Signatures of gravitational atoms from black hole mergers
physics.aps.org
physics.aps.org
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.
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.
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.
But yeah, particles in energy levels gravitationally bound to a black hole in a similar way electrons are electrically bound to a nucleus.
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.
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.
[1]: https://news.harvard.edu/gazette/story/2022/10/black-hole-bu...
Sorry, our Universe is just a spacetime (array [x,y,z;t]), while gravitation is not a force but a curvature of spacetime.
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").
naked singularities themselves, however, do not exist.
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.
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
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.
>space cone
>light cone
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.
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.
> 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 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.
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?
No, it isn't. It's a 4-dimensional region of spacetime bounded by a null cone.
> Care to explain how?
What you think you know about all this is so far off base that I'm not sure where to start. Pretty much everything you've said has been wrong.
> Once you cross the event horizon, your time will end in that same point, regardless of your movement in space.
Wrong. The singularity is not a point. It's a spacelike line. Different people that fall through the event horizon separately will not meet each other at the singularity. In fact they will not even be able to see each other reach the singularity.
> This projection would be an ever-narrowing cone.
Wrong.
> I am wondering where my mental model is imprecise
It's not just "imprecise", it's wrong, pretty much everywhere. I would strongly suggest taking the time to look at some spacetime diagrams--the best ones would be a diagram in Kruskal coordinates or a Penrose diagram.
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.
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.
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:
? Not if there's Hawking radiations.
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.
[0] https://en.wikipedia.org/wiki/Hawking_radiation#Black_hole_e...
Dark matter is a WIMP
The universe was built on a scaffold of dark matter like an old spiderweb that slowly collects dust.
BTW primordial black holes could still exist even if they aren't a significant dark matter component.
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.
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?
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.
Of course these kinds of things are probably 100% untestable.
Expanding and collapsing are two different things. So I don't see how your suggestion here makes any sense.
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.
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.
"Understand" in the sense of being able to make accurate predictions about events that have not yet been observed, or more generally in the sense of having a generative model that can give accurate explanations of things you haven't encountered before, even if they are things that have been observed (by others), is black and white: either you can do it or you can't.
If you have limited time to spend on understanding in the above sense, then your ability to do the things described above will be limited. And note that that is not just true of science; it's true of the other areas you mention (law and health) as well. If your knowledge of the law is limited, your ability to predict the legal risks involved with a planned action, or the likely outcome of a legal dispute, will also be limited. Similarly, if your knowledge of medicine is limited, your ability to judge what doctors and other medical professionals tell you--whether it has an actual firm basis or is just them guessing (and the latter is far more prevalent than many people like to think)--will be limited.
> if you know the limits of your understanding. You need to know when the time has come to seek help of a qualified specialist.
You're assuming that there is a qualified specialist in the area in question. And you're also assuming that you can trust the qualified specialist, or at least that you can spot when the qualified specialist, because of some other agenda involved besides helping you, is giving you information that you shoudn't trust.
None of those assumptions are likely to be valid in cases where it matters. First, if "qualified specialist" means someone who does understand the domain in question in the sense I described above--they can make accurate predictions and they have generative models that give them accurate explanations--then there are no qualified specialists in most domains of interest. Certainly that is the case for the law (lawyers would say they are "qualified specialists", but that doesn't mean they can actually do the things I described above--when they predict an outcome, what they're actually doing is telling you they believe they can manipulate the outcome that way, and that depends on how much money you have to spend and how good the opposing lawyers are). It is also the case for many areas of medicine. (Some areas of medicine, such as particular surgical procedures or particular well-understood diseases, do have qualified specialists who can do those things. But that is a small subset of all of medicine.)
Second, even if we take a domain like physics, where in many areas there are qualified specialists, that doesn't mean that you can read pop science books by those qualified specialists and get an understanding of the physics from them, even if you accept that any such understanding will be limited. Many of the things even Nobel Prize winning physicists say in pop science books and articles and videos are not well established physics, they are just that particular physicist's opinons. And if you yourself aren't a qualified specialist, you have no way of knowing when the physicist is telling you well established physics and when they are just giving their opinions. So even in this hardest of hard sciences, "seek help of a qualified specialist" doesn't actually work well as a strategy.
This is a necessary assumption, because you cannot be a specialist in the most fields. You can probably be a specialist in one narrow field, if you spend your life to become one.
> So even in this hardest of hard sciences, "seek help of a qualified specialist" doesn't actually work well as a strategy.
In my experience it works. The trick is to talk with the specialist, to lay out your understanding of the problem to them, to get their critique, fix your understanding and then do several iterations of this. If you really need to be sure that your understanding is adequate for the task ahead of you, you could try to talk with several specialists.
And in overall I have the same feeling of black-and-white worldview on your part. Trying to guess what is different between you and me I come to this:
Truth is not Real, it is Ideal. You cannot reach it. Any understanding is Real, so it is not ideal, it is not perfect. Any prediction is probabilistic. There is Reality itself and there is my limited understanding of it, and there is a vast ocean of information on how others understand Reality. This ocean of information is not the Ideal understanding either. So the crucial skill is to learn how to drink from the ocean a couple of gulps that will be enough for my current task. And it is not just my preference how to deal with the ocean, it is the only viable way to deal with it, because I cannot drink all the ocean. I can't even drink it faster than it gets new information, so even if I had infinite time to drink it, I would be able to bottom it up.
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.)
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.
This is a bit like asking why Jupiter isn't part of the Sun but other stuff is.
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?
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.
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.
OK, 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.
Wait, what? Of course, they do!
It's just not localized, like in regular classic EM waves.
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".
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.
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?
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.
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.
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, but we would of course never observe those, and they would not reduce the externally measured mass of the merged hole.
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.
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).
Stephen Hawking told otherwise, actually: https://en.wikipedia.org/wiki/Hawking_radiation
In 1974, and that's now 50 years ago.