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Can we make a black hole? And if we could, what could we do with it?

ajuc

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.

ben_w

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

The paper you linked, https://arxiv.org/abs/0908.1803, is also a fun read.

hammock

We could throw garbage or nuclear waste into it

restalis

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.

sliken

True, but that's tunable, the bigger it is the less comes out.

jacquesc

Also a great (short) one by Kurtzgesagt

https://youtu.be/ulCdoCfw-bY

bell-cot

Extremely Understated summary answer (to the first question), from the article:

> So some engineering challenges that remain to be solved.

sylware

"indeed, we need to fit half the universe in a grain of sand, more funding is required to overcome this challenge".

...

catmanjan

How many story points would you allocate for this one?

samstave

Twitter takeover funding has entered the chat.

sharkweek

“If you wish to make an apple pie from scratch, you must first invent the universe”

gradschool

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

codethief

> 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

> 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

> 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.

at_a_remove

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

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?

platz

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

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.

pdonis

> 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.

varajelle

(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.

gus_massa

> If it was possible to concentrate a proton to make a blackhole, when it evaporates, I'd say it "eject" itself (a proton)

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...

XorNot

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

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

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".

a1369209993

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).)

slowmovintarget

Every mass has a corresponding Schwarzchild radius because mass is just a variable in the equation. Almost everything in the universe has an actual radius far far larger than it's Schwartzchild radius, hence most objects in the universe are not black holes.

vbezhenar

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

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.

andrekandre

  > 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?

XorNot

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

Good way to clean up space junk

fennecfoxen

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

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.

snarfy

> 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.

theptip

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.

null

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magicalhippo

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.

mrfusion

I’d imagine you could keep feeding it an electric charge to counter any charge it loses.

null

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kevin_thibedeau

You can put a small one in orbit around a body of mass. Or let it orbit inside and wait for the spectacle.

blincoln

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...

mrkramer

Maybe we could make Black Hole Computers[0]?

[0] https://cse.buffalo.edu/~rapaport/111F04/lloyd-ng-sciam-04.p...

DerekBickerton

    ♩ ♪ ♫ ♬
    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

sidlls

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...

bjt2n3904

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?

helldritch

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.

TheDudeMan

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

> 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.

justsomeshmuck

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

> 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?

justsomeshmuck

https://academic.oup.com/mnras/article/152/1/75/2604549?logi...

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.

kqr

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

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

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?

codethief

> 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.

al2o3cr

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!

Sharlin

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.

DJBunnies

That's called the event horizon, which is proportional to its mass.

Mizza

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

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

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.

xg15

> 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

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.

xen0

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.

zmgsabst

> 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.

lilgreenland

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.

null

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platz

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.

null

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cletus

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

Are free electron lasers fundamentally incapable of operating up into gamma? Maybe we just need to wiggle harder.

daniel-thompson

This is the kind of question that makes me believe in the Great Filter¹.

¹https://en.wikipedia.org/wiki/Great_Filter

BiteCode_dev

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

Came here to post this but couldn't remember the name "Great filter", thank you. :)