Transcription
Let's start with something we all know.
You throw a ball at a wall,
the ball comes back. Simple, right? But
what if that wall isn't a wall at all,
but a speeding train? If you throw a
ball at a train moving toward you, the
ball will come back much faster than
when you released it. In space, we have
such trains. They are black holes,
[music] objects with gravity so powerful
that they bend the very fabric of
reality. David Kipping asks a question
that changes the rules of the game. What
if instead of running away, we use them
as propulsion?
>> You could use it to move civilization.
>> What is um the mechanism of the Halo
drive that you proposed?
>> The Halo drive. Yeah, this was a fun
little uh project I worked on about
black holes and uh really asking what
are the limits of transportation in the
galaxy. So uh Freeman Dyson to give a
little backstory behind this um had this
idea of using two neutron stars that
were in a very compact orbit circling
around one another and they get so close
that they move close to the speed of
light in in their in spiral phase. And
so he suggested you could do a
gravitational slingshot around one of
those stars. And because they're moving
so quickly, you could steal velocity
essentially close to the speed of light
and then travel between the stars. And
the beauty of this is that you're
stealing energy. So your spaceship
doesn't really require a propulsion
system. It just drifts in at the right
time and comes out. The problem with
this is that that's like a blender,
right? So these stars are moving so fast
in those final moments. It's like trying
to throw a stone into a blender and hope
that it bounces off the propeller at the
right moment. And it's a very hazardous
environment to fly into a high radiation
environment. So maybe not a healthy
thing to do. So I suggested, hey, why
not replace those black ho those neutron
stars with black holes. Um, and a black
hole has the advantage that you don't
need to get so close to it because we
could use light. So we shine a light
beam and we just miss the black hole
just to the side.
>> Black hole as a cosmic engine.
>> Yes. We're using as an engine to power
our spaceship. So there's there's two
black holes or maybe even just one
that's moving very quickly and we fire a
light beam, a laser beam, and it skirts
around the edge around the event
horizon. Doesn't quite go into the event
horizon, just off the event horizon. And
so it will orbit around and complete
one. It's called a boomerang geodessic.
It kind of looks like a mirror. So you
can actually see your reflection. If you
looked at just the right angle around a
black hole, you could see yourself. So
this light beam skirts right around and
comes back to your spaceship. And when
it does, it will like throwing a ping
pong ball off a moving wall. It will
pick up energy. Imagine like a tennis
racket that's moving through space and a
ball hits it. It comes off with more
energy than it initially hit. And so
this black hole that's moving towards
you will force the light beam to pick up
more energy. So it will get blueshifted
and then that will hit your spaceship
and propel you forward. So the beauty of
this system is that you could propel
very very large vehicles through space
very very fast. So you could literally
take Jupiter, the planet Jupiter, and
propel it at relativistic speeds through
the galaxy with this thing and it
wouldn't and the black hole wouldn't
even notice because it's so massive. So
if you wanted to move an entire
civilization or a huge amount of mass,
this would be the great way to do it.
And there's about a million black holes
in the galaxy altogether. We don't know
where they all are, but we expect there
about a million from stellar formation
history. Um, and so there's a network
essentially out there waiting for us to
tap into. And I like to think of it a
bit of like a highway system, right? So
these are the highway points between
each black hole and you can accelerate
and decelerate between these points and
then you get off the offramp at each one
and you go to your local star system.
Could the hell dry mechanism push a ship
to the speed of light?
>> Not to the speed of light. It would be
limited by the speed of the black hole
itself. So these in the fire in you know
these black holes have varying speeds
but some
>> close to speed of light. Right.
>> Yeah. I I would say um maybe like 30 40%
speed light something like this. Yeah.
Is it technically possible to create a
prototype
or of the hurdle drive?
>> Um, possibly. We don't obviously have a
black hole. That's the big problem. So,
you need a black hole to test this.
There are some analogies to black holes
we've been able to make in the
laboratory setting called acoustic black
holes where instead of light being
trapped in an event horizon, you can get
sound waves to be trapped in an event
horizon. And so you might be able to do
a kind of sonic version of it more or
less just to demonstrate the idea. Um
but really if you wanted to truly
utilize this thing you need something
which can do this light reflection
technique which is what the black hole
serves. So you need something that's
moving fast and can bend light around
it. So for that you really do need a
black hole. Um yeah I mean my when I
when I approach problems like this I
think of stories as science as a
conversation. So, you have to listen to
what's been said before. And so, imagine
you're at a cocktail party and there's a
group of people talking. So, I walk into
the room and I hear Freeman Dyson
talking and he's talking about these
neutron stars and how they merge
together. And in my mind, I'm realizing
there's a problem with that suggestion.
And so, I hear his what he's added to
the conversation. And I think we can all
do this as scientists. We can all think,
hm, is there anything [clears throat]
about that which could be improved? Is
there anything about that which may be
uh an assumption there that I don't like
that maybe I might challenge? So our job
as scientists is not to ne necessarily
reinvent the wheel but to take ideas
that have come before we stand on the
shoulders of giants and to tweak it and
to say is there a better way of doing
that. So this is a tweak and I hope
other people will tweak it in the
future. Hope someone else will come
along and find an even better way.
>> So one futuristic question if you had a
hello drive how would you use it?
>> You could use it to move civilizations
across the galaxy.
>> How would you
>> how would I use it?
>> Yeah. Uh I would I guess I would love to
uh travel um and see another earthlike
system and just see what is it like?
Yeah. Are there other creatures on
there? So for me I mean some scientists
are astronomers are drawn by the
question of how the universe works. So
maybe some people would travel to the
center of Sagittarius a star or
something. Maybe they'd fly themselves
into a black hole to see like what
happens. Well, how does the physics
work? But other scientists and other
astronomers like myself, I think we're
more drawn to the question of life. And
that has always been the ultimate
question for me. So I would I would want
to travel and understand um how special
are we?
>> What are Davidson's figures?
>> Yeah. So this is again one of Freeman
Dyson's brilliant ideas. Um and he was
thinking about the ultimate limits of
energy harvesting. So, we know we're
going through a period on the earth of
building more and more solar panels on
this planet of harvesting solar energy.
And of course, we're kind of limited by
the surface area of the Earth
eventually. I mean, we're nowhere near
that limit right now, but in principle,
you could tile one hemisphere of the
Earth completely in solar panels, and
you wouldn't be able to do any better
than that. So, the next step might be to
go to space. And in fact, some companies
are trying to do this as well right now.
They're trying to build um space
stations, space satellites that will
have solar panels and then maybe beam
the energy back to the earth. And so you
might grow more and more and more of
these things. And eventually you would
have so many of them in orbit of the
sun, which of course is your energy
source, that the sun is a basically
enshrouded in satellites to such a
degree it almost becomes invisible from
another star system. So when Dyson
described it, he did use the term
sphere, I believe, in that original
paper. But most of the time we think of
it today, we think of it not as a
monolithic structure, but more of a a
swarm of material of some kind. It could
be I mean a solid structure just isn't
stable. So that's why we tend not to
focus on that. It would it would have
enormous tensile strength. It would
break itself apart and even the
strongest materials we know of, no way
could sustain this kind of force. It'd
also be unstable to gravity. If you if
you just prodded it on one side, the
sphere would fall into the star. So
there's lots and lots of problems with a
solid sphere. But a swarm material is is
quite reasonable and it would be the
ultimate way for a civilization to
harvest vast amounts of energy from that
star. So what's happening is the on the
inside of that sphere or the inside of
that swarm, they are collecting energy
from the star. Now that energy can't be
destroyed and by conservation of energy,
energy has to be conserved. So the
energy has to come out somehow.
Otherwise, the thing would just get
hotter and hotter and hotter and all
boil to death on the inside. So that
energy has to come back out. So the
question is how does it come back out?
If they think about your laptop or or a
piece of uh like a camera that's
working, it will get warm. So it's
turning the chemical energy in the
battery into thermal energy is
essentially what it's doing. And so the
amount of thermal energy that comes off
your laptop will be the same as the
chemical energy that went into it plus
the light plus the sound. That's the
other two sources of light of of energy
which come off it. But all of those
energy sources have to add up.
Everything that comes out have to equals
everything that goes in. So these Dyson
spheres have to be emitting energy, a
lot of energy, a sum a some amount of
energy, a star amount of energy in some
way. And if they're if they're doing
calculations, if they're doing
computation, it would come out as
thermal waste heat in the infrared. But
it doesn't necessarily it could come out
in nutrinos. It could come out in
gravitational waves. But it has to come
out somehow.
>> Thank you for your time.