Is it possible to travel to other stars?

Daniel and Kelly explore the hurdles and potential technologies for bringing humans to alien solar systems.

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Episode Transcript

Speaker 1 (00:06):
We know so much more about the universe than our
ancestors did. Go far enough back, and they didn't even
know that the pinpricks of light they see in the
sky are other suns. A few thousand years ago, they
had no idea how far away those other stars were,
and a few decades ago nobody knew for sure whether
they were planets around those stars. We know so much

(00:27):
more than they do, But we've also visited exactly the
same number of solar systems as they have, just the one.
Will we ever get out of our solar system and
make a home for humanity around an alien star? Is
there a physics obstacle? Or is it just political will
or lots of engineering. If it's actually impossible, that might

(00:48):
explain another great mystery why no aliens have visited us.
Maybe we aren't alone in being marooned on our home stars.
Maybe everyone is just stuck at home. Today on the pod,
we'll dive into the challenges, the technologies, and the potential
for taking humanity to those distant stars. Welcome to Daniel
and Kelly's Extraordinary Accessible Universe.

Speaker 2 (01:25):
Hello.

Speaker 3 (01:25):
I'm Kelly Winer Smith. I study parasites and space, and
if I could travel to the next nearest star, I wouldn't.

Speaker 1 (01:34):
What about you, Daniel, Hi, I'm Daniel. I'm a particle physicist,
and I want to send somebody to the nearest star,
but I definitely don't want to go myself.

Speaker 3 (01:44):
So why would you not want to go yourself? Can
you imagine all the physics stuff you could ponder and
maybe even figure out on an interstellar trip.

Speaker 1 (01:51):
Oh yeah, I'd be desperate to talk to the aliens
about physics, to see what kind of weird technology they've invented.
But I'm just not that much of a traveler these Honestly,
I don't even like to get on an airplane, So
a spaceship absolutely not. The seeds you're gonna be uncomfortable
and the snacks are gonna be weird. You know, I'm
a homebody these days.

Speaker 3 (02:10):
But you were born in one country, lived in another country,
and had kids in a third country.

Speaker 4 (02:16):
Right.

Speaker 3 (02:16):
You used to be an amazing traveler, but now it's home.

Speaker 1 (02:20):
Huh time marches on? Absolutely? Yes, I can no longer
sleep anywhere anytime. My stomach is more sensitive. You know,
youth is wasted on the young.

Speaker 3 (02:29):
Well, it sounds like you made good use of your
youth traveling all those places.

Speaker 1 (02:34):
How about you, Why don't you want to go to
another planet.

Speaker 3 (02:36):
If we ended up in another planet and there was
life there, that would be incredible. But I feel like
you don't necessarily know what you're gonna get until you
get there. But the thought of leaving, Like, so it's
spring while we're recording, which means in the next couple
weeks on the side of my barn, the light that's
on outside is going to attract little tree frogs and
all kinds of colorful moths. I just can't imagine leaving

(02:58):
this planet and leaving all that stuff behind to spend
like decades traveling in a tin can. But maybe they'd
have even better moths, and then I would feel regret.

Speaker 1 (03:08):
It'd be amazing, though, if we got to that planet
and then we're like, this place is kind of ugly,
you know. I wonder if, like every planet has its
own beauty, or if our evolutionary history on Earth primes
us to only find, you know, the Sierras and the
Blue Ridge Mountains beautiful. See how I included Virginia.

Speaker 3 (03:25):
I appreciate that. Yeah, No, we're being nice to each
other on this episode. I guess that's great. I also
it would really stink to know that you were never
going to see any anybody else that you had known
your whole life ever again. And like the farther away
you get, the harder it is to communicate. But so
let's dig into the to the meat of our discussion today,
and we're talking about is it possible for humans to

(03:45):
travel to other stars?

Speaker 1 (03:47):
Yeah? And I think this question is interesting and important
because while we want to explore the universe robotically and
gather information telescopically, I think also we have a primal
need to explore, to go places, and to expand out
into the universe. I think it's a question a lot
of people have about whether it's possible today, whether it
might be possible in a thousand years, or whether it

(04:08):
might never be possible for humans to cross the vast
oceans of space to other stars. So I went out
and I asked our listeners if they thought it was possible.
If you would like to play for this part of
the podcast in the future, please don't be shy. Write
to us at questions at Danielankelly dot org. We would
love to have your voice on the pod. So think

(04:29):
about it for a minute. Do you think it's possible
for humans to travel to other stars? Here's what our
audience had to say.

Speaker 5 (04:36):
We can imagine traveling to other solar systems, but can
we deal with all the questions radiation, food, power sources, generationships.
We just don't know enough at this point.

Speaker 1 (04:49):
I would say no for the foreseeable future, but in
multiple generations, after multiple generations, I think that would be possible.
What it would take thousand of years and the ship
would have to survive. You'd go through accidents, there would
be warring factions on the ship. You need a multi
generational ship.

Speaker 6 (05:08):
Well, I'd say it's possible, but not probable within the
next one hundred years. There are a lot of hurdles
to overcome, propulsion being a major one in supplies. Maybe
if you had a fusion powered plasma or something.

Speaker 7 (05:24):
I bet we could get a human being there in
their lifetime with acceleration that won't kill them, But I
think stopping will be really hard and definitely turning around
will be nearly impossible, so they can't come back.

Speaker 4 (05:34):
Humans don't have enough time to live, and our bodies
would be destroyed by the acceleration required to reach another
solar system.

Speaker 1 (05:47):
With today's technology. I don't believe it is strictly possible.
I think it's definitely possible. There's no law that says
we couldn't do it. There's still some major challenges ahead
of us. Anything is possible, but humans traveling to another
solar system may be a stretch. Now it is impossible.

Speaker 5 (06:11):
I don't think a single person could make it to
another solar system, but maybe multiple generations.

Speaker 8 (06:18):
Even if you could travel at the speed of light,
it would still take years to get to the nearest star,
which we don't even know if there's a solar system around,
and you'd have to confirm that first. Even if we
could technology got better, we'd still probably need a generational
star here.

Speaker 9 (06:34):
Unless we destroy ourselves with war or refusal to confront
climate change. We will eventually reach other solar systems.

Speaker 10 (06:47):
Maybe if money isn't a problem in the future, if
we tackles certain things, maybe we could. But I think
it's for now the ultimate pipe dream.

Speaker 2 (06:58):
Yes it is possible, but whether it is probable is
a different question. And even if it is probable, and
even if it's undertaken, I don't think that the humans
who would leave our solar system to get to the
other solar system would be alive. When we get to
the other.

Speaker 1 (07:15):
Solar system, we should assume that the aliens at the
solar systems will be hostile, and therefore we should send
all the people that we dislike the most.

Speaker 3 (07:25):
Maybe through like a cryo sleep or human hibernation type thing,
something like that.

Speaker 9 (07:31):
I believe we are marooned here.

Speaker 3 (07:33):
No, we can't do that right now, but maybe some
day in the future.

Speaker 8 (07:37):
From a physical point yes, From engineering point likely no.

Speaker 3 (07:43):
I loved the variability of answers that we got here,
and I should say that as someone who interacts with
the space settlement community, I have no doubt that even
if somebody were to say, like, we've made a generationship,
there's a one percent chance it's going to make it.
Every seat on that ship would get filled. So, you know,
I think there's a lot of people who really love
this idea.

Speaker 1 (08:02):
Well, why do you think we would have no shortage
of volunteers? You think there are people who, like in reality,
would actually sign up to go. They're not just like
excited about the concept.

Speaker 3 (08:12):
Oh my gosh, they send me angry emails. There have
been so many people who have written me to tell
me that I cannot stop them from settling space, and
I write them back and I say, I cannot stop you.
That's right, And I'm not crying too. I don't think
I have any power over these kinds of decisions. I
just wrote a book saying it's kind of dangerous.

Speaker 1 (08:30):
And maybe we should think this all through before we go.

Speaker 3 (08:33):
But hey, do what you want, Yep, yep, do your things.
So anyway, I'm sure there'd be a lot of people,
and you know, it would be an absolutely incredible thing
if our species did send a generationship, for example, to
another star.

Speaker 1 (08:45):
It would be incredible. And I love how this topic
is so deeply inspired and informed by science fiction. You know,
obviously there's science here, and we're going to talk about
all the nerdy details of propulsion mechanisms, et cetera. But
so many the ideas here come from the creativity of
science fiction authors casting their minds forward to imagine what
we might be able to build, what we might need

(09:06):
to build, what we might have to do to survive.

Speaker 3 (09:09):
Yeah, what is your favorite interstellar travel sci fi book?

Speaker 6 (09:13):
Oh?

Speaker 1 (09:14):
Wow, such a good question. One of my favorites is
a book by Alistair Reynolds. I think it's called the
House of Suns, in which they tackle this problem by
dragging stars closer to each other. So they want to
have like a galactic empire across many solar systems, but
they don't have faster than light travel, and they recognize
that it's basically impossible to govern somebody if you're there

(09:36):
so far away, So they bring a bunch of suns
closer to each other, make a little solar neighborhood, so
you can have different solar systems but they're not so
far away.

Speaker 3 (09:44):
I like that idea, but it sounds kind of dangerous.

Speaker 1 (09:47):
Well, we're going to talk about that technology, which isn't
as far fetched as you might imagine at the end
of the episode.

Speaker 3 (09:54):
So let's go ahead and dig right in. But first,
let's talk about where would we be going. Where is
our closest option here?

Speaker 1 (10:00):
Yes, so the Milky Way galaxy has hundreds of billions
of stars, but the whole thing is like one hundred
thousand light years across, which is really big, and the
density of stars in our neighborhood is not so high.
It actually varies a lot. In the center of the
Milky Way. It's much much denser. But around where we are,
we're like in the suburbs, not quite the ex serbs,

(10:21):
in the very fringes of the Milky Way. But out
here in the suburbs, you can expect to find a
star a few light years away, and that's what we find.
Alpha Centauri and Proxima Centari are like just around four
light years away. So if you wanted to get to
the nearest star uneasy mode, you'd be going to the
closest one. It's still four light years away. And remember
the speed of light, super duper fast. If you shined

(10:43):
a laser beam at one of these stars, it'd be
zipping through the cosmos at an incredible speed for four
full years before it got there.

Speaker 3 (10:50):
And so say you get to Alpha Centauri, do we
know that there are earth like planets there that we
could try to explore? What would we see once we
got there?

Speaker 1 (10:58):
Yeah, there's actually good news there. You know, until like
twenty ish years ago, we had no idea what planets
were like around other stars, or if there even were any.
We'd only ever seen the planets in our Solar system
until the mid nineties, when we started developing the technology
to see exoplanets. Now we specifically identified five thousand exo planets.
At least the number keeps going up and up and

(11:20):
up and up. It's like a real pivot point in
human history. And because of that we can make all
sorts of really interesting statistical statements, like, on average, stars
have a good number of planets, and specifically Proximusentari and
Alpha Centauri do have some planets, and so it's very
unusual actually for stars to have no planets as far

(11:40):
as we can tell. So if you're going to go
to a nearby star, it's very likely you'll find some
planets there. Whether they're Earth like and whether they are
capable of supporting life a whole other question that we
think the next generation of space telescopes will really help
us crack. But from the point of view today's conversation,
let's just imagine getting to that Solar system, not necessarily
finding a cozy how there.

Speaker 3 (12:00):
Okay, so let's see I'm forty two. Now, if I
were going to jump on one of these ships, and
I was hoping that we would arrive by you know,
the average lifespan of a human woman, So what that's
like eighty six or something like that. So we've got
let's say we've got about forty years to get there.
How fast do we need to go?

Speaker 1 (12:17):
Yeah, so if you traveled at the speed of light,
you get there in four years. Of course, you can't
travel at the speed of light because nothing that has
mask can travel at the speed of light. So let's
say you could go at ten percent of the speed
of light already blazingly fast, much much faster than any
human ship has achieved crude or uncrued. But if you
did somehow manage that, you would get to altha centauri
in about forty years, right, a tenth of the speed

(12:39):
of light four light years, so forty years. So that's
basically what you need to achieve. But the sort of
space technology we have now really just isn't capable of that.
Like the fastest crude rocket or the Space Shuttle, for example,
their top speeds would take them about eighty thousand years
to get there, not to mention the question of like
bringing in a fuel that will dig into in a minute.

(13:00):
And even the uncrewed stuff like the Parker solar Probe
is the fastest thing humanity has ever built. Its top
speed is about zero point zero six four percent of
the speed of light. Oh no, you take about seven
thousand years to get to Alpha Centauri. So nothing we've
built can go nearly fast enough to get Kelly to
Alpha Centauri before her eighty fifth birthday.

Speaker 3 (13:22):
Oh that's right. I wasn't going to go anyway, although
maybe maybe if they had really great moths. I'm disappointed.
But so I feel like there's there's a couple problems here.
It's like, one, can you even get to the speed
that you want? But then two, how do you get
to that speed? Because like, if you're sending humans, we've
got these squishy bodies, and if you accelerate us too fast,

(13:42):
we like we break and smoosh, and so you need
to like get fast but not too fast.

Speaker 1 (13:47):
Yeah, so there's a lot going on here. I mean,
one thing is just the limitation of relativity. Number one.
You can't get faster than the speed of light. We'll
talk about warp drives in a minute, but assuming that
you're going through space, through flat space, you can't travel
faster than that. And that's a hard limit. And I
think it's important for people to think about that as
sort of setting the length scale of the universe, Because
we talked a minute ago about like, wow, it's super

(14:09):
duper fast. It is super duper fast. But space is
vast compared to the speed of light. Like, we wouldn't
think space was so big if the speed of light
was ten times or one hundred times what it is,
because then these things would be like less than a
light year away, or we would think space was much
bigger if the speed of light was smaller. So the
speed of light sort of determines like what is far

(14:29):
and what is close, And it just so happens that
because of our galactic dynamics, things are a few light
years away instead of tenths of light year away. But
even if you're not going to get to the speed
of light, this limit at the speed of light makes
it hard to accelerate. Like you keep pouring energy into
your rocket, you're not going to increase your velocity by
the same amount. As you go faster and faster, it

(14:50):
takes more and more energy to increase your velocity. And
as I think you were hinting, there are also limits
on how quickly you can accelerate, like biologically.

Speaker 3 (14:59):
Yeah, so that's the interesting part.

Speaker 1 (15:01):
Well, it's true that we do want to deliver our
passengers to Alvis Centauri, not as bags of dead goo. Right,
we want to take care of all their fragile little
organs and make sure that they actually get there. And
so if you want to get to some sort of
reasonable speed so your trip doesn't take too long, you
need to accelerate, and humans are not really built for
huge acceleration. I was reading some papers that said the

(15:22):
humans can tolerate like twenty G of acceleration G there,
of course referring to the acceleration of gravity here on
Earth as basic standard units of one G. So twenty
G is pretty intense, and we can't really tolerate that
for more than like a few seconds, maybe ten seconds. Humans,
like the really tough ones, can tolerate like ten G
for a minute, five G for a few minutes. But

(15:45):
imagine being on this ship. You're going to be on
it for years at least. You don't want more than
like one G or maybe even two G for long periods.

Speaker 3 (15:55):
You know, we got a lot of the early data
on how many g's humans can survive because there was
the one scientist who kept getting in a sled and
then slamming himself into a foam wall. And so anyway,
human ingenuity. I love it, so just to make sure
I have the physics understanding of this. So like if
you speed up and then you stay at that speed,

(16:16):
you only experience the G as you're accelerating, right, not
just because you're going fast, but because you are going
faster every second. Is that right?

Speaker 1 (16:23):
That's right? Okay, that's right. You can't experience velocity directly.
It's a relative thing right inside your ship. You can't
tell how faster ship is going. But if your ship
turns on the engines and tries to increase its speed,
you can measure acceleration locally. It's not relative, So as
your ship tries to increase its speed, you can feel that.
And something that's sort of surprising to me is that
you can actually accelerate at one G and reach near

(16:47):
the speed of light in a reasonable amount of time.
Like if you're on a rocket that can do one
G of acceleration, you can just do that for a year,
and you'll get up to like ninety nine percent of
the speed of light relative to your departure location.

Speaker 3 (17:00):
And in that case, you would get there in less
than forty years. Right, because now instead of going ten
percent the speed of light, you're going the speed of light.

Speaker 1 (17:06):
Yeah, that's right, but you need a technology that can
provide one g of acceleration for a whole year, as
we're going to talk about. That's not so easy to do, right.
That's an enormous amount of thrust or momentum you're imparting
on your ship.

Speaker 3 (17:21):
There's always something in the way.

Speaker 1 (17:23):
There's always something in the way. And the flip side
of all of this is deceleration or negative acceleration, because
you could get up to near the speed of light,
and then you could get to Alpha Centauri, but then
you're going to be in that Solar system for about
zero point zero seven seconds if you're traveling at near
the speed of light. But what you want to do
is arrive there and stop, which means decelerating. And you

(17:44):
don't want to decelerate from the speed of light to
zero too quickly, otherwise you'll again go splat.

Speaker 3 (17:51):
Yeah, humans, it's a shame. We're so squishy.

Speaker 1 (17:55):
And I think on the next episode we're going to
talk about making humans less squishy by like turning into
human sickles, and that might be a better way to
accelerate human bodies. I don't know, you'll have to tell
me all about it.

Speaker 3 (18:06):
We are going to talk about the human side of
things in the next episode. I'm not sure that human
sickles is on my outline, but we'll see what I
come up with.

Speaker 1 (18:14):
It is now, because I'm going to ask you about it.

Speaker 3 (18:16):
Okay, great.

Speaker 1 (18:17):
And so a typical strategy is to accelerate on the
first half of the trip and then basically turn your
ship around and decelerate all the way back to your
initial velocity now relative to your destination. And so you
accelerate and you reach top speed momentarily halfway there, and
you turn around and you're slowing down the whole second
half of the trip. And this is actually kind of

(18:38):
cool because along the way you might want to feel
some artificial gravity. As you're probably going to tell us,
humans don't like to float in space forever. It's not
good for us, and so you want to feel one G.
And so having one G of acceleration and then one
G of deceleration the whole trip is actually kind of cozy.

Speaker 3 (18:54):
So if you had one G of acceleration for one year,
you would still have what two or three years just
staying at that velocity before you start decelerating, so there
would be a period where you would have no g's
in between.

Speaker 1 (19:07):
Yeah, absolutely, depending on the length of the trip. If
you wanted to go further. For example, you could accelerate
at one G for a year, get up to near
the speed of light, zoom around super duper fast, and
then flip around and decelerate. So, yeah, you can have
a period in the middle where you're not accelerating or decelerating.
Then you got to solve that gravity problem another way,
all right.

Speaker 3 (19:24):
All right, and we'll talk about that in the next episode.

Speaker 1 (19:26):
And that's not the only thing that's going to potentially
kill you along the way. You know, we think of
space as empty, but it's not really like there's a
lot of particles out there. There's huge amounts of gas
the interstellar medium. There's lots of little bits of tiny rocks.
We call that dust. It's out there, and if you're
traveling at relativistic speeds relative to that dust, you can

(19:46):
be in danger. You know, these tiny particles, A millimeter
sized particle at like even if half of the speed
of light is an enormous amount of energy deposited on
your ship. And so you got to really worry about
this and cosmic rays and radiation, So your ship has
to be pretty robust. You need shielding, you need like
titanium or water or lead or something. All this is

(20:06):
going to make your ship heavier. So we'll dig into
that more in the next episode where we talk about
the fragility of the human body and how to survive this.
But keep that in mind as we're talking about the
propulsion designs, because it's going to affect how much you
got to move on the way to another star.

Speaker 3 (20:20):
So to me, the dust feels like the first showstopper
that we've encountered. What makes us think that, you know,
when each piece of dust hitting us is like getting
hit with a bomb, what makes us think that we
can like, I mean, we're clearly not going to dodge
the dust. So what is the dust solution?

Speaker 1 (20:37):
Well, you know, I've read about some cool shields. There's
like these whipple shields. I basically break up the dust
into smaller pieces so that none of them are likely
to like, really be devastating. There's some cool technology like
self healing shields. So I think it's an engineering problem
and one that we're likely to be able to crack.
But Yeah, it's definitely an important one.

Speaker 3 (20:58):
I love your optimism, Dan, I always love your optimism,
all right, So we're going to be talking about ways
to get there. Are the ways that you're going to
talk to us about ways that could get us there
in a lifetime or is there anything else that might
work for us here?

Speaker 1 (21:13):
Some of these solutions really can get you there in
a lifetime. But because it's physics, time is a slippery concept,
like are we talking about the lifetime for the people
you left behind or lifetime for people on board? Because
as soon as you get up to really high speed
relative to your departure planet, those are not the same thing. So,
for example, say you accelerate at one G and you

(21:34):
get up to near the speed of light, you could
travel for just a few years your time, a decade
your time, and like one hundred thousand years will have
passed back home. And if you're traveling near the speed
of light, one hundred thousand years is enough time to
get you across the galaxy in only like a decade
of your time. So Kelly gets on board the ship.

(21:55):
She arrives at the other side of the Milky Way
that no human has even clearly seen before because all
a gasl and dust and she's only fifty ish. Meanwhile,
back home, Zach is one hundred thousand years old.

Speaker 3 (22:07):
Oh my gosh. And I'm a narcissist. So what I
care about is how long it takes me. When we
say it's gonna take eighty it would take like eighty
years to get there if you went ten percent the
speed of light. Is that that's eighty my years as
a person on the ship, right, So our frame of
reference is always the people on the ship.

Speaker 1 (22:24):
Well, it was gonna take forty years to get there
at ten percent the speed of light in human years,
but at ten percent the speed of light is not
that much of a relativistic time dilation effect. That really
kicks up when you go half or three quarters the
speed of light, So that's still going to be decades
earth time and ship time. If you do get like
up above fifty sixty seventy percent the speed of light,

(22:46):
then you start to benefit from these time dilation effects.
So on the ship it takes less time.

Speaker 3 (22:51):
Got it, Okay? And on the next episode we're going
to talk about generationships where if you just accept it's
not going to happen in a lifetime. Because your technology
can't get you that fast, how do you carry generations
of humans to still get there? But we're going to
take a break now, and when we get back from
the break, Daniel's going to walk us through our rocket
options for our trip to the stars. All right, let's

(23:29):
talk about our transport methods to get us to Alpha Centauri,
starting with the most near term likely technology.

Speaker 1 (23:38):
So we want to get to Alpha Centauri, which means
we've got to move away from Earth, which means we
need to gain momentum away from Earth. In our universe,
momentum is conserved. So you have your ship. You wanted
to gain momentum in one direction, there needs to be
some sort of compensating momentum in the other direction. This
is something you feel if you like fire a gun,

(23:59):
for example, you feel that kickback. That's the conservation of momentum.
The rifle is shooting the bullet super duper fast, but
the bullet has a small mass, and the rifle itself
has that larger mass is moving backwards in the other
direction with the compensating velocity.

Speaker 3 (24:15):
See I always imagine it as I'm trying to get
a boat to move and I'm imagining Daniel on a
cruise ship taking all of the white chocolate and throwing
it in the ocean to get the cruise ship to
move faster while also getting rid of the bad chocolate.

Speaker 1 (24:27):
Yeah, that's exactly right. You need to build momentum in
the other direction. So imagine you are on a boat
and you're tossing stones or equivalently, white chocolate or hot
garbage or whatever useless stuff you happen to have on
the boat. Right, you create momentum in one direction for
the stones, and in recoil you go the other way.
And so all rocket drives operate under this same principle.

(24:51):
You need two things. You need energy and then you
need mass. So you use the energy to throw the
mass out the back and you go the other way.
That's the way all the rockets we're going to talk
about work.

Speaker 3 (25:01):
And that's how like the Falcon nine or starship works
when it takes off too right.

Speaker 1 (25:06):
Yeah, exactly. And the issue here is that you need
something to produce that energy, and you need something to
throw out the back, and when you run out of that,
you can't go anymore. And because you have to bring
that fuel with you, you need enough fuel to push that fuel,
and then you need more fuel to push that fuel.
And so there's this famous rocket equation which tells you
like how much fuel you need to get up to

(25:27):
a certain velocity. It depends on the mass of the
ship and also depends on the specific impulse that your
engine is able to provide. It's just basically just like
a number. Some of them are high, some of them
are low. But the bottom line is that the math
tells us that there's an exponential need for fuel. If
you want to get up to higher velocity. So you
want to go twice as fast, you don't need twice

(25:48):
as much fuel, You need much much more. You need
exponentially more fuel, and as you increase that velocity, the
amount of fuel grows ridiculously. So for example, even like
the Saturn rockets, the ones that took us to the Moon,
when they launched, they were like ninety five percent fuel.
It's mostly fuel being taken off and that fuel is
mostly being used to push the rest of the fuel.

Speaker 3 (26:08):
That absolutely blew my mind when I first learned it
that like less than ten percent of that giant that
you know, that giant tube was actually going to be
going to the Moon.

Speaker 1 (26:17):
And people are often confused about rockets versus escape velocity. Remember,
escape velocity is a calculation you do if you're like
throwing something from the surface of the Earth, you need
a certain velocity because gravity is going to slow you down,
and if you have higher than the escape velocity, you
can leave the orbit. But rockets are not about escape
velocity because rockets have constant thrust. Rockets can lift off

(26:39):
it basically zero points zero zero zero zero zero one
meters per second and still make it to space because
they're pushing themselves constantly. They're like climbing a ladder rather
than just getting a single push. So escape velocity is
not relevant for rockets. What is relevant for rockets is
this specific impulse and how fast you want to go.

Speaker 3 (26:59):
So in this case, the rocket would be not just
getting us off Earth, but it would stay with us
and it would continue to propel us through space.

Speaker 1 (27:05):
Yeah, exactly. And the sort of bog standard rocket we
have is a chemical rocket where the thing that you're
throwing at the back is also the way you're getting energy. Basically,
you have like exploding stones that you're throwing out the back.
The stones throw themselves out the back, right, because the
fuel is the propellant and the source of energy. You
light it on fire and the explosion goes out the back.

(27:27):
You get pushed the other direction, and so that's cool.
And you know, obviously fuel we can find here on Earth,
but the specific impulse of these engines is not huge, right,
So it's not a great way to get going really
really fast unless you have incredible quantities of fuel. So
this is the rocket equation at work here. So if

(27:47):
you do a little calculation, like how much fuel does
it take to get off of Earth and to the
Moon an enormous quantity, right, filling a huge Saturn rocket.
How much fuel does it take to get to Alpha
Centauri if you've got to burn that chemical engine the
whole way, Well, that goes exponential, and the fuel tank
is something like the size of Jupiter.

Speaker 3 (28:07):
What there's a showstopper. Kelly's gonna keep track of these
showstoppers as we go because she's the wet blanket.

Speaker 1 (28:13):
But I'm gonna be optimistic because in the end I'm
really hopeful that we do get to another star, and
we do, or somebody, not me, but some human gets
to go and set their eyes on an alien planet.

Speaker 3 (28:24):
I think we will eventually.

Speaker 1 (28:26):
All Right, you heard it there, folks said it.

Speaker 3 (28:29):
I do, I do, but I'm not gonna put any
money on a date, all right. So when I was
writing a city on Mars, the engineers would get grumpy
with me for occasionally using the words fuel and propellant interchangeably,
which we didn't do in the final manuscript. Nobody needs
to freak out and write me. Now, this was in
an early draft. So, Daniel, what is the difference between
fuel and propellant?

Speaker 1 (28:50):
So, propellant is anything you want to throw out the
back of your rockets, right, and fuel is a special
combination which is both a source of energy and a propellant,
but it doesn't have to be. Another example of a
propellant that separates these things is a nuclear rocket. So
rather than using fuel to explode and create energy and
propellant simultaneously, use something like a nuclear reactor a fission

(29:14):
reactor to produce the energy, which you then use to
throw some inert mass out the back. You heat up
a gas, for example, and it bubbles out the back
of your rocket.

Speaker 6 (29:24):
Chip.

Speaker 1 (29:24):
The fuel there is like uranium which is powering your
nuclear reactor, which is providing the energy to toss the
propellant out the back. The propellant and the fuel are
very separate in this technology, and.

Speaker 3 (29:35):
So with the nuclear rocket, what would the propellant be.
Could it be like anything that you heat up.

Speaker 1 (29:41):
Yeah, it could be anything you can heat up. But
you've got to bring some mass to throw out the back, right, stones,
white chocolate, xenon, whatever, you want. Something pretty inert so
it's not reacting, but you also need to bring enough
of it, and it's going to be dense enough that
it's not going to be huge. And nuclear rockets are
cool because it's something we've actually built. We had an
episode where you and I talked about new clear jet planes,
and it's the same principle, right, A jet engine operates,

(30:04):
and the same principle is very similar to a rocket.
You have the fuel which explodes and pushes something out
the jet airplane, this whole air compression thing. So jets
don't work in space, but you could also have a
nuclear jet engine. We're using a nuclear reactor to heat
the stuff up and shoot it out the back, same
basic principle, and that applies to rockets in space as well.
So in this case, you heat the stuff up and

(30:25):
you shoot the gas at the back, and that could
be a nuclear rocket.

Speaker 3 (30:28):
But we haven't actually sent a nuclear rocket to space, right.
The only kind of rocket we've ever sent to space
is the chemical one.

Speaker 1 (30:34):
That's right. We do have test nuclear engines which people
have built and tested and shown to work, and they
once did fly an airplane with a working nuclear reactor
on board. Scary stuff, but it wasn't actually powering the
plane anyway. This is like a viable technology, not just
science fiction.

Speaker 3 (30:50):
And so you said that for chemical rockets, the container
that would store the fuel would need to be as
big as Jupiter. How big are we working on now?
If it's a new So.

Speaker 1 (31:00):
It doesn't have to be nearly as big because the
fuel is much more dense, right, Uranium incredibly dense compared
to like diesel or even like oxygen or whatever you're
using as fuel, and so that doesn't need to be
nearly as big. But you'd still have to bring the propellant, right,
You still need a lot of stuff to throw out
the back. So we're not talking about the massa jubutter,

(31:21):
but we're still talking a very very large ship with
a huge amount of propellant. Now, there's some folks that
have ideas for like gathering propellant along the way that
dust you talked about, or the interstellar medium that's stuff, right,
you could use that as propellant. So there are technologies
like ramjets or buzzard jets that people talk about where
you have like a scoop that gathers propellant up and

(31:42):
then your engine whatever you're using, a nuclear reactor or
something else, for example, is throwing that out the back.
And so there are ways to avoid like having to
have a cataclysmically large ship in that way. Though there
are also a lot of people who think that those
ramjets and bussard jets are totally impractical for other reasons.
Same enough said.

Speaker 3 (32:05):
What if the thing that you're throwing out the back
of your rocket is nuclear bombs? Cause why not?

Speaker 10 (32:14):
Right?

Speaker 1 (32:16):
Why now? This is actually not a terrible idea in
some ways because it separates the ship from the propulsion
in a way that we'll talk about for solar sales.
If you could blow up a series of nuclear weapons
between here and Alpha Centauri, and you had a ship
with like a huge shield in the back that could
absorb all the radiation and the energy that was dumped

(32:36):
out by the nuclear bombs. Then you could just sort
of like ride this wave of nuclear explosions all the
way to Alpha Centauri. And you know, this is the
basis of Project Orion. And then later Project Data lists
the idea having like a series of small bombs providing
like this smooth acceleration. Now you know, how do you
get those bombs? How do you lay a trail of

(32:57):
bombs from here to the next star. It was more
about like near Earth navigation or getting things off planet
than like actually going from star to star. But we
can't not talk about blowing up nuclear bombs as a
way to propel a ship. It's just got to be
in the conversation.

Speaker 3 (33:13):
Project Datalus had a follow up project called Project Icarus
because Icarus was Datalus's son. But Icris is the one
who flew too close to the Sun and his wings
melted and he fell down and died. And I always
remember feeling like, isn't this supposed to be inspirational and like?
But but I was told I just wasn't looking at
it the right way. And again, this is why I

(33:33):
don't get invited to the space parties.

Speaker 1 (33:35):
Do you think it's hard to sign up test pilots
for Project Icarus.

Speaker 3 (33:39):
It could be, but again, I bet somebody would show
would sign up. There's a lot of people who are
much braver than I.

Speaker 1 (33:45):
Am looking for volunteers for a project Crash and Burn. Anybody, anybody, nobody,
Probably a lot. Anyway, that's a cool technology, and the
cool thing there is if you could somehow manage it.
It separates the ship from the source of energy, right,
and also from the propellant, and so the ship itself
doesn't have to be very big. Of course, that's sort

(34:06):
of assuming a solution to the core problem, which is
how to get all these nuclear bombs from here to
Alpha Centauri, which is basically impossible.

Speaker 3 (34:13):
What do you think the aliens would think as we
were like leaving a trail of nuclear explosions on our
way to their galaxy? Do you think they'd be like, Wow,
they've really conquered technology. Or do you think they'd be like,
oh my gosh, how do we get them to turn around?

Speaker 2 (34:26):
Yeah?

Speaker 1 (34:27):
I can't wait for them to show up, right. I
think it's cool because we can imagine how we might
detect aliens doing the same, Right, Like, if aliens have
come up with this idea, and they're using it around
their star. We might be able to detect it if
they're close enough, So that's pretty cool. But yeah, I
don't think it'd be a great way to announce our
presence to the universe.

Speaker 3 (34:45):
They would definitely have time to set up the welcome
party or the go home party.

Speaker 1 (34:50):
But along these lines, there's lots of permutations on this
kind of propulsion once you separate the explosions from the propellant. So,
for example, there are other ways to accelerate stuff, Like
you could have an electric field and you have ions.
An electric field will push ions, that's what it does,
and so if you had like an electric field and
a bunch of ionized propellant, you could shoot that out

(35:12):
the back. Basically, we're talking about a particle accelerator. That's
exactly what a particle accelerator like the large hadron collider does.
It pushes particles with electric fields and makes them go
really really fast. So build a particle accelerator, point it
out the back of your ship. That's going to give
you some impulse.

Speaker 3 (35:29):
This seems like another very large design, right How big
would your particle accelerator need to be?

Speaker 1 (35:34):
Well, not that big. Actually, and it's cool because it
separates the two systems, and so your power source can
be anything. It could be solar power, it could be
some other crazy system that doesn't necessarily have to be
super duper big. In this case, it's nice because it
doesn't even have to generate a lot of heat, right,
and so for those hand wringers aboard, you don't have
to worry about it like melting down or something like that.

(35:56):
The downside to this is that the thrust is really
tiny accelerating particles and particles don't have a lot of mass,
and they sort of limit to how many particles you
can effectively shoot out the back, and so it can
provide very long term gentle thrust, which is nice for
constant acceleration, but it can't really give you a lot

(36:16):
of specific impulse, and so it's not a great way
to like get up to a high speed in a
short amount of time. But it's cool for like navigating
around space a little bit.

Speaker 3 (36:26):
So this could be like a generation ship thing. And
so can you remember what the difference is between thrust
and specific impulse.

Speaker 1 (36:33):
They're basically the same thrust a specific impulse times the
constant of gravity, but you can think of them as interchangeable.
They're just different by units essentially.

Speaker 3 (36:40):
All Right, we're going to take a break now, and
when we come back, we're going to talk about using
anti matter to get you to the stars. All right,

(37:05):
So we just finished talking about ion drives as a
way to get you to the stars, and I see
that next we're going to talk about antimatter, and I
am immediately thinking that dangerous explosions are maybe not what
I want happening, you know, on the ship that I'm
living on. But why is Kelly being a wimp?

Speaker 1 (37:23):
No, Kelly is not being a wimp. We are steadily
moving from reliable technologies we know can work and probably
won't kill you, to crazy ideas that might not ever
work and are much more likely to kill anybody on board.

Speaker 3 (37:37):
O good, all right.

Speaker 1 (37:40):
But antimatter is cool because it's the most efficient way
to store energy. Like matter, and antimatter annihilation is perfect
conversion of matter into energy. Compare that to for example,
chemical fuel. Right, chemical fuel has a lot of energy
in it, but when you burn it, you only release
a little bit of that energy from the chemical bonds.
But inside those protons and inside those electrons is an

(38:02):
enormous amount of stored energy, which we call mass. If
you could capture all that will release all of that,
you would need to bring less fuel, right, and so
matter antimatter annihilation is the best way to do that.
You have protons and anti protons. They turn directly into
photons which you can shoot out the back of your ship.
And that's awesome because the propellant there is moving at
the speed of light, right, so like you can't be

(38:24):
that for maximum thrust and impulse. So far this sounds
great now. The downsides are, of course, Kelly worries about
being annihilated herself because antimatter is pretty dangerous stuff. Yeah,
so you need some sort of magnetic confinement for antimatter,
basically a bottle that doesn't touch it. You know, a
bottle made of matter that builds a magnetic field that

(38:45):
confines it, sort of the way we do for plasmas
in Tokomax infusion reactors. That's not totally implausible, But then again,
you basically have a bomb on board and any loss
of containment and everybody's dead, yeah before you can do anything.
So that's bad. But on the flip side, antimatter is
basically impossible to make in large enough quantities, so you're
pretty much safe. You know, we make antimatter. We made

(39:08):
it for the previous collider. We used to have the Tevatron,
which was a proton anti proton machine, and we produced
antimatter at the Large Hadron Collider all the time in collisions,
so it's not actually that exotic. It's made in the atmosphere,
like cosmic rays hit the atmosphere turn into a antimatter briefly.
But the quantities we're talking about are like nanograms of antimatter.

(39:29):
You know, we can like count the atoms of antimatter
we make. There's no large scale production of antimatter in
order to make enough fuel to get anybody near Alpha Centauri.
I read one estimate that said making one hundred milligrams
of antimatter would cost about one hundred trillion dollars.

Speaker 3 (39:46):
Oh my gosh. All right, so I'm curious since we're
starting to get towards the really crazy ones. Out of
the technologies we've talked about so far, if you had
to go to Alpha Centauri, which one of these would
you want to use?

Speaker 1 (39:58):
Probably none of these? Okay, my favorite is one we
haven't talked about yet it's a little bit ridiculous and speculative,
but it's still my favorite.

Speaker 3 (40:08):
All right, let's keep going. Then, what's next next?

Speaker 1 (40:11):
I want to talk about a nonsense idea which is
out there people are probably imagining might save the day,
and that's propulsion list drives. People have been thinking, okay, well,
conservation of momentum requires we throw something out the back.
We're tossing stones or white chocolate out the back of
our spaceboat to get it moving. That's frustrating that it
limits us, right because you've got to bring all this

(40:31):
stuff to throw out the back. Wouldn't it be amazing
if we could generate a drive which didn't need that, Yeah,
that would be amazing and also violate conservation of momentum.
But that has to stop people from trying and go
for it. Guys, like it wouldn't be the first time
that we discovered and sit you something that revealed we
didn't understand the universe. So I'm all in favor of
people doing crazy experiments.

Speaker 3 (40:52):
That's just like a Friday in physics, right where you
discover you were wrong about something.

Speaker 1 (40:56):
Yeah, those are the best moments in physics, So nobody
should be limited by like conventional wisdom about what's possible
or impossible, but we should also be clear eyed about
what we have actually proven. And there are folks out
there who claim to have built one of these things.
It's called an em drive, and about fifteen years ago
there was a lot of hoopla about it. There's a
lot of coverage and the New Scientist. But these folks

(41:18):
who had some like tenuous NASA affiliation, who claim to
have built the impossible space drive, And if you look
for articles, you'll see them there in Popular Mechanics, they're
and wired, they're in the New Scientist. But the journalists
here really didn't do their work, Like if you look
carefully at the claims, you see that the thrust that
these things produce is really really tiny. It's basically smaller

(41:40):
than the uncertainties, you know, like they just have jitter
in their measurements that have sources of noise and they
measure a thrust, but the thrust is consistent with zero
within errors. So while I'm all for crazy new technologies
and exploding understanding the universe, the EM drive is not
something that's done that. These are fascinating ideas, and there's

(42:00):
not nothing to support the concepts. One idea is that
there's a vacuum in space, and that vacuum has energy
to it, and experiments like the Casimir effects show us
that the vacuum is real and it's there, and people
wonder if we can extract energy from the vacuum and
use it to propel ourselves. But you know, the vacuum
is special. You can't like row against the vacuum. You
can't like absorb momentum or get momentum. It's emotional the

(42:23):
way space is. For example, you can't like put an
ore down and row through space in the same way.
And this is part of space. So anyway, em drives
not something we can rely on and not something I
would bet on. But hey, if you're out there and
you're building em drive, I hope you make it work.

Speaker 3 (42:39):
Fingers crossed, all right? So I have heard proposals where
you know, the Sun is shooting out photons all the time.
What if you could capture those photons and let the
Sun sort of push you forward? How would that work?

Speaker 1 (42:52):
This is my favorite idea because it separates the ship
from the propulsion completely, right. So this is called a
solar sale, and the idea is that you're right. The
sun is putting out photons, and not just photons but
other particles. The solar wind has momentum, So why like
generate momentum if we have an enormous momentum generating machine already,

(43:15):
and so all you need to do to capture that
momentum is build a huge sail. So you know, when
you're on a sailboat, a sail is just a piece
of cloth that gathers that momentum. Here, the best kind
of sale would be something very thin, so low mass
and reflective. And imagine a photon hits the sail, it
bounces off the same way a photon hits a mirror
and bounces off. Right, what happens, Well, the photon is

(43:37):
now changing its momentum. It's going one way. Now it's
going the other way. Conservation momentum says that can't happen
unless something is going the opposite direction. Right, something is
now going the way the photon originally was to conserve momentum,
and that's the sail. This is a confusing concept for
people because it's hard to imagine like light pushing something
because light has no mass, and you're probably thinking, well,

(43:59):
momentum is mass times velocity, and photons have no mass,
so therefore they have no momentum. Right, Yeah, wrong, And
the reason is that momentum is mass times velocity only
for very slow stuff. As you approach the speed of light,
the equation changes a little bit. So photons do in
fact have a momentum even though they have no mass.
So yeah, their momentum can push along a sail. So

(44:22):
imagine a tiny little ship with an enormous sail and
the photons are bouncing off of it and giving it
a push. Basically, you don't need an engine.

Speaker 3 (44:30):
So one of the things that always sounded limiting to
me with this method is that it seems like it
would work great when you're close to the sun. But
the farther you get from the Sun, the fewer photons
are going to be hitting your sail. How would this
work when you get too far away from the sun.

Speaker 1 (44:45):
Yeah, this is tricky. As you say, you get further
from the Sun, the photon density drops by one over
are squared. That's bad. So this is a good idea
for moving around the Solar system, like navigating from here
to Mercury or here to Neptune. A very light without
fuel would be awesome. Getting from here to another star
would be hard. And what you need to do is

(45:06):
build an enormous laser. Like think about a really big laser,
now make it ten times bigger. That's too small. You
need an enormous laser, right, really huge laser, or like
a big laser array that I'll focus their energy on
this sale. But the cool thing is, again, you can
build this on Earth, or you can have it in

(45:26):
space or something. You don't need to bring it with you,
and you can point it at your ship and push
it to another star. So it's not a solar sale anymore.
It's like a photonic sail.

Speaker 3 (45:37):
And I can't imagine that a laser of that size
is going to cause any geopolitical conflict at all. A
weapon of that magnitude.

Speaker 1 (45:48):
Yeah, we're building the Death Star basically for good reasons
to go to space. We're just making space smores. What's
the big deal, right, But there's a project to do this.
It's called Breakthrough Star Shot and they want to take
a bunch of nanocraft like tiny little devices, and they
want to build ground based lasers and send those devices

(46:08):
to Alpha Centauri. Now you push these tiny little devices
long enough you can get them up to like twenty
percent of the speed of light. And so you do
the math and these things. They're estimating to launch them
in like twenty thirty ish twenty thirty five, they would
take about twenty years. They'd be there about like twenty
fifty five. So if I'm lucky, i'd be around when

(46:29):
the signal comes back, you know, from Alpha Centauri. This
is something that really could happen, which is why I
think it's my favorite technology. The challenge, of course, is
getting a big enough sale to push a ship with
people on it. You know, so far we're just talking
about sending tiny nano robots. But you know, if I
want to go there, you got to bring me and
my toilet, my bed, you know, all sorts of stuff

(46:51):
needs to go with me. So we're not talking nano
ships anymore. So we're talking enormous sales, and we really
need like better technology for enormous sales that are going
to somehow survive the interstellar trip those micro meteorites tearing
it apart. So you know, there's potential there, but there's
a lot of engineering challenges to solve.

Speaker 3 (47:10):
Yeah, this is a cool technology. Are the are the
little nanoships that break through starshot is sending Are they
going to have like cameras and scientific instruments on them
or are they just able to say we're here and
that's it TBD.

Speaker 1 (47:22):
But I hope they're gonna put some cameras on there.
I mean to be amazingly ridiculous to get something all
the way there and take no data, right.

Speaker 3 (47:29):
Yeah, that would be a major bummer. We haven't talked
yet about a method to me that seems perhaps likely
something that we have some experience with, which is gravity slingshots,
which which we're used in Aurora Kim Stanley Robinson's book
to slow down on the way back to Earth. Is
that something that we could use to speed up to
get there?

Speaker 1 (47:46):
Absolutely, Gravitational slingshots are amazing. You know, you whiz near
a planet basically steal a little bit of its speed.
We should dig into the physics of that in a
whole episode because there's some subtleties there about like why
you end up with a little bit of speed, And
the short version of it is that you slow down
the planet's rotation around the star, which is really cool,
and we've done this. You know, Voyager one, for example,

(48:08):
one of our only interstellar probes. It's swung around the Sun,
but it's not going that fast. You know, it's traveling
like a light year in about eighteen thousand years. So
you can't get going to like interstellar speeds unless you're
getting crazy close to the star, and that's got its
own dangers. So gravitational slingshots are a good way to
boost your speed and to get going, but on their

(48:29):
own they're not going to provide the speed that you
need to get to another star.

Speaker 3 (48:32):
Got it all right, So let's wrap things up on
the most sci fi methods. So what can we do
to can we like bend space or time to make
this happen?

Speaker 1 (48:43):
Yeah, so far we're considering flat space. We're imagining you know,
light is going to take a few years to get there.
What can we do to approach the speed of light?
But of course we know that space is not just flat.
Space bends, it curves, and in the presence of mass,
it can do all sorts of things. They can wiggle,
not something we fully understand, but you know, we know
that this kind of thing is possible, and so in
the last few years or so, people have been thinking about, like,

(49:05):
could we actually build a warp drive. This would be
something that bends space so that effectively the journey is shorter.
And that's really what space curvature means, that you're changing
the relative distance between two points. So hey, why not
make Alpha centaur really really close so that doesn't take
as long to get there. And that's the idea of
a warp bubble that you like, shrink the space between

(49:25):
you and the star and expand the space behind you.
And then when you get there, you pop out of
this warp bubble and you're like, hey, that wasn't a
big deal.

Speaker 3 (49:32):
How likely is it that these warp bubbles actually exist
or could be created?

Speaker 1 (49:37):
That's a topic of hot debate. On the positive side,
there's a guy who's figured out that warp bubbles do
not violate general relativity, meaning like a warp bubble doesn't
break any of those rules. That doesn't mean that a
warp bubble could actually exist in the universe because you
create something because it's allowed in the universe. Like everybody
knows chocolatesou fleas are allowed in the universe, Does I

(50:00):
mean everybody knows how to make them? You have to
have a very delicate process to get from no chocolate
sooufle to chocolates sooufle, right, and there's lots of ways
to fail. We don't have a recipe for building a
warp drive, but just know that the resulting drive is
not disallowed by general relativity. It could be that some
step between no warp drive and warp drive is disallowed
or is impossible. And so if you could just like

(50:22):
magically pop a warp drive into existence, then physics is
cool with it. But we don't know if it's possible
to create one in our universe.

Speaker 3 (50:31):
All right, Well, I'm going to hope that it is,
because that would make things really convenient. At the beginning
of the show, you mentioned that in your favorite book
they just moved stars closer together. How would that work?
And why would everyone be dead?

Speaker 1 (50:47):
This is basically like the think big version of the
solar sale. Right. In this version, you build a huge
sale like half the size of the sun. Yeah, that's right,
half the size of the sun. Wow, wrap half of
the sun a big mirror that points back at the Sun. Okay,
And so you might think, well, what's gonna happen? That
mirror is just gonna shoot off it's a big solar sale.

(51:08):
It gets pushed away by the Sun. Right, Well, you
bring it close to enough and you make it massive
enough that it's gravitationally captured by the Sun. So now
basically the mirror and the Sun are like a single
gravitational object. The Sun is shooting half of its photons
to the mirror, but they get bounced back so basically recaptured.
On the other side, the Sun is shooting off its
photons out into space. So now it's like an ion drive.

(51:32):
So one half of the Sun is basically captured and nullified,
the other half is not. Now the Sun can move right.
The Sun is basically like a rocket, and so this
could move the whole Solar system. And Kelly should feel
great about this because you could travel to another star
without even leaving your house. You could like literally sleep

(51:53):
in your bed at home and we could go visit
Alpha Centauri move the whole Solar system.

Speaker 3 (51:58):
Okay, all right, so that sounds awesome. I love that
you dream big. But like, so you know we've talked before,
if like suns get too close to each other, one
of them gets like thrown off into the vastness of space.
This feels like a high risk method.

Speaker 1 (52:13):
Well, it's hard to turn a star, you know, if
you realize you're going in the wrong direction. This is
harder to turn than like one of those U hauls
that are already pretty hard to turn. Yeah, there's a
lot of ways this could go wrong. You know, maybe
a safer method is to use a black hole instead, because.

Speaker 3 (52:30):
Black holes, You physicists, wouldn't it be safer if we
used a black hole?

Speaker 1 (52:37):
I like, you just laugh in my face at that one.

Speaker 3 (52:39):
I'm sorry.

Speaker 1 (52:40):
I mean a black hole also converts mass into energy. Right,
black holes evaporate, they have energy stored inside them because
of their mass, but they generate Hawking radiation, which is energy.
So put a black hole next to a mirror and
in the same way, it will generate propulsion in one direction,
right if it's gravitationally captured the mirror, and so that's
absorbing that radiation. Now you have a black hole which

(53:03):
is turning its mass into radiation and pushing your ship
so you don't have to move a whole star. Now
you have a black hole power and spaceship. And of
course there's technical problems here, like how do you actually
make the black hole? We don't know how to do that.
Maybe you could find a black hole. We don't know
where any of them are. Also, there are some risks
involved in having a black hole on board your ship.

(53:23):
Please sign these waivers, all.

Speaker 3 (53:27):
Right, So I'm going to ask myself the question, which
one of those methods do I think I would use
if I was forced to go on a ship to
Alpha Centauri. I think that I would agree with you
about the solar sale technique. But what would make me
nervous is that somebody else is in control of the
propulsion and so like, I imagine that keeping a giant

(53:48):
laser constantly powered has got to take a lot of energy.
And so what if one day, you know, the Americans
are like, you know what, We're not powering this laser anymore.
It's just too expensive. And then what do you do?

Speaker 1 (54:00):
Yeah, well there's not much you can do.

Speaker 4 (54:02):
You know.

Speaker 1 (54:03):
The other issue with a solar sale is slowing down.
Like it gets you up to near the speed of
light using that big laser, then you have to use
the destination sun to slow down, but it is no
laser there to give you that boost, and so you
got to like combine that with gravitational sling shots. It's tricky. Yeah,
there's no way I'm getting on any of these ships ever,

(54:25):
But I encourage all of you to, like, please go
explore the universe and tell us all about it.

Speaker 3 (54:30):
Send me a postcard.

Speaker 1 (54:32):
All right. So, I think we surveyed some of the
technologies that might get us to other stars, and my
take is that there's some promise here. Obviously there are
kinks to be worked out, and Kelly and her legal
team need to be put at ease about the black
hole on board, you know, or moving the entire sun.
Do we need to take a vote before we do that.
I'm not sure, But to me, these feel like solvable problems.

(54:54):
And you know, we're young as a species technologically. In
one hundred years and a thousand years will good this out,
and maybe even by then somebody will have built an
em drive.

Speaker 3 (55:03):
Well, And to surprise everybody, I am actually optimistic about
some of this stuff, and I feel like these are
really interesting problems that we have to solve, and imagine
the other things that we're gonna learn along the way,
where the new technologies will come up with as we
try to make some of these methods work. I think
it's all very.

Speaker 1 (55:19):
Exciting, all right, But before you get too excited, next episode,
we're gonna talk about all the other tricky problems you
would have to solve to get humans to another solar system,
giving birth on board? Is it okay to have children
born between planets? Embryos, robots, cryogenics, radiation, all that good stuff.
So tune in next time for Kelly to throw a
wet blanket on your interstellar dreams.

Speaker 3 (55:40):
That's what I do, so well out, all right.

Speaker 1 (55:47):
Tune in next time everyone.

Speaker 3 (55:55):
Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
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Speaker 1 (56:01):
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