[HN Gopher] Can we make a black hole? And if we could, what coul...
___________________________________________________________________
Can we make a black hole? And if we could, what could we do with
it?
Author : nsoonhui
Score : 130 points
Date : 2022-05-14 12:43 UTC (10 hours ago)
(HTM) web link (backreaction.blogspot.com)
(TXT) w3m dump (backreaction.blogspot.com)
| zw123456 wrote:
| I dunno what you could do with it but the black hole laser bit
| blew my mind https://arxiv.org/abs/1409.6550
| donutshop wrote:
| Would be neat to suck up all the garbage
| mrkramer wrote:
| Maybe we could make Black Hole Computers[0]?
|
| [0] https://cse.buffalo.edu/~rapaport/111F04/lloyd-ng-
| sciam-04.p...
| CryptoPunk wrote:
| cletus wrote:
| Black holes created from energy are called Kugelblitz black holes
| [1]. The article correctly points out the difficulty of doing so
| with traditional lasers.
|
| 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)
|
| [2]: https://en.wikipedia.org/wiki/Gamma-ray_laser
| thfuran wrote:
| Are free electron lasers fundamentally incapable of operating
| up into gamma? Maybe we just need to wiggle harder.
| swayvil wrote:
| If we had "reverse centrifugal force" you could create a black
| hole by "spinning" the thing really fast.
| tsukurimashou wrote:
| Just spin it the other way around :^)
| swayvil wrote:
| Maybe flip it in 4d
| swayvil wrote:
| Maybe a donut shaped black hole could be made by spinning. Or
| a vortex.
| xg15 wrote:
| > _So, if you hold the mass fixed and compress an object into a
| smaller and smaller radius, then the gravitational pull gets
| stronger._
|
| 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)?
| walnutclosefarm wrote:
| She's cheating a bit, to make a valid point. The gravitational
| force exerted by an object is due, as you say, to the object's
| mass-energy. So, a solar mass black hole centered on the center
| of mass of the sun would have the same gravitational effect on
| earth as the sun does. But the force a test particle
| experiences due to the gravity of either object depends on the
| the square of distance of the test particle from the center of
| mass of the the object. The physical expanse of the object
| doesn't really matter, if you're outside of the object. But,
| with the sun, the closest you can get to the center of mass is
| roughly 700,000 km. Any closer than that and you're inside the
| sun. Once you're inside the mass radius of an object, the force
| you experience is due only to the proportion of the object's
| mass that is closer than you to the object's center of mass. So
| the gravitational force you experience (if you could survive
| being inside the sun) declines as you get closer to the center
| of mass, until it's zero at the center (the pressure you
| experience is a different matter - it steadily increases as you
| journey down the mass). The black hole's radius, though is only
| about 3km, and so you can approach to within that distance of
| its center of mass. At that distance from a solar mass, the
| gravitational force is enormous - sufficient to overcome the
| momentum of a photon, "drag" it back into the black hole. So,
| the gravitational force you can experience from an object does
| depend on it's size, even though the total force at
| astronomical and mere macro scale distances does not.
| [deleted]
| lilgreenland wrote:
| Mass and energy are same thing. They effect gravitational pull
| the same. If you compressed the Earth the energy it takes to
| compress the Earth would increase the mass-energy of the Earth,
| and this would change the orbits of planets.
| [deleted]
| platz wrote:
| If you make an object smaller, you can get closer to it's
| center of mass, increasing your experience of it's
| gravitational force.
|
| 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.
| zmgsabst wrote:
| > If you remember Newton's gravitational law, then, sure, a
| higher mass means a higher gravitational pull. But a smaller
| radius also means a higher gravitational pull. So, if you hold
| the mass fixed and compress an object into a smaller and
| smaller radius, then the gravitational pull gets stronger.
| Eventually, it becomes so strong that not even light can
| escape. You've made a black hole.
|
| 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.
| xen0 wrote:
| Gravitationally, nothing would change if the sun was replaced
| by a black hole of the same mass, at least for objects above
| the surface of the current sun. But being 1 kilometer above the
| event horizon of that black hole would be very different to
| being 1 km above the surface of the sun.
|
| 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.
| _jal wrote:
| "Io, corner pocket."
| h2odragon wrote:
| there's a potential video game there. planet pool. dropping
| things into the sun would be a "scratch"?
| DerekBickerton wrote:
| 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?
|
| https://www.youtube.com/watch?v=efc7njKAfgo
| bjt2n3904 wrote:
| One question I had, prompted by a fever dream in which a black
| hole spawned in my house...
|
| 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?
| kqr wrote:
| Follow-up question: are black holes generally a question of
| density and not mass? If I could take a laptop and squeeze it
| hard enough to overcome various nuclear forces, would I get a
| black hole with an event horizon the size of a laptop's
| gravitational field?
|
| What would it take to get an event horizon on a human scale (a
| feet or two across?)
| jfengel wrote:
| Sort of. It depends on both density and mass. The more mass
| there is, the less density is required to make a black hole.
|
| 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.
| kqr wrote:
| In this comment, are you defining density as mass per
| volume contained by event horizon? Or do we know how the
| mass is distributed inside the black hole? Does it even
| make sense to discuss distribution of mass in a black hole?
| Would clues about that leak out through dynamics like
| rotation?
| jfengel wrote:
| You only need total mass and total volume. No other
| details leak out.
|
| 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.
| kqr wrote:
| Total volume of... what? Contained within event horizon?
| Surely not singularity? (Which I would assume to be a...
| well, singularity.)
| codethief wrote:
| > are black holes generally a question of density and not
| mass?
|
| 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.
| TheDudeMan wrote:
| There is no "smallest one". The small ones evaporate to smaller
| and then nothing very quickly. "Evaporate" as in, emit huge
| amounts of radiation -- like a bomb.
| codethief wrote:
| > The small ones evaporate to smaller and then nothing very
| quickly.
|
| 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.
| InCityDreams wrote:
| You may enjoy The Aleph.
| https://en.m.wikipedia.org/wiki/The_Aleph_(short_story)
| al2o3cr wrote:
| The event horizon is the least of your worries: the real
| problem is tidal forces.
|
| 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!
| helldritch wrote:
| The equation for escape velocity is: v = [?](2GM/R)
|
| 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.
| DJBunnies wrote:
| That's called the event horizon, which is proportional to its
| mass.
| justsomeshmuck wrote:
| It's theorized that there is a grapefruit-sized black hole
| orbiting our sun in the outer reaches of our solar system with
| a mass of 5 to 10 earths. A black hole spontaneously appearing
| in your home small enough to not rip apart the entire planet
| immediately would probably be too small to notice without some
| sort of detection equipment.
| codethief wrote:
| > It's theorized that there is a grapefruit-sized black hole
| orbiting our sun in the outer reaches of our solar system
| with a mass of 5 to 10 earths.
|
| 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?
| paulmd wrote:
| Ah yes, the tachyon detection grid. ;)
|
| https://memory-alpha.fandom.com/wiki/Tachyon_detection_grid
| justsomeshmuck wrote:
| https://academic.oup.com/mnras/article/152/1/75/2604549?log
| i...
|
| 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.
| codethief wrote:
| Thanks for the link!
|
| > 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.
| Sharlin wrote:
| Well, if a black hole somehow appeared on Earth, with a low-ish
| velocity relative to the ground, it would immediately fall
| inside Earth so "standing" near it would be pretty difficult.
| serenitylater wrote:
| gradschool wrote:
| I admit I know next to nothing about this stuff, but something
| doesn't add up. If everything has a Schwarzchild radius
| determined by its mass, then should we conclude that particles
| like electrons and protons also have a (very small) Schwarzchild
| radius? If the smaller it is, the sooner it explodes, then
| shouldn't atomic particles have all finished exploding a long
| time ago? When they explode, what do they eject, if not more
| subatomic particles like themselves? Alternatively, is the
| explanation that atomic particles are extended bodies whose sizes
| exceed their Schwarzchild radii instead being of point masses? If
| so, then what kind of stuff fills the interior of an electron? I
| don't have any answers but I have a feeling we're on shaky ground
| when we start trying to extrapolate general relativity concepts
| to atomic scales.
|
| edit: typo
| a1369209993 wrote:
| You're forgetting quantum mechanical effects. Effectively, a
| electron is constantly quantum-tunneling out of its own event
| horizon. (Or, equivalently, a electron, considered as a black
| hole, always immediately decays into Hawking radiation
| consisting of exactly one electron (with the same position,
| momentum, electric charge, etc, as the supposed black hole,
| since black holes aren't exempt from the various conservaton
| laws).)
| pdonis wrote:
| _> If everything has a Schwarzchild radius determined by its
| mass_
|
| 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.
| awiesenhofer wrote:
| > edit: typo
|
| > Schwarzchild
|
| Nitpick, but you missed one ;)
|
| https://en.m.wikipedia.org/wiki/Karl_Schwarzschild
| wildmanx wrote:
| To add some understanding: the name does not mean "the child
| of Schwarz".
|
| It's composed of two German words: "schwarz" which means
| "black" and "Schild" which means "shield". So "Blackshield".
| No children involved here.
| vbezhenar wrote:
| According to my calculations, schwarzschild radius of electron
| is 1.4e-59 m, and electron radius is 2.82e-15 m, so electron is
| huge and electron density (if such thing exists) is not enough
| to form black hole.
| platz wrote:
| your "electron radius" is the "classical electron radius"
| which is a ficticious radius one uses i lf disires. in modern
| theory electrons have no radius.
| codethief wrote:
| > If everything has a Schwarzchild radius determined by its
| mass, then should we conclude that particles like electrons and
| protons also have a (very small) Schwarzchild radius?
|
| 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.
| tsimionescu wrote:
| > https://en.m.wikipedia.org/wiki/Black_hole_electron
|
| 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.
| codethief wrote:
| > 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.)
|
| 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.
| dr_dshiv wrote:
| Seems like an ultraviolet catastrophe situation
| varajelle wrote:
| (Not a physicist myself)
|
| 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.
| XorNot wrote:
| I'm not sure what the issue you see here is: a very small
| Schwarzchild radius would be smaller then the size of the
| particle, and as a result the particle cannot collapse itself
| into a black hole.
| tsimionescu wrote:
| The problem is that electrons and quarks and other leptons
| are considered 0-size (point like) particles, but they do
| have mass - so, according to GR, they should "collapse" into
| black holes.
|
| 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.
| XorNot wrote:
| If they're incompressible (i.e. fundamental) particles
| though, then there's no inconsistency: any single electron
| can't compress itself into a black hole, because it's
| experienced gravitational attraction can't increase - it
| doesn't can't pull on itself because it has no internal
| structure.
|
| 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".
| platz wrote:
| Is a black hole electron consistent with hawking
| radiation theory? or is that the naked singularity part;
| since there is no event horizon, they dont radiate. it
| seems strange to even call it a black hole at that point.
| at_a_remove wrote:
| You have some misconceptions.
|
| 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.
| gradschool wrote:
| Thank you for your comments. I might have at least one other
| misconception in need of clearing up. My impression from
| reading about it somewhere was that the Hawking radiation is
| predicted to happen as a consequence of vacuum fluctuations.
| When an electron-positron pair spontaneously forms close to
| the event horizon, and one particle falls in but the other
| doesn't, they can't annihilate so the one that's left outside
| appears to emanate from the black hole. Is that not the
| consensus, or if it is, why should the amount of radiation
| depend on anything but the surface area of the event horizon?
| at_a_remove wrote:
| You are pretty close. It's the _curvature_ of the surface
| area. Smaller black holes have a less ... homogenous
| orbital space near the event horizon. More tidal forces,
| etc, so a particle-antiparticle production would be more
| likely to be torn apart.
| platz wrote:
| Your description of hawking radiation isn't quite accurate.
| It's a popular misconception. the actual process is not as
| easy to understand. see below:
|
| https://youtu.be/qPKj0YnKANw
|
| That said, what the OP said about "borrowing" electrons I
| am not sure about.
| at_a_remove wrote:
| It's more of an accounting deal. There's mass where there
| didn't used to be, and it was pretty near _here_ so ...
| we gotta make the books balance.
| techdragon wrote:
| Surprised no one has mentioned the Kugelblitz yet, so I'll drop
| this fun hit of exotic theoretical engineering here.
|
| https://en.wikipedia.org/wiki/Kugelblitz_(astrophysics)
| sidlls wrote:
| One of my favorite science fiction stories, "The Krone
| Experiment", has this question as a central plot element.
| https://www.goodreads.com/book/show/16032842-the-krone-exper...
| dmje wrote:
| daniel-thompson wrote:
| This is the kind of question that makes me believe in the Great
| Filter1.
|
| 1https://en.wikipedia.org/wiki/Great_Filter
| BiteCode_dev wrote:
| This is the kind if questions which justifies the need for
| humanity to colonize multiple planets if it doesn't want to go
| extinct.
| codethief wrote:
| Came here to post this but couldn't remember the name "Great
| filter", thank you. :)
| PaulHoule wrote:
| If a 'Type III' civilization is meaningful it could be one that
| uses a quasar the way we use a star.
| morekozhambu wrote:
| juanani wrote:
| [deleted]
| Mizza wrote:
| When I was a kid I was really afraid that particle colliders
| would create a black hole that would sink to the center of the
| earth and eventually eat us all, so I find this article quite
| soothing.
| sohkamyung wrote:
| Cosmic rays with higher energies than that from human particle
| accelerators hit the Earth on a regular basis. If Black holes
| could have been formed by them, we wouldn't be around to ask,
| so actually not much to worry about particle accelerators
| generating Black holes.
|
| > https://www.pbs.org/wgbh/nova/article/the-astronomical-
| parti...
| tzs wrote:
| You can't infer from our failure to not exist that cosmic
| rays hitting Earth never create black holes. All you can
| infer is that any such black holes aren't dangerous. That
| still is sufficient to support your overall thesis that since
| cosmic ray black holes are not a problem we don't have to
| worry about black holes from colliders so your overall point
| stands.
|
| 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.
| badrabbit wrote:
| I think this discussion is too focused towards stable blackholes.
| How useful can unstable (even nanosecs) blacholes be?
| andrekandre wrote:
| > 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.
|
| im not even sure how to begin there... probably the only wait
| contain a black hole would be... warping space-time negatively?
| like kind of warp bubble?
| snarfy wrote:
| > They can be electrically charged but since they radiate
| they'll shed their electric charge quickly
|
| 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.
| [deleted]
| theptip wrote:
| Electrons can't lose their charge through radiation because
| they can't have fractional charge. They radiate photons to
| lose momentum. (They can become uncharged by combining, eg
| e+P = N).
|
| 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.
| kevin_thibedeau wrote:
| You can put a small one in orbit around a body of mass. Or let
| it orbit inside and wait for the spectacle.
| blincoln wrote:
| I skimmed over Crane and Westmoreland's paper[1] and an
| article that discusses specific designs[2], and I'm still
| unsure how one would keep the vehicle and black hole moving
| together while also generating thrust. It seems like there
| would be a conservation of energy problem, regardless of the
| design. I'm not a physicist, so I'm probably missing
| 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...
| XorNot wrote:
| It's just a gravitationally attractive body: it moves towards
| the net gravitational force acting on it. So you could control
| it by trucking sufficiently large masses closer or farther away
| within a suitably large containment area, provided it wasn't
| too massive.
|
| Easiest thing to do though would be to build it in orbit.
| GlenTheMachine wrote:
| Good way to clean up space junk
| fennecfoxen wrote:
| No better than any random orbiting lump with the same mass,
| and quite possibly worse. If you want to clean space debris
| put up something like a big disc of aerogel.
| swayvil wrote:
| Unlike the trash bucket in Linux. 1 time out of 20 you go
| back and restore that thing you trashed. And damn glad you
| are to have that power.
|
| Black holes, otoh, are forever.
| platz wrote:
| they are not forever.
| swayvil wrote:
| hammyhavoc wrote:
| How on Earth did you twist this discussion about
| blackholes to bring up Linux?
| swayvil wrote:
| The whole idea of irrevocable trash disposal vs the less
| irrevocable kind.
| [deleted]
| mrfusion wrote:
| I'd imagine you could keep feeding it an electric charge to
| counter any charge it loses.
| magicalhippo wrote:
| I recall reading that any magnetic fields present when the
| black hole formed would be "frozen in place". If so, couldn't
| that be used?
|
| That said, I found that very surprising and expected the
| magnetic fields to disappear, so maybe I misunderstood
| something.
| doodlebugging wrote:
| I remember back in the day when cartoons had black holes you pull
| out of a pocket and throw down to use either as a portal to a
| different part of the cartoon or as a way to send your
| antagonists somewhere else.
|
| 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.
| imiric wrote:
| Now you're thinking with portals.
| a1369209993 wrote:
| While that is a hole, and is black, it's a totally different
| and unrelated kind of black hole from what TFA is talking about
| (and is more commonly called a "portable hole", after the
| version in Dungeons and Dragons).
| doodlebugging wrote:
| I understand that there may be other things to consider here.
| But, if given the opportunity to dink around with the physics
| and end up with an instant pocket portal that can do the cool
| cartoony stuff I am willing to give it a whirl.
|
| 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.
| a1369209993 wrote:
| > if given the opportunity
|
| 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.
| [deleted]
| [deleted]
| xwdv wrote:
| It'd be cool if we made a black hole type bullet that would suck
| someone or something in completely on impact and dissolve. Not
| sure if feasible though.
| h2odragon wrote:
| Vastly increasing the target's density would do for that; no
| need to go past that into full singularity. cf "Neutronium
| Alchemist" in Peter F Hamilton stories.
|
| It'll never be as simple or satisfying as the old school
| hammer.
| pas wrote:
| yes, but no :)
|
| 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 :)
| shusaku wrote:
| Outlaw Star had it!
| InCityDreams wrote:
| Some parts of heyjackass.com immediately sprang to mind.
| [deleted]
| nyc111 wrote:
| > So, if you hold the mass fixed and compress an object into a
| smaller and smaller radius, then the gravitational pull gets
| stronger. Eventually, it becomes so strong that not even light
| can escape. You've made a black hole.
|
| 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.
| marcosdumay wrote:
| That's an approximation that works at some (very small)
| distance from the surface. It does really not work at the
| center of the object.
| al2o3cr wrote:
| attracts -as if- all its mass is concentrated at its center
|
| That's only 100% true for a radius _outside_ of the object.
|
| 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.
| jfengel wrote:
| No, because that approximation only works when you're outside
| the object. Once you're inside the object, any shell of mass
| outside your distance from the center cancels itself out
| (produces zero net force).
|
| 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.
| _Microft wrote:
| If GP wants to read about this, the name is actually "shell
| theorem":
|
| https://en.wikipedia.org/wiki/Shell_theorem
| llIIllIIllIIl wrote:
| Send trash in it.
| amelius wrote:
| First two sentences of the article:
|
| > Wouldn't it be cool to have a little black hole in your
| office? You know, maybe as a trash bin.
| dioramayuanito wrote:
| Awesome
| ck2 wrote:
| The horrible but obviously accurate answer is it would be
| weaponized.
|
| 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.
| XorNot wrote:
| Why though?
|
| 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.
| ravi-delia wrote:
| It's handier interstellar if you can find a way to accelerate
| it at any real velocity I guess. At that point I can't
| imagine it's easier than just chucking a projectile at some
| absurd fraction of c
| rolph wrote:
| you are suggesting singularity munitions, as others have
| before. the process is not known but the desired product is-
| arbitrarily create an unstable singularity that converts
| surroundings out to a radius into energetic content leading to
| explosive "jetting" and gravity wave propagation until
| spacetime re-normalizes.
| bell-cot wrote:
| Extremely Understated summary answer (to the first question),
| from the article:
|
| > So some engineering challenges that remain to be solved.
| sylware wrote:
| "indeed, we need to fit half the universe in a grain of sand,
| more funding is required to overcome this challenge".
|
| ...
| samstave wrote:
| Twitter takeover funding has entered the chat.
| catmanjan wrote:
| How many story points would you allocate for this one?
| toxicFork wrote:
| 12.1
| adbachman wrote:
| Anything over 8 is probably an epic.
| deforciant wrote:
| Could you please split it into multiple tickets that we
| no bigger than 3 points
| ben_w wrote:
| Splitting it into 3-point tickets an 11 point ticket all
| by itself.
| dekken_ wrote:
| I sure love doing things that aren't actual work
| sharkweek wrote:
| "If you wish to make an apple pie from scratch, you must first
| invent the universe"
| Victerius wrote:
| > Roger Penrose already pointed out in the early 1970s that it's
| possible to extract energy from a big, spinning black hole by
| throwing an object just past it. This slows down the black hole
| by a tiny bit, but speeds up the object you've thrown
|
| 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.
| Jenk wrote:
| surely the law of conservation applies, in that it would be
| more efficient to take the energy used to generate the black
| hole and apply it directly to launching the projectile instead?
| Out_of_Characte wrote:
| Well, its essentially a black hole railgun. Exept a railgun
| uses the magnetic force instead of gravity. and black holes
| are 'theoretically' really efficient at converting mass to
| energy.
| XorNot wrote:
| It would, although the utility of using a black hole has a
| universal mass-energy converter would be substantial. Take
| any matter you want, toss it in to be crushed and then
| extract it back out as kinetic energy you can use to make
| electrical power.
| samstave wrote:
| How would one "rods from god" on a timely manner..
|
| You cannot harvest the energy given to you by a blackhole...
| unless the impacts of tungsten objects yield harvestable
| energy.
| ravi-delia wrote:
| You don't have to chuck in rods, that's just the intuitive
| explanation for why you oughta be able to take energy back
| out. Realistically (for a certain value of realism) you'd use
| the magnetic field generated by charged particles accelerated
| in such a fashion, or something like that
| flatiron wrote:
| small black holes are there for nanoseconds, im not really sure
| you could find a good method to "shoot" them
|
| 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
| gentleman11 wrote:
| > what could we do with it
|
| 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
| amelius wrote:
| We could put a black hole over Russia, so that any ballistic
| missiles they launch get sucked up in it.
| ajuc wrote:
| Some other uses of black holes:
|
| - 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.
| jacquesc wrote:
| Also a great (short) one by Kurtzgesagt
|
| https://youtu.be/ulCdoCfw-bY
| hammock wrote:
| We could throw garbage or nuclear waste into it
| restalis wrote:
| From the article: _" if the black hole's temperature is high,
| the radiation is composed of all elementary particles,
| photons, electrons, quarks, and so on. It's really unhealthy.
| And a small black hole converts energy into a lot of those
| particles very quickly. This means a small black hole is
| black basically a bomb."_
|
| The nuclear waste thrown into it may be much cleaner than the
| stuff it will throw back out.
| ben_w wrote:
| Thanks for reminding me I needed to blog about why I think
| Hawking radiation drives aren't really as good as they look:
| https://kitsunesoftware.wordpress.com/2022/05/14/no-a-black-...
|
| (I agree that Isaac Arthur's channel is good).
| flaghacker wrote:
| The paper you linked, https://arxiv.org/abs/0908.1803, is
| also a fun read.
| devoutsalsa wrote:
| Not from the video... What blew my mind was to learn that a black
| hole get bigger when it absorbs light. Light from a campfire you
| had as a kid could be feeding a black hole right now.
| beeforpork wrote:
| Well, yeah, it is weird at first. But once you think about it,
| it is not unintuitive: if the light was just gone, that would
| be wrong, too, right? Also, energy == mass, so of course, it is
| equivalent to throw mass into a black hole or energy. The
| longer I think about it, the more it is mass that is the weird
| thing. What is mass? Something like frozen energy...
| abhaynayar wrote:
| > Light from a campfire you had as a kid could be feeding a
| black hole right now.
|
| I don't think we have a close enough black hole for this to be
| true for anyone reading this right now.
| samatman wrote:
| The Earth gets bigger as well, and by the same mass per photon,
| when it absorbs light.
|
| 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.
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