September 24, 2020 • 40 mins
Daniel and Jorge tackle the physics, engineering and safety questions of using a black hole to visit nearby stars.
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Speaker 1 (00:08):
Hey or heey. Have you ever wanted to go visit
another star or even a far away galaxy? Totally? I
mean wouldn't, although you know, it kind of depends on
what the accommodations are over there, Like are we going
to be camping on a rock basically for the rest
of my life? Or isn't going to be a beautiful place. Well,
it's kind of hard to get pictures in advance. If
you're the first human to ever land on this surface.
(00:31):
There aren't any Airbnb reviews yet. You can't trust YEP
to do everything for you. But I guess the problem
is how would we even get there? Isn't it really
hard to go to another star or galaxy? It is
really hard, which means we have to be really creative
and sometimes looking unexpected places for sources of inspiration and
power than in a fusion use the energy trapped in
(00:52):
bad punts. Well what if I told you you could
actually make use of a black hole? But I thought
black holes were just like traps that trapped you there forever.
I mean, they can actually be useful. You might get
nervous when we talk about black holes in a positive light,
but they do have a possible practical applications. I am
(01:25):
more handmade cartoonists and the creator of PhD comments. Hi.
I'm Daniel. I'm a particle physicist and I'm paid by
the Big black Hole corporate consortium to talk positively about
black holes wherever I can. Really, you've switched to black
hole PR now or astronomical PR. That's right, I'm funded
by Big black Hole. You went from physics research to
(01:45):
public relations PR. No, but I like black holes. I'm
definitely pro black hole. I mean, I'm not pro the
Earth getting sucked into one or you and your loved
ones being killed by one, but I'm fascinated by them,
and I would love to study one and to create one,
and of course do it all very safely. Yet would
you visit one? I would visit a black hole if
(02:06):
it was big enough that you could come close to
the event horizon without being torn apart by the tidal forces.
So yeah, are you starting a tour company to the
center of the galaxy? And I am definitely anti black hole,
But in this universe it's hard to tell sometimes what
could be useful or what could be something that will
kill you instantly. So welcome to our podcast. Daniel and
(02:28):
Jorge Explain the Universe, a production of My Heart Radio
in which we examine everything in the universe, from the
tiny to the massive, from the dangerous to the cozy,
and we talk about whether it could help us answer
our questions, whether it could take us on a journey
to the stars, or whether it just helps us zoom
in and understand the universe at the smallest, most microscopic level. Yeah,
(02:49):
we like to talk about all the possible ways out
there that we could maybe visit or travel to other
places in our galaxy or in the universe, because it
seems like it's all out they're waiting for us to
go visit and study. That's right. I feel like we
are in the early days of the human age of exploration,
where we learn about what our galaxy looks like and
(03:11):
what's out there and who is out there. But so
far it's still sort of shrouded in mystery for us.
And if we could only get out there, if we
could send people or probes or something, we could learn
so much about what's out there in the universe and
how things work. Yeah, I feel like we're almost like
stuck in a deserted island in the middle of the ocean.
You know, like there's such a huge gap between us
(03:32):
and maybe other things, and we don't even know if
we can make it out there, or what would happen
if we went out there. That it's kind of preventing
us from spreading out into the cosmos. It is, and
it's frustrating to know that that knowledge is just sitting
out there waiting for us. Alien civilizations or not, crazy
planets or not. Whatever is out there, it's just waiting
(03:52):
for us, literally sitting there, waiting for us to come
and check it out and learn things about the universe.
And whenever there's like a bare year between us and deep,
powerful cosmic knowledge about the universe, it just drives me crazy.
I just want to pierce through it or around it,
or whatever preposition you need to use. But I want
to get that knowledge, and I want us to understand
(04:13):
how the universe works. Doesn't make you want to be
an engineer, Daniel, so you could actually make something useful.
It makes me want to be a physicist so I
could have a clever idea which I could then pass
to the engineers who would make something useful. I see,
there are limits to your curiosities. What you're saying there's
limits to my practical ability to build something, but no
limits to my imagination. All right, Well, it is a
(04:37):
very big problem to get to other stars, into other galaxies.
And we've talked about in the program before about different
ways to power our spaceship out into the cosmos, because
it's really hard to bring all the fuel with you
that you'll need to get to somewhere far away. Yeah,
you need to build a really big ship if you're
gonna bring a lot of people and you're going to
keep them safe from cosmic radiation, and then you need
(05:00):
to bring some source of fuel to get you there.
So people have been struggling with this question for decades,
for maybe even longer than that. And there's some crazy
ideas out there. We've talked before about instead of just
building a ship, move the whole Solar system by building
a stellar engine, something that would turn our star into
an engine. Yeah, and so on the episode today, we'll
(05:23):
be talking about another crazy idea that physicists are toy with,
thinking about and spitballing about. And this one involves black holes.
All the craziest, most fun ideas involved black holes. It's
about as crazy as you can get I guess in
this universe. So today on the program, we'll be asking
the question could a black hole power a starship? Wow?
(05:50):
That's crazy? What what does that even mean? Well, first
of all, it's stemmed me through like where did this
idea come from that? Did you wake up with it
one morning? Or is this something that's actually being discussed
at like physics conferences? Oh? Man, I wish I could
take credit for this idea, but no, this idea, like
many great creative ideas in science, came from science fiction.
(06:11):
This was first written about by Arthur C. Clark in
a short story he wrote called Imperial Earth. Wow, so
a long time ago, quite a while ago. Yeah, it's
a fairly old idea. And then since Hawking revolutionized our
understanding of black holes, and in the last ten or
fifteen years we've made some progress in quantum gravity. People
have started sitting down, like doing the calculations and figuring
(06:33):
out like, couldn't you do this? Is this possible? Is
there a fundamental physics reason that says no? Or could
we just pass it off to the engineers to figure
it out? Didn't Arthur C. Clark sort of foresee, another
huge thing, wasn't it the Internet or something like that.
I'm sure that he and other science fiction writers foresaw
a lot of what's real. The cool thing is that
they also foresaw a lot of stuff that didn't happen. Right,
(06:55):
So I see, you don't really pay attention to the denominator.
Just like spew a bunch of crazy predictions, and if
you hit a few, then you know, you become famous
for foreseeing the future. Your visionary right, even if your
hit rate is low. That's right. I got a room
full of monkeys predicting the future. One of them is
a genius, because I make real a genius for having
the monkeys or but anyways, it's a crazy idea. So
(07:18):
the idea is to use a black hole to power
your starship. And so we'll get into the diesel because
I have a lot of questions about this crazy idea.
But first we were wondering how many people out there
I thought this was a good idea, or I had
heard of this idea. So Daniel went out there and
asked to the Internet if they knew the answer to
this question. That's right, And we're always looking for volunteers,
(07:41):
people who are interested in speculating baselessly on questions. We
asked them for future episodes, so if you'd like to participate,
please write to us two questions at Daniel and Jorge
dot com. So think about it for a second. If
someone asked you if you thought you could use a
black hole to power a starship, what would you as?
There here's what people had to say. If he wants
(08:02):
you to use an actual like black hole as an
engine to propel yourself around, I don't think that would
work because surely for a normal engine you need something
that applies a force in the opposite direction that you're moving,
so that the resulting force pushes you to where you
want to go. But surely a black hole would just
(08:23):
suck everything in. Well that would be cool, yes, I well,
probably theoretically can be done. I don't know in how
much time can this be put in practic cern For sure,
it's working on it, of course, because they usually want
(08:44):
to start trek the next generation. I think you could
use it in part for a spaceship that's designed for
faster than light travel. It's the idea of compressing the
space in front of you and expanding it behind you
is a primary engine. I don't think so you can
definitely use a stellar stationary black hole to propel your
(09:05):
ship in an arbitrary direction. You just calibrate a trajectory
so that you avoid falling in and avoid being destroyed
by tidal forces, and have the black holes link shot
you to an arbitrary direction. I think that you cannot
use the black hole as a spaceship engine because you
everything New York gets sucked in, so it can suck
(09:27):
in bits of your spaceship blue by little, depending on
its size. I'm sure that a space draft can use
a black hool as an as an engine. I'm trying
to think, how would you use the energy from the
black hole? Alright, Well, we got about as many different
answers as people answering the question. Yeah, well it seems
(09:47):
like people think it's cool. It's a cool idea, but
there was some skepticism like how would that even work?
And there are lots of different ideas here about how
it could work, like could you use it to make
a warp drive by compressing spased run of you? Very
cool idea, or just like the gravitational assist right using
as a slingshot, or people thinking that certain is currently
(10:08):
working on a black hole drive are you. I can
either confirm nor deny that. Do you have a room
full of monkeys working on it? There at certain one
of my monkeys is working on it. I bet you do. Look, monkeys,
just don't press this button. I'll be back in an hour.
I have to do a podcast. Well, these are pretty
good monkeys if they can understand instructions like that, Danny. Yeah,
(10:30):
they come from the best universities. So it's kind of
a crazy idea, and people seem to think it was
maybe possible, And you're right, there are many different ways
that you could attack this, Like you could use the
black hole itself, like as a gateway. Isn't that a possibility? Oh?
I suppose if a black hole is just like a
doorway to a wormhole connected to a white hole somewhere
(10:54):
else in space, then yeah, I suppose you could use
that as a way to get through the universe. I
love that this question and has inspired so much creative thinking.
But nobody who answered these questions hit on what is
actually the idea that's being considered in the community for
how a black hole could power a starship. Nobody had
read Arthur's c Clark. I guess or all of his
(11:14):
collected works. No, none of those folks are up on
the latest there. All right, well let's jump right into Daniel.
How would you even use a black hole to power
your starship? And if it's powered by a black hole,
do you have to call it a black hole ship?
I'll leave it to you to name the eventual ship
once we build it. But the idea is that a
black hole actually satisfies a lot of the requirements you
(11:36):
need for fueling a starship. It's very very dense, and
so it's a great way to store energy, and it's
very efficient because it turns that energy into radiation. Remember,
many people think about black holes as a fold in space,
a place where nothing can escape, not even light. But
black holes are not actually totally black. They radiate a
(12:00):
very small amount of radiation, and they're turning essentially their
own mass into radiation. And the basic idea of the
black hole starship is to take advantage of that, the
black hole turning its mass into radiation and using that
radiation to provide thrust for a starship. Oh I see,
all right, So a pro idea for using black holes
(12:23):
as fuel is that one. It's first of all, you
said it's very dense. I guess it is very dense
in that you can crame a lot into it but
not require like a big chamber to hold it. What
do you mean precisely? I mean it doesn't get more
dense than a black hole. Anything else you get to
that same density is just going to turn into a
black hole. So the black hole is by definition the
(12:43):
most dense storage of energy. So I guess, like if
you had to pack a star that would be pretty
hard because you need a big container. Yes, exactly, exactly,
And that's the other advantage about black holes is that
they contain themselves. What are the common alternatives for using
a starship? Is like antimatter? What if you store antimatter
(13:03):
in your starship and use matter antimatter reactions to provide
the energy, Right, that seems like a better idea. Yeah, well,
the problem is antimatter is really hard to store. It's
very reactive. It could blow up your ship. Black hole
store themselves. They contain themselves, They are their own bottle,
and so they really have an advantage there over antimatter. Oh,
(13:24):
I see what you're saying, Like, it doesn't have anything
like dangerous that could get out. I mean as long
as you don't slip and fall into the black hole,
you're pretty safe, right, that seems kind of We'll just
put up a sign, you know. I'm sure we'll put
a sign. People will sign a waiver. They'll be fine.
Those yellow cones or prop up things. Which is like
a stick figure falling into a black hole, that would
(13:45):
be the warning. We'll let you draw the sign. Yeah,
exactly where a helmet. And the basic problem that you're
trying to solve by using a black hole is efficient
conversion of fuel into thrust because as a lot of
the other more common methods of accelerating the starship are
just very inefficient, like fusion or fission. They're wonderful, but
(14:08):
they don't capture most of the mass in your fuel
and turn it into energy. There's a very low efficiency there,
and so you end up bringing a huge amount of
fuel and then more fuel to carry that fuel, and
more fuel to carry that fuel. So you want a
source of energy that's very, very efficient in converting its
mass into your thrust. And that's where black holes really
can't be beaten. Like literally, you can't beat them. There's
(14:31):
nothing hit him with a stick. It just eats up
the stick. That's right. And there's another really fascinating feature
about black holes that makes them well suited to being
a source of energy for a starship. There's a lot
of details to get right to get your black hole
to power your starship. Well, let's get into that, and
also a lot of these details about how you would
make a black hole power your starship. But first let's
(14:54):
take a quick break. All right, we're talking about the
idea of using a black hole to power your starship
to get to another galaxy or another star, or maybe
(15:15):
to another galaxy cluster even and so, Daniel, the idea
is that I would somehow bottle a black hole and
then bring it with me. You're saying, the first advantage
is that it's really compact, meaning like I could keep
it in my pocket even. Yeah, the kind of black
hole we're talking about that would power a reasonable flight
would have a radius, you know, less than ten to
(15:36):
the eighteen meters. It would be really really small. Oh wow,
would be like a microscopic Yeah, microscopic. And you wouldn't
even need to bottle it. Remember, black holes are their
own bottles, so you don't really need to put it
in anything. You could just have the raw black hole bear. Well,
I guess that's my first question about this idea is like,
how would you even carry it around? Like does it
(15:57):
sit on something? Does it you just let it flow
next to you. I'd even like bring it with you. Well,
you don't bring it with you. It brings you with it, right,
that's the idea. It's like you're hitching a ride. You're
hitching a ride on a black hole exactly. And so
how do you turn a black hole into an engine?
All right? Remember that black holes radiate or they shoot
off this hawking radiation, and this is theoretical. Still nobody's
(16:21):
ever actually seen hawking radiation, but they shoot off hawking radiation.
And the fascinating things that this happens more for small
black holes, like really big black holes from stars or
supermassive black holes hardly radiate at all. But the theory
is that as black holes get smaller, they radiate even more.
(16:41):
Like how much more like like it's shining, like it's
like a small black hole would actually be bright, Yes,
it would be bright. It would be dangerous. You would
have to wear protection. The kind of black hole we're
talking about when it's like, you know about a billion kilograms.
This is like two times the mass of the Empire
State building. This thing would really a hundred and sixty
(17:02):
petal whites of energy, two thousand times the worldwide energy
consumption every year. Okay, so let's walk through this scenario.
So I take two Empire State buildings and I somehow
compressed them into a black hole, which would be about
ten to the minus eighteen meters. I like, how you're
making this like an internet recipe sugar cookies or black
(17:25):
hole dry. I'm an engineer. I gotta I gotta know
the instructions here. So I take the two Empire State's building,
I compressed them into tents of the minus meters and
now have a black hole. It's really tiny. It's like
a basically a pinpoint. It's basically a pin point. And
we can talk later about more practical ways to actually
make these black holes and involves enormous space lasers, but
(17:46):
that's basically the recipe. Get that much amount of energy
into that small or radius and you have a black hole.
And black holes that are that small. That's very small
for a black hole. You know, black holes out in
the universe are measured in units of the mass of
the Sun. This is a tiny, tiny, little black hole,
and so it radiates a lot, a lot more than
any black hole that's out there sort of scattered around
(18:08):
the universe. A synthetic black hole on a human scale
would radiate a lot more than natural black holes. Oh,
I see, so a small black hole is actually and
not black, it's really shiny. Yeah. The smaller the black hole,
the more radiated because the amount of things radiate depend
on their temperature. And this is something that Stephen Hawking
discovered that black holes have a temperature, and everything in
(18:31):
the universe that has a temperature gives off radiation. It's
called black body radiation. Everything glows, even black holes, because
they have a temperature, and the temperature the black hole
is connected to its mass, and as its mask it's smaller,
it's temperature goes up. And there's some complicated arguments there
about entropying quantum mechanics that we shouldn't get into. But
(18:52):
smaller black holes have higher temperatures and so they radiate more,
and so it's a sort of a runaway process like
it radiates more or like surface area or like total
like it's hard to imagine that a you know, like
the supermassive black hole in the middle of the galaxy
would be radiating less than a little tiny empire state
building black hole. It's definitely more per mass, like per
(19:13):
unit mass of the black hole, but I think it's
also an absolute levels more. I mean, these little black
holes they radiate more, and then they lose mass because
they have radiated that mass away, and then they radiate
even more, so it becomes a runaway effect. And the
last few moments of the life of one of these
black holes they're extraordinarily bright. Wow. All right, So it
(19:35):
has something to do with, I don't know, some sort
of weird relationship inside of the black hole that did.
The less mass you have, the more it radiates. Yes, precisely.
And that's why this works because you don't have to
build a black hole the size of the Sun. You
can build one that's pretty small and it will be
pretty bright. So it's a great way to store that
energy and then have that energy be released over time.
(19:57):
All right, So I just compressed to empire state buildings.
I created a black hole, and I guess I did
it in space? Where my did I do it here
on Earth? Better? Do that in space, please, sir? Yes? Absolutely. Okay,
don't do this in your backyard. And I have this
in space, and what does it do? Does it get
attracted to the Earth when it also kind of like
act as if I had to empire state buildings out
(20:19):
in orbit. Yeah, it would, and so you could have
it in orbit around the Earth. Right, You can have
anything in orbit around the Earth, a black hole, anything else.
It has a strong gravity to it, but it's not
like actively sucking in the Earth. So it can be
in a stable orbit around the Earth. And then you
build your spaceship around the black hole. But I think
I have to keep feeding it, right, because it's radiating
(20:41):
and so it's shrinking at the same time. You don't
have to keep feeding it, though, that's an option. You
can just sort of build your spaceship around it and
then use it up and by the time you get
to your destination, it will have evaporated into nothing. Oh,
I see, so it takes years and years for it
to evaporate. That's right. A two empire state building black
hole will evaporate in about three or four years. All right.
(21:02):
I guess my question is like how do you hold it,
or like how do you move it? Or how do
you nudget because wouldn't anything that it touches gets sucked
into the black hole. Well, remember that black holes have
strong gravity, but they're not like actively sucking stuff. Right.
You can be in a stable configuration near a black
hole as long as the tidal forces are not too great.
(21:24):
So the way you take a black hole, which is
just shooting energy out in every direction and turn that
into a spaceship is actually the same way that we
talked about for turning a star into a spaceship. Is
that you capture half of the radiation, like all the
radiation on one side you capture in some sort of
parabolic mirror and focus at the other direction, so that
(21:44):
effectively it's only radiating in one direction. And if it's
only radiating in one direction, that's basically thrust. It's like
it's shooting particles at one side. And that's how an
engine works. It pushes something away, gives off mass and
energy in one direction, and so by conservation momentum it
will go the other direction. So that's the second critical
piece you need the black hole shooting off energy. Then
(22:06):
you need this reflector which turns the black hole into
an engine, like you put a mirror to one side
of it, and then some of them gets reflected into
the black hole. You put a mirror to one side
of the black hole, near the black hole, not in it, right,
You don't want your engine to get into the black hole.
If you put a parabolic reflector around the black hole,
then all of its radiation will get reflected to be
(22:28):
in parallel lines and all shooting out in one direction. Right,
But to the black hole, it's just radiating out in
all directions. So what would cause it to move? Well,
it's reading out in all directions. But now you have
this reflector, and the reflector is gravitationally bound to the
black hole, right, It's being held in place by the
black holes gravity. So you can think of them like
(22:48):
as a system. The black hole plus this reflector are
now like one gravitational system, and the two together are
only shooting out radiation in one direction, so they have
to move in the other direct Oh, I see, So
you kind of have to put the black hole behind
you almost right, Yes, the black holes in the back
and the reflectors in the front, and then you end
up moving in the direction of the reflector like it's
(23:11):
pushing you. The black hole is pushing you away, but
you're also pulling the black hole with your own gravity. Yes,
that's a good way to think about it exactly. So
you're right, the black hole all it knows is that
it's just shooting off radiation in every direction because you've
built it into this system with a reflector. The combined
system has to move, you know, in whatever direction you
were pointing in order to balance the momentum that's coming
(23:33):
out the back of the ship. Right, But isn't that
a really tricky balance? Like how do you know the
black hole is gonna follow you? Do? You have to
be as big as two empire state buildings too. You
have to build a pretty big ship. But you want
to build a pretty big ship anyway, because if you're
going for three and a half or four years, you
need like a lot of room for you know, canned
soup and people, and you have to build a lot
(23:53):
of shielding to protect yourself from radiation. So you want
to build a really big ship. But yes, it is
not easy engineering problems, so I do not envy the
engineers who have to work on that. But also, but
it's isn't it a little bit dangerous? Like how far
away would you have to build this reflector, and like
if something knocks the ship but in it potentially knock
(24:14):
get into the black hole and then with destroyership. Yeah,
it's not necessarily a stable configuration, you're right, And if
something gets too close to the black hole, then the
whole thing could just get sucked in. Right, So yeah,
there are definitely problems to solve. But you know, my
department is is this theoretically possible? And then you know,
I put my stamp on it, and then we send
(24:34):
it off to you know, safety and configuration and engineering
to make it actually work. But so there's definitely some
challenges that you just just said, a worry somewhere which is unstable,
Like is this a unstable configuration? What did you mean,
my dad? Like, I can put the black hole behind me,
but it's very precarious. Yes, some things in equilibrium are
stable so that if you perturb them, they'll naturally go
(24:54):
back to the original configuration, right, But some things are unstable,
and in this case, if the mirror gets too close
to the black hole, then it will eventually fall into
the event horizon the black hole or would be very
difficult to take too much energy to move it away. So, right,
it's pretty tricky. It's like, if you're in orbit around
the Earth and something knocks you out of orbit, then
(25:17):
you're not going to fall back into orbit. You're going
to fall into Earth, right, And the same problem happens here.
So basically you're saying on this trip, nobody can move
on the ship. It's like, alright, three and a half years,
nobody move, or else we're going to fall into this
black hole that we made and are bringing with us. Yeah, yeah,
(25:37):
you know, maybe don't have assault the party right next
to the black hole. Yeah, no aerobics classes on this cruise,
no jumping up and down. It might be a boring trip,
but hey, it means it's a shorter trip because a
black hole could get you up to a significant fraction
of the speed of light. Really, if you build this
ship and you can use the black hole that we
(25:59):
talked about, like two masses of the Empire state building,
it can give off enough radiation to accelerate a large
ship to ten of the speed of light in just
twenty days. Wow, and is that a lot ten percent?
What is that per second? It's a lot of meters
per second and at that speed you could get to
the nearby star in like forty years instead of five
(26:22):
years or five thousand years. And you also could do
it without depleting the energy resources of the entire planet.
All Right, well, I still think it's a crazy idea, Daniel.
But let's get into whether it could actually work and
if we could actually build one. But first let's take
another quick break. All right, Daniel, you found something useful
(26:55):
to do with black holes, and that is to power
your starship to a nearby star or galaxy. And it theoretically,
it sounds like it could work, but it feels kind
of practically dangerous, like you know, you can put it
in the bag and it's pushing you, but if something happens,
it could also destroy. And that's a pretty good summary.
And you know, I'm not asking you to invest or
(27:16):
to buy a ticket on the black hole starship. I'm
just asking you to examine with me whether or not
this is theoretically possible. Because things that seemed I thought
you were pro prol black hole, which is why we're
talking about this. But I totally recognize that a lot
of problems to solve. But you know, today's impossible problem
is tomorrow's app Written by Middle schoolers. So let's leave
(27:37):
these open problems out there and maybe one of our
listeners will be inspired and think of a solution. Right, Okay,
so you're saying it can maybe accelerate a large ship
up to ten percent of the speed of light in
twenty days, which means we would get to the nearest
star you said in forty years. Yeah, the nearest stars
are like four light years away, and so if you
go at ten percent of the speed of light, you
could get there in forty years, which means you could
(27:58):
step on this ship and you actually step off of it.
You could visit those stars and not just your kids
or your grandkids, your great great grandkids who are mad
at you for having relegated them to being born in space,
but you could actually get there yourself. But you said
the black hole itself would only last three and a
half years. Yes, the black hole itself would last three
and a half years, but it only needs to last
(28:19):
long enough to accelerate you, and you know, then you're
up to the right speed. You know, there are other
questions about like deceleration and how do you stop. Yes, well,
I guess maybe this is one one thing I'm curious
about is can you feed the black hole? Like, can
you supply with more energy as you're going? No, you
(28:40):
certainly can. Two solutions they're one is start with a
bigger black hole and then halfway through the trip, flip
the reflector around if you think that's a safe procedure,
so that now the black hole is decelerating you, so
that by the time you get to your destination you're
at a reasonable speed. You don't fly through the system
at a zillion miles an hour. And the other thing
(29:01):
you can do is, as you say you can feed
the black hole, you can like gather interstellar gas and
micro meteorites and all that stuff and just sort of
like directed into the black hole. Because the cool thing
is everything is fuel for a black hole, right, even
bad punts, even bananas. Banana now that would just slip
on by. But I mean, is that the work math workout?
(29:23):
Like can I bring another empire state building with me?
Or does that take away them from the excelaration. The
way that you build the synthetic black hole that you
need to power this drive is not by bringing all
that mass, because we don't know how to take that
mass and compact it into a black hole size object.
That's not something we know how to do. Instead, the
best ideas for how to build a synthetic black hole
(29:45):
of the right size involved just essentially dumping energy into
a point in space using massive lasers. All right, now
we're getting more exciting here. So step us through how
would we actually make a black hole? Like, can we
make a black hole? As I guess you make black
holes at a large hadrant collider, but you don't keep
them around. Well, we don't know if we've made black
(30:05):
holes at the large hadron collider. We're trying to. We're
hoping to see one. We've never spotted one before. But
the idea is that to make a black hole, you
don't just need a huge amount of mass. What you
really need is high energy density. Any kind of energy
will curve space. Einstein's general relativity told us that matter
curve space, but also anything with energy in it. And
(30:28):
so what you need to do is just pour a
whole huge pile of energy into a small part of space.
And you can do that by focusing a bunch of
lasers on the same place. Oh, I see, you can
make a black hole, but just pure energy, just pure energy. Yeah,
And so you build a huge laser, a lot of
huge laser and you focus them on the same place,
(30:48):
and in principle, you pour enough energy into that dot,
it will turn into a black hole. It will capture
all that energy story gravitationally and then gradually release it,
which is what you need. Wait, what do he means?
So you can make a black hole just by pointing
lasers together. Yes, nobody's ever done it. We haven't ever
seen this, but the math tells us. The theory tells us.
General relativity says that you get enough energy density in
(31:12):
one spot, it will turn into a black and that
includes laser light. And lasers are actually great because photons
have no problem being close to each other. Like the
reason you can't take the Empire State building and turn
into a black hole is that that matter resists being
squeezed down right, there are chemical bonds there. But photons,
they are the kind of particle we call bosons that
(31:34):
are very happy to be right on top of each
other and all doing the same thing. And there's no
photon photon repulsion, and so you can pile as many
photons as you want. They will not resist. Then wouldn't
it take a lot of energy to power your lasers,
like could you wouldn't that take me all the energy
on Earth just to make a mini black hole. It
would take a lot of energy to make this black hole,
(31:55):
but it's much more energy efficient than for example, antimatter creation.
Ant a matter is something we can make and it's
a good way to convert mass into energy, but making
antimatter is very, very inefficient, whereas making a black hole
is much more efficient because all the energy goes into
the black hole. So yes, it's a huge energy consumption.
(32:15):
Anytime you want to accelerate something up to the speed
of light that's very massive, it's going to take a
lot of energy. But it's much more efficient to turn
lasers into a black hole than to build antimatter, which
is very difficult to do. And so the idea is
that then you just point lasers like at a point
or at each other, or just the laser itself would
create the black hole. And you need a bunch of
(32:36):
lasers altogether focused on a point. And people have done
some calculations to think like well, how much would you need,
how much energy would you need? And it's about like
point one second of all the energy coming out of
the sun, like the sun you know, really it's a
lot of energy. And you know, if you get like
a tenth of a second of all the solar energy,
that's about as much as you need to build this
(32:58):
synthetic black hole we were talking about. You can't capture
the whole Sun. But you know, people did other calculations.
If you build like a lot of solar panels, you know,
something like a few hundred kilometer sized solar panels in
circular orbit around the Sun, then it takes about a
year to get enough energy to power these lasers to
(33:18):
build the synthetic black hole. Oh I see, so you
would have to store all that energy for a year
and then release it at once. Yes, exactly, so big
batteries from Tesla Ellen, get on that. No, don't get
on that doing in space Wait, wait until you have
a space station. Yeah. And there's you know, lots of
(33:40):
other practical problems with building a black hole starship that
we sort of just you know, waved our hands over all. Right, Yes,
what are those problems? Well, number one is that black
holes don't just shoot off photons that can be easily
reflected by like a nice mirror. And we talked about
how you have to redirect the radiation of half of
the black all the other direction. If you want to
(34:01):
move anywhere, that works great if the black hole is
giving off photons, because we know how to bounce those
off a mirror. But black holes are very democratic. The
reason Hawking radiation exists is that you have random particles
coming out of the vacuum. So those could be photons,
they could be top corks, they could be Higgs bosons,
they could be electrons. Oh, they're spewing out all kinds
(34:22):
of stuff, all kinds of stuff. Yeah, and some of
those things are hard or impossible to reflect. Oh, so
you don't even know if you could reflect all of
that energy. You're pretty sure you can't reflect all of it.
And so there's some ideas that, like you could reflect
part of it, and the rest of it you could
try to absorb and then capture in terms of heat
and use that somehow, either funnel it back into the
(34:43):
black hole or use it to power you know, an
ion beam or something like that. But it gets pretty
tricky because this is very intense radiation and anything you
build nearby that can't reflect the radiation is going to
absorb it and get really hot and probably melt. Can
it spew out antimatter? It will. It will absolutely spew
out equal amounts of matter and antimatter, so that it
(35:06):
might even destroy your ship just from what it it's radiating. Yeah,
that is a concern. Actually a small concern is that
it's spewing out antimatter, which would and I lead your space. Yeah.
I don't think this idea is you know, consumer ready yet,
but the bones of it are there, you know. Oh man, Yeah,
(35:27):
the black holes antimatter. That's right. Because the Hawking radiation
is random, it creates pairs of particles and antiparticles, and
sometimes the particles fall into the black hole, and sometimes
the antiparticles do. That's one of the really cool things
about black holes is that they radiate all the particles,
and so it's actually kind of a cool way to ask, like, well,
what particles are there? We'll just make a black hole
(35:49):
and have it radiate everything that there is. It's sort
of like the world's best particle collider. But I guess
if it's being out antimatter, then I mean, if some
of that touches you, then you're you're dead. Yes, if
some of that touches you, then you know, I recommend
you go immediately to the met deck or whatever it
is on this ship, which just when did it explode
(36:09):
on you or something? Well, if an individual particle eventimatter
hits you, it's not a big deal. You know, like
bananas emit anti matter. They're emitting positrons all the time,
but they don't hurt you, just a very small amount
of energy. But they could cause cancer. But we're talking
about a black hole emitting a lot of radiation. A
significant fraction of that would be radiation that you can't
easily absorb and reflect like photons, and some of it
(36:32):
would be antimatter. So yeah, there are big technical issues
they're remaining how to handle all this radiation. It's crazy.
A black hole is too bright maybe to be a
starship drive? Could you just use a smaller one, Like
with a smaller one help a smaller one would help perhaps,
but then it might not have enough power. So this
sort of a sweet spot there. You need to be
big enough to provide power to drive your ship and
(36:55):
to last long enough, because the smaller black hole is
the shorterest lifespan. Just so, there is actually like a
literature on this idea, like there are papers out there Yeah,
I've read some papers in the last few days about
making black hole starships and whether it's reasonable. And in
addition to all the practical questions that you asked and
all the reasonable concerns you how about whether this thing
(37:17):
would survive, there are also fundamental physics questions about whether
this would work. Because you know, we're talking about Hawking
radiation that nobody's frankly ever seen in real life, and
we're relying on a sort of semi classical understanding of
black holes because we don't have a good theory for
what's going on inside black holes of quantum gravity. We
(37:38):
can't really explain what's going on inside black holes, and
we can't really explain whether they're radiating, and we've never
validated Hawking's predictions about how much they're radiating. So a
lot of whether or not this is possible depends on
a quantum understanding of gravity that we just don't have yet. Wow,
all right, well, it sounds like a good idea to you.
Something we don't understand and may potentially kill is to
(38:00):
power a starship. We'll just ask for volunteers and we'll
have a really long waiver. I'm sure a lot of
people on the internet would sign up. I would think
about it for a moment. I'd be like, Wow, I
get to see an alien world and they get to
ride in a spaceship with a black hole. That sounds
pretty cool. You would sign up, you who never want
(38:20):
to leave your house. Well, I said, I would think
about it, and I would entertain it for a moment.
I probably wouldn't actually sign up, but you know, I
might post it on Twitter and encourage you might think
about it for point one second. Solar energy All right, Well,
it sounds like a pretty cool idea, and it's kind
of interesting, I guess to think about, you know, using
(38:40):
something like a black hole, which I think in popular
culture just has you know, death and destruction associated with it,
to use it for actually something useful. Yeah, and it
shows you how we should be creative. We should think
this thing which seems crazy and dangerous, maybe we can
put it into work, although maybe not too creative, or like,
let's just double check these calculations before we start selling tickets.
(39:05):
Maybe do it a little bit ways out into the
solar system when you try it out. Yeah, and we'll
try it with hamsters first, or those monkeys you have
in your lab no comment. Well, we hope you enjoyed
that and that it made you think a little bit
about black holes and how maybe they could somehow get
us out to see other black holes. And even if
this isn't the idea which cracks open this decades long
(39:27):
problem of how to get us to alien stars, I
have confidence that humans will one day figure this out.
We'll come up with a crazy idea that even Jorney
thinks sounds safe, and it'll get us to those star systems,
and we will learn the answers to these crazy questions
we've been asking basically since we've been asking questions. Thanks
for joining us, see you next time. Thanks for listening,
(39:56):
and remember that Daniel and Jorge explained. The universe is
a pretty auction of I heart Radio. Or more podcast
from my heart Radio, visit the i heart Radio app,
Apple Podcasts, or wherever you listen to your favorite shows.
Hey or heey. Have you ever wanted to go visit
another star or even a far away galaxy? Totally? I
mean wouldn't, although you know, it kind of depends on
what the accommodations are over there, Like are we going
to be camping on a rock basically for the rest
of my life? Or isn't going to be a beautiful place. Well,
it's kind of hard to get pictures in advance. If
you're the first human to ever land on this surface.
(00:31):
There aren't any Airbnb reviews yet. You can't trust YEP
to do everything for you. But I guess the problem
is how would we even get there? Isn't it really
hard to go to another star or galaxy? It is
really hard, which means we have to be really creative
and sometimes looking unexpected places for sources of inspiration and
power than in a fusion use the energy trapped in
(00:52):
bad punts. Well what if I told you you could
actually make use of a black hole? But I thought
black holes were just like traps that trapped you there forever.
I mean, they can actually be useful. You might get
nervous when we talk about black holes in a positive light,
but they do have a possible practical applications. I am
(01:25):
more handmade cartoonists and the creator of PhD comments. Hi.
I'm Daniel. I'm a particle physicist and I'm paid by
the Big black Hole corporate consortium to talk positively about
black holes wherever I can. Really, you've switched to black
hole PR now or astronomical PR. That's right, I'm funded
by Big black Hole. You went from physics research to
(01:45):
public relations PR. No, but I like black holes. I'm
definitely pro black hole. I mean, I'm not pro the
Earth getting sucked into one or you and your loved
ones being killed by one, but I'm fascinated by them,
and I would love to study one and to create one,
and of course do it all very safely. Yet would
you visit one? I would visit a black hole if
(02:06):
it was big enough that you could come close to
the event horizon without being torn apart by the tidal forces.
So yeah, are you starting a tour company to the
center of the galaxy? And I am definitely anti black hole,
But in this universe it's hard to tell sometimes what
could be useful or what could be something that will
kill you instantly. So welcome to our podcast. Daniel and
(02:28):
Jorge Explain the Universe, a production of My Heart Radio
in which we examine everything in the universe, from the
tiny to the massive, from the dangerous to the cozy,
and we talk about whether it could help us answer
our questions, whether it could take us on a journey
to the stars, or whether it just helps us zoom
in and understand the universe at the smallest, most microscopic level. Yeah,
(02:49):
we like to talk about all the possible ways out
there that we could maybe visit or travel to other
places in our galaxy or in the universe, because it
seems like it's all out they're waiting for us to
go visit and study. That's right. I feel like we
are in the early days of the human age of exploration,
where we learn about what our galaxy looks like and
(03:11):
what's out there and who is out there. But so
far it's still sort of shrouded in mystery for us.
And if we could only get out there, if we
could send people or probes or something, we could learn
so much about what's out there in the universe and
how things work. Yeah, I feel like we're almost like
stuck in a deserted island in the middle of the ocean.
You know, like there's such a huge gap between us
(03:32):
and maybe other things, and we don't even know if
we can make it out there, or what would happen
if we went out there. That it's kind of preventing
us from spreading out into the cosmos. It is, and
it's frustrating to know that that knowledge is just sitting
out there waiting for us. Alien civilizations or not, crazy
planets or not. Whatever is out there, it's just waiting
(03:52):
for us, literally sitting there, waiting for us to come
and check it out and learn things about the universe.
And whenever there's like a bare year between us and deep,
powerful cosmic knowledge about the universe, it just drives me crazy.
I just want to pierce through it or around it,
or whatever preposition you need to use. But I want
to get that knowledge, and I want us to understand
(04:13):
how the universe works. Doesn't make you want to be
an engineer, Daniel, so you could actually make something useful.
It makes me want to be a physicist so I
could have a clever idea which I could then pass
to the engineers who would make something useful. I see,
there are limits to your curiosities. What you're saying there's
limits to my practical ability to build something, but no
limits to my imagination. All right, Well, it is a
(04:37):
very big problem to get to other stars, into other galaxies.
And we've talked about in the program before about different
ways to power our spaceship out into the cosmos, because
it's really hard to bring all the fuel with you
that you'll need to get to somewhere far away. Yeah,
you need to build a really big ship if you're
gonna bring a lot of people and you're going to
keep them safe from cosmic radiation, and then you need
(05:00):
to bring some source of fuel to get you there.
So people have been struggling with this question for decades,
for maybe even longer than that. And there's some crazy
ideas out there. We've talked before about instead of just
building a ship, move the whole Solar system by building
a stellar engine, something that would turn our star into
an engine. Yeah, and so on the episode today, we'll
(05:23):
be talking about another crazy idea that physicists are toy with,
thinking about and spitballing about. And this one involves black holes.
All the craziest, most fun ideas involved black holes. It's
about as crazy as you can get I guess in
this universe. So today on the program, we'll be asking
the question could a black hole power a starship? Wow?
(05:50):
That's crazy? What what does that even mean? Well, first
of all, it's stemmed me through like where did this
idea come from that? Did you wake up with it
one morning? Or is this something that's actually being discussed
at like physics conferences? Oh? Man, I wish I could
take credit for this idea, but no, this idea, like
many great creative ideas in science, came from science fiction.
(06:11):
This was first written about by Arthur C. Clark in
a short story he wrote called Imperial Earth. Wow, so
a long time ago, quite a while ago. Yeah, it's
a fairly old idea. And then since Hawking revolutionized our
understanding of black holes, and in the last ten or
fifteen years we've made some progress in quantum gravity. People
have started sitting down, like doing the calculations and figuring
(06:33):
out like, couldn't you do this? Is this possible? Is
there a fundamental physics reason that says no? Or could
we just pass it off to the engineers to figure
it out? Didn't Arthur C. Clark sort of foresee, another
huge thing, wasn't it the Internet or something like that.
I'm sure that he and other science fiction writers foresaw
a lot of what's real. The cool thing is that
they also foresaw a lot of stuff that didn't happen. Right,
(06:55):
So I see, you don't really pay attention to the denominator.
Just like spew a bunch of crazy predictions, and if
you hit a few, then you know, you become famous
for foreseeing the future. Your visionary right, even if your
hit rate is low. That's right. I got a room
full of monkeys predicting the future. One of them is
a genius, because I make real a genius for having
the monkeys or but anyways, it's a crazy idea. So
(07:18):
the idea is to use a black hole to power
your starship. And so we'll get into the diesel because
I have a lot of questions about this crazy idea.
But first we were wondering how many people out there
I thought this was a good idea, or I had
heard of this idea. So Daniel went out there and
asked to the Internet if they knew the answer to
this question. That's right, And we're always looking for volunteers,
(07:41):
people who are interested in speculating baselessly on questions. We
asked them for future episodes, so if you'd like to participate,
please write to us two questions at Daniel and Jorge
dot com. So think about it for a second. If
someone asked you if you thought you could use a
black hole to power a starship, what would you as?
There here's what people had to say. If he wants
(08:02):
you to use an actual like black hole as an
engine to propel yourself around, I don't think that would
work because surely for a normal engine you need something
that applies a force in the opposite direction that you're moving,
so that the resulting force pushes you to where you
want to go. But surely a black hole would just
(08:23):
suck everything in. Well that would be cool, yes, I well,
probably theoretically can be done. I don't know in how
much time can this be put in practic cern For sure,
it's working on it, of course, because they usually want
(08:44):
to start trek the next generation. I think you could
use it in part for a spaceship that's designed for
faster than light travel. It's the idea of compressing the
space in front of you and expanding it behind you
is a primary engine. I don't think so you can
definitely use a stellar stationary black hole to propel your
(09:05):
ship in an arbitrary direction. You just calibrate a trajectory
so that you avoid falling in and avoid being destroyed
by tidal forces, and have the black holes link shot
you to an arbitrary direction. I think that you cannot
use the black hole as a spaceship engine because you
everything New York gets sucked in, so it can suck
(09:27):
in bits of your spaceship blue by little, depending on
its size. I'm sure that a space draft can use
a black hool as an as an engine. I'm trying
to think, how would you use the energy from the
black hole? Alright, Well, we got about as many different
answers as people answering the question. Yeah, well it seems
(09:47):
like people think it's cool. It's a cool idea, but
there was some skepticism like how would that even work?
And there are lots of different ideas here about how
it could work, like could you use it to make
a warp drive by compressing spased run of you? Very
cool idea, or just like the gravitational assist right using
as a slingshot, or people thinking that certain is currently
(10:08):
working on a black hole drive are you. I can
either confirm nor deny that. Do you have a room
full of monkeys working on it? There at certain one
of my monkeys is working on it. I bet you do. Look, monkeys,
just don't press this button. I'll be back in an hour.
I have to do a podcast. Well, these are pretty
good monkeys if they can understand instructions like that, Danny. Yeah,
(10:30):
they come from the best universities. So it's kind of
a crazy idea, and people seem to think it was
maybe possible, And you're right, there are many different ways
that you could attack this, Like you could use the
black hole itself, like as a gateway. Isn't that a possibility? Oh?
I suppose if a black hole is just like a
doorway to a wormhole connected to a white hole somewhere
(10:54):
else in space, then yeah, I suppose you could use
that as a way to get through the universe. I
love that this question and has inspired so much creative thinking.
But nobody who answered these questions hit on what is
actually the idea that's being considered in the community for
how a black hole could power a starship. Nobody had
read Arthur's c Clark. I guess or all of his
(11:14):
collected works. No, none of those folks are up on
the latest there. All right, well let's jump right into Daniel.
How would you even use a black hole to power
your starship? And if it's powered by a black hole,
do you have to call it a black hole ship?
I'll leave it to you to name the eventual ship
once we build it. But the idea is that a
black hole actually satisfies a lot of the requirements you
(11:36):
need for fueling a starship. It's very very dense, and
so it's a great way to store energy, and it's
very efficient because it turns that energy into radiation. Remember,
many people think about black holes as a fold in space,
a place where nothing can escape, not even light. But
black holes are not actually totally black. They radiate a
(12:00):
very small amount of radiation, and they're turning essentially their
own mass into radiation. And the basic idea of the
black hole starship is to take advantage of that, the
black hole turning its mass into radiation and using that
radiation to provide thrust for a starship. Oh I see,
all right, So a pro idea for using black holes
(12:23):
as fuel is that one. It's first of all, you
said it's very dense. I guess it is very dense
in that you can crame a lot into it but
not require like a big chamber to hold it. What
do you mean precisely? I mean it doesn't get more
dense than a black hole. Anything else you get to
that same density is just going to turn into a
black hole. So the black hole is by definition the
(12:43):
most dense storage of energy. So I guess, like if
you had to pack a star that would be pretty
hard because you need a big container. Yes, exactly, exactly,
And that's the other advantage about black holes is that
they contain themselves. What are the common alternatives for using
a starship? Is like antimatter? What if you store antimatter
(13:03):
in your starship and use matter antimatter reactions to provide
the energy, Right, that seems like a better idea. Yeah, well,
the problem is antimatter is really hard to store. It's
very reactive. It could blow up your ship. Black hole
store themselves. They contain themselves, They are their own bottle,
and so they really have an advantage there over antimatter. Oh,
(13:24):
I see what you're saying, Like, it doesn't have anything
like dangerous that could get out. I mean as long
as you don't slip and fall into the black hole,
you're pretty safe, right, that seems kind of We'll just
put up a sign, you know. I'm sure we'll put
a sign. People will sign a waiver. They'll be fine.
Those yellow cones or prop up things. Which is like
a stick figure falling into a black hole, that would
(13:45):
be the warning. We'll let you draw the sign. Yeah,
exactly where a helmet. And the basic problem that you're
trying to solve by using a black hole is efficient
conversion of fuel into thrust because as a lot of
the other more common methods of accelerating the starship are
just very inefficient, like fusion or fission. They're wonderful, but
(14:08):
they don't capture most of the mass in your fuel
and turn it into energy. There's a very low efficiency there,
and so you end up bringing a huge amount of
fuel and then more fuel to carry that fuel, and
more fuel to carry that fuel. So you want a
source of energy that's very, very efficient in converting its
mass into your thrust. And that's where black holes really
can't be beaten. Like literally, you can't beat them. There's
(14:31):
nothing hit him with a stick. It just eats up
the stick. That's right. And there's another really fascinating feature
about black holes that makes them well suited to being
a source of energy for a starship. There's a lot
of details to get right to get your black hole
to power your starship. Well, let's get into that, and
also a lot of these details about how you would
make a black hole power your starship. But first let's
(14:54):
take a quick break. All right, we're talking about the
idea of using a black hole to power your starship
to get to another galaxy or another star, or maybe
(15:15):
to another galaxy cluster even and so, Daniel, the idea
is that I would somehow bottle a black hole and
then bring it with me. You're saying, the first advantage
is that it's really compact, meaning like I could keep
it in my pocket even. Yeah, the kind of black
hole we're talking about that would power a reasonable flight
would have a radius, you know, less than ten to
(15:36):
the eighteen meters. It would be really really small. Oh wow,
would be like a microscopic Yeah, microscopic. And you wouldn't
even need to bottle it. Remember, black holes are their
own bottles, so you don't really need to put it
in anything. You could just have the raw black hole bear. Well,
I guess that's my first question about this idea is like,
how would you even carry it around? Like does it
(15:57):
sit on something? Does it you just let it flow
next to you. I'd even like bring it with you. Well,
you don't bring it with you. It brings you with it, right,
that's the idea. It's like you're hitching a ride. You're
hitching a ride on a black hole exactly. And so
how do you turn a black hole into an engine?
All right? Remember that black holes radiate or they shoot
off this hawking radiation, and this is theoretical. Still nobody's
(16:21):
ever actually seen hawking radiation, but they shoot off hawking radiation.
And the fascinating things that this happens more for small
black holes, like really big black holes from stars or
supermassive black holes hardly radiate at all. But the theory
is that as black holes get smaller, they radiate even more.
(16:41):
Like how much more like like it's shining, like it's
like a small black hole would actually be bright, Yes,
it would be bright. It would be dangerous. You would
have to wear protection. The kind of black hole we're
talking about when it's like, you know about a billion kilograms.
This is like two times the mass of the Empire
State building. This thing would really a hundred and sixty
(17:02):
petal whites of energy, two thousand times the worldwide energy
consumption every year. Okay, so let's walk through this scenario.
So I take two Empire State buildings and I somehow
compressed them into a black hole, which would be about
ten to the minus eighteen meters. I like, how you're
making this like an internet recipe sugar cookies or black
(17:25):
hole dry. I'm an engineer. I gotta I gotta know
the instructions here. So I take the two Empire State's building,
I compressed them into tents of the minus meters and
now have a black hole. It's really tiny. It's like
a basically a pinpoint. It's basically a pin point. And
we can talk later about more practical ways to actually
make these black holes and involves enormous space lasers, but
(17:46):
that's basically the recipe. Get that much amount of energy
into that small or radius and you have a black hole.
And black holes that are that small. That's very small
for a black hole. You know, black holes out in
the universe are measured in units of the mass of
the Sun. This is a tiny, tiny, little black hole,
and so it radiates a lot, a lot more than
any black hole that's out there sort of scattered around
(18:08):
the universe. A synthetic black hole on a human scale
would radiate a lot more than natural black holes. Oh,
I see, so a small black hole is actually and
not black, it's really shiny. Yeah. The smaller the black hole,
the more radiated because the amount of things radiate depend
on their temperature. And this is something that Stephen Hawking
discovered that black holes have a temperature, and everything in
(18:31):
the universe that has a temperature gives off radiation. It's
called black body radiation. Everything glows, even black holes, because
they have a temperature, and the temperature the black hole
is connected to its mass, and as its mask it's smaller,
it's temperature goes up. And there's some complicated arguments there
about entropying quantum mechanics that we shouldn't get into. But
(18:52):
smaller black holes have higher temperatures and so they radiate more,
and so it's a sort of a runaway process like
it radiates more or like surface area or like total
like it's hard to imagine that a you know, like
the supermassive black hole in the middle of the galaxy
would be radiating less than a little tiny empire state
building black hole. It's definitely more per mass, like per
(19:13):
unit mass of the black hole, but I think it's
also an absolute levels more. I mean, these little black
holes they radiate more, and then they lose mass because
they have radiated that mass away, and then they radiate
even more, so it becomes a runaway effect. And the
last few moments of the life of one of these
black holes they're extraordinarily bright. Wow. All right, So it
(19:35):
has something to do with, I don't know, some sort
of weird relationship inside of the black hole that did.
The less mass you have, the more it radiates. Yes, precisely.
And that's why this works because you don't have to
build a black hole the size of the Sun. You
can build one that's pretty small and it will be
pretty bright. So it's a great way to store that
energy and then have that energy be released over time.
(19:57):
All right, So I just compressed to empire state buildings.
I created a black hole, and I guess I did
it in space? Where my did I do it here
on Earth? Better? Do that in space, please, sir? Yes? Absolutely. Okay,
don't do this in your backyard. And I have this
in space, and what does it do? Does it get
attracted to the Earth when it also kind of like
act as if I had to empire state buildings out
(20:19):
in orbit. Yeah, it would, and so you could have
it in orbit around the Earth. Right, You can have
anything in orbit around the Earth, a black hole, anything else.
It has a strong gravity to it, but it's not
like actively sucking in the Earth. So it can be
in a stable orbit around the Earth. And then you
build your spaceship around the black hole. But I think
I have to keep feeding it, right, because it's radiating
(20:41):
and so it's shrinking at the same time. You don't
have to keep feeding it, though, that's an option. You
can just sort of build your spaceship around it and
then use it up and by the time you get
to your destination, it will have evaporated into nothing. Oh,
I see, so it takes years and years for it
to evaporate. That's right. A two empire state building black
hole will evaporate in about three or four years. All right.
(21:02):
I guess my question is like how do you hold it,
or like how do you move it? Or how do
you nudget because wouldn't anything that it touches gets sucked
into the black hole. Well, remember that black holes have
strong gravity, but they're not like actively sucking stuff. Right.
You can be in a stable configuration near a black
hole as long as the tidal forces are not too great.
(21:24):
So the way you take a black hole, which is
just shooting energy out in every direction and turn that
into a spaceship is actually the same way that we
talked about for turning a star into a spaceship. Is
that you capture half of the radiation, like all the
radiation on one side you capture in some sort of
parabolic mirror and focus at the other direction, so that
(21:44):
effectively it's only radiating in one direction. And if it's
only radiating in one direction, that's basically thrust. It's like
it's shooting particles at one side. And that's how an
engine works. It pushes something away, gives off mass and
energy in one direction, and so by conservation momentum it
will go the other direction. So that's the second critical
piece you need the black hole shooting off energy. Then
(22:06):
you need this reflector which turns the black hole into
an engine, like you put a mirror to one side
of it, and then some of them gets reflected into
the black hole. You put a mirror to one side
of the black hole, near the black hole, not in it, right,
You don't want your engine to get into the black hole.
If you put a parabolic reflector around the black hole,
then all of its radiation will get reflected to be
(22:28):
in parallel lines and all shooting out in one direction. Right,
But to the black hole, it's just radiating out in
all directions. So what would cause it to move? Well,
it's reading out in all directions. But now you have
this reflector, and the reflector is gravitationally bound to the
black hole, right, It's being held in place by the
black holes gravity. So you can think of them like
(22:48):
as a system. The black hole plus this reflector are
now like one gravitational system, and the two together are
only shooting out radiation in one direction, so they have
to move in the other direct Oh, I see, So
you kind of have to put the black hole behind
you almost right, Yes, the black holes in the back
and the reflectors in the front, and then you end
up moving in the direction of the reflector like it's
(23:11):
pushing you. The black hole is pushing you away, but
you're also pulling the black hole with your own gravity. Yes,
that's a good way to think about it exactly. So
you're right, the black hole all it knows is that
it's just shooting off radiation in every direction because you've
built it into this system with a reflector. The combined
system has to move, you know, in whatever direction you
were pointing in order to balance the momentum that's coming
(23:33):
out the back of the ship. Right, But isn't that
a really tricky balance? Like how do you know the
black hole is gonna follow you? Do? You have to
be as big as two empire state buildings too. You
have to build a pretty big ship. But you want
to build a pretty big ship anyway, because if you're
going for three and a half or four years, you
need like a lot of room for you know, canned
soup and people, and you have to build a lot
(23:53):
of shielding to protect yourself from radiation. So you want
to build a really big ship. But yes, it is
not easy engineering problems, so I do not envy the
engineers who have to work on that. But also, but
it's isn't it a little bit dangerous? Like how far
away would you have to build this reflector, and like
if something knocks the ship but in it potentially knock
(24:14):
get into the black hole and then with destroyership. Yeah,
it's not necessarily a stable configuration, you're right, And if
something gets too close to the black hole, then the
whole thing could just get sucked in. Right, So yeah,
there are definitely problems to solve. But you know, my
department is is this theoretically possible? And then you know,
I put my stamp on it, and then we send
(24:34):
it off to you know, safety and configuration and engineering
to make it actually work. But so there's definitely some
challenges that you just just said, a worry somewhere which is unstable,
Like is this a unstable configuration? What did you mean,
my dad? Like, I can put the black hole behind me,
but it's very precarious. Yes, some things in equilibrium are
stable so that if you perturb them, they'll naturally go
(24:54):
back to the original configuration, right, But some things are unstable,
and in this case, if the mirror gets too close
to the black hole, then it will eventually fall into
the event horizon the black hole or would be very
difficult to take too much energy to move it away. So, right,
it's pretty tricky. It's like, if you're in orbit around
the Earth and something knocks you out of orbit, then
(25:17):
you're not going to fall back into orbit. You're going
to fall into Earth, right, And the same problem happens here.
So basically you're saying on this trip, nobody can move
on the ship. It's like, alright, three and a half years,
nobody move, or else we're going to fall into this
black hole that we made and are bringing with us. Yeah, yeah,
(25:37):
you know, maybe don't have assault the party right next
to the black hole. Yeah, no aerobics classes on this cruise,
no jumping up and down. It might be a boring trip,
but hey, it means it's a shorter trip because a
black hole could get you up to a significant fraction
of the speed of light. Really, if you build this
ship and you can use the black hole that we
(25:59):
talked about, like two masses of the Empire state building,
it can give off enough radiation to accelerate a large
ship to ten of the speed of light in just
twenty days. Wow, and is that a lot ten percent?
What is that per second? It's a lot of meters
per second and at that speed you could get to
the nearby star in like forty years instead of five
(26:22):
years or five thousand years. And you also could do
it without depleting the energy resources of the entire planet.
All Right, well, I still think it's a crazy idea, Daniel.
But let's get into whether it could actually work and
if we could actually build one. But first let's take
another quick break. All right, Daniel, you found something useful
(26:55):
to do with black holes, and that is to power
your starship to a nearby star or galaxy. And it theoretically,
it sounds like it could work, but it feels kind
of practically dangerous, like you know, you can put it
in the bag and it's pushing you, but if something happens,
it could also destroy. And that's a pretty good summary.
And you know, I'm not asking you to invest or
(27:16):
to buy a ticket on the black hole starship. I'm
just asking you to examine with me whether or not
this is theoretically possible. Because things that seemed I thought
you were pro prol black hole, which is why we're
talking about this. But I totally recognize that a lot
of problems to solve. But you know, today's impossible problem
is tomorrow's app Written by Middle schoolers. So let's leave
(27:37):
these open problems out there and maybe one of our
listeners will be inspired and think of a solution. Right, Okay,
so you're saying it can maybe accelerate a large ship
up to ten percent of the speed of light in
twenty days, which means we would get to the nearest
star you said in forty years. Yeah, the nearest stars
are like four light years away, and so if you
go at ten percent of the speed of light, you
could get there in forty years, which means you could
(27:58):
step on this ship and you actually step off of it.
You could visit those stars and not just your kids
or your grandkids, your great great grandkids who are mad
at you for having relegated them to being born in space,
but you could actually get there yourself. But you said
the black hole itself would only last three and a
half years. Yes, the black hole itself would last three
and a half years, but it only needs to last
(28:19):
long enough to accelerate you, and you know, then you're
up to the right speed. You know, there are other
questions about like deceleration and how do you stop. Yes, well,
I guess maybe this is one one thing I'm curious
about is can you feed the black hole? Like, can
you supply with more energy as you're going? No, you
(28:40):
certainly can. Two solutions they're one is start with a
bigger black hole and then halfway through the trip, flip
the reflector around if you think that's a safe procedure,
so that now the black hole is decelerating you, so
that by the time you get to your destination you're
at a reasonable speed. You don't fly through the system
at a zillion miles an hour. And the other thing
(29:01):
you can do is, as you say you can feed
the black hole, you can like gather interstellar gas and
micro meteorites and all that stuff and just sort of
like directed into the black hole. Because the cool thing
is everything is fuel for a black hole, right, even
bad punts, even bananas. Banana now that would just slip
on by. But I mean, is that the work math workout?
(29:23):
Like can I bring another empire state building with me?
Or does that take away them from the excelaration. The
way that you build the synthetic black hole that you
need to power this drive is not by bringing all
that mass, because we don't know how to take that
mass and compact it into a black hole size object.
That's not something we know how to do. Instead, the
best ideas for how to build a synthetic black hole
(29:45):
of the right size involved just essentially dumping energy into
a point in space using massive lasers. All right, now
we're getting more exciting here. So step us through how
would we actually make a black hole? Like, can we
make a black hole? As I guess you make black
holes at a large hadrant collider, but you don't keep
them around. Well, we don't know if we've made black
(30:05):
holes at the large hadron collider. We're trying to. We're
hoping to see one. We've never spotted one before. But
the idea is that to make a black hole, you
don't just need a huge amount of mass. What you
really need is high energy density. Any kind of energy
will curve space. Einstein's general relativity told us that matter
curve space, but also anything with energy in it. And
(30:28):
so what you need to do is just pour a
whole huge pile of energy into a small part of space.
And you can do that by focusing a bunch of
lasers on the same place. Oh, I see, you can
make a black hole, but just pure energy, just pure energy. Yeah,
And so you build a huge laser, a lot of
huge laser and you focus them on the same place,
(30:48):
and in principle, you pour enough energy into that dot,
it will turn into a black hole. It will capture
all that energy story gravitationally and then gradually release it,
which is what you need. Wait, what do he means?
So you can make a black hole just by pointing
lasers together. Yes, nobody's ever done it. We haven't ever
seen this, but the math tells us. The theory tells us.
General relativity says that you get enough energy density in
(31:12):
one spot, it will turn into a black and that
includes laser light. And lasers are actually great because photons
have no problem being close to each other. Like the
reason you can't take the Empire State building and turn
into a black hole is that that matter resists being
squeezed down right, there are chemical bonds there. But photons,
they are the kind of particle we call bosons that
(31:34):
are very happy to be right on top of each
other and all doing the same thing. And there's no
photon photon repulsion, and so you can pile as many
photons as you want. They will not resist. Then wouldn't
it take a lot of energy to power your lasers,
like could you wouldn't that take me all the energy
on Earth just to make a mini black hole. It
would take a lot of energy to make this black hole,
(31:55):
but it's much more energy efficient than for example, antimatter creation.
Ant a matter is something we can make and it's
a good way to convert mass into energy, but making
antimatter is very, very inefficient, whereas making a black hole
is much more efficient because all the energy goes into
the black hole. So yes, it's a huge energy consumption.
(32:15):
Anytime you want to accelerate something up to the speed
of light that's very massive, it's going to take a
lot of energy. But it's much more efficient to turn
lasers into a black hole than to build antimatter, which
is very difficult to do. And so the idea is
that then you just point lasers like at a point
or at each other, or just the laser itself would
create the black hole. And you need a bunch of
(32:36):
lasers altogether focused on a point. And people have done
some calculations to think like well, how much would you need,
how much energy would you need? And it's about like
point one second of all the energy coming out of
the sun, like the sun you know, really it's a
lot of energy. And you know, if you get like
a tenth of a second of all the solar energy,
that's about as much as you need to build this
(32:58):
synthetic black hole we were talking about. You can't capture
the whole Sun. But you know, people did other calculations.
If you build like a lot of solar panels, you know,
something like a few hundred kilometer sized solar panels in
circular orbit around the Sun, then it takes about a
year to get enough energy to power these lasers to
(33:18):
build the synthetic black hole. Oh I see, so you
would have to store all that energy for a year
and then release it at once. Yes, exactly, so big
batteries from Tesla Ellen, get on that. No, don't get
on that doing in space Wait, wait until you have
a space station. Yeah. And there's you know, lots of
(33:40):
other practical problems with building a black hole starship that
we sort of just you know, waved our hands over all. Right, Yes,
what are those problems? Well, number one is that black
holes don't just shoot off photons that can be easily
reflected by like a nice mirror. And we talked about
how you have to redirect the radiation of half of
the black all the other direction. If you want to
(34:01):
move anywhere, that works great if the black hole is
giving off photons, because we know how to bounce those
off a mirror. But black holes are very democratic. The
reason Hawking radiation exists is that you have random particles
coming out of the vacuum. So those could be photons,
they could be top corks, they could be Higgs bosons,
they could be electrons. Oh, they're spewing out all kinds
(34:22):
of stuff, all kinds of stuff. Yeah, and some of
those things are hard or impossible to reflect. Oh, so
you don't even know if you could reflect all of
that energy. You're pretty sure you can't reflect all of it.
And so there's some ideas that, like you could reflect
part of it, and the rest of it you could
try to absorb and then capture in terms of heat
and use that somehow, either funnel it back into the
(34:43):
black hole or use it to power you know, an
ion beam or something like that. But it gets pretty
tricky because this is very intense radiation and anything you
build nearby that can't reflect the radiation is going to
absorb it and get really hot and probably melt. Can
it spew out antimatter? It will. It will absolutely spew
out equal amounts of matter and antimatter, so that it
(35:06):
might even destroy your ship just from what it it's radiating. Yeah,
that is a concern. Actually a small concern is that
it's spewing out antimatter, which would and I lead your space. Yeah.
I don't think this idea is you know, consumer ready yet,
but the bones of it are there, you know. Oh man, Yeah,
(35:27):
the black holes antimatter. That's right. Because the Hawking radiation
is random, it creates pairs of particles and antiparticles, and
sometimes the particles fall into the black hole, and sometimes
the antiparticles do. That's one of the really cool things
about black holes is that they radiate all the particles,
and so it's actually kind of a cool way to ask, like, well,
what particles are there? We'll just make a black hole
(35:49):
and have it radiate everything that there is. It's sort
of like the world's best particle collider. But I guess
if it's being out antimatter, then I mean, if some
of that touches you, then you're you're dead. Yes, if
some of that touches you, then you know, I recommend
you go immediately to the met deck or whatever it
is on this ship, which just when did it explode
(36:09):
on you or something? Well, if an individual particle eventimatter
hits you, it's not a big deal. You know, like
bananas emit anti matter. They're emitting positrons all the time,
but they don't hurt you, just a very small amount
of energy. But they could cause cancer. But we're talking
about a black hole emitting a lot of radiation. A
significant fraction of that would be radiation that you can't
easily absorb and reflect like photons, and some of it
(36:32):
would be antimatter. So yeah, there are big technical issues
they're remaining how to handle all this radiation. It's crazy.
A black hole is too bright maybe to be a
starship drive? Could you just use a smaller one, Like
with a smaller one help a smaller one would help perhaps,
but then it might not have enough power. So this
sort of a sweet spot there. You need to be
big enough to provide power to drive your ship and
(36:55):
to last long enough, because the smaller black hole is
the shorterest lifespan. Just so, there is actually like a
literature on this idea, like there are papers out there Yeah,
I've read some papers in the last few days about
making black hole starships and whether it's reasonable. And in
addition to all the practical questions that you asked and
all the reasonable concerns you how about whether this thing
(37:17):
would survive, there are also fundamental physics questions about whether
this would work. Because you know, we're talking about Hawking
radiation that nobody's frankly ever seen in real life, and
we're relying on a sort of semi classical understanding of
black holes because we don't have a good theory for
what's going on inside black holes of quantum gravity. We
(37:38):
can't really explain what's going on inside black holes, and
we can't really explain whether they're radiating, and we've never
validated Hawking's predictions about how much they're radiating. So a
lot of whether or not this is possible depends on
a quantum understanding of gravity that we just don't have yet. Wow,
all right, well, it sounds like a good idea to you.
Something we don't understand and may potentially kill is to
(38:00):
power a starship. We'll just ask for volunteers and we'll
have a really long waiver. I'm sure a lot of
people on the internet would sign up. I would think
about it for a moment. I'd be like, Wow, I
get to see an alien world and they get to
ride in a spaceship with a black hole. That sounds
pretty cool. You would sign up, you who never want
(38:20):
to leave your house. Well, I said, I would think
about it, and I would entertain it for a moment.
I probably wouldn't actually sign up, but you know, I
might post it on Twitter and encourage you might think
about it for point one second. Solar energy All right, Well,
it sounds like a pretty cool idea, and it's kind
of interesting, I guess to think about, you know, using
(38:40):
something like a black hole, which I think in popular
culture just has you know, death and destruction associated with it,
to use it for actually something useful. Yeah, and it
shows you how we should be creative. We should think
this thing which seems crazy and dangerous, maybe we can
put it into work, although maybe not too creative, or like,
let's just double check these calculations before we start selling tickets.
(39:05):
Maybe do it a little bit ways out into the
solar system when you try it out. Yeah, and we'll
try it with hamsters first, or those monkeys you have
in your lab no comment. Well, we hope you enjoyed
that and that it made you think a little bit
about black holes and how maybe they could somehow get
us out to see other black holes. And even if
this isn't the idea which cracks open this decades long
(39:27):
problem of how to get us to alien stars, I
have confidence that humans will one day figure this out.
We'll come up with a crazy idea that even Jorney
thinks sounds safe, and it'll get us to those star systems,
and we will learn the answers to these crazy questions
we've been asking basically since we've been asking questions. Thanks
for joining us, see you next time. Thanks for listening,
(39:56):
and remember that Daniel and Jorge explained. The universe is
a pretty auction of I heart Radio. Or more podcast
from my heart Radio, visit the i heart Radio app,
Apple Podcasts, or wherever you listen to your favorite shows.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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