This Episode is sponsored by Skillshare Black holes are often portrayed as scary world-eating monsters, but what if they are actually the
batteries that will power our future among the stars? So today we are looking at how we can potentially use black holes in the future, and it’s
a topic we actually covered early in the channel but I thought it deserved a second visit and
an expansion. Black holes offer a lot of options for any civilization that can master them
and it’s too much for one episode, so we’ll do a crossover series looking at their implications
for some of our other episodes over the next few months, and today we will focus on their
use in moving spaceships in our Generation Ships series. We’ll follow that up with
an Outward Bound episode on Colonizing Black Holes, and then a visit to our Space Warfare
series with Weaponizing Black Holes. But we should start by talking about what
black holes are and what they aren’t, and how artificial ones might differ from natural
ones and the various ways we can draw energy from them. Contrary to popular belief in fiction,
black holes do not just suck material into them, indeed a star that’s turned into one
has a lot less gravitational force than it used to and you could normally fly by one
far closer than you could fly by a star of the same mass without being harmed in the
least bit. It’s common to say that black holes are
so massive that even light cannot escape them, but this is wrong. It’s less common and
less inaccurate to say that black holes are so dense, that even light can’t escape them.
But both remarks paint a false portrait that’s only right because our most common known examples
of black holes are those naturally created by stars dying, which are of course quite
massive. There is a concept in physics called an event
horizon, which like the normal horizon on Earth, is a place where you can’t see events
occurring beyond it. The difference is that on Earth, if you live in a village you can
walk over to that horizon, see what’s going on, and walk back home to tell everyone what
you saw. Obviously if you lived on a planet that was a big balloon, constantly expanding,
you’d have to walk further to get to that horizon as it’s further away on larger spheres,
and you’d have to walk faster than it was expanding in order to take a look and come
home. At an extragalactic scale, this is gives us something called the Cosmological Event
Horizon, from the expansion of the Universe, and in general in physics it means light speed
because that’s the fastest we, or any information, can go. While a Black Hole is a name more
fitting for the Event Horizon of an object, where gravity prevents light from escaping,
rather than what that object is, we’re rather stuck with the term these days.
Every object in this Universe has gravity it gives off, based on its mass, though in
fact it’s the total energy it has, not its mass that really matters, mass just happens
to be the type of energy most usually relevant for this. The gravity generated by this pulls
on you and there’s a speed, based on that mass and how far you are from it, that you
could be moving away from it so you’d never be pulled back to it and thus would escape…
the escape velocity. The equation for this is just the square root of twice the mass
over the distance from that object, usually we’re talking about launching from its surface
so that distance is that object’s radius. Looking at that equation though, you’d note
that if the mass increases or the distance from it decreases, the escape velocity will
rise, and if either the mass rises enough or the distance drops enough, that escape
velocity will rise until it reaches the speed of light. It doesn’t magically stop there
or anything, you can go higher, but no photons are going to reach you from that place, you
will see darkness even if someone were shining a flashlight at you from in there, a black
hole, and you can’t see what they’re doing, as they are over the horizon where you can
see events. Any mass, at all, is going to have a distance
this would occur at, but it’s usually less than the radius of the object and once you
get lower down, a lot of the mass generating that gravity is above you and has to be discounted.
If you could compress it all down to a tiny point, then any mass would have an event horizon,
but to generate an event horizon the size of a typical living room, you’d have to
compress the planet Jupiter down into a space that size, and Earth would have to be compressed
to the size of a marble. The problem is, when you compress stuff it
heats up, and little particles that are hot enough can escape from a planet if you do,
and naturally occurring massive objects are inevitably composed mostly of hydrogen and
helium, which fuse and release more heat shoving things apart. Even if you took iron, which
cannot fuse, and packed it all in one place, the heat released as it crunched up would
vaporize those outer layers and blow them off, so just stacking endless trillions of
tons of iron somewhere would only make a black hole if you took your time about it, letting
it cool as you added mass. Hypothetical Iron Stars collapsing into black holes is something
we looked at in Civilizations at the End of Time, and can exist exactly because they have
eons to cool down as they slowly form by quantum processes. Given the series title, this approach
isn’t too fast, though you can do it faster than that.
So black holes just don’t form naturally below a certain mass, a mass greater than
our own Sun, but that only covers natural formation and we’re not limited to that
approach, and the physics doesn’t change for how they operate if they’re smaller
either, though a lot of their properties do. Now, we’ll focus on small artificial black
holes throughout this series but there are ways to use existing black holes, natural
ones, for useful purposes including propelling spaceships. The problem is that naturally
occurring black holes are really very uncommon. Only about 1 in 1000 stars that form is massive
enough to die as a black hole and they tend not to be located where they’d be very useful
for the typical civilization, particularly considering their presence would be prone
to discourage civilizations evolving there. We’ll talk more about how civilizations
could find them useful in Colonizing Black Holes in three weeks, but in terms of running
starships, we do have a few options. First off, the easiest way to locate black
holes these days is by their accretion discs, matter that falls into orbit around them and
slams into other matter as they slowly decay in orbit and fall down. The same as anything
falling down a gravity well, it gains a lot of energy as it does so, and will release
this as radiation, which so long as it does it outside the event horizon can be captured
and used like any other energy. This is the conceptually easiest way to tap black holes
for power, you spray a jet of matter at it, aiming just off to the side so it enters a
close and elliptical orbit, and that jet will create a nice whirlpool of matter that gets
crowded and hot and turns that black hole into a big power plant.
For a non-rotating black hole, such a process can let you achieve a 6% matter to energy
conversion rate. That sounds measly, but remember that’s matter to energy, E=mc², throw a
gallon of gasoline on a fire, 2.75 kilograms of mass, and you’ll release 120 million
joules of energy, throw it down a non-rotating black hole yielding a 6% mass-energy conversion,
and you will get almost 15 quadrillion joules back, 124 million times more energy than burning
it got you, of course the black hole gets even more, but it did a lot of work to get
that so it deserves the lion’s share. This is also much better than using a Sun,
since Fusion generally doesn’t even give you 1% mass to energy conversion, and most
stars don’t fuse all their matter and take a long time doing it, indeed the most efficient
ones live half of eternity, whereas the really bright ones that give off the most power tend
to explode long before they’ve burned more than a fraction of their mass. Your default
black hole is thus a way more efficient power reactor and you can also throttle it a lot
better than a star. You are also decently likely to find a nice big source of matter
nearby a black hole since even though they have explosive births, a supernova is not
actually powerful enough to rip apart gas giants in outer planetary orbits. In fact,
one of the ways to find a black hole is to notice a brighter binary companion wobbling
around it. Another way to make one is to start with a less massive neutron star and stuff
it’s binary companion into it too. Needless to say, if you’ve got a giant power
reactor you’ve got an engine, but in this case it would be a slow one like the Shkadov
Thruster method of turning a star into a big spaceship, except you can achieve a higher
final speed with one, though it will be gaining mass while you do this. We’ve a better way
of converting black holes into engines we’ll get to in a moment.
The other obvious method would be to fly a spaceship near one to slingshot off it, but
you are not a cloud of gas so you can’t afford to get too close. This still offers
a fairly nice bump in speed even to ships moving fast enough to consider interstellar
trips on reasonable timelines, but it’s also a very good way to change your direction
on the cheap, one reason black holes might be popular colonial spots down the road, ships
planning really long trips might tend to aim in their general direction so they can change
their course closer to their destination, which might be prone to changing if you’re
part of big colonial efforts where folks might need to change plans as they get closer and
find out more about possible destinations. However, we’re not a gas and we are not
likely to have thousands of ships trying to use one for course changes all the time, so
it’s actually better to turn it into a big power plant and use that to run giant pushing
lasers or matter beams to shove ships with instead, not to mention power a civilization
nearby... or vaporize one, which we’ll discuss when we get to Weaponizing Black Holes.
Despite these problems, we have some other ways to tap black holes of this size for power
and the first is just about remembering what I said about non-rotating black holes earlier,
and in nature they are inevitably rotating and very, very quickly. We’ve got two methods
that take advantage of this: the Penrose Process and the Blandford–Znajek Process, which
allow much better than 6%, at more like 20 to 43% of mass energy conversion, partially
by robbing energy off the black hole from its ergosphere, which incidentally isn’t
a sphere. We will not delve into that today, beyond
noting that ergospheres, are messed up regions of spacetime above the event horizon created
by rotation from which you can extract way more energy than you could by skimming over
the event horizon of a non-rotating black hole. You could never plausibly take a spaceship
into the ergosphere of a typical solar mass black hole and bring anything living out,
even for the more extreme definitions of ‘living’ we use on the channel. But you can extract
energy and we think it is what powers quasars, those enormously energetic events we see in
distant galaxies which we believe to be accretion disks of supermassive black holes. Given that
a quasar is usually pumping out thousands of times more energy than an entire galaxy,
you can see why a scaled down version of this makes a nice power plant.
However, these approaches, while they can be used for moving ships, mostly do so by
otherwise mundane methods, acting as a power source for matter or energy beams to push
ships or a gravity well for slingshotting. The exception to this is turning it directly
into an engine of a truly enormous ship, which I will go ahead and name a quasar drive, and
we’ll talk about that and why you’d do that more in two weeks in Fleet of Stars.
Channel regulars are probably already assuming we’ll be moving on to hawking radiation
next, since these big black holes are obviously not ideal for regular size spaceships, but
there’s a very large mass gap between natural black holes and the kind we’d want to use
for Hawking drives, and trying to make black holes in that range and use their power is
tricky, maybe impossible, so let’s consider scaling our quasar drive down a bit first
instead. To make a black hole you just need to get
a bunch of mass or energy in one spot at a density high enough that it would be inside
its own event horizon. This can potentially be done several ways. The conceptually simplest
is to replicate nature, build yourself a great big ball of iron and wrap that sucker in H-bombs
and implode it. The second would be to slam two such bodies together at very high speed,
amusingly a similar process to how the gun-type nuke works, and also mimicking nature a bit
here too, as colliding neutron stars are thought to produce black holes, not to mention earthloads
of gold and other heavy metals. We’ve discussed the concept of a Relativistic
Kill Missile here before, a plain old hunk of metal accelerated to relativistic speeds,
usually by turning huge stellasers on them to push them up to speed. One way to make
a black hole would be to have two star systems with laser pushing devices shoving a pair
of RKM’s up to enormous speed which then slam into each other, and since a RKM need
not be a simple metal slug but could have some computers, propellant, and guidance on
it, such a terminal rendezvous should be doable. Indeed, you could probably time things to
have a whole bunch slam together at once. An RKM potentially carries many times more
kinetic energy than its mass energy too, and as mentioned, it’s really energy, not specifically
mass, that matters for gravity. A black hole event horizon has a radius or
diameter linear to its mass, double the mass, double the width, so it’s actually easier
to make bigger ones than smaller ones because you don’t need as high a density. For Hawking
Radiation driven ships, these really are only useful in the low megaton range and preferably
kilotons, and we’ll explain why in a moment, but while that seems great for a ship, practically
ideal, there’s no guarantee we could make let alone refuel such a black hole, so a much
bigger artificial black hole, but still a relatively tiny one, might be all we can do.
There’s no real technological hurdles to making an artificial black hole by implosion
or collision, it’s just brute force. Ramming two big trillion ton iron spikes into each
other at 99.9% of light speed is no easy task, but requires no new physics to do it. You
make the smallest black hole you can, then feed it matter and grow it if you need to,
because this method of black hole power generation benefits from size and is about feeding the
black hole. Your feed mechanism then also doubles as your attachment for keeping your
ship tied to the black hole. Black holes respond to force same as anything else does, you just
don’t want to shove on it with your hand or anything else you want back, so your ship
is basically being pulled toward the black hole, and you use the matter beam feeding
it to shove you away from it, and everything involved here is ionized and carrying a charge
so you can use magnetics to direct things. I want to emphasize though, these are BIG
ships, even by this channel’s standards. Hardly the biggest ships we’ve discussed
or will discuss but we’re not talking the Millenium Falcon or Firefly here, or even
the Enterprise. You only go this route if you can’t make black holes less than a megaton,
which is already ten times more massive than an aircraft carrier and would just be the
drive. If the smallest black hole you can make this way is a billion tons, then your
ship and black hole fuel presumably mass in that range too, and now you’re talking about
something O’Neill Cylinder-sized. If the smallest you can make and feed is one with
a nanometer radius, just a bit bigger than an atom, so you can cram atoms into it, then
you’re looking at ships massing around a quadrillion tons, which are likely to be Death
Star sized objects, or if more long and skinny, dozens of kilometers across and hundreds long,
assuming a density just short of water. However, we do have a couple other ways to
pack matter in tight. One example is dark matter, which to the best of our currently
limited knowledge only interacts via gravity, so if you can find another way to interact
with it, and move it about, you could potentially pack the stuff in absurdly tight without having
to worry about it slamming together to heat stuff or fusing. Incidentally, dark matter
would just tend to buzz around a black hole only falling in when it actually rammed the
event horizon. Needless to say, we currently have no idea how to manipulate dark matter
or even what it is for sure, indeed micro-black holes left over from the big bang is one of
the candidates for dark matter, but if we ever figure out how to manipulate it, employing
it for gravity and mass is one possible usage. However, we have other particles that don’t
mind being close to each other or indeed occupying the exact same spot; these are called bosons.
Examples include the Higgs Boson, the gluons that glue quarks together, the Z and W bosons
that mediate the weak nuclear force, and photons. Photons are lightwaves and even a laser pointer
can make, aim and focus them, so this really is old school technology. Much more precisely
aimed photons become much more handy than using them in a Powerpoint presentation. So
the notion would be to make a huge laser and mirror array that lets us dump a huge number
of them into the same spot at the same time. This creates a Kugelblitz black hole. It’s
what lets us seriously contemplate making black holes down beneath the megaton range
that would produce a lot of hawking radiation. Needless to say, this likely requires a huge
power source like a star to get all that energy together and an awful lot of mirrors to keep
it all bouncing and focused. Light moves rather fast so if you’re trying to make something
smaller than an atomic nucleus, which light would fly by in a mere billionth of a trillionth
of a second, you need a lot of juice and a lot of precision.
This is where we get into Hawking Radiation, because other methods all involve big and
massive ships or infrastructure and generally need to be bigger and more massive to produce
more energy, and often grow in mass as you produce energy. Hawking Radiation is the reverse,
the less massive it is, the more power it gives off. It falls off with the square of
mass, half the mass, four times the power, make it ten times more massive, get only a
hundredth the power. Lifetimes go with the cube of mass, ten times more massive, a thousand
times longer lived, as they evaporate slower and have more to evaporate.
Your typical natural black hole gives off so little Hawking Radiation that you’d have
problems detecting it even with our best equipment. Natural black holes are expected to live nearly
forever. That Hawking Radiation is why it is ‘nearly’ forever. We’ve got two common
explanations for this, the Virtual Particle explanation and the classical Hawking explanation
which is similar to the Unruh Effect. Most of us find the virtual particle explanation
easier to give folks, but it really isn’t ideal, virtual particles are always a bit
dubious as an explanatory tool anyway and always leave folks wondering why the negative
mass ones are the ones that fall into the black hole.
Still it is the one I’ve used in the past for discussing the matter mostly because I
hadn’t heard any other examples I felt didn’t require a heavy familiarity with special or
even general relativity to make sense, and we’re really only interested in how much
power these things produce. Last year PBS Spacetime did a really good explanation of
Hawking Radiation and of the Unruh Effect not long after, so I’ll link that instead
for today. For our purposes what matters is that black
holes are theorized to produce a lot of power when they are tiny, again falling off with
the square of mass. I will also link Viktor Toth’s Hawking Radiation Calculator, based
off Jim Wisniewski’s one a lot of us use to save time, though there’s always some
debate about Hawking Radiation values as we’ve no solid model for quantum gravity which certainly
matters when you’re packing a black hole’s large mass into an horizon that’s quantum-sized.
Using that method, a 1 megaton black hole would emit 356 Terawatts of power and live
2665 years, slowly evaporating mass and also growing brighter as it did. One ten times
as massive, 10 megatons, would give off a hundredth of that, 3.56 Terawatts, and live
a thousand times longer, 2.7 million years. One a tenth the mass, 100 kilotons, would
give off a hundred times the power, 35.6 Petawatts, and live a thousandth the time, just 2.7 years.
Needless to say, if you can feed them matter as fast as they expel it as energy, they will
keep emitting power at the same rate and never evaporate. For that 100 kiloton one, you need
to feed it about 396 grams a second or 34 tons of matter a day, any matter you can stuff
down its tiny gullet. The megaton one would need a hundredth of that, 34 kilograms a day,
and the 10 megaton a mere 340 grams a day, not bad considering this big weak one puts
out 2000 times more power than the Hoover Dam for power output.
If you can’t feed them mass, which is dubious because you can make them, that’s still
a very long-lived battery you’ve got there. One important reason why it might end up being
a battery is if the process for making it is wasteful. Grasers, basically lasers operating
in the very small wavelength gamma ray frequency band, would be the best candidates to create
these kugelblitz black holes and they don’t currently exist. So, we have no idea what
their efficiencies would be or what energy source we could use to run a graser.
If it turns out we need fission or solar power, that could limit the black hole to being a
battery as creating it could be less energy efficient than powering the ship using a conventional
reactor generator. Until we actually build a graser and a kugelblitz black hole, we have
little idea of what the feeding of the black hole will entail or its efficiencies.
Incidentally, since someone always asks why I tend to give black holes in tons not kilograms
or pounds, it’s mostly the same reason I do it for spaceships or space stations, normal
seagoing craft are usually discussed in their tonnage and scifi tends to ape that, thus
so do I, and since we’re talking about it as a ship component usually, values get given
in metric tons. Plus I think the kilogram is a stupid basic unit.
Battery or generator, there’s a lot of ways to use the kugelblitz black hole’s power
to run a spaceship’s engine, but if you happen to have something reflective to gamma-rays,
which we don’t yet, you can just spit it all out the back as a giant photon drive,
and if we use the megaton example, and assume nothing but near weightless ship around it,
that thing would experience .12 gees of thrust, or 10 milligee if we assumed the whole ship,
black hole included, weighed 12 megatons, or about 120 aircraft carriers.
Okay, that doesn’t sound fast, but like an ion drive it’s not that it has a lot
of thrust it’s that it will keep it up a long time. Now, we could boost that by the
same method we could run the thing if we didn’t have gamma-reflective materials, which is
by dumping gas in around it to soak up the gamma rays and get hot and ionized and shoved
out the back. But that is paying a mass penalty, as you will run out of fuel much faster than
if you crammed it into that black hole. Incidentally it is not sucking any or much of that gas
in itself, because it is smaller than an atom and emitting a lot of energy. So it’s like
trying to cram a basketball into a spewing garden hose nozzle.
Now the 10 megaton version produces a hundredth the power and has 10 times the mass to push
around, a thousandth the acceleration. While the 100 kiloton version is emitting 100 times
the power and has a tenth the mass, so we’re getting a thousand times the acceleration
out of it. You will also see much higher figures for power output in this mass range in some
discussions, like I mentioned there’s debate about models and I’m opting to use the one
with the handy calculator available online because I know my audience and many will want
to put in their own values. Kicking it down to 10 kilotons of black hole
and that same ratio of ship, you’ve got 10,000 times the power of the 1 megaton black
hole pushing a hundredth the mass, a million times more acceleration, but your black hole
would only live a single day unless fed and would be emitting about 15 times as much power
as hits the Earth from the Sun, as a giant gamma beam out the back side, just as a reminder
of why we say there’s no such thing as an unarmed spaceship and why space travel is
very energy expensive, since you could light several planets up with that much power, instead
of pushing a few thousand folks around. Again depending on models each tends to have
a sweetspot for the ideal mass of a black hole as a ship drive, and it always depends
on if you can feed the thing, and whether you can do the straight photon drive. If you
can feed it, you can also just add more smaller black holes to up your power output for a
bigger ship, need twice the power, slap in two black holes, if you can’t do a smaller
one or it’s not practical to feed it matter. They’re great for efficiency and high maximum
speed anyway, as they match antimatter for mass-energy, and even if you lose a lot of
that by using mass superheated by absorbing the gamma it gives off as your thrust, it
still beats a fusion drive and that version is easy to throttle. Get a megaton one and
you’ve got a power source that’s quite good compared to a fusion drive. Even adding
propellant to get that higher thrust, and that will last you millennia, you just have
to refill on propellant occasionally and literally anything works, and if your fuel storage gets
ruptured, you can still slow down the slow way. Even without a gamma-reflective material,
you can make a large containment chamber and let that heat up to produce radiation in wavelengths
you can reflect. That’s the same trick we discussed using for making black holes into
fake suns earlier this year. Plus, unlike antimatter, they don’t explode, or at least
do so at a set and easily calculable time. Since they are subject to the rocket equation,
they do not quite match a laser-pushed system, which also gets to double up by bouncing light
off a ship not just emitting it. However, you can use them to power those lasers far
more efficiently than a star or fusion reactor will, assuming you can make larger stationary
ones you can feed, an unfeedable black hole is just a battery, not a generator, though
that’s often handy too. The big problem with laser highways is that you are dependent
on that beam. Someone can shut it off, and there are problems keeping it on target especially
at long distances, so you get back that freedom of being able to steer your ship wherever
you want when you want. They work great in combination with laser
highways too, same as we discussed for a fusion economy in Colonizing Neptune, you use the
beams when you can and the engine when you want, and you can get up to a very decent
fraction of light speed this way, such a ship ought to be able to pull off half-light speed,
depending on what you’re carrying and how efficient your setup is and if you’ve got
help speeding up or slowing down. A black hole based ship though, of any of
these varieties we’ve discussed today, is but the tip of the iceberg that a black hole
economy and civilization offer, if we can master them and if our theories about them
are mostly correct. And we’ll be looking at them in more detail in the coming episodes,
so stay tuned… So I get asked fairly frequently about a lot
of the graphics we have on the channel these days and a great number of those are done
in-house by various animators and graphic designers who volunteer their time to bring
these awesome ideas to life. Indeed that’s part of the reason we revisited the topic
of black hole ships, as the original video only had animations I’d done and my talent
for that, especially back then, was nowhere near as good as what they produce. Needless
to say I can’t thank them enough and you can always see more of their work by clicking
on the links to their various art pages down in the video description, where we always
list the editors and musicians who help on the show too, and if you’ve an interest
and time to volunteer helping out, we’re always glad to add to our numbers and I’d
also always encourage more folks to try their hand at making their own YouTube videos.
Animations and graphic design take practice to get real good at, but it doesn’t take
too much to get started and if it’s something you’ve an interest in learning, it is topic
that there are a lot of top notch courses for over at Skillshare. I’d particularly
recommend PolyMatter’s “How to Make an Animated YouTube Video”, since Evan starts
at the beginning and walks you through how to do an entire video and how to do it without
buying lots of expensive software or hardware. And that includes learning to do it, because
you can join Skillshare for 2 months for free, and have access to that and many other courses
on graphic design or browse from over 20,000 courses on a host of other useful topics.
Skillshare is an online learning community with over 20,000 classes covering everything
from practical daily skills to things like programming, writing, or science. A Premium
Membership gives you unlimited access to high quality classes on must-know topics, so you
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Join the millions of students already learning on Skillshare today with a special offer just
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classes for free. Act now for this special offer, and start learning today.
So as mentioned, we’ll be looking at Colonizing Black Holes in three weeks, and dig more into
a lot of terraforming and industrial application black holes might have. Next week though,
we’ll be returning to the Upward Bound Series for Sky Platforms, and look at some of the
launch concepts for getting into space by starting off already high up in the sky.
And two weeks from now, we’ll be back to this series to look at the possibility of
using entire stars or whole fleets of them for colonizing the Universe and reshaping
our galaxy, or even our whole Supercluster, in Fleet of Stars.
For alerts when those and other episodes come out, make sure to subscribe to the channel,
and if you enjoyed this episode, please like it and share it with others.
Until next time, thanks for watching, and have a Great Week!
Making a black hole "Gather a massive ball of iron, wrap that sucker in H-bombs and implode it." This is the quality content I come here for.
Man made mini black hole, the solution to garbage in the future.
What is his accent? I can’t quite identify it