Sci-hype: or how I learned to stop worrying and love the black-hole starship
There's a lot of, to put it mildly, hair-brained ideas being put forth these years in the service of "pop-sci". Yeah, I suppose they sorta illustrate some concepts, maybe, but they aren't really worth much. Like, say, that thought experiment from Michio Kaku about destroying a planet with nuke-powered orbital lasers. Given the notoriously low efficiency of lasers, why not scrap them and just use the nukes?
Every so often though, an idea finds its way under the rock where I live and sometimes that idea can warm my cynical hater heart. Case in point- what if we had, instead of an engine, a black hole to power our spaceship to the stars?
I need to start with the disclaimer that I can't even pretend to be competent in the relevant physics of black hole evaporation. What I do know is that black holes are deformed regions of space in which "all directions are inward" (also explained as, the escape velocity exceeds the speed of light in a vacuum), and that from quantum mechanical theoretical grounds, a group of theorists have argued that black holes must, after all, emit radiation. A somewhat curious feature of this theoretically predicted radiation is that smaller black holes radiate more intensely, and thus lose mass more readily, than larger ones.
There's some debate as to whether that radiation has actually been observed.
And that, incidentally, brings me to my first, if rather poetic, argument for the idea. It is genuinely cool, in that it relies on the interaction between quantum and gravitational effects, and thus would provide an experimental test-bench/application for unification theories. Should we somehow decide we wanted to build a black hole star ship (BHSS), then we'd need to run a few experiments on black hole behavior, specifically things like Hawking radiation, black hole evaporation, and what a black hole does as it dies.
Another, again rather poetic, argument for the BHSS idea is that, should we decide to build one eventually for some reason, we'd need to up the space program first. Because no way will a black hole be built on Earth. Scientists have kids too, after all.
*cough*, well ok, there were concerns about micro-blackholes being, maybe, generated at LHC. There are several papers, like this one, about what the appearance of such micro-black-holes at LHC energy scales would show about the structure of spacetime; the concerns were mostly dismissed because even more energetic impacts occur in the higher atmosphere with cosmic rays, and that the predicted Hawking radiation for such tiny black holes would make them disappear nigh-instantly. You'd need a bigger hole for it to stick around long enough to allow you a good look at what it emits. So no, such a black hole would be made, if ever, in a space lab.
Poetry dispensed with, the main technical reasons for the idea are a basic plausibility, and an elegant way to convert mass into energy.
We already had to contend with the possibility of creating micro-black holes at the LHC. Set up a big enough accelerator in space and that becomes a nigh certainty. Whether or not the resulting black holes are big enough to be used for space travel is then an engineering problem, not one of scientific knowledge.
And of course, the best thing of all is that, by eventually converting the mass it absorbed into radiated energy, a black hole provides an efficient way to 'burn' fuel. Certainly more efficient than even nuclear, which only converts a few percent of the mass into energy. The only other perfect converter is the matter-antimatter reaction, but you need to make antimatter for that, which isn't very energy efficient in itself, and the resulted antimatter is a bit more awkward to store than a black hole, funnily enough. As long as you keep yourself out of its event horizon, a black hole is, essentially, just like any regular old mass that you could tow, or be towed by, using gravity or somesuch design.
The paper proposing the idea suggests that a black hole useful for interstellar travel would weigh on the order of a million tons (aka, a billion kilograms). For comparison, 99942 Apophis, an asteroid that was suspected of being on an Earth-colliding trajectory, has more than ten times that. So a BHSS could, more or less, be like the black hole, an asteroid for it to orbit around plus a mirror to collect the radiation plus the shielding and cargo of the ship. (Though, the weird way that the thrust would be generated in that design would result in a corkscrew motion, I think; not very comfortable, but I'm sure practical designs can be worked out.)
(EDIT: the reason for the gravity tether in the paragraph above is that the paper on BHSS uses a 'simple', non-rotating, non-charged black hole.Have a spinning black hole, preferably with charge in it, and you can use magnetic fields to contain it so you gain more options. Plus, apparently something called the Penrose process allows one to store/remove energy from a spinning black hole. I wonder what energy density such storage may achieve, because that is always a problem. Still. This needs to happen. Just not on Earth, obviously.)
Besides, once constructed, you can keep feeding mass to the black hole, so while the initial energy investment may be high, your new 'engine' may work for a long time running on ordinary matter. Dirt cheap, literally. You'd need to figure out when/how/how much mass to inject of course, that's where a little experimental study comes in handy (see poetic argument 1). Antimatter, meanwhile, once used up, is used up. You'd need to make another batch.
Of course, radiation moves out in all directions and won't all be converted into useful thrust; but all realistic engines, including nuclear and anti-matter, would have that problem.
The articles proposing the BHSS concept are from 2009- so fairly old. I do wonder why they didn't make more of a splash in the pop-sci press, instead of all the warp engine crap. Maybe it's because BHSSs would coast about at a realistic, slower than light-speed. And they don't have the cool star trek cred. Eh. Plebeians.
Finally, there's no reason to use artificial black holes just for engines. You could use their mass-to-energy conversion as a simple power source, assuming that, for some reason, the Sun isn't available in the place where you're at (maybe because it's too far away).
So all in all, a seemingly plausible and elegant idea. There may be quite a future to it!
Oh, PS: according to the "Tough guide to the known galaxy", you can date Hard SF by what speculation was trendy 5 years before its publication. Does that mean I'll get to publish a Hard SF novel featuring a BHSS by 2014? Fingers crossed, lol.
Every so often though, an idea finds its way under the rock where I live and sometimes that idea can warm my cynical hater heart. Case in point- what if we had, instead of an engine, a black hole to power our spaceship to the stars?
I need to start with the disclaimer that I can't even pretend to be competent in the relevant physics of black hole evaporation. What I do know is that black holes are deformed regions of space in which "all directions are inward" (also explained as, the escape velocity exceeds the speed of light in a vacuum), and that from quantum mechanical theoretical grounds, a group of theorists have argued that black holes must, after all, emit radiation. A somewhat curious feature of this theoretically predicted radiation is that smaller black holes radiate more intensely, and thus lose mass more readily, than larger ones.
There's some debate as to whether that radiation has actually been observed.
And that, incidentally, brings me to my first, if rather poetic, argument for the idea. It is genuinely cool, in that it relies on the interaction between quantum and gravitational effects, and thus would provide an experimental test-bench/application for unification theories. Should we somehow decide we wanted to build a black hole star ship (BHSS), then we'd need to run a few experiments on black hole behavior, specifically things like Hawking radiation, black hole evaporation, and what a black hole does as it dies.
Another, again rather poetic, argument for the BHSS idea is that, should we decide to build one eventually for some reason, we'd need to up the space program first. Because no way will a black hole be built on Earth. Scientists have kids too, after all.
*cough*, well ok, there were concerns about micro-blackholes being, maybe, generated at LHC. There are several papers, like this one, about what the appearance of such micro-black-holes at LHC energy scales would show about the structure of spacetime; the concerns were mostly dismissed because even more energetic impacts occur in the higher atmosphere with cosmic rays, and that the predicted Hawking radiation for such tiny black holes would make them disappear nigh-instantly. You'd need a bigger hole for it to stick around long enough to allow you a good look at what it emits. So no, such a black hole would be made, if ever, in a space lab.
Poetry dispensed with, the main technical reasons for the idea are a basic plausibility, and an elegant way to convert mass into energy.
We already had to contend with the possibility of creating micro-black holes at the LHC. Set up a big enough accelerator in space and that becomes a nigh certainty. Whether or not the resulting black holes are big enough to be used for space travel is then an engineering problem, not one of scientific knowledge.
And of course, the best thing of all is that, by eventually converting the mass it absorbed into radiated energy, a black hole provides an efficient way to 'burn' fuel. Certainly more efficient than even nuclear, which only converts a few percent of the mass into energy. The only other perfect converter is the matter-antimatter reaction, but you need to make antimatter for that, which isn't very energy efficient in itself, and the resulted antimatter is a bit more awkward to store than a black hole, funnily enough. As long as you keep yourself out of its event horizon, a black hole is, essentially, just like any regular old mass that you could tow, or be towed by, using gravity or somesuch design.
The paper proposing the idea suggests that a black hole useful for interstellar travel would weigh on the order of a million tons (aka, a billion kilograms). For comparison, 99942 Apophis, an asteroid that was suspected of being on an Earth-colliding trajectory, has more than ten times that. So a BHSS could, more or less, be like the black hole, an asteroid for it to orbit around plus a mirror to collect the radiation plus the shielding and cargo of the ship. (Though, the weird way that the thrust would be generated in that design would result in a corkscrew motion, I think; not very comfortable, but I'm sure practical designs can be worked out.)
(EDIT: the reason for the gravity tether in the paragraph above is that the paper on BHSS uses a 'simple', non-rotating, non-charged black hole.Have a spinning black hole, preferably with charge in it, and you can use magnetic fields to contain it so you gain more options. Plus, apparently something called the Penrose process allows one to store/remove energy from a spinning black hole. I wonder what energy density such storage may achieve, because that is always a problem. Still. This needs to happen. Just not on Earth, obviously.)
Besides, once constructed, you can keep feeding mass to the black hole, so while the initial energy investment may be high, your new 'engine' may work for a long time running on ordinary matter. Dirt cheap, literally. You'd need to figure out when/how/how much mass to inject of course, that's where a little experimental study comes in handy (see poetic argument 1). Antimatter, meanwhile, once used up, is used up. You'd need to make another batch.
Of course, radiation moves out in all directions and won't all be converted into useful thrust; but all realistic engines, including nuclear and anti-matter, would have that problem.
The articles proposing the BHSS concept are from 2009- so fairly old. I do wonder why they didn't make more of a splash in the pop-sci press, instead of all the warp engine crap. Maybe it's because BHSSs would coast about at a realistic, slower than light-speed. And they don't have the cool star trek cred. Eh. Plebeians.
Finally, there's no reason to use artificial black holes just for engines. You could use their mass-to-energy conversion as a simple power source, assuming that, for some reason, the Sun isn't available in the place where you're at (maybe because it's too far away).
So all in all, a seemingly plausible and elegant idea. There may be quite a future to it!
Oh, PS: according to the "Tough guide to the known galaxy", you can date Hard SF by what speculation was trendy 5 years before its publication. Does that mean I'll get to publish a Hard SF novel featuring a BHSS by 2014? Fingers crossed, lol.
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