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Are Earths rare in the Universe? · Daniel and Kelly’s Extraordinary Universe

• 0:05
  Speaker 1: Humans have been looking at the night sky and asking
• 0:08
  Speaker 1: basic questions about it for a long time. What are
• 0:11
  Speaker 1: those points of light? Why do some of them move?
• 0:13
  Speaker 1: Are their patterns that we can understand? And though it's
• 0:16
  Speaker 1: taken us thousands of years, we've actually made a lot
• 0:20
  Speaker 1: of progress.
• 0:20
  Speaker 2: In figuring it out.
• 0:22
  Speaker 1: Unlike our ancient ancestors, we know something about what we're
• 0:26
  Speaker 1: looking at. We can appreciate that the points of light
• 0:28
  Speaker 1: are not nearby, but our mind bogglingly distant, that we're
• 0:32
  Speaker 1: looking at over a vast black ocean of space, seeing
• 0:36
  Speaker 1: the few and incredibly distant islands of light in the cosmos,
• 0:40
  Speaker 1: it's really one of the most spectacular views you'll ever see.
• 0:45
  Speaker 1: And from that view we have extrapolated quite incredibly into
• 0:49
  Speaker 1: an understanding of the bigger picture of the universe. We
• 0:53
  Speaker 1: now know a lot about how vast the universe is,
• 0:56
  Speaker 1: how galaxies form, how they cluster, how the universe expands.
• 1:00
  Speaker 1: But in all of those thousands of years, we've made
• 1:03
  Speaker 1: almost zero progress on one of the most basic questions,
• 1:07
  Speaker 1: one of the most pressing. And as we've been able
• 1:10
  Speaker 1: to expand our mental picture of the universe from just
• 1:13
  Speaker 1: the neighborhood of Earth, to the ninety some billion light
• 1:17
  Speaker 1: years of the observable universe, this unanswered question has just
• 1:21
  Speaker 1: become more pressing. That question is, of course, are we alone?
• 1:27
  Speaker 1: As we stare up into the night sky and do
• 1:30
  Speaker 1: our best to unravel its workings, to put pen to
• 1:33
  Speaker 1: paper and capture the mechanisms of the universe in our
• 1:36
  Speaker 1: little mathematical stories, we wonder if we are the only
• 1:40
  Speaker 1: ones doing that. Is there someone else up there around
• 1:43
  Speaker 1: a distant planet looking back at us, wondering if we
• 1:46
  Speaker 1: two are here and looking back at them? Well, until
• 1:50
  Speaker 1: the aliens arrive, or send us an email, Instagram, DM
• 1:53
  Speaker 1: or LinkedIn connection request, do we have any hope of
• 1:56
  Speaker 1: figuring this out? We have managed to learn incredible things
• 2:00
  Speaker 1: about the nature of the wider universe without ever leaving
• 2:04
  Speaker 1: the immediate neighborhood of our planet, just from gathering the
• 2:07
  Speaker 1: photons that happen.
• 2:08
  Speaker 2: To splash down here.
• 2:09
  Speaker 1: Can we do the same to understand the prevalence of
• 2:12
  Speaker 1: alien life, what it might be like, and whether it
• 2:15
  Speaker 1: thinks and wonders and eats and screams When this steps
• 2:18
  Speaker 1: on a lego at three am. We are curious humans,
• 2:21
  Speaker 1: and so we are never satisfied just throwing our hands
• 2:24
  Speaker 1: in the air and giving up because it's hard. We
• 2:27
  Speaker 1: want to extract every last bit of knowledge from the
• 2:30
  Speaker 1: rare data that we have, So on today's episode, we're
• 2:33
  Speaker 1: going to explore one particular theory that tries to answer
• 2:37
  Speaker 1: the age old question, is life rare in the universe?
• 2:56
  Speaker 3: Hi, I'm Kelly Leener Smith. I'm an edge of faculty
• 2:59
  Speaker 3: at University, and welcome to Daniel and Kelly's Extraordinary Universe.
• 3:06
  Speaker 3: We're happy to have you here, and I'm here with
• 3:08
  Speaker 3: my co host Daniel.
• 3:09
  Speaker 2: Hey. Everyone, I'm Daniel.
• 3:10
  Speaker 1: I'm a particle physicist and a professor at UC Irvine,
• 3:14
  Speaker 1: and I'm so happy to be here today with you
• 3:16
  Speaker 1: Kelly on our extraordinary podcast about the Extraordinary Universe.
• 3:20
  Speaker 3: Yeah, super exciting. I have an extraordinary question for you.
• 3:23
  Speaker 3: So I wrote this book about space, which means I
• 3:26
  Speaker 3: get to talk to the space community. The question that
• 3:28
  Speaker 3: I get most often that I don't know how to answer.
• 3:32
  Speaker 3: I'm going to ask you what you think is what
• 3:35
  Speaker 3: about all that UFO stuff that we've been hearing about lately,
• 3:38
  Speaker 3: like the Senate hearing and stuff. What is your thought
• 3:42
  Speaker 3: on the UFO situation?
• 3:44
  Speaker 2: My thought is that.
• 3:45
  Speaker 1: There are two totally different categories of work. One is
• 3:49
  Speaker 1: like real scientific questions about where alien life might be
• 3:53
  Speaker 1: and how we might find it, and like hard hitting
• 3:56
  Speaker 1: scientific projects to look for bios signatures or out other stars.
• 4:01
  Speaker 1: And then there's ufology, which is a very fascinating community
• 4:05
  Speaker 1: of folks who desperately want to believe that aliens are
• 4:08
  Speaker 1: already here and the government is covering it up somehow,
• 4:11
  Speaker 1: and the fact that we don't have evidence for it
• 4:13
  Speaker 1: is somehow evidence of that cover up. And there are
• 4:16
  Speaker 1: some folks in there who are doing their best try
• 4:18
  Speaker 1: to sort through the evidence in a methodical way. And
• 4:20
  Speaker 1: I think there are also a lot of gristers in
• 4:22
  Speaker 1: there who are playing on people who really want to believe.
• 4:25
  Speaker 1: And I think you'll find a lot of scientists are
• 4:27
  Speaker 1: eager to dig into the alien life stuff and eager
• 4:30
  Speaker 1: to avoid the conspiracy theories of ufology.
• 4:33
  Speaker 3: I think our takes pretty much agreed. If anybody wants
• 4:36
  Speaker 3: to check my Goodreads account, there's this great book and
• 4:38
  Speaker 3: I'm forgetting the title and the name, which is very helpful,
• 4:41
  Speaker 3: But there was a woman who essentially engaged with the
• 4:43
  Speaker 3: UFO community, and it was sort of like an anthropological
• 4:46
  Speaker 3: look at that community, and it was a very fun
• 4:48
  Speaker 3: book to read. But my take on most of these
• 4:51
  Speaker 3: things that are coming through the Senate hearing is that
• 4:53
  Speaker 3: it's probably technology from some other country that's like in
• 4:57
  Speaker 3: our airspace and we happen to run upon it at
• 4:59
  Speaker 3: the wrong time and they didn't mean for us to
• 5:01
  Speaker 3: see it, or it's a US technology that we're working
• 5:04
  Speaker 3: on and some pilot saw it when they weren't supposed to.
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  Speaker 3: I think there's almost always some explanation that doesn't require aliens.
• 5:10
  Speaker 3: And it would also surprise me if aliens like came
• 5:13
  Speaker 3: and were accidentally seen and then left, like that's a
• 5:16
  Speaker 3: long journey to just like go home. Yeah, But anyway,
• 5:19
  Speaker 3: I think we're on the same page.
• 5:20
  Speaker 1: No, I totally agree, and I want to emphasize that,
• 5:22
  Speaker 1: like I want to believe if there was really any
• 5:26
  Speaker 1: sort of shred of hard evidence that we could dig
• 5:29
  Speaker 1: into about aliens, I would be the first one to
• 5:31
  Speaker 1: trumpet it. I'm definitely a mark for these folks, and
• 5:35
  Speaker 1: I want to believe it, but it just doesn't really
• 5:37
  Speaker 1: hold up. But I know that what we've seen is
• 5:39
  Speaker 1: a tiny fraction of what the government has, which is
• 5:42
  Speaker 1: something that the UFO community talks about a lot. I
• 5:45
  Speaker 1: actually once had a congressman reach out to me say, Daniel,
• 5:49
  Speaker 1: I have questions about what I've been shown. Can we talk?
• 5:53
  Speaker 1: And so I gave him a call, of course, and
• 5:56
  Speaker 1: I tried to explain to him what we were looking
• 5:58
  Speaker 1: at and what we knew and what phys said and
• 6:00
  Speaker 1: what we didn't know about the universe. And then I
• 6:02
  Speaker 1: asked him, I said, hey, have you seen all the
• 6:04
  Speaker 1: classified footage from the DUD He said, yes, I have,
• 6:07
  Speaker 1: and I said what's in it? And he says, nothing interesting.
• 6:11
  Speaker 1: It's all drones and balloons, and it's less interesting than
• 6:15
  Speaker 1: the stuff you have seen, which was like exciting to
• 6:18
  Speaker 1: get a glimpse behind the scenes, but also deflating because
• 6:20
  Speaker 1: I was really hoping he was going to say, oh,
• 6:22
  Speaker 1: with amazing stuff, you won't believe it when they finally
• 6:25
  Speaker 1: release it.
• 6:26
  Speaker 2: So unfortunately, but I do want to believe.
• 6:28
  Speaker 1: I'm waiting for the day that the aliens come and
• 6:31
  Speaker 1: I will be first in line to talk to them
• 6:32
  Speaker 1: about the secrets.
• 6:33
  Speaker 2: Of the universe.
• 6:34
  Speaker 3: I'm excited too, and I think if our species persists
• 6:36
  Speaker 3: long enough, it's just a matter of time before we
• 6:39
  Speaker 3: encounter something. But this is a good transition into today's topic.
• 6:43
  Speaker 3: So the title of today's show is is life rare
• 6:46
  Speaker 3: in the universe? So what is the probability that there's
• 6:49
  Speaker 3: life out there that we could encounter. We've reached out
• 6:52
  Speaker 3: to the listeners and we told them that one approach
• 6:55
  Speaker 3: to thinking about life in the universe is the rare
• 6:57
  Speaker 3: Earth hypothesis. We wanted to know what they had heard
• 7:00
  Speaker 3: about this, and here are their responses.
• 7:03
  Speaker 4: I think the rare Earth hypothesis is the idea that
• 7:05
  Speaker 4: Earth and specifically its conditions for life are really rare
• 7:09
  Speaker 4: in the universe, and that life being able to form
• 7:12
  Speaker 4: is rare because a planet able to support life is rare.
• 7:16
  Speaker 5: I don't know, but I think it's that Earth is
• 7:18
  Speaker 5: the only planet that has life that we know of.
• 7:22
  Speaker 6: I think the rare Earth hypothesis has to do with
• 7:24
  Speaker 6: how common it is that a planet just like ours
• 7:27
  Speaker 6: would form with all the crazy factors that went into
• 7:31
  Speaker 6: our history, or it has to do with the composition
• 7:35
  Speaker 6: of elements that we can find in our crust, mantle,
• 7:38
  Speaker 6: and core. Either way, rare.
• 7:39
  Speaker 7: Earth planets that can foster life orbit in the Goldilock zone,
• 7:44
  Speaker 7: allowing for liquid water. They have a molten core, iron core,
• 7:48
  Speaker 7: creating a magnetic field protecting it from high energy, harmful radiation,
• 7:52
  Speaker 7: and many other characteristics required to sustain life. So I
• 7:55
  Speaker 7: think the rare Earth hypothesis hypothesizes its rare but possible
• 8:01
  Speaker 7: to have planets swiat to Earth throughout the universal.
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  Speaker 5: Because I have no idea, I will use context clues
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  Speaker 5: and say maybe it has something to do with minerals.
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  Speaker 8: The rare Earth hypothesis is the way our earthborn does
• 8:20
  Speaker 8: compared to other rocky planets and other solo systems. Is
• 8:24
  Speaker 8: not a common occurrence, Like it's rare, Like we don't
• 8:27
  Speaker 8: see them every day.
• 8:29
  Speaker 3: All right, Daniel, what do you think?
• 8:30
  Speaker 1: Yeah, I think the listeners are right on here. The
• 8:33
  Speaker 1: rare hypothesis is one of those ideas in science that
• 8:37
  Speaker 1: is rare because it's well named, you know, you can
• 8:39
  Speaker 1: actually understand what it means.
• 8:40
  Speaker 2: Run the title. It's a hypothesis that.
• 8:43
  Speaker 1: Earth is rare, that life on Earth is rare, that
• 8:45
  Speaker 1: our existence is unusual in the universe, which of course
• 8:49
  Speaker 1: would be a devastating outcome for those of us who
• 8:51
  Speaker 1: hope that the universe is builled with all sorts of
• 8:54
  Speaker 1: intelligent alien life we can one day talk to. But
• 8:57
  Speaker 1: it's a possibility we have to face, right, It's one
• 8:59
  Speaker 1: of the potential outcomes to this question. Are we alone
• 9:02
  Speaker 1: in the universe? It might be yes, it might be
• 9:05
  Speaker 1: that we're the only thinking creatures out there trying to
• 9:07
  Speaker 1: understand how the universe works.
• 9:10
  Speaker 3: Yeah. Maybe, or maybe they've just seen human history and
• 9:13
  Speaker 3: they're like, they're just not ready for us yet. So
• 9:16
  Speaker 3: every conversation about aliens has to start with the Drake equation,
• 9:20
  Speaker 3: which I think is both interesting and useful. I've reviewed
• 9:24
  Speaker 3: a lot of proposals for students who are into science communication,
• 9:28
  Speaker 3: and almost everyone who's in physics wants to do a
• 9:31
  Speaker 3: video about the Drake equation, and so I'm like, I'm
• 9:34
  Speaker 3: kind of over it. Oh no, it's like mitosis for biologists,
• 9:38
  Speaker 3: Like everybody does the video on mitosis. But all right,
• 9:40
  Speaker 3: so Daniel the bar is high. Make the Drake equation
• 9:44
  Speaker 3: interesting to me again, like it was the first time
• 9:46
  Speaker 3: I heard it.
• 9:47
  Speaker 1: All right, all right, Well, this episode is not just
• 9:50
  Speaker 1: about the Drake equation, but I think that Drake equation
• 9:53
  Speaker 1: is a very useful way to organize our thinking. Like, look,
• 9:56
  Speaker 1: this is a big problem, right, is there life elsewhere
• 9:59
  Speaker 1: in the.
• 9:59
  Speaker 2: Universe and in science.
• 10:01
  Speaker 1: When we tackle a really big problem, what our strategies
• 10:04
  Speaker 1: is like, hey, break it into pieces. You know, every
• 10:07
  Speaker 1: time I have a big research project, I don't know
• 10:09
  Speaker 1: how many get from here to there. You got to
• 10:11
  Speaker 1: break it into steps and then take on each of
• 10:13
  Speaker 1: those steps. And the Drake equation is just that. It
• 10:15
  Speaker 1: is to say, look, if there is going to be
• 10:17
  Speaker 1: life elsewhere in the universe, then a lot of things
• 10:20
  Speaker 1: have to line up. You need to have enough stars,
• 10:23
  Speaker 1: you need to have enough planets around those stars, you
• 10:24
  Speaker 1: need to have life on those planets. That life has
• 10:26
  Speaker 1: to develop intelligence, that intelligence has to be technological. And
• 10:31
  Speaker 1: so it breaks it up into all these sub questions like, well,
• 10:33
  Speaker 1: we can think about how many stars there are, and
• 10:35
  Speaker 1: we can think about the physics of whether there are
• 10:37
  Speaker 1: planets around them, and we can argue about whether there
• 10:41
  Speaker 1: is life on planets or what the.
• 10:43
  Speaker 2: Probability of those is.
• 10:45
  Speaker 1: So it's a really useful way to try to think
• 10:47
  Speaker 1: about the problem. It also shows you how hard this
• 10:50
  Speaker 1: problem is because you know, how do you know what
• 10:52
  Speaker 1: fraction of planets have life on them? Remember that all
• 10:56
  Speaker 1: the information we have comes either from Earth or from
• 10:59
  Speaker 1: the a few Measley photons that have crawled their way
• 11:02
  Speaker 1: through the universe to get to Earth, and so it's
• 11:05
  Speaker 1: a really difficult task, but that doesn't mean we shouldn't
• 11:08
  Speaker 1: take it on, Right, Every really big question in science
• 11:11
  Speaker 1: got started at some point when people were like, hmm,
• 11:13
  Speaker 1: this seems really hard. What's the first thing we can
• 11:16
  Speaker 1: do to tackle it? So, to me, the Drake equation
• 11:18
  Speaker 1: is just like, hey, let's take a step towards answering
• 11:21
  Speaker 1: this really hard but really important problem.
• 11:24
  Speaker 3: Yeah, I think that's fair. Figuring out the like parameters
• 11:28
  Speaker 3: that need to be measured and trying to get a
• 11:30
  Speaker 3: handle on the errors in our data, those are all
• 11:33
  Speaker 3: good things to do. When was the Drake equation proposed?
• 11:35
  Speaker 3: Because I think we have actually like made pretty good
• 11:38
  Speaker 3: progress on getting sort of estimates for some of these
• 11:42
  Speaker 3: things since the Drake equation was proposed, Right, Yeah.
• 11:45
  Speaker 1: The Drake equation is pretty old by now. It's nineteen
• 11:47
  Speaker 1: sixty one by Frank Drake, famous astronomer, of course, and
• 11:52
  Speaker 1: so that's you know, sixty years ago, and we definitely
• 11:54
  Speaker 1: know a lot more about some of these numbers than
• 11:56
  Speaker 1: we did when it was first proposed, which is really
• 11:58
  Speaker 1: fascinating because in the Earth they had to do a
• 12:01
  Speaker 1: lot more sort of guessing, and it's interesting to read
• 12:04
  Speaker 1: like what Carl Sagan thought about these things. He was
• 12:07
  Speaker 1: a big believer in this principle of mediocrity. I mean,
• 12:10
  Speaker 1: I know, his famous quote is like extraordinary claims require
• 12:13
  Speaker 1: extraordinary evidence. But he also hit hard on this principle
• 12:16
  Speaker 1: of mediocrity, which I think is fascinating. And it's a
• 12:18
  Speaker 1: very simple argument. It says, like, look, if you only
• 12:21
  Speaker 1: have one example of something, probably it's a typical example.
• 12:25
  Speaker 1: You know, imagine, for example, you have a bag full
• 12:28
  Speaker 1: of marbles, You draw one. It's an orange one. What
• 12:31
  Speaker 1: are the chances it's the only orange marble in a
• 12:34
  Speaker 1: bag of millions of marbles. Pretty small? Probably it's the
• 12:38
  Speaker 1: most likely kind of marble. Right, Probably it's mostly orange marbles.
• 12:41
  Speaker 1: So that's a pretty basic argument, and Carl Sagan uses
• 12:45
  Speaker 1: it to suggest, Hey, look there's life here on Earth.
• 12:48
  Speaker 2: There's planets around this star. You know, we.
• 12:50
  Speaker 1: Develop technological civilization. So probably all of these numbers in
• 12:54
  Speaker 1: the Drake equation are not zero or very very very
• 12:57
  Speaker 1: close to zero. They're probably around half right. And so
• 13:01
  Speaker 1: that's like a really powerful, not that convincing, but useful
• 13:06
  Speaker 1: first argument to say, like Hey, look, life in the
• 13:09
  Speaker 1: universe shouldn't be rare, and it's sort of astonishing how
• 13:12
  Speaker 1: far you can get from just like, hey, we're going
• 13:14
  Speaker 1: to write down all the numbers you have to multiply
• 13:16
  Speaker 1: together to calculate the number of alien species. We're going
• 13:19
  Speaker 1: to make this very vague argument, and then we're going
• 13:22
  Speaker 1: to basically conclude that life is everywhere in the universe.
• 13:24
  Speaker 3: So, I don't remember, does the Drake equation give you
• 13:27
  Speaker 3: an estimated number of intelligent civilizations out there or like
• 13:31
  Speaker 3: a probability of finding it? And are there recent estimates
• 13:34
  Speaker 3: that we could point to.
• 13:36
  Speaker 1: Yeah, So the Drake equation calculates the number of civilizations
• 13:39
  Speaker 1: in the galaxy with which communication might be possible. Right,
• 13:44
  Speaker 1: So it has the rate of star formation in the galaxy,
• 13:46
  Speaker 1: the fraction of those that have planets, the number of
• 13:49
  Speaker 1: planets that have life, the fraction of those that actually
• 13:52
  Speaker 1: develop life, the fraction of those that have intelligent life,
• 13:54
  Speaker 1: fraction of those that have civilization, and then the time that.
• 13:57
  Speaker 2: They survive like the length of their Bible.
• 14:00
  Speaker 1: Because if aliens are civilized for only five seconds before
• 14:03
  Speaker 1: they nuke themselves to smithereens, then we're not likely to
• 14:06
  Speaker 1: hear from them. We might get the shock waves from
• 14:08
  Speaker 1: their nuclear holocaust, but that's not exactly communication.
• 14:12
  Speaker 3: Yeah, No, I mean that would be a lesson that
• 14:14
  Speaker 3: would be important to learn that.
• 14:16
  Speaker 1: Yeah, but you're right that More recently people have started
• 14:19
  Speaker 1: to wonder about this because we've learned some things about
• 14:21
  Speaker 1: these numbers, Like we know that there are billions and
• 14:24
  Speaker 1: billions more than one hundred billion stars in the Milky Way,
• 14:27
  Speaker 1: so like we're starting from a really big number. And
• 14:30
  Speaker 1: more recently we've learned thanks to exoplanets, that there are
• 14:33
  Speaker 1: a lot of planets out there. There's like many planets
• 14:37
  Speaker 1: per star, and a significant fraction of stars out there
• 14:40
  Speaker 1: have Earth like planets inhabitable zone, you know. So that's
• 14:44
  Speaker 1: not a tiny number. So now we're talking like tens
• 14:47
  Speaker 1: of billions of rocky planets out there in the Milky Way.
• 14:51
  Speaker 1: And even a few decades after the drig equation, people
• 14:53
  Speaker 1: were wondering, like, hmm, there are all these stars out
• 14:56
  Speaker 1: there in the galaxy, there are all these planets out there.
• 14:59
  Speaker 1: Life can't be that rare to form, So where are
• 15:03
  Speaker 1: all the aliens?
• 15:04
  Speaker 4: Right?
• 15:04
  Speaker 1: And so that's the famous Fermi paradox. People are wondering
• 15:06
  Speaker 1: like Sagan's principle of mediocrity, and the Drake equation all
• 15:10
  Speaker 1: suggests that the universe should be teeming with life, that
• 15:13
  Speaker 1: the galaxy should be overflowing with life, and also crucially,
• 15:17
  Speaker 1: that there's time for it to have reached us. Like,
• 15:20
  Speaker 1: the galaxy is about one hundred thousand light years across,
• 15:24
  Speaker 1: and it's more than ten billion years old, So there's
• 15:27
  Speaker 1: time for like a civilization to flourish, to form, to
• 15:31
  Speaker 1: travel the stars, to even explore the galaxy. I once
• 15:35
  Speaker 1: sat down and calculated, like, how long would it take
• 15:38
  Speaker 1: for a civilization to send a probe to every single
• 15:42
  Speaker 1: rocky planet in the galaxy? And the answer is not
• 15:45
  Speaker 1: that long. If you can build self replicating probes that
• 15:49
  Speaker 1: land on a planet, do a little bit of mining,
• 15:52
  Speaker 1: make more of themselves, then the number of probes grows exponentially,
• 15:56
  Speaker 1: and so it takes like much less than a million
• 15:58
  Speaker 1: years to explore the entire galaxy. In the galaxies billions
• 16:02
  Speaker 1: of years old, surely somebody would have thought of this idea.
• 16:05
  Speaker 1: I mean, if I've had this idea and other people
• 16:06
  Speaker 1: have had it, certainly some clever alien has done it,
• 16:09
  Speaker 1: and yet we haven't been visited as far as we
• 16:12
  Speaker 1: know by self replicating alien robots.
• 16:15
  Speaker 3: But timing matters too, So you know, if those self
• 16:17
  Speaker 3: replicating alien robots showed up in the age of the dinosaurs,
• 16:21
  Speaker 3: then they would have missed us.
• 16:22
  Speaker 1: The Drick equation definitely accommodates those windows. And you're right
• 16:26
  Speaker 1: that self replicating anian robots had shown up in the
• 16:28
  Speaker 1: age of the dinosaurs, we wouldn't have been here to
• 16:30
  Speaker 1: greet them. But you know, they might have left a mark,
• 16:33
  Speaker 1: and maybe we'll discover traces of them on the Moon
• 16:36
  Speaker 1: or something, and they probably would have replicated themselves and
• 16:39
  Speaker 1: occupied nearby solar systems. I don't know that they would
• 16:42
  Speaker 1: have been really subtle, but hey, maybe that's a possibility.
• 16:45
  Speaker 1: It's certainly one of the answers to this question of
• 16:47
  Speaker 1: the Fermi paradox of where is everybody? Why haven't we
• 16:50
  Speaker 1: been yet visited by aliens? If it seems like the
• 16:54
  Speaker 1: universe should be filled with them. It's not like a
• 16:56
  Speaker 1: claim that there have to be aliens out there. It's
• 16:58
  Speaker 1: more like a response to say this argument. It says, like, okay,
• 17:02
  Speaker 1: you make that argument. It suggests that there should be
• 17:04
  Speaker 1: aliens everywhere, but there aren't, So what's.
• 17:06
  Speaker 2: Wrong, right? Which piece have we misunderstood?
• 17:10
  Speaker 3: Sure, and the co host with anxiety and insecurity is thinking,
• 17:14
  Speaker 3: maybe we're the stinky kids and that's why we haven't
• 17:17
  Speaker 3: been visited. But let's assume that it's not about us,
• 17:19
  Speaker 3: that it's not that they just dislike us. So one
• 17:22
  Speaker 3: rebuttal here is that actually we've overestimated the probability that
• 17:26
  Speaker 3: there's intelligent life out there that could visit us. And
• 17:29
  Speaker 3: this is the rare Earth hypothesis. And we will dive
• 17:33
  Speaker 3: into the rare Earth hypothesis after this break. All right, Daniel,
• 17:53
  Speaker 3: We're not the stinky kids in the universe. I'm sure
• 17:57
  Speaker 3: of it.
• 17:57
  Speaker 1: Wait, first, I want to know why that makes you
• 17:59
  Speaker 1: feel like if we are rejected by aliens, you're going
• 18:02
  Speaker 1: to take that personally, like it matters to you what
• 18:04
  Speaker 1: aliens think.
• 18:05
  Speaker 3: I would be a little bit bummed out if there
• 18:07
  Speaker 3: was like a network of alien civilizations that were all
• 18:11
  Speaker 3: sort of sharing secrets and information about science together, but
• 18:15
  Speaker 3: they just decided that the humans were not quite ready
• 18:17
  Speaker 3: for it. Maybe we're too violent at this point and
• 18:20
  Speaker 3: we couldn't handle what they had to teach us. That
• 18:22
  Speaker 3: would kind of bum me out. I think my psychiatrist
• 18:25
  Speaker 3: calls that catastrophizing. It would bum me out if there
• 18:29
  Speaker 3: were aliens and they decided we're not worth talking to you.
• 18:31
  Speaker 3: What about you?
• 18:32
  Speaker 1: Well, it would bum me out, but not in a
• 18:34
  Speaker 1: personal way. I wouldn't feel like, Wow, all the cool
• 18:37
  Speaker 1: kids don't think I'm cool. I just feel like it'd
• 18:39
  Speaker 1: be a tragedy if they're out there and we don't
• 18:42
  Speaker 1: get to meet them. We're going to learn about how
• 18:43
  Speaker 1: the universe works and how life could be so different
• 18:46
  Speaker 1: or so similar to ours.
• 18:48
  Speaker 2: It just seems like.
• 18:49
  Speaker 1: A tragic, missed opportunity. So it's not really important to
• 18:51
  Speaker 1: me that aliens think we're awesome or that we smell good.
• 18:54
  Speaker 1: But I do want to meet them. So anything that
• 18:56
  Speaker 1: stands in the way of that is definitely a big bummer.
• 18:59
  Speaker 3: Yeah, and all right, So the rare Earth hypothesis posits
• 19:05
  Speaker 3: that we should expect to see life like ours much
• 19:07
  Speaker 3: less in the universe. So give me some background here.
• 19:10
  Speaker 3: Whose idea is this?
• 19:12
  Speaker 2: Yeah, So the Rare.
• 19:12
  Speaker 1: Earth hypothesis came out around two thousand. It's a famous
• 19:16
  Speaker 1: book by the astronomer Donald Brownlee and the geologist Peter Ward,
• 19:21
  Speaker 1: and they try to take a careful look at some
• 19:23
  Speaker 1: of these numbers, like how often is there a planet
• 19:27
  Speaker 1: in a habitable zone that could develop life like ours?
• 19:29
  Speaker 1: What are the conditions that are really necessary and how
• 19:32
  Speaker 1: common are those conditions? And again, there's a lot of
• 19:34
  Speaker 1: guesswork here, but there's always going to be a lot
• 19:36
  Speaker 1: of guesswork. You can't just criticize any work in this
• 19:39
  Speaker 1: area by saying it's not definitive. You know, the first
• 19:41
  Speaker 1: steps are never definitive. But their studies lead them to
• 19:44
  Speaker 1: conclude the opposite of Sagan. Sagan says, you know, hey,
• 19:48
  Speaker 1: we should be typical because we're one of many. But
• 19:50
  Speaker 1: they say, essentially, maybe we're the only one of many
• 19:53
  Speaker 1: because we're unusual, we're weird, and we're different, and we're
• 19:57
  Speaker 1: the only place in the universe that life could arise.
• 20:00
  Speaker 1: So their argument is that we're not typical. There are
• 20:03
  Speaker 1: not many other cases. You know, that we are the
• 20:05
  Speaker 1: one orange marble from the bag, and that's why we're
• 20:08
  Speaker 1: the ones asking the question.
• 20:10
  Speaker 3: We're one and there's not many.
• 20:12
  Speaker 2: Yeah, that's right, Yeah, okay, got it.
• 20:14
  Speaker 3: Got it. What factors did we look into then to
• 20:17
  Speaker 3: be the ones who ended up evolving as the intelligent species?
• 20:20
  Speaker 2: Yeah?
• 20:20
  Speaker 1: So I like their book a lot because it does
• 20:23
  Speaker 1: dig into the details of what it takes for.
• 20:26
  Speaker 2: Life to form, and they start big.
• 20:28
  Speaker 1: So let's think about the galaxy, like where in a
• 20:31
  Speaker 1: typical galaxy could you have life. We talked about one
• 20:34
  Speaker 1: hundred billion stars, but could you really have intelligent life
• 20:38
  Speaker 1: around all of those stars? And it turns out the
• 20:40
  Speaker 1: answer is no. There's a lot of the galaxy that's
• 20:43
  Speaker 1: basically a dead zone for life like hours. So, for example,
• 20:46
  Speaker 1: if you're near the center of the galaxy, there's a
• 20:49
  Speaker 1: lot more radiation. Like we talk about often, how out
• 20:52
  Speaker 1: in space, it's not just a vacuum where there's nothing.
• 20:55
  Speaker 1: There's a lot of radiation out there in space. Astronauts
• 20:57
  Speaker 1: to get dosed with radiation on the Internet space station.
• 21:00
  Speaker 1: They have basically a panic room where they can go
• 21:02
  Speaker 1: if there's a solar flare. Space is filled with flying
• 21:05
  Speaker 1: particles that will kill you, and we're buffered from that
• 21:09
  Speaker 1: because of our atmosphere. But also our solar system is
• 21:12
  Speaker 1: not of the most intensely radiation filled part of the galaxy.
• 21:16
  Speaker 2: As you get.
• 21:17
  Speaker 1: Closer and closer to the center, the black hole and
• 21:19
  Speaker 1: all the other stars are pumping out a lot of
• 21:22
  Speaker 1: radiation that could really damage you.
• 21:25
  Speaker 3: This is a different kind of radiation, So maybe this
• 21:27
  Speaker 3: argument isn't a good one. But so like, there's fungus
• 21:29
  Speaker 3: that are growing in like the abandoned Chernobyl nuclear reactors,
• 21:34
  Speaker 3: and so there are apparently species that can handle much
• 21:39
  Speaker 3: higher levels of radiation. They do it better than humans do.
• 21:42
  Speaker 3: Maybe Merlin Sheldrake or some other fungus enthusiasts would say
• 21:47
  Speaker 3: that they communicate intelligently with one another, But I know
• 21:49
  Speaker 3: that's not what we're quite talking about. But could there
• 21:51
  Speaker 3: be species that are intelligent and are just way more
• 21:54
  Speaker 3: radiation resistant than we are?
• 21:56
  Speaker 1: Of course there might be, right, and you put your
• 21:58
  Speaker 1: finger on the fundamentalntal weakness of this entire argument, which
• 22:03
  Speaker 1: is that they're thinking about lifelike hours. Sure, if you
• 22:06
  Speaker 1: took humans and you teleported them to some planet around
• 22:09
  Speaker 1: a star close to the center of the galaxy, they
• 22:11
  Speaker 1: wouldn't last very long. They'd all get cancer, and it
• 22:13
  Speaker 1: wouldn't be very fun because lifelike ours didn't evolve.
• 22:16
  Speaker 2: In those conditions. But it's much harder to.
• 22:19
  Speaker 1: Say could life that's not like ours arise under different conditions?
• 22:23
  Speaker 1: And that's really the challenge of thinking about alien life
• 22:26
  Speaker 1: is thinking out of the box of earth like life.
• 22:29
  Speaker 1: So really this book is asking what's the probability of
• 22:32
  Speaker 1: earth like life arising not on Earth, which of course
• 22:36
  Speaker 1: is going to be a small number. And so that's
• 22:39
  Speaker 1: the fundamental criticism of this book. You really put your
• 22:41
  Speaker 1: finger on it. But it does highlight how different the
• 22:44
  Speaker 1: conditions are in different parts of the galaxy and therefore
• 22:47
  Speaker 1: how different life might be. If you are evolving close
• 22:50
  Speaker 1: to the center of the galaxy and near the black hole,
• 22:53
  Speaker 1: you're going to somehow have to have a different biochemistry
• 22:55
  Speaker 1: because you're getting pummeled by radiation all the time, and
• 22:58
  Speaker 1: maybe you figure it out a way to take advantage
• 23:00
  Speaker 1: of that. Maybe radiation is like lunch for you, right.
• 23:03
  Speaker 3: I wonder if these factors would also influence like the
• 23:07
  Speaker 3: order that visits would have to happen. Like humans couldn't
• 23:10
  Speaker 3: go towards a high radiation area to like try to
• 23:14
  Speaker 3: meet those aliens because we'd get cancer and die. But
• 23:17
  Speaker 3: organisms that are from a high radiation part of the
• 23:21
  Speaker 3: galaxy could come visit us if they could handle less radiation.
• 23:25
  Speaker 3: Unless they're eating radiation, then they might be very hungry,
• 23:28
  Speaker 3: but we could feed them at Chernobyl or something.
• 23:30
  Speaker 2: Yeah exactly.
• 23:31
  Speaker 3: I guess you don't have to physically go somewhere to
• 23:32
  Speaker 3: communicate with someone.
• 23:34
  Speaker 2: Yeah, that's right.
• 23:34
  Speaker 1: I think the Drake equation is mostly thinking about communication,
• 23:37
  Speaker 1: But of course I want to meet the aliens. And
• 23:40
  Speaker 1: I think if we found a civilization near the center
• 23:42
  Speaker 1: of the galaxy that was eating radiation, we just have
• 23:45
  Speaker 1: to develop good technology to protect ourselves.
• 23:47
  Speaker 2: We could probably figure out how to get there.
• 23:49
  Speaker 1: But it's fascinating to think about which parts of the
• 23:51
  Speaker 1: galaxy life could evolve in and how it would be different.
• 23:54
  Speaker 1: So there's the center of the galaxy filled with radiation.
• 23:56
  Speaker 1: That's a dead zone for lifelike hours. It's also less
• 23:59
  Speaker 1: likely to develop lifel like hours at the edge of
• 24:02
  Speaker 1: the galaxy, like far out from the center is also
• 24:06
  Speaker 1: not a great place to have life like ours because
• 24:09
  Speaker 1: far out there the stars have less metal, so the
• 24:11
  Speaker 1: solar systems have less like hard rocky stuff in order
• 24:15
  Speaker 1: to build life.
• 24:16
  Speaker 3: So does that mean you're more likely to get gas
• 24:19
  Speaker 3: giants that you can't land on out there?
• 24:21
  Speaker 1: Yeah exactly. And remember where stuff comes from in the universe.
• 24:24
  Speaker 1: Very abbreviated history of the universe is you have like
• 24:27
  Speaker 1: protons and electrons, and they form hydrogen. So most of
• 24:29
  Speaker 1: the universe is hydrogen, with a little bit of helium
• 24:33
  Speaker 1: from fusion during the Big Bang. But then the universe
• 24:36
  Speaker 1: is just like clouds of hydrogen for a long long time,
• 24:39
  Speaker 1: and that hasn't really changed. You know, we have stars
• 24:42
  Speaker 1: that have formed and have made helium and carbon and
• 24:44
  Speaker 1: nitrogen and oxygen all the way up to iron, and
• 24:47
  Speaker 1: then we have supernova that make really heavy stuff. But
• 24:50
  Speaker 1: the fraction of the universe that is anything but hydrogen
• 24:52
  Speaker 1: and helium is still pretty small. So this is the
• 24:56
  Speaker 1: stuff that like makes life interesting, It makes complicated biochemistry possible,
• 25:00
  Speaker 1: and like you know, information storage and DNA, all that
• 25:03
  Speaker 1: stuff needs more complex molecules. Those who rely on those
• 25:06
  Speaker 1: heavier atoms, and those are still pretty rare, and they
• 25:09
  Speaker 1: tend to be near the center of the galaxy. That's
• 25:12
  Speaker 1: where the masses the heavy stuff falls there, and so
• 25:15
  Speaker 1: out in the sort of backwaters of the galaxy there
• 25:18
  Speaker 1: are fewer metals, and so yeah, you have stars there
• 25:22
  Speaker 1: that are more hydrogen, more helium, less metallic, which changes
• 25:25
  Speaker 1: how they operate. And then you have fewer rocky planets
• 25:28
  Speaker 1: and more gas giants, and again that's bad for life,
• 25:31
  Speaker 1: Like hours. But if you're some sort of weird alien
• 25:34
  Speaker 1: that's like a plasma cyclone in a star, you don't
• 25:37
  Speaker 1: really care.
• 25:37
  Speaker 2: Or if you're a weird.
• 25:38
  Speaker 1: Alien that evolved in the clouds of a gas giant,
• 25:42
  Speaker 1: you also don't necessarily care.
• 25:44
  Speaker 2: But for lifelike hours, it would be harder to evolve
• 25:47
  Speaker 2: far away from the center of the galaxy.
• 25:49
  Speaker 3: In our atmosphere, there's bacteria that are you know, floating
• 25:52
  Speaker 3: around up in the sky in the clouds and stuff
• 25:54
  Speaker 3: like that. You couldn't even get stuff like that at
• 25:57
  Speaker 3: the far reaches of the galaxy because bacteria have more
• 26:00
  Speaker 3: than hydrogen and helium in them.
• 26:03
  Speaker 2: Yeah, exactly.
• 26:04
  Speaker 1: And it's not like there're no metals out there, it's
• 26:06
  Speaker 1: just rarer and so that like suppresses the chances for
• 26:09
  Speaker 1: all those kind of stuff happening. So that makes the
• 26:12
  Speaker 1: galaxy have like a window of habitability, you know, habitable zone.
• 26:16
  Speaker 1: You can't get too close to the center or you
• 26:18
  Speaker 1: get fried. You can't get too far out, or there
• 26:21
  Speaker 1: aren't enough of the building blocks. And then in the
• 26:23
  Speaker 1: habitable zone you're not even safe. Like there are places
• 26:26
  Speaker 1: in the habitable zone that are more dangerous for life
• 26:29
  Speaker 1: like ours than other places.
• 26:31
  Speaker 3: And how is this danger measured? Does this radiation?
• 26:35
  Speaker 1: This is the chances that a nearby star are going
• 26:38
  Speaker 1: to come by disturb the Solar System and cause an
• 26:41
  Speaker 1: extinction event due to like a comet hitting a planet.
• 26:44
  Speaker 1: So the density of stars nearby really affects how likely
• 26:47
  Speaker 1: you are to have a comet get nudged from the
• 26:49
  Speaker 1: outer Solar System and fall into the inner Solar System
• 26:52
  Speaker 1: and impact on your planet and fry everybody. If you
• 26:55
  Speaker 1: have a lot of nearby stars, then their little gravitational
• 26:58
  Speaker 1: tugs are going to interfere with your Solar system and
• 27:00
  Speaker 1: make it very chaotic. If you're pretty far away from
• 27:03
  Speaker 1: everybody else, then you're safer.
• 27:05
  Speaker 3: But we've been hit by comets and have massive extinction events,
• 27:09
  Speaker 3: but still some stuff eaked through and humans popped out.
• 27:14
  Speaker 3: They feel like chaos just kind of pushes diversity back
• 27:16
  Speaker 3: a little bit. Yeah, and then it rebounds. Whoever makes
• 27:20
  Speaker 3: it through. That doesn't seem like a showstop er so
• 27:22
  Speaker 3: much as a show slower downer.
• 27:26
  Speaker 2: Yeah, and it might also be crucial.
• 27:27
  Speaker 1: Right, maybe evolution gets stuck in some local minimum and
• 27:30
  Speaker 1: it needs a reboot and needs to get like kicked
• 27:32
  Speaker 1: into higher gear. Right, we certainly know that a massive
• 27:35
  Speaker 1: impactor played a big role in the history of life
• 27:37
  Speaker 1: on Earth, and we wouldn't be here if it hadn't
• 27:39
  Speaker 1: hit sixty five million years ago. So I agree with
• 27:42
  Speaker 1: you this is not an open and shutcase. But again
• 27:44
  Speaker 1: it does show you that elements of the galaxy are different,
• 27:48
  Speaker 1: and that growing up in different parts of the galaxy,
• 27:51
  Speaker 1: the neighborhoods really are different. There are more crowded neighborhoods
• 27:54
  Speaker 1: and then there are quiet and peaceful neighborhoods. And you know,
• 27:57
  Speaker 1: where we are in the galaxy changes because the most
• 28:01
  Speaker 1: dangerous parts and the habitable zone are in the galactic arms.
• 28:05
  Speaker 1: Like you know, the galaxy is a big flat disc,
• 28:07
  Speaker 1: but it spins and has these arms. You see these
• 28:10
  Speaker 1: when you look at pictures of galaxies, and it's not
• 28:12
  Speaker 1: like the Sun is either in the arms or not
• 28:14
  Speaker 1: in the arms.
• 28:15
  Speaker 2: Those arms pass through the galaxy.
• 28:18
  Speaker 1: So sometimes during the galactic cycle, we are in an
• 28:20
  Speaker 1: arm and arm passes through us. It's more of a
• 28:23
  Speaker 1: density wave than a structure. It's sort of like traffic, right.
• 28:26
  Speaker 1: Sometimes you can be on the road there's no traffic,
• 28:28
  Speaker 1: and then a traffic wave will pass through you. So
• 28:31
  Speaker 1: there are epics when you're inside one of these arms
• 28:34
  Speaker 1: and there are more stars around you and more comments
• 28:36
  Speaker 1: are hitting your planet.
• 28:37
  Speaker 2: For good or for ill.
• 28:39
  Speaker 1: But where you are in the galaxy really influences the
• 28:42
  Speaker 1: experience of life on that planet.
• 28:44
  Speaker 3: What if instead that spurs innovation, Like what if you're
• 28:47
  Speaker 3: a civilization that's sort of on the edge of being
• 28:50
  Speaker 3: able to do space travel and you're like, all right,
• 28:52
  Speaker 3: we really got to figure it out. Our neighborhoods are
• 28:54
  Speaker 3: going to be colliding. It's time to go. I can
• 28:57
  Speaker 3: imagine that spurring innovation if the timing works out.
• 28:59
  Speaker 2: Yeah.
• 29:00
  Speaker 1: Think that really highlights the weakness of these arguments that
• 29:02
  Speaker 1: you can almost always make the opposite argument, like this
• 29:05
  Speaker 1: seems plausible, So does the opposite argument. I guess the
• 29:08
  Speaker 1: answer is we really just don't know. And I think
• 29:11
  Speaker 1: that's the takeaway message, is like, we really don't know
• 29:13
  Speaker 1: anything about any of these questions, and what.
• 29:15
  Speaker 2: We really need is more data. We have an equals one.
• 29:18
  Speaker 2: We really need an equals to.
• 29:19
  Speaker 1: We need another example of life out there in the
• 29:22
  Speaker 1: universe to tell us like, oh, wow, it's very similar.
• 29:24
  Speaker 1: Hours are wow, it's dramatically different. But right now we
• 29:27
  Speaker 1: just have an equals one, and we're extrapolating blindly.
• 29:30
  Speaker 5: You know.
• 29:31
  Speaker 3: I think maybe we should have called the show Daniel
• 29:34
  Speaker 3: and Kelly's not really explainable yet universe. But oh, that's
• 29:40
  Speaker 3: all right. We're enjoying ourselves, all right, So what's the
• 29:43
  Speaker 3: next thing that they want us to think about?
• 29:45
  Speaker 1: The next thing is to think about where you are
• 29:47
  Speaker 1: in the Solar System, right, So, say you have a
• 29:49
  Speaker 1: star where you are convinced Earth like life could evolve,
• 29:53
  Speaker 1: Then do you have a planet that's in the right region?
• 29:55
  Speaker 1: And so people talk a lot about this habitable zone.
• 29:58
  Speaker 1: You have to be close enough to the star for
• 30:00
  Speaker 1: water to melt, but not so close that water is
• 30:03
  Speaker 1: going to get turned into vapor and everything on the
• 30:05
  Speaker 1: planet is going to get fried. And again, this is
• 30:07
  Speaker 1: assuming that you have water based life, and so you
• 30:11
  Speaker 1: need liquid water on the surface, and like, we certainly
• 30:14
  Speaker 1: have water based life here on Earth, but it's also
• 30:17
  Speaker 1: not that hard to imagine life on a planet where
• 30:20
  Speaker 1: there isn't liquid water on the surface.
• 30:22
  Speaker 3: I disagree as a biologist, it's hard for me to
• 30:27
  Speaker 3: imagine life without water, but I think that's just because
• 30:31
  Speaker 3: this is the planet that I'm on, and this is
• 30:33
  Speaker 3: what I know, but questions like this, I waffle between thinking, well,
• 30:36
  Speaker 3: maybe it could be totally different than what we know,
• 30:38
  Speaker 3: and then thinking, okay, but still we have all these
• 30:40
  Speaker 3: different conditions on Earth and we're not seeing like life
• 30:43
  Speaker 3: evolving independently on our deserts. Like if it was that easy,
• 30:47
  Speaker 3: we'd expect an equals too on Earth for the origin
• 30:50
  Speaker 3: of life coming up in the desert, and so we
• 30:52
  Speaker 3: don't know.
• 30:53
  Speaker 1: Yeah, and that's actually a question I have. It's like,
• 30:55
  Speaker 1: how do we know that life didn't start multiple times
• 30:57
  Speaker 1: on Earth? That there aren't of that somewhere or history
• 31:01
  Speaker 1: of that somewhere.
• 31:02
  Speaker 2: You know.
• 31:03
  Speaker 1: Let me give you a counter example. What about life
• 31:06
  Speaker 1: forming on subsurface oceans. Say you have, for example, the
• 31:10
  Speaker 1: moon or of a gas giant, and it's frozen solid
• 31:13
  Speaker 1: on the surface because it's cold and far from the sun,
• 31:16
  Speaker 1: but there's enough pressure and enough tidal forces that internally
• 31:19
  Speaker 1: there's heat. And then you have a subsurface ocean. Why
• 31:22
  Speaker 1: can't you have life forming there? So it's still water,
• 31:24
  Speaker 1: but it's not liquid water on the surface, and technically
• 31:28
  Speaker 1: that's outside of these guys' habitable zone.
• 31:30
  Speaker 3: I would not be too surprised if we did find
• 31:33
  Speaker 3: life there. It would be really fun to have someone
• 31:35
  Speaker 3: on the show who studies extremophiles and see what their
• 31:38
  Speaker 3: take is on this stuff. But yeah, I guess I
• 31:40
  Speaker 3: wouldn't be surprised to find life on Mars like in
• 31:44
  Speaker 3: the caves, because it used to be a wet planet
• 31:46
  Speaker 3: and maybe bacteria might still be living under the surface
• 31:49
  Speaker 3: or something that looks like bacteria at Us or on
• 31:52
  Speaker 3: these subsurface oceans.
• 31:54
  Speaker 1: Yeah, I think the extremophiles are a really important lesson for.
• 31:57
  Speaker 2: Those of you who don't know.
• 31:57
  Speaker 1: These are examples of life that live in extreme can
• 32:01
  Speaker 1: And my wife is a microbiologist, and she basically tells
• 32:03
  Speaker 1: me it's impossible to ever make anything sterile because life
• 32:06
  Speaker 1: is everywhere and it always will be. And she tells
• 32:09
  Speaker 1: me these examples of like probes that we send up
• 32:12
  Speaker 1: into space, we try to make them sterile because we
• 32:14
  Speaker 1: don't want to like land on Mars and infect it
• 32:16
  Speaker 1: with Earth microbes and then later rediscover those microbes and
• 32:19
  Speaker 1: think we're finding Mars life. But every time we do,
• 32:21
  Speaker 1: we discover that there are some microbes that are gonna
• 32:23
  Speaker 1: be happy living in whatever conditions we put this probe in.
• 32:27
  Speaker 1: You know, they develop all these poison to kill microbes,
• 32:29
  Speaker 1: and then some microbe evolves to eat that poison and
• 32:31
  Speaker 1: it's like yum, thanks. And so it's basically impossible to
• 32:36
  Speaker 1: kill off life on Earth, which tells you that life
• 32:38
  Speaker 1: is pretty hardy and it might survive or even evolve
• 32:41
  Speaker 1: in crazy conditions. The other thing that's really going to
• 32:44
  Speaker 1: change your experience on the planet is not just are
• 32:47
  Speaker 1: you inhabitable zone, but what kind of star do you have?
• 32:50
  Speaker 1: Like do you have a star that's very stable, it's
• 32:53
  Speaker 1: always pumping out the same amount of energy all the time,
• 32:56
  Speaker 1: so that the habitable zone is constant, you're always in it.
• 32:59
  Speaker 1: Or you could also have a that's pretty variable. Some
• 33:01
  Speaker 1: stars out there get much brighter and then much dimmer,
• 33:03
  Speaker 1: and then much brighter and than much dimmer again. What
• 33:06
  Speaker 1: would it be like for life to evolve under those conditions?
• 33:10
  Speaker 1: You know, like Acephid, the famous variable stars that get
• 33:13
  Speaker 1: brighter and dimmer and very regular cycles. We use those
• 33:17
  Speaker 1: to learn about the distance ladder in the universe, how
• 33:19
  Speaker 1: far away things are.
• 33:21
  Speaker 3: I could imagine that spurring competition for plants at least,
• 33:25
  Speaker 3: you know, the trees that get the tallest are the
• 33:27
  Speaker 3: ones that are going to get the sunlight during those
• 33:28
  Speaker 3: dim light periods. I don't necessarily see that that would
• 33:32
  Speaker 3: have to kill life on the planet so much as
• 33:35
  Speaker 3: spur competition so that you're the one who succeeds during
• 33:38
  Speaker 3: the less good periods.
• 33:39
  Speaker 2: Yeah, exactly.
• 33:40
  Speaker 1: It might just create different conditions, and it might just
• 33:44
  Speaker 1: create a different kind of life. It's fascinating to think about.
• 33:47
  Speaker 1: The other component here is how many stars there are
• 33:51
  Speaker 1: in your solar system. We used to think of the
• 33:53
  Speaker 1: galaxies just a bunch of individual stars, and maybe under
• 33:57
  Speaker 1: exotic conditions you would have two stars and a system,
• 34:00
  Speaker 1: a fun topic for science fiction novels. But recently we've
• 34:03
  Speaker 1: learned that actually it's not uncommon to have two stars
• 34:06
  Speaker 1: in a system. That binary stars are very common, and
• 34:10
  Speaker 1: this is because of how stars form. Stars don't form
• 34:13
  Speaker 1: from like one gas cloud that collapses into a star.
• 34:16
  Speaker 1: Typically you have a huge star forming region that simultaneous
• 34:20
  Speaker 1: seeks is collapsing into a bunch of stars. So you
• 34:23
  Speaker 1: have like baby star neighbors and they're not isolated gravitationally,
• 34:27
  Speaker 1: they come together and they form a binary or even
• 34:29
  Speaker 1: a trinary system. And so something like fifty percent of
• 34:33
  Speaker 1: stars out there have a partner.
• 34:35
  Speaker 3: Oh wow, that probably would have been very surprising to Drake.
• 34:38
  Speaker 3: So the Drake's equation came out before we even landed
• 34:40
  Speaker 3: on the Moon. Yeah, and to think about how mind
• 34:43
  Speaker 3: blowing it would be to be able to get an
• 34:45
  Speaker 3: update on all of this stuff that we know. Okay,
• 34:46
  Speaker 3: so this is common. Why would it be harder to
• 34:50
  Speaker 3: evolve in a neighborhood with two sons. It's just twice
• 34:53
  Speaker 3: as much to photosynthesize.
• 34:58
  Speaker 1: Yeah, it also makes for less regular cycles though, Right,
• 35:01
  Speaker 1: you don't have the kind of cycles we have here
• 35:03
  Speaker 1: on Earth with seasons and days that are so regular.
• 35:06
  Speaker 1: You have a more chaotic system, right, you could be
• 35:09
  Speaker 1: like swapped between the two stars, or the stars themselves
• 35:12
  Speaker 1: could be fairly chaotic. So you might just not have
• 35:14
  Speaker 1: as regular a system. I don't know that that means
• 35:17
  Speaker 1: that life can't evolve. It might just have to be
• 35:20
  Speaker 1: more hearty and more adaptable, or just different from the
• 35:23
  Speaker 1: kind of life that we have. Again, I think this
• 35:25
  Speaker 1: is evidence that like these rare Earth guys are not
• 35:28
  Speaker 1: really thinking that far out of the box of.
• 35:30
  Speaker 2: Like what life could be like.
• 35:32
  Speaker 1: They're really just asking how common are our specific conditions
• 35:36
  Speaker 1: in the galaxy, and that could be very unusual but
• 35:39
  Speaker 1: that doesn't mean that there are no aliens.
• 35:41
  Speaker 3: Yeah, I can imagine the dynamics you just discussed just
• 35:44
  Speaker 3: driving life underground, for example, where things like temperature extremes
• 35:48
  Speaker 3: would be less pronounced and things would just kind of
• 35:50
  Speaker 3: be more stable.
• 35:51
  Speaker 1: In general, it basically means there's no California over there, right,
• 35:55
  Speaker 1: no place with like constant good weather all year long.
• 35:59
  Speaker 3: Well that's good, because that's so boring to constant good
• 36:01
  Speaker 3: weather all year long.
• 36:03
  Speaker 1: No, I want to meet the alien Californians. They're gonna
• 36:05
  Speaker 1: be the nicest ones. They're gonna be the chillest, you know.
• 36:08
  Speaker 2: I don't want to meet the grumpy Aliens.
• 36:10
  Speaker 1: They'll have to dig out of the snow and like
• 36:12
  Speaker 1: survive the serious heat.
• 36:15
  Speaker 3: You know, in Virginia, we have seasons and I love it.
• 36:18
  Speaker 3: And you know, not everybody in the California cities, you know,
• 36:22
  Speaker 3: some of them are a little snooty there.
• 36:25
  Speaker 1: Really, Oh my gosh, we're new snooty because we know
• 36:28
  Speaker 1: we live in the best place in the universe and
• 36:30
  Speaker 1: we're not shy to say it.
• 36:32
  Speaker 3: I think Virginia is more beautiful.
• 36:34
  Speaker 1: I said it all right right in if you have
• 36:37
  Speaker 1: an opinion about that, and whether aliens are more likely
• 36:39
  Speaker 1: to sit down in California or Virginia when they come.
• 36:42
  Speaker 3: Virginia is so much better come to Virginia Aliens. All right,
• 36:46
  Speaker 3: let's take a break and then we'll get back on track. So, Daniel,
• 37:06
  Speaker 3: what was the next criteria that Brownlee and Ward wanted
• 37:10
  Speaker 3: us to think about?
• 37:11
  Speaker 1: They wanted us to think about not just where you
• 37:14
  Speaker 1: are around the star, but what other planets there are
• 37:17
  Speaker 1: and whether that's an important part of life evolving. They
• 37:21
  Speaker 1: argue that the reason life evolved on Earth is not
• 37:23
  Speaker 1: just because the Earth is an in habitable zone where
• 37:26
  Speaker 1: water can be liquid on the surface and therefore you
• 37:28
  Speaker 1: can have a California, which we all know is super important,
• 37:31
  Speaker 1: but that the other planets in our Solar system have
• 37:34
  Speaker 1: played a big role. For example, having a big cousin
• 37:37
  Speaker 1: like Jupiter out in the outer Solar System might be
• 37:41
  Speaker 1: shielding us from comets. So again, they're like, really trying
• 37:44
  Speaker 1: to create a situation where you don't get hit by
• 37:46
  Speaker 1: comments a lot. I know you're a big fan of
• 37:47
  Speaker 1: life evolving under multiple cometary impacts.
• 37:51
  Speaker 3: But life is hard, man. You gotta be able to survive.
• 37:55
  Speaker 1: Is that what you teach your kids you're like, hey, kids,
• 37:57
  Speaker 1: asteroids could hit any day.
• 37:59
  Speaker 2: Check the weather.
• 38:00
  Speaker 3: As you know from our prior interactions, I try to
• 38:02
  Speaker 3: not make my kids lives filled with existential dread, but
• 38:05
  Speaker 3: I do try to prepare them for difficult situations.
• 38:08
  Speaker 2: That's a difficult line to walk there, Kelly, I'm not
• 38:10
  Speaker 2: sure you're doing it.
• 38:13
  Speaker 3: Thanks for critiquing my.
• 38:16
  Speaker 1: Yeah, exactly, I'm gonna have to talk to your kids
• 38:17
  Speaker 1: and let them know that you're actually pro asteroid impact.
• 38:21
  Speaker 3: I'm not going to let you talk to my kids,
• 38:25
  Speaker 3: all right.
• 38:25
  Speaker 1: Fair enough, I wouldn't either anyway. The idea is that
• 38:28
  Speaker 1: Jupiter's out there, and when comments do fall towards the
• 38:31
  Speaker 1: Inner Solar System, maybe it's acting like a celestial vacuum cleaner.
• 38:35
  Speaker 1: It's like blocking for us, you know. It's making sure
• 38:38
  Speaker 1: that these things are not hitting the Earth. It's making
• 38:41
  Speaker 1: the Inner Solar System like a little walled garden where
• 38:44
  Speaker 1: life is free to evolve while it's still vulnerable.
• 38:47
  Speaker 3: All right, Well, so we've already talked about how I
• 38:50
  Speaker 3: don't necessarily think asteroids are a showstopper, But how common
• 38:54
  Speaker 3: is it for other systems to have a Jupiter to
• 38:58
  Speaker 3: act as the celestial vacus and cleaner.
• 39:01
  Speaker 1: So we actually really don't know the answer to that question,
• 39:03
  Speaker 1: and it's one where the answer has been changing a
• 39:06
  Speaker 1: lot in the last few years. When we first developed
• 39:08
  Speaker 1: the ability to see planets around other stars, it was
• 39:11
  Speaker 1: a huge moment, right because we'd only ever seen planets
• 39:14
  Speaker 1: around our stars, so we didn't know how common is
• 39:17
  Speaker 1: it to have planets at all, and it is our
• 39:19
  Speaker 1: arrangement common or totally unusual. But the first planets we
• 39:23
  Speaker 1: could see were planets that were really big, and planets
• 39:26
  Speaker 1: that were really close to their star, And that's because
• 39:29
  Speaker 1: we were seeing the effects of those planets tugging on
• 39:31
  Speaker 1: their stars, like the gravity of the planet wiggling the
• 39:34
  Speaker 1: star a little bit. And later on we were seeing
• 39:36
  Speaker 1: planets pass in front of their stars, making like little
• 39:39
  Speaker 1: mini planet eclipses. Both of those are really good for
• 39:43
  Speaker 1: seeing planets that are big and close to their star,
• 39:46
  Speaker 1: and really bad at seeing anything else. So of course,
• 39:49
  Speaker 1: first planets we discover are hot jupiters, big planets close
• 39:53
  Speaker 1: to their star. So then everybody thought, oh my gosh, wow,
• 39:55
  Speaker 1: maybe the universe was filled with hot jupiters, And then
• 39:58
  Speaker 1: folks really well or maybe that's all we can and see,
• 40:00
  Speaker 1: and there's a bunch of invisible planets out there that
• 40:02
  Speaker 1: we don't know about. But it made people think really
• 40:05
  Speaker 1: carefully about the history of our own Solar system, because
• 40:07
  Speaker 1: they're like, well, if hot jupiters are really common, why
• 40:10
  Speaker 1: don't we have one. Why is our Jupiter so cold?
• 40:13
  Speaker 1: It's so far out in the Solar System. And that
• 40:16
  Speaker 1: inspired a lot of really interesting theory about like the
• 40:19
  Speaker 1: origins of the arrangements of our planets. And one fascinating
• 40:24
  Speaker 1: theory is that the typical thing is for a gas
• 40:26
  Speaker 1: giant to form in the outer Solar System, it has
• 40:29
  Speaker 1: to be far out there so it can grab enough
• 40:31
  Speaker 1: gas because the Sun tends to grab all the gas
• 40:33
  Speaker 1: in the inner Solar System. But then they typically fall
• 40:36
  Speaker 1: into the inner Solar System because of chaos and dynamical
• 40:39
  Speaker 1: friction and whatever. They migrate inwards. And so that's what
• 40:43
  Speaker 1: we're seeing out there in other Solar systems, jupiters that
• 40:46
  Speaker 1: form far out and then work their way in and
• 40:50
  Speaker 1: eventually those planets are going to plummet into their stars.
• 40:53
  Speaker 1: They're not really stable. But that's not what we have here.
• 40:56
  Speaker 1: And so the theory is that our Jupiter formed and
• 40:59
  Speaker 1: our Saturn formed and some now lost other gas giant
• 41:03
  Speaker 1: in our Solar system formed and they migrated in as
• 41:06
  Speaker 1: you typically expect. But then some chaotic interaction happened and
• 41:10
  Speaker 1: Jupiter and Saturn got kicked to the outer Solar System
• 41:13
  Speaker 1: and the now lost gas giant ejected from the Solar System.
• 41:17
  Speaker 1: So we have a missing planet that got like rejected
• 41:20
  Speaker 1: from the Solar System is now out there floating alone
• 41:23
  Speaker 1: in space.
• 41:24
  Speaker 3: Wow. Would we expect to be able to find it?
• 41:26
  Speaker 3: Or could it have gotten pretty far away?
• 41:28
  Speaker 2: It could have gotten pretty far away.
• 41:30
  Speaker 1: And these days we know that there are lots and
• 41:32
  Speaker 1: lots of these planets, they're called rogue planets that have
• 41:34
  Speaker 1: been ejected from their Solar system. So like our pretty
• 41:37
  Speaker 1: picture of planets having nice circular orbits around their stars,
• 41:41
  Speaker 1: it's kind of an ancient idea, and now we know
• 41:43
  Speaker 1: that like Solar system dynamics are pretty chaotic. It's not
• 41:46
  Speaker 1: that unusual to lose a planet. In fact, it's kind
• 41:48
  Speaker 1: of amazing if you don't, if you can onto a
• 41:51
  Speaker 1: planet for billions of years. And so anyway, that's how
• 41:54
  Speaker 1: we ended up with this Jupiter in the outer Solar System,
• 41:57
  Speaker 1: sort of protecting us that might be unusual. It could
• 41:59
  Speaker 1: be that typically the big giants just end up falling
• 42:02
  Speaker 1: into their stars, and that's what we're seeing out there
• 42:05
  Speaker 1: in other solar systems. But this is a question where
• 42:07
  Speaker 1: we're learning new stuff every day because we've only seen
• 42:10
  Speaker 1: a few thousand exoplanets and we're rapidly seeing more and
• 42:13
  Speaker 1: more and more, and so the picture is changing constantly,
• 42:16
  Speaker 1: which is my favorite thing in science when we're like
• 42:19
  Speaker 1: our eyeballs are opening up and we're learning more and
• 42:21
  Speaker 1: more about the universe.
• 42:22
  Speaker 3: Yeah, no, it's exciting. Also, I think someone should start
• 42:25
  Speaker 3: a band hot Jupiter and the Road planets.
• 42:28
  Speaker 1: And there are also people who make the opposite argument.
• 42:30
  Speaker 1: They say that actually having a Jupiter in your solar
• 42:33
  Speaker 1: system is not good for reducing impacts, that actually having
• 42:37
  Speaker 1: a Jupiter could cause impacts because it makes these gravitational
• 42:40
  Speaker 1: instabilities like tugs on stuff, and it might actually pull
• 42:44
  Speaker 1: stuff towards the Earth. There was a case in our
• 42:47
  Speaker 1: solar system in seventeen seventy there's a near miss when
• 42:50
  Speaker 1: a comet came really close to the Earth. It was
• 42:52
  Speaker 1: called Lexel's comet, and you can reconstruct its path and
• 42:56
  Speaker 1: they're pretty sure that it was Jupiter's fault that it
• 42:59
  Speaker 1: was not going to anywhere near the Earth, and then
• 43:01
  Speaker 1: Jupiter tugged on it and basically aimed it right at
• 43:04
  Speaker 1: the Earth. It was a really close call. And so
• 43:07
  Speaker 1: there's examples there were like, yeah, Jupiter can save you,
• 43:10
  Speaker 1: but Jupiter could also, you know, send something bad your way.
• 43:14
  Speaker 3: So how would you figure out if, on balance it
• 43:16
  Speaker 3: was better to have a Jupiter. I guess it would
• 43:19
  Speaker 3: depend on so many different factors. Then, with what we know,
• 43:23
  Speaker 3: you couldn't come down in this argument one way or another. Probably.
• 43:25
  Speaker 1: Yeah, it's a really chaotic thing, right If you start
• 43:28
  Speaker 1: with the solar system, you don't really know whether having
• 43:30
  Speaker 1: a Jupiter would be better or worse. You can't sit
• 43:32
  Speaker 1: down and calculate it. All you can do is run
• 43:34
  Speaker 1: a bunch of simulations, and those simulations depend on the
• 43:37
  Speaker 1: initial conditions, like what is the distribution of gas, and
• 43:40
  Speaker 1: where are the metals and where the rock and the ice.
• 43:42
  Speaker 1: Very sensitive to all those details, and we don't know
• 43:45
  Speaker 1: how most solar systems start, and so people run a
• 43:47
  Speaker 1: lot of simulations, but everybody starts from different places and
• 43:50
  Speaker 1: gets different answers, and so it's a big mystery.
• 43:53
  Speaker 2: Right now.
• 43:53
  Speaker 1: We just really don't know the answer to this question.
• 43:56
  Speaker 1: So in the rare Earth hypothesis, they suggest our Jupiter
• 43:59
  Speaker 1: is rare and it was really important, But we actually
• 44:02
  Speaker 1: don't know how rare it is, and we don't know
• 44:04
  Speaker 1: it's important or not. So it's really much more of
• 44:07
  Speaker 1: an open question.
• 44:08
  Speaker 3: All right, So what's the next level that we need
• 44:10
  Speaker 3: to be considering.
• 44:12
  Speaker 1: The next thing is about the size of our planet,
• 44:14
  Speaker 1: Like rocky planets have to be the right size, they argue,
• 44:18
  Speaker 1: in order to have life on them. And you know,
• 44:20
  Speaker 1: we have some examples of that, like if you look
• 44:22
  Speaker 1: at Mars, it's basically an the habitable zone, but it's
• 44:25
  Speaker 1: kind of small. It's lots smaller than Earth, and it's
• 44:28
  Speaker 1: so small that it doesn't have much of an atmosphere.
• 44:30
  Speaker 1: It's like one percent of the atmosphere of Earth because
• 44:33
  Speaker 1: it doesn't have the gravity to hold onto it the
• 44:35
  Speaker 1: way the Moon doesn't, for example. So you can't have
• 44:38
  Speaker 1: Earth like life evolving on Mars the way it is now.
• 44:42
  Speaker 1: And if you have too much stuff, you're over dense.
• 44:45
  Speaker 1: Then you can have a really dense atmosphere the way
• 44:47
  Speaker 1: like Venus does. You know, their atmosphere is like something
• 44:50
  Speaker 1: you couldn't even breathe. It's like soup, right, It's also
• 44:52
  Speaker 1: like sulphuric acid. But it's very different from the conditions
• 44:56
  Speaker 1: on Earth. And so they argue that like having a
• 44:58
  Speaker 1: rocky planet with just right mass, to have an atmosphere
• 45:02
  Speaker 1: like ours so we can all enjoy breezy sunny days
• 45:05
  Speaker 1: in California is pretty unusual.
• 45:07
  Speaker 6: You know.
• 45:08
  Speaker 3: The breezy sunny days in Virginia are nice. Also, there's
• 45:11
  Speaker 3: maybe a little more humidity. But the deal with needing
• 45:13
  Speaker 3: an atmosphere is that what it protects you from radiation,
• 45:16
  Speaker 3: it moderates temperature swings. Are those the main reasons why
• 45:21
  Speaker 3: you need an atmosphere.
• 45:22
  Speaker 1: You need an atmosphere absolutely for those reasons. And if
• 45:25
  Speaker 1: you think oxygen is important for all the biochemistry of Earth,
• 45:28
  Speaker 1: then you need to be able to hang on to
• 45:30
  Speaker 1: the oxygen when it's produced. You know, oxygen is not
• 45:33
  Speaker 1: something that we had in our atmosphere early on. It
• 45:35
  Speaker 1: took a long long time for oxygen to be produced
• 45:38
  Speaker 1: by early life, so that more complex life that used
• 45:42
  Speaker 1: oxygen it could be very efficient, could evolve.
• 45:44
  Speaker 2: I'm sure you know more about that than I do.
• 45:47
  Speaker 2: And you have to be able.
• 45:47
  Speaker 1: To hold onto that oxygen, right, if it I'll just
• 45:49
  Speaker 1: drift it out into space. Then you wouldn't be able
• 45:52
  Speaker 1: to use it for more complex life.
• 45:54
  Speaker 3: So right now we probably don't know, like even for
• 45:58
  Speaker 3: Earth like life to evolve, does fifty to one hundred
• 46:01
  Speaker 3: and fifty percent of Earth's atmosphere work? Like, could life
• 46:06
  Speaker 3: still have evolved if we had, you know, fifty percent
• 46:08
  Speaker 3: the atmosphere we have? Now we don't know that.
• 46:11
  Speaker 2: I assume we don't know anything about that.
• 46:14
  Speaker 1: Yeah, Like we still have really no idea about how
• 46:16
  Speaker 1: life started on Earth or what the crucial points were,
• 46:19
  Speaker 1: how many times it started on Earth.
• 46:21
  Speaker 2: As we talked about earlier.
• 46:23
  Speaker 1: This is the place where we're really in the dark.
• 46:25
  Speaker 1: And so I don't want to be too negative about it,
• 46:27
  Speaker 1: because I think it is useful just try to think
• 46:29
  Speaker 1: about these things and to take first attempts and then
• 46:32
  Speaker 1: the next generation of scientists coming along being like, okay,
• 46:34
  Speaker 1: reasonable first step, but actually, and you know that's the
• 46:37
  Speaker 1: way progress is made. It's incremental. But I also really
• 46:40
  Speaker 1: think we really haven't gotten anywhere this question, because as
• 46:44
  Speaker 1: you say, twice as much atmosphere might be fine, or
• 46:47
  Speaker 1: maybe it's even better if you have a denser atmosphere.
• 46:50
  Speaker 1: Just because no life evolved on Venus as far as
• 46:52
  Speaker 1: we know, doesn't mean that life can't evolve on Venus.
• 46:55
  Speaker 1: Like planets, it might be a little different. It might
• 46:58
  Speaker 1: enjoy the humidity, and it might like to lie and in Virginia.
• 47:01
  Speaker 1: But you know, that's okay, I'm open minded.
• 47:04
  Speaker 3: I mean, it would be so awesome if we could
• 47:06
  Speaker 3: just find microbial life somewhere else in the Solar System
• 47:10
  Speaker 3: to give us like a handle on this kind of stuff.
• 47:12
  Speaker 3: But all right, so say that you are on a
• 47:14
  Speaker 3: planet that's the right size and has the right atmosphere,
• 47:19
  Speaker 3: are there other criteria?
• 47:20
  Speaker 2: They argue in.
• 47:21
  Speaker 1: The book that there's an internal criteria that having a
• 47:24
  Speaker 1: planet with internal dynamics like lava or magma flow under
• 47:29
  Speaker 1: the mantle, having plate tectonics and volcanic activity is crucial
• 47:34
  Speaker 1: for creating the conditions for life to evolve on Earth.
• 47:37
  Speaker 1: And I think the argument is that like plate tectonics
• 47:41
  Speaker 1: lead to like continental drift, and so you take populations
• 47:44
  Speaker 1: and like separate them and then you can protect them.
• 47:47
  Speaker 1: You get more diversity rather than like if you have
• 47:49
  Speaker 1: a static planet. And it's just like when one big
• 47:51
  Speaker 1: British competition for life, you might have like one winner
• 47:55
  Speaker 1: instead of like a bunch of different populations and different
• 47:57
  Speaker 1: ecosystems with multiple winners. That's the argument. I don't know
• 48:01
  Speaker 1: how effective that argument is. It's more just like a, hey,
• 48:04
  Speaker 1: this seem to have played an important role in the
• 48:07
  Speaker 1: way that life evolved on Earth. Maybe it's also important everywhere.
• 48:11
  Speaker 1: What do you think about that as a biologist.
• 48:13
  Speaker 3: I mean, certainly plate tectonics has had interesting implications for
• 48:17
  Speaker 3: biodiversity on Earth, and so you know, you have gotten
• 48:21
  Speaker 3: species that look very similar on different continents that do
• 48:24
  Speaker 3: have you know, shared evolutionary history, and now they look
• 48:28
  Speaker 3: and act very different, and so that diversity is interesting.
• 48:31
  Speaker 3: But you know, we didn't, for example, see one winner
• 48:34
  Speaker 3: on each of the different continents. You see lots of
• 48:37
  Speaker 3: different solutions to problems. And I would imagine tectonics would
• 48:41
  Speaker 3: be helpful for increasing biodiversity, but not necessarily needed, especially
• 48:45
  Speaker 3: if you have other things in the environment that are
• 48:48
  Speaker 3: problems that need to be solved that drive adaptations.
• 48:51
  Speaker 1: Yeah, and people have tried to actually answer this question,
• 48:54
  Speaker 1: and there are some recent studies that show that plate
• 48:57
  Speaker 1: tectonics are sort of episodic that you have like times
• 49:00
  Speaker 1: when there's a lot of activity in times when it's stagnant,
• 49:03
  Speaker 1: and some of the crucial developments in the evolution of
• 49:05
  Speaker 1: life as we know it may come during those like
• 49:07
  Speaker 1: stagnant periods when things are more chill. So again, like
• 49:11
  Speaker 1: with everything on this topic, you could see it going
• 49:12
  Speaker 1: both ways. You could like convince yourself of a or
• 49:15
  Speaker 1: not about equally well.
• 49:19
  Speaker 3: But again I think that you noted. It gives us
• 49:21
  Speaker 3: interesting things that we should try to drill down and
• 49:23
  Speaker 3: understand better and sort of focuses where we might want
• 49:25
  Speaker 3: to do research in the future.
• 49:27
  Speaker 1: Yeah, and one thing we've learned is that volcanic activity
• 49:30
  Speaker 1: and internal motion in a planet might not be that
• 49:32
  Speaker 1: rare we thought for a long time. For example, Earth
• 49:34
  Speaker 1: was the only place in the Solar System that had
• 49:37
  Speaker 1: volcanoes and had internal tectonics. But now we know that
• 49:40
  Speaker 1: like volcanoes are everywhere in the Solar System, they're on
• 49:43
  Speaker 1: some of those moons that we talked about. We think
• 49:45
  Speaker 1: that Pluto had volcanoes for a while. The Moon used
• 49:49
  Speaker 1: to have internal activity before it cooled, and so did Mars,
• 49:52
  Speaker 1: and so it might not even be as rare as
• 49:55
  Speaker 1: people thought when this book was written. So maybe it
• 49:58
  Speaker 1: is crucial for life to form, but that doesn't that
• 50:00
  Speaker 1: life is rare, because it might be the plate tectonics
• 50:02
  Speaker 1: are everywhere.
• 50:03
  Speaker 3: Yeah, okay enough.
• 50:04
  Speaker 1: One of the last bits they talk about is having
• 50:06
  Speaker 1: a moon. You know, we have a big, fat moon
• 50:09
  Speaker 1: in the sky, which is kind of cool and beautiful,
• 50:12
  Speaker 1: even if you're in Virginia. But people speculate about the
• 50:15
  Speaker 1: role of the moon in the evolution of life on Earth.
• 50:18
  Speaker 1: Having a big moon does seem a little bit unusual,
• 50:21
  Speaker 1: like in our Solar system. There are not other planets
• 50:24
  Speaker 1: that have just one big moon. And having a big
• 50:27
  Speaker 1: moon like this makes for tidal effects. You know, the
• 50:30
  Speaker 1: moon pulls on the ocean and you get high tide
• 50:32
  Speaker 1: and low tide. It's really fascinating physics. And there's this
• 50:36
  Speaker 1: theory I've heard before that having these tides helps life
• 50:39
  Speaker 1: evolve because you get like the brackish conditions between the
• 50:42
  Speaker 1: salt water and the fresh water. You get all the
• 50:45
  Speaker 1: sloshing around which mixes up the amino acids, and imagining
• 50:49
  Speaker 1: some like bubbling cauldron of prebiotic soup, and you might
• 50:52
  Speaker 1: get life evolving more easily if you're stirring that cauldron
• 50:56
  Speaker 1: rather than just like letting it sit and be stagnant.
• 50:59
  Speaker 1: But again, you're sort of talking yourself into this argument.
• 51:01
  Speaker 1: What do you think about that?
• 51:02
  Speaker 3: Is there no other way that stirring would happen? Like,
• 51:05
  Speaker 3: wouldn't you still get rivers going into the sea and
• 51:08
  Speaker 3: do Coriolis effects influence the way water sort of moves
• 51:12
  Speaker 3: around the Earth. It wouldn't be as extreme or as
• 51:15
  Speaker 3: fun to surf on, But I think you could still
• 51:18
  Speaker 3: get it to happen.
• 51:20
  Speaker 2: How's the surfing in Virginia?
• 51:21
  Speaker 3: By the way, I am not cool enough to answer
• 51:23
  Speaker 3: that question. Well, we have beaches and they're beautiful.
• 51:26
  Speaker 2: Okay, I believe you. I believe you. I don't know
• 51:29
  Speaker 2: the answer that question.
• 51:29
  Speaker 1: I don't know that anybody knows the answer that question
• 51:32
  Speaker 1: until we make the discovery you talked about, which is like, fine,
• 51:34
  Speaker 1: microbe somewhere else and learn about the history there. But
• 51:38
  Speaker 1: you know, it's easy to point to these things which
• 51:40
  Speaker 1: affected life on Earth and say, oh, this must have
• 51:42
  Speaker 1: been crucial and without it life couldn't have evolved or
• 51:45
  Speaker 1: would be so dramatically different. We wouldn't even recognize it.
• 51:48
  Speaker 2: You know.
• 51:49
  Speaker 1: Another example is like the Earth's axial tilt. You know,
• 51:51
  Speaker 1: we have enough axial tilt to give us variation, which
• 51:55
  Speaker 1: leads to beautiful falls in Virginia, I'm sure, But it's.
• 51:58
  Speaker 3: Boring in California. Yes, And you don't get snow for Christmas,
• 52:04
  Speaker 3: which makes it feel like not Christmas, which I know
• 52:06
  Speaker 3: because I lived in California for a while.
• 52:08
  Speaker 1: Hey, it snows in California and you can drive to
• 52:10
  Speaker 1: the snow. It's optional. That's the best thing about the snow.
• 52:13
  Speaker 1: You know, like stuck with it?
• 52:15
  Speaker 3: All right, that's fair. I grew up in Ohio and
• 52:17
  Speaker 3: I did feel stuck with it sometimes.
• 52:19
  Speaker 2: Yeah, exactly.
• 52:20
  Speaker 1: And if you didn't have any axial tilt, that wouldn't
• 52:22
  Speaker 1: give you any seasonal variations. And there's some suggestion that
• 52:26
  Speaker 1: like having some variation is good for creating diversity and
• 52:29
  Speaker 1: competition and all this kind of stuff. And again, these
• 52:32
  Speaker 1: arguments are not from evidence. There's no like experiments or
• 52:34
  Speaker 1: calculations that say this tilt is perfect. It's really just
• 52:38
  Speaker 1: like retrospective is saying we had it, this seems important
• 52:42
  Speaker 1: and therefore it must have been crucial. But I don't
• 52:44
  Speaker 1: think the argument really holds up.
• 52:46
  Speaker 3: I mean, so many of these arguments seem to be
• 52:48
  Speaker 3: things that like maybe turned the diversity nub up or
• 52:51
  Speaker 3: down and maybe speed up or slow down the process.
• 52:55
  Speaker 3: But human intelligence only popped up once. Yeah, and so
• 52:58
  Speaker 3: I don't like, do you need seven million species before
• 53:02
  Speaker 3: you get intelligence or like, I'm not entirely sure how
• 53:05
  Speaker 3: this relates to intelligent life that you could communicate with.
• 53:09
  Speaker 3: I think it just creates diversity, but maybe it just
• 53:11
  Speaker 3: creates a lot more beetles wasps, which is awesome. I
• 53:15
  Speaker 3: want to be in the world with the most beetles species.
• 53:18
  Speaker 3: But I don't necessarily know that all of these things
• 53:20
  Speaker 3: are necessary for creating intelligent life. I don't think we
• 53:23
  Speaker 3: really understand why we ended up the way we are.
• 53:26
  Speaker 1: So if we find an alien planet and is covered
• 53:28
  Speaker 1: in wasps and beetles, we can drop you on that planet.
• 53:31
  Speaker 3: Yes, if I can convince my kids.
• 53:36
  Speaker 1: And you want credibility for your opinions about life in Virginia, huh,
• 53:39
  Speaker 1: I think you just blew up your credibility there.
• 53:41
  Speaker 3: Virginia's motto is Virginia is for lovers. And when we
• 53:45
  Speaker 3: first moved here, we were amazed by how many different
• 53:48
  Speaker 3: kinds of spiders there were. And I know I'm not
• 53:50
  Speaker 3: selling Virginia very well, but we kept joking about getting
• 53:52
  Speaker 3: shirts of Virginia is for spiders. But anyway, there's lots
• 53:56
  Speaker 3: of cool diversity here is my point.
• 53:58
  Speaker 1: Yeah, so you know in the and a lot of
• 54:00
  Speaker 1: these arguments again are like, here's how life evolved on Earth.
• 54:04
  Speaker 1: This seemed to be an important factor, but we don't know, right.
• 54:07
  Speaker 1: The takeaway message here is that we just don't know.
• 54:10
  Speaker 1: And by focusing on the particular outcome of life on Earth,
• 54:14
  Speaker 1: it makes the argument pretty weak. And you could equivalently
• 54:17
  Speaker 1: argue like, hey, what are the chances that Daniel is
• 54:20
  Speaker 1: here and is on this podcast?
• 54:22
  Speaker 2: You know?
• 54:23
  Speaker 1: And you could even say, given that my parents existed
• 54:25
  Speaker 1: and that they meet and all these things, what are
• 54:27
  Speaker 1: the chances Well, of course the chances are tiny, right,
• 54:30
  Speaker 1: But what are the chances of my parents have some
• 54:33
  Speaker 1: kid that maybe then grows up to be a physicist
• 54:35
  Speaker 1: and starts some kind of podcast like not that small?
• 54:38
  Speaker 1: And that's really the question we're asking, right, is we
• 54:41
  Speaker 1: know this is a huge variation of conditions out there
• 54:44
  Speaker 1: in the universe, but what does that mean about how
• 54:46
  Speaker 1: common life is? If we only ask where are there
• 54:50
  Speaker 1: humans that look like us? Then of course the answer
• 54:52
  Speaker 1: is going to be nowhere.
• 54:53
  Speaker 2: Or almost nowhere.
• 54:55
  Speaker 1: But that's not the question we want to answer, right,
• 54:57
  Speaker 1: We just want to know if there's anybody else out
• 54:58
  Speaker 1: there thinking about.
• 54:59
  Speaker 3: The uni right, and if they care how we smell.
• 55:04
  Speaker 1: Exactly, and if they like nice weather or not, you know,
• 55:08
  Speaker 1: and what they mean by nice weather anyway.
• 55:10
  Speaker 2: That's right. But fortunately we are going to learn.
• 55:13
  Speaker 1: A lot about this in the coming years. It's fairly
• 55:15
  Speaker 1: recently that we've even seen planets around other stars. That
• 55:18
  Speaker 1: whole science is now like only twenty five years old,
• 55:22
  Speaker 1: and it's growing exponentially.
• 55:23
  Speaker 2: You know.
• 55:23
  Speaker 1: The number of planets that humans knew about went from
• 55:27
  Speaker 1: like six for like thousands of years to like seven, eight, nine,
• 55:32
  Speaker 1: and then back to eight, and now it's exploding. Now
• 55:34
  Speaker 1: we're like we've seen five thousand planets around other stars.
• 55:38
  Speaker 2: It's an incredible time to be a human.
• 55:41
  Speaker 1: It's like pre this moment and post this moment, and
• 55:44
  Speaker 1: it really turns the page scientifically in terms of our
• 55:47
  Speaker 1: knowledge of the universe. But we're still in that like
• 55:50
  Speaker 1: exponential growth. We're building all sorts of crazy new space telescopes,
• 55:55
  Speaker 1: Like there's the haveb X telescope, which is designed exactly
• 55:58
  Speaker 1: just to do this. It's to float in space and
• 56:01
  Speaker 1: look at other stars, and it's got this amazing sunshade
• 56:04
  Speaker 1: that's going to block out the light from the stars
• 56:06
  Speaker 1: so we can just see the planet. It's going to
• 56:09
  Speaker 1: be incredible to discover planets. So we're gonna look back
• 56:12
  Speaker 1: at the time when we only saw five thousand planets
• 56:15
  Speaker 1: as like the early days of this kind of science,
• 56:17
  Speaker 1: And in ten years we're going to know so much
• 56:19
  Speaker 1: more about the kind of planets that are out there.
• 56:22
  Speaker 1: We're going to be measuring what's in the atmosphere of
• 56:24
  Speaker 1: those planets. We might detect oxygen, we might see biosignatures,
• 56:27
  Speaker 1: we could see techno signatures. So it's an exciting moment
• 56:31
  Speaker 1: because we don't know the answers to these crucial questions,
• 56:33
  Speaker 1: but we might be about to find.
• 56:35
  Speaker 3: Out, I hope. So I can imagine HabEx giving us
• 56:39
  Speaker 3: a lot of data to tinker with Drake's equation. I'm
• 56:42
  Speaker 3: already super excited, but I will be really super duper
• 56:45
  Speaker 3: excited when we find a second example of any life,
• 56:48
  Speaker 3: intelligent or not, somewhere else. I feel like that will
• 56:52
  Speaker 3: give us a lot of information that we really need
• 56:54
  Speaker 3: to try to nail this stuff down absolutely.
• 56:56
  Speaker 1: Even just two examples, you get to draw second marble
• 56:59
  Speaker 1: from the huge bag. If it's also an orange marble,
• 57:02
  Speaker 1: you're like, wow, Okay, maybe they really are just orange marbles,
• 57:04
  Speaker 1: but it's something weird and crazy, which is my personal preference.
• 57:08
  Speaker 1: And then we're going to learn so much about life
• 57:09
  Speaker 1: in the universe. And the frustrating thing to me and
• 57:12
  Speaker 1: the exciting thing is that the answers.
• 57:13
  Speaker 2: Are out there. There's either life.
• 57:15
  Speaker 1: Out there right now sliming around and enjoying its various weather,
• 57:20
  Speaker 1: or there's not. You know, the facts are out there.
• 57:22
  Speaker 1: We just need to like gather them. We just need
• 57:24
  Speaker 1: to like scoop up the information. We need to be
• 57:26
  Speaker 1: smart enough and devote enough energy and frankly money to
• 57:30
  Speaker 1: just like purchasing this information from the universe.
• 57:33
  Speaker 2: Yep.
• 57:34
  Speaker 3: My bet is that the alien life is hiking in
• 57:36
  Speaker 3: the equivalent of Shannandoah National Park because there's nowhere more
• 57:39
  Speaker 3: beautiful on this planet. But I guess we're just going
• 57:42
  Speaker 3: to have to wait and see.
• 57:43
  Speaker 1: Yeah, well, I guess we'll find out. Is the universe
• 57:45
  Speaker 1: for lovers or is the universe for spiders?
• 57:48
  Speaker 4: Oh?
• 57:48
  Speaker 3: I hope it's for lovers. I really hope there's a
• 57:52
  Speaker 3: whole book about turns out life somewhere else as spiders
• 57:54
  Speaker 3: and how we interact with them, But I can't remember
• 57:56
  Speaker 3: the name of it now. Matt Inman, though, was the
• 57:58
  Speaker 3: one who suggested that I read it.
• 58:00
  Speaker 1: There's a great science fiction novel by Adrian Tchaikowsky called
• 58:02
  Speaker 1: Children of Time where spiders become intelligent and.
• 58:06
  Speaker 2: It's really fascinating.
• 58:07
  Speaker 3: That's it.
• 58:08
  Speaker 1: Thanks, it's a great book, totally recommended. Well, anyway, thanks
• 58:12
  Speaker 1: everyone for joining us on this tour of one of
• 58:15
  Speaker 1: the most important, most ancient, and least answered questions in
• 58:19
  Speaker 1: all of science, whether we are alone in the universe,
• 58:22
  Speaker 1: what we can know, what we do know, and what
• 58:24
  Speaker 1: we might know soon in the future.
• 58:26
  Speaker 3: I thought it was going to be as California or
• 58:28
  Speaker 3: Virginia better, but no, probably you're right, that's probably a bigger.
• 58:30
  Speaker 1: Question, and that's a question we actually already know the
• 58:33
  Speaker 1: answer to. All right, bye, everyone, have a great time,
• 58:37
  Speaker 1: even those of you.
• 58:37
  Speaker 2: Who live in Virginia.
• 58:38
  Speaker 3: Thanks everyone. Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio.
• 58:50
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• 58:53
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• 58:55
  Speaker 1: Extraordinary Universe.
• 58:57
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• 59:00
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• 59:03
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• 59:04
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• 59:07
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• 59:10
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• 59:12
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• 59:20
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