Using Black Holes for Terraforming?

[K^2]

and the center is singularity, which could also be called nothing because it has zero dimensions. It's a point.

So is an electron. So are quarks. I guess, they are nothing as well. In fact, black hole singularities don't have to be points. There can be ring singularities, for example. While elementary particles are always just points.

Singularity in the black hole has energy, momentum, mass, angular momentum, and an electrical charge. Just among the significant qualities of matter. Furthermore, there is a definite phase transition when neutron star collapses into a black hole.

So singularity is certainly matter, black hole is certainly a state of matter, and just because something disagrees with how it should be, doesn't make it "nothing". So please, stop claiming that modern science is on your side on this issue.

[lajoswinkler]

If stellar black holes are very small by your standards, then yes. Those still rip you apart long before you cross the horizon. You may just be able to make out their gravity lensing effect with the naked eye if you fly closely past one, the stars would twitch a little bit.

I really doubt that's the case. Someone should do the math, but as far as I know, you'd need very small black holes (artificial) for the tidal forces before the event horizon to be so huge that a human body od 180 cm would be torn apart.

So is an electron. So are quarks. I guess, they are nothing as well. In fact, black hole singularities don't have to be points. There can be ring singularities, for example. While elementary particles are always just points.

Singularity in the black hole has energy, momentum, mass, angular momentum, and an electrical charge. Just among the significant qualities of matter. Furthermore, there is a definite phase transition when neutron star collapses into a black hole.

So singularity is certainly matter, black hole is certainly a state of matter, and just because something disagrees with how it should be, doesn't make it "nothing". So please, stop claiming that modern science is on your side on this issue.

So an electron is a state of matter? No, it's not. It's an electron. State of matter requires a system of particles. Therefore a black hole can not be a state of matter. It's a point surrounded by a horribly warped spacetime.

You're using semantics to get your way, and it's not the first time.

[N_las]

Event horizon is space, which is "nothing" by traditional sense of speaking (let's ignore particles foaming in vacuum), and the center is singularity, which could also be called nothing because it has zero dimensions. It's a point. According to our current knowledge, of course. Who knows what's the actual bussiness inside. I was always fond of hypothesis that it's still a kind of star, but a totally degenerated and very small.

So, curved space... that's not a state of matter.

You're using semantics to get your way, and it's not the first time.

People who live in glass houses...

[K^2]

I really doubt that's the case. Someone should do the math, but as far as I know, you'd need very small black holes (artificial) for the tidal forces before the event horizon to be so huge that a human body od 180 cm would be torn apart.

That's absolutely wrong. A stelar black hole will tear you to shreads. But hey, why don't you do the math, eh? Since, apparently, you know more about black holes and phase transition than a theoretical physicist.

Don't forget that you can't be using Newtonian gravity for it. I'll let you get away with assuming Schwarzschild metric to start from. Have fun.

[lajoswinkler]

That's absolutely wrong. A stelar black hole will tear you to shreads. But hey, why don't you do the math, eh? Since, apparently, you know more about black holes and phase transition than a theoretical physicist.

Don't forget that you can't be using Newtonian gravity for it. I'll let you get away with assuming Schwarzschild metric to start from. Have fun.

So only theoretical physicists should be able to talk about this? I've been reading about this in the 90s and I remember it's one of those things you hear in older documentary movies. OK, I'm wrong, I've mixed something. Why are you constantly behaving like a bickering old lady? Normal people provide others with a link. You're being a pain in the ass all the time and behaving like a god almighty towards everyone. You'd be a lousy teacher. Please stop with such behaviour or I'll report you the next time. I'm sick of it.

Also, you could finally say what's the state of matter of a single electron whizzing by Neptune. I've never heard that lonesome elementary particles represent a state of matter, but what the hell do I know, right?

[ZetaX]

To check whether a black hole with the mass of our sun shreds you, just calculate it Newtonian style. This is obviously not entirely correct, but the order of magnitude is (non-rotating black hole assumed).

[K^2]

So only theoretical physicists should be able to talk about this?

No, but when you keep insisting that one is wrong without being able to do even the basic computations on the problem, you're doing it wrong.

Also, you could finally say what's the state of matter of a single electron whizzing by Neptune.

Same as that of any other single electron. Or any other elementary particle. States are defined by transitions, not in absolute. Since there are no transitions to/from one-particle state, there isn't usually anything to talk about.

There is, most certainly, a transition to the black hole state. Which is accompanied with a jump discontinuity in the entropy, characteristic of first-order phase transition. Similarly, black hole evaporation has characteristics of phase transition.

More importantly, you didn't just insist that black holes don't have a state. You insisted that they are "nothing". Not matter at all. Which is specifically when I brought up elementary particles. Care to try and address that? Or do you just want to continue being obtuse and hostile when someone who spent time studying the subject is simply telling you that you are wrong, and giving you plenty of examples why.

And no, I'm not going to try and explain it to you. I do not have time to read a course on black hole collapse to someone who isn't familiar with basic statistical mechanics. I can point you to some textbooks if you want to learn, but expecting me to actually explain it to you is neither reasonable nor appropriate.

but what the hell do I know, right?

Typically, that statement is made once you've established some authority on the subject. As it is, I don't really understand the point you're trying to make with it.

[Kerbart]

To solve problem x, we use solution y. Never mind that solution y is about 100,000× more difficult to solve than problem x...

[Seret]

So only theoretical physicists should be able to talk about this?

No, but when you're discussing a topic with someone who's a professional in that field (and you're just an enthusiastic amateur) you should probably recognise that you're not going to be able to speak with much authority.

We've all got topics we can speak with authority on, and some where we should be a bit more humble.

[impyre]

Seems like a lot of going about on what black holes are. It seems to me that there's two ways you could easily define a black hole... You could define it as the matter/energy singularity that causes the gravitational effects, and only that singularity. But it seems that an equally useful definition is that a black hole is said singularity and it's associated sphere of influence and the effects it has on space-time. Of course, if you define it as only the singularity, the event horizon then is not part of the black hole proper. I think most people consider the event horizon to be part of a black hole... or at least part of the hole anyhow, heh.

On to the OP, I seriously doubt it. As someone else mentioned, if you had the technology to do this (assuming it's even possible), then you'd likely have the technology to find a much better solution. Also, there are low-tech solutions that seem to be overlooked. Sufficiently advanced technology could add mass to the planet by physically adding matter to it (maybe having automated drones sprinkle a steady supply of dust over it), or possibly by generating said matter from massive energy sources in a reverse fission/fusion reaction. Put the genie back in the bottle so to speak.

[N_las]

You'd be a lousy teacher. Please stop with such behaviour or I'll report you the next time. I'm sick of it.

Why are you constantly behaving like a bickering old lady?

The glass house again...

[WestAir]

Stupid [black Hole Related] question for the physicists in the thread:

If a stellar object that is massive enough to fall into its own schwarzschild radius, but doesn't collapse into a singularity because it is spinning fast enough for centripetal force to counteract the force of gravity, finally slows down enough to begin collapsing into a black hole, can you stop the collapse by spinning the stellar object faster again?

If so, is it possible to undue a collapse by introducing centripetal force?

[K^2]

Stupid [black Hole Related] question for the physicists in the thread:

If a stellar object that is massive enough to fall into its own schwarzschild radius, but doesn't collapse into a singularity because it is spinning fast enough for centripetal force to counteract the force of gravity, finally slows down enough to begin collapsing into a black hole, can you stop the collapse by spinning the stellar object faster again?

If so, is it possible to undue a collapse by introducing centripetal force?

First things first. Such events are predicted to happen. A neutron star with sufficient angular momentum can be past the gravitational collapse limit for a static object. And they do slow down because they lose a lot of energy due to electromagnetic and gravitational radiation. When it slows down sufficiently, it will collapse in an event known as blitzar. We do have observations of events that match blitzar hypothesis, but no confirmation yet that this is the actual cause.

Next part is slightly more complicated, but the key is to understand that while location for event horizon is defined only by the mass, angular momentum, and charge of the black hole, it's not until well into collapse that the horizon appears. The collapse starts simply because gravitational forces overcome various sources of repulsion in matter. Before the event horizon forms, could you spin the object back up to revert collapse? In principle, yes. At least, partially. The hard question, one which I don't have an answer to, is what happens to matter that has already become more compact than neutron matter. There could be some intermediate states, such as quark or strange matter. Whether these will remain as such, expand back to neutron matter, or continue to collapse, I don't know. This could lead to any number of outcomes from most of the star collapsing anyway, to it exploding instead.

Of course, since there is no plausible way to supply required angular momentum anyways, this is purely academic.

Completely separate is the question of what happens if we supply angular momentum once the black hole has formed. At first, not much interesting happens. You will, of course, have a Kerr black hole, which has a more interesting event horizon structure than Schwarzschild black hole, but real black holes are already going to have angular momentum and will already have that feature to some extent. There is, however, an extreme amount of angular momentum that a Kerr black hole can hold and still be a black hole. As the angular momentum increases, the size of the event horizon shrinks, until at some point, it goes away completely. Such an overextreme Kerr solution becomes a naked singularity.

What happens from there is not known. Kerr solutions are known not to be stable in the interior of a black hole or in the naked singularity case. But what that means is subject of some debate. There could be another solution for overextreme angular momentum, which still includes an event horizon. Or there might be one that truly does present a naked singularity. Or the singularity itself can be unstable, emitting all or part of its energy to shed excess angular momentum. Note that this can happen without violations of cosmic censor in a way similar to black hole evaporation.

In any case, it's clear that you will not be able to reverse the collapse once you have a black hole. But it might be possible to destroy a black hole by making it spin too fast or create a new, completely different kind of object.

[CleverWalrus]

Also, we still have no idea about the effects of low gravity on human health. ZERO gravity is bad, yes, but there has been NO research on long term exposure to low gravity. What is the minimum gravity to keep a human healthy? No clue. It might be 1g, it also might be much less.

We have evolved on a planet with 1g so, for now, we know this is the "best" value for our organism.. sadly i'm skeptical that we will be able to easily adapt outside of our planet... took us billions of years to end up adapted to it... unless we heavily genetically engineer people i think life elsewhere will be a big ordeal.

[Zzabur]

The energy required to create such a black hole would be really huge, i think it would requires more than the whole universe's energy.

[Duxwing]

it would be a relatively trivial engineering project to build large city sized centrifuges on the moon.

i would build them under ground in circular tubes drilled out by tunnel boring machines. they would ride on maglev tracks at an angle such that the the natural gravity would complement the centrifugal gravity for 1g acceleration. this would require non planar deck space on larger modules.

Why would people want to live in hollow halls beneath the fells?

-Duxwing

[ZetaX]

The energy required to create such a black hole would be really huge, i think it would requires more than the whole universe's energy.

That's just nonsense. Your claim implies that a supernova has more energy than the entire universe...

[Zzabur]

That's just nonsense. Your claim implies that a supernova has more energy than the entire universe...

The smallest the black hole is, the more energy it requires because of higher density to collapse. It's why nowadays, a black hole smaller than 1.84 solar mass can't appear. If you want a smaller black hole, you need to bring more energy, and if you want a black hole that fits inside a planet like earth, it would requires too much energy to be created.

Recent discover suggests that the LHC could provide enough energy to create a quantum black hole, but it relies on more dimensions, so this is pure theory.

A supernova can create a black hole, but it won't fit inside a planet.

[ZetaX]

Please just stop that nonsense. A stellar black hole is some kilometers in size (rough guess by calculating the sun's schwarzschild radius), which obviously would fit inside a planet. It would just not be very pleasant.

You could always wait for a black hole to get small enough by Hawking radiation. Just a matter of (really a lot of) time.

Anyway, a smaller black hole consists of less energy than a bigger one (without any exception as long as we do not let them rotate). Thus your claim could at beast be about how to make one, which creates lots of other questions on your dubious claim.

[Nuke]

Why would people want to live in hollow halls beneath the fells?

-Duxwing

because radiation. by all means live on the surface if you want.

[Awaras]

We have evolved on a planet with 1g so, for now, we know this is the "best" value for our organism.. sadly i'm skeptical that we will be able to easily adapt outside of our planet... took us billions of years to end up adapted to it... unless we heavily genetically engineer people i think life elsewhere will be a big ordeal.

And what exactly do you base that on? Humans have adapted to live in every enviroment imaginable on Earth, from the arctic circle to the worst deserts, from the sea shores to extreme altitudes where 'normal', non-adapted people can barely breathe. What makes you think we would not be able to adapt to a low-g enviroment?

[ZetaX]

The fact that all environments you mentioned only differ by temperature, ecosystem and such. Not by gravity.

Anyway, there is no real reason to live on the moon. Most stuff we would want there can probably be best done by robots, and the (maybe even nonexistent) few exceptions can get a centrifuge.

[WestAir]

The reason to live on the moon is the reason itself. Ask yourself why did man move to the isle of Manhattan hundreds of years ago? London, Rome and Paris were doing just fine. Why would anyone make a city in Las Vegas, Nevada where there was nothing but a dry desert with a 115*F summer and no land suitable for farming or herding?

Because we can. Because someone wanted to. You can't tell me no body wants to take the challenge of moving to the moon. The people that want to exist. And that's all the reason we need.

[Z-Man]

The reason to live on the moon is the reason itself. Ask yourself why did man move to the isle of Manhattan hundreds of years ago?

Because they imagined a better life over there one way or another. Millions went because they were starving at home.

Why would anyone make a city in Las Vegas, Nevada where there was nothing but a dry desert with a 115*F summer and no land suitable for farming or herding?

You mean the modern Las Vegas we know now? Liberal gambling laws.

That may apply to the moon, actually. No laws for now. You can do all the organized low gravity man on bear fighting you want!

[ZetaX]

Because we can. Because someone wanted to. You can't tell me no body wants to take the challenge of moving to the moon. The people that want to exist. And that's all the reason we need.

Living on the moon is like living on earth, but at a hundredfold cost and with less goods. Not much of an advantage here. And "because we can" works for sending a few to make a scientific colony, but not for something like a small city. And the part about people wanting to exist simply makes no sense.