Apparently I am not watching enough PBS SpaceTime because I still do understand what a "gravitational atom" might be.
They are not implying a particle that causes gravity right? Because I thought it is pretty well accepted there isn't a "gravaton" like there are photons.
They also don't mean atom-sized black-holes, so I still don't get it.
Hoping Matt does an episode on this so I can grasp it.
I think they are more drawing an analogy between the atom one or more black holes with a cloud of particles around them. Black holes are quantum mechanical and so the resulting system could behave much like an atom, including having things that look like energy levels. The universe rhymes.
> I thought it is pretty well accepted there isn't a "gravaton" like there are photons.
Different branch of physics that we can't quite mesh with GR yet. A graviton is the quantized "piece" of gravity, like phonon is for sound/mechanical waves, or photons for EM. It exists as much as a photon or any other "messenger particles" exists, in that it's a useful mathematical model. It's not something we have isolated/observed with equipment though.
In an atom, the electrons orbiting the nucleus are only allowed to be at discrete energy levels (the energy levels are "quantized"). In a classical model of an orbit, the energy level of a spaceship orbiting a planet can be thought of as the speed it has that allows it to orbit at a certain altitude, assuming no friction or other effects. Velocity is energy in that case (E=m*v^2 in classical mechanics). Unlike electrons in an atom, the spaceship can be in any one of a continuous range of energy levels (up to escape velocity).
The proposal in the article is (I think) that bosons orbit certain black holes in quantized energy states, like electrons would orbit an atomic nucleus.
Stupid question, but between two singularities merging, there is tiny space, with gravitation zeroing out and appearing plank matter being ripped towards one and the other. Can one spot that location in the middle where anti-matter and matter bleed from the nothing on modern telescopes?
Regardless of the gravity canceling out in this region (which is more complicated and probably will not happen). The current LIGO and Virgo wouldn't have enough spatial resolution to pinpoint tiny regions between black holes.
To explain what will happen is that gravitational field in region you are describing would have a steep spacetime curvature and a point where it will cancel gravitational forces would be more of a saddle (lagrange point classically) point rather than zero gravity region.
Now you also have quantum fluctuations that now with this strong gravitational field you will have virtual particle - anti particle paris pop in and out of vaccum. This is not going to be only in thia region but all around. Also merging process will enhance this phenomenon but deciding where actually this middle point will be difficult.
Now it would be impossible at least for our current observational tools to have resolution for the scale we are talking about. Event horizon telescope for example is designed to observe areas around singularities on much larger scales that what you are interested in here.
But the interesting part would be If matter and antimatter pairs were produced between merging black holes, they would likely be short-lived. In this intense gravitational environment, any particles created would be rapidly torn apart or accelerated towards one of the black holes. The annihilation of such pairs might emit gamma rays, but this signal would be extraordinarily faint compared to the other high-energy processes occurring during a black hole merge.
So the answer is probably No, at least with our current technology.
Gravity is not a force in GR. The spacetime curvature in a spacetime with two black holes that merge is not describable in terms of a simple "gravitational field". Spacetime curvature is a fourth rank tensor with twenty independent components. In vacuum ten of those vanish identically, leaving ten independent components.
Two black holes merging does not mean two singularities merging. The singularity (singular, not plural) is a moment of time that is to the future of all other moments inside the hole. If two black holes merge, there is just one singularity inside the merged hole.
Remember that GR is a model of spacetime, not space. In spacetime, a single black hole looks, heuristically, like a cylinder, and the singularity inside is at the future end of the cylinder. Two black holes merging look, heuristically, like a pair of trousers, and the (one) singularity inside the merged hole is at the future end of the trousers (the "waist").
very good, but I would say (since "light cone" is of such common parlance) that the physical 3d analogous projection would be two slightly overlapping 3d-venn diagram funnels conjoining at an "indefinitely" (asymptotically smaller) small space-time minkowski manifold.
naked singularities themselves, however, do not exist.
> the physical 3d analogous projection would be two slightly overlapping 3d-venn diagram funnels conjoining at an "indefinitely" (asymptotically smaller) small space-time minkowski manifold.
I'm not sure what you mean by this, but it doesn't seem to correspond to any actual physical model that I'm aware of.
both objects have a space cone that is overlapping - since they can observe each other, but also have a small bit they xor can observe, since they are a spatialtime distance apart.
regardless, once they are inside the event horizon, their spacetime ends in a "singularity" - that only they experience, since everyone else just saw an ever-slowing couple of observers that never quite reached the event horizon (to the outside observer, who would eventually be either iron or protons, depending if God had decided if they protons should decay or not yet)
i was just pointing out cone versus cylinder, since the black holes' effect is polynomial af
> both objects have a space cone that is overlapping
Again, I don't know what you mean by this, but it doesn't look like any actual physical model that I'm aware of.
> i was just pointing out cone versus cylinder
The cylinder I referred to is the outgoing side of the light cones at the horizon. The horizon itself is a lightlike surface. So the distinction you appear to be trying to draw here is simply invalid for a black hole horizon.
outside of an event horizon the 3d projection of a `light cone` (all possible spacetime causality/light/info could observe) would be an omni-directional sphere - your own observable universe, essentially - composed of ever-reddening beam of causality, being drag thru the 4th dimension, time...which results in a cone
but inside of an event horizon, that cone is actually an ever-narrowing beam in an ever-increasing gravitational field, slowing on the 4-d axis too. all ending in one 'point'.
my point being that the waist is infinitesimally, but not actually infinitely, small.
The cylinder I referred to is the outgoing side of the light cones at the horizon. The horizon itself is a lightlike surface. So the distinction you appear to be trying to draw here is simply invalid for a black hole horizon.
hawking radiation evaporates larger black holes more than smaller black holes. even if not the most testable (understatement), 4/3 * pi * r^3 where r gets smaller infinitesimally is a cone when plotted over the 4th dimension.
outside of the event horizon the "light cone" would "be" a "barely-parallel" "cylinder" yes.
the universe with all of its forever-unreachable parties outside each others sphere of causality would be like a 4-d porcupine ball.
but it doesn't look like any actual physical model that I'm aware of.
Sorry, but your statements still don't describe an actual physical model.
> the 3d projection of a `light cone`
Is not well-defined.
> all possible spacetime causality/light/info could observe...your own observable universe
This is a past light cone. The light cone whose outgoing side is the event horizon of a black hole is a future light cone.
> inside of an event horizon, that cone is actually an ever-narrowing beam in an ever-increasing gravitational field, slowing on the 4-d axis too. all ending in one 'point'.
Nope, wrong.
> hawking radiation evaporates larger black holes more than smaller black holes
Wrong. The intensity of Hawking radiation goes like the inverse cube of the mass. Smaller holes radiate more than larger holes.
> these aren't exactly intuitive geometries
Yes, indeed. Which means you shouldn't be trying to understand them intuitively the way you are doing. You should be looking at the actual math.
> the 3d projection of a `light cone`
Is not well-defined.
A future light cone is a spherical* (Lorentz transformations count? idk kinda breaks the analogy) volume of space that's radius is light speed, c. Depending on the cosmological 'constant' either being 0±ε and/or photon decay/beta omission, all light cones may one day be one singular omega one, an island of universes of estranged galaxies of un-affecting causality, or a moot memory of eternal timeless iron.
a this 4d-cone's shadow (projection unto a lower plane) is a sphere, unless one deviates the cone or observation point from it's axis/dimension of projection, then it 'sharply' becomes a pointy-hemisphere, then a cone, as the projection approaches the perpendicular axis. This deviation is the effect of Lorentz transformation affect on spacetime. The higher the deviation, the closer to C, the more stretched the projection - space - becomes for an observer.
> inside of an event horizon, that cone is actually an ever-narrowing beam in an ever-increasing gravitational field, slowing on the 4-d axis too. all ending in one 'point'.
Nope, wrong.
Care to explain how?
Once you cross the event horizon, your time will end in that same point, regardless of your movement in space.
This projection would be an ever-narrowing cone.
I appreciate the discourse, and I know projections/analogously breaking are the bane of the physicists, but I am wondering where my mental model is imprecise - at the edge of the impossible singularity, or the edge of the 'hairy' black hole?
> there's still two singularities until one falls into the other.
No, there aren't. There is just one, at the "waist" of the trousers. Again, the singularity is not a thing in space. It's a moment of time. A moment of time can't fall into anything.
One odd thing that never occurred to me until now is that two black holes that pass each other at near light speed, if they intersect by even a nanometer, will be guaranteed to merge. That nanometer has to fall into both singularities due to the properties of black holes, so transitively they have to merge. Kind of weird. I'm guessing it would create a bunch of angular momentum and throw out almost all their masses as gravitational waves. Will be a fun experiment for someone in a few hundred years.
> I'm guessing it would create a bunch of angular momentum and throw out almost all their masses as gravitational waves. Will be a fun experiment for someone in a few hundred years.
I'm not a physicist but it sounds to me like a gravitational bomb. I wonder how it will affect its surroundings? Stars being torn apart? I wouldn't like to watch such an experiment in person. Though if someone tried it a couple billions light years away from me, and then sent a video record, I'm all for it. I'd prefer to wait a couple billions years for the record to be downloaded, than to watch an online stream.
Why we should prefer the GR model, which lacks mapping from the model back to physical reality, over a physical explanation? It's clear that GR is wrong in case of black hole, because mass CAN escape black holes[1], while GR says that nothing can escape black hole after crossing of event horizon, because of [internal implementation of their model] nonsense.
OpenGL can predict nice images about black holes. Thus, our Universe is just a frame buffer (array [x,y,z;t]), while gravitation is not a force but a shader.
Sorry, our Universe is just a spacetime (array [x,y,z;t]), while gravitation is not a force but a curvature of spacetime.
Is the reason these are coherent quantum states that the postulated ultralight axions don't strongly interact with anything except gravity, so they see very little environmental noise to decohere them? Would they also predict there's (much smaller) dark matter halos around ordinary planets and stars, and these also have quantized atom-like states?
yes, just heard about it on Physics Frontiers. Monsalve & Kaiser are talking about primordial black holes, and are offering a theory that if they were imbalanced in color charge, they could be surrounded by a particle cloud, in a big quantum state.
My most recent physics rabbit hole was the black hole hole. They are fascinating.
My favorite is the idea of primordial black holes which formed in the instants after the Big Bang. Many models and theories predict them and they could be an excellent dark matter candidate. The universe could be full of black holes in the asteroid mass range the size of hydrogen atoms.
There is also a hypothesis that the predicted (by many solar system simulations and models) planet nine far beyond Neptune could be a captured primordial black hole in the 1-5 Earth mass range and about the size of a golf ball to a tennis ball.
I really really hope that exists because if it did it would be within probe range. Going and checking out a black hole could allow us to solve physics and develop a complete tested unified theory.
No, we're not. The universe is rapidly expanding. Equating the Schwarzschild radius for a given blob of matter with the event horizon of a black hole requires that the matter be static or collapsing.
The "black hole cosmology" models referred to in the Wikipedia article are misnamed. It is theoretically possible that our observable universe is a patch of a Schwarzschild spacetime, which is what the models referred to are asserting, but if it is, then, since the universe is expanding, it would be a patch of the white hole portion of the spacetime, not the black hole portion. And the "horizon" would be a white hole horizon, i.e., one from which the universe's expansion would eventually cause us to pass out of.
However, such a model is extremely unlikely because it has no way of explaining where the white hole horizon came from. A black hole horizon can come into being from gravitational collapse, but a white hole horizon would have to have been "built in" to the overall universe from the very beginning. Nobody has any reason to think that is actually possible, even if we have a theoretical mathematical model that includes it.
What if we're expanding because we are in a black hole that is being fed by a collapsing star or other object in a many orders of magnitude larger scale universe?
Of course these kinds of things are probably 100% untestable.
> What if we're expanding because we are in a black hole that is being fed by a collapsing star or other object in a many orders of magnitude larger scale universe?
Expanding and collapsing are two different things. So I don't see how your suggestion here makes any sense.
complexity of life's scale somehow trillions of magnitudes "smaller" than a similarly constructed universe is not only completely irreconcilably untestable (outside of one thought one) but also reminiscent of m-theory (11 dimensions) and the plot of men in black
I recall seeing something (likely a youtube video on cosmology) that suggested that the Big Bang would be the white hole horizon (i.e. a singularity in out past) and that does make some kind of sense as it'd be impossible to go inside the Big Bang. I recall there being some good reasons as to why that's not believed to be the case though and also why the visible universe doesn't have an event horizon.
> the Big Bang would be the white hole horizon (i.e. a singularity in out past)
The white hole horizon is not the same thing as the white hole singularity. The "Big Bang" as an initial singularity in our universe (which is not actually the correct usage of the term "Big Bang", but that's a whole other discussion) would be the white hole singularity, not the horizon.
Note also that in a white hole model of our universe, we would be inside the white hole horizon, not outside it.
> Equating the Schwarzschild radius for a given blob of matter with the event horizon of a black hole requires that the matter be static or collapsing.
If the space containing the matter is stretching does that still count as expansion?
> If the space containing the matter is stretching does that still count as expansion?
"Space stretching" is a vague pop science description that doesn't really correspond to anything in the actual physics model. So it doesn't count as anything; you should just ignore it.
I believe we shouldn't ignore it. I know about physics from pop-science mostly, so I have limited choices, either "space stretching", or (if I just ignore pop-science) "I have no clue what is happening", or I should stop doing all I'm doing now and dig into physics textbooks, to get real understanding. The last option is not really tempting, I have better ways to spend my free time, the second option doesn't seem constructive at all, so the only viable option is to not ignore vague pop-science description.
To be more precisely, you should ignore it if you want to actually understand the science. Pop science presentations will not help you understand the science. That's not what they're for. Being as charitable as possible (i.e., ignoring the obvious money-making and eyeball-capturing motives), pop science is for getting people interested in a science topic--so that at least some of them will be motivated to learn more about it, from sources like textbooks or peer-reviewed papers or class lecture notes and other teaching materials (many universities now have those available online for free) which can help you actually understand the science.
> the only viable option is to not ignore vague pop-science description.
As long as you are ok with not understanding the actual science. Nature doesn't care how much time and effort it takes to actually understand something in science. So it is no argument at all to say that you have better ways to spend your time, if you actually want to understand the science. The time required to do that is not dictated by your convenience.
It seems to me as too black-and-white view: either you understand the science, or you don't understand it, with no ground in between.
I want to understand nature, but I have limited amount of time to spend on this goal. So what? Wouldn't be my chosen strategy appropriate? Yeah, I know, my understanding will be limited and sometimes wrong, but it is understanding, isn't it? Isn't it better than total ignorance?
It works not only with nature, there are legal laws for example. Knowledge of laws have a much bigger potential to have an impact on my life, than a nuanced understanding nature. Still I'm not trying to become a lawyer using the same excuse: I have not enough time for that. Instead I maintain some vague understanding of laws and rely on it.
It works for health related issues. I can treat some minor illnesses on my own, because I have some understanding how my body works. I benefit from my limited knowledge of medicine and if my knowledge was better, I would benefit more, but still I have a limited time to study biology and medicine, so while I'm always ready to absorb some more facts, I'm not ready to get a formal education in medicine. Moreover I'm not sure it is possible, to know all the medicine, because qualified doctors are specializing, and I have no chance to be on par with all these specialists.
To my mind it is ok, but with one condition: if you know the limits of your understanding. You need to know when the time has come to seek help of a qualified specialist.
My point was to illustrate that our physics models don't agree on the nature of this expansion (Hubble tension) so using it to dismiss the fact that the observable universe is dense enough to form an event horizon seems like a stretch.
> My point was to illustrate that our physics models don't agree on the nature of this expansion (Hubble tension)
The Hubble tension is not an uncertainty about the "nature" of the expansion. No matter how that tension gets resolved, our underlying mathematical model of "the expanding universe" will not change. All that will change is that the value we use for one particular parameter in that model will be more accurately known.
> using it to dismiss the fact that the observable universe is dense enough to form an event horizon
I have not dismissed that fact at all. I have simply pointed out that, as a matter of physics, that fact does not mean our universe actually has an event horizon. "Dense enough to form a event horizon" is just a mathematical calculation. Whether that calculation actually means something, physically, does not just depend on the value it gives you. It also depends on the underlying spacetime model, and our underlying spacetime model for the universe as a whole (which, as noted above, is not in dispute at all, Hubble tension or no) is not the one in which the mathematical calculation of "dense enough to form an event horizon" has any physical meaning. (In more technical language, that calculation only has physical meaning in the Kerr-Newman family of spacetimes, but the FRW spacetime used to model our universe as a whole is not in that family.)
> However, Carter's calculations also show that a would-be black hole with these parameters would be "super-extremal". Thus, unlike a true black hole, this object would display a naked singularity, meaning a singularity in spacetime not hidden behind an event horizon. It would also give rise to closed timelike curves.
I wonder if there's a fun sci-fi story in the discovery that all electrons are in fact naked singularities.
In quantum field theory electrons are excitations in the electron field.
If they also were tiny black holes, what would it mean to be an excitation in the electron field which when the wave function collapses it would behave like a black hole. Does it mean that it's not a black hole anymore when the wave function spreads out?
If we did have a tennis-ball-sized black hole out beyond Neptune, it would be far beyond our capabilities to locate and track - we can barely track debris that small in low Earth orbit, and black holes aren't even courteous enough to provide a radar return. We would not be able to send probes near it any time soon.
If the Hawking temperature is below the CMB no net evaporation happens. This means there is a mass cutoff and it’s below asteroid mass. Any smaller PBHs would have evaporated by now assuming we are right about Hawking radiation. The math says it should exist but we have AFAIK not proven it.
The big black holes will last insanely long amounts of time.
Hawking temperature is inversely proportional to the mass. I assume most black holes except the very small ones would thus have a hawking temperature lower than the CMB.
Does that mean that effectively no black holes will ever evaporate not even a tiny bit well until the future time when the CMB will be so red shifted that black holes will start to have net radiation?
"However, since the universe contains the cosmic microwave background radiation, in order for the black hole to dissipate, the black hole must have a temperature greater than that of the present-day blackbody radiation of the universe of 2.7 K. A study suggests that M must be less than 0.8% of the mass of the Earth – approximately the mass of the Moon."
I'm not sure where the discrepancy between the mass of the Moon vs. an asteroid comes from, though.
The CMB temperature is declining as the universe expands. When it was first created it was the temperature of incandescent plasma, and it shone like the Sun.
> But gravity is the curvature of space caused by mass, it is not described as a form of mass.
Gravitational waves carry momentum and energy (and therefore mass), just like electromagnetic waves. Theoretically, you can extract that energy from gravitational waves, by using oscillating masses tuned to the wave's frequency.
> Gravitational waves carry momentum and energy (and therefore mass), just like electromagnetic waves.
No, EM waves do not have mass. They are massless. They carry momentum and energy, yes, but not mass.
In GR, the source of gravity is not "mass", it's stress-energy. EM waves carry stress-energy even though they are massless.
Gravitational waves do have some aspects that are analogous to EM waves, but there is a key difference: gravitational waves do not have any stress-energy. They are pure spacetime curvature in vacuum. So while there is a sense in which they carry momentum and energy, since properly constructed detectors can extract momentum and energy from them, they do not carry any stress-energy and the momentum and energy they carry cannot be localized the way momentum and energy in EM waves can.
No, they don't. Read what I said carefully. I did not say gravitational waves do not carry "energy". I said they do not have any "stress-energy". In other words, they are vacuum solutions of the Einstein Field Equation--their stress-energy tensor is zero. That is a true statement, and I contrasted it with EM waves, whose stress-energy tensor is not zero.
> It's just not localized
This is a consequence of the fact that their stress-energy tensor is zero, so there is no tensor that describes "energy carried by gravitational waves".
> How do you understand this process of matter escaping a black hole?
No matter escapes. Gravitational waves are not matter. They are spacetime curvature. Nor do they "escape" the black hole; they are emitted from outside the horizon. The reason the mass of the merged hole can be smaller than the combined masses of the original holes, with the difference being emitted as gravitational waves, is that black holes are not made of matter, they are made of spacetime curvature, and when they merge, some of the spacetime curvature doesn't get included in the merged hole. That's just how spacetime curvature works.
> Nor do they "escape" the black hole; they are emitted from outside the horizon.
That's interesting, I'd never really thought about that before. Does GR predict that there would be any waves confined to the inside of the merged black hole?
If there is anything combined inside the resulting event horizon it doesn't matter what it was: as far as GR is concerned it has been reduced to the effect of its mass, charge and spin. But we already know that GR isn't the whole story when it comes to BHs. See "soft hair" black holes.
> we already know that GR isn't the whole story when it comes to BHs. See "soft hair" black holes
More precisely, most physicists believe that GR isn't the whole story. But we have no actual evidence for quantum gravity speculations like "soft hair". They're just speculations at this point. We don't know that any of them will actually turn out to be right.
You are right. GR being or not the whole story is a thing, "soft hair" black holes is another thing with a much more speculative edge.
But I would say that the first assertion, that GR is not the whole story, is more or less a given knowing that GR returns non-physical infinities when trying to describe what's inside the BH.
> he first assertion, that GR is not the whole story, is more or less a given knowing that GR returns non-physical infinities when trying to describe what's inside the BH.
Only at the singularity, but the singularity itself is not even part of the spacetime manifold in GR.
In cases like black holes, there are physical invariants that do increase without bound as the singularity is approached, i.e., still within the spacetime, but their values are still finite at every point within the spacetime.
It is true that most physicists believe that when those invariants reach some particular scale, such as the Planck scale, the GR description in terms of spacetime geometry will break down. But that scale is about twenty orders of magnitude away from what we can currently probe observationally, so this is another of those speculations that, however plausible it seems, is not going to be testable any time soon.
Yes, of course there'd be no external effects. I was just curious, since the region between the event horizon and the singularity is an interesting place to think about, even if we're forever confined to predictions rather than real observations.
Which is caused by matter achieving a particular density. What we observe is not the matter but the _effects_ of the curvature created by that matter but to say they're not "made of matter" seems overly reductive here.
> some of the spacetime curvature doesn't get included in the merged hole
The observable mechanics of a black hole are (probably) controlled by it's surface area and not it's volume. When two spherical objects merge the surface area is less than the sum of the two original objects.
> Which is caused by matter achieving a particular density.
More precisely, by an isolated blob of collapsing matter surrounded by vacuum achieving a particular density.
> to say they're not "made of matter" seems overly reductive here.
No, it isn't, it is making a very important point: that the matter that originally formed the hole is not there any more. The hole itself is vacuum. If you fall into it, you won't see any matter, even though the hole was originally formed by collapsing matter.
> The observable mechanics of a black hole are (probably) controlled by it's surface area and not it's volume.
Only in the sense that the horizon area is proportional to the square of the mass, whereas the volume is not even well-defined. The actual thing that is controlling the "observable mechanics" is the mass (and spin, and charge if present, but in any actual hole it probably won't be).
Apparently I am not watching enough PBS SpaceTime because I still do understand what a "gravitational atom" might be.
They are not implying a particle that causes gravity right? Because I thought it is pretty well accepted there isn't a "gravaton" like there are photons.
They also don't mean atom-sized black-holes, so I still don't get it.
Hoping Matt does an episode on this so I can grasp it.
https://www.pbs.org/show/pbs-space-time/
I think they are more drawing an analogy between the atom one or more black holes with a cloud of particles around them. Black holes are quantum mechanical and so the resulting system could behave much like an atom, including having things that look like energy levels. The universe rhymes.
> I thought it is pretty well accepted there isn't a "gravaton" like there are photons.
Different branch of physics that we can't quite mesh with GR yet. A graviton is the quantized "piece" of gravity, like phonon is for sound/mechanical waves, or photons for EM. It exists as much as a photon or any other "messenger particles" exists, in that it's a useful mathematical model. It's not something we have isolated/observed with equipment though.
> I still do understand what a "gravitational atom" might be.
It's a vague gesture in the direction of a speculative theory of quantum gravity. It's not anything we have any actual evidence for.
In an atom, the electrons orbiting the nucleus are only allowed to be at discrete energy levels (the energy levels are "quantized"). In a classical model of an orbit, the energy level of a spaceship orbiting a planet can be thought of as the speed it has that allows it to orbit at a certain altitude, assuming no friction or other effects. Velocity is energy in that case (E=m*v^2 in classical mechanics). Unlike electrons in an atom, the spaceship can be in any one of a continuous range of energy levels (up to escape velocity).
The proposal in the article is (I think) that bosons orbit certain black holes in quantized energy states, like electrons would orbit an atomic nucleus.
As far as I know the existence of the graviton is 100% up in the air, not well accepted either way.
But yeah, particles in energy levels gravitationally bound to a black hole in a similar way electrons are electrically bound to a nucleus.
Stupid question, but between two singularities merging, there is tiny space, with gravitation zeroing out and appearing plank matter being ripped towards one and the other. Can one spot that location in the middle where anti-matter and matter bleed from the nothing on modern telescopes?
Regardless of the gravity canceling out in this region (which is more complicated and probably will not happen). The current LIGO and Virgo wouldn't have enough spatial resolution to pinpoint tiny regions between black holes.
To explain what will happen is that gravitational field in region you are describing would have a steep spacetime curvature and a point where it will cancel gravitational forces would be more of a saddle (lagrange point classically) point rather than zero gravity region.
Now you also have quantum fluctuations that now with this strong gravitational field you will have virtual particle - anti particle paris pop in and out of vaccum. This is not going to be only in thia region but all around. Also merging process will enhance this phenomenon but deciding where actually this middle point will be difficult.
Now it would be impossible at least for our current observational tools to have resolution for the scale we are talking about. Event horizon telescope for example is designed to observe areas around singularities on much larger scales that what you are interested in here.
But the interesting part would be If matter and antimatter pairs were produced between merging black holes, they would likely be short-lived. In this intense gravitational environment, any particles created would be rapidly torn apart or accelerated towards one of the black holes. The annihilation of such pairs might emit gamma rays, but this signal would be extraordinarily faint compared to the other high-energy processes occurring during a black hole merge.
So the answer is probably No, at least with our current technology.
> gravitational forces
Gravity is not a force in GR. The spacetime curvature in a spacetime with two black holes that merge is not describable in terms of a simple "gravitational field". Spacetime curvature is a fourth rank tensor with twenty independent components. In vacuum ten of those vanish identically, leaving ten independent components.
> between two singularities merging
Two black holes merging does not mean two singularities merging. The singularity (singular, not plural) is a moment of time that is to the future of all other moments inside the hole. If two black holes merge, there is just one singularity inside the merged hole.
Remember that GR is a model of spacetime, not space. In spacetime, a single black hole looks, heuristically, like a cylinder, and the singularity inside is at the future end of the cylinder. Two black holes merging look, heuristically, like a pair of trousers, and the (one) singularity inside the merged hole is at the future end of the trousers (the "waist").
very good, but I would say (since "light cone" is of such common parlance) that the physical 3d analogous projection would be two slightly overlapping 3d-venn diagram funnels conjoining at an "indefinitely" (asymptotically smaller) small space-time minkowski manifold.
naked singularities themselves, however, do not exist.
> the physical 3d analogous projection would be two slightly overlapping 3d-venn diagram funnels conjoining at an "indefinitely" (asymptotically smaller) small space-time minkowski manifold.
I'm not sure what you mean by this, but it doesn't seem to correspond to any actual physical model that I'm aware of.
both objects have a space cone that is overlapping - since they can observe each other, but also have a small bit they xor can observe, since they are a spatialtime distance apart.
regardless, once they are inside the event horizon, their spacetime ends in a "singularity" - that only they experience, since everyone else just saw an ever-slowing couple of observers that never quite reached the event horizon (to the outside observer, who would eventually be either iron or protons, depending if God had decided if they protons should decay or not yet)
i was just pointing out cone versus cylinder, since the black holes' effect is polynomial af
> both objects have a space cone that is overlapping
Again, I don't know what you mean by this, but it doesn't look like any actual physical model that I'm aware of.
> i was just pointing out cone versus cylinder
The cylinder I referred to is the outgoing side of the light cones at the horizon. The horizon itself is a lightlike surface. So the distinction you appear to be trying to draw here is simply invalid for a black hole horizon.
but inside of an event horizon, that cone is actually an ever-narrowing beam in an ever-increasing gravitational field, slowing on the 4-d axis too. all ending in one 'point'.
my point being that the waist is infinitesimally, but not actually infinitely, small.
hawking radiation evaporates larger black holes more than smaller black holes. even if not the most testable (understatement), 4/3 * pi * r^3 where r gets smaller infinitesimally is a cone when plotted over the 4th dimension.outside of the event horizon the "light cone" would "be" a "barely-parallel" "cylinder" yes.
the universe with all of its forever-unreachable parties outside each others sphere of causality would be like a 4-d porcupine ball.
these aren't exactly intuitive geometries XDSorry, but your statements still don't describe an actual physical model.
> the 3d projection of a `light cone`
Is not well-defined.
> all possible spacetime causality/light/info could observe...your own observable universe
This is a past light cone. The light cone whose outgoing side is the event horizon of a black hole is a future light cone.
> inside of an event horizon, that cone is actually an ever-narrowing beam in an ever-increasing gravitational field, slowing on the 4-d axis too. all ending in one 'point'.
Nope, wrong.
> hawking radiation evaporates larger black holes more than smaller black holes
Wrong. The intensity of Hawking radiation goes like the inverse cube of the mass. Smaller holes radiate more than larger holes.
> these aren't exactly intuitive geometries
Yes, indeed. Which means you shouldn't be trying to understand them intuitively the way you are doing. You should be looking at the actual math.
a this 4d-cone's shadow (projection unto a lower plane) is a sphere, unless one deviates the cone or observation point from it's axis/dimension of projection, then it 'sharply' becomes a pointy-hemisphere, then a cone, as the projection approaches the perpendicular axis. This deviation is the effect of Lorentz transformation affect on spacetime. The higher the deviation, the closer to C, the more stretched the projection - space - becomes for an observer.
Care to explain how?Once you cross the event horizon, your time will end in that same point, regardless of your movement in space.
This projection would be an ever-narrowing cone.
I appreciate the discourse, and I know projections/analogously breaking are the bane of the physicists, but I am wondering where my mental model is imprecise - at the edge of the impossible singularity, or the edge of the 'hairy' black hole?
But there's still two singularities until one falls into the other.
> there's still two singularities until one falls into the other.
No, there aren't. There is just one, at the "waist" of the trousers. Again, the singularity is not a thing in space. It's a moment of time. A moment of time can't fall into anything.
One odd thing that never occurred to me until now is that two black holes that pass each other at near light speed, if they intersect by even a nanometer, will be guaranteed to merge. That nanometer has to fall into both singularities due to the properties of black holes, so transitively they have to merge. Kind of weird. I'm guessing it would create a bunch of angular momentum and throw out almost all their masses as gravitational waves. Will be a fun experiment for someone in a few hundred years.
> I'm guessing it would create a bunch of angular momentum and throw out almost all their masses as gravitational waves. Will be a fun experiment for someone in a few hundred years.
I'm not a physicist but it sounds to me like a gravitational bomb. I wonder how it will affect its surroundings? Stars being torn apart? I wouldn't like to watch such an experiment in person. Though if someone tried it a couple billions light years away from me, and then sent a video record, I'm all for it. I'd prefer to wait a couple billions years for the record to be downloaded, than to watch an online stream.
What you're asking for is a naked singularity. Nothing can produce that, not even another black hole.
Each black hole has tiny spot with zero gravitation in the centre.
In some Newtonian or pseudo-Newtonian models, possibly? Not in GR/General Relativity.
Why we should prefer the GR model, which lacks mapping from the model back to physical reality, over a physical explanation? It's clear that GR is wrong in case of black hole, because mass CAN escape black holes[1], while GR says that nothing can escape black hole after crossing of event horizon, because of [internal implementation of their model] nonsense.
[1]: https://news.harvard.edu/gazette/story/2022/10/black-hole-bu...
Internal model implementations? You mean the speed of light?
OpenGL can predict nice images about black holes. Thus, our Universe is just a frame buffer (array [x,y,z;t]), while gravitation is not a force but a shader.
Sorry, our Universe is just a spacetime (array [x,y,z;t]), while gravitation is not a force but a curvature of spacetime.
You need some sort of relativity to explain the Michelson–Morley result.
Is the reason these are coherent quantum states that the postulated ultralight axions don't strongly interact with anything except gravity, so they see very little environmental noise to decohere them? Would they also predict there's (much smaller) dark matter halos around ordinary planets and stars, and these also have quantized atom-like states?
yes, just heard about it on Physics Frontiers. Monsalve & Kaiser are talking about primordial black holes, and are offering a theory that if they were imbalanced in color charge, they could be surrounded by a particle cloud, in a big quantum state.
https://pca.st/episode/f0db6ab1-18ff-4201-a6b2-a30b780a266a
My most recent physics rabbit hole was the black hole hole. They are fascinating.
My favorite is the idea of primordial black holes which formed in the instants after the Big Bang. Many models and theories predict them and they could be an excellent dark matter candidate. The universe could be full of black holes in the asteroid mass range the size of hydrogen atoms.
There is also a hypothesis that the predicted (by many solar system simulations and models) planet nine far beyond Neptune could be a captured primordial black hole in the 1-5 Earth mass range and about the size of a golf ball to a tennis ball.
I really really hope that exists because if it did it would be within probe range. Going and checking out a black hole could allow us to solve physics and develop a complete tested unified theory.
Then there’s spooky shit like:
https://en.m.wikipedia.org/wiki/Black_hole_electron
Let's not forget that the radius of the observable universe is ~= the Schwarzschild radius i.e. we're all almost certainly inside a black hole ;)
https://en.wikipedia.org/wiki/Black_hole_cosmology
> we're all almost certainly inside a black hole
No, we're not. The universe is rapidly expanding. Equating the Schwarzschild radius for a given blob of matter with the event horizon of a black hole requires that the matter be static or collapsing.
The "black hole cosmology" models referred to in the Wikipedia article are misnamed. It is theoretically possible that our observable universe is a patch of a Schwarzschild spacetime, which is what the models referred to are asserting, but if it is, then, since the universe is expanding, it would be a patch of the white hole portion of the spacetime, not the black hole portion. And the "horizon" would be a white hole horizon, i.e., one from which the universe's expansion would eventually cause us to pass out of.
However, such a model is extremely unlikely because it has no way of explaining where the white hole horizon came from. A black hole horizon can come into being from gravitational collapse, but a white hole horizon would have to have been "built in" to the overall universe from the very beginning. Nobody has any reason to think that is actually possible, even if we have a theoretical mathematical model that includes it.
What if we're expanding because we are in a black hole that is being fed by a collapsing star or other object in a many orders of magnitude larger scale universe?
Of course these kinds of things are probably 100% untestable.
> What if we're expanding because we are in a black hole that is being fed by a collapsing star or other object in a many orders of magnitude larger scale universe?
Expanding and collapsing are two different things. So I don't see how your suggestion here makes any sense.
complexity of life's scale somehow trillions of magnitudes "smaller" than a similarly constructed universe is not only completely irreconcilably untestable (outside of one thought one) but also reminiscent of m-theory (11 dimensions) and the plot of men in black
I recall seeing something (likely a youtube video on cosmology) that suggested that the Big Bang would be the white hole horizon (i.e. a singularity in out past) and that does make some kind of sense as it'd be impossible to go inside the Big Bang. I recall there being some good reasons as to why that's not believed to be the case though and also why the visible universe doesn't have an event horizon.
> the Big Bang would be the white hole horizon (i.e. a singularity in out past)
The white hole horizon is not the same thing as the white hole singularity. The "Big Bang" as an initial singularity in our universe (which is not actually the correct usage of the term "Big Bang", but that's a whole other discussion) would be the white hole singularity, not the horizon.
Note also that in a white hole model of our universe, we would be inside the white hole horizon, not outside it.
Thanks - that makes it a bit more precise.
> Equating the Schwarzschild radius for a given blob of matter with the event horizon of a black hole requires that the matter be static or collapsing.
If the space containing the matter is stretching does that still count as expansion?
> If the space containing the matter is stretching does that still count as expansion?
"Space stretching" is a vague pop science description that doesn't really correspond to anything in the actual physics model. So it doesn't count as anything; you should just ignore it.
> you should just ignore it.
I believe we shouldn't ignore it. I know about physics from pop-science mostly, so I have limited choices, either "space stretching", or (if I just ignore pop-science) "I have no clue what is happening", or I should stop doing all I'm doing now and dig into physics textbooks, to get real understanding. The last option is not really tempting, I have better ways to spend my free time, the second option doesn't seem constructive at all, so the only viable option is to not ignore vague pop-science description.
> I believe we shouldn't ignore it.
To be more precisely, you should ignore it if you want to actually understand the science. Pop science presentations will not help you understand the science. That's not what they're for. Being as charitable as possible (i.e., ignoring the obvious money-making and eyeball-capturing motives), pop science is for getting people interested in a science topic--so that at least some of them will be motivated to learn more about it, from sources like textbooks or peer-reviewed papers or class lecture notes and other teaching materials (many universities now have those available online for free) which can help you actually understand the science.
> the only viable option is to not ignore vague pop-science description.
As long as you are ok with not understanding the actual science. Nature doesn't care how much time and effort it takes to actually understand something in science. So it is no argument at all to say that you have better ways to spend your time, if you actually want to understand the science. The time required to do that is not dictated by your convenience.
It seems to me as too black-and-white view: either you understand the science, or you don't understand it, with no ground in between.
I want to understand nature, but I have limited amount of time to spend on this goal. So what? Wouldn't be my chosen strategy appropriate? Yeah, I know, my understanding will be limited and sometimes wrong, but it is understanding, isn't it? Isn't it better than total ignorance?
It works not only with nature, there are legal laws for example. Knowledge of laws have a much bigger potential to have an impact on my life, than a nuanced understanding nature. Still I'm not trying to become a lawyer using the same excuse: I have not enough time for that. Instead I maintain some vague understanding of laws and rely on it.
It works for health related issues. I can treat some minor illnesses on my own, because I have some understanding how my body works. I benefit from my limited knowledge of medicine and if my knowledge was better, I would benefit more, but still I have a limited time to study biology and medicine, so while I'm always ready to absorb some more facts, I'm not ready to get a formal education in medicine. Moreover I'm not sure it is possible, to know all the medicine, because qualified doctors are specializing, and I have no chance to be on par with all these specialists.
To my mind it is ok, but with one condition: if you know the limits of your understanding. You need to know when the time has come to seek help of a qualified specialist.
My point was to illustrate that our physics models don't agree on the nature of this expansion (Hubble tension) so using it to dismiss the fact that the observable universe is dense enough to form an event horizon seems like a stretch.
> My point was to illustrate that our physics models don't agree on the nature of this expansion (Hubble tension)
The Hubble tension is not an uncertainty about the "nature" of the expansion. No matter how that tension gets resolved, our underlying mathematical model of "the expanding universe" will not change. All that will change is that the value we use for one particular parameter in that model will be more accurately known.
> using it to dismiss the fact that the observable universe is dense enough to form an event horizon
I have not dismissed that fact at all. I have simply pointed out that, as a matter of physics, that fact does not mean our universe actually has an event horizon. "Dense enough to form a event horizon" is just a mathematical calculation. Whether that calculation actually means something, physically, does not just depend on the value it gives you. It also depends on the underlying spacetime model, and our underlying spacetime model for the universe as a whole (which, as noted above, is not in dispute at all, Hubble tension or no) is not the one in which the mathematical calculation of "dense enough to form an event horizon" has any physical meaning. (In more technical language, that calculation only has physical meaning in the Kerr-Newman family of spacetimes, but the FRW spacetime used to model our universe as a whole is not in that family.)
magnitude difference between dark energy and the schwarzschild radius
I guess that'd explain the big bang nicely. It does make it the "outer universe" disappointingly unobservable though.
> Then there’s spooky shit like: > https://en.m.wikipedia.org/wiki/Black_hole_electron
From the article:
> However, Carter's calculations also show that a would-be black hole with these parameters would be "super-extremal". Thus, unlike a true black hole, this object would display a naked singularity, meaning a singularity in spacetime not hidden behind an event horizon. It would also give rise to closed timelike curves.
I wonder if there's a fun sci-fi story in the discovery that all electrons are in fact naked singularities.
In quantum field theory electrons are excitations in the electron field.
If they also were tiny black holes, what would it mean to be an excitation in the electron field which when the wave function collapses it would behave like a black hole. Does it mean that it's not a black hole anymore when the wave function spreads out?
If we did have a tennis-ball-sized black hole out beyond Neptune, it would be far beyond our capabilities to locate and track - we can barely track debris that small in low Earth orbit, and black holes aren't even courteous enough to provide a radar return. We would not be able to send probes near it any time soon.
Why wouldn't the primordial black holes condense into bigger ones like the matter that makes up planets and stars did?
Some would, but the vast majority of matter is not found in planets and stars. Most stuff just floats around on it's own out there.
Some of them would, some wouldn't, depends on where they were and how they were moving.
This is a bit like asking why Jupiter isn't part of the Sun but other stuff is.
> The universe could be full of black holes in the asteroid mass range the size of hydrogen atoms.
? Not if there's Hawking radiations.
If the Hawking temperature is below the CMB no net evaporation happens. This means there is a mass cutoff and it’s below asteroid mass. Any smaller PBHs would have evaporated by now assuming we are right about Hawking radiation. The math says it should exist but we have AFAIK not proven it.
The big black holes will last insanely long amounts of time.
I'm confused.
Hawking temperature is inversely proportional to the mass. I assume most black holes except the very small ones would thus have a hawking temperature lower than the CMB.
Does that mean that effectively no black holes will ever evaporate not even a tiny bit well until the future time when the CMB will be so red shifted that black holes will start to have net radiation?
Wikipedia suggests that this is the case [0]:
"However, since the universe contains the cosmic microwave background radiation, in order for the black hole to dissipate, the black hole must have a temperature greater than that of the present-day blackbody radiation of the universe of 2.7 K. A study suggests that M must be less than 0.8% of the mass of the Earth – approximately the mass of the Moon."
I'm not sure where the discrepancy between the mass of the Moon vs. an asteroid comes from, though.
[0] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
The CMB temperature is declining as the universe expands. When it was first created it was the temperature of incandescent plasma, and it shone like the Sun.
Black holes can't be dark matter.
Dark matter is a WIMP
The universe was built on a scaffold of dark matter like an old spiderweb that slowly collects dust.
That's another leading hypothesis. Some classes of WIMPs have been ruled out but the whole idea hasn't been.
BTW primordial black holes could still exist even if they aren't a significant dark matter component.
We were told that nothing can escape a black hole.
But when black holes merge, the combined mass is smaller.
It is described that the lost mass is converted to gravitational waves.
But gravity is the curvature of space caused by mass, it is not described as a form of mass.
How do you understand this process of matter escaping a black hole?
Is it that the gravitational waves are caused by a "quantum gravity" particle that can't be converted back to any of the other quantum particles?
> But gravity is the curvature of space caused by mass, it is not described as a form of mass.
Gravitational waves carry momentum and energy (and therefore mass), just like electromagnetic waves. Theoretically, you can extract that energy from gravitational waves, by using oscillating masses tuned to the wave's frequency.
> Gravitational waves carry momentum and energy (and therefore mass), just like electromagnetic waves.
No, EM waves do not have mass. They are massless. They carry momentum and energy, yes, but not mass.
In GR, the source of gravity is not "mass", it's stress-energy. EM waves carry stress-energy even though they are massless.
Gravitational waves do have some aspects that are analogous to EM waves, but there is a key difference: gravitational waves do not have any stress-energy. They are pure spacetime curvature in vacuum. So while there is a sense in which they carry momentum and energy, since properly constructed detectors can extract momentum and energy from them, they do not carry any stress-energy and the momentum and energy they carry cannot be localized the way momentum and energy in EM waves can.
> No, EM waves do not have mass. They are massless. They carry momentum and energy, yes, but not mass.
OK, EM waves can get _transformed_ into mass.
> EM waves can get _transformed_ into mass.
In the sense that they can be absorbed by matter and (possibly) increase the invariant mass of the matter, yes.
> gravitational waves do not have any stress-energy
Wait, what? Of course, they do!
It's just not localized, like in regular classic EM waves.
> Of course, they do!
No, they don't. Read what I said carefully. I did not say gravitational waves do not carry "energy". I said they do not have any "stress-energy". In other words, they are vacuum solutions of the Einstein Field Equation--their stress-energy tensor is zero. That is a true statement, and I contrasted it with EM waves, whose stress-energy tensor is not zero.
> It's just not localized
This is a consequence of the fact that their stress-energy tensor is zero, so there is no tensor that describes "energy carried by gravitational waves".
> How do you understand this process of matter escaping a black hole?
No matter escapes. Gravitational waves are not matter. They are spacetime curvature. Nor do they "escape" the black hole; they are emitted from outside the horizon. The reason the mass of the merged hole can be smaller than the combined masses of the original holes, with the difference being emitted as gravitational waves, is that black holes are not made of matter, they are made of spacetime curvature, and when they merge, some of the spacetime curvature doesn't get included in the merged hole. That's just how spacetime curvature works.
> Nor do they "escape" the black hole; they are emitted from outside the horizon.
That's interesting, I'd never really thought about that before. Does GR predict that there would be any waves confined to the inside of the merged black hole?
If there is anything combined inside the resulting event horizon it doesn't matter what it was: as far as GR is concerned it has been reduced to the effect of its mass, charge and spin. But we already know that GR isn't the whole story when it comes to BHs. See "soft hair" black holes.
> we already know that GR isn't the whole story when it comes to BHs. See "soft hair" black holes
More precisely, most physicists believe that GR isn't the whole story. But we have no actual evidence for quantum gravity speculations like "soft hair". They're just speculations at this point. We don't know that any of them will actually turn out to be right.
You are right. GR being or not the whole story is a thing, "soft hair" black holes is another thing with a much more speculative edge.
But I would say that the first assertion, that GR is not the whole story, is more or less a given knowing that GR returns non-physical infinities when trying to describe what's inside the BH.
> he first assertion, that GR is not the whole story, is more or less a given knowing that GR returns non-physical infinities when trying to describe what's inside the BH.
Only at the singularity, but the singularity itself is not even part of the spacetime manifold in GR.
In cases like black holes, there are physical invariants that do increase without bound as the singularity is approached, i.e., still within the spacetime, but their values are still finite at every point within the spacetime.
It is true that most physicists believe that when those invariants reach some particular scale, such as the Planck scale, the GR description in terms of spacetime geometry will break down. But that scale is about twenty orders of magnitude away from what we can currently probe observationally, so this is another of those speculations that, however plausible it seems, is not going to be testable any time soon.
> Does GR predict that there would be any waves confined to the inside of the merged black hole?
Yes, but we would of course never observe those, and they would not reduce the externally measured mass of the merged hole.
Yes, of course there'd be no external effects. I was just curious, since the region between the event horizon and the singularity is an interesting place to think about, even if we're forever confined to predictions rather than real observations.
> matter, they are made of spacetime curvature
Which is caused by matter achieving a particular density. What we observe is not the matter but the _effects_ of the curvature created by that matter but to say they're not "made of matter" seems overly reductive here.
> some of the spacetime curvature doesn't get included in the merged hole
The observable mechanics of a black hole are (probably) controlled by it's surface area and not it's volume. When two spherical objects merge the surface area is less than the sum of the two original objects.
> Which is caused by matter achieving a particular density.
More precisely, by an isolated blob of collapsing matter surrounded by vacuum achieving a particular density.
> to say they're not "made of matter" seems overly reductive here.
No, it isn't, it is making a very important point: that the matter that originally formed the hole is not there any more. The hole itself is vacuum. If you fall into it, you won't see any matter, even though the hole was originally formed by collapsing matter.
> The observable mechanics of a black hole are (probably) controlled by it's surface area and not it's volume.
Only in the sense that the horizon area is proportional to the square of the mass, whereas the volume is not even well-defined. The actual thing that is controlling the "observable mechanics" is the mass (and spin, and charge if present, but in any actual hole it probably won't be).
> We were told that nothing can escape a black hole.
Stephen Hawking told otherwise, actually: https://en.wikipedia.org/wiki/Hawking_radiation
In 1974, and that's now 50 years ago.
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