Speaker 1: We know so much more about the universe than our
Speaker 1: ancestors did. Go far enough back, and they didn't even
Speaker 1: know that the pinpricks of light they see in the
Speaker 1: sky are other suns. A few thousand years ago, they
Speaker 1: had no idea how far away those other stars were,
Speaker 1: and a few decades ago nobody knew for sure whether
Speaker 1: they were planets around those stars. We know so much
Speaker 1: more than they do, But we've also visited exactly the
Speaker 1: same number of solar systems as they have, just the one.
Speaker 1: Will we ever get out of our solar system and
Speaker 1: make a home for humanity around an alien star? Is
Speaker 1: there a physics obstacle? Or is it just political will
Speaker 1: or lots of engineering. If it's actually impossible, that might
Speaker 1: explain another great mystery why no aliens have visited us.
Speaker 1: Maybe we aren't alone in being marooned on our home stars.
Speaker 1: Maybe everyone is just stuck at home. Today on the pod,
Speaker 1: we'll dive into the challenges, the technologies, and the potential
Speaker 1: for taking humanity to those distant stars. Welcome to Daniel
Speaker 1: and Kelly's Extraordinary Accessible Universe.
Speaker 2: Hello.
Speaker 3: I'm Kelly Winer Smith. I study parasites and space, and
Speaker 3: if I could travel to the next nearest star, I wouldn't.
Speaker 1: What about you, Daniel, Hi, I'm Daniel. I'm a particle physicist,
Speaker 1: and I want to send somebody to the nearest star,
Speaker 1: but I definitely don't want to go myself.
Speaker 3: So why would you not want to go yourself? Can
Speaker 3: you imagine all the physics stuff you could ponder and
Speaker 3: maybe even figure out on an interstellar trip.
Speaker 1: Oh yeah, I'd be desperate to talk to the aliens
Speaker 1: about physics, to see what kind of weird technology they've invented.
Speaker 1: But I'm just not that much of a traveler these Honestly,
Speaker 1: I don't even like to get on an airplane, So
Speaker 1: a spaceship absolutely not. The seeds you're gonna be uncomfortable
Speaker 1: and the snacks are gonna be weird. You know, I'm
Speaker 1: a homebody these days.
Speaker 3: But you were born in one country, lived in another country,
Speaker 3: and had kids in a third country.
Speaker 4: Right.
Speaker 3: You used to be an amazing traveler, but now it's home.
Speaker 1: Huh time marches on? Absolutely? Yes, I can no longer
Speaker 1: sleep anywhere anytime. My stomach is more sensitive. You know,
Speaker 1: youth is wasted on the young.
Speaker 3: Well, it sounds like you made good use of your
Speaker 3: youth traveling all those places.
Speaker 1: How about you, Why don't you want to go to
Speaker 1: another planet.
Speaker 3: If we ended up in another planet and there was
Speaker 3: life there, that would be incredible. But I feel like
Speaker 3: you don't necessarily know what you're gonna get until you
Speaker 3: get there. But the thought of leaving, Like, so it's
Speaker 3: spring while we're recording, which means in the next couple
Speaker 3: weeks on the side of my barn, the light that's
Speaker 3: on outside is going to attract little tree frogs and
Speaker 3: all kinds of colorful moths. I just can't imagine leaving
Speaker 3: this planet and leaving all that stuff behind to spend
Speaker 3: like decades traveling in a tin can. But maybe they'd
Speaker 3: have even better moths, and then I would feel regret.
Speaker 1: It'd be amazing, though, if we got to that planet
Speaker 1: and then we're like, this place is kind of ugly,
Speaker 1: you know. I wonder if, like every planet has its
Speaker 1: own beauty, or if our evolutionary history on Earth primes
Speaker 1: us to only find, you know, the Sierras and the
Speaker 1: Blue Ridge Mountains beautiful. See how I included Virginia.
Speaker 3: I appreciate that. Yeah, No, we're being nice to each
Speaker 3: other on this episode. I guess that's great. I also
Speaker 3: it would really stink to know that you were never
Speaker 3: going to see any anybody else that you had known
Speaker 3: your whole life ever again. And like the farther away
Speaker 3: you get, the harder it is to communicate. But so
Speaker 3: let's dig into the to the meat of our discussion today,
Speaker 3: and we're talking about is it possible for humans to
Speaker 3: travel to other stars?
Speaker 1: Yeah? And I think this question is interesting and important
Speaker 1: because while we want to explore the universe robotically and
Speaker 1: gather information telescopically, I think also we have a primal
Speaker 1: need to explore, to go places, and to expand out
Speaker 1: into the universe. I think it's a question a lot
Speaker 1: of people have about whether it's possible today, whether it
Speaker 1: might be possible in a thousand years, or whether it
Speaker 1: might never be possible for humans to cross the vast
Speaker 1: oceans of space to other stars. So I went out
Speaker 1: and I asked our listeners if they thought it was possible.
Speaker 1: If you would like to play for this part of
Speaker 1: the podcast in the future, please don't be shy. Write
Speaker 1: to us at questions at Danielankelly dot org. We would
Speaker 1: love to have your voice on the pod. So think
Speaker 1: about it for a minute. Do you think it's possible
Speaker 1: for humans to travel to other stars? Here's what our
Speaker 1: audience had to say.
Speaker 5: We can imagine traveling to other solar systems, but can
Speaker 5: we deal with all the questions radiation, food, power sources, generationships.
Speaker 5: We just don't know enough at this point.
Speaker 1: I would say no for the foreseeable future, but in
Speaker 1: multiple generations, after multiple generations, I think that would be possible.
Speaker 1: What it would take thousand of years and the ship
Speaker 1: would have to survive. You'd go through accidents, there would
Speaker 1: be warring factions on the ship. You need a multi
Speaker 1: generational ship.
Speaker 6: Well, I'd say it's possible, but not probable within the
Speaker 6: next one hundred years. There are a lot of hurdles
Speaker 6: to overcome, propulsion being a major one in supplies. Maybe
Speaker 6: if you had a fusion powered plasma or something.
Speaker 7: I bet we could get a human being there in
Speaker 7: their lifetime with acceleration that won't kill them, But I
Speaker 7: think stopping will be really hard and definitely turning around
Speaker 7: will be nearly impossible, so they can't come back.
Speaker 4: Humans don't have enough time to live, and our bodies
Speaker 4: would be destroyed by the acceleration required to reach another
Speaker 4: solar system.
Speaker 1: With today's technology. I don't believe it is strictly possible.
Speaker 1: I think it's definitely possible. There's no law that says
Speaker 1: we couldn't do it. There's still some major challenges ahead
Speaker 1: of us. Anything is possible, but humans traveling to another
Speaker 1: solar system may be a stretch. Now it is impossible.
Speaker 5: I don't think a single person could make it to
Speaker 5: another solar system, but maybe multiple generations.
Speaker 8: Even if you could travel at the speed of light,
Speaker 8: it would still take years to get to the nearest star,
Speaker 8: which we don't even know if there's a solar system around,
Speaker 8: and you'd have to confirm that first. Even if we
Speaker 8: could technology got better, we'd still probably need a generational
Speaker 8: star here.
Speaker 9: Unless we destroy ourselves with war or refusal to confront
Speaker 9: climate change. We will eventually reach other solar systems.
Speaker 10: Maybe if money isn't a problem in the future, if
Speaker 10: we tackles certain things, maybe we could. But I think
Speaker 10: it's for now the ultimate pipe dream.
Speaker 2: Yes it is possible, but whether it is probable is
Speaker 2: a different question. And even if it is probable, and
Speaker 2: even if it's undertaken, I don't think that the humans
Speaker 2: who would leave our solar system to get to the
Speaker 2: other solar system would be alive. When we get to
Speaker 2: the other.
Speaker 1: Solar system, we should assume that the aliens at the
Speaker 1: solar systems will be hostile, and therefore we should send
Speaker 1: all the people that we dislike the most.
Speaker 3: Maybe through like a cryo sleep or human hibernation type thing,
Speaker 3: something like that.
Speaker 9: I believe we are marooned here.
Speaker 3: No, we can't do that right now, but maybe some
Speaker 3: day in the future.
Speaker 8: From a physical point yes, From engineering point likely no.
Speaker 3: I loved the variability of answers that we got here,
Speaker 3: and I should say that as someone who interacts with
Speaker 3: the space settlement community, I have no doubt that even
Speaker 3: if somebody were to say, like, we've made a generationship,
Speaker 3: there's a one percent chance it's going to make it.
Speaker 3: Every seat on that ship would get filled. So, you know,
Speaker 3: I think there's a lot of people who really love
Speaker 3: this idea.
Speaker 1: Well, why do you think we would have no shortage
Speaker 1: of volunteers? You think there are people who, like in reality,
Speaker 1: would actually sign up to go. They're not just like
Speaker 1: excited about the concept.
Speaker 3: Oh my gosh, they send me angry emails. There have
Speaker 3: been so many people who have written me to tell
Speaker 3: me that I cannot stop them from settling space, and
Speaker 3: I write them back and I say, I cannot stop you.
Speaker 3: That's right, And I'm not crying too. I don't think
Speaker 3: I have any power over these kinds of decisions. I
Speaker 3: just wrote a book saying it's kind of dangerous.
Speaker 1: And maybe we should think this all through before we go.
Speaker 3: But hey, do what you want, Yep, yep, do your things.
Speaker 3: So anyway, I'm sure there'd be a lot of people,
Speaker 3: and you know, it would be an absolutely incredible thing
Speaker 3: if our species did send a generationship, for example, to
Speaker 3: another star.
Speaker 1: It would be incredible. And I love how this topic
Speaker 1: is so deeply inspired and informed by science fiction. You know,
Speaker 1: obviously there's science here, and we're going to talk about
Speaker 1: all the nerdy details of propulsion mechanisms, et cetera. But
Speaker 1: so many the ideas here come from the creativity of
Speaker 1: science fiction authors casting their minds forward to imagine what
Speaker 1: we might be able to build, what we might need
Speaker 1: to build, what we might have to do to survive.
Speaker 3: Yeah, what is your favorite interstellar travel sci fi book?
Speaker 6: Oh?
Speaker 1: Wow, such a good question. One of my favorites is
Speaker 1: a book by Alistair Reynolds. I think it's called the
Speaker 1: House of Suns, in which they tackle this problem by
Speaker 1: dragging stars closer to each other. So they want to
Speaker 1: have like a galactic empire across many solar systems, but
Speaker 1: they don't have faster than light travel, and they recognize
Speaker 1: that it's basically impossible to govern somebody if you're there
Speaker 1: so far away, So they bring a bunch of suns
Speaker 1: closer to each other, make a little solar neighborhood, so
Speaker 1: you can have different solar systems but they're not so
Speaker 1: far away.
Speaker 3: I like that idea, but it sounds kind of dangerous.
Speaker 1: Well, we're going to talk about that technology, which isn't
Speaker 1: as far fetched as you might imagine at the end
Speaker 1: of the episode.
Speaker 3: So let's go ahead and dig right in. But first,
Speaker 3: let's talk about where would we be going. Where is
Speaker 3: our closest option here?
Speaker 1: Yes, so the Milky Way galaxy has hundreds of billions
Speaker 1: of stars, but the whole thing is like one hundred
Speaker 1: thousand light years across, which is really big, and the
Speaker 1: density of stars in our neighborhood is not so high.
Speaker 1: It actually varies a lot. In the center of the
Speaker 1: Milky Way. It's much much denser. But around where we are,
Speaker 1: we're like in the suburbs, not quite the ex serbs,
Speaker 1: in the very fringes of the Milky Way. But out
Speaker 1: here in the suburbs, you can expect to find a
Speaker 1: star a few light years away, and that's what we find.
Speaker 1: Alpha Centauri and Proxima Centari are like just around four
Speaker 1: light years away. So if you wanted to get to
Speaker 1: the nearest star uneasy mode, you'd be going to the
Speaker 1: closest one. It's still four light years away. And remember
Speaker 1: the speed of light, super duper fast. If you shined
Speaker 1: a laser beam at one of these stars, it'd be
Speaker 1: zipping through the cosmos at an incredible speed for four
Speaker 1: full years before it got there.
Speaker 3: And so say you get to Alpha Centauri, do we
Speaker 3: know that there are earth like planets there that we
Speaker 3: could try to explore? What would we see once we
Speaker 3: got there?
Speaker 1: Yeah, there's actually good news there. You know, until like
Speaker 1: twenty ish years ago, we had no idea what planets
Speaker 1: were like around other stars, or if there even were any.
Speaker 1: We'd only ever seen the planets in our Solar system
Speaker 1: until the mid nineties, when we started developing the technology
Speaker 1: to see exoplanets. Now we specifically identified five thousand exo planets.
Speaker 1: At least the number keeps going up and up and
Speaker 1: up and up. It's like a real pivot point in
Speaker 1: human history. And because of that we can make all
Speaker 1: sorts of really interesting statistical statements, like, on average, stars
Speaker 1: have a good number of planets, and specifically Proximusentari and
Speaker 1: Alpha Centauri do have some planets, and so it's very
Speaker 1: unusual actually for stars to have no planets as far
Speaker 1: as we can tell. So if you're going to go
Speaker 1: to a nearby star, it's very likely you'll find some
Speaker 1: planets there. Whether they're Earth like and whether they are
Speaker 1: capable of supporting life a whole other question that we
Speaker 1: think the next generation of space telescopes will really help
Speaker 1: us crack. But from the point of view today's conversation,
Speaker 1: let's just imagine getting to that Solar system, not necessarily
Speaker 1: finding a cozy how there.
Speaker 3: Okay, so let's see I'm forty two. Now, if I
Speaker 3: were going to jump on one of these ships, and
Speaker 3: I was hoping that we would arrive by you know,
Speaker 3: the average lifespan of a human woman, So what that's
Speaker 3: like eighty six or something like that. So we've got
Speaker 3: let's say we've got about forty years to get there.
Speaker 3: How fast do we need to go?
Speaker 1: Yeah, so if you traveled at the speed of light,
Speaker 1: you get there in four years. Of course, you can't
Speaker 1: travel at the speed of light because nothing that has
Speaker 1: mask can travel at the speed of light. So let's
Speaker 1: say you could go at ten percent of the speed
Speaker 1: of light already blazingly fast, much much faster than any
Speaker 1: human ship has achieved crude or uncrued. But if you
Speaker 1: did somehow manage that, you would get to altha centauri
Speaker 1: in about forty years, right, a tenth of the speed
Speaker 1: of light four light years, so forty years. So that's
Speaker 1: basically what you need to achieve. But the sort of
Speaker 1: space technology we have now really just isn't capable of that.
Speaker 1: Like the fastest crude rocket or the Space Shuttle, for example,
Speaker 1: their top speeds would take them about eighty thousand years
Speaker 1: to get there, not to mention the question of like
Speaker 1: bringing in a fuel that will dig into in a minute.
Speaker 1: And even the uncrewed stuff like the Parker solar Probe
Speaker 1: is the fastest thing humanity has ever built. Its top
Speaker 1: speed is about zero point zero six four percent of
Speaker 1: the speed of light. Oh no, you take about seven
Speaker 1: thousand years to get to Alpha Centauri. So nothing we've
Speaker 1: built can go nearly fast enough to get Kelly to
Speaker 1: Alpha Centauri before her eighty fifth birthday.
Speaker 3: Oh that's right. I wasn't going to go anyway, although
Speaker 3: maybe maybe if they had really great moths. I'm disappointed.
Speaker 3: But so I feel like there's there's a couple problems here.
Speaker 3: It's like, one, can you even get to the speed
Speaker 3: that you want? But then two, how do you get
Speaker 3: to that speed? Because like, if you're sending humans, we've
Speaker 3: got these squishy bodies, and if you accelerate us too fast,
Speaker 3: we like we break and smoosh, and so you need
Speaker 3: to like get fast but not too fast.
Speaker 1: Yeah, so there's a lot going on here. I mean,
Speaker 1: one thing is just the limitation of relativity. Number one.
Speaker 1: You can't get faster than the speed of light. We'll
Speaker 1: talk about warp drives in a minute, but assuming that
Speaker 1: you're going through space, through flat space, you can't travel
Speaker 1: faster than that. And that's a hard limit. And I
Speaker 1: think it's important for people to think about that as
Speaker 1: sort of setting the length scale of the universe, Because
Speaker 1: we talked a minute ago about like, wow, it's super
Speaker 1: duper fast. It is super duper fast. But space is
Speaker 1: vast compared to the speed of light. Like, we wouldn't
Speaker 1: think space was so big if the speed of light
Speaker 1: was ten times or one hundred times what it is,
Speaker 1: because then these things would be like less than a
Speaker 1: light year away, or we would think space was much
Speaker 1: bigger if the speed of light was smaller. So the
Speaker 1: speed of light sort of determines like what is far
Speaker 1: and what is close, And it just so happens that
Speaker 1: because of our galactic dynamics, things are a few light
Speaker 1: years away instead of tenths of light year away. But
Speaker 1: even if you're not going to get to the speed
Speaker 1: of light, this limit at the speed of light makes
Speaker 1: it hard to accelerate. Like you keep pouring energy into
Speaker 1: your rocket, you're not going to increase your velocity by
Speaker 1: the same amount. As you go faster and faster, it
Speaker 1: takes more and more energy to increase your velocity. And
Speaker 1: as I think you were hinting, there are also limits
Speaker 1: on how quickly you can accelerate, like biologically.
Speaker 3: Yeah, so that's the interesting part.
Speaker 1: Well, it's true that we do want to deliver our
Speaker 1: passengers to Alvis Centauri, not as bags of dead goo. Right,
Speaker 1: we want to take care of all their fragile little
Speaker 1: organs and make sure that they actually get there. And
Speaker 1: so if you want to get to some sort of
Speaker 1: reasonable speed so your trip doesn't take too long, you
Speaker 1: need to accelerate, and humans are not really built for
Speaker 1: huge acceleration. I was reading some papers that said the
Speaker 1: humans can tolerate like twenty G of acceleration G there,
Speaker 1: of course referring to the acceleration of gravity here on
Speaker 1: Earth as basic standard units of one G. So twenty
Speaker 1: G is pretty intense, and we can't really tolerate that
Speaker 1: for more than like a few seconds, maybe ten seconds. Humans,
Speaker 1: like the really tough ones, can tolerate like ten G
Speaker 1: for a minute, five G for a few minutes. But
Speaker 1: imagine being on this ship. You're going to be on
Speaker 1: it for years at least. You don't want more than
Speaker 1: like one G or maybe even two G for long periods.
Speaker 3: You know, we got a lot of the early data
Speaker 3: on how many g's humans can survive because there was
Speaker 3: the one scientist who kept getting in a sled and
Speaker 3: then slamming himself into a foam wall. And so anyway,
Speaker 3: human ingenuity. I love it, so just to make sure
Speaker 3: I have the physics understanding of this. So like if
Speaker 3: you speed up and then you stay at that speed,
Speaker 3: you only experience the G as you're accelerating, right, not
Speaker 3: just because you're going fast, but because you are going
Speaker 3: faster every second. Is that right?
Speaker 1: That's right? Okay, that's right. You can't experience velocity directly.
Speaker 1: It's a relative thing right inside your ship. You can't
Speaker 1: tell how faster ship is going. But if your ship
Speaker 1: turns on the engines and tries to increase its speed,
Speaker 1: you can measure acceleration locally. It's not relative, So as
Speaker 1: your ship tries to increase its speed, you can feel that.
Speaker 1: And something that's sort of surprising to me is that
Speaker 1: you can actually accelerate at one G and reach near
Speaker 1: the speed of light in a reasonable amount of time.
Speaker 1: Like if you're on a rocket that can do one
Speaker 1: G of acceleration, you can just do that for a year,
Speaker 1: and you'll get up to like ninety nine percent of
Speaker 1: the speed of light relative to your departure location.
Speaker 3: And in that case, you would get there in less
Speaker 3: than forty years. Right, because now instead of going ten
Speaker 3: percent the speed of light, you're going the speed of light.
Speaker 1: Yeah, that's right, but you need a technology that can
Speaker 1: provide one g of acceleration for a whole year, as
Speaker 1: we're going to talk about. That's not so easy to do, right.
Speaker 1: That's an enormous amount of thrust or momentum you're imparting
Speaker 1: on your ship.
Speaker 3: There's always something in the way.
Speaker 1: There's always something in the way. And the flip side
Speaker 1: of all of this is deceleration or negative acceleration, because
Speaker 1: you could get up to near the speed of light,
Speaker 1: and then you could get to Alpha Centauri, but then
Speaker 1: you're going to be in that Solar system for about
Speaker 1: zero point zero seven seconds if you're traveling at near
Speaker 1: the speed of light. But what you want to do
Speaker 1: is arrive there and stop, which means decelerating. And you
Speaker 1: don't want to decelerate from the speed of light to
Speaker 1: zero too quickly, otherwise you'll again go splat.
Speaker 3: Yeah, humans, it's a shame. We're so squishy.
Speaker 1: And I think on the next episode we're going to
Speaker 1: talk about making humans less squishy by like turning into
Speaker 1: human sickles, and that might be a better way to
Speaker 1: accelerate human bodies. I don't know, you'll have to tell
Speaker 1: me all about it.
Speaker 3: We are going to talk about the human side of
Speaker 3: things in the next episode. I'm not sure that human
Speaker 3: sickles is on my outline, but we'll see what I
Speaker 3: come up with.
Speaker 1: It is now, because I'm going to ask you about it.
Speaker 3: Okay, great.
Speaker 1: And so a typical strategy is to accelerate on the
Speaker 1: first half of the trip and then basically turn your
Speaker 1: ship around and decelerate all the way back to your
Speaker 1: initial velocity now relative to your destination. And so you
Speaker 1: accelerate and you reach top speed momentarily halfway there, and
Speaker 1: you turn around and you're slowing down the whole second
Speaker 1: half of the trip. And this is actually kind of
Speaker 1: cool because along the way you might want to feel
Speaker 1: some artificial gravity. As you're probably going to tell us,
Speaker 1: humans don't like to float in space forever. It's not
Speaker 1: good for us, and so you want to feel one G.
Speaker 1: And so having one G of acceleration and then one
Speaker 1: G of deceleration the whole trip is actually kind of cozy.
Speaker 3: So if you had one G of acceleration for one year,
Speaker 3: you would still have what two or three years just
Speaker 3: staying at that velocity before you start decelerating, so there
Speaker 3: would be a period where you would have no g's
Speaker 3: in between.
Speaker 1: Yeah, absolutely, depending on the length of the trip. If
Speaker 1: you wanted to go further. For example, you could accelerate
Speaker 1: at one G for a year, get up to near
Speaker 1: the speed of light, zoom around super duper fast, and
Speaker 1: then flip around and decelerate. So, yeah, you can have
Speaker 1: a period in the middle where you're not accelerating or decelerating.
Speaker 1: Then you got to solve that gravity problem another way,
Speaker 1: all right.
Speaker 3: All right, and we'll talk about that in the next episode.
Speaker 1: And that's not the only thing that's going to potentially
Speaker 1: kill you along the way. You know, we think of
Speaker 1: space as empty, but it's not really like there's a
Speaker 1: lot of particles out there. There's huge amounts of gas
Speaker 1: the interstellar medium. There's lots of little bits of tiny rocks.
Speaker 1: We call that dust. It's out there, and if you're
Speaker 1: traveling at relativistic speeds relative to that dust, you can
Speaker 1: be in danger. You know, these tiny particles, A millimeter
Speaker 1: sized particle at like even if half of the speed
Speaker 1: of light is an enormous amount of energy deposited on
Speaker 1: your ship. And so you got to really worry about
Speaker 1: this and cosmic rays and radiation, So your ship has
Speaker 1: to be pretty robust. You need shielding, you need like
Speaker 1: titanium or water or lead or something. All this is
Speaker 1: going to make your ship heavier. So we'll dig into
Speaker 1: that more in the next episode where we talk about
Speaker 1: the fragility of the human body and how to survive this.
Speaker 1: But keep that in mind as we're talking about the
Speaker 1: propulsion designs, because it's going to affect how much you
Speaker 1: got to move on the way to another star.
Speaker 3: So to me, the dust feels like the first showstopper
Speaker 3: that we've encountered. What makes us think that, you know,
Speaker 3: when each piece of dust hitting us is like getting
Speaker 3: hit with a bomb, what makes us think that we
Speaker 3: can like, I mean, we're clearly not going to dodge
Speaker 3: the dust. So what is the dust solution?
Speaker 1: Well, you know, I've read about some cool shields. There's
Speaker 1: like these whipple shields. I basically break up the dust
Speaker 1: into smaller pieces so that none of them are likely
Speaker 1: to like, really be devastating. There's some cool technology like
Speaker 1: self healing shields. So I think it's an engineering problem
Speaker 1: and one that we're likely to be able to crack.
Speaker 1: But Yeah, it's definitely an important one.
Speaker 3: I love your optimism, Dan, I always love your optimism,
Speaker 3: all right, So we're going to be talking about ways
Speaker 3: to get there. Are the ways that you're going to
Speaker 3: talk to us about ways that could get us there
Speaker 3: in a lifetime or is there anything else that might
Speaker 3: work for us here?
Speaker 1: Some of these solutions really can get you there in
Speaker 1: a lifetime. But because it's physics, time is a slippery concept,
Speaker 1: like are we talking about the lifetime for the people
Speaker 1: you left behind or lifetime for people on board? Because
Speaker 1: as soon as you get up to really high speed
Speaker 1: relative to your departure planet, those are not the same thing. So,
Speaker 1: for example, say you accelerate at one G and you
Speaker 1: get up to near the speed of light, you could
Speaker 1: travel for just a few years your time, a decade
Speaker 1: your time, and like one hundred thousand years will have
Speaker 1: passed back home. And if you're traveling near the speed
Speaker 1: of light, one hundred thousand years is enough time to
Speaker 1: get you across the galaxy in only like a decade
Speaker 1: of your time. So Kelly gets on board the ship.
Speaker 1: She arrives at the other side of the Milky Way
Speaker 1: that no human has even clearly seen before because all
Speaker 1: a gasl and dust and she's only fifty ish. Meanwhile,
Speaker 1: back home, Zach is one hundred thousand years old.
Speaker 3: Oh my gosh. And I'm a narcissist. So what I
Speaker 3: care about is how long it takes me. When we
Speaker 3: say it's gonna take eighty it would take like eighty
Speaker 3: years to get there if you went ten percent the
Speaker 3: speed of light. Is that that's eighty my years as
Speaker 3: a person on the ship, right, So our frame of
Speaker 3: reference is always the people on the ship.
Speaker 1: Well, it was gonna take forty years to get there
Speaker 1: at ten percent the speed of light in human years,
Speaker 1: but at ten percent the speed of light is not
Speaker 1: that much of a relativistic time dilation effect. That really
Speaker 1: kicks up when you go half or three quarters the
Speaker 1: speed of light, So that's still going to be decades
Speaker 1: earth time and ship time. If you do get like
Speaker 1: up above fifty sixty seventy percent the speed of light,
Speaker 1: then you start to benefit from these time dilation effects.
Speaker 1: So on the ship it takes less time.
Speaker 3: Got it, Okay? And on the next episode we're going
Speaker 3: to talk about generationships where if you just accept it's
Speaker 3: not going to happen in a lifetime. Because your technology
Speaker 3: can't get you that fast, how do you carry generations
Speaker 3: of humans to still get there? But we're going to
Speaker 3: take a break now, and when we get back from
Speaker 3: the break, Daniel's going to walk us through our rocket
Speaker 3: options for our trip to the stars. All right, let's
Speaker 3: talk about our transport methods to get us to Alpha Centauri,
Speaker 3: starting with the most near term likely technology.
Speaker 1: So we want to get to Alpha Centauri, which means
Speaker 1: we've got to move away from Earth, which means we
Speaker 1: need to gain momentum away from Earth. In our universe,
Speaker 1: momentum is conserved. So you have your ship. You wanted
Speaker 1: to gain momentum in one direction, there needs to be
Speaker 1: some sort of compensating momentum in the other direction. This
Speaker 1: is something you feel if you like fire a gun,
Speaker 1: for example, you feel that kickback. That's the conservation of momentum.
Speaker 1: The rifle is shooting the bullet super duper fast, but
Speaker 1: the bullet has a small mass, and the rifle itself
Speaker 1: has that larger mass is moving backwards in the other
Speaker 1: direction with the compensating velocity.
Speaker 3: See I always imagine it as I'm trying to get
Speaker 3: a boat to move and I'm imagining Daniel on a
Speaker 3: cruise ship taking all of the white chocolate and throwing
Speaker 3: it in the ocean to get the cruise ship to
Speaker 3: move faster while also getting rid of the bad chocolate.
Speaker 1: Yeah, that's exactly right. You need to build momentum in
Speaker 1: the other direction. So imagine you are on a boat
Speaker 1: and you're tossing stones or equivalently, white chocolate or hot
Speaker 1: garbage or whatever useless stuff you happen to have on
Speaker 1: the boat. Right, you create momentum in one direction for
Speaker 1: the stones, and in recoil you go the other way.
Speaker 1: And so all rocket drives operate under this same principle.
Speaker 1: You need two things. You need energy and then you
Speaker 1: need mass. So you use the energy to throw the
Speaker 1: mass out the back and you go the other way.
Speaker 1: That's the way all the rockets we're going to talk
Speaker 1: about work.
Speaker 3: And that's how like the Falcon nine or starship works
Speaker 3: when it takes off too right.
Speaker 1: Yeah, exactly. And the issue here is that you need
Speaker 1: something to produce that energy, and you need something to
Speaker 1: throw out the back, and when you run out of that,
Speaker 1: you can't go anymore. And because you have to bring
Speaker 1: that fuel with you, you need enough fuel to push that fuel,
Speaker 1: and then you need more fuel to push that fuel.
Speaker 1: And so there's this famous rocket equation which tells you
Speaker 1: like how much fuel you need to get up to
Speaker 1: a certain velocity. It depends on the mass of the
Speaker 1: ship and also depends on the specific impulse that your
Speaker 1: engine is able to provide. It's just basically just like
Speaker 1: a number. Some of them are high, some of them
Speaker 1: are low. But the bottom line is that the math
Speaker 1: tells us that there's an exponential need for fuel. If
Speaker 1: you want to get up to higher velocity. So you
Speaker 1: want to go twice as fast, you don't need twice
Speaker 1: as much fuel, You need much much more. You need
Speaker 1: exponentially more fuel, and as you increase that velocity, the
Speaker 1: amount of fuel grows ridiculously. So for example, even like
Speaker 1: the Saturn rockets, the ones that took us to the Moon,
Speaker 1: when they launched, they were like ninety five percent fuel.
Speaker 1: It's mostly fuel being taken off and that fuel is
Speaker 1: mostly being used to push the rest of the fuel.
Speaker 3: That absolutely blew my mind when I first learned it
Speaker 3: that like less than ten percent of that giant that
Speaker 3: you know, that giant tube was actually going to be
Speaker 3: going to the Moon.
Speaker 1: And people are often confused about rockets versus escape velocity. Remember,
Speaker 1: escape velocity is a calculation you do if you're like
Speaker 1: throwing something from the surface of the Earth, you need
Speaker 1: a certain velocity because gravity is going to slow you down,
Speaker 1: and if you have higher than the escape velocity, you
Speaker 1: can leave the orbit. But rockets are not about escape
Speaker 1: velocity because rockets have constant thrust. Rockets can lift off
Speaker 1: it basically zero points zero zero zero zero zero one
Speaker 1: meters per second and still make it to space because
Speaker 1: they're pushing themselves constantly. They're like climbing a ladder rather
Speaker 1: than just getting a single push. So escape velocity is
Speaker 1: not relevant for rockets. What is relevant for rockets is
Speaker 1: this specific impulse and how fast you want to go.
Speaker 3: So in this case, the rocket would be not just
Speaker 3: getting us off Earth, but it would stay with us
Speaker 3: and it would continue to propel us through space.
Speaker 1: Yeah, exactly. And the sort of bog standard rocket we
Speaker 1: have is a chemical rocket where the thing that you're
Speaker 1: throwing at the back is also the way you're getting energy. Basically,
Speaker 1: you have like exploding stones that you're throwing out the back.
Speaker 1: The stones throw themselves out the back, right, because the
Speaker 1: fuel is the propellant and the source of energy. You
Speaker 1: light it on fire and the explosion goes out the back.
Speaker 1: You get pushed the other direction, and so that's cool.
Speaker 1: And you know, obviously fuel we can find here on Earth,
Speaker 1: but the specific impulse of these engines is not huge, right,
Speaker 1: So it's not a great way to get going really
Speaker 1: really fast unless you have incredible quantities of fuel. So
Speaker 1: this is the rocket equation at work here. So if
Speaker 1: you do a little calculation, like how much fuel does
Speaker 1: it take to get off of Earth and to the
Speaker 1: Moon an enormous quantity, right, filling a huge Saturn rocket.
Speaker 1: How much fuel does it take to get to Alpha
Speaker 1: Centauri if you've got to burn that chemical engine the
Speaker 1: whole way, Well, that goes exponential, and the fuel tank
Speaker 1: is something like the size of Jupiter.
Speaker 3: What there's a showstopper. Kelly's gonna keep track of these
Speaker 3: showstoppers as we go because she's the wet blanket.
Speaker 1: But I'm gonna be optimistic because in the end I'm
Speaker 1: really hopeful that we do get to another star, and
Speaker 1: we do, or somebody, not me, but some human gets
Speaker 1: to go and set their eyes on an alien planet.
Speaker 3: I think we will eventually.
Speaker 1: All Right, you heard it there, folks said it.
Speaker 3: I do, I do, but I'm not gonna put any
Speaker 3: money on a date, all right. So when I was
Speaker 3: writing a city on Mars, the engineers would get grumpy
Speaker 3: with me for occasionally using the words fuel and propellant interchangeably,
Speaker 3: which we didn't do in the final manuscript. Nobody needs
Speaker 3: to freak out and write me. Now, this was in
Speaker 3: an early draft. So, Daniel, what is the difference between
Speaker 3: fuel and propellant?
Speaker 1: So, propellant is anything you want to throw out the
Speaker 1: back of your rockets, right, and fuel is a special
Speaker 1: combination which is both a source of energy and a propellant,
Speaker 1: but it doesn't have to be. Another example of a
Speaker 1: propellant that separates these things is a nuclear rocket. So
Speaker 1: rather than using fuel to explode and create energy and
Speaker 1: propellant simultaneously, use something like a nuclear reactor a fission
Speaker 1: reactor to produce the energy, which you then use to
Speaker 1: throw some inert mass out the back. You heat up
Speaker 1: a gas, for example, and it bubbles out the back
Speaker 1: of your rocket.
Speaker 6: Chip.
Speaker 1: The fuel there is like uranium which is powering your
Speaker 1: nuclear reactor, which is providing the energy to toss the
Speaker 1: propellant out the back. The propellant and the fuel are
Speaker 1: very separate in this technology, and.
Speaker 3: So with the nuclear rocket, what would the propellant be.
Speaker 3: Could it be like anything that you heat up.
Speaker 1: Yeah, it could be anything you can heat up. But
Speaker 1: you've got to bring some mass to throw out the back, right, stones,
Speaker 1: white chocolate, xenon, whatever, you want. Something pretty inert so
Speaker 1: it's not reacting, but you also need to bring enough
Speaker 1: of it, and it's going to be dense enough that
Speaker 1: it's not going to be huge. And nuclear rockets are
Speaker 1: cool because it's something we've actually built. We had an
Speaker 1: episode where you and I talked about new clear jet planes,
Speaker 1: and it's the same principle, right, A jet engine operates,
Speaker 1: and the same principle is very similar to a rocket.
Speaker 1: You have the fuel which explodes and pushes something out
Speaker 1: the jet airplane, this whole air compression thing. So jets
Speaker 1: don't work in space, but you could also have a
Speaker 1: nuclear jet engine. We're using a nuclear reactor to heat
Speaker 1: the stuff up and shoot it out the back, same
Speaker 1: basic principle, and that applies to rockets in space as well.
Speaker 1: So in this case, you heat the stuff up and
Speaker 1: you shoot the gas at the back, and that could
Speaker 1: be a nuclear rocket.
Speaker 3: But we haven't actually sent a nuclear rocket to space, right.
Speaker 3: The only kind of rocket we've ever sent to space
Speaker 3: is the chemical one.
Speaker 1: That's right. We do have test nuclear engines which people
Speaker 1: have built and tested and shown to work, and they
Speaker 1: once did fly an airplane with a working nuclear reactor
Speaker 1: on board. Scary stuff, but it wasn't actually powering the
Speaker 1: plane anyway. This is like a viable technology, not just
Speaker 1: science fiction.
Speaker 3: And so you said that for chemical rockets, the container
Speaker 3: that would store the fuel would need to be as
Speaker 3: big as Jupiter. How big are we working on now?
Speaker 3: If it's a new So.
Speaker 1: It doesn't have to be nearly as big because the
Speaker 1: fuel is much more dense, right, Uranium incredibly dense compared
Speaker 1: to like diesel or even like oxygen or whatever you're
Speaker 1: using as fuel, and so that doesn't need to be
Speaker 1: nearly as big. But you'd still have to bring the propellant, right,
Speaker 1: You still need a lot of stuff to throw out
Speaker 1: the back. So we're not talking about the massa jubutter,
Speaker 1: but we're still talking a very very large ship with
Speaker 1: a huge amount of propellant. Now, there's some folks that
Speaker 1: have ideas for like gathering propellant along the way that
Speaker 1: dust you talked about, or the interstellar medium that's stuff, right,
Speaker 1: you could use that as propellant. So there are technologies
Speaker 1: like ramjets or buzzard jets that people talk about where
Speaker 1: you have like a scoop that gathers propellant up and
Speaker 1: then your engine whatever you're using, a nuclear reactor or
Speaker 1: something else, for example, is throwing that out the back.
Speaker 1: And so there are ways to avoid like having to
Speaker 1: have a cataclysmically large ship in that way. Though there
Speaker 1: are also a lot of people who think that those
Speaker 1: ramjets and bussard jets are totally impractical for other reasons.
Speaker 1: Same enough said.
Speaker 3: What if the thing that you're throwing out the back
Speaker 3: of your rocket is nuclear bombs? Cause why not?
Speaker 10: Right?
Speaker 1: Why now? This is actually not a terrible idea in
Speaker 1: some ways because it separates the ship from the propulsion
Speaker 1: in a way that we'll talk about for solar sales.
Speaker 1: If you could blow up a series of nuclear weapons
Speaker 1: between here and Alpha Centauri, and you had a ship
Speaker 1: with like a huge shield in the back that could
Speaker 1: absorb all the radiation and the energy that was dumped
Speaker 1: out by the nuclear bombs. Then you could just sort
Speaker 1: of like ride this wave of nuclear explosions all the
Speaker 1: way to Alpha Centauri. And you know, this is the
Speaker 1: basis of Project Orion. And then later Project Data lists
Speaker 1: the idea having like a series of small bombs providing
Speaker 1: like this smooth acceleration. Now you know, how do you
Speaker 1: get those bombs? How do you lay a trail of
Speaker 1: bombs from here to the next star. It was more
Speaker 1: about like near Earth navigation or getting things off planet
Speaker 1: than like actually going from star to star. But we
Speaker 1: can't not talk about blowing up nuclear bombs as a
Speaker 1: way to propel a ship. It's just got to be
Speaker 1: in the conversation.
Speaker 3: Project Datalus had a follow up project called Project Icarus
Speaker 3: because Icarus was Datalus's son. But Icris is the one
Speaker 3: who flew too close to the Sun and his wings
Speaker 3: melted and he fell down and died. And I always
Speaker 3: remember feeling like, isn't this supposed to be inspirational and like?
Speaker 3: But but I was told I just wasn't looking at
Speaker 3: it the right way. And again, this is why I
Speaker 3: don't get invited to the space parties.
Speaker 1: Do you think it's hard to sign up test pilots
Speaker 1: for Project Icarus.
Speaker 3: It could be, but again, I bet somebody would show
Speaker 3: would sign up. There's a lot of people who are
Speaker 3: much braver than I.
Speaker 1: Am looking for volunteers for a project Crash and Burn. Anybody, anybody, nobody,
Speaker 1: Probably a lot. Anyway, that's a cool technology, and the
Speaker 1: cool thing there is if you could somehow manage it.
Speaker 1: It separates the ship from the source of energy, right,
Speaker 1: and also from the propellant, and so the ship itself
Speaker 1: doesn't have to be very big. Of course, that's sort
Speaker 1: of assuming a solution to the core problem, which is
Speaker 1: how to get all these nuclear bombs from here to
Speaker 1: Alpha Centauri, which is basically impossible.
Speaker 3: What do you think the aliens would think as we
Speaker 3: were like leaving a trail of nuclear explosions on our
Speaker 3: way to their galaxy? Do you think they'd be like, Wow,
Speaker 3: they've really conquered technology. Or do you think they'd be like,
Speaker 3: oh my gosh, how do we get them to turn around?
Speaker 2: Yeah?
Speaker 1: I can't wait for them to show up, right. I
Speaker 1: think it's cool because we can imagine how we might
Speaker 1: detect aliens doing the same, Right, Like, if aliens have
Speaker 1: come up with this idea, and they're using it around
Speaker 1: their star. We might be able to detect it if
Speaker 1: they're close enough, So that's pretty cool. But yeah, I
Speaker 1: don't think it'd be a great way to announce our
Speaker 1: presence to the universe.
Speaker 3: They would definitely have time to set up the welcome
Speaker 3: party or the go home party.
Speaker 1: But along these lines, there's lots of permutations on this
Speaker 1: kind of propulsion once you separate the explosions from the propellant. So,
Speaker 1: for example, there are other ways to accelerate stuff, Like
Speaker 1: you could have an electric field and you have ions.
Speaker 1: An electric field will push ions, that's what it does,
Speaker 1: and so if you had like an electric field and
Speaker 1: a bunch of ionized propellant, you could shoot that out
Speaker 1: the back. Basically, we're talking about a particle accelerator. That's
Speaker 1: exactly what a particle accelerator like the large hadron collider does.
Speaker 1: It pushes particles with electric fields and makes them go
Speaker 1: really really fast. So build a particle accelerator, point it
Speaker 1: out the back of your ship. That's going to give
Speaker 1: you some impulse.
Speaker 3: This seems like another very large design, right How big
Speaker 3: would your particle accelerator need to be?
Speaker 1: Well, not that big. Actually, and it's cool because it
Speaker 1: separates the two systems, and so your power source can
Speaker 1: be anything. It could be solar power, it could be
Speaker 1: some other crazy system that doesn't necessarily have to be
Speaker 1: super duper big. In this case, it's nice because it
Speaker 1: doesn't even have to generate a lot of heat, right,
Speaker 1: and so for those hand wringers aboard, you don't have
Speaker 1: to worry about it like melting down or something like that.
Speaker 1: The downside to this is that the thrust is really
Speaker 1: tiny accelerating particles and particles don't have a lot of mass,
Speaker 1: and they sort of limit to how many particles you
Speaker 1: can effectively shoot out the back, and so it can
Speaker 1: provide very long term gentle thrust, which is nice for
Speaker 1: constant acceleration, but it can't really give you a lot
Speaker 1: of specific impulse, and so it's not a great way
Speaker 1: to like get up to a high speed in a
Speaker 1: short amount of time. But it's cool for like navigating
Speaker 1: around space a little bit.
Speaker 3: So this could be like a generation ship thing. And
Speaker 3: so can you remember what the difference is between thrust
Speaker 3: and specific impulse.
Speaker 1: They're basically the same thrust a specific impulse times the
Speaker 1: constant of gravity, but you can think of them as interchangeable.
Speaker 1: They're just different by units essentially.
Speaker 3: All Right, we're going to take a break now, and
Speaker 3: when we come back, we're going to talk about using
Speaker 3: anti matter to get you to the stars. All right,
Speaker 3: So we just finished talking about ion drives as a
Speaker 3: way to get you to the stars, and I see
Speaker 3: that next we're going to talk about antimatter, and I
Speaker 3: am immediately thinking that dangerous explosions are maybe not what
Speaker 3: I want happening, you know, on the ship that I'm
Speaker 3: living on. But why is Kelly being a wimp?
Speaker 1: No, Kelly is not being a wimp. We are steadily
Speaker 1: moving from reliable technologies we know can work and probably
Speaker 1: won't kill you, to crazy ideas that might not ever
Speaker 1: work and are much more likely to kill anybody on board.
Speaker 3: O good, all right.
Speaker 1: But antimatter is cool because it's the most efficient way
Speaker 1: to store energy. Like matter, and antimatter annihilation is perfect
Speaker 1: conversion of matter into energy. Compare that to for example,
Speaker 1: chemical fuel. Right, chemical fuel has a lot of energy
Speaker 1: in it, but when you burn it, you only release
Speaker 1: a little bit of that energy from the chemical bonds.
Speaker 1: But inside those protons and inside those electrons is an
Speaker 1: enormous amount of stored energy, which we call mass. If
Speaker 1: you could capture all that will release all of that,
Speaker 1: you would need to bring less fuel, right, and so
Speaker 1: matter antimatter annihilation is the best way to do that.
Speaker 1: You have protons and anti protons. They turn directly into
Speaker 1: photons which you can shoot out the back of your ship.
Speaker 1: And that's awesome because the propellant there is moving at
Speaker 1: the speed of light, right, so like you can't be
Speaker 1: that for maximum thrust and impulse. So far this sounds
Speaker 1: great now. The downsides are, of course, Kelly worries about
Speaker 1: being annihilated herself because antimatter is pretty dangerous stuff. Yeah,
Speaker 1: so you need some sort of magnetic confinement for antimatter,
Speaker 1: basically a bottle that doesn't touch it. You know, a
Speaker 1: bottle made of matter that builds a magnetic field that
Speaker 1: confines it, sort of the way we do for plasmas
Speaker 1: in Tokomax infusion reactors. That's not totally implausible, But then again,
Speaker 1: you basically have a bomb on board and any loss
Speaker 1: of containment and everybody's dead, yeah before you can do anything.
Speaker 1: So that's bad. But on the flip side, antimatter is
Speaker 1: basically impossible to make in large enough quantities, so you're
Speaker 1: pretty much safe. You know, we make antimatter. We made
Speaker 1: it for the previous collider. We used to have the Tevatron,
Speaker 1: which was a proton anti proton machine, and we produced
Speaker 1: antimatter at the Large Hadron Collider all the time in collisions,
Speaker 1: so it's not actually that exotic. It's made in the atmosphere,
Speaker 1: like cosmic rays hit the atmosphere turn into a antimatter briefly.
Speaker 1: But the quantities we're talking about are like nanograms of antimatter.
Speaker 1: You know, we can like count the atoms of antimatter
Speaker 1: we make. There's no large scale production of antimatter in
Speaker 1: order to make enough fuel to get anybody near Alpha Centauri.
Speaker 1: I read one estimate that said making one hundred milligrams
Speaker 1: of antimatter would cost about one hundred trillion dollars.
Speaker 3: Oh my gosh. All right, so I'm curious since we're
Speaker 3: starting to get towards the really crazy ones. Out of
Speaker 3: the technologies we've talked about so far, if you had
Speaker 3: to go to Alpha Centauri, which one of these would
Speaker 3: you want to use?
Speaker 1: Probably none of these? Okay, my favorite is one we
Speaker 1: haven't talked about yet it's a little bit ridiculous and speculative,
Speaker 1: but it's still my favorite.
Speaker 3: All right, let's keep going. Then, what's next next?
Speaker 1: I want to talk about a nonsense idea which is
Speaker 1: out there people are probably imagining might save the day,
Speaker 1: and that's propulsion list drives. People have been thinking, okay, well,
Speaker 1: conservation of momentum requires we throw something out the back.
Speaker 1: We're tossing stones or white chocolate out the back of
Speaker 1: our spaceboat to get it moving. That's frustrating that it
Speaker 1: limits us, right because you've got to bring all this
Speaker 1: stuff to throw out the back. Wouldn't it be amazing
Speaker 1: if we could generate a drive which didn't need that, Yeah,
Speaker 1: that would be amazing and also violate conservation of momentum.
Speaker 1: But that has to stop people from trying and go
Speaker 1: for it. Guys, like it wouldn't be the first time
Speaker 1: that we discovered and sit you something that revealed we
Speaker 1: didn't understand the universe. So I'm all in favor of
Speaker 1: people doing crazy experiments.
Speaker 3: That's just like a Friday in physics, right where you
Speaker 3: discover you were wrong about something.
Speaker 1: Yeah, those are the best moments in physics, So nobody
Speaker 1: should be limited by like conventional wisdom about what's possible
Speaker 1: or impossible, but we should also be clear eyed about
Speaker 1: what we have actually proven. And there are folks out
Speaker 1: there who claim to have built one of these things.
Speaker 1: It's called an em drive, and about fifteen years ago
Speaker 1: there was a lot of hoopla about it. There's a
Speaker 1: lot of coverage and the New Scientist. But these folks
Speaker 1: who had some like tenuous NASA affiliation, who claim to
Speaker 1: have built the impossible space drive, And if you look
Speaker 1: for articles, you'll see them there in Popular Mechanics, they're
Speaker 1: and wired, they're in the New Scientist. But the journalists
Speaker 1: here really didn't do their work, Like if you look
Speaker 1: carefully at the claims, you see that the thrust that
Speaker 1: these things produce is really really tiny. It's basically smaller
Speaker 1: than the uncertainties, you know, like they just have jitter
Speaker 1: in their measurements that have sources of noise and they
Speaker 1: measure a thrust, but the thrust is consistent with zero
Speaker 1: within errors. So while I'm all for crazy new technologies
Speaker 1: and exploding understanding the universe, the EM drive is not
Speaker 1: something that's done that. These are fascinating ideas, and there's
Speaker 1: not nothing to support the concepts. One idea is that
Speaker 1: there's a vacuum in space, and that vacuum has energy
Speaker 1: to it, and experiments like the Casimir effects show us
Speaker 1: that the vacuum is real and it's there, and people
Speaker 1: wonder if we can extract energy from the vacuum and
Speaker 1: use it to propel ourselves. But you know, the vacuum
Speaker 1: is special. You can't like row against the vacuum. You
Speaker 1: can't like absorb momentum or get momentum. It's emotional the
Speaker 1: way space is. For example, you can't like put an
Speaker 1: ore down and row through space in the same way.
Speaker 1: And this is part of space. So anyway, em drives
Speaker 1: not something we can rely on and not something I
Speaker 1: would bet on. But hey, if you're out there and
Speaker 1: you're building em drive, I hope you make it work.
Speaker 3: Fingers crossed, all right? So I have heard proposals where
Speaker 3: you know, the Sun is shooting out photons all the time.
Speaker 3: What if you could capture those photons and let the
Speaker 3: Sun sort of push you forward? How would that work?
Speaker 1: This is my favorite idea because it separates the ship
Speaker 1: from the propulsion completely, right. So this is called a
Speaker 1: solar sale, and the idea is that you're right. The
Speaker 1: sun is putting out photons, and not just photons but
Speaker 1: other particles. The solar wind has momentum, So why like
Speaker 1: generate momentum if we have an enormous momentum generating machine already,
Speaker 1: and so all you need to do to capture that
Speaker 1: momentum is build a huge sail. So you know, when
Speaker 1: you're on a sailboat, a sail is just a piece
Speaker 1: of cloth that gathers that momentum. Here, the best kind
Speaker 1: of sale would be something very thin, so low mass
Speaker 1: and reflective. And imagine a photon hits the sail, it
Speaker 1: bounces off the same way a photon hits a mirror
Speaker 1: and bounces off. Right, what happens, Well, the photon is
Speaker 1: now changing its momentum. It's going one way. Now it's
Speaker 1: going the other way. Conservation momentum says that can't happen
Speaker 1: unless something is going the opposite direction. Right, something is
Speaker 1: now going the way the photon originally was to conserve momentum,
Speaker 1: and that's the sail. This is a confusing concept for
Speaker 1: people because it's hard to imagine like light pushing something
Speaker 1: because light has no mass, and you're probably thinking, well,
Speaker 1: momentum is mass times velocity, and photons have no mass,
Speaker 1: so therefore they have no momentum. Right, Yeah, wrong, And
Speaker 1: the reason is that momentum is mass times velocity only
Speaker 1: for very slow stuff. As you approach the speed of light,
Speaker 1: the equation changes a little bit. So photons do in
Speaker 1: fact have a momentum even though they have no mass.
Speaker 1: So yeah, their momentum can push along a sail. So
Speaker 1: imagine a tiny little ship with an enormous sail and
Speaker 1: the photons are bouncing off of it and giving it
Speaker 1: a push. Basically, you don't need an engine.
Speaker 3: So one of the things that always sounded limiting to
Speaker 3: me with this method is that it seems like it
Speaker 3: would work great when you're close to the sun. But
Speaker 3: the farther you get from the Sun, the fewer photons
Speaker 3: are going to be hitting your sail. How would this
Speaker 3: work when you get too far away from the sun.
Speaker 1: Yeah, this is tricky. As you say, you get further
Speaker 1: from the Sun, the photon density drops by one over
Speaker 1: are squared. That's bad. So this is a good idea
Speaker 1: for moving around the Solar system, like navigating from here
Speaker 1: to Mercury or here to Neptune. A very light without
Speaker 1: fuel would be awesome. Getting from here to another star
Speaker 1: would be hard. And what you need to do is
Speaker 1: build an enormous laser. Like think about a really big laser,
Speaker 1: now make it ten times bigger. That's too small. You
Speaker 1: need an enormous laser, right, really huge laser, or like
Speaker 1: a big laser array that I'll focus their energy on
Speaker 1: this sale. But the cool thing is, again, you can
Speaker 1: build this on Earth, or you can have it in
Speaker 1: space or something. You don't need to bring it with you,
Speaker 1: and you can point it at your ship and push
Speaker 1: it to another star. So it's not a solar sale anymore.
Speaker 1: It's like a photonic sail.
Speaker 3: And I can't imagine that a laser of that size
Speaker 3: is going to cause any geopolitical conflict at all. A
Speaker 3: weapon of that magnitude.
Speaker 1: Yeah, we're building the Death Star basically for good reasons
Speaker 1: to go to space. We're just making space smores. What's
Speaker 1: the big deal, right, But there's a project to do this.
Speaker 1: It's called Breakthrough Star Shot and they want to take
Speaker 1: a bunch of nanocraft like tiny little devices, and they
Speaker 1: want to build ground based lasers and send those devices
Speaker 1: to Alpha Centauri. Now you push these tiny little devices
Speaker 1: long enough you can get them up to like twenty
Speaker 1: percent of the speed of light. And so you do
Speaker 1: the math and these things. They're estimating to launch them
Speaker 1: in like twenty thirty ish twenty thirty five, they would
Speaker 1: take about twenty years. They'd be there about like twenty
Speaker 1: fifty five. So if I'm lucky, i'd be around when
Speaker 1: the signal comes back, you know, from Alpha Centauri. This
Speaker 1: is something that really could happen, which is why I
Speaker 1: think it's my favorite technology. The challenge, of course, is
Speaker 1: getting a big enough sale to push a ship with
Speaker 1: people on it. You know, so far we're just talking
Speaker 1: about sending tiny nano robots. But you know, if I
Speaker 1: want to go there, you got to bring me and
Speaker 1: my toilet, my bed, you know, all sorts of stuff
Speaker 1: needs to go with me. So we're not talking nano
Speaker 1: ships anymore. So we're talking enormous sales, and we really
Speaker 1: need like better technology for enormous sales that are going
Speaker 1: to somehow survive the interstellar trip those micro meteorites tearing
Speaker 1: it apart. So you know, there's potential there, but there's
Speaker 1: a lot of engineering challenges to solve.
Speaker 3: Yeah, this is a cool technology. Are the are the
Speaker 3: little nanoships that break through starshot is sending Are they
Speaker 3: going to have like cameras and scientific instruments on them
Speaker 3: or are they just able to say we're here and
Speaker 3: that's it TBD.
Speaker 1: But I hope they're gonna put some cameras on there.
Speaker 1: I mean to be amazingly ridiculous to get something all
Speaker 1: the way there and take no data, right.
Speaker 3: Yeah, that would be a major bummer. We haven't talked
Speaker 3: yet about a method to me that seems perhaps likely
Speaker 3: something that we have some experience with, which is gravity slingshots,
Speaker 3: which which we're used in Aurora Kim Stanley Robinson's book
Speaker 3: to slow down on the way back to Earth. Is
Speaker 3: that something that we could use to speed up to
Speaker 3: get there?
Speaker 1: Absolutely, Gravitational slingshots are amazing. You know, you whiz near
Speaker 1: a planet basically steal a little bit of its speed.
Speaker 1: We should dig into the physics of that in a
Speaker 1: whole episode because there's some subtleties there about like why
Speaker 1: you end up with a little bit of speed, And
Speaker 1: the short version of it is that you slow down
Speaker 1: the planet's rotation around the star, which is really cool,
Speaker 1: and we've done this. You know, Voyager one, for example,
Speaker 1: one of our only interstellar probes. It's swung around the Sun,
Speaker 1: but it's not going that fast. You know, it's traveling
Speaker 1: like a light year in about eighteen thousand years. So
Speaker 1: you can't get going to like interstellar speeds unless you're
Speaker 1: getting crazy close to the star, and that's got its
Speaker 1: own dangers. So gravitational slingshots are a good way to
Speaker 1: boost your speed and to get going, but on their
Speaker 1: own they're not going to provide the speed that you
Speaker 1: need to get to another star.
Speaker 3: Got it all right, So let's wrap things up on
Speaker 3: the most sci fi methods. So what can we do
Speaker 3: to can we like bend space or time to make
Speaker 3: this happen?
Speaker 1: Yeah, so far we're considering flat space. We're imagining you know,
Speaker 1: light is going to take a few years to get there.
Speaker 1: What can we do to approach the speed of light?
Speaker 1: But of course we know that space is not just flat.
Speaker 1: Space bends, it curves, and in the presence of mass,
Speaker 1: it can do all sorts of things. They can wiggle,
Speaker 1: not something we fully understand, but you know, we know
Speaker 1: that this kind of thing is possible, and so in
Speaker 1: the last few years or so, people have been thinking about, like,
Speaker 1: could we actually build a warp drive. This would be
Speaker 1: something that bends space so that effectively the journey is shorter.
Speaker 1: And that's really what space curvature means, that you're changing
Speaker 1: the relative distance between two points. So hey, why not
Speaker 1: make Alpha centaur really really close so that doesn't take
Speaker 1: as long to get there. And that's the idea of
Speaker 1: a warp bubble that you like, shrink the space between
Speaker 1: you and the star and expand the space behind you.
Speaker 1: And then when you get there, you pop out of
Speaker 1: this warp bubble and you're like, hey, that wasn't a
Speaker 1: big deal.
Speaker 3: How likely is it that these warp bubbles actually exist
Speaker 3: or could be created?
Speaker 1: That's a topic of hot debate. On the positive side,
Speaker 1: there's a guy who's figured out that warp bubbles do
Speaker 1: not violate general relativity, meaning like a warp bubble doesn't
Speaker 1: break any of those rules. That doesn't mean that a
Speaker 1: warp bubble could actually exist in the universe because you
Speaker 1: create something because it's allowed in the universe. Like everybody
Speaker 1: knows chocolatesou fleas are allowed in the universe, Does I
Speaker 1: mean everybody knows how to make them? You have to
Speaker 1: have a very delicate process to get from no chocolate
Speaker 1: sooufle to chocolates sooufle, right, and there's lots of ways
Speaker 1: to fail. We don't have a recipe for building a
Speaker 1: warp drive, but just know that the resulting drive is
Speaker 1: not disallowed by general relativity. It could be that some
Speaker 1: step between no warp drive and warp drive is disallowed
Speaker 1: or is impossible. And so if you could just like
Speaker 1: magically pop a warp drive into existence, then physics is
Speaker 1: cool with it. But we don't know if it's possible
Speaker 1: to create one in our universe.
Speaker 3: All right, Well, I'm going to hope that it is,
Speaker 3: because that would make things really convenient. At the beginning
Speaker 3: of the show, you mentioned that in your favorite book
Speaker 3: they just moved stars closer together. How would that work?
Speaker 3: And why would everyone be dead?
Speaker 1: This is basically like the think big version of the
Speaker 1: solar sale. Right. In this version, you build a huge
Speaker 1: sale like half the size of the sun. Yeah, that's right,
Speaker 1: half the size of the sun. Wow, wrap half of
Speaker 1: the sun a big mirror that points back at the Sun. Okay,
Speaker 1: And so you might think, well, what's gonna happen? That
Speaker 1: mirror is just gonna shoot off it's a big solar sale.
Speaker 1: It gets pushed away by the Sun. Right, Well, you
Speaker 1: bring it close to enough and you make it massive
Speaker 1: enough that it's gravitationally captured by the Sun. So now
Speaker 1: basically the mirror and the Sun are like a single
Speaker 1: gravitational object. The Sun is shooting half of its photons
Speaker 1: to the mirror, but they get bounced back so basically recaptured.
Speaker 1: On the other side, the Sun is shooting off its
Speaker 1: photons out into space. So now it's like an ion drive.
Speaker 1: So one half of the Sun is basically captured and nullified,
Speaker 1: the other half is not. Now the Sun can move right.
Speaker 1: The Sun is basically like a rocket, and so this
Speaker 1: could move the whole Solar system. And Kelly should feel
Speaker 1: great about this because you could travel to another star
Speaker 1: without even leaving your house. You could like literally sleep
Speaker 1: in your bed at home and we could go visit
Speaker 1: Alpha Centauri move the whole Solar system.
Speaker 3: Okay, all right, so that sounds awesome. I love that
Speaker 3: you dream big. But like, so you know we've talked before,
Speaker 3: if like suns get too close to each other, one
Speaker 3: of them gets like thrown off into the vastness of space.
Speaker 3: This feels like a high risk method.
Speaker 1: Well, it's hard to turn a star, you know, if
Speaker 1: you realize you're going in the wrong direction. This is
Speaker 1: harder to turn than like one of those U hauls
Speaker 1: that are already pretty hard to turn. Yeah, there's a
Speaker 1: lot of ways this could go wrong. You know, maybe
Speaker 1: a safer method is to use a black hole instead, because.
Speaker 3: Black holes, You physicists, wouldn't it be safer if we
Speaker 3: used a black hole?
Speaker 1: I like, you just laugh in my face at that one.
Speaker 3: I'm sorry.
Speaker 1: I mean a black hole also converts mass into energy. Right,
Speaker 1: black holes evaporate, they have energy stored inside them because
Speaker 1: of their mass, but they generate Hawking radiation, which is energy.
Speaker 1: So put a black hole next to a mirror and
Speaker 1: in the same way, it will generate propulsion in one direction,
Speaker 1: right if it's gravitationally captured the mirror, and so that's
Speaker 1: absorbing that radiation. Now you have a black hole which
Speaker 1: is turning its mass into radiation and pushing your ship
Speaker 1: so you don't have to move a whole star. Now
Speaker 1: you have a black hole power and spaceship. And of
Speaker 1: course there's technical problems here, like how do you actually
Speaker 1: make the black hole? We don't know how to do that.
Speaker 1: Maybe you could find a black hole. We don't know
Speaker 1: where any of them are. Also, there are some risks
Speaker 1: involved in having a black hole on board your ship.
Speaker 1: Please sign these waivers, all.
Speaker 3: Right, So I'm going to ask myself the question, which
Speaker 3: one of those methods do I think I would use
Speaker 3: if I was forced to go on a ship to
Speaker 3: Alpha Centauri. I think that I would agree with you
Speaker 3: about the solar sale technique. But what would make me
Speaker 3: nervous is that somebody else is in control of the
Speaker 3: propulsion and so like, I imagine that keeping a giant
Speaker 3: laser constantly powered has got to take a lot of energy.
Speaker 3: And so what if one day, you know, the Americans
Speaker 3: are like, you know what, We're not powering this laser anymore.
Speaker 3: It's just too expensive. And then what do you do?
Speaker 1: Yeah, well there's not much you can do.
Speaker 4: You know.
Speaker 1: The other issue with a solar sale is slowing down.
Speaker 1: Like it gets you up to near the speed of
Speaker 1: light using that big laser, then you have to use
Speaker 1: the destination sun to slow down, but it is no
Speaker 1: laser there to give you that boost, and so you
Speaker 1: got to like combine that with gravitational sling shots. It's tricky. Yeah,
Speaker 1: there's no way I'm getting on any of these ships ever,
Speaker 1: But I encourage all of you to, like, please go
Speaker 1: explore the universe and tell us all about it.
Speaker 3: Send me a postcard.
Speaker 1: All right. So, I think we surveyed some of the
Speaker 1: technologies that might get us to other stars, and my
Speaker 1: take is that there's some promise here. Obviously there are
Speaker 1: kinks to be worked out, and Kelly and her legal
Speaker 1: team need to be put at ease about the black
Speaker 1: hole on board, you know, or moving the entire sun.
Speaker 1: Do we need to take a vote before we do that.
Speaker 1: I'm not sure, But to me, these feel like solvable problems.
Speaker 1: And you know, we're young as a species technologically. In
Speaker 1: one hundred years and a thousand years will good this out,
Speaker 1: and maybe even by then somebody will have built an
Speaker 1: em drive.
Speaker 3: Well, And to surprise everybody, I am actually optimistic about
Speaker 3: some of this stuff, and I feel like these are
Speaker 3: really interesting problems that we have to solve, and imagine
Speaker 3: the other things that we're gonna learn along the way,
Speaker 3: where the new technologies will come up with as we
Speaker 3: try to make some of these methods work. I think
Speaker 3: it's all very.
Speaker 1: Exciting, all right, But before you get too excited, next episode,
Speaker 1: we're gonna talk about all the other tricky problems you
Speaker 1: would have to solve to get humans to another solar system,
Speaker 1: giving birth on board? Is it okay to have children
Speaker 1: born between planets? Embryos, robots, cryogenics, radiation, all that good stuff.
Speaker 1: So tune in next time for Kelly to throw a
Speaker 1: wet blanket on your interstellar dreams.
Speaker 3: That's what I do, so well out, all right.
Speaker 1: Tune in next time everyone.
Speaker 3: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
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