear superposition law for gravitation is consequently unavailable - again, this can be seen in the solar system, where a linear superposition model helped find a real mass (Neptune, where ultimately the telescope targetting was driven by Urbain Le Varrier's detailed study of the orbit of Uranus in the 1840s, assuming the validity of Newtonian gravitation), but misled astronomers into decades of futile searches for "Vulcan", a hypothetical body inside Mercury's orbit.
There are a bunch of ways one can capture the nonlinearity of observed gravitation. A nice slogan: gravitation self-gravitates. A nice theoretical framework: Newton-Cartan gravity is great for exploring the failure of linear gravity. An easier theoretical approach: the relativistic two-body effective radial potential energy <https://en.wikipedia.org/wiki/Two-body_problem_in_general_re...> or less encyclopedically <https://spaceengine.org/articles/the-anomalous-advance-of-th...> where you can see the same effective potential term written slightly differently, with more about Mercury's orbit.
Quoting the latter:
Again I don't want to get lost in math, but it's worthwhile
just to look briefly at what the math is saying here.
Notice this still has the exact same two terms from the
Newtonian effective potential: an attraction that goes as
-1/r, and a repulsion that goes as +1/r^2. But a new term
is added: another attractive term that goes as -1/r^3. This
means that at very small radii, the -1/r^3 term dominates,
and gravitation becomes attractive again, dominating even
over the centrifugal effect of your orbital velocity.
The increased attraction mimics an additional mass in a linear theory.
No linear theory of gravitation is viable for known planetary and astrophysics. At best one can come up with a quasi-linear theory.
This is calculationally unfortunate: solving the full nonlinear Einstein Field Equations exactly is fiendishly hard. Where one can use a linear approximation, essentially every physicist would choose to do so. Indeed, Einstein invented linearized gravity (and various other approximation techniques). Unfortunately, linear theories of gravity can only ever be approximate, as they fail to deal with multibody systems, systems where orbital velocities are even only thousands of kilometres per second, where one wants to trace out radiation (including gravitational radiation), and so forth. Convincing proof of incompatibility between any possible linear theories of gravity and numerous observed physical orbits have been known since the 1960s. Roman Sexl did some really interesting work (alone and with collaborators like Otto Nachtmann) in that area in that decade.
These days one can turn to box 7.1 (sec. H) of Misner Thorne & Wheeler as a textbook starting point.
None of this really has anything to do with quantum mechanics, except with respect to a correspondence principle (e.g. Fraunhofer-like spectral lines have their origin in quantum mechanics, and we can see how gravity rather than just motion affects them).
Decoherence splits your state into superposition of several coherent states then you observe one classical result in each state in superposition, that's why it looks classical.
As far as I know the limits on physical collapse theories are extremely strong and there are some reasonably good philosophical reasons to doubt them as well. I don't have the text in front of me at the moment but Aaronson's Quantum Computing Since Democritus has a section on this, I think. If physical collapse were true then the implications for quantum computing would beggar belief. P=NP stuff.
Sabine doesn't even say it's disproven, and the paper doesn't claim that it's disproven, it just claims that one of the earliest proofs that it was a singularity was incorrect. There's an important distinction there. If someone points out a flaw in a proof of the pythagorean theorem, that doesn't mean the theorem is disproved, it just means that the proof was wrong.
To the extent anything in this discussion can be absolute, it's the wrongness of your statement. Nothing about singularities has been empirically proven (or disproven).
You don’t seem to be new around here, so this quote from this forum’s guidelines is more for the benefit of others
> When disagreeing, please reply to the argument instead of calling names. "That is idiotic; 1 + 1 is 2, not 3" can be shortened to "1 + 1 is 2, not 3."
But that is not name-calling. In your words, that is snark. Are all snarky comments also name calling now, and vice-versa? One could argue that the comment stands factually with just the first sentence, too. It’s strong, yes, but very different from name calling. I think it’s a valuable tool in learning in that it [snark] reminds us to choose our words very carefully, and we all need reminders of that sometimes. Also…
There are plenty of various oblique ways of expressing similar sentiment that can hurt an educated person much more than name-calling (which, conversely, can be more amusing than anything). Digs like “the wrongness of your statement” are definitely far on relevant spectrum.
Therefore, I believe the rules against name-calling are not literal. As you noticed, attempting to restrict discussion more strictly would make it bland, but on the other hand when it comes to literal name-calling in a civilized discussion it’s way past all limits.
Tangentially, I was surprised to learn recently that merely the use of specific “you” in an argument is already considered unnecessary and perceived as somewhat confrontational. Haven’t confirmed it from multiple sources (not sure how to search for), but in hindsight it makes sense: the mood changes, and the argument can quickly devolve thereafter. I suspect it might be something from psychotherapy practice.
> merely the use of specific “you” in an argument is already considered unnecessary
Not necessarily unnecessary, but necessarily personal.
If I changed the “your” in the top comment to “this,” I think it would better communicate both my issue and reasonable irritation with the comment I was responding to. At the same time there is another commenter in this thread who refused to back down, and at that point a “you’re bordering on trolling” seems appropriate. It is confrontational, but not unnecessarily so.
One divided by zero is a singularity. Singularity, mathematically speaking, means your math breaks. Calculus gets around this problem with limits. But there is absolutely nothing about physics that prohibits singularities, even gravitational singularities, in a zero G space because by definition a gravitational singularity per se has an undefined G.
Anyway, I propose to dig tunnel to the center of the Moon with plasma cutters and make a lab there. IMHO, the result will be worthy.
As non-native speaker, it's hard for me to argue with native speakers (especially when I sick, tired, in army, and at war), and I refuse to use AI to translate, because I suspect that such messages will be automatically rejected by future archivists.
Why not dig a tunnel to the center of a smaller body like an asteroid?
I think you're talking about the fact that the gravitational force inside of a symmetric shell of matter is zero. But the potential is not, as can be (and has been, I believe) demonstrated quite easily by just putting a clock in a hole and measuring the time dilation relative to the surface.
AFAIK, asteroids are nor solid, nor round. Moreover, their gravitational field is very low already. They are much further than Moon, so it will be harder to communicate.
Moreover, the tunnel itself will create much stronger impact on results on asteroid, than on Moon. If we will dig ∅1 cm tunnel to the center of the Moon, it missing volume will be pretty insignificant and easy to compensate, e.g. with lead plug.
Moreover, big and rigid Moon will be much better antenna for lot of experiments, than small and soft asteroid.
If they don’t doesn’t that imply that a superextremal black hole could exist since there would be no naked singularity whose observation is forbidden by any cosmic censorship hypothesis?
> Singularity means that at least some barions will be at the same place in the same time
The singularity in a black hole has no conception of baryons, hadrons or fermions. Those are quantum particles. The singularity is in general relativity.
Also, 0G doesn’t mean zero gravity. An object in freefall is still subject to gravity despite experiencing 0G.
(Side note: fermions can occupy the same place at the same time. They cannot occupy the same state. This seeming mathematic fuckery goes on to describe many real-world weirdos like neutron stars.)
If matter falling into a singularity never reaches it because time slows down infinitely as you approach, wouldn’t this be a physical representation of a mathematical limit from calculus? The actual literal 1d singularity never forms but it is approached infinitely close.
I am a physicist but I think he is more or less technically correct. We have photos of black hole like objects but no evidence that they conform to the object described in general relativity except in broad terms. There are the obvious issues with quantization, for example, but there are also multiple ways we can formulate GR-style theories which give different black-hole solutions which have not yet been disambiguated by experiment.
I don't think there is any harm really in calling the objects we have "taken photographs of" (these images are model dependent, so to call them photographs is a bit of a stretch) "black holes," but if we want to be totally precise a black hole is a specific concept in GR, a theory which most people think is incomplete, and we have only found some correspondences between that theoretical object and some observations in the world.
It is an interesting exercise to apply this sort of thinking to (for example) electrons. Do we know electrons exist? In an informal sense, obviously, but in a more detailed sense I would argue care must be taken. We know that QED, for example, is not renormalizable, and thus we ought to be careful to distinguish the notion of "QED electrons" from "Standard Model Electrons" from "the things that leave exposures on our detectors."
But we do know considerably more about the qualities of the physical objects we measure and call electrons than we know about the qualities of the physical objects we measure and call black holes. I don't think its unreasonable to be careful about these things.
Observation of collapsars nicely corresponds to GR predictions about collapsars without event horizon, there's no real need to invoke black holes here. You might call them black holes, but I imagine people will be confused why these kinda black holes don't have event horizon, singularity, coordinate discontinuity, information paradox, cosmic censorship and all that stuff black holes are famous for. They already conclude there's evidence for event horizon, because it's a widely advertized feature of black holes and there's a photo of black hole.
Yes, we have photos of collapsed stars, some of which were above the Tolman–Oppenheimer–Volkoff limit and became black holes. When they are not above it, they either become white dwarf or neutron stars.
Volkoff's calculation demonstrates that a star above the limit begins to collapse. It doesn't support the claim that they already became black holes, especially this can't happen globally with galilean synchronism even under slightly unrealistic assumptions. In the end, it's a mathematical calculation under assumptions; if you want to connect it to reality, you need to understand what it claims exactly and estimate what error is introduced by difference between its assumptions and reality.
A photo of a star is cool, why not give a prize for it. Or maybe they use attention economy. You can't exactly blame them for attention economy, can you?
Photos as the only evidence of existence are a very convenient way of claming the nonexistence of something that reflects zero light. The baby-out-with-the-bathwater is that it also means there's no proof for anything outside the visible range of light, that's too small to show up on a CCD, or that predates the camera. Or you.
On the other hand, arbitrary conjecture in absence of evidence should be treated exactly as such.
It's worth noting that there are a number of phenomena for which we have built detectors to find this mysterious "dark matter", all of which have failed to turn anything up whatsoever. In fact they are less than useless in that we still don't know if any of the proposed mechanisms can even be ruled out yet. The experiments achieved basically zero information gain in that regard.
Occam's razor flashes bright in the cold dark of space.
Two event horizons, because gravitation cancels out in the center of a black hole.
ps.
Energy is sucked up from the center by second event horizon, but matter is pushed inside, forming a dense and cool crystal, a solid foundation for second order effects to play.
Black holes are a prediction of general relativity. The same theory predicts that all properties of spacetime exist up until the singularity. You cannot simultaneously believe in black holes and some sort of discontinuation of spacetime before the singularity.
It doesn't make sense to talk about black holes outside the context of GR. What do you even mean by black hole if you can't describe it in the language of GR?
> What do you even mean by black hole if you can't describe it in the language of GR?
You’re right. But playing devil’s advocate, there are QM objects that look like black holes [1] as well as observations of a supermassive object at Sagittarius A*.
The parts of GR we trust in order to interpret the data from our instruments is trusted precisely because there is evidence to back up those parts of the theory. We have no idea if that theory holds on the other side of a boundary across which no causation can occur.
The data we have about black holes is nothing more than evidence of objects with a size and density which are only consistent with black holes according to GR. Without assuming GR is true, you have only evidence of unusually dense objects, nothing more.
The alignment of certain evidence of certain parts of GR does not necessarily imply the correctness of the parts of GR that are not relevant to the evidence we have access to.
However, we can see that stars are eaten by black holes, and then can be partially released back years later, so it's proven that 1) «an event horizon» exists, 2) matter can pass the «event horizon» in both directions, 3) light cannot pass the «event horizon» in one direction.
I do not introduce a new physics, like a «singularity», without any evidence. Occam's razor is in my hands now.
The Wikipedia article is fairly loose with language, but at any rate Hawking radiation does not originate past the event horizon itself but just before it.
I suppose it's a philosophical matter, but it seems legitimate to me to view this as matter moving out of the event horizon, even if the mechanism of that motion is very indirect. One's answer would depend on whether you consider a photon that travels to your eyes from the sun after reflecting from a mirror to be the same photon that was originally emitted by the sun, because it carries that photon's energy and information, even if it was actually absorbed and then coherently re-emitted by the mirror after a staggeringly complicated sea of particle-particle interactions.
Okay in terms of philosophy sure you could maybe make an argument, I don't know.
What we can, however, say that is more tangible is that the make-up of Hawking radiation cannot depend whatsoever on the matter that falls into the black hole apart from three properties: mass, charge and momentum. Other than those three properties, all other information that crosses the event horizon is lost and can't escape.
So, if one black hole was formed purely from 1 kg of protons with 0 momentum, and another black hole was formed from 1 kg of positrons with 0 momentum, these two black holes would be indistinguishable from each other. There would be nothing that could be emitted by either black hole via Hawking radiation or any other mechanism that could allow you to deduce that one was formed from protons and the other from positrons.
It's in this stricter information theoretic sense that nothing escapes from beyond the event horizon of a black hole.
Of course, but it looks like this accretion disk was below the «event horizon», because speed is much higher, 50% of speed of light, instead of typical 10%.
> > it looks like this accretion disk was below the «event horizon»
> No it doesn’t.
It is, because of the silence before the sudden «burp». Something consumed all the radiation produced by the accretion disk. I know the only one possible solution: the «event horizon».
Astronomers says that they are not sure:
> "Black holes are very extreme gravitational environments even before you pass that event horizon, and that's what’s really driving this," Cendes said. "We don’t fully understand if the material observed in radio waves is coming from the accretion disk or if it is being stored somewhere closer to the black hole. Black holes are definitely messy eaters, though."
but I can use this as evidence that the center of black hole contains a dense and cold crystal. Why not?
Moreover, if fractal theory is right, then we are inside infinite number of black holes of increasing sizes (or other objects). But, if we are inside a black hole, why sky is black and space is cold then?
> but I can use this as evidence that the center of black hole contains a dense and cold crystal. Why not?
The definitional trait of an event horizon is that it is causally disconnected from the outside universe. It is the "horizon" beyond which "events" cannot be causally connected to some observer.
A consequence of this is that nothing we observe on the outside can definitely tell us what's going on inside.
Closest we can get is creating a complete and consistent set of laws of physics and asking those laws what happens — it's fairly trivial to show there's an infinite number of such laws (such a demonstration is why Occam's Razor is even a thing), even despite the fact that right now we don't have a single one of them.
> Moreover, if fractal theory is right, then we are inside infinite number of black holes of increasing sizes (or other objects). But, if we are inside a black hole, why sky is black and space is cold then?
I don't even know what you think you mean with "fractal theory", but the reason space is black and cold is that (1) the hot surface visible in every direction to the right telescopes is very far away, and (2) the universe is expanding, and the combination of (1) and (2) means (3) it's been red-shifted so hard you can't see it with the naked eye.
The question of if the entire visible universe is the interior of a black hole in a bigger universe, has no apparent relationship in either direction to 1, 2 or 3.
> The definitional trait of an event horizon is that it is causally disconnected from the outside universe. It is the "horizon" beyond which "events" cannot be causally connected to some observer.
It's just a theory. When theory doesn't match reality — we replace theory.
> I don't even know what you think you mean with "fractal theory",
Fractal theory is simple: Universe is a 3D fractal, which means that if we will zoom in or zoom out for long time, we will see similar structures again and again and again, for infinity.
Thus, if we will zoom out, we will find our Universe as part of an unknown object of giant size, such as a dust particle in space.
However, if we zoom long enough, we will see that we are also part of a known object of even larger size: a dust particle, a star, a black hole, an grain on a beach, etc.
> universe is expanding
Nope. Imagine that we are sitting at surface of a rubber balloon and it deflates. We also see lot of rubber balloons around us, which are doing the same. We will see that surfaces of all balloons are moving away from us, so you may think that this rubber Universe is expanding. Surfaces of larger balloons further away are moving away even faster that surfaces of smaller balloons near to us, so you may think that this rubber Universe is expanding with acceleration, but this is just an illusion. In reality, balloons are deflating, their centers are barely moving.
> but the reason space is black and cold is that (1) the hot surface visible in every direction to the right telescopes is very far away
Yep, but why? Look, I'm trying to guess our location in outer Universe. Our base space is very rigid, it able to withstand powerful forces without hitting it limits. Black holes are able to hit limits of the space, so I suspect that equally strong forces are holding our space, thus we are inside in a black hole. But where we are in the black hole? We don't see curvature of space, thus we are in a flat part of the black hole. Where this flat part can be? IMHO, we are near to center of black hole, in the north hemisphere.
> It's just a theory. When theory doesn't match reality — we replace theory.
Sure.
But if you throw away the theory of relativity, you don't have any evidence that black holes exist in the first place — every observation of something that points to the concept of "a black hole" presupposes that relativity is close enough to correct for event horizons to be exactly as one-directional as time. (That't not a metaphor, literally).
If GR is not close enough to correct for the event horizon to be there, then black holes don't exist either, they are meaningless words.
Most actual researchers know there's a problem with GR specifically because of black holes' singularities, and at least one of GR and QM because of the EH — but nobody knows what to do about it as all the attempts to fix it either violate existing observations or have no testable consequences.
> Fractal theory is simple: Universe is a 3D fractal, which means that if we will zoom in or zoom out for long time, we will see similar structures again and again and again, for infinity.
Then it is false. The universe is not scale-invariant.
If anything, the opposite of your claim: at large scales even within the range we can sense, the "End of Greatness" scale is around 100 megaparsecs, at which point everything starts to look homogeneous and isotropic; conversely at the quantum scale, concepts of "position" and "momentum" cease to be independent. Electrons don't orbit their nucleus the way planets do, every measurement of position is random from the distribution of the corresponding "orbital".
There's nothing to even suggest what you say.
> Nope. Imagine that we are sitting at surface of a rubber balloon and it deflates. We also see lot of rubber balloons around us, which are doing the same. We will see that surfaces of all balloons are moving away from us, so you may think that this rubber Universe is expanding. Surfaces of larger balloons further away are moving away even faster that surfaces of smaller balloons near to us, so you may think that this rubber Universe is expanding with acceleration, but this is just an illusion. In reality, balloons are deflating, their centers are barely moving.
What do the balloons represent here? Because if it's space, and the more distant ones are bigger, you've just put a funny map onto an expanding spacetime.
> Yep, but why? Look, I'm trying to guess our location in outer Universe.
Meaningless.
> Our base space is very rigid, it able to withstand powerful forces without hitting it limits. Black holes are able to hit limits of the space, so I suspect that equally strong forces are holding our space, thus we are inside in a black hole. But where we are in the black hole? We don't see curvature of space, thus we are in a flat part of the black hole. Where this flat part can be? IMHO, we are near to center of black hole, in the north hemisphere.
Now I'm sure you're trolling.
These words do not seem to connect to anything tangible.
There is no testable interior of a black hole, so we cannot say if they "hit limits of space" or not — the singularity in the middle is a mathematical consequence of a divide-by-zero that no actual researcher in the field takes seriously, in part because the maths underpinning general relativity presupposes singularities never happen. (To be more precise, spacetime is presumed to be differentiable, and thus sufficiently small patches can be treated as if they were flat — singularities can never be treated this way).
Black holes get more curved, less flat as you get closer to where the maths says the singularity would be. Outside a black hole this can be directly observed, it was one of the initial tests of GR that meant it was ever taken seriously in the first place.
And "in the north hemisphere"? There's no universe-spanning magnetic field to give that meaning.
One can see the dynamics like this: the star is tidally disrupted and produces energy discharge via frictional heating (basically). Then the remnant gas is sufficiently spread out so as not to radiate much, then the dynamics of the accretion disk concentrate the infalling matter enough to heat up again and some of the material is ejected.
Given our simultaneous understanding of GR and other physical phenomena this seems like the most likely explanation.
Your first link goes to a 2023 arXiv pre-print that never landed in any journals as far as I can tell (could be wrong though). And there seems to be some controversy about whether Kerr's math shows what he says it shows.
This is the danger of trying to sensationalize science and putting any special weight on science influencers, especially ones who very often seem gung-ho about any story that challenges the status quo despite the evidence.
Layman opinion here: If a black hole forms, the point where it forms is an event horizon, but not a singularity. Then, while things get worse, it disappear from the universe.
So why would a singularity ever form? And what can't be formed, can't exist.
Cosmologist here, the event horizon is not a true singularity. There is a singularity in certain coordinates, but it goes away when doing a coordinate transformation. There is nothing physically strange going on at the event horizon. The physical singularity is only at the center.
I have the (layman) impression that there is no inside - that spacetime is so stretched around the event horizon that there is no spacetime beyond it.
But, then, I've never seen anywhere that the mass of the black hole (which is very much a real thing that exists in spacetime) is distributed over the event horizon, which would be at the biggest amount of mass a given region of spacetime can hold, and is not concentrated on a point with infinite density inside it.
1) you'd see infinite space dilation. Distance between you and anything would increase to infinity. It doesn't even matter if it's closer to the black hole from you or further away. I wonder if it even occurs with things that fall into the black hole with you.
2) You'd see time pass infinitely fast. I'd say "behind you", but not really of course: anything already fallen in you wouldn't see, and you wouldn't see anything exactly at the same position as you do, so anything you can see would see time pass infinitely fast. You'd be "transported to the end of time".
3) You'd see the whole universe compress into a single point (like in a lens I presume)
I wonder if this wouldn't present problems. The whole point of Hawking radiation is that the black hole will stretch out the wave function of light, in both ways (it "transports energy" from the virtual photon falling in to the particle escaping. The particle falling in loses energy, and keeps losing energy forever, while the particle escaping gains energy and since gravity has infinite range, it also keeps gaining energy forever, it's just that the amount decreases exponentially, never quite reaching zero. The particles never quite become real particles, however virtual particles do interact, so I'm not quite sure what makes them virtual, aside from their origin). Wouldn't it stretch out the wave function of any particle? And if you stretch out the wave function of a particle, you reduce it's energy. If you stretch it out infinitely you reduce it's energy, in the limit (but the limit is the event horizon), to zero. And the particles themselves aren't zero size: they would "see" this happen. Even the famous "point-particle" that is the electron has a wave function that occupies a portion of space (in fact, it occupies a surprisingly big volume)
So the mass of black holes could be in these frozen particles being teleported to the end of time, while losing energy.
I've often wondered about that - whether you'd see to the end of the universe. However, I've seen various descriptions using Penrose diagrams that show that events from far enough in the future would never be able to reach the intrepid explorer before they hit the singularity at the middle of the black hole (assuming that one exists).
You won't. Infinitely fast time means infinitely strong Hawking radiation that will just burn you instantly before you reach event horizon, but you will first catch a glimpse of heat death of the universe.
But is it? The event horizon will eventually be receding again, maybe enough to prevent you from actually falling in. However fast you're falling, you'll still need time to actually move forward. Time that time dilation doesn't give you.
Which of course is infinite, but not QUITE infinite infinite. The last light to reach you will be from the time the black hole ceases to exist, which is "close" (in relative terms) to the heat death of the universe, even if it's incredibly far away from it measured in years.
The notion you are referring to has to do with a particular set of coordinates you could use to describe the spacetime around a black hole. In that coordinate system the signature of the metric looks like (-+++) outside and(+-++) inside (roughly speaking, as it is not appropriate to think of these coordinates as t, x, y, z)1.
But the true insight of GR is that coordinates are not physical and that any physical question must have an answer that is coordinate invariant. So the whole exercise of imagining a "time direction" is moot. One can pose questions like "what do the null geodesics between two points look like as they move along their trajectories and one passes the event horizon" or questions like that. Ultimately only such questions have a physical meaning in GR and related theories.
Practically speaking in the local coordinates of an infalling observer passing the event horizon all the parts of the observer on the other side of the horizon, including signals, are simply destined to move towards the center of the black hole and the parts on the outside have some dynamical freedom not to. This is, in fact, what the inversion of the two coordinates means physically.
Footnote 1:
In Schwarzschild Coordinates the line element is given by:
ds^2 = -(1 - 2GM/r) dt^2 + (1 / (1 - 2GM/r)) dr^2 + r^2 dθ^2 + r^2 sin^2(θ) dφ^2
Note that if 2GM/r is less than 2 then the sign in front of dt^2 is negative and the sign in front of dr^2 is positive. If 2GM/r is greater than one then the sign in front of dt^2 becomes positive and the sign in front of dr^2 is negative. This is the so-called inversion between a spatial dimension (r) and time. But it doesn't do to take this too seriously, as, again, the physics of the situation are entirely separate from any coordinatization we might choose.
I think it overstates things a bit to say we have no idea. We have good reason to believe in the theory of general relativity over a broad range of scales and that theory provides reasonable predictions beyond the event horizon. While its certainly unclear how quantization modifies that picture, the possibilities are not infinite and we can speculate about them to some degree.
> "At the beginning of time and the center of every black hole lies a point of infinite density called a singularity"
my understanding was that this was d̶i̶s̶p̶r̶o̶v̶e̶n̶ mathematically incorrect:
- https://news.ycombinator.com/item?id=38636225
- sabine's take: https://www.youtube.com/watch?v=nz55jONtFAU
edit: disproven -> mathematically incorrect
PBS Space Time's take on Kerr's paper:
https://www.pbs.org/video/what-if-singularities-do-not-exist...
Echoing JumpCrisscross' sentiment, though. "Disproven" is way too strong of a word.
"kerr black holes" should surely have been "black-kerr holes" ;-)
They are singularities in the framework of general relativity, i.e. while ignoring quantum mechanics. I think most people expect the right version of quantum gravity to make the singularities go away, but studying classical GR is worth it on its own, so it's often ignored like in this statement you quoted.
What if gravity is non-linear and thus collapses the wave function? I think Penrose has suggested gravity as an objective collapse interpretation. The measurement problem still hasn't been resolved, but we observe a classical world around us, despite the fact that decoherence simply spreads the superposition of interacting quantum systems to the world. Gravity could be what prevents the linearity of quantum systems from putting the entire universe into superposition.
Gravity is non-linear (as in: the Einstein field equations are non-linear differential equations).
That has nothing to do with the measurement problem. Also, the measurement problem is only a problem of the Copenhagen interpretation. It doesn't exist in the many worlds interpretation.
> Also, the measurement problem is only a problem of the Copenhagen interpretation. It doesn't exist in the many worlds interpretation.
Doesn't many worlds require branching into numbers of branches that would in some cases be irrational numbers? And you have to have some kind of index on the branch to make some of them physically distinguishable enough to still maintain probability. If equivalent branches are in there it's hard to explain how a 75%/25% branch would be distinguishable as a probability to an observer without some kind of extra index like information that has them land in the 75% more often. ( https://en.wikipedia.org/wiki/Many-worlds_interpretation#Pro...)
> That has nothing to do with the measurement problem.
He refered to I think the Diósi-Penrose model, where it would:
https://en.wikipedia.org/wiki/Di%C3%B3si%E2%80%93Penrose_mod...
Born rule doesn't need index, it needs statistics of a sequence of measurements, then statistics is rationalized as a result of a stochastic process.
In that link that says that was Everett's initial attempt to solve but it has been debated and extended. I only have a podcast understanding of it, and have heard the popular proponents of many worlds like Sean Carrol say that is the biggest problem that needs more development, he has his own self-locating thing but there are many other approaches.
But on the other point, how can there be an irrational number of branches to sample these statistics from? I just can't visualize the type of structure that would have that but I'm sure it is more subtle. I've heard the branches aren't branches under MWI but instead are something more continuous and I guess I don't understand it at that point.
Wikipdeia references https://arxiv.org/abs/0905.0624 and first thing I noticed in section IV the author incorrectly calculates copenhagen prediction (because probabilities are counterintuitive), but correctly everettian prediction (because marginal outcomes are obvious there) and claims this discrepancy disproves MWI, he conveniently forgets about empirical equivalence of interpretations, so that it's easier to make an error and get different predictions. Then makes incorrect claim about MWI. Any given observer will probably observe confirmation of Born rule due to the law of large numbers.
The structure of superposition is given by solution of the Schrodinger equation. It's often continuous, e.g. electron's s orbital in atom is a continuum of coordinate eigenstates. In this case a discrete sum is replaced with an integral and Born rule becomes a function on this continuum, but a discrete case can be easier to understand, so I recommend to start with that. The proof follows the law of large numbers https://en.wikipedia.org/wiki/Law_of_large_numbers
Gravity as in the actual force or field, not the current equations. You mentioned quantizing gravity, a few physicists like Penrose doubt it can be done. MWI is not a consensus, and there are more than two interpretations. Objective collapse theories have also been proposed, at least one involves gravity as the mechanism.
The nonlinearity of gravity is obvious even in the solar system - it was discovered because Mercury's orbit, when described with the linear theory of Newton's universal gravitation, behaved as if there were an additional hidden mass between its orbit's periastron point and the sun. Or, if you prefer, summing all the sources of gravitation in the solar system is insufficient for describing all the observed orbits in the solar system. (Indeed, even if you summed all the sources of gravity in the galaxy, you wouldn't get the evolution of the relatively eccentric elliptical orbit of Mercury right.)
Precision measurements by satellites around Earth and spacecraft scattered around the solar system reveal the nonlinearity of gravitation, as do precision measurements of systems like Hulse-Taylor and PSR J2222-0137.
A linear superposition law for gravitation is consequently unavailable - again, this can be seen in the solar system, where a linear superposition model helped find a real mass (Neptune, where ultimately the telescope targetting was driven by Urbain Le Varrier's detailed study of the orbit of Uranus in the 1840s, assuming the validity of Newtonian gravitation), but misled astronomers into decades of futile searches for "Vulcan", a hypothetical body inside Mercury's orbit.
There are a bunch of ways one can capture the nonlinearity of observed gravitation. A nice slogan: gravitation self-gravitates. A nice theoretical framework: Newton-Cartan gravity is great for exploring the failure of linear gravity. An easier theoretical approach: the relativistic two-body effective radial potential energy <https://en.wikipedia.org/wiki/Two-body_problem_in_general_re...> or less encyclopedically <https://spaceengine.org/articles/the-anomalous-advance-of-th...> where you can see the same effective potential term written slightly differently, with more about Mercury's orbit.
Quoting the latter:
The increased attraction mimics an additional mass in a linear theory.No linear theory of gravitation is viable for known planetary and astrophysics. At best one can come up with a quasi-linear theory.
This is calculationally unfortunate: solving the full nonlinear Einstein Field Equations exactly is fiendishly hard. Where one can use a linear approximation, essentially every physicist would choose to do so. Indeed, Einstein invented linearized gravity (and various other approximation techniques). Unfortunately, linear theories of gravity can only ever be approximate, as they fail to deal with multibody systems, systems where orbital velocities are even only thousands of kilometres per second, where one wants to trace out radiation (including gravitational radiation), and so forth. Convincing proof of incompatibility between any possible linear theories of gravity and numerous observed physical orbits have been known since the 1960s. Roman Sexl did some really interesting work (alone and with collaborators like Otto Nachtmann) in that area in that decade.
These days one can turn to box 7.1 (sec. H) of Misner Thorne & Wheeler as a textbook starting point.
None of this really has anything to do with quantum mechanics, except with respect to a correspondence principle (e.g. Fraunhofer-like spectral lines have their origin in quantum mechanics, and we can see how gravity rather than just motion affects them).
Decoherence splits your state into superposition of several coherent states then you observe one classical result in each state in superposition, that's why it looks classical.
As far as I know the limits on physical collapse theories are extremely strong and there are some reasonably good philosophical reasons to doubt them as well. I don't have the text in front of me at the moment but Aaronson's Quantum Computing Since Democritus has a section on this, I think. If physical collapse were true then the implications for quantum computing would beggar belief. P=NP stuff.
Sabine doesn't even say it's disproven, and the paper doesn't claim that it's disproven, it just claims that one of the earliest proofs that it was a singularity was incorrect. There's an important distinction there. If someone points out a flaw in a proof of the pythagorean theorem, that doesn't mean the theorem is disproved, it just means that the proof was wrong.
> my understanding was that this was disproven
To the extent anything in this discussion can be absolute, it's the wrongness of your statement. Nothing about singularities has been empirically proven (or disproven).
You don’t seem to be new around here, so this quote from this forum’s guidelines is more for the benefit of others
You’re right. My apologies to OP and y’all. Can’t edit, but the snark was uncalled for.
I don't see any name calling. Could you eplicitly state what the problem is?
The comment stands factually with just the second sentence.
But that is not name-calling. In your words, that is snark. Are all snarky comments also name calling now, and vice-versa? One could argue that the comment stands factually with just the first sentence, too. It’s strong, yes, but very different from name calling. I think it’s a valuable tool in learning in that it [snark] reminds us to choose our words very carefully, and we all need reminders of that sometimes. Also…
There are plenty of various oblique ways of expressing similar sentiment that can hurt an educated person much more than name-calling (which, conversely, can be more amusing than anything). Digs like “the wrongness of your statement” are definitely far on relevant spectrum.
Therefore, I believe the rules against name-calling are not literal. As you noticed, attempting to restrict discussion more strictly would make it bland, but on the other hand when it comes to literal name-calling in a civilized discussion it’s way past all limits.
Tangentially, I was surprised to learn recently that merely the use of specific “you” in an argument is already considered unnecessary and perceived as somewhat confrontational. Haven’t confirmed it from multiple sources (not sure how to search for), but in hindsight it makes sense: the mood changes, and the argument can quickly devolve thereafter. I suspect it might be something from psychotherapy practice.
> merely the use of specific “you” in an argument is already considered unnecessary
Not necessarily unnecessary, but necessarily personal.
If I changed the “your” in the top comment to “this,” I think it would better communicate both my issue and reasonable irritation with the comment I was responding to. At the same time there is another commenter in this thread who refused to back down, and at that point a “you’re bordering on trolling” seems appropriate. It is confrontational, but not unnecessarily so.
We can empirically prove that gravitation cancels out in the gravitational center of an object, if we will dig into Moon.
What does this have to do with singularities? No one expects any kind of singularity anywhere around or in the moon.
Singularity is not possible at 0G, isn't?
> Singularity is not possible at 0G, isn't?
One divided by zero is a singularity. Singularity, mathematically speaking, means your math breaks. Calculus gets around this problem with limits. But there is absolutely nothing about physics that prohibits singularities, even gravitational singularities, in a zero G space because by definition a gravitational singularity per se has an undefined G.
Singularity means that at least some barions will be at the same place in the same time, which against nature of fermions.
Moreover, it hard to imagine that Higgs bosons will act at same place and time with same effectiveness.
So, I cannot believe in a singularity unless it will be physically demonstrated.
Sounds like you mean fermions. Bosons absolutely can occupy the same quantum states, look up the Bose-Einstein condensate.
Also, no one serious claims that singularities exist when taking quantum mechanics into account. It's completely unknown territory.
They’re mixing up barycentres [1] and baryons [2].
[1] https://en.m.wikipedia.org/wiki/Barycenter_(astronomy)
[2] https://en.m.wikipedia.org/wiki/Baryon
Anyway, I propose to dig tunnel to the center of the Moon with plasma cutters and make a lab there. IMHO, the result will be worthy.
As non-native speaker, it's hard for me to argue with native speakers (especially when I sick, tired, in army, and at war), and I refuse to use AI to translate, because I suspect that such messages will be automatically rejected by future archivists.
Why not dig a tunnel to the center of a smaller body like an asteroid?
I think you're talking about the fact that the gravitational force inside of a symmetric shell of matter is zero. But the potential is not, as can be (and has been, I believe) demonstrated quite easily by just putting a clock in a hole and measuring the time dilation relative to the surface.
Sorry you are at war. Good luck.
AFAIK, asteroids are nor solid, nor round. Moreover, their gravitational field is very low already. They are much further than Moon, so it will be harder to communicate.
Moreover, the tunnel itself will create much stronger impact on results on asteroid, than on Moon. If we will dig ∅1 cm tunnel to the center of the Moon, it missing volume will be pretty insignificant and easy to compensate, e.g. with lead plug.
Moreover, big and rigid Moon will be much better antenna for lot of experiments, than small and soft asteroid.
If they don’t doesn’t that imply that a superextremal black hole could exist since there would be no naked singularity whose observation is forbidden by any cosmic censorship hypothesis?
I wrote «barions», but yes, you are right, I meant «fermions». Fixed.
> Singularity means that at least some barions will be at the same place in the same time
The singularity in a black hole has no conception of baryons, hadrons or fermions. Those are quantum particles. The singularity is in general relativity.
Also, 0G doesn’t mean zero gravity. An object in freefall is still subject to gravity despite experiencing 0G.
(Side note: fermions can occupy the same place at the same time. They cannot occupy the same state. This seeming mathematic fuckery goes on to describe many real-world weirdos like neutron stars.)
If matter falling into a singularity never reaches it because time slows down infinitely as you approach, wouldn’t this be a physical representation of a mathematical limit from calculus? The actual literal 1d singularity never forms but it is approached infinitely close.
Matter falling into a singularity reaches it in a fairly short time, according to the falling observer's clock.
It's just that the _light_ that this observer emits takes infinitely long to reach observers outside of the singularity.
In the GR model of black holes, the singularity is at the end of time inside the hole, not the beginning.
I think the "singularity at the beginning of time" being referenced here is the one postulated before / at the instant of the Big Bang.
Ah, I see, I was parsing the sentence wrong.
A more diplomatic and uncontroversial way to put it is that the event horizon is the only thing we have any evidence for.
We don't have evidence for event horizon. Black hole is a hypothetical object to begin with, it exists only in mathematics, what evidence.
The photos we have of black holes?
I am a physicist but I think he is more or less technically correct. We have photos of black hole like objects but no evidence that they conform to the object described in general relativity except in broad terms. There are the obvious issues with quantization, for example, but there are also multiple ways we can formulate GR-style theories which give different black-hole solutions which have not yet been disambiguated by experiment.
I don't think there is any harm really in calling the objects we have "taken photographs of" (these images are model dependent, so to call them photographs is a bit of a stretch) "black holes," but if we want to be totally precise a black hole is a specific concept in GR, a theory which most people think is incomplete, and we have only found some correspondences between that theoretical object and some observations in the world.
It is an interesting exercise to apply this sort of thinking to (for example) electrons. Do we know electrons exist? In an informal sense, obviously, but in a more detailed sense I would argue care must be taken. We know that QED, for example, is not renormalizable, and thus we ought to be careful to distinguish the notion of "QED electrons" from "Standard Model Electrons" from "the things that leave exposures on our detectors."
But we do know considerably more about the qualities of the physical objects we measure and call electrons than we know about the qualities of the physical objects we measure and call black holes. I don't think its unreasonable to be careful about these things.
Observation of collapsars nicely corresponds to GR predictions about collapsars without event horizon, there's no real need to invoke black holes here. You might call them black holes, but I imagine people will be confused why these kinda black holes don't have event horizon, singularity, coordinate discontinuity, information paradox, cosmic censorship and all that stuff black holes are famous for. They already conclude there's evidence for event horizon, because it's a widely advertized feature of black holes and there's a photo of black hole.
We only have photos of collapsars, not black holes. For mathematics the difference is big, only black holes have peculiar mathematical properties.
> We only have photos of collapsars
Yes, we have photos of collapsed stars, some of which were above the Tolman–Oppenheimer–Volkoff limit and became black holes. When they are not above it, they either become white dwarf or neutron stars.
Volkoff's calculation demonstrates that a star above the limit begins to collapse. It doesn't support the claim that they already became black holes, especially this can't happen globally with galilean synchronism even under slightly unrealistic assumptions. In the end, it's a mathematical calculation under assumptions; if you want to connect it to reality, you need to understand what it claims exactly and estimate what error is introduced by difference between its assumptions and reality.
That definition requires a higher standard of proof than a Nobel prize committee.
A photo of a star is cool, why not give a prize for it. Or maybe they use attention economy. You can't exactly blame them for attention economy, can you?
Photos as the only evidence of existence are a very convenient way of claming the nonexistence of something that reflects zero light. The baby-out-with-the-bathwater is that it also means there's no proof for anything outside the visible range of light, that's too small to show up on a CCD, or that predates the camera. Or you.
The photo is consistent with predictions of general theory of relativity about collapsars, there's no real need to invoke black holes here.
On the other hand, arbitrary conjecture in absence of evidence should be treated exactly as such.
It's worth noting that there are a number of phenomena for which we have built detectors to find this mysterious "dark matter", all of which have failed to turn anything up whatsoever. In fact they are less than useless in that we still don't know if any of the proposed mechanisms can even be ruled out yet. The experiments achieved basically zero information gain in that regard.
Occam's razor flashes bright in the cold dark of space.
Two event horizons, because gravitation cancels out in the center of a black hole.
ps. Energy is sucked up from the center by second event horizon, but matter is pushed inside, forming a dense and cool crystal, a solid foundation for second order effects to play.
That assumes there is gravity, or even universe, "inside" the black hole. We don't have any evidence of that.
Black holes are a prediction of general relativity. The same theory predicts that all properties of spacetime exist up until the singularity. You cannot simultaneously believe in black holes and some sort of discontinuation of spacetime before the singularity.
That is a theory that makes predictions, not evidence. As you may note in my comments above, I am speaking exclusively to evidence.
It doesn't make sense to talk about black holes outside the context of GR. What do you even mean by black hole if you can't describe it in the language of GR?
> What do you even mean by black hole if you can't describe it in the language of GR?
You’re right. But playing devil’s advocate, there are QM objects that look like black holes [1] as well as observations of a supermassive object at Sagittarius A*.
[1] https://arxiv.org/html/2307.06164v2
The parts of GR we trust in order to interpret the data from our instruments is trusted precisely because there is evidence to back up those parts of the theory. We have no idea if that theory holds on the other side of a boundary across which no causation can occur.
The data we have about black holes is nothing more than evidence of objects with a size and density which are only consistent with black holes according to GR. Without assuming GR is true, you have only evidence of unusually dense objects, nothing more.
The alignment of certain evidence of certain parts of GR does not necessarily imply the correctness of the parts of GR that are not relevant to the evidence we have access to.
Occam's razor says that you must present a proof that they are not existing in a black hole.
> Occam's razor says that you must present a proof that they are not existing in a black hole
Occam’s razor absolutely doesn’t predict that the weird thing that breaks physics occurs twice and then precipitates a crystal.
Physics is fine, it just model, which breaks.
However, we can see that stars are eaten by black holes, and then can be partially released back years later, so it's proven that 1) «an event horizon» exists, 2) matter can pass the «event horizon» in both directions, 3) light cannot pass the «event horizon» in one direction.
I do not introduce a new physics, like a «singularity», without any evidence. Occam's razor is in my hands now.
> 2) matter can pass the «event horizon» in both directions
Where was this proven?
The comment you're responding to didn't assert that it is proven, but regardless: https://en.wikipedia.org/wiki/Hawking_radiation#Emission_pro...
Hawking radiation is almost painfully constructed to avoid the problem of anything, even information, crossing back through the event horizon.
The Wikipedia article is fairly loose with language, but at any rate Hawking radiation does not originate past the event horizon itself but just before it.
I suppose it's a philosophical matter, but it seems legitimate to me to view this as matter moving out of the event horizon, even if the mechanism of that motion is very indirect. One's answer would depend on whether you consider a photon that travels to your eyes from the sun after reflecting from a mirror to be the same photon that was originally emitted by the sun, because it carries that photon's energy and information, even if it was actually absorbed and then coherently re-emitted by the mirror after a staggeringly complicated sea of particle-particle interactions.
Okay in terms of philosophy sure you could maybe make an argument, I don't know.
What we can, however, say that is more tangible is that the make-up of Hawking radiation cannot depend whatsoever on the matter that falls into the black hole apart from three properties: mass, charge and momentum. Other than those three properties, all other information that crosses the event horizon is lost and can't escape.
So, if one black hole was formed purely from 1 kg of protons with 0 momentum, and another black hole was formed from 1 kg of positrons with 0 momentum, these two black holes would be indistinguishable from each other. There would be nothing that could be emitted by either black hole via Hawking radiation or any other mechanism that could allow you to deduce that one was formed from protons and the other from positrons.
It's in this stricter information theoretic sense that nothing escapes from beyond the event horizon of a black hole.
That's a very contestable point; there are strong reasons to believe the information content is indeed preserved (albeit in a scrambled form).
https://en.m.wikipedia.org/wiki/Black_hole_information_parad...
Energy, even if it doesn’t convey information is still a “thing”. Photons with a black body spectrum - thermal noise, are still things.
Hawking himself originally had an idea of photons that tunnelled through the event horizon as a possible mechanism.
See there: https://news.harvard.edu/gazette/story/2022/10/black-hole-bu...
These are ejecta from the black hole’s accretion disk.
Of course, but it looks like this accretion disk was below the «event horizon», because speed is much higher, 50% of speed of light, instead of typical 10%.
> it looks like this accretion disk was below the «event horizon»
No it doesn’t.
> because speed is much higher, 50% of speed of light
Spin the singularity.
I’d love to see a source for the authors claiming they believe matter exited the event horizon. That’s literally Nobel prize groundbreaking.
> > it looks like this accretion disk was below the «event horizon»
> No it doesn’t.
It is, because of the silence before the sudden «burp». Something consumed all the radiation produced by the accretion disk. I know the only one possible solution: the «event horizon».
Astronomers says that they are not sure:
> "Black holes are very extreme gravitational environments even before you pass that event horizon, and that's what’s really driving this," Cendes said. "We don’t fully understand if the material observed in radio waves is coming from the accretion disk or if it is being stored somewhere closer to the black hole. Black holes are definitely messy eaters, though."
but I can use this as evidence that the center of black hole contains a dense and cold crystal. Why not?
Moreover, if fractal theory is right, then we are inside infinite number of black holes of increasing sizes (or other objects). But, if we are inside a black hole, why sky is black and space is cold then?
> but I can use this as evidence that the center of black hole contains a dense and cold crystal. Why not?
The definitional trait of an event horizon is that it is causally disconnected from the outside universe. It is the "horizon" beyond which "events" cannot be causally connected to some observer.
A consequence of this is that nothing we observe on the outside can definitely tell us what's going on inside.
Closest we can get is creating a complete and consistent set of laws of physics and asking those laws what happens — it's fairly trivial to show there's an infinite number of such laws (such a demonstration is why Occam's Razor is even a thing), even despite the fact that right now we don't have a single one of them.
> Moreover, if fractal theory is right, then we are inside infinite number of black holes of increasing sizes (or other objects). But, if we are inside a black hole, why sky is black and space is cold then?
I don't even know what you think you mean with "fractal theory", but the reason space is black and cold is that (1) the hot surface visible in every direction to the right telescopes is very far away, and (2) the universe is expanding, and the combination of (1) and (2) means (3) it's been red-shifted so hard you can't see it with the naked eye.
The question of if the entire visible universe is the interior of a black hole in a bigger universe, has no apparent relationship in either direction to 1, 2 or 3.
> The definitional trait of an event horizon is that it is causally disconnected from the outside universe. It is the "horizon" beyond which "events" cannot be causally connected to some observer.
It's just a theory. When theory doesn't match reality — we replace theory.
> I don't even know what you think you mean with "fractal theory",
Fractal theory is simple: Universe is a 3D fractal, which means that if we will zoom in or zoom out for long time, we will see similar structures again and again and again, for infinity.
Thus, if we will zoom out, we will find our Universe as part of an unknown object of giant size, such as a dust particle in space.
However, if we zoom long enough, we will see that we are also part of a known object of even larger size: a dust particle, a star, a black hole, an grain on a beach, etc.
> universe is expanding
Nope. Imagine that we are sitting at surface of a rubber balloon and it deflates. We also see lot of rubber balloons around us, which are doing the same. We will see that surfaces of all balloons are moving away from us, so you may think that this rubber Universe is expanding. Surfaces of larger balloons further away are moving away even faster that surfaces of smaller balloons near to us, so you may think that this rubber Universe is expanding with acceleration, but this is just an illusion. In reality, balloons are deflating, their centers are barely moving.
> but the reason space is black and cold is that (1) the hot surface visible in every direction to the right telescopes is very far away
Yep, but why? Look, I'm trying to guess our location in outer Universe. Our base space is very rigid, it able to withstand powerful forces without hitting it limits. Black holes are able to hit limits of the space, so I suspect that equally strong forces are holding our space, thus we are inside in a black hole. But where we are in the black hole? We don't see curvature of space, thus we are in a flat part of the black hole. Where this flat part can be? IMHO, we are near to center of black hole, in the north hemisphere.
> It's just a theory. When theory doesn't match reality — we replace theory.
Sure.
But if you throw away the theory of relativity, you don't have any evidence that black holes exist in the first place — every observation of something that points to the concept of "a black hole" presupposes that relativity is close enough to correct for event horizons to be exactly as one-directional as time. (That't not a metaphor, literally).
If GR is not close enough to correct for the event horizon to be there, then black holes don't exist either, they are meaningless words.
Most actual researchers know there's a problem with GR specifically because of black holes' singularities, and at least one of GR and QM because of the EH — but nobody knows what to do about it as all the attempts to fix it either violate existing observations or have no testable consequences.
> Fractal theory is simple: Universe is a 3D fractal, which means that if we will zoom in or zoom out for long time, we will see similar structures again and again and again, for infinity.
Then it is false. The universe is not scale-invariant.
If anything, the opposite of your claim: at large scales even within the range we can sense, the "End of Greatness" scale is around 100 megaparsecs, at which point everything starts to look homogeneous and isotropic; conversely at the quantum scale, concepts of "position" and "momentum" cease to be independent. Electrons don't orbit their nucleus the way planets do, every measurement of position is random from the distribution of the corresponding "orbital".
There's nothing to even suggest what you say.
> Nope. Imagine that we are sitting at surface of a rubber balloon and it deflates. We also see lot of rubber balloons around us, which are doing the same. We will see that surfaces of all balloons are moving away from us, so you may think that this rubber Universe is expanding. Surfaces of larger balloons further away are moving away even faster that surfaces of smaller balloons near to us, so you may think that this rubber Universe is expanding with acceleration, but this is just an illusion. In reality, balloons are deflating, their centers are barely moving.
What do the balloons represent here? Because if it's space, and the more distant ones are bigger, you've just put a funny map onto an expanding spacetime.
> Yep, but why? Look, I'm trying to guess our location in outer Universe.
Meaningless.
> Our base space is very rigid, it able to withstand powerful forces without hitting it limits. Black holes are able to hit limits of the space, so I suspect that equally strong forces are holding our space, thus we are inside in a black hole. But where we are in the black hole? We don't see curvature of space, thus we are in a flat part of the black hole. Where this flat part can be? IMHO, we are near to center of black hole, in the north hemisphere.
Now I'm sure you're trolling.
These words do not seem to connect to anything tangible.
There is no testable interior of a black hole, so we cannot say if they "hit limits of space" or not — the singularity in the middle is a mathematical consequence of a divide-by-zero that no actual researcher in the field takes seriously, in part because the maths underpinning general relativity presupposes singularities never happen. (To be more precise, spacetime is presumed to be differentiable, and thus sufficiently small patches can be treated as if they were flat — singularities can never be treated this way).
Black holes get more curved, less flat as you get closer to where the maths says the singularity would be. Outside a black hole this can be directly observed, it was one of the initial tests of GR that meant it was ever taken seriously in the first place.
And "in the north hemisphere"? There's no universe-spanning magnetic field to give that meaning.
Hardly.
One can see the dynamics like this: the star is tidally disrupted and produces energy discharge via frictional heating (basically). Then the remnant gas is sufficiently spread out so as not to radiate much, then the dynamics of the accretion disk concentrate the infalling matter enough to heat up again and some of the material is ejected.
Given our simultaneous understanding of GR and other physical phenomena this seems like the most likely explanation.
> I know the only one possible solution: the «event horizon»
Try the unstable region between the ISCO and EH.
> Astronomers says that they are not sure
They’re not sure where outside the EH.
> I can use this as evidence that the center of black hole contains a dense and cold crystal. Why not?
You’re bordering on trolling, but simply, it’s because the evidence doesn’t work.
Your first link goes to a 2023 arXiv pre-print that never landed in any journals as far as I can tell (could be wrong though). And there seems to be some controversy about whether Kerr's math shows what he says it shows.
This is the danger of trying to sensationalize science and putting any special weight on science influencers, especially ones who very often seem gung-ho about any story that challenges the status quo despite the evidence.
To be fair, it's written by literal Roy Kerr.
https://en.wikipedia.org/wiki/Roy_Kerr
Layman opinion here: If a black hole forms, the point where it forms is an event horizon, but not a singularity. Then, while things get worse, it disappear from the universe.
So why would a singularity ever form? And what can't be formed, can't exist.
Cosmologist here, the event horizon is not a true singularity. There is a singularity in certain coordinates, but it goes away when doing a coordinate transformation. There is nothing physically strange going on at the event horizon. The physical singularity is only at the center.
I have the (layman) impression that there is no inside - that spacetime is so stretched around the event horizon that there is no spacetime beyond it.
But, then, I've never seen anywhere that the mass of the black hole (which is very much a real thing that exists in spacetime) is distributed over the event horizon, which would be at the biggest amount of mass a given region of spacetime can hold, and is not concentrated on a point with infinite density inside it.
black holes have an interior, you wouldn't notice if you passed the event horizon of a large enough black hole.
Wouldn't you?
1) you'd see infinite space dilation. Distance between you and anything would increase to infinity. It doesn't even matter if it's closer to the black hole from you or further away. I wonder if it even occurs with things that fall into the black hole with you.
2) You'd see time pass infinitely fast. I'd say "behind you", but not really of course: anything already fallen in you wouldn't see, and you wouldn't see anything exactly at the same position as you do, so anything you can see would see time pass infinitely fast. You'd be "transported to the end of time".
3) You'd see the whole universe compress into a single point (like in a lens I presume)
I wonder if this wouldn't present problems. The whole point of Hawking radiation is that the black hole will stretch out the wave function of light, in both ways (it "transports energy" from the virtual photon falling in to the particle escaping. The particle falling in loses energy, and keeps losing energy forever, while the particle escaping gains energy and since gravity has infinite range, it also keeps gaining energy forever, it's just that the amount decreases exponentially, never quite reaching zero. The particles never quite become real particles, however virtual particles do interact, so I'm not quite sure what makes them virtual, aside from their origin). Wouldn't it stretch out the wave function of any particle? And if you stretch out the wave function of a particle, you reduce it's energy. If you stretch it out infinitely you reduce it's energy, in the limit (but the limit is the event horizon), to zero. And the particles themselves aren't zero size: they would "see" this happen. Even the famous "point-particle" that is the electron has a wave function that occupies a portion of space (in fact, it occupies a surprisingly big volume)
So the mass of black holes could be in these frozen particles being teleported to the end of time, while losing energy.
> You'd see time pass infinitely fast
I've often wondered about that - whether you'd see to the end of the universe. However, I've seen various descriptions using Penrose diagrams that show that events from far enough in the future would never be able to reach the intrepid explorer before they hit the singularity at the middle of the black hole (assuming that one exists).
You won't. Infinitely fast time means infinitely strong Hawking radiation that will just burn you instantly before you reach event horizon, but you will first catch a glimpse of heat death of the universe.
> but you will first catch a glimpse of heat death of the universe
That doesn't seem to be possible as information/light from the end of the universe would not be able to reach you.
There's a discussion of it here: https://physics.stackexchange.com/questions/82678/does-someo...
But is it? The event horizon will eventually be receding again, maybe enough to prevent you from actually falling in. However fast you're falling, you'll still need time to actually move forward. Time that time dilation doesn't give you.
Which of course is infinite, but not QUITE infinite infinite. The last light to reach you will be from the time the black hole ceases to exist, which is "close" (in relative terms) to the heat death of the universe, even if it's incredibly far away from it measured in years.
That diagram feels unstable. The region near event horizon is infinity valley, a small perturbation there can have arbitrarily large effect.
So I've read that inside a black hole spacetime becomes so distorted that space and time eventually swap places.
I can't wrap my head around what it means for your future to become a destination that you can't escape in the same way you can't escape tomorrow.
How would an imaginary indestructible being that fell into a black hole make sense of this. Does intuition just flip to accomodate this?
The notion you are referring to has to do with a particular set of coordinates you could use to describe the spacetime around a black hole. In that coordinate system the signature of the metric looks like (-+++) outside and(+-++) inside (roughly speaking, as it is not appropriate to think of these coordinates as t, x, y, z)1.
But the true insight of GR is that coordinates are not physical and that any physical question must have an answer that is coordinate invariant. So the whole exercise of imagining a "time direction" is moot. One can pose questions like "what do the null geodesics between two points look like as they move along their trajectories and one passes the event horizon" or questions like that. Ultimately only such questions have a physical meaning in GR and related theories.
Practically speaking in the local coordinates of an infalling observer passing the event horizon all the parts of the observer on the other side of the horizon, including signals, are simply destined to move towards the center of the black hole and the parts on the outside have some dynamical freedom not to. This is, in fact, what the inversion of the two coordinates means physically.
Footnote 1:
In Schwarzschild Coordinates the line element is given by: ds^2 = -(1 - 2GM/r) dt^2 + (1 / (1 - 2GM/r)) dr^2 + r^2 dθ^2 + r^2 sin^2(θ) dφ^2
Note that if 2GM/r is less than 2 then the sign in front of dt^2 is negative and the sign in front of dr^2 is positive. If 2GM/r is greater than one then the sign in front of dt^2 becomes positive and the sign in front of dr^2 is negative. This is the so-called inversion between a spatial dimension (r) and time. But it doesn't do to take this too seriously, as, again, the physics of the situation are entirely separate from any coordinatization we might choose.
We have NO idea. The movie was fun and all, but still.
I think it overstates things a bit to say we have no idea. We have good reason to believe in the theory of general relativity over a broad range of scales and that theory provides reasonable predictions beyond the event horizon. While its certainly unclear how quantization modifies that picture, the possibilities are not infinite and we can speculate about them to some degree.
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can confirm just delivered an amazon package in one
trying to find the PBS Space Time for that but meanwhile enjoy
https://www.youtube.com/@pbsspacetime/search?query=hole