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Is it possible to travel to other stars? · Daniel and Kelly’s Extraordinary Universe

• 0:06
  Speaker 1: We know so much more about the universe than our
• 0:08
  Speaker 1: ancestors did. Go far enough back, and they didn't even
• 0:11
  Speaker 1: know that the pinpricks of light they see in the
• 0:13
  Speaker 1: sky are other suns. A few thousand years ago, they
• 0:17
  Speaker 1: had no idea how far away those other stars were,
• 0:20
  Speaker 1: and a few decades ago nobody knew for sure whether
• 0:24
  Speaker 1: they were planets around those stars. We know so much
• 0:27
  Speaker 1: more than they do, But we've also visited exactly the
• 0:31
  Speaker 1: same number of solar systems as they have, just the one.
• 0:35
  Speaker 1: Will we ever get out of our solar system and
• 0:37
  Speaker 1: make a home for humanity around an alien star? Is
• 0:41
  Speaker 1: there a physics obstacle? Or is it just political will
• 0:44
  Speaker 1: or lots of engineering. If it's actually impossible, that might
• 0:48
  Speaker 1: explain another great mystery why no aliens have visited us.
• 0:53
  Speaker 1: Maybe we aren't alone in being marooned on our home stars.
• 0:57
  Speaker 1: Maybe everyone is just stuck at home. Today on the pod,
• 1:00
  Speaker 1: we'll dive into the challenges, the technologies, and the potential
• 1:03
  Speaker 1: for taking humanity to those distant stars. Welcome to Daniel
• 1:07
  Speaker 1: and Kelly's Extraordinary Accessible Universe.
• 1:25
  Speaker 2: Hello.
• 1:25
  Speaker 3: I'm Kelly Winer Smith. I study parasites and space, and
• 1:29
  Speaker 3: if I could travel to the next nearest star, I wouldn't.
• 1:34
  Speaker 1: What about you, Daniel, Hi, I'm Daniel. I'm a particle physicist,
• 1:40
  Speaker 1: and I want to send somebody to the nearest star,
• 1:42
  Speaker 1: but I definitely don't want to go myself.
• 1:44
  Speaker 3: So why would you not want to go yourself? Can
• 1:46
  Speaker 3: you imagine all the physics stuff you could ponder and
• 1:49
  Speaker 3: maybe even figure out on an interstellar trip.
• 1:51
  Speaker 1: Oh yeah, I'd be desperate to talk to the aliens
• 1:54
  Speaker 1: about physics, to see what kind of weird technology they've invented.
• 1:58
  Speaker 1: But I'm just not that much of a traveler these Honestly,
• 2:00
  Speaker 1: I don't even like to get on an airplane, So
• 2:02
  Speaker 1: a spaceship absolutely not. The seeds you're gonna be uncomfortable
• 2:06
  Speaker 1: and the snacks are gonna be weird. You know, I'm
• 2:09
  Speaker 1: a homebody these days.
• 2:10
  Speaker 3: But you were born in one country, lived in another country,
• 2:14
  Speaker 3: and had kids in a third country.
• 2:16
  Speaker 4: Right.
• 2:16
  Speaker 3: You used to be an amazing traveler, but now it's home.
• 2:20
  Speaker 1: Huh time marches on? Absolutely? Yes, I can no longer
• 2:24
  Speaker 1: sleep anywhere anytime. My stomach is more sensitive. You know,
• 2:27
  Speaker 1: youth is wasted on the young.
• 2:29
  Speaker 3: Well, it sounds like you made good use of your
• 2:31
  Speaker 3: youth traveling all those places.
• 2:34
  Speaker 1: How about you, Why don't you want to go to
• 2:35
  Speaker 1: another planet.
• 2:36
  Speaker 3: If we ended up in another planet and there was
• 2:38
  Speaker 3: life there, that would be incredible. But I feel like
• 2:41
  Speaker 3: you don't necessarily know what you're gonna get until you
• 2:44
  Speaker 3: get there. But the thought of leaving, Like, so it's
• 2:46
  Speaker 3: spring while we're recording, which means in the next couple
• 2:49
  Speaker 3: weeks on the side of my barn, the light that's
• 2:52
  Speaker 3: on outside is going to attract little tree frogs and
• 2:55
  Speaker 3: all kinds of colorful moths. I just can't imagine leaving
• 2:58
  Speaker 3: this planet and leaving all that stuff behind to spend
• 3:01
  Speaker 3: like decades traveling in a tin can. But maybe they'd
• 3:04
  Speaker 3: have even better moths, and then I would feel regret.
• 3:08
  Speaker 1: It'd be amazing, though, if we got to that planet
• 3:10
  Speaker 1: and then we're like, this place is kind of ugly,
• 3:13
  Speaker 1: you know. I wonder if, like every planet has its
• 3:15
  Speaker 1: own beauty, or if our evolutionary history on Earth primes
• 3:18
  Speaker 1: us to only find, you know, the Sierras and the
• 3:22
  Speaker 1: Blue Ridge Mountains beautiful. See how I included Virginia.
• 3:25
  Speaker 3: I appreciate that. Yeah, No, we're being nice to each
• 3:27
  Speaker 3: other on this episode. I guess that's great. I also
• 3:30
  Speaker 3: it would really stink to know that you were never
• 3:32
  Speaker 3: going to see any anybody else that you had known
• 3:35
  Speaker 3: your whole life ever again. And like the farther away
• 3:38
  Speaker 3: you get, the harder it is to communicate. But so
• 3:40
  Speaker 3: let's dig into the to the meat of our discussion today,
• 3:43
  Speaker 3: and we're talking about is it possible for humans to
• 3:45
  Speaker 3: travel to other stars?
• 3:47
  Speaker 1: Yeah? And I think this question is interesting and important
• 3:50
  Speaker 1: because while we want to explore the universe robotically and
• 3:53
  Speaker 1: gather information telescopically, I think also we have a primal
• 3:57
  Speaker 1: need to explore, to go places, and to expand out
• 4:01
  Speaker 1: into the universe. I think it's a question a lot
• 4:03
  Speaker 1: of people have about whether it's possible today, whether it
• 4:06
  Speaker 1: might be possible in a thousand years, or whether it
• 4:08
  Speaker 1: might never be possible for humans to cross the vast
• 4:12
  Speaker 1: oceans of space to other stars. So I went out
• 4:15
  Speaker 1: and I asked our listeners if they thought it was possible.
• 4:18
  Speaker 1: If you would like to play for this part of
• 4:20
  Speaker 1: the podcast in the future, please don't be shy. Write
• 4:22
  Speaker 1: to us at questions at Danielankelly dot org. We would
• 4:26
  Speaker 1: love to have your voice on the pod. So think
• 4:29
  Speaker 1: about it for a minute. Do you think it's possible
• 4:31
  Speaker 1: for humans to travel to other stars? Here's what our
• 4:34
  Speaker 1: audience had to say.
• 4:36
  Speaker 5: We can imagine traveling to other solar systems, but can
• 4:40
  Speaker 5: we deal with all the questions radiation, food, power sources, generationships.
• 4:46
  Speaker 5: We just don't know enough at this point.
• 4:49
  Speaker 1: I would say no for the foreseeable future, but in
• 4:54
  Speaker 1: multiple generations, after multiple generations, I think that would be possible.
• 4:59
  Speaker 1: What it would take thousand of years and the ship
• 5:01
  Speaker 1: would have to survive. You'd go through accidents, there would
• 5:04
  Speaker 1: be warring factions on the ship. You need a multi
• 5:07
  Speaker 1: generational ship.
• 5:08
  Speaker 6: Well, I'd say it's possible, but not probable within the
• 5:11
  Speaker 6: next one hundred years. There are a lot of hurdles
• 5:13
  Speaker 6: to overcome, propulsion being a major one in supplies. Maybe
• 5:19
  Speaker 6: if you had a fusion powered plasma or something.
• 5:24
  Speaker 7: I bet we could get a human being there in
• 5:26
  Speaker 7: their lifetime with acceleration that won't kill them, But I
• 5:29
  Speaker 7: think stopping will be really hard and definitely turning around
• 5:32
  Speaker 7: will be nearly impossible, so they can't come back.
• 5:34
  Speaker 4: Humans don't have enough time to live, and our bodies
• 5:40
  Speaker 4: would be destroyed by the acceleration required to reach another
• 5:45
  Speaker 4: solar system.
• 5:47
  Speaker 1: With today's technology. I don't believe it is strictly possible.
• 5:55
  Speaker 1: I think it's definitely possible. There's no law that says
• 5:59
  Speaker 1: we couldn't do it. There's still some major challenges ahead
• 6:02
  Speaker 1: of us. Anything is possible, but humans traveling to another
• 6:05
  Speaker 1: solar system may be a stretch. Now it is impossible.
• 6:11
  Speaker 5: I don't think a single person could make it to
• 6:15
  Speaker 5: another solar system, but maybe multiple generations.
• 6:18
  Speaker 8: Even if you could travel at the speed of light,
• 6:21
  Speaker 8: it would still take years to get to the nearest star,
• 6:24
  Speaker 8: which we don't even know if there's a solar system around,
• 6:27
  Speaker 8: and you'd have to confirm that first. Even if we
• 6:30
  Speaker 8: could technology got better, we'd still probably need a generational
• 6:33
  Speaker 8: star here.
• 6:34
  Speaker 9: Unless we destroy ourselves with war or refusal to confront
• 6:40
  Speaker 9: climate change. We will eventually reach other solar systems.
• 6:47
  Speaker 10: Maybe if money isn't a problem in the future, if
• 6:49
  Speaker 10: we tackles certain things, maybe we could. But I think
• 6:54
  Speaker 10: it's for now the ultimate pipe dream.
• 6:58
  Speaker 2: Yes it is possible, but whether it is probable is
• 7:01
  Speaker 2: a different question. And even if it is probable, and
• 7:04
  Speaker 2: even if it's undertaken, I don't think that the humans
• 7:07
  Speaker 2: who would leave our solar system to get to the
• 7:10
  Speaker 2: other solar system would be alive. When we get to
• 7:14
  Speaker 2: the other.
• 7:15
  Speaker 1: Solar system, we should assume that the aliens at the
• 7:18
  Speaker 1: solar systems will be hostile, and therefore we should send
• 7:22
  Speaker 1: all the people that we dislike the most.
• 7:25
  Speaker 3: Maybe through like a cryo sleep or human hibernation type thing,
• 7:30
  Speaker 3: something like that.
• 7:31
  Speaker 9: I believe we are marooned here.
• 7:33
  Speaker 3: No, we can't do that right now, but maybe some
• 7:36
  Speaker 3: day in the future.
• 7:37
  Speaker 8: From a physical point yes, From engineering point likely no.
• 7:43
  Speaker 3: I loved the variability of answers that we got here,
• 7:46
  Speaker 3: and I should say that as someone who interacts with
• 7:49
  Speaker 3: the space settlement community, I have no doubt that even
• 7:53
  Speaker 3: if somebody were to say, like, we've made a generationship,
• 7:55
  Speaker 3: there's a one percent chance it's going to make it.
• 7:57
  Speaker 3: Every seat on that ship would get filled. So, you know,
• 8:00
  Speaker 3: I think there's a lot of people who really love
• 8:02
  Speaker 3: this idea.
• 8:02
  Speaker 1: Well, why do you think we would have no shortage
• 8:05
  Speaker 1: of volunteers? You think there are people who, like in reality,
• 8:08
  Speaker 1: would actually sign up to go. They're not just like
• 8:10
  Speaker 1: excited about the concept.
• 8:12
  Speaker 3: Oh my gosh, they send me angry emails. There have
• 8:14
  Speaker 3: been so many people who have written me to tell
• 8:16
  Speaker 3: me that I cannot stop them from settling space, and
• 8:19
  Speaker 3: I write them back and I say, I cannot stop you.
• 8:23
  Speaker 3: That's right, And I'm not crying too. I don't think
• 8:25
  Speaker 3: I have any power over these kinds of decisions. I
• 8:27
  Speaker 3: just wrote a book saying it's kind of dangerous.
• 8:30
  Speaker 1: And maybe we should think this all through before we go.
• 8:33
  Speaker 3: But hey, do what you want, Yep, yep, do your things.
• 8:35
  Speaker 3: So anyway, I'm sure there'd be a lot of people,
• 8:37
  Speaker 3: and you know, it would be an absolutely incredible thing
• 8:41
  Speaker 3: if our species did send a generationship, for example, to
• 8:44
  Speaker 3: another star.
• 8:45
  Speaker 1: It would be incredible. And I love how this topic
• 8:48
  Speaker 1: is so deeply inspired and informed by science fiction. You know,
• 8:52
  Speaker 1: obviously there's science here, and we're going to talk about
• 8:54
  Speaker 1: all the nerdy details of propulsion mechanisms, et cetera. But
• 8:57
  Speaker 1: so many the ideas here come from the creativity of
• 9:00
  Speaker 1: science fiction authors casting their minds forward to imagine what
• 9:04
  Speaker 1: we might be able to build, what we might need
• 9:06
  Speaker 1: to build, what we might have to do to survive.
• 9:09
  Speaker 3: Yeah, what is your favorite interstellar travel sci fi book?
• 9:13
  Speaker 6: Oh?
• 9:14
  Speaker 1: Wow, such a good question. One of my favorites is
• 9:16
  Speaker 1: a book by Alistair Reynolds. I think it's called the
• 9:18
  Speaker 1: House of Suns, in which they tackle this problem by
• 9:23
  Speaker 1: dragging stars closer to each other. So they want to
• 9:26
  Speaker 1: have like a galactic empire across many solar systems, but
• 9:30
  Speaker 1: they don't have faster than light travel, and they recognize
• 9:33
  Speaker 1: that it's basically impossible to govern somebody if you're there
• 9:36
  Speaker 1: so far away, So they bring a bunch of suns
• 9:38
  Speaker 1: closer to each other, make a little solar neighborhood, so
• 9:41
  Speaker 1: you can have different solar systems but they're not so
• 9:43
  Speaker 1: far away.
• 9:44
  Speaker 3: I like that idea, but it sounds kind of dangerous.
• 9:47
  Speaker 1: Well, we're going to talk about that technology, which isn't
• 9:50
  Speaker 1: as far fetched as you might imagine at the end
• 9:53
  Speaker 1: of the episode.
• 9:54
  Speaker 3: So let's go ahead and dig right in. But first,
• 9:56
  Speaker 3: let's talk about where would we be going. Where is
• 9:58
  Speaker 3: our closest option here?
• 10:00
  Speaker 1: Yes, so the Milky Way galaxy has hundreds of billions
• 10:03
  Speaker 1: of stars, but the whole thing is like one hundred
• 10:06
  Speaker 1: thousand light years across, which is really big, and the
• 10:10
  Speaker 1: density of stars in our neighborhood is not so high.
• 10:13
  Speaker 1: It actually varies a lot. In the center of the
• 10:16
  Speaker 1: Milky Way. It's much much denser. But around where we are,
• 10:19
  Speaker 1: we're like in the suburbs, not quite the ex serbs,
• 10:21
  Speaker 1: in the very fringes of the Milky Way. But out
• 10:23
  Speaker 1: here in the suburbs, you can expect to find a
• 10:25
  Speaker 1: star a few light years away, and that's what we find.
• 10:28
  Speaker 1: Alpha Centauri and Proxima Centari are like just around four
• 10:32
  Speaker 1: light years away. So if you wanted to get to
• 10:33
  Speaker 1: the nearest star uneasy mode, you'd be going to the
• 10:36
  Speaker 1: closest one. It's still four light years away. And remember
• 10:40
  Speaker 1: the speed of light, super duper fast. If you shined
• 10:43
  Speaker 1: a laser beam at one of these stars, it'd be
• 10:45
  Speaker 1: zipping through the cosmos at an incredible speed for four
• 10:48
  Speaker 1: full years before it got there.
• 10:50
  Speaker 3: And so say you get to Alpha Centauri, do we
• 10:52
  Speaker 3: know that there are earth like planets there that we
• 10:55
  Speaker 3: could try to explore? What would we see once we
• 10:57
  Speaker 3: got there?
• 10:58
  Speaker 1: Yeah, there's actually good news there. You know, until like
• 11:01
  Speaker 1: twenty ish years ago, we had no idea what planets
• 11:04
  Speaker 1: were like around other stars, or if there even were any.
• 11:08
  Speaker 1: We'd only ever seen the planets in our Solar system
• 11:10
  Speaker 1: until the mid nineties, when we started developing the technology
• 11:13
  Speaker 1: to see exoplanets. Now we specifically identified five thousand exo planets.
• 11:18
  Speaker 1: At least the number keeps going up and up and
• 11:20
  Speaker 1: up and up. It's like a real pivot point in
• 11:22
  Speaker 1: human history. And because of that we can make all
• 11:25
  Speaker 1: sorts of really interesting statistical statements, like, on average, stars
• 11:29
  Speaker 1: have a good number of planets, and specifically Proximusentari and
• 11:34
  Speaker 1: Alpha Centauri do have some planets, and so it's very
• 11:37
  Speaker 1: unusual actually for stars to have no planets as far
• 11:40
  Speaker 1: as we can tell. So if you're going to go
• 11:41
  Speaker 1: to a nearby star, it's very likely you'll find some
• 11:43
  Speaker 1: planets there. Whether they're Earth like and whether they are
• 11:46
  Speaker 1: capable of supporting life a whole other question that we
• 11:49
  Speaker 1: think the next generation of space telescopes will really help
• 11:52
  Speaker 1: us crack. But from the point of view today's conversation,
• 11:55
  Speaker 1: let's just imagine getting to that Solar system, not necessarily
• 11:59
  Speaker 1: finding a cozy how there.
• 12:00
  Speaker 3: Okay, so let's see I'm forty two. Now, if I
• 12:04
  Speaker 3: were going to jump on one of these ships, and
• 12:05
  Speaker 3: I was hoping that we would arrive by you know,
• 12:07
  Speaker 3: the average lifespan of a human woman, So what that's
• 12:11
  Speaker 3: like eighty six or something like that. So we've got
• 12:13
  Speaker 3: let's say we've got about forty years to get there.
• 12:15
  Speaker 3: How fast do we need to go?
• 12:17
  Speaker 1: Yeah, so if you traveled at the speed of light,
• 12:19
  Speaker 1: you get there in four years. Of course, you can't
• 12:21
  Speaker 1: travel at the speed of light because nothing that has
• 12:23
  Speaker 1: mask can travel at the speed of light. So let's
• 12:25
  Speaker 1: say you could go at ten percent of the speed
• 12:27
  Speaker 1: of light already blazingly fast, much much faster than any
• 12:31
  Speaker 1: human ship has achieved crude or uncrued. But if you
• 12:34
  Speaker 1: did somehow manage that, you would get to altha centauri
• 12:36
  Speaker 1: in about forty years, right, a tenth of the speed
• 12:39
  Speaker 1: of light four light years, so forty years. So that's
• 12:42
  Speaker 1: basically what you need to achieve. But the sort of
• 12:44
  Speaker 1: space technology we have now really just isn't capable of that.
• 12:48
  Speaker 1: Like the fastest crude rocket or the Space Shuttle, for example,
• 12:51
  Speaker 1: their top speeds would take them about eighty thousand years
• 12:55
  Speaker 1: to get there, not to mention the question of like
• 12:57
  Speaker 1: bringing in a fuel that will dig into in a minute.
• 13:00
  Speaker 1: And even the uncrewed stuff like the Parker solar Probe
• 13:03
  Speaker 1: is the fastest thing humanity has ever built. Its top
• 13:06
  Speaker 1: speed is about zero point zero six four percent of
• 13:10
  Speaker 1: the speed of light. Oh no, you take about seven
• 13:13
  Speaker 1: thousand years to get to Alpha Centauri. So nothing we've
• 13:17
  Speaker 1: built can go nearly fast enough to get Kelly to
• 13:20
  Speaker 1: Alpha Centauri before her eighty fifth birthday.
• 13:22
  Speaker 3: Oh that's right. I wasn't going to go anyway, although
• 13:24
  Speaker 3: maybe maybe if they had really great moths. I'm disappointed.
• 13:28
  Speaker 3: But so I feel like there's there's a couple problems here.
• 13:31
  Speaker 3: It's like, one, can you even get to the speed
• 13:35
  Speaker 3: that you want? But then two, how do you get
• 13:37
  Speaker 3: to that speed? Because like, if you're sending humans, we've
• 13:40
  Speaker 3: got these squishy bodies, and if you accelerate us too fast,
• 13:42
  Speaker 3: we like we break and smoosh, and so you need
• 13:45
  Speaker 3: to like get fast but not too fast.
• 13:47
  Speaker 1: Yeah, so there's a lot going on here. I mean,
• 13:49
  Speaker 1: one thing is just the limitation of relativity. Number one.
• 13:52
  Speaker 1: You can't get faster than the speed of light. We'll
• 13:54
  Speaker 1: talk about warp drives in a minute, but assuming that
• 13:57
  Speaker 1: you're going through space, through flat space, you can't travel
• 14:00
  Speaker 1: faster than that. And that's a hard limit. And I
• 14:02
  Speaker 1: think it's important for people to think about that as
• 14:04
  Speaker 1: sort of setting the length scale of the universe, Because
• 14:07
  Speaker 1: we talked a minute ago about like, wow, it's super
• 14:09
  Speaker 1: duper fast. It is super duper fast. But space is
• 14:12
  Speaker 1: vast compared to the speed of light. Like, we wouldn't
• 14:15
  Speaker 1: think space was so big if the speed of light
• 14:17
  Speaker 1: was ten times or one hundred times what it is,
• 14:20
  Speaker 1: because then these things would be like less than a
• 14:22
  Speaker 1: light year away, or we would think space was much
• 14:24
  Speaker 1: bigger if the speed of light was smaller. So the
• 14:26
  Speaker 1: speed of light sort of determines like what is far
• 14:29
  Speaker 1: and what is close, And it just so happens that
• 14:32
  Speaker 1: because of our galactic dynamics, things are a few light
• 14:35
  Speaker 1: years away instead of tenths of light year away. But
• 14:37
  Speaker 1: even if you're not going to get to the speed
• 14:39
  Speaker 1: of light, this limit at the speed of light makes
• 14:41
  Speaker 1: it hard to accelerate. Like you keep pouring energy into
• 14:44
  Speaker 1: your rocket, you're not going to increase your velocity by
• 14:47
  Speaker 1: the same amount. As you go faster and faster, it
• 14:50
  Speaker 1: takes more and more energy to increase your velocity. And
• 14:53
  Speaker 1: as I think you were hinting, there are also limits
• 14:55
  Speaker 1: on how quickly you can accelerate, like biologically.
• 14:59
  Speaker 3: Yeah, so that's the interesting part.
• 15:01
  Speaker 1: Well, it's true that we do want to deliver our
• 15:02
  Speaker 1: passengers to Alvis Centauri, not as bags of dead goo. Right,
• 15:07
  Speaker 1: we want to take care of all their fragile little
• 15:09
  Speaker 1: organs and make sure that they actually get there. And
• 15:12
  Speaker 1: so if you want to get to some sort of
• 15:14
  Speaker 1: reasonable speed so your trip doesn't take too long, you
• 15:16
  Speaker 1: need to accelerate, and humans are not really built for
• 15:19
  Speaker 1: huge acceleration. I was reading some papers that said the
• 15:22
  Speaker 1: humans can tolerate like twenty G of acceleration G there,
• 15:26
  Speaker 1: of course referring to the acceleration of gravity here on
• 15:29
  Speaker 1: Earth as basic standard units of one G. So twenty
• 15:33
  Speaker 1: G is pretty intense, and we can't really tolerate that
• 15:36
  Speaker 1: for more than like a few seconds, maybe ten seconds. Humans,
• 15:39
  Speaker 1: like the really tough ones, can tolerate like ten G
• 15:42
  Speaker 1: for a minute, five G for a few minutes. But
• 15:45
  Speaker 1: imagine being on this ship. You're going to be on
• 15:47
  Speaker 1: it for years at least. You don't want more than
• 15:51
  Speaker 1: like one G or maybe even two G for long periods.
• 15:55
  Speaker 3: You know, we got a lot of the early data
• 15:57
  Speaker 3: on how many g's humans can survive because there was
• 15:59
  Speaker 3: the one scientist who kept getting in a sled and
• 16:02
  Speaker 3: then slamming himself into a foam wall. And so anyway,
• 16:06
  Speaker 3: human ingenuity. I love it, so just to make sure
• 16:09
  Speaker 3: I have the physics understanding of this. So like if
• 16:12
  Speaker 3: you speed up and then you stay at that speed,
• 16:16
  Speaker 3: you only experience the G as you're accelerating, right, not
• 16:19
  Speaker 3: just because you're going fast, but because you are going
• 16:21
  Speaker 3: faster every second. Is that right?
• 16:23
  Speaker 1: That's right? Okay, that's right. You can't experience velocity directly.
• 16:26
  Speaker 1: It's a relative thing right inside your ship. You can't
• 16:29
  Speaker 1: tell how faster ship is going. But if your ship
• 16:31
  Speaker 1: turns on the engines and tries to increase its speed,
• 16:34
  Speaker 1: you can measure acceleration locally. It's not relative, So as
• 16:37
  Speaker 1: your ship tries to increase its speed, you can feel that.
• 16:40
  Speaker 1: And something that's sort of surprising to me is that
• 16:42
  Speaker 1: you can actually accelerate at one G and reach near
• 16:47
  Speaker 1: the speed of light in a reasonable amount of time.
• 16:50
  Speaker 1: Like if you're on a rocket that can do one
• 16:52
  Speaker 1: G of acceleration, you can just do that for a year,
• 16:55
  Speaker 1: and you'll get up to like ninety nine percent of
• 16:57
  Speaker 1: the speed of light relative to your departure location.
• 17:00
  Speaker 3: And in that case, you would get there in less
• 17:02
  Speaker 3: than forty years. Right, because now instead of going ten
• 17:04
  Speaker 3: percent the speed of light, you're going the speed of light.
• 17:06
  Speaker 1: Yeah, that's right, but you need a technology that can
• 17:10
  Speaker 1: provide one g of acceleration for a whole year, as
• 17:13
  Speaker 1: we're going to talk about. That's not so easy to do, right.
• 17:16
  Speaker 1: That's an enormous amount of thrust or momentum you're imparting
• 17:20
  Speaker 1: on your ship.
• 17:21
  Speaker 3: There's always something in the way.
• 17:23
  Speaker 1: There's always something in the way. And the flip side
• 17:26
  Speaker 1: of all of this is deceleration or negative acceleration, because
• 17:30
  Speaker 1: you could get up to near the speed of light,
• 17:32
  Speaker 1: and then you could get to Alpha Centauri, but then
• 17:34
  Speaker 1: you're going to be in that Solar system for about
• 17:36
  Speaker 1: zero point zero seven seconds if you're traveling at near
• 17:39
  Speaker 1: the speed of light. But what you want to do
• 17:41
  Speaker 1: is arrive there and stop, which means decelerating. And you
• 17:44
  Speaker 1: don't want to decelerate from the speed of light to
• 17:46
  Speaker 1: zero too quickly, otherwise you'll again go splat.
• 17:51
  Speaker 3: Yeah, humans, it's a shame. We're so squishy.
• 17:55
  Speaker 1: And I think on the next episode we're going to
• 17:57
  Speaker 1: talk about making humans less squishy by like turning into
• 18:00
  Speaker 1: human sickles, and that might be a better way to
• 18:02
  Speaker 1: accelerate human bodies. I don't know, you'll have to tell
• 18:05
  Speaker 1: me all about it.
• 18:06
  Speaker 3: We are going to talk about the human side of
• 18:08
  Speaker 3: things in the next episode. I'm not sure that human
• 18:10
  Speaker 3: sickles is on my outline, but we'll see what I
• 18:13
  Speaker 3: come up with.
• 18:14
  Speaker 1: It is now, because I'm going to ask you about it.
• 18:16
  Speaker 3: Okay, great.
• 18:17
  Speaker 1: And so a typical strategy is to accelerate on the
• 18:20
  Speaker 1: first half of the trip and then basically turn your
• 18:23
  Speaker 1: ship around and decelerate all the way back to your
• 18:26
  Speaker 1: initial velocity now relative to your destination. And so you
• 18:30
  Speaker 1: accelerate and you reach top speed momentarily halfway there, and
• 18:34
  Speaker 1: you turn around and you're slowing down the whole second
• 18:36
  Speaker 1: half of the trip. And this is actually kind of
• 18:38
  Speaker 1: cool because along the way you might want to feel
• 18:40
  Speaker 1: some artificial gravity. As you're probably going to tell us,
• 18:43
  Speaker 1: humans don't like to float in space forever. It's not
• 18:45
  Speaker 1: good for us, and so you want to feel one G.
• 18:49
  Speaker 1: And so having one G of acceleration and then one
• 18:51
  Speaker 1: G of deceleration the whole trip is actually kind of cozy.
• 18:54
  Speaker 3: So if you had one G of acceleration for one year,
• 18:56
  Speaker 3: you would still have what two or three years just
• 19:01
  Speaker 3: staying at that velocity before you start decelerating, so there
• 19:03
  Speaker 3: would be a period where you would have no g's
• 19:06
  Speaker 3: in between.
• 19:07
  Speaker 1: Yeah, absolutely, depending on the length of the trip. If
• 19:09
  Speaker 1: you wanted to go further. For example, you could accelerate
• 19:11
  Speaker 1: at one G for a year, get up to near
• 19:12
  Speaker 1: the speed of light, zoom around super duper fast, and
• 19:16
  Speaker 1: then flip around and decelerate. So, yeah, you can have
• 19:18
  Speaker 1: a period in the middle where you're not accelerating or decelerating.
• 19:21
  Speaker 1: Then you got to solve that gravity problem another way,
• 19:23
  Speaker 1: all right.
• 19:24
  Speaker 3: All right, and we'll talk about that in the next episode.
• 19:26
  Speaker 1: And that's not the only thing that's going to potentially
• 19:28
  Speaker 1: kill you along the way. You know, we think of
• 19:30
  Speaker 1: space as empty, but it's not really like there's a
• 19:32
  Speaker 1: lot of particles out there. There's huge amounts of gas
• 19:35
  Speaker 1: the interstellar medium. There's lots of little bits of tiny rocks.
• 19:39
  Speaker 1: We call that dust. It's out there, and if you're
• 19:42
  Speaker 1: traveling at relativistic speeds relative to that dust, you can
• 19:46
  Speaker 1: be in danger. You know, these tiny particles, A millimeter
• 19:49
  Speaker 1: sized particle at like even if half of the speed
• 19:52
  Speaker 1: of light is an enormous amount of energy deposited on
• 19:54
  Speaker 1: your ship. And so you got to really worry about
• 19:57
  Speaker 1: this and cosmic rays and radiation, So your ship has
• 20:01
  Speaker 1: to be pretty robust. You need shielding, you need like
• 20:04
  Speaker 1: titanium or water or lead or something. All this is
• 20:06
  Speaker 1: going to make your ship heavier. So we'll dig into
• 20:08
  Speaker 1: that more in the next episode where we talk about
• 20:11
  Speaker 1: the fragility of the human body and how to survive this.
• 20:13
  Speaker 1: But keep that in mind as we're talking about the
• 20:15
  Speaker 1: propulsion designs, because it's going to affect how much you
• 20:18
  Speaker 1: got to move on the way to another star.
• 20:20
  Speaker 3: So to me, the dust feels like the first showstopper
• 20:25
  Speaker 3: that we've encountered. What makes us think that, you know,
• 20:29
  Speaker 3: when each piece of dust hitting us is like getting
• 20:31
  Speaker 3: hit with a bomb, what makes us think that we
• 20:33
  Speaker 3: can like, I mean, we're clearly not going to dodge
• 20:35
  Speaker 3: the dust. So what is the dust solution?
• 20:37
  Speaker 1: Well, you know, I've read about some cool shields. There's
• 20:40
  Speaker 1: like these whipple shields. I basically break up the dust
• 20:42
  Speaker 1: into smaller pieces so that none of them are likely
• 20:46
  Speaker 1: to like, really be devastating. There's some cool technology like
• 20:49
  Speaker 1: self healing shields. So I think it's an engineering problem
• 20:53
  Speaker 1: and one that we're likely to be able to crack.
• 20:57
  Speaker 1: But Yeah, it's definitely an important one.
• 20:58
  Speaker 3: I love your optimism, Dan, I always love your optimism,
• 21:03
  Speaker 3: all right, So we're going to be talking about ways
• 21:06
  Speaker 3: to get there. Are the ways that you're going to
• 21:07
  Speaker 3: talk to us about ways that could get us there
• 21:10
  Speaker 3: in a lifetime or is there anything else that might
• 21:12
  Speaker 3: work for us here?
• 21:13
  Speaker 1: Some of these solutions really can get you there in
• 21:15
  Speaker 1: a lifetime. But because it's physics, time is a slippery concept,
• 21:19
  Speaker 1: like are we talking about the lifetime for the people
• 21:21
  Speaker 1: you left behind or lifetime for people on board? Because
• 21:25
  Speaker 1: as soon as you get up to really high speed
• 21:27
  Speaker 1: relative to your departure planet, those are not the same thing. So,
• 21:31
  Speaker 1: for example, say you accelerate at one G and you
• 21:34
  Speaker 1: get up to near the speed of light, you could
• 21:37
  Speaker 1: travel for just a few years your time, a decade
• 21:39
  Speaker 1: your time, and like one hundred thousand years will have
• 21:42
  Speaker 1: passed back home. And if you're traveling near the speed
• 21:45
  Speaker 1: of light, one hundred thousand years is enough time to
• 21:47
  Speaker 1: get you across the galaxy in only like a decade
• 21:51
  Speaker 1: of your time. So Kelly gets on board the ship.
• 21:55
  Speaker 1: She arrives at the other side of the Milky Way
• 21:58
  Speaker 1: that no human has even clearly seen before because all
• 22:00
  Speaker 1: a gasl and dust and she's only fifty ish. Meanwhile,
• 22:04
  Speaker 1: back home, Zach is one hundred thousand years old.
• 22:07
  Speaker 3: Oh my gosh. And I'm a narcissist. So what I
• 22:09
  Speaker 3: care about is how long it takes me. When we
• 22:12
  Speaker 3: say it's gonna take eighty it would take like eighty
• 22:14
  Speaker 3: years to get there if you went ten percent the
• 22:16
  Speaker 3: speed of light. Is that that's eighty my years as
• 22:20
  Speaker 3: a person on the ship, right, So our frame of
• 22:22
  Speaker 3: reference is always the people on the ship.
• 22:24
  Speaker 1: Well, it was gonna take forty years to get there
• 22:26
  Speaker 1: at ten percent the speed of light in human years,
• 22:29
  Speaker 1: but at ten percent the speed of light is not
• 22:31
  Speaker 1: that much of a relativistic time dilation effect. That really
• 22:34
  Speaker 1: kicks up when you go half or three quarters the
• 22:36
  Speaker 1: speed of light, So that's still going to be decades
• 22:40
  Speaker 1: earth time and ship time. If you do get like
• 22:42
  Speaker 1: up above fifty sixty seventy percent the speed of light,
• 22:46
  Speaker 1: then you start to benefit from these time dilation effects.
• 22:49
  Speaker 1: So on the ship it takes less time.
• 22:51
  Speaker 3: Got it, Okay? And on the next episode we're going
• 22:53
  Speaker 3: to talk about generationships where if you just accept it's
• 22:56
  Speaker 3: not going to happen in a lifetime. Because your technology
• 22:58
  Speaker 3: can't get you that fast, how do you carry generations
• 23:01
  Speaker 3: of humans to still get there? But we're going to
• 23:04
  Speaker 3: take a break now, and when we get back from
• 23:06
  Speaker 3: the break, Daniel's going to walk us through our rocket
• 23:08
  Speaker 3: options for our trip to the stars. All right, let's
• 23:29
  Speaker 3: talk about our transport methods to get us to Alpha Centauri,
• 23:33
  Speaker 3: starting with the most near term likely technology.
• 23:38
  Speaker 1: So we want to get to Alpha Centauri, which means
• 23:40
  Speaker 1: we've got to move away from Earth, which means we
• 23:43
  Speaker 1: need to gain momentum away from Earth. In our universe,
• 23:47
  Speaker 1: momentum is conserved. So you have your ship. You wanted
• 23:50
  Speaker 1: to gain momentum in one direction, there needs to be
• 23:53
  Speaker 1: some sort of compensating momentum in the other direction. This
• 23:57
  Speaker 1: is something you feel if you like fire a gun,
• 23:59
  Speaker 1: for example, you feel that kickback. That's the conservation of momentum.
• 24:04
  Speaker 1: The rifle is shooting the bullet super duper fast, but
• 24:06
  Speaker 1: the bullet has a small mass, and the rifle itself
• 24:09
  Speaker 1: has that larger mass is moving backwards in the other
• 24:12
  Speaker 1: direction with the compensating velocity.
• 24:15
  Speaker 3: See I always imagine it as I'm trying to get
• 24:17
  Speaker 3: a boat to move and I'm imagining Daniel on a
• 24:19
  Speaker 3: cruise ship taking all of the white chocolate and throwing
• 24:22
  Speaker 3: it in the ocean to get the cruise ship to
• 24:24
  Speaker 3: move faster while also getting rid of the bad chocolate.
• 24:27
  Speaker 1: Yeah, that's exactly right. You need to build momentum in
• 24:30
  Speaker 1: the other direction. So imagine you are on a boat
• 24:32
  Speaker 1: and you're tossing stones or equivalently, white chocolate or hot
• 24:36
  Speaker 1: garbage or whatever useless stuff you happen to have on
• 24:40
  Speaker 1: the boat. Right, you create momentum in one direction for
• 24:43
  Speaker 1: the stones, and in recoil you go the other way.
• 24:47
  Speaker 1: And so all rocket drives operate under this same principle.
• 24:51
  Speaker 1: You need two things. You need energy and then you
• 24:53
  Speaker 1: need mass. So you use the energy to throw the
• 24:55
  Speaker 1: mass out the back and you go the other way.
• 24:58
  Speaker 1: That's the way all the rockets we're going to talk
• 25:00
  Speaker 1: about work.
• 25:01
  Speaker 3: And that's how like the Falcon nine or starship works
• 25:05
  Speaker 3: when it takes off too right.
• 25:06
  Speaker 1: Yeah, exactly. And the issue here is that you need
• 25:09
  Speaker 1: something to produce that energy, and you need something to
• 25:12
  Speaker 1: throw out the back, and when you run out of that,
• 25:14
  Speaker 1: you can't go anymore. And because you have to bring
• 25:17
  Speaker 1: that fuel with you, you need enough fuel to push that fuel,
• 25:20
  Speaker 1: and then you need more fuel to push that fuel.
• 25:22
  Speaker 1: And so there's this famous rocket equation which tells you
• 25:25
  Speaker 1: like how much fuel you need to get up to
• 25:27
  Speaker 1: a certain velocity. It depends on the mass of the
• 25:30
  Speaker 1: ship and also depends on the specific impulse that your
• 25:33
  Speaker 1: engine is able to provide. It's just basically just like
• 25:35
  Speaker 1: a number. Some of them are high, some of them
• 25:37
  Speaker 1: are low. But the bottom line is that the math
• 25:39
  Speaker 1: tells us that there's an exponential need for fuel. If
• 25:43
  Speaker 1: you want to get up to higher velocity. So you
• 25:46
  Speaker 1: want to go twice as fast, you don't need twice
• 25:48
  Speaker 1: as much fuel, You need much much more. You need
• 25:50
  Speaker 1: exponentially more fuel, and as you increase that velocity, the
• 25:53
  Speaker 1: amount of fuel grows ridiculously. So for example, even like
• 25:57
  Speaker 1: the Saturn rockets, the ones that took us to the Moon,
• 26:00
  Speaker 1: when they launched, they were like ninety five percent fuel.
• 26:02
  Speaker 1: It's mostly fuel being taken off and that fuel is
• 26:05
  Speaker 1: mostly being used to push the rest of the fuel.
• 26:08
  Speaker 3: That absolutely blew my mind when I first learned it
• 26:10
  Speaker 3: that like less than ten percent of that giant that
• 26:14
  Speaker 3: you know, that giant tube was actually going to be
• 26:16
  Speaker 3: going to the Moon.
• 26:17
  Speaker 1: And people are often confused about rockets versus escape velocity. Remember,
• 26:22
  Speaker 1: escape velocity is a calculation you do if you're like
• 26:25
  Speaker 1: throwing something from the surface of the Earth, you need
• 26:28
  Speaker 1: a certain velocity because gravity is going to slow you down,
• 26:30
  Speaker 1: and if you have higher than the escape velocity, you
• 26:32
  Speaker 1: can leave the orbit. But rockets are not about escape
• 26:35
  Speaker 1: velocity because rockets have constant thrust. Rockets can lift off
• 26:39
  Speaker 1: it basically zero points zero zero zero zero zero one
• 26:42
  Speaker 1: meters per second and still make it to space because
• 26:45
  Speaker 1: they're pushing themselves constantly. They're like climbing a ladder rather
• 26:49
  Speaker 1: than just getting a single push. So escape velocity is
• 26:52
  Speaker 1: not relevant for rockets. What is relevant for rockets is
• 26:56
  Speaker 1: this specific impulse and how fast you want to go.
• 26:59
  Speaker 3: So in this case, the rocket would be not just
• 27:01
  Speaker 3: getting us off Earth, but it would stay with us
• 27:03
  Speaker 3: and it would continue to propel us through space.
• 27:05
  Speaker 1: Yeah, exactly. And the sort of bog standard rocket we
• 27:08
  Speaker 1: have is a chemical rocket where the thing that you're
• 27:11
  Speaker 1: throwing at the back is also the way you're getting energy. Basically,
• 27:15
  Speaker 1: you have like exploding stones that you're throwing out the back.
• 27:18
  Speaker 1: The stones throw themselves out the back, right, because the
• 27:21
  Speaker 1: fuel is the propellant and the source of energy. You
• 27:24
  Speaker 1: light it on fire and the explosion goes out the back.
• 27:27
  Speaker 1: You get pushed the other direction, and so that's cool.
• 27:30
  Speaker 1: And you know, obviously fuel we can find here on Earth,
• 27:33
  Speaker 1: but the specific impulse of these engines is not huge, right,
• 27:37
  Speaker 1: So it's not a great way to get going really
• 27:39
  Speaker 1: really fast unless you have incredible quantities of fuel. So
• 27:44
  Speaker 1: this is the rocket equation at work here. So if
• 27:47
  Speaker 1: you do a little calculation, like how much fuel does
• 27:49
  Speaker 1: it take to get off of Earth and to the
• 27:52
  Speaker 1: Moon an enormous quantity, right, filling a huge Saturn rocket.
• 27:56
  Speaker 1: How much fuel does it take to get to Alpha
• 27:59
  Speaker 1: Centauri if you've got to burn that chemical engine the
• 28:01
  Speaker 1: whole way, Well, that goes exponential, and the fuel tank
• 28:05
  Speaker 1: is something like the size of Jupiter.
• 28:07
  Speaker 3: What there's a showstopper. Kelly's gonna keep track of these
• 28:11
  Speaker 3: showstoppers as we go because she's the wet blanket.
• 28:13
  Speaker 1: But I'm gonna be optimistic because in the end I'm
• 28:16
  Speaker 1: really hopeful that we do get to another star, and
• 28:18
  Speaker 1: we do, or somebody, not me, but some human gets
• 28:22
  Speaker 1: to go and set their eyes on an alien planet.
• 28:24
  Speaker 3: I think we will eventually.
• 28:26
  Speaker 1: All Right, you heard it there, folks said it.
• 28:29
  Speaker 3: I do, I do, but I'm not gonna put any
• 28:31
  Speaker 3: money on a date, all right. So when I was
• 28:33
  Speaker 3: writing a city on Mars, the engineers would get grumpy
• 28:35
  Speaker 3: with me for occasionally using the words fuel and propellant interchangeably,
• 28:41
  Speaker 3: which we didn't do in the final manuscript. Nobody needs
• 28:44
  Speaker 3: to freak out and write me. Now, this was in
• 28:45
  Speaker 3: an early draft. So, Daniel, what is the difference between
• 28:48
  Speaker 3: fuel and propellant?
• 28:50
  Speaker 1: So, propellant is anything you want to throw out the
• 28:51
  Speaker 1: back of your rockets, right, and fuel is a special
• 28:55
  Speaker 1: combination which is both a source of energy and a propellant,
• 28:58
  Speaker 1: but it doesn't have to be. Another example of a
• 29:01
  Speaker 1: propellant that separates these things is a nuclear rocket. So
• 29:05
  Speaker 1: rather than using fuel to explode and create energy and
• 29:09
  Speaker 1: propellant simultaneously, use something like a nuclear reactor a fission
• 29:14
  Speaker 1: reactor to produce the energy, which you then use to
• 29:17
  Speaker 1: throw some inert mass out the back. You heat up
• 29:20
  Speaker 1: a gas, for example, and it bubbles out the back
• 29:23
  Speaker 1: of your rocket.
• 29:24
  Speaker 6: Chip.
• 29:24
  Speaker 1: The fuel there is like uranium which is powering your
• 29:27
  Speaker 1: nuclear reactor, which is providing the energy to toss the
• 29:30
  Speaker 1: propellant out the back. The propellant and the fuel are
• 29:32
  Speaker 1: very separate in this technology, and.
• 29:35
  Speaker 3: So with the nuclear rocket, what would the propellant be.
• 29:39
  Speaker 3: Could it be like anything that you heat up.
• 29:41
  Speaker 1: Yeah, it could be anything you can heat up. But
• 29:42
  Speaker 1: you've got to bring some mass to throw out the back, right, stones,
• 29:45
  Speaker 1: white chocolate, xenon, whatever, you want. Something pretty inert so
• 29:49
  Speaker 1: it's not reacting, but you also need to bring enough
• 29:52
  Speaker 1: of it, and it's going to be dense enough that
• 29:53
  Speaker 1: it's not going to be huge. And nuclear rockets are
• 29:56
  Speaker 1: cool because it's something we've actually built. We had an
• 29:58
  Speaker 1: episode where you and I talked about new clear jet planes,
• 30:01
  Speaker 1: and it's the same principle, right, A jet engine operates,
• 30:04
  Speaker 1: and the same principle is very similar to a rocket.
• 30:06
  Speaker 1: You have the fuel which explodes and pushes something out
• 30:08
  Speaker 1: the jet airplane, this whole air compression thing. So jets
• 30:12
  Speaker 1: don't work in space, but you could also have a
• 30:14
  Speaker 1: nuclear jet engine. We're using a nuclear reactor to heat
• 30:17
  Speaker 1: the stuff up and shoot it out the back, same
• 30:19
  Speaker 1: basic principle, and that applies to rockets in space as well.
• 30:23
  Speaker 1: So in this case, you heat the stuff up and
• 30:25
  Speaker 1: you shoot the gas at the back, and that could
• 30:27
  Speaker 1: be a nuclear rocket.
• 30:28
  Speaker 3: But we haven't actually sent a nuclear rocket to space, right.
• 30:31
  Speaker 3: The only kind of rocket we've ever sent to space
• 30:33
  Speaker 3: is the chemical one.
• 30:34
  Speaker 1: That's right. We do have test nuclear engines which people
• 30:36
  Speaker 1: have built and tested and shown to work, and they
• 30:39
  Speaker 1: once did fly an airplane with a working nuclear reactor
• 30:42
  Speaker 1: on board. Scary stuff, but it wasn't actually powering the
• 30:45
  Speaker 1: plane anyway. This is like a viable technology, not just
• 30:49
  Speaker 1: science fiction.
• 30:50
  Speaker 3: And so you said that for chemical rockets, the container
• 30:54
  Speaker 3: that would store the fuel would need to be as
• 30:55
  Speaker 3: big as Jupiter. How big are we working on now?
• 30:59
  Speaker 3: If it's a new So.
• 31:00
  Speaker 1: It doesn't have to be nearly as big because the
• 31:02
  Speaker 1: fuel is much more dense, right, Uranium incredibly dense compared
• 31:06
  Speaker 1: to like diesel or even like oxygen or whatever you're
• 31:10
  Speaker 1: using as fuel, and so that doesn't need to be
• 31:13
  Speaker 1: nearly as big. But you'd still have to bring the propellant, right,
• 31:17
  Speaker 1: You still need a lot of stuff to throw out
• 31:19
  Speaker 1: the back. So we're not talking about the massa jubutter,
• 31:21
  Speaker 1: but we're still talking a very very large ship with
• 31:24
  Speaker 1: a huge amount of propellant. Now, there's some folks that
• 31:27
  Speaker 1: have ideas for like gathering propellant along the way that
• 31:30
  Speaker 1: dust you talked about, or the interstellar medium that's stuff, right,
• 31:34
  Speaker 1: you could use that as propellant. So there are technologies
• 31:36
  Speaker 1: like ramjets or buzzard jets that people talk about where
• 31:39
  Speaker 1: you have like a scoop that gathers propellant up and
• 31:42
  Speaker 1: then your engine whatever you're using, a nuclear reactor or
• 31:45
  Speaker 1: something else, for example, is throwing that out the back.
• 31:48
  Speaker 1: And so there are ways to avoid like having to
• 31:51
  Speaker 1: have a cataclysmically large ship in that way. Though there
• 31:54
  Speaker 1: are also a lot of people who think that those
• 31:56
  Speaker 1: ramjets and bussard jets are totally impractical for other reasons.
• 31:59
  Speaker 1: Same enough said.
• 32:05
  Speaker 3: What if the thing that you're throwing out the back
• 32:09
  Speaker 3: of your rocket is nuclear bombs? Cause why not?
• 32:14
  Speaker 10: Right?
• 32:16
  Speaker 1: Why now? This is actually not a terrible idea in
• 32:18
  Speaker 1: some ways because it separates the ship from the propulsion
• 32:22
  Speaker 1: in a way that we'll talk about for solar sales.
• 32:24
  Speaker 1: If you could blow up a series of nuclear weapons
• 32:27
  Speaker 1: between here and Alpha Centauri, and you had a ship
• 32:31
  Speaker 1: with like a huge shield in the back that could
• 32:33
  Speaker 1: absorb all the radiation and the energy that was dumped
• 32:36
  Speaker 1: out by the nuclear bombs. Then you could just sort
• 32:39
  Speaker 1: of like ride this wave of nuclear explosions all the
• 32:42
  Speaker 1: way to Alpha Centauri. And you know, this is the
• 32:45
  Speaker 1: basis of Project Orion. And then later Project Data lists
• 32:48
  Speaker 1: the idea having like a series of small bombs providing
• 32:52
  Speaker 1: like this smooth acceleration. Now you know, how do you
• 32:55
  Speaker 1: get those bombs? How do you lay a trail of
• 32:57
  Speaker 1: bombs from here to the next star. It was more
• 33:00
  Speaker 1: about like near Earth navigation or getting things off planet
• 33:04
  Speaker 1: than like actually going from star to star. But we
• 33:07
  Speaker 1: can't not talk about blowing up nuclear bombs as a
• 33:10
  Speaker 1: way to propel a ship. It's just got to be
• 33:12
  Speaker 1: in the conversation.
• 33:13
  Speaker 3: Project Datalus had a follow up project called Project Icarus
• 33:16
  Speaker 3: because Icarus was Datalus's son. But Icris is the one
• 33:20
  Speaker 3: who flew too close to the Sun and his wings
• 33:23
  Speaker 3: melted and he fell down and died. And I always
• 33:25
  Speaker 3: remember feeling like, isn't this supposed to be inspirational and like?
• 33:29
  Speaker 3: But but I was told I just wasn't looking at
• 33:32
  Speaker 3: it the right way. And again, this is why I
• 33:33
  Speaker 3: don't get invited to the space parties.
• 33:35
  Speaker 1: Do you think it's hard to sign up test pilots
• 33:37
  Speaker 1: for Project Icarus.
• 33:39
  Speaker 3: It could be, but again, I bet somebody would show
• 33:42
  Speaker 3: would sign up. There's a lot of people who are
• 33:44
  Speaker 3: much braver than I.
• 33:45
  Speaker 1: Am looking for volunteers for a project Crash and Burn. Anybody, anybody, nobody,
• 33:51
  Speaker 1: Probably a lot. Anyway, that's a cool technology, and the
• 33:55
  Speaker 1: cool thing there is if you could somehow manage it.
• 33:58
  Speaker 1: It separates the ship from the source of energy, right,
• 34:01
  Speaker 1: and also from the propellant, and so the ship itself
• 34:04
  Speaker 1: doesn't have to be very big. Of course, that's sort
• 34:06
  Speaker 1: of assuming a solution to the core problem, which is
• 34:09
  Speaker 1: how to get all these nuclear bombs from here to
• 34:11
  Speaker 1: Alpha Centauri, which is basically impossible.
• 34:13
  Speaker 3: What do you think the aliens would think as we
• 34:15
  Speaker 3: were like leaving a trail of nuclear explosions on our
• 34:19
  Speaker 3: way to their galaxy? Do you think they'd be like, Wow,
• 34:21
  Speaker 3: they've really conquered technology. Or do you think they'd be like,
• 34:24
  Speaker 3: oh my gosh, how do we get them to turn around?
• 34:26
  Speaker 2: Yeah?
• 34:27
  Speaker 1: I can't wait for them to show up, right. I
• 34:29
  Speaker 1: think it's cool because we can imagine how we might
• 34:32
  Speaker 1: detect aliens doing the same, Right, Like, if aliens have
• 34:34
  Speaker 1: come up with this idea, and they're using it around
• 34:37
  Speaker 1: their star. We might be able to detect it if
• 34:39
  Speaker 1: they're close enough, So that's pretty cool. But yeah, I
• 34:42
  Speaker 1: don't think it'd be a great way to announce our
• 34:44
  Speaker 1: presence to the universe.
• 34:45
  Speaker 3: They would definitely have time to set up the welcome
• 34:47
  Speaker 3: party or the go home party.
• 34:50
  Speaker 1: But along these lines, there's lots of permutations on this
• 34:52
  Speaker 1: kind of propulsion once you separate the explosions from the propellant. So,
• 34:57
  Speaker 1: for example, there are other ways to accelerate stuff, Like
• 35:01
  Speaker 1: you could have an electric field and you have ions.
• 35:04
  Speaker 1: An electric field will push ions, that's what it does,
• 35:07
  Speaker 1: and so if you had like an electric field and
• 35:09
  Speaker 1: a bunch of ionized propellant, you could shoot that out
• 35:12
  Speaker 1: the back. Basically, we're talking about a particle accelerator. That's
• 35:15
  Speaker 1: exactly what a particle accelerator like the large hadron collider does.
• 35:19
  Speaker 1: It pushes particles with electric fields and makes them go
• 35:22
  Speaker 1: really really fast. So build a particle accelerator, point it
• 35:25
  Speaker 1: out the back of your ship. That's going to give
• 35:27
  Speaker 1: you some impulse.
• 35:29
  Speaker 3: This seems like another very large design, right How big
• 35:32
  Speaker 3: would your particle accelerator need to be?
• 35:34
  Speaker 1: Well, not that big. Actually, and it's cool because it
• 35:36
  Speaker 1: separates the two systems, and so your power source can
• 35:40
  Speaker 1: be anything. It could be solar power, it could be
• 35:42
  Speaker 1: some other crazy system that doesn't necessarily have to be
• 35:45
  Speaker 1: super duper big. In this case, it's nice because it
• 35:48
  Speaker 1: doesn't even have to generate a lot of heat, right,
• 35:50
  Speaker 1: and so for those hand wringers aboard, you don't have
• 35:53
  Speaker 1: to worry about it like melting down or something like that.
• 35:56
  Speaker 1: The downside to this is that the thrust is really
• 35:59
  Speaker 1: tiny accelerating particles and particles don't have a lot of mass,
• 36:03
  Speaker 1: and they sort of limit to how many particles you
• 36:06
  Speaker 1: can effectively shoot out the back, and so it can
• 36:09
  Speaker 1: provide very long term gentle thrust, which is nice for
• 36:13
  Speaker 1: constant acceleration, but it can't really give you a lot
• 36:16
  Speaker 1: of specific impulse, and so it's not a great way
• 36:19
  Speaker 1: to like get up to a high speed in a
• 36:22
  Speaker 1: short amount of time. But it's cool for like navigating
• 36:24
  Speaker 1: around space a little bit.
• 36:26
  Speaker 3: So this could be like a generation ship thing. And
• 36:29
  Speaker 3: so can you remember what the difference is between thrust
• 36:31
  Speaker 3: and specific impulse.
• 36:33
  Speaker 1: They're basically the same thrust a specific impulse times the
• 36:36
  Speaker 1: constant of gravity, but you can think of them as interchangeable.
• 36:39
  Speaker 1: They're just different by units essentially.
• 36:40
  Speaker 3: All Right, we're going to take a break now, and
• 36:42
  Speaker 3: when we come back, we're going to talk about using
• 36:44
  Speaker 3: anti matter to get you to the stars. All right,
• 37:05
  Speaker 3: So we just finished talking about ion drives as a
• 37:08
  Speaker 3: way to get you to the stars, and I see
• 37:10
  Speaker 3: that next we're going to talk about antimatter, and I
• 37:12
  Speaker 3: am immediately thinking that dangerous explosions are maybe not what
• 37:17
  Speaker 3: I want happening, you know, on the ship that I'm
• 37:20
  Speaker 3: living on. But why is Kelly being a wimp?
• 37:23
  Speaker 1: No, Kelly is not being a wimp. We are steadily
• 37:26
  Speaker 1: moving from reliable technologies we know can work and probably
• 37:30
  Speaker 1: won't kill you, to crazy ideas that might not ever
• 37:34
  Speaker 1: work and are much more likely to kill anybody on board.
• 37:37
  Speaker 3: O good, all right.
• 37:40
  Speaker 1: But antimatter is cool because it's the most efficient way
• 37:44
  Speaker 1: to store energy. Like matter, and antimatter annihilation is perfect
• 37:48
  Speaker 1: conversion of matter into energy. Compare that to for example,
• 37:52
  Speaker 1: chemical fuel. Right, chemical fuel has a lot of energy
• 37:55
  Speaker 1: in it, but when you burn it, you only release
• 37:57
  Speaker 1: a little bit of that energy from the chemical bonds.
• 37:59
  Speaker 1: But inside those protons and inside those electrons is an
• 38:02
  Speaker 1: enormous amount of stored energy, which we call mass. If
• 38:05
  Speaker 1: you could capture all that will release all of that,
• 38:07
  Speaker 1: you would need to bring less fuel, right, and so
• 38:10
  Speaker 1: matter antimatter annihilation is the best way to do that.
• 38:13
  Speaker 1: You have protons and anti protons. They turn directly into
• 38:16
  Speaker 1: photons which you can shoot out the back of your ship.
• 38:19
  Speaker 1: And that's awesome because the propellant there is moving at
• 38:22
  Speaker 1: the speed of light, right, so like you can't be
• 38:24
  Speaker 1: that for maximum thrust and impulse. So far this sounds
• 38:28
  Speaker 1: great now. The downsides are, of course, Kelly worries about
• 38:31
  Speaker 1: being annihilated herself because antimatter is pretty dangerous stuff. Yeah,
• 38:36
  Speaker 1: so you need some sort of magnetic confinement for antimatter,
• 38:39
  Speaker 1: basically a bottle that doesn't touch it. You know, a
• 38:42
  Speaker 1: bottle made of matter that builds a magnetic field that
• 38:45
  Speaker 1: confines it, sort of the way we do for plasmas
• 38:47
  Speaker 1: in Tokomax infusion reactors. That's not totally implausible, But then again,
• 38:52
  Speaker 1: you basically have a bomb on board and any loss
• 38:55
  Speaker 1: of containment and everybody's dead, yeah before you can do anything.
• 38:59
  Speaker 1: So that's bad. But on the flip side, antimatter is
• 39:01
  Speaker 1: basically impossible to make in large enough quantities, so you're
• 39:05
  Speaker 1: pretty much safe. You know, we make antimatter. We made
• 39:08
  Speaker 1: it for the previous collider. We used to have the Tevatron,
• 39:10
  Speaker 1: which was a proton anti proton machine, and we produced
• 39:14
  Speaker 1: antimatter at the Large Hadron Collider all the time in collisions,
• 39:17
  Speaker 1: so it's not actually that exotic. It's made in the atmosphere,
• 39:20
  Speaker 1: like cosmic rays hit the atmosphere turn into a antimatter briefly.
• 39:24
  Speaker 1: But the quantities we're talking about are like nanograms of antimatter.
• 39:29
  Speaker 1: You know, we can like count the atoms of antimatter
• 39:31
  Speaker 1: we make. There's no large scale production of antimatter in
• 39:35
  Speaker 1: order to make enough fuel to get anybody near Alpha Centauri.
• 39:39
  Speaker 1: I read one estimate that said making one hundred milligrams
• 39:43
  Speaker 1: of antimatter would cost about one hundred trillion dollars.
• 39:46
  Speaker 3: Oh my gosh. All right, so I'm curious since we're
• 39:49
  Speaker 3: starting to get towards the really crazy ones. Out of
• 39:51
  Speaker 3: the technologies we've talked about so far, if you had
• 39:54
  Speaker 3: to go to Alpha Centauri, which one of these would
• 39:57
  Speaker 3: you want to use?
• 39:58
  Speaker 1: Probably none of these? Okay, my favorite is one we
• 40:03
  Speaker 1: haven't talked about yet it's a little bit ridiculous and speculative,
• 40:06
  Speaker 1: but it's still my favorite.
• 40:08
  Speaker 3: All right, let's keep going. Then, what's next next?
• 40:11
  Speaker 1: I want to talk about a nonsense idea which is
• 40:13
  Speaker 1: out there people are probably imagining might save the day,
• 40:16
  Speaker 1: and that's propulsion list drives. People have been thinking, okay, well,
• 40:20
  Speaker 1: conservation of momentum requires we throw something out the back.
• 40:24
  Speaker 1: We're tossing stones or white chocolate out the back of
• 40:26
  Speaker 1: our spaceboat to get it moving. That's frustrating that it
• 40:30
  Speaker 1: limits us, right because you've got to bring all this
• 40:31
  Speaker 1: stuff to throw out the back. Wouldn't it be amazing
• 40:34
  Speaker 1: if we could generate a drive which didn't need that, Yeah,
• 40:37
  Speaker 1: that would be amazing and also violate conservation of momentum.
• 40:40
  Speaker 1: But that has to stop people from trying and go
• 40:43
  Speaker 1: for it. Guys, like it wouldn't be the first time
• 40:45
  Speaker 1: that we discovered and sit you something that revealed we
• 40:48
  Speaker 1: didn't understand the universe. So I'm all in favor of
• 40:50
  Speaker 1: people doing crazy experiments.
• 40:52
  Speaker 3: That's just like a Friday in physics, right where you
• 40:54
  Speaker 3: discover you were wrong about something.
• 40:56
  Speaker 1: Yeah, those are the best moments in physics, So nobody
• 40:59
  Speaker 1: should be limited by like conventional wisdom about what's possible
• 41:02
  Speaker 1: or impossible, but we should also be clear eyed about
• 41:05
  Speaker 1: what we have actually proven. And there are folks out
• 41:08
  Speaker 1: there who claim to have built one of these things.
• 41:10
  Speaker 1: It's called an em drive, and about fifteen years ago
• 41:13
  Speaker 1: there was a lot of hoopla about it. There's a
• 41:14
  Speaker 1: lot of coverage and the New Scientist. But these folks
• 41:18
  Speaker 1: who had some like tenuous NASA affiliation, who claim to
• 41:21
  Speaker 1: have built the impossible space drive, And if you look
• 41:25
  Speaker 1: for articles, you'll see them there in Popular Mechanics, they're
• 41:27
  Speaker 1: and wired, they're in the New Scientist. But the journalists
• 41:30
  Speaker 1: here really didn't do their work, Like if you look
• 41:33
  Speaker 1: carefully at the claims, you see that the thrust that
• 41:36
  Speaker 1: these things produce is really really tiny. It's basically smaller
• 41:40
  Speaker 1: than the uncertainties, you know, like they just have jitter
• 41:43
  Speaker 1: in their measurements that have sources of noise and they
• 41:46
  Speaker 1: measure a thrust, but the thrust is consistent with zero
• 41:49
  Speaker 1: within errors. So while I'm all for crazy new technologies
• 41:53
  Speaker 1: and exploding understanding the universe, the EM drive is not
• 41:56
  Speaker 1: something that's done that. These are fascinating ideas, and there's
• 42:00
  Speaker 1: not nothing to support the concepts. One idea is that
• 42:02
  Speaker 1: there's a vacuum in space, and that vacuum has energy
• 42:05
  Speaker 1: to it, and experiments like the Casimir effects show us
• 42:09
  Speaker 1: that the vacuum is real and it's there, and people
• 42:11
  Speaker 1: wonder if we can extract energy from the vacuum and
• 42:13
  Speaker 1: use it to propel ourselves. But you know, the vacuum
• 42:16
  Speaker 1: is special. You can't like row against the vacuum. You
• 42:19
  Speaker 1: can't like absorb momentum or get momentum. It's emotional the
• 42:23
  Speaker 1: way space is. For example, you can't like put an
• 42:25
  Speaker 1: ore down and row through space in the same way.
• 42:28
  Speaker 1: And this is part of space. So anyway, em drives
• 42:32
  Speaker 1: not something we can rely on and not something I
• 42:34
  Speaker 1: would bet on. But hey, if you're out there and
• 42:37
  Speaker 1: you're building em drive, I hope you make it work.
• 42:39
  Speaker 3: Fingers crossed, all right? So I have heard proposals where
• 42:43
  Speaker 3: you know, the Sun is shooting out photons all the time.
• 42:47
  Speaker 3: What if you could capture those photons and let the
• 42:49
  Speaker 3: Sun sort of push you forward? How would that work?
• 42:52
  Speaker 1: This is my favorite idea because it separates the ship
• 42:56
  Speaker 1: from the propulsion completely, right. So this is called a
• 42:59
  Speaker 1: solar sale, and the idea is that you're right. The
• 43:02
  Speaker 1: sun is putting out photons, and not just photons but
• 43:05
  Speaker 1: other particles. The solar wind has momentum, So why like
• 43:09
  Speaker 1: generate momentum if we have an enormous momentum generating machine already,
• 43:15
  Speaker 1: and so all you need to do to capture that
• 43:17
  Speaker 1: momentum is build a huge sail. So you know, when
• 43:20
  Speaker 1: you're on a sailboat, a sail is just a piece
• 43:23
  Speaker 1: of cloth that gathers that momentum. Here, the best kind
• 43:26
  Speaker 1: of sale would be something very thin, so low mass
• 43:28
  Speaker 1: and reflective. And imagine a photon hits the sail, it
• 43:32
  Speaker 1: bounces off the same way a photon hits a mirror
• 43:34
  Speaker 1: and bounces off. Right, what happens, Well, the photon is
• 43:37
  Speaker 1: now changing its momentum. It's going one way. Now it's
• 43:39
  Speaker 1: going the other way. Conservation momentum says that can't happen
• 43:43
  Speaker 1: unless something is going the opposite direction. Right, something is
• 43:45
  Speaker 1: now going the way the photon originally was to conserve momentum,
• 43:50
  Speaker 1: and that's the sail. This is a confusing concept for
• 43:53
  Speaker 1: people because it's hard to imagine like light pushing something
• 43:56
  Speaker 1: because light has no mass, and you're probably thinking, well,
• 43:59
  Speaker 1: momentum is mass times velocity, and photons have no mass,
• 44:03
  Speaker 1: so therefore they have no momentum. Right, Yeah, wrong, And
• 44:07
  Speaker 1: the reason is that momentum is mass times velocity only
• 44:10
  Speaker 1: for very slow stuff. As you approach the speed of light,
• 44:13
  Speaker 1: the equation changes a little bit. So photons do in
• 44:16
  Speaker 1: fact have a momentum even though they have no mass.
• 44:19
  Speaker 1: So yeah, their momentum can push along a sail. So
• 44:22
  Speaker 1: imagine a tiny little ship with an enormous sail and
• 44:26
  Speaker 1: the photons are bouncing off of it and giving it
• 44:28
  Speaker 1: a push. Basically, you don't need an engine.
• 44:30
  Speaker 3: So one of the things that always sounded limiting to
• 44:34
  Speaker 3: me with this method is that it seems like it
• 44:36
  Speaker 3: would work great when you're close to the sun. But
• 44:39
  Speaker 3: the farther you get from the Sun, the fewer photons
• 44:41
  Speaker 3: are going to be hitting your sail. How would this
• 44:43
  Speaker 3: work when you get too far away from the sun.
• 44:45
  Speaker 1: Yeah, this is tricky. As you say, you get further
• 44:47
  Speaker 1: from the Sun, the photon density drops by one over
• 44:50
  Speaker 1: are squared. That's bad. So this is a good idea
• 44:53
  Speaker 1: for moving around the Solar system, like navigating from here
• 44:56
  Speaker 1: to Mercury or here to Neptune. A very light without
• 45:00
  Speaker 1: fuel would be awesome. Getting from here to another star
• 45:03
  Speaker 1: would be hard. And what you need to do is
• 45:06
  Speaker 1: build an enormous laser. Like think about a really big laser,
• 45:11
  Speaker 1: now make it ten times bigger. That's too small. You
• 45:14
  Speaker 1: need an enormous laser, right, really huge laser, or like
• 45:18
  Speaker 1: a big laser array that I'll focus their energy on
• 45:22
  Speaker 1: this sale. But the cool thing is, again, you can
• 45:24
  Speaker 1: build this on Earth, or you can have it in
• 45:26
  Speaker 1: space or something. You don't need to bring it with you,
• 45:29
  Speaker 1: and you can point it at your ship and push
• 45:31
  Speaker 1: it to another star. So it's not a solar sale anymore.
• 45:35
  Speaker 1: It's like a photonic sail.
• 45:37
  Speaker 3: And I can't imagine that a laser of that size
• 45:40
  Speaker 3: is going to cause any geopolitical conflict at all. A
• 45:45
  Speaker 3: weapon of that magnitude.
• 45:48
  Speaker 1: Yeah, we're building the Death Star basically for good reasons
• 45:52
  Speaker 1: to go to space. We're just making space smores. What's
• 45:55
  Speaker 1: the big deal, right, But there's a project to do this.
• 45:58
  Speaker 1: It's called Breakthrough Star Shot and they want to take
• 46:01
  Speaker 1: a bunch of nanocraft like tiny little devices, and they
• 46:05
  Speaker 1: want to build ground based lasers and send those devices
• 46:08
  Speaker 1: to Alpha Centauri. Now you push these tiny little devices
• 46:11
  Speaker 1: long enough you can get them up to like twenty
• 46:14
  Speaker 1: percent of the speed of light. And so you do
• 46:16
  Speaker 1: the math and these things. They're estimating to launch them
• 46:20
  Speaker 1: in like twenty thirty ish twenty thirty five, they would
• 46:23
  Speaker 1: take about twenty years. They'd be there about like twenty
• 46:26
  Speaker 1: fifty five. So if I'm lucky, i'd be around when
• 46:29
  Speaker 1: the signal comes back, you know, from Alpha Centauri. This
• 46:33
  Speaker 1: is something that really could happen, which is why I
• 46:34
  Speaker 1: think it's my favorite technology. The challenge, of course, is
• 46:37
  Speaker 1: getting a big enough sale to push a ship with
• 46:40
  Speaker 1: people on it. You know, so far we're just talking
• 46:42
  Speaker 1: about sending tiny nano robots. But you know, if I
• 46:46
  Speaker 1: want to go there, you got to bring me and
• 46:47
  Speaker 1: my toilet, my bed, you know, all sorts of stuff
• 46:51
  Speaker 1: needs to go with me. So we're not talking nano
• 46:53
  Speaker 1: ships anymore. So we're talking enormous sales, and we really
• 46:58
  Speaker 1: need like better technology for enormous sales that are going
• 47:00
  Speaker 1: to somehow survive the interstellar trip those micro meteorites tearing
• 47:04
  Speaker 1: it apart. So you know, there's potential there, but there's
• 47:07
  Speaker 1: a lot of engineering challenges to solve.
• 47:10
  Speaker 3: Yeah, this is a cool technology. Are the are the
• 47:12
  Speaker 3: little nanoships that break through starshot is sending Are they
• 47:16
  Speaker 3: going to have like cameras and scientific instruments on them
• 47:18
  Speaker 3: or are they just able to say we're here and
• 47:20
  Speaker 3: that's it TBD.
• 47:22
  Speaker 1: But I hope they're gonna put some cameras on there.
• 47:24
  Speaker 1: I mean to be amazingly ridiculous to get something all
• 47:27
  Speaker 1: the way there and take no data, right.
• 47:29
  Speaker 3: Yeah, that would be a major bummer. We haven't talked
• 47:32
  Speaker 3: yet about a method to me that seems perhaps likely
• 47:34
  Speaker 3: something that we have some experience with, which is gravity slingshots,
• 47:38
  Speaker 3: which which we're used in Aurora Kim Stanley Robinson's book
• 47:41
  Speaker 3: to slow down on the way back to Earth. Is
• 47:44
  Speaker 3: that something that we could use to speed up to
• 47:46
  Speaker 3: get there?
• 47:46
  Speaker 1: Absolutely, Gravitational slingshots are amazing. You know, you whiz near
• 47:50
  Speaker 1: a planet basically steal a little bit of its speed.
• 47:53
  Speaker 1: We should dig into the physics of that in a
• 47:55
  Speaker 1: whole episode because there's some subtleties there about like why
• 47:58
  Speaker 1: you end up with a little bit of speed, And
• 48:00
  Speaker 1: the short version of it is that you slow down
• 48:02
  Speaker 1: the planet's rotation around the star, which is really cool,
• 48:05
  Speaker 1: and we've done this. You know, Voyager one, for example,
• 48:08
  Speaker 1: one of our only interstellar probes. It's swung around the Sun,
• 48:11
  Speaker 1: but it's not going that fast. You know, it's traveling
• 48:14
  Speaker 1: like a light year in about eighteen thousand years. So
• 48:18
  Speaker 1: you can't get going to like interstellar speeds unless you're
• 48:21
  Speaker 1: getting crazy close to the star, and that's got its
• 48:23
  Speaker 1: own dangers. So gravitational slingshots are a good way to
• 48:26
  Speaker 1: boost your speed and to get going, but on their
• 48:29
  Speaker 1: own they're not going to provide the speed that you
• 48:31
  Speaker 1: need to get to another star.
• 48:32
  Speaker 3: Got it all right, So let's wrap things up on
• 48:34
  Speaker 3: the most sci fi methods. So what can we do
• 48:40
  Speaker 3: to can we like bend space or time to make
• 48:42
  Speaker 3: this happen?
• 48:43
  Speaker 1: Yeah, so far we're considering flat space. We're imagining you know,
• 48:46
  Speaker 1: light is going to take a few years to get there.
• 48:48
  Speaker 1: What can we do to approach the speed of light?
• 48:51
  Speaker 1: But of course we know that space is not just flat.
• 48:53
  Speaker 1: Space bends, it curves, and in the presence of mass,
• 48:56
  Speaker 1: it can do all sorts of things. They can wiggle,
• 48:58
  Speaker 1: not something we fully understand, but you know, we know
• 49:00
  Speaker 1: that this kind of thing is possible, and so in
• 49:02
  Speaker 1: the last few years or so, people have been thinking about, like,
• 49:05
  Speaker 1: could we actually build a warp drive. This would be
• 49:08
  Speaker 1: something that bends space so that effectively the journey is shorter.
• 49:12
  Speaker 1: And that's really what space curvature means, that you're changing
• 49:15
  Speaker 1: the relative distance between two points. So hey, why not
• 49:18
  Speaker 1: make Alpha centaur really really close so that doesn't take
• 49:21
  Speaker 1: as long to get there. And that's the idea of
• 49:23
  Speaker 1: a warp bubble that you like, shrink the space between
• 49:25
  Speaker 1: you and the star and expand the space behind you.
• 49:28
  Speaker 1: And then when you get there, you pop out of
• 49:30
  Speaker 1: this warp bubble and you're like, hey, that wasn't a
• 49:32
  Speaker 1: big deal.
• 49:32
  Speaker 3: How likely is it that these warp bubbles actually exist
• 49:36
  Speaker 3: or could be created?
• 49:37
  Speaker 1: That's a topic of hot debate. On the positive side,
• 49:40
  Speaker 1: there's a guy who's figured out that warp bubbles do
• 49:44
  Speaker 1: not violate general relativity, meaning like a warp bubble doesn't
• 49:48
  Speaker 1: break any of those rules. That doesn't mean that a
• 49:50
  Speaker 1: warp bubble could actually exist in the universe because you
• 49:54
  Speaker 1: create something because it's allowed in the universe. Like everybody
• 49:57
  Speaker 1: knows chocolatesou fleas are allowed in the universe, Does I
• 50:00
  Speaker 1: mean everybody knows how to make them? You have to
• 50:02
  Speaker 1: have a very delicate process to get from no chocolate
• 50:05
  Speaker 1: sooufle to chocolates sooufle, right, and there's lots of ways
• 50:07
  Speaker 1: to fail. We don't have a recipe for building a
• 50:10
  Speaker 1: warp drive, but just know that the resulting drive is
• 50:13
  Speaker 1: not disallowed by general relativity. It could be that some
• 50:15
  Speaker 1: step between no warp drive and warp drive is disallowed
• 50:19
  Speaker 1: or is impossible. And so if you could just like
• 50:22
  Speaker 1: magically pop a warp drive into existence, then physics is
• 50:26
  Speaker 1: cool with it. But we don't know if it's possible
• 50:28
  Speaker 1: to create one in our universe.
• 50:31
  Speaker 3: All right, Well, I'm going to hope that it is,
• 50:33
  Speaker 3: because that would make things really convenient. At the beginning
• 50:36
  Speaker 3: of the show, you mentioned that in your favorite book
• 50:39
  Speaker 3: they just moved stars closer together. How would that work?
• 50:43
  Speaker 3: And why would everyone be dead?
• 50:47
  Speaker 1: This is basically like the think big version of the
• 50:50
  Speaker 1: solar sale. Right. In this version, you build a huge
• 50:54
  Speaker 1: sale like half the size of the sun. Yeah, that's right,
• 50:57
  Speaker 1: half the size of the sun. Wow, wrap half of
• 51:00
  Speaker 1: the sun a big mirror that points back at the Sun. Okay,
• 51:04
  Speaker 1: And so you might think, well, what's gonna happen? That
• 51:06
  Speaker 1: mirror is just gonna shoot off it's a big solar sale.
• 51:08
  Speaker 1: It gets pushed away by the Sun. Right, Well, you
• 51:10
  Speaker 1: bring it close to enough and you make it massive
• 51:12
  Speaker 1: enough that it's gravitationally captured by the Sun. So now
• 51:16
  Speaker 1: basically the mirror and the Sun are like a single
• 51:18
  Speaker 1: gravitational object. The Sun is shooting half of its photons
• 51:22
  Speaker 1: to the mirror, but they get bounced back so basically recaptured.
• 51:26
  Speaker 1: On the other side, the Sun is shooting off its
• 51:28
  Speaker 1: photons out into space. So now it's like an ion drive.
• 51:32
  Speaker 1: So one half of the Sun is basically captured and nullified,
• 51:35
  Speaker 1: the other half is not. Now the Sun can move right.
• 51:39
  Speaker 1: The Sun is basically like a rocket, and so this
• 51:43
  Speaker 1: could move the whole Solar system. And Kelly should feel
• 51:46
  Speaker 1: great about this because you could travel to another star
• 51:50
  Speaker 1: without even leaving your house. You could like literally sleep
• 51:53
  Speaker 1: in your bed at home and we could go visit
• 51:55
  Speaker 1: Alpha Centauri move the whole Solar system.
• 51:58
  Speaker 3: Okay, all right, so that sounds awesome. I love that
• 52:00
  Speaker 3: you dream big. But like, so you know we've talked before,
• 52:03
  Speaker 3: if like suns get too close to each other, one
• 52:05
  Speaker 3: of them gets like thrown off into the vastness of space.
• 52:08
  Speaker 3: This feels like a high risk method.
• 52:13
  Speaker 1: Well, it's hard to turn a star, you know, if
• 52:15
  Speaker 1: you realize you're going in the wrong direction. This is
• 52:17
  Speaker 1: harder to turn than like one of those U hauls
• 52:20
  Speaker 1: that are already pretty hard to turn. Yeah, there's a
• 52:23
  Speaker 1: lot of ways this could go wrong. You know, maybe
• 52:26
  Speaker 1: a safer method is to use a black hole instead, because.
• 52:30
  Speaker 3: Black holes, You physicists, wouldn't it be safer if we
• 52:35
  Speaker 3: used a black hole?
• 52:37
  Speaker 1: I like, you just laugh in my face at that one.
• 52:39
  Speaker 3: I'm sorry.
• 52:40
  Speaker 1: I mean a black hole also converts mass into energy. Right,
• 52:44
  Speaker 1: black holes evaporate, they have energy stored inside them because
• 52:47
  Speaker 1: of their mass, but they generate Hawking radiation, which is energy.
• 52:50
  Speaker 1: So put a black hole next to a mirror and
• 52:53
  Speaker 1: in the same way, it will generate propulsion in one direction,
• 52:57
  Speaker 1: right if it's gravitationally captured the mirror, and so that's
• 53:00
  Speaker 1: absorbing that radiation. Now you have a black hole which
• 53:03
  Speaker 1: is turning its mass into radiation and pushing your ship
• 53:06
  Speaker 1: so you don't have to move a whole star. Now
• 53:09
  Speaker 1: you have a black hole power and spaceship. And of
• 53:12
  Speaker 1: course there's technical problems here, like how do you actually
• 53:14
  Speaker 1: make the black hole? We don't know how to do that.
• 53:16
  Speaker 1: Maybe you could find a black hole. We don't know
• 53:18
  Speaker 1: where any of them are. Also, there are some risks
• 53:21
  Speaker 1: involved in having a black hole on board your ship.
• 53:23
  Speaker 1: Please sign these waivers, all.
• 53:27
  Speaker 3: Right, So I'm going to ask myself the question, which
• 53:29
  Speaker 3: one of those methods do I think I would use
• 53:32
  Speaker 3: if I was forced to go on a ship to
• 53:34
  Speaker 3: Alpha Centauri. I think that I would agree with you
• 53:37
  Speaker 3: about the solar sale technique. But what would make me
• 53:40
  Speaker 3: nervous is that somebody else is in control of the
• 53:44
  Speaker 3: propulsion and so like, I imagine that keeping a giant
• 53:48
  Speaker 3: laser constantly powered has got to take a lot of energy.
• 53:51
  Speaker 3: And so what if one day, you know, the Americans
• 53:54
  Speaker 3: are like, you know what, We're not powering this laser anymore.
• 53:57
  Speaker 3: It's just too expensive. And then what do you do?
• 54:00
  Speaker 1: Yeah, well there's not much you can do.
• 54:02
  Speaker 4: You know.
• 54:03
  Speaker 1: The other issue with a solar sale is slowing down.
• 54:05
  Speaker 1: Like it gets you up to near the speed of
• 54:07
  Speaker 1: light using that big laser, then you have to use
• 54:10
  Speaker 1: the destination sun to slow down, but it is no
• 54:13
  Speaker 1: laser there to give you that boost, and so you
• 54:16
  Speaker 1: got to like combine that with gravitational sling shots. It's tricky. Yeah,
• 54:21
  Speaker 1: there's no way I'm getting on any of these ships ever,
• 54:25
  Speaker 1: But I encourage all of you to, like, please go
• 54:28
  Speaker 1: explore the universe and tell us all about it.
• 54:30
  Speaker 3: Send me a postcard.
• 54:32
  Speaker 1: All right. So, I think we surveyed some of the
• 54:34
  Speaker 1: technologies that might get us to other stars, and my
• 54:37
  Speaker 1: take is that there's some promise here. Obviously there are
• 54:40
  Speaker 1: kinks to be worked out, and Kelly and her legal
• 54:43
  Speaker 1: team need to be put at ease about the black
• 54:45
  Speaker 1: hole on board, you know, or moving the entire sun.
• 54:48
  Speaker 1: Do we need to take a vote before we do that.
• 54:50
  Speaker 1: I'm not sure, But to me, these feel like solvable problems.
• 54:54
  Speaker 1: And you know, we're young as a species technologically. In
• 54:58
  Speaker 1: one hundred years and a thousand years will good this out,
• 55:00
  Speaker 1: and maybe even by then somebody will have built an
• 55:02
  Speaker 1: em drive.
• 55:03
  Speaker 3: Well, And to surprise everybody, I am actually optimistic about
• 55:06
  Speaker 3: some of this stuff, and I feel like these are
• 55:08
  Speaker 3: really interesting problems that we have to solve, and imagine
• 55:11
  Speaker 3: the other things that we're gonna learn along the way,
• 55:13
  Speaker 3: where the new technologies will come up with as we
• 55:16
  Speaker 3: try to make some of these methods work. I think
• 55:18
  Speaker 3: it's all very.
• 55:19
  Speaker 1: Exciting, all right, But before you get too excited, next episode,
• 55:22
  Speaker 1: we're gonna talk about all the other tricky problems you
• 55:25
  Speaker 1: would have to solve to get humans to another solar system,
• 55:27
  Speaker 1: giving birth on board? Is it okay to have children
• 55:30
  Speaker 1: born between planets? Embryos, robots, cryogenics, radiation, all that good stuff.
• 55:35
  Speaker 1: So tune in next time for Kelly to throw a
• 55:38
  Speaker 1: wet blanket on your interstellar dreams.
• 55:40
  Speaker 3: That's what I do, so well out, all right.
• 55:47
  Speaker 1: Tune in next time everyone.
• 55:55
  Speaker 3: Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We
• 55:59
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• 56:01
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• 56:04
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