Using Black Holes for Terraforming?

[Awaras]

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.

He meant that people that want to *live on the moon* exist.

[ZetaX]

Ah, that makes some sense.

But I am not so sure if those people still think that way after a year on the moon of almost-solitude and with much less than they were used to in a industrialised country.

[WestAir]

Sometimes humanity doesn't consider purpose or efficiency when partaking in an endeavor. Now that I think about it, that's probably the cause of a lot of our issues.

[ZetaX]

Efficiency is not the problem here. Impossibility is

[WestAir]

I'm not sure it's impossible to create a settlement on the moon.

[ZetaX]

Settlements in the sense of a science station¿ Sure. Settlements in the sense of a metropolis¿ Nope, won't happen anytime soon, and also has not much reason to exist to begin with.

You can make the moon a tourist trap at best, and this sounds rather 22st century-ish. It is simply much too expensive for your average person now and will stay that way for quite some time.

[WestAir]

True, but that doesn't make it impossible. I imagine if we both Googled the number of impractical endeavors we've overtaken since 3100BC, we'd have a list long enough to read all night.

[i know you were just joking, but at this point I'm just messing with you. ]

[Zzabur]

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.

I think you are talking about the singularity? the event horizon?

If you want to CREATE a black hole, you need to compress matter to a density high enough for the mass to collapse. The higher is the mass, the more gravitational energy you get from it, so the less energy you'll need to create it. That's why black hole with mass higher than 1.84 solar mass can appear nowadays (not in all cases, it requires 3 or 4 solar mass to get a black hole for sure). In early times just after big bang, the universe energy was supposed high enough to create theoricals primordial black holes, but this kind of black holes can't appear anymore.

If you want to create a black hole higher than 1.84 solar mass (Chandrasekhar limit), the total mass can collapse and create a black hole, for mass lower than 1.84 solar mass, you'll get a neutron star or even another kind of star, and you'll need to bring more energy to turn it into a black hole, and this energy becomes higher as the mass is lighter.

Anyway, talking about Hawking radiation, starting from a 1 solar mass black hole (admitting you got enough energy to create it, which seems impossible at the moment), it would requires something like 2*10^67 years to evaporate, so far more than the total universe lifespan.

Admitting you manage to get a 200t black hole (that means compressing 200t in a bubble of 3*10^-22 m, that's about the distance of the electron from the nucleus), the hawking radiation would evaporate it in 0.67 seconds. Hawking radiation is very important for small black holes, but is only theorical for stellar black holes. That's why we think that primordial black holes can't exist anymore, and why we think that most stellar black holes will remain the same until the end of time....

Anyway, a black hole small enough to fit into a planet, and assuming you can prevent the planet from collapsing into the singularity (which would require a very high angular momentum, and is still not demonstrated that a naked singularity can even exist), it would evaporate in a very short time.

I guess there are easier options to get a higher gravitational energy.

Sorry for my english.

PS : the sun would turn into a black hole if you can compress it to a density of at least 1.84*10^19 kg.m^-3, and the event horizon would be about 3km radius and a singularity of about 9mm. It would fit inside a planet, but it would change drastically any planet trajectories around.

Source : http://cerncourier.com/cws/article/cern/29199

From the astrophysics point of view, it is thought that only massive black holes - with masses several times that of the Sun - are possible, as they are the only ones able to form in the final stages of stellar evolution. Although they have many fascinating properties, these large black holes are not as rich as their smaller cousins could be. The lighter the black hole the greater its surface gravity - and the more interesting the associated physical effects. This is simply due to the fact that Newton's gravitational force is linearly dependent on mass but quadratically dependent on the inverse distance (which is itself proportional to the Schwarzschild radius of the black hole).

Edited August 10, 2014 by Zzabur

[ZetaX]

Why should my diameters talk about the singularity¿! A point has no diameter.

You really, really do not need to show me those numbers. I know those numbers magnitudes pretty well. What you missed completely is any argument why we should suddenly need a universe of energy to create microscopic black holes (those with a size that does only evaporate after several minutes till hours, not milliseconds; then just feed them). You claimed it needs essentially nonexistent amounts of energy, and that's just plain wrong. Your argument did nowhere contradict what I said and even less show why your weird numbers on energies required to make artificial black holes are correct (and they are most likely not).

The energy contained in a black hole is essentially its mass. Thus smaller ones consist of less energy. Or of you want another argument: any large one gets small some day, thus if your weird claim would be correct, it would gain energy by shrinking.

[Rickenbacker]

Where would you get the mass? The solar system doesn't contain enough mass to create a black hole, so you'd have to go visit other solar systems. And if you can do that, you can surely find other planets that are more suitable for terraforming in the first place.

[ZetaX]

Theoretically, you can "create" black holes of almost any mass, assuming enough energy and lots of tech. Practically, you would never want to use a stellar black hole for this, as this is a liiiiittle bit too much gravity to make something like the moon earth-like. You want a mass somewhere betwen the moon's and the earths's for that.

[LaytheAerospace]

If you want to create a black hole higher than 1.84 solar mass (Chandrasekhar limit), the total mass can collapse and create a black hole, for mass lower than 1.84 solar mass, you'll get a neutron star or even another kind of star, and you'll need to bring more energy to turn it into a black hole, and this energy becomes higher as the mass is lighter.

The Chandrasekhar limit is the point beyond which a neutron star forms, not black holes. Specifically, it's the point beyond which electron degeneracy pressure is no longer sufficient to prevent gravitational collapse. Beyond about 3 solar masses, the Tolman–Oppenheimer–Volkoff limit, neutron degeneracy pressure is no longer enough and you collapse yet again. It's possible, but unproven, that there are additional exotic things after neutron stars, like quark stars, but it's probably a black hole at this point.

Anyway, talking about Hawking radiation, starting from a 1 solar mass black hole (admitting you got enough energy to create it, which seems impossible at the moment), it would requires something like 2*10^67 years to evaporate, so far more than the total universe lifespan.

It's actually even worse than that. All black holes radiate energy, but they also absorb it from the cosmic microwave background. For there to be a net shrinkage, the black hole must be hotter (on average) than its surroundings, otherwise it will absorb more energy than it radiates and grow. As it happens, the CMB is ~2.75K, while a stellar mass black hole is 6.16 * 10^-8K. We can solve for temperature to find out the point beyond which black holes will actually start to evaporate, 2.26 * 10^-8 solar masses. Essentially, every black hole that's ever been (probably including primordial black holes) still exists and is growing.

Admitting you manage to get a 200t black hole (that means compressing 200t in a bubble of 3*10^-22 m, that's about the distance of the electron from the nucleus), the hawking radiation would evaporate it in 0.67 seconds. Hawking radiation is very important for small black holes, but is only theorical for stellar black holes. That's why we think that primordial black holes can't exist anymore, and why we think that most stellar black holes will remain the same until the end of time....

Anyway, a black hole small enough to fit into a planet, and assuming you can prevent the planet from collapsing into the singularity (which would require a very high angular momentum, and is still not demonstrated that a naked singularity can even exist), it would evaporate in a very short time.

It's again even worse. The evaporation of a black hole is a terrifyingly energetic event. Your theoretical 200t black hole is not at all black anymore. In fact, it's absurdly hot, at around 6.1 * 10^8 gigakelvin. 1 gigakelvin, as it happens, should be about as hot as the core of the hottest stars in the universe (it's the temperature at which iron fuses). But still, you can't keep a 200t black hole stable without feeding it mass equivalent to the amount of radiated energy. It's radiating about 8.9 * 10^21 Watts, so it needs about 99t of matter every second of every day. Any interruption would result in an explosion equal to half the mass in antimatter (antimatter gets double the power because it annihilates an equal amount of matter, which also releases its energy).

This thing might still technically be a black hole, but it's also probably the brightest thing in the universe. You'll want to wear some sunscreen.

Edited August 11, 2014 by LaytheAerospace

[ZetaX]

It's actually even worse than that. All black holes radiate energy, but they also absorb it from the cosmic microwave background. For there to be a net shrinkage, the black hole must be hotter (on average) than its surroundings, otherwise it will absorb more energy than it radiates and grow. As it happens, the CMB is ~2.75K, while a stellar mass black hole is 6.16 * 10^-8K. We can solve for temperature to find out the point beyond which black holes will actually start to evaporate, 2.26 * 10^-8 solar masses. Essentially, every black hole that's ever been (probably including primordial black holes) still exists and is growing.

It is not really worse than that: after something like 2·10^67 years (assuming there is no big crunch), the background radiation will be much less than today as it decreases with the universe's expansion.

[LaytheAerospace]

It is not really worse than that: after something like 2·10^67 years (assuming there is no big crunch), the background radiation will be much less than today as it decreases with the universe's expansion.

That's just the solution to how long it takes a solar mass black hole to evaporate, and has nothing to do with the CMB. Any evaporation must take place only after the CMB has decayed. So it's 2 * 10^67 years, plus whatever time it takes for the CMB to decay below the temperature of a stellar mass black hole. If the CMB decays slower than black holes do, then it will also limit the rate at which black holes decay.

[ZetaX]

Whatever time it takes for the CMB to be below 10^-8 K, it is rather likely not even close to 2·10^67. CMB is probably mostly inversely proportional to the universe's volume or something similiar.

[LaytheAerospace]

Whatever time it takes for the CMB to be below 10^-8 K, it is rather likely not even close to 2·10^67. CMB is probably mostly inversely proportional to the universe's volume or something similiar.

We know very little about the CMB. Making assertions about what it will or won't do based on your gut feeling is a mistake. Best to stick to the math we do know, rather than assume the math we don't will agree with us. Think of it like the + C in calculus. It doesn't make a difference most of the time, but you're still wrong when you omit it.

[ZetaX]

It can't be much higher than what I wrote to not violate conservation of energy. If there is more volume to fill, the amount of energy per cubic lightyear has to decrease. Even of you add all the mass to the energy, which should be far too large then, you would still get something smaller I think (did not check myself, too tired right now, maybe later if needed).

And the +C in calculus is a thing you don't see outside some introductory course. Unless I am given a question to determine all antiderivatives of a function, the +C is not needed. Most other cases where you encounter such a thing are when it actually has a special value (it just encodes the initial condition of a simple differential equation).

[LaytheAerospace]

It can't be much higher than what I wrote to not violate conservation of energy. If there is more volume to fill, the amount of energy per cubic lightyear has to decrease. Even of you add all the mass to the energy, which should be far too large then, you would still get something smaller I think (did not check myself, too tired right now, maybe later if needed).

And this is predicated upon us understanding how the universe is going to expand in the far future. Something we know very little about. The expansion may accelerate, leading to a Big Rip. It may stop, letting the existing matter decay no matter how long it takes. It may reverse, leading to a Big Crunch/Bounce. Nobody can say with much authority which of those it will do. Right now it looks like the expansion is accelerating, though we cannot explain why and just wave our hands at it saying "dark energy." It seems likely to me that our understanding of the expansion of the universe will change dramatically as we start to understand the force that drives it (if it exists at all). There are fringe cosmological models which don't require an expanding universe to explain the existing observations, so it's possible there isn't any expansion at all (though this seems extremely unlikely).

And the +C in calculus is a thing you don't see outside some introductory course. Unless I am given a question to determine all antiderivatives of a function, the +C is not needed. Most other cases where you encounter such a thing are when it actually has a special value (it just encodes the initial condition of a simple differential equation).

My point is that the initial condition matters in this case. Nobody knows when the CMB will decay to the point to allow black holes to evaporate. Maybe the expansion will reverse before the CMB cools enough, and black holes never begin to evaporate. Maybe the Big Rip happens before significant evaporation occurs. Absent deeper understanding of the CMB and expansion of the universe, we just don't know.

Why not acknowledge this gap in understanding, rather than asserting it doesn't matter?

[ZetaX]

It does not matter because the prime assertion of my post was, as I mentioned there, that there is no Big Crunch, as that would render all those calculations quite obsolete due to the universe never reaching that age. It is by the best of my knowledge not possible for the expansion to stop and stay that way (essentially because the second after it would start falling back into itself). Thus it's either infinite expansion (then my calculation applies) or Big Crunch (then my assumption applies).

If you come with such an argument as "but everything could be different", you can also doubt the existence of Hawking radiation; or the existence if the universe after the year 2100 because "god" might delete it. I am using the current understanding of the universe, everything else would just be very hypothetical.

[LaytheAerospace]

If you come with such an argument as "but everything could be different", you can also doubt the existence of Hawking radiation; or the existence if the universe after the year 2100 because "god" might delete it. I am using the current understanding of the universe, everything else would just be very hypothetical.

Strawman in the extreme. My point is that we're already in an area we know nothing about. I'm not saying "what if it's different" I'm saying "the only thing we know is that we don't understand it." This is well known as the single worst understood area of cosmology. I'm not being unreasonable to say you should consider your unknowns.

The expansion and ultimate fate of the universe? Biggest unknown there is. Arguing otherwise is...bizarre.

[Zzabur]

@LaytheAerospace : Thank you for your informations, I agree about :

-What might exist between Chandrasekhar limit and Tolman–Oppenheimer–Volkoff limit : we don't know exactly, but it could be a black hole...or something else from a neutron star to any unknown exotic stuff like strangelets. I assume it's a black hole in order to keep things easier, but you're right, it's certainly not ^^

-A black hole "eats" matter, often more than it radiates, but i wanted to show that even if there is no matter, no accretion disk, a stellar black hole would take ages to evaporate. But you're right, it's even longer because it tends to grow bigger. By the way, here's a nice article about formation of supermassive black holes soon after the Big Bang : http://arxiv.org/pdf/1304.7787v2.pdf . And it's even worse than you said (that was worse than i wrote before lol) ! Because it seems that these black holes have moved a lot around young galaxies, and caught a lot of matter directly in it without accretion disk. So they eat, and they used to move to eat even more matter, so it seems that Hawking radiation will start to evaporate black holes when there is few matter remaining outside of BH in the universe (that was the main hypothesis before Hawking radiation, BH are going to eat all matter, then bigger BH will "eat" smallest ones, and then the universe will end as a BH containing all matter? Because it breaks thermodynamic laws, entropy should always grow with time).

Anyway that means that even if it seems much too long to evaporate completely, i guess it's even longer because i don't take in account matter that fall inside.

-Hell yeah, a 200t BH would evaporate so quickly that it would be more like an interstellar nuke lol. Again, i just wanted to show that smaller BH are far more unstable (theorically) than big ones. And i have to tell again that it's only hypothetical, like naked singularity. To create the smallest BH, assuming 3dimensions of space and 1 of time, it would require 10^19GeV, for proton-proton collision, LHC can reach 14*10^3GeV, so not even in dream....It's been theorically calculated that with extra-dimensions though, the energy to provide would be far less because of extra gravitational energy provided (source : http://arxiv.org/pdf/0908.1780v2.pdf).

Anyway, all these calculations are a bit useless because we can't prove them by experience at the moment, no one has ever prove the existence of small, micro and primordial black holes, and i guess we won't get an answer before a very long time....if we ever manage to get one.

@ZetaX : mathematics can seem "nonsense", it is indeed when you can't prove them by physics, but i rely more on them than on "guess" "thought" or "what should be". Math tells us what could exist, but not if it exists really, lots of mathematicals answers can't apply in the universe, as long as we don't know things like how much dimensions exist in the universe, we can't tell much about it.

PS : Well, it seems that you are far more clear than me LaytheAerospace I would conclude and fully agree about this assertion :

I'm not saying "what if it's different" I'm saying "the only thing we know is that we don't understand it." This is well known as the single worst understood area of cosmology. I'm not being unreasonable to say you should consider your unknowns.

Edited August 12, 2014 by Zzabur

[ZetaX]

Strawman in the extreme. My point is that we're already in an area we know nothing about. I'm not saying "what if it's different" I'm saying "the only thing we know is that we don't understand it." This is well known as the single worst understood area of cosmology. I'm not being unreasonable to say you should consider your unknowns.

The expansion and ultimate fate of the universe? Biggest unknown there is. Arguing otherwise is...bizarre.

I find it more bizarre to argue that we know nothing about something we observe right now. Also, you completely ignored the first half of my post, which argued even without detailed knowledge why your objection is invalid.

[LaytheAerospace]

find it more bizarre to argue that we know nothing about something we observe right now.

Just because we've observed a redshift and attributed that redshift to an expanding universe doesn't mean we know anything about said expansion. The force that drives it, if it even exists, has been labeled Dark precisely because we know nothing about it. I assume that, since you're arguing so strongly against this, that you can explain to me the nature of Dark Energy. Specifically, why does it exist, what natural laws drive it, and how do you calculate its strength?

You can observe an airplane flying far overhead. Does that mean you know anything about why it flies?Can you assert that the airplane will fly forever on the same trajectory? What if the plane is accelerating, do you assume it will accelerate infinitely just because you haven't seen it stop accelerating yet? Can you build your own airplane based on that observation? Of course not.

But you know so much about the airplane! You can measure its size, speed, reflectivity. Make educated guesses about composition and energy production. But still, you really don't know anything about why it flies until you dig deeper. In this case, it's the laws of aerodynamics that we really need to understand to claim to have any understandings of why airplanes fly. In the case of our debate, it's Dark Energy.

Also, you completely ignored the first half of my post, which argued even without detailed knowledge why your objection is invalid.

Sorry, when somebody invokes god on my behalf, it distracts from any legitimate points you might have been making. But I'll bite, and go back and respond to the other half of your post. It will be simpler in the future if you leave the strawmen, and god, at the door.

It does not matter because the prime assertion of my post was, as I mentioned there, that there is no Big Crunch, as that would render all those calculations quite obsolete due to the universe never reaching that age.

Begging the question. It's easy to be right when you assume your hypothesis from the outset. My entire point is that you can't simply assume there will be no Big Crunch. This is very much not settled science. As I've repeatedly pointed out, it's the most poorly understood area of cosmology. It's probably the most poorly understood area in all of science, though I won't claim to know enough to make that assertion.

It is by the best of my knowledge not possible for the expansion to stop and stay that way (essentially because the second after it would start falling back into itself). Thus it's either infinite expansion (then my calculation applies) or Big Crunch (then my assumption applies).

Flawed assumptions. Given that we have no idea what's even driving the expansion of the universe (one of those big unknowns you don't want to admit to), we cannot say what a post-expansion universe (if it exists) will look like. Will it collapse at an accelerated rate? Collapse at a constant rate? Not collapse at all? Expansion stop accelerating and remain constant? Expansion approach zero asymptotically? What if the universe keeps expanding to the Big Rip, but takes a really, really long time to do it? Say, 10^10^67 years. Now the decay of the CMB dominates the time needed for a black hole to evaporate, and the universe is still expanding without bound. Just because we've observed what looks like a past acceleration doesn't mean there will be a future acceleration.

I'd challenge you to find an astrophysicist who claims they understand why the universe is expanding, or whether it will stop. But that's a Sisyphean task, and we both know it.

[ZetaX]

I did not invoke god, but "god" (if you can't make out the difference from the ", then I can't help you); to give an example that your claim that "not fully understanding something implies we cannot make predictions about it" is quite wrong. That's just a pretty huge fallacy. By the way, stop calling this a strawman, because a strawman would be arguing about something different, which this isn't.

And again: it is rather irrelevant that we do not fully understand dark energy, or even understand it at all. My claim follows mostly from general relativity, and all your counterarguments are if type "you can't prove that there is no mysterious force that stops it in 10^10 years"; yes I can't, but this kind of argument is stupid and the reaon why I invoked "god".

And to take your example back to you: prove to me that airplanes won't stop flying by 2100. Be it by gravity suddenly being twice as today, aerodynamics changing differently, or whatever randomly sounding reason.

[fenderzilla]

but what was that thing about centrifuge cities? How would that work? the centrifugal force pushes you out, away from the circle's center. would it be oriented Vertically? that would mean the moon's gravity would compliment you as you went down but not as you went up, and everyone would be bouncing up and down like jackhammers. If it were horizontal, the moon's gravity would pull you down as the centrifuge pushed you sideways, and you'd end up at like a 45 degree angle to the horizon. that's better, but then there's not much point in putting them on the moon's surface as apposed to in orbit.