Can we make a black hole? And if we could, what could we do with it?
backreaction.blogspot.com
backreaction.blogspot.com
- space propulsion https://www.youtube.com/watch?v=oAocMzxPjjo
- colonization and energy source https://www.youtube.com/watch?v=Qam5BkXIEhQ
- weapons https://www.youtube.com/watch?v=zTMxO1nJaA4
I highly recommend the whole channel.
The nuclear waste thrown into it may be much cleaner than the stuff it will throw back out.
(I agree that Isaac Arthur’s channel is good).
> So some engineering challenges that remain to be solved.
...
edit: typo
https://en.m.wikipedia.org/wiki/Black_hole_electron
> If the smaller it is, the sooner it explodes, then shouldn't atomic particles have all finished exploding a long time ago?
See my other comment here: https://news.ycombinator.com/item?id=31378092
> I have a feeling we're on shaky ground when we start trying to extrapolate general relativity concepts to atomic scales.
Correct. We know nothing about how to marry General Relativity with atomic-scale physics (quantum mechanics). That's why everyone and their dog are looking for a theory of quantum gravity.
Very interesting link - I suppose this could potentially make the problem slightly moot for electrons. Still, I don't think this works for other elementary particles, as black holes can't have color charge or weak hypercharge as far as I know (so they can't behave like quarks, gluons, W or Z bosons etc.)
> We know nothing about how to marry General Relativity with atomic-scale physics (quantum mechanics). That's why everyone and their dog are looking for a theory of quantum gravity.
True, though I think this is not even a problem in matching GR and QM, it is a problem in GR itself. The math of GR has infinities when looking at the center of a black hole, so we know there must be some other math that prevents the curvature from reaching infinity. We can of course easily invent infinitely many solutions to this problem, but there is no way to choose between them on an empirical basis, even in principle (since we can't ever experiment with the inside of a black hole).
A theory of quantum gravity would solve a different problem: GR is nonlinear, while QM is linear (if we ignore the Born rule) - so they can't describe the same system. Relatedly, if applying GR to a system described by a wave function, we are not able to compute how space time will curve given that a single particle(with its mass) is usually present at many points in space-time.
It is hoped that solving the second problem will also solve the first, but I'm not sure this is guaranteed.
I think it is expected they can. The simple reason there are no explicit BH solutions with color charge is that, in contrast to electrodynamics, there's no classic field theory for the strong interaction that we could put into our Einstein-Hilbert action.
> I think this is not even a problem in matching GR and QM, it is a problem in GR itself.
Yes and no.
All kinds of theories have singularities and infinities. Classic electrodynamics is full of them and quantum field theory is, too. Nevertheless we still say the theories are fine and treat the singularities as pretty much nonphysical. ("Point particles don't really exist / a better theory will get rid of them", "We don't see the bare particles anyway, so let's remove the infinities using renormalization", et cetera.) Yes, spacetime singularities seem somewhat more severe, but I think we have good reasons to believe (e.g. the uncertainty relations) that a theory of quantum gravity would solve this conundrum. I mean, every single singularity we worry about in GR comes with infinite curvature and/or infinite energy densities, hence necessarily requires quantum mechanics to study.
On an unrelated note: Why is no one complaining that quantum field theory, from a mathematical point of view, is completely ill-defined? It surprises me time and again that people ascribe severe issues to GR ("It has singularities", "It's not quantum") and yet completely forget that the issues in quantum mechanics (both philophical and mathematical) are much more severe. GR, at the very least, is a mathematically absolutely rigorous theory, with well-defined objects and axioms and such. QFT, in turn, to this day is a toolbox of weird "shut-up-and-calculate" heuristics.
> We can of course easily invent infinitely many solutions to this problem, but there is no way to choose between them on an empirical basis, even in principle (since we can't ever experiment with the inside of a black hole).
There is one way: Come up with candidate theories of quantum gravity and with experiments to test quantum-gravitational effects outside a black hole (there are a few ideas) and select the right theory based on the experimental results and then have the theory predict what happens inside a black hole. Boom. If you say this approach is not valid as it'll remain a theoretical prediction and we still won't be able to peek inside a black hole, you're somewhat right. But right now we're having a discussion about spacetime singularities, which are a purely theoretical problem, too. No one has ever seen them.
> GR is nonlinear, while QM is linear (if we ignore the Born rule) - so they can't describe the same system.
We already know they are incompatible but linearity has nothing to do with it. The equations of motion of interacting quantum fields are non-linear, too. In fact, electrodynamics is, too, in some sense (backreaction & self-force), and we still managed to quantize it.
> Relatedly, if applying GR to a system described by a wave function, we are not able to compute how space time will curve given that a single particle(with its mass) is usually present at many points in space-time.
I wouldn't say this is just a related problem. This is the problem of quantum gravity.
> It is hoped that solving the second problem will also solve the first, but I'm not sure this is guaranteed.
Again, I think the reason people are hopeful are the uncertainty relations. A theory of quantum gravity necessarily has to incorporate them somehow.
https://scholar.google.com/scholar?q=related:FV3voSY5-kYJ:sc...
"Gravity as a fluid dynamic phenomenon in a superfluid quantum space. Fluid quantum gravity and relativity." (2017)
> The hypothesis starts from considering the physical vacuum as a superfluid quantum medium, that we call superfluid quantum space (SQS), close to the previous concepts of quantum vacuum, quantum foam, superfluid vacuum etc. We usually believe that quantum vacuum is populated by an enormous amount of particle-antiparticle pairs whose life is extremely short, in a continuous foaming of formation and annihilation. Here we move further and we hypothesize that these particles are superfluid symmetric vortices of those quanta constituting the cosmic superfluid (probably dark energy). Because of superfluidity, these vortices can have an indeterminately long life. Vorticity is interpreted as spin (a particle's internal motion). Due to non-zero, positive viscosity of the SQS, and to Bernoulli pressure, these vortices attract the surrounding quanta, pressure decreases and the consequent incoming flow of quanta lets arise a gravitational potential. This is called superfluid quantum gravity. In this model we don't resort to gravitons. Once comparing superfluid quantum gravity with general relativity, it is evident how a hydrodynamic gravity could fully account for the relativistic effects attributed to spacetime distortion, where the space curvature is substituted by flows of quanta. Also special relativity can be merged in the hydrodynamics of a SQS and we obtain a general simplification of Einstein's relativity under the single effect of superfluid quantum gravity.
IIRC, when I searched gscholar for "wave-particle-[fluid]" duality" a few weeks ago there were even more recent papers.
Does Quantum Chaos describe fluids or superfluids? https://en.wikipedia.org/wiki/Quantum_chaos
Do CAS tools must stop reducing symbolic expressions describe infinity such that?:
assert n*x*oo == oo
Unfortunately, Einstein's field equations are not linear, so in contrast to other (linear) field theories, this case is not as simple as superposing several black hole solutions to a global solution and then averaging or zooming out in an appropriate way, since the sum of two solutions won't give another solution.
I'm wondering whether anyone has ever looked into the scaling behavior of the Einstein field equations but the answer from most people in the community that I've talked to has been no.
Of course, experiments so far are also consistent with leptons having very small but non-0 size. Since their Schwarzschild radius is much smaller than a Planck length, we will probably never be able to design an experiment that would show a disagreement here.
It's also notable that GR predicting a mathematical singularity at the center of a black hole shows that it can't be right at such extreme scales - there must be some unknown limit that prevents the density of a back hole from reaching infinity, and that would probably solve this issue as well.
Two electrons on the other hand can, because above some point when you push them close together the force between them rises above electrostatic repulsive and they'll pull their 0-size closer and closer until a singularity forms.
Of note, black holes on this scale aren't going to be stable though: they'll evaporate pretty much as fast as they form from Hawking radiation.
EDIT: Of note - at this sort of scale it's not entirely clear to me that whether an electron is a black hole is a meaningful question either. Black holes can have spin and charge, so an electron and an black hole masquerading as an electron would be superficially indistinguishable - it would weigh the same as an electron, and so electrostatic force would dominate all its interactions. This has been speculated: https://en.wikipedia.org/wiki/Black_hole_electron though not observed at the moment. But the inconsistency isn't because it would not be sufficiently "electron-like".
Blackholes are just a solution to Einstein equations for an object in which all its mass is concentrated in its Schwarzchild radius. Protons and electrons are bigger than that so they are not Blackholes and they will not "explode".
> When they explode, what do they eject
If it was possible to concentrate a proton to make a blackhole, when it evaporates, I'd say it "eject" itself (a proton)
That said, Einstein's equations do not really apply at quantum scales. So what happens with such blackhole is unknown. We never observed micro blackholes, and the Hawking radiation is just a theory which may or may not be true.
From Wipedia:
> Quantum gravity (via virtual black holes and Hawking radiation) may also provide a venue of proton decay at magnitudes or lifetimes well beyond the GUT scale decay range above, as well as extra dimensions in supersymmetry.
Perhaps it's possible that a proton get transformed into a black hole and then the black hole decays into a positron and a pion (or a positron and a few photons). Nobody is sure about this, and nobody has seen this or other decays of protons. More speculative details in https://en.wikipedia.org/wiki/Proton_decay#Theoretical_motiv...
1) For all that we have been able to measure it, the electron is a point particle. It does not have a radius. The concept of radius does not apply. Every time we try to measure it, we just end up setting a smaller upper bound for the radius than last time. This is true of all of the leptons ("lightweight particles"). The same sorts of probes of electrons suggest that there is no "stuff" in them. That's all you get, this point with some numbers associated with it (charge, mass, angular momentum, lepton number, etc).
2) Black holes -- and I am going to constrain myself to a "no-hair" situation for those of you in the know -- have only three variables that describe them: mass, charge, and angular momentum. Anything else describes its position and how it is moving at the time. They're really quite dull. (Exploration of where the information that fell into the black hole went is ... contentious, abandoned, frustrating, etc). Radius is a function of mass (and angular momentum, you can distort the event horizon if it had enough spin).
3) They don't "explode." The theorized-but-not-yet-observed Hawking radiation is about chucking out the occasional particle and "borrowing" it from the black hole. This is done under conservation of the above mass, charge, and angular momentum. The smaller they get, the more chance they throw something out, so it is really a runaway process that only looks like an explosion at the end.
4) Due to this conservation, if you somehow made a single electron into a black hole, that black hole could only ever spit out one thing in its lifetime: an electron.
5) The proton is quite different. It is not the opposite of an electron. It is known as what is called a baryon ("heavyweight particle") and it has a size. It is also composed of smaller things, unlike the electron, three quarks and some gluons (which serve to hold the whole thing together).
6) Atomic scales are fine. We can understand things about relativity at the atomic scale. For example, we use the surprisingly extended half-lives of certain incoming particles to verify time dilation. Or just look up how relativity affects the orbital radii of very heavy atoms, in particular gold. Subatomic scales are more interesting.
That said, what the OP said about "borrowing" electrons I am not sure about.
> Schwarzchild
Nitpick, but you missed one ;)
It's composed of two German words: "schwarz" which means "black" and "Schild" which means "shield". So "Blackshield". No children involved here.
It doesn't, not in the sense you mean. You can calculate a Schwarzschild radius for any mass, but that radius only means something physically for an actual black hole. You can use the calculated radius to estimate how hard it would be to turn some ordinary object into a black hole; that's what the article does by comparing the Schwarzschild radius for various masses or energies to the actual radius within which we can compress them by processes we can currently control (and of course the latter radius is very, very much larger than the Schwarzschild radius for those masses or energies, which means we have no feasible way of turning any of those objects into black holes). But that in no way means that those ordinary objects have some actual, physical Schwarzschild radius that acts like the horizon of a black hole. They don't.
> Slight problem with this is that you can’t touch black holes, so there’s nothing to hold them with. A black hole isn’t really anything, it’s just strongly curved space. They can be electrically charged but since they radiate they’ll shed their electric charge quickly, and then they are neutral again and electric fields won’t hold them. So some engineering challenges that remain to be solved.
Easiest thing to do though would be to build it in orbit.
Black holes, otoh, are forever.
This view is not right, e.g. electrons radiate and keep their charge. Black holes lose their electric charge when opposite charged matter falls in.
A black hole can presumably radiate charged Hawkings radiation? I.e. if an electron-positron pair is created near the event horizon of a negatively-charged black hole then it would disproportionately capture positrons and repel electrons, thus radiating away its charge. (Could be wrong here, I’ve not looked into charged black holes before). I would assume here that charge radiates away at a different rate than mass, and by her statements it sounds like ch argue evaporates away quicker.
She’s not making a general claim that “everything that radiates loses charge”, that would be silly.
That said, I found that very surprising and expected the magnetic fields to disappear, so maybe I misunderstood something.
Most things one would use for thrust in space are inherently repulsive. The part I'm having trouble with is that it seems like even though a black hole would put out a lot of energy, it wouldn't be inherently repulsive, and so any vehicle would have to exert a station-keeping (or orbit-keeping) force equivalent to whatever the over-all black hole engine was emitting, making the engine itself useless. This seems especially true for the design in the second article, where the Dyson shell weighs 600 times as much as the singularity. But again, I'm probably missing something obvious since it's outside my areas of expertise.
[1] https://arxiv.org/abs/0908.1803 [2] https://www.space.com/24306-interstellar-flight-black-hole-p...
[0] https://cse.buffalo.edu/~rapaport/111F04/lloyd-ng-sciam-04.p...
♩ ♪ ♫ ♬
Black hole sun, won't you come
And wash away the rain?
Black hole sun, won't you come?
Won't you come? Won't you come?
♩ ♪ ♫ ♬
If a black hole were to come into sustained existence, assume the smallest one. How long could we stand near it before being unable to escape? And how far is that distance?
R = distance (radius, really) M = Mass of the body G = Universal gravitation constant
We can modify this equation to find for the distance at which you can escape:
r = 2GM/v^2
The answer is largely: it depends on how fast you can go, at the speed of light you can escape from further away, since the pull will increase the closer your are to the "event horizon".
I'm in a car right now (as a passenger ofc) doing this from my phone so not in a situation where I can put together a model, but you should be able to plug in some numbers and estimate a result, just make sure you convert to SI units so you don't accidentally end up 3 orders of magnitude off.
A black hole with the mass of the earth would have a radius of about 2cm, so things less massive than a planet start to get very small, very fast, and you end up fighting quantum effects which become less intuitive.
Source: https://arxiv.org/abs/2004.14192 (There was also a pretty good discussion about it here on HN.)
> would probably be too small to notice without some sort of detection equipment.
What makes you think that?
Theoretically, black holes can have a mass of the tiniest fraction of a gram which would be unimaginabley small. It's my own speculation that you wouldn't be able to detect that with a naked eye.
> you wouldn't be able to detect that with a naked eye.
What if you touched it? No idea what the spacetime would look like near a gram-sized black hole with lots of heavier matter surrounding it but I suppose there would still be pretty severe tidal forces.
Keep in mind that event horizon isn't a shell, just a point at which your future (which is in the singularity) is certain.
Yeah, exactly my thought. Then again, we're silently assuming here that spacetime would pretty much look like one of the vacuum black hole solutions plus some additional matter (our body) near it. That doesn't seem too likely, given that our body is much heavier and can't just be treated as a test particle. OTOH it doesn't seem too likely, either, that the actual spacetime would look completely different: There will surely still be a black hole and an event horizon.
What would it take to get an event horizon on a human scale (a feet or two across?)
Correct. Any mass M taking up a spherical volume of radius less than 2GM/c² (the Schwarzschild radius) will necessarily be a black hole. Black holes are thus the objects in the universe with the highest mass density and, coincidentally, the highest entropy density.
> What would it take to get an event horizon on a human scale (a feet or two across?)
A mass M = Lc²/2G, where L = 1ft for a black hole 2ft across.
A solar mass black hole is stupid dense. But a supermassive black hole is less dense than the earth, and can be less dense than water. That's still an insane amount of mass, but it's not really all that dense.
A human scale black hole would be even denser than a solar mass black hole. It would require over 200 earth masses, though that's still a tiny fraction of a solar mass.
A non spinning black hole is an absolutely perfect sphere, with no "hair". A spinning black hole is flattened, or maybe even a torus, but is still mathematically perfect.
Unless quantum mechanics intervenes in ways nobody has yet figured out.
The singularity occurs at a nominal point at the center (or a ring for a rotating black hole). It has no volume, but all of the mass ends up there, causing divide by zero errors.
This is not at all known, as we have no idea what a theory of quantum gravity would look like (which would necessarily enter the game here). We might end up with a black hole remnant, or Hawking radiation might behave differently for microscopic black holes etc.
https://spacemath.gsfc.nasa.gov/blackh/4Page33.pdf
The calculation in that document is representative: for a solar-mass hole (event horizon radius 2.9km) the tidal forces on a human are 51000x Earth gravity at 100km away!
> https://www.pbs.org/wgbh/nova/article/the-astronomical-parti...
Black holes formed by cosmic rays hitting Earth would not be dangerous because they would be very very small. Most likely they would very quickly decay via Hawking radiation, but even if they did not decay for some reason they would be so small that very little would actually fall into them.
Small black holes created in the early universe, big enough to not noticeably decay in the billions of years since and so much bigger than those cosmic rays hitting Earth might create, are actually taken seriously as one of the candidates for dark matter. Even those, which would be much larger than anything cosmic rays or colliders might make, would be sufficiently hard for things to actually fall into that they could pass right through you without you noticing.
I find this bit interesting because I'm pretty sure I've read the exact opposite before. My previous understanding was that the gravitational pull is only determined mass - but a black hole can put an almost arbitrary amount of matter into the same space, therefore the gravitational pull is factually much stronger than for any "ordinary" object of the same radius.
However she is saying the compression itself is already increasing the pull.
So as an example, suppose our sun got replaced by a black hole of identical mass (but much smaller radius). Would this cause orbits of the planets to shrink (increased gravitational pull) or stay the same (identical gravitational pull)?
I think this is discussing the gravity on itself — or the peak gravitational pull, for nearby objects.
Compressing the Earth wouldn’t make far away objects experience it differently, but compressing Earth would increase the peak pull nearby — to the point of creating a black hole. Much more gravitational pull than anywhere on Earth experiences now. But that radius would be far, far inside of where the surface currently is.
Density increases nearby gravity by focusing mass.
As the radius of a object shrinks (but with mass held constant), the _surface_ gravity increases. Remember that the pull of gravity decreases with the square of the distance away from the object. With a smaller object, you can get a lot 'closer' to all that mass, so gravity is stronger at its surface.
your experience of its gravitional force is dependant on distance.
the description of force experienced being spoken about is from the frame of a variable distance observer, not the gravitating body.
But if we can ever figure out a way to reflect (and thus lase) gamma rays (or some other much higher energy radiation) this then becomes possible.
Of course we don't even have a plausible theory on how we might construct "grasers" [2].
[1]: https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
I think that's where we should start in looking at potential use cases for personal, instant black holes.
I'm not young any more so I would volunteer to help in development and testing of any portals as long as I get good Cajun coffee and a smoked brisket sandwich in the lunchbox with a blood orange and a slice of Mom's apple pie.
I can see where it could be used in hot climates to help avoid energy waste. Buildings could be built with no doors and using UV reflecting glass for windows and people would enter and exit with their own personal pocket portals. Had enough for one day and feel like a cold brew? Flip that pocket portal like a disc golf disc and when it sticks to the wall just jump thru it to the street. It closes up behind you allowing for the absolute lowest conditioned air loss situation. No more door and threshold gaskets to replace, ever. Just keep your portal tuned to the right energy level and make sure that you never let it work like your money, burning a hole in your pocket.
You don't have that opprotunity. Black holes and portable holes have as much to do with each other as computer chips and potato chips.
From where I'm at, that gives me all the opportunity that I need. I described the type of black hole that I would like to create, gave evidence from the historical record for some of its attributes, and described how it would or should be used.
I'm not sure why you are unable to acknowledge this. OP asked people to think about it. I thought about it and replied. Perhaps you didn't see the same cartoons or are not seeing the utility of the personal instant black hole.
I don't think we have a close enough black hole for this to be true for anyone reading this right now.
Would be crazy if true, we could verify all kinds of things by tinkering with a live black hole.
It loses this mass through radiation, but then, so does a black hole. That's fancy Proper Noun Hawking Radiation, but radiation it remains.
Not trying to be a downer, I find the fact that a photon doesn't /have/ mass but still /is/ mass endlessly fascinating.
Black hole railguns/artillery?
Or, in the name of safety, mobile satellites in low earth orbit armed with hard tungsten rods, accelerated by temporarily generated black holes to relativistic velocities for prompt global strikes on time sensitive targets. Could make for a good movie.
the whole "you can shoot somin near a black hole and speed it wayyyyy up" reminded me of the three body problem. some advanced species just tossing crap at black holes and blowing up stars
You cannot harvest the energy given to you by a blackhole... unless the impacts of tungsten objects yield harvestable energy.
This is what I worry about with fusion, it's not going to be used for free power for the world, it's going to be used to power war-machines.
The only value of a black hole you can build would be as a doomsday weapon: do what we want or we end the world. Except...that's been the case since the Cold War with regular nuclear weapons.
As for fusion: you need to do more research. We've had fusion bombs since 1952. Practical fusion power for electrical generation is what we don't have since the constraints are very different.
It'll never be as simple or satisfying as the old school hammer.
so as the blackhole gets smaller the more energy it radiates, eventually basically blowing up. so simply put a small BH in a magnetic trap next to someone.
but if you shoot it it'll go too fast to stay put.
though it might be possible to release a small one next to someone slowly.
small means ~ 1 million kg, which evaporates in 84 seconds, though it will emit so much energy that... well it will turn a city into plasma almost instantly
https://www.omnicalculator.com/physics/black-hole-temperatur...
basically the problem is that either general relativity and Hawking are correct, which mean that there is simply no way to have a small (compared to human mass, so like a big bomb, eg a few metric tons) black hole that doesn't violently want to turn back into a non-blackhole, or if it's possible then our theories are incorrect and all bets are off :)
In Newtonian doctrine, a spherical object, like earth, attracts -as if- all its mass is concentrated at its center. So, if her reasoning is correct, the earth must already be a black hole, because all its mass is supposed to be concentrated at its center.
attracts -as if- all its mass is concentrated at its center
At a radius _inside_ the object, only the mass closer to the origin counts so the "effective" mass of the object drops smoothly to zero.
So the escape velocity from earth at its surface is well below the speed of light. And below the surface, gravity is even less. Only a black hole packs enough mass into a small enough place to get the escape velocity above the speed of light.
And yes as far as anything else in the solar system is concerned, if the earth was compressed into a blackhole no orbits would change. Well relativistic effects mean there's no stable orbits below 2 radii (maybe it's 1.5), so various sats would get sucked in.
However just because that's true, doesn't imply the earth is a blackhole, just that the orbits in the solar system wouldn't change. Similarly if the sun collapsed into a blackhole the earth's orbit wouldn't change, but it would get much colder.
> Wouldn’t it be cool to have a little black hole in your office? You know, maybe as a trash bin.
Putin merely has access to nuclear weapons. I suppose the “I win or the earth gets it” is the same whether we’re talking nukes or a black hole