Exoplanets and the search for life in the universe – with Chris Impey

(gentle music) (audience applauds) – Thanks Peter. I’m delighted to be here. I first lectured here I think six or seven years ago about the future of space and then did black holes during COVID, that was an online. And today I’m gonna talk about, I think one of the most exciting subjects, I’ll be a little presumptuous, not just in astronomy, but in all of science, which is the search for exoplanets. And I’m gonna frame it more broadly as the search for life in the universe and give you a sort of status report on that. So I work at the University of Arizona, and right away the whole search for life in the universe, if successful, is essentially continuing the Copernican revolution. So the history of astronomy since Copernicus is to displace us in centrality in the universe. We’re not special, we’re not special in the solar system, our galaxy is not special in a universe with hundreds of billions of galaxies. And so it would be consistent with this evolution of the Copernican principle if life were not unique to this planet. And so it’s a compelling question to answer in science. Since I’m a cosmologist, I also put in there the fact that there might be parallel universes, the multiverse, that’s another talk. But astrobiology is really an exciting subject, but it has no subject matter, this is the only place in the universe we know with life, this planet. So why are astronomers fairly confident that we’re gonna detect it elsewhere, soon, not just within all of our lifetimes, perhaps within the next few years? It’s a series of indirect arguments. The fact that the ingredients for life are widely available. Carbon is made by stars everywhere in the universe. Water is one of the most abundant molecules in the universe. Not that special. Life formed very early in the history of the Earth when the Earth was a very inhospitable place, with volcanism on the surface, barely solidified from magma, oceans barely condensed from steam, impact rates hundreds of times the present day, and yet biology started then 4 billion years ago. That doesn’t prove anything. Also, life exists in some very inhospitable environments on the Earth, deep under the oceans, inside rock and so on. And then we also know that there are a lot of places where life could exist if we make some minimal principle that life’s needs carbon, water, and energy. If we only assume that then, we’ve now found many, many places, and I’ll put a number on that tonight. But it’s a young subject. So remember, not just have we not found life anywhere else yet, but there’s a lot we still don’t know about the world we live on. Most of the biosphere is unexplored. This is a microbial planet, the Earth, most species are microbes, not plants and animals. And only 1% of all microbes have ever been cultured in a lab ’cause it’s quite hard to do. So we don’t really understand the microbial world we live on. We’ve maybe been to a few places in the solar system, but it’s expensive, difficult, and time consuming, so we haven’t explored the solar system fully, and we certainly haven’t characterized the large number of exoplanets that we’re gonna talk about, they’re mostly just known by their mass or their size, and that’s it. And then I’ll also talk briefly about a subject that goes beyond the idea of microbes and looks for intelligent technological civilizations. It’s called SETI. And SETI is also a young subject that has not yet explored most of the range of parameters it could. So it’s a young subject, Buckminster Fuller, visionary architect and inventor framed it as a dichotomy, either we’re alone in the universe or we’re not. And I think he’s right, either way, the implications are staggering. If you see the number of habitable spots in the universe and this is the only one that actually has biology, that would be extraordinary. If there’s biology elsewhere, that’s extraordinary too, and we have to find it and understand it. So let’s start on Earth. Well, we’ll talk about life on Earth a little bit because it frames the whole subject of astrobiology since it’s the only biology we know. And we start by defining life, which even biologists don’t agree on. So me, a mere physicist wouldn’t dare to define life. But we all know life, life is something where the behavior is complex and interesting and something’s clearly going on. (gentle music) So if NASA had a little camera on a rover and saw that, you’d say, wow, that’s amazing. Well it’s flour, it’s water and a bass drum and a plate. So you know, interesting things happen, and they’re not all biology. Here’s the world we live on and this is unfamiliar, all these Latin names are microbial life. And this is the real estate, this is the genetic real estate of life on Earth. And the origin at the root there is 4 billion years ago. And these branches of the tree of life are essentially microbes, they’re bacteria, they’re either with nuclei or without. And if you are looking for something familiar, you see plants and animals are two twigs on the tree of life. And if you’re wondering where humans and our ape cousins live, we are smaller than the I, the dot on the I of animals in terms of genetic real estate. That’s what I mean by this is a microbial world, it’s overwhelmingly microbes in terms of genetic material. Does that telling us something about the universe as well? We don’t know, but it’s certainly interesting. And then when it comes to defining higher levels of life, intelligence, perhaps, it gets even trickier. And the trouble is we have theories of evolution, microscopic with DNA, and macro with natural selection. And we don’t know if these are universal theories, we simply don’t know. We don’t know if genetic material elsewhere is based on DNA and RNA and we don’t really know if natural selection will sculpt biology on other environments. And so not knowing that we actually have to think outside the box. So all this is speculation, ’cause we have no evidence yet. But if I were speculating about micro-life, microscopic levels of life, I could easily imagine other amino acids or base pairs and synthetic biologists have altered the toolkit of life already. They’ve actually edited DNA and made replicating molecules. So it doesn’t have to be the way we see it. You could go beyond what’s called the central dogma, which is the triad of DNA as the vault of information, RNA as the messenger, the carrying of the information, and then its expression through proteins in the functional form of an organism. Maybe that doesn’t have to be the way it is. What about not using carbon? What about not using water as the liquid medium for interactions? There are other molecules, there are other elements like silicon, the same column of the periodic table. And then you could have very weird biochemistry. We think it’s impressive that a single human cell has the information of a DVD, but you could imagine theoretically high density forms of biochemistry where the information storage is millions of times denser, maybe that happens. And then on the large scale, you can clearly have other possibilities. We are made of about 50 different types of cells, you could have many more types of cells, you could have genetic progression that involves changing large packets of DNA like genes. There’s some gene swapping in the history of life on Earth, but it’s modest. Mostly it’s just the gradual mutation of DNA and then sexual reproduction, mixing the genetic material, but you could accelerate that in principle. What if you didn’t have a cell at all? Why does the cell have to be the unit of organization? No obvious reason, it just is here. And then what about life that takes over a planet, even microbes that operate cooperatively on a geo-scale? All these are possibilities, so we should think about these. And like I said, I’m just already defining, life is tricky, defining intelligence is even harder. And what about us? We seem special. We act like we’re special, obviously, on this planet. We act as if it’s a disposable thing. But if you look at the relationship between body and brain mass, yeah, we’re off the top, we have bigger brains per body mass than other creatures, other animals, reptiles, birds, but not by a large amount. And obviously you can see at the top, we don’t have the biggest brains, those belong to orcas and whales. So we are special at some level, but intelligence is on a continuum and we have to think of it that way, especially when we’re going beyond our planet. And to give a little perspective on this, on the top left, you see with time going forward to the present day on the left, the evolution of our brain size. And you can see that until a last surge of brain size just a few hundred thousand years ago, modern homo sapiens doubling of brain size and the development of speech centers and so on, our brains were modest in size. And on the right, an interesting argument here, so what you’re looking at is encephalization quotient, which is the ratio of brain to body mass. So bigger brains relative to bodies are to the right. And now you’re looking at 50 million years of evolution and you’re looking at the skulls, fossilized skulls of dolphins and toothed whales, the ancestors of our present dolphins and whales. And the pink line and then the green line is their gradual evolution of braininess in the last tens of millions of years. And the black lines are our ancestors. And so the point is that if aliens, intelligent aliens, had come to the Earth almost any time in the last 50 million years, and asked where the smartest creatures were, they would’ve been in the oceans. We are very recent and late arrivals on this intelligence spectrum. So that’s a perspective because there’s a lot of time in play, on Earth and also in the universe beyond us. We don’t know what happens in the skulls of those creatures. Maybe they have abstract thought, maybe they have sentience. I think those creatures are clearly smart, their behaviors are complex orcas and whales, clearly, but we don’t really know what goes on with them. And then if you want an alien, we’re looking for aliens out in the universe. Well, why look there? This is a creature that branched from us in the tree of life almost half a billion years ago, it’s an extraordinary creature. It has nine brains, one centrally and one on each arm. It has a skin that consists of 300 million chromatophores, which are dye sacs that can change texture, as you can see, and color 10 times a second. This is an extraordinary creature, an octopus, it has complex, interesting behavior. It’s tricky ascribing intelligence, but here’s the alien right on Earth and we don’t understand it very well. So what kind of creatures are there out in the universe? We don’t know, we really don’t know. And I’ll also point out, because this is around us all the time, I’ll bring this talk right to the present day, we are on the cusp perhaps of post-biologic evolution. So we are a species that could potentially go through the membrane from biology to machine. And it’s happening all around us, we know. Here is the exponential progress in computers, in AI, and you think it’s fast, remember, Moore’s law is a doubling of semiconductors, and that’s every 24 months and it’s sustained for decades. For 60 years, in terms of computational capability, we’ve had a gain, doubling every 18 months, so a factor of 10 trillion in that half century or so. And look at it, the uptick in the last five years, that’s actually now doubling every two months. And I’ve got GPT4 on there just from a few months ago. It’s an extraordinary rate of progress. So how do we interpret this? How do we digest this because it’s around us, the capability of AI and computers. Well here’s that same graph. And now what I’ve put on the right is the equivalent organism that you could create, a robot. So a robotic organism that has a computer, a processor, has senses, senses its environment. And what is the equivalent? Well, the equivalent now is something like a mouse or a lizard, not very impressive, but it’s an autonomous creature that’s based on computation and sensing, there’s no biology at all. And the point is this fantastic progression projects to a human level of both computation and behavior in about 10 years. Now whether you believe we’re gonna get there, I’m not speculating whether AIs will ever be sentient or general artificial intelligence. I don’t have to do that, just look at the progression, look at where we’ve been. And notice that computers have done essentially what biology took 3 billion years to do and they’ve done it in half a century, that’s extraordinary. And then for an astrobiologist, the question is if it’s happened here, has it happened anywhere else? Why should we be the first or the only to get to this level of technological capability in the universe or in our galaxy? It’s a good question. Astrobiologists want to know the answer. And we can play out what happens in this scenario. And you’ve seen this before, we know how it plays out. So you have to use your imagination as Philip K. Dick did in the story that led to this movie. Yeah, we have smart robots that go to Mars and explore Mars, we have robots that help our industry and vacuum our houses, but you gotta play this forward. And when our AIs are sentient, they will do our bidding on Earth and off earth, and maybe we’ll have to install the kill switch to make sure we don’t come into conflict with them. This is on our horizon, this is happening around us right now. Just read the headlines and just play it forward. So what about the rest of the universe? Makes it pretty compelling to want to know the answer beyond here, but let’s just start in our backyard. I’ll get to exoplanets soon, but we start by looking nearby and we see places where there could well be life. Mars was warmer and wetter, almost certainly had liquid water on its surface 3 billion years ago and could’ve easily had life. The atmosphere was thicker, the planet was warmer, it dried out, the atmosphere seeped into space. And all these geological features tell the geologists there was water here. And not just in the ancient past, you can see seasonal flows, seepage of water on the left. You can see pictures three years apart of an escarpment, where an aquifer burst and 10 swimming pools worth of water ran down a hillside and carved out a channel. So there’s water under the surface of Mars now, not on the surface, it couldn’t exist, the pressure’s too low, the temperature’s too low. But you could easily have microbial life on Mars right in our backyard. But this is how NASA is gonna look for microbial life. And these samples are gonna come back to the Earth within five or six years. And the rover, Perseverance, is caching rocks, cores as we speak. (gentle music) These samples will come back and they would be fossilized. If they’re microbes, they’re ancient microbes, but they’re not taking chances. They will go to Johnson Space Center where there’s a level four biohazard containment facility that holds the moon rocks, can handle Lassa fever and dengue fever and so on. So they’re not gonna take any chances in case there is life in those rocks. But that’s gonna happen soon, maybe sooner than you are aware. Meanwhile, there are other places in the outer solar system. This is Europa, moon of Jupiter that’s covered in ice, and underneath the ice is an ocean. And the best estimates are tens of kilometers deep ocean around the entire moon. There’s tepid heating from geological activity in the core. So it’s obviously liquid water, it has nutrients, possible life in there. And there was a mission plan from decades ago, it’s unfunded to melt through the ice pack with a nuclear plant and then release a hydrobot to look for life. Maybe that’ll get funded, that’ll be an exciting mission. There’s Enceladus, a tiny little moon, about the size of Norfolk. So pretty small moon beneath most people’s notice until we found icy jets, and we now know there’s liquid water and all the ingredients for life on this little moon of Saturn, two billion miles away from the Earth. And then this moon, a much larger moon of Saturn, Titan, which looks terrestrial, there’s liquid, there’s deltas, there’s clouds, there’s precipitation, but it’s alien because it’s too cold for water, there’s a little water, but it’s ethane, methane and ammonia and a little water in those lakes. And if there was life there, it would be life 2.0, it would be a different biochemical basis. So that’s a compelling place to go, and there’s a mission heading there too, using drone technology. And now NASA’s flown drones on Mars where the atmosphere is very thin, it’s actually hard to fly helicopters on Mars. Titan’s air or atmosphere is about as thick as the air you’re breathing, so that’s really easy to do. And this is the Dragonfly mission. We’ll head there in perhaps 10 years, it takes a while to get out there. (gentle music) So Dragonfly will land in these lakes, these ethane, methane lakes and sample the material, look for hydrocarbons of course, and possible biological activity, an amazing mission. It’s hours away, so these will have to be autonomous, AIs essentially, because you can’t real time control them when it takes hours for the signals to get there. And if you’re keeping track, that’s one known habitable world in the solar system, the Earth, one potentially on the edge of habitable world, Mars, and several moons of outer planets. And the full sense is there’s probably a dozen moons of outer planets including Uranus and Neptune, that have all the ingredients for life under the surface. So we have a lot of habitable potential even in our own solar system. But let’s move on to exoplanets ’cause that’s really what this is about, that’s where all the excitement has been. And the discovery rate of exoplanets, it rivals the things I’ve been talking about in technology. This is the discovery rate of exoplanets in the last few decades, and actually driven by technology. if you analogize it to information technology or say cell phones, it’s actually as fast as the development of those technologies. So this field of science is moving incredibly quickly. And the year, or the first decade or so of discovery, and the first Earth-like planet was found over a decade ago. So now it’s routine to find earth-mass, earth-sized planets. And it’s all driven by technology, by spectrographs of incredible precision, telescopes that do this work don’t have to be that large. The Nobel Prize to Mayor and Queloz a few years ago was for the first exoplanet, which used a one meter telescope in Switzerland, you don’t need large telescopes to do this work. But you need exquisite instrumentation and precision there. And the methods are indirect detection, because an Earth-like planet reflects a billionth of the light of the sun and it’s very close in the sky. So it’s like looking for a firefly in a football stadium floodlight right next to it, that’s hard to do. So you don’t really see the planet. What you look for is the tugging of the planet on the star, which creates a doppler shift, a periodic doppler shift. And the first few hundred exoplanets are found by this doppler method. And then if it’s in the equatorial plane, the orbit, you have a second effect, which is a dimming of the starlight every time the planet crosses. If it’s a Jupiter and a sun, Jupiter’s 10 times smaller than the sun, square that, it’s 1%. Earth is 10 times smaller than the Jupiter, so it’s 0.01% dip, and it only lasts a short time, but it will repeat every orbit and you add the data together. And the next few thousand exoplanets were mostly found by this method, the transit or the eclipse method, incredibly successful. And so now after less than three decades of this work, first discovery, 1995, we have over 5,300 exoplanets of all different kinds, including Earth-like planets, but rocky planets, incredibly hot lava worlds, incredibly hot Jupiter’s even, and very cold planets and ice worlds, an amazing abundance. And as I mentioned, the majority of them in the last decade or so have been found by the transit method. And this one mission, the Kepler mission of NASA, was incredibly successful in finding several 1000 exoplanets, also only a one meter telescope, not huge. So what about habitable worlds? Thousands of exoplanets, but many are probably not habitable. I think biology could not exist on many of them, but that’s fine, there are huge statistics in play here. And these are the full projections in the Milky Way based on this initial sample. And the exoplanets found, all 5,000, are mostly within a few hundred to a few thousand light years. That’s our backyard, the Milky Way is a 100,000 light years across. But it’s enough to extrapolate, and these are the numbers that are projected. And you can see that one in six stars has an Earth-like planet, and another one in five has a super Earth. And the best guess of biologists is that slightly larger and more massive than Earth planets are just as habitable as Earths, and they’re actually the most abundant kind of planet, you can see. The solar system doesn’t have a super Earth, Earth and Venus are almost twins, and then you jump up to Uranus and Neptune, so our solar system is a little unusual. Well you add those two and you’ve got one in three stars in the Milky Way with a habitable planet, that’s extraordinary, and that’s the raw material. What about the ingredients for life? Well, we don’t know, we haven’t looked for all the ingredients on those planets, we mostly know their size or their mass. But simulations and computation suggest what the water content will be. And those simulations suggest that the Earth inventory of water is not special. In fact, the Earth is even a slightly dry planet for its size, because simulations find water content that’s 10 times the Earth’s oceans, or 100 times the Earth’s oceans, so there’s plenty of water out there if water is a requirement for life. And so we can imagine these water worlds, we can’t go there yet, they’re too far away, but there are a lot of them out there. (gentle music) So will we find a true Earth clone? Maybe, maybe not. It doesn’t actually matter because habitable planets will have a range of properties. And Earth 2.0 will not be exactly like the Earth. The spectral signature of the star may be different. The genetic material on the planet may be different, but it’ll be eerily similar. And just in case there’s any doubt, I know you would not have this doubt, finding Earth 2.0 does not relieve us of our obligation of taking care of Earth 1, because the nearest Earth, best guess, is gonna be 1000 trillion miles away. We’re not gonna go there, we’re not gonna send people, there is not a planet B or a plan B for us, we have to take care of this planet. That’s just the way it is unfortunately. But for astronomers, very exciting to know that there are Earth clones out there and astronomers go further, and they define a habitability index and they put all the information they have on the size, the mass, the orbit, the likelihood of the right chemistry and atmosphere into a habitability index. And this is just a sampling from Kepler and other sources where Earth is one, the best of all possible worlds. But that’s not actually true, biologists think this is not the best of all possible worlds. Life was nearly extinguished two times in a snowball Earth episode. Our violent, our climate is violently variable on geological timescales. So there are more stable, tranquil Earth-like planets out there where life may persist for longer. But anyway, just say for now, Earth is the best. Mars is 0.64 on the scale, which makes sense sort of on the edge of life. And you have dozens now of exoplanets that are more habitable than Mars and almost as habitable as the Earth by all the numbers you can bring to bear in calculating it. And so we’re ready for a little travel log, again, we can’t go there, but that’s just whet our appetites for our next vacation. (gentle music) So let’s put numbers on this again, from the sample we have 5,000, but a lot of them are habitable. It would be 300 Earth-like habitable planets in the inventory so far. It’s the number of sand grains that might stick to your finger if you put it in sand. And each one is a separate world, bringing to mind William Blake’s quote, to see heaven in a grain of sand, each one geologically unique, chemically unique, biologically unique, perhaps, that’s the sample we know and now we can project to the Milky Way. And the number is 10 to 20 billion habitable worlds in the Milky Way, that’s our galaxy. And analogously, that would be the number of sand grains in the child sandbox. It’s an incredible amount of habitable real estate in just our galaxy, you have to think about it a little. And to help you think about it, we’ll make an analogy, we’ll do a little travel log, again, we can’t get these pictures, these are space artists imagining it. And we’ll look at each one, we’ll roam around the galaxy, five seconds each. And we’ll just look at a dozen of them just to imagine what they might be like. Some dead, some living, they’re not all gonna be living even if they have the ingredients. (gentle music) So astronomers are blase with their big numbers, their billions and so on. So you need a little more visceral sense of the numbers. What does 10 billion really mean if they’re habitable worlds? Well, we just watched a minute, and if we were gonna do that little travel log of all the habitable worlds in the Milky Way, you’d all be sitting here for 10,000 years. But that’s just one galaxy, I’m a cosmologist, there are a lot of galaxies out there. And so the number of habitable worlds by projection, extrapolation, because the galaxy we live in is not special. All of the water and carbon and habitable worlds and planets are there, we found some planets in other galaxies even, we know they exist, of course. That total number is 1,000 billion billion. And that would be the number of sand grains on a beach like this, that’s 10 miles long and 10 meters deep. It’s an unimaginable number. But just think each of those is a potential biological experiment. So do you see why astronomers think there’s life in the universe at this point and at this level? And to quote my, I’ve lost the accent over the years, but I was born in Edinburgh, to quote my countryman Thomas Carlisle, hundreds of years ago, “If they be inhabited, what a scope for misery and folly. If they’d be uninhabited, what a waste of space.” And I’ve not told you the full story because I’m just talking about the planets, the exoplanets, and we’ve already alluded to moons of giant planets, which could be habitable. And so they’re exomoons, and James Cameron did a nice movie about life on an exomoon, “Avatar.” We’ve not found any exomoons, we know they exist. So habitable exomoons is just too hard for astronomers, we haven’t found any of those yet. So that’s another unventured realm of possible life in the universe. And then there’s a third category called nomads. So when people simulate the formation of a solar system with computers, turns out it’s a very chaotic, early phase, there are a lot of collisions, planets grow by collisions, and some of those are violent, Some of them destroy the planets before they get put together and some of them eject planets. There’s very good indirect evidence that the Earth, that the solar system had five terrestrial planets and one got booted out early on. And in the simulations, sometimes there are as many surviving terrestrial planets as ones that get booted out, and they’re called nomads or orphan planets. So there are almost certainly huge numbers of planets sailing through space with no star, ’cause they were gravitationally kicked out of their star system. And we’ve actually found them by microlensing so that’s not speculation anymore, they do exist, and the numbers are huge, they could rival the number of exoplanets. And because there’s no star, we don’t have those two techniques, their planet isn’t tugging on a star and it can’t of eclipse a star ’cause there’s no star, they’re just dark objects floating through space and we know they’re out there. (gentle music) So what you say, nomad planets, who cares? Well remember the super Earths, there are more super Earth than Earth-like planets. So if you make a model of a larger than Earth terrestrial planet, it has gravity to hold a very thick atmosphere, has a lot of geological heating ’cause it has a bigger core, and so these are in completely self-contained ecosystems. They’re completely plausibly habitable because there’s plenty of energy there from geological heating, there’s a dense atmosphere which just acts like a blanket, and so these nomad earths or super Earths more particularly, are absolutely habitable. And moreover, their lifetime with biology is not determined by the life of their star. I mean whatever good, bad, or ugly happens on Earth in 4 billion, four and a half billion years, that’s all she wrote, the sun will die, the red giant phase will engulf the Earth, life on Earth if it exists will be extinguished. But not the nomad planets, they have their own ecosystem and they could sustain life for tens of billions of years. So that’s an incredible thought. And we’ve not found any nomad planets, there’s some claims in the literature, but they’re not confirmed. So that’s another frontier of astrobiology, of exoplanet searching. So there’s plenty to do in this field. So what’s the next phase, having found lots and lots of exoplanets, how do you get to the next phase? How do you find life? Well you look for what are called biosignatures or biomarkers. So the experiment is simple. You look at the atmosphere of that planet, you can’t really see the surface, you can’t look for things on the surface, they’re too small. You look at the global atmosphere and you look for alteration of the atmosphere by biology. And by reference to the Earth that might be chlorophyll, which plants have, which creates an edge in the spectrum and very particularly, oxygen and ozone, which create great absorption troughs, those are biomarkers. Methane, also a biomarker produced mostly by life on Earth. But oxygen’s the good one because the one part in five of the air you’re breathing, that’s oxygen was produced by microbes billions of years ago. It’s a total tell for life. Because if the biosphere of the earth shut down overnight, just do the thought experiment, all life on Earth extinguished overnight, then that one part in five oxygen, 18%, would disappear in 5 million years, blink of an eye, geologically, ’cause oxygen is so reactive, it’ll rust things, it’ll dissolve in sea water, making it acidic, it’ll bind with rock and it’ll be gone. And so logically, if you see free oxygen in an atmosphere, it must be sustained by biology. And that’s the experiment astronomers are gonna do, and they’re gonna do it soon. And this is how it works. James Webb will do some of this, but really the best experiments are by a set of huge telescopes being built right now. So you take the light from the star, make a spectrum, and then you take light that’s filtered through the atmosphere of the planet from the star, and imprints absorption on it. And so you have two spectra, and you take the difference, and the difference is what’s in the atmosphere of the planet. And then you try and match those features with things you know, like oxygen, ozone. I mean in this case you’re matching it against something like water, which you’d expect to be there, water vapor. And you’re matching it in this case, with methane, but it could be oxygen, ozone, other biosignatures. So that’s the experiment that is being done now, not very well by James Webb. ’cause James Webb is a great telescope, it was never built for this experiment. James Webb was designed before exoplanets were discovered, so it’s not optimized for this, but these 20 and 30 meter telescopes that are being built, one by my university down in Chile, one by California universities in Hawaii, if they get permission, and one by European Southern Observatory in Chile, these are all gonna take data in a few years, and this is their killer experiment, this is their killer app if you like, to look for life this way. And it’s gonna happen soon, three, five, maybe seven years. Don’t know if it’ll succeed, if it’s successful, game on, biology elsewhere. If they fail with the first few dozen exoplanets, we might decide if they’re all habitable but have no evidence of microbes, maybe mean life is not as easy to form as we think it is. Do we only have the sample of one? So we can’t say. And you can go beyond that with these spectral methods, you can also look for advanced life, you don’t have to look for just microbes, you can look for something like nitrous oxide, which is an industrial pollutant. So you could look for things that only humans and civilization and technology produce that are chemicals, and that’s a tell for technological civilizations, so the same data will be used for that experiment too. And then as I’ll describe, SETI, the Search for Extraterrestrial Intelligence or Technology, is using radio and optical methods. And so this is the question now, we’re framing a question, we’re jumping ahead ’cause we haven’t found life anywhere else, so we’re kinda getting ahead of ourselves, but why not? And we’re asking are we alone? And the formalism for this that I’m sure you’re familiar with is the Drake Equation. I won’t show it as an equation, but it’s basically a series of factors that start with how many stars in the galaxy, what fraction of them have planets., and it could be all of them, but let’s be conservative and say half, and what fraction or habitable, about one in five, and there’s your 20 billion in the galaxy. And then what fraction of those that are habitable, that have the potential for life, does life actually happen? I mean it’s not gonna be 100%, it could be, but probably not, so let’s say it’s 50%, you’re down to 10 billion. And what fraction of those does life become intelligent? Hard to tell, we don’t know. I mean there’s been millions of species on Earth, and only a handful are intelligent, elephants, orcas, us, whatever your favorite smart creature is. So maybe that’s a small fraction, I’m putting one in 100, 1% of them eventually become intelligent. What fraction of those get technology and can travel in space and build telescopes and do all that stuff? One in 100. So with those small fractions, you’re still at a million in the galaxy, a million technological, intelligent civilizations. But to be correct and logical, the answer still could be one, it could just be us, we don’t know. But it’s certainly interesting, it’s certainly worthy of an experiment. And so we’ve sent messages in a bottle out into space. This was attached to the leg of the Voyager spacecraft, twin spacecraft have now left the solar system, there are metaphorical messages in a bottle. I say metaphorical because they’re not heading to any star and at their pace, it will be tens of thousands of years before they enter the realm of any nearby star. These are messages to us rather than realistic attempts to communicate. (speaking foreign language) I’m sure you all know what that is, that’s Quechua, so the Voyager record has greetings of the Earth in 119 languages, was also sent in the 1970s, also twin gold records that have left the solar system. So the Voyagers and the Pioneers are four of five manmade objects to leave the solar system, New Horizons is the fifth, and they carry messages. And you might be snarky and say, well you’re sending a technology into space that’s kind of obsolete on the Earth. Well, it’s making a resurgence, LPs are making a resurgence on the Earwth. But really, I mean technology is wonderful, but our modern digital technologies are degrading. CDs from the ’70s and ’80s are disintegrating at a rapid rate, DVDs also. So we don’t have durable digital technology. This analog technology will last, gold plated, for 100 000 years, so a pretty reasonable way to communicate, actually. On the other hand, really, this is a creature we share 99% of our DNA with and we can’t talk to this creature, so what are the odds we could communicate with an alien of unknown function and form that might not even have DNA or anything like it? It’s a presumption. So you see how fraught this whole issue is of communication. I mean, it’s a thing you can try, why not? But you have to be realistic about the implausibility of it, really. And yet we’re doing the experiment, we’re listening, and we can speak too. And we use our most powerful technologies at radio and optical wavelengths. And so with radio telescopes, we listen for signals that are narrow bandwidth and artificial and could not have a natural, astrophysical source. And so we know that they would have to be created by some sentient beings with radio technology. And with optical telescopes, the same thing, we look for pulses of light that would have to be narrow bandwidth, typically a laser, and would not have a natural astronomical source. And then in the reverse experiment, which is not done as frequently, we can speak, and it’s the same idea. We send out pulsed signals, radio or optical, out into space. So what’s happened with this? Because we’ve been doing it since Frank Drake, who’s coined the Drake equation in 1960, he did the first SETI experiment in 1959, actually. And so there’s been 65 years of what’s called The Great Silence, not a very successful experiment. But to the people who do it, it’s only just getting interesting because our technology is improving so fast. So let’s play that technology forward, our radio transmitters and our lasers. And if you do that in 20 years, the equivalence of our best lasers and radio transmitters could be detected if they exist from civilizations on any planet out to about a 1000, 3000 light years, which includes 100 million stars. And the new set of telescopes are gonna look at the whole sky at once. So if you then don’t hear anything or see anything, you’re gonna start to think, it’s pretty rare, that it just doesn’t happen with this technology, it’s a big assumption, isn’t it? And so there’s another strategy which avoids this assumption of communication which looks for aliens by their artifact, physical artifact, or just by their energy use, their inefficiency, their leakage if you like, of energy. So you don’t have to assume communication. That’s harder to do ’cause there are many false positives in that experiment. Whereas when you see these pulsed signals, you know you’re onto something. So these are experiments that are going on as we speak. And so this is a part of astrobiology too, to jump ahead and look for intelligent life. ‘Cause if there are microbes everywhere, and surely in some fraction of those cases, something like this, like on Earth has happened out there. And this was very presumptuous, very presciently anticipated by Enrico Fermi in 1950, and he asked, the question is framed, as are we alone? And this is amazing, ’cause in 1950 computers were half the size of a family home, there was no digital technology that we’re used to, but he put together the logic that there should be a lot of life out there and that we shouldn’t be the most advanced or the first. And so he inverted the question, are we alone to where are they? So he really thought there they should be there and we should see it. And and so Fermi asked this question, it’s a Fermi question, very well posed, Fermi, incidentally, Nobel prize winning physicist for fission reaction was nicknamed by his colleagues in physics, the Pope, because he was Catholic, because he was essentially infallible when it came to physics. And there are many answers to the Fermi question, without knowing the real answer yet, maybe they’ve already visited, astronomers don’t tend to buy that one. It’s possible we’re unique or it’s more probable, I would say, that this is rare, that intelligent civilizations, technology civilizations are just rare, thinly sparse, thinly spread in the galaxy, and so communication is hard. The voids of time and space beat against it. It’s also possible they’re unrecognizable. I kinda like that one, or they don’t care about us. And then if you want to get a little creepy, you could say, well yes they do exist and maybe we’re their progeny, maybe we’re their experiment. And I like this one too. The answer to Fermi question is yes, they’re here, and they’re just watching us and taking notice of everything that happens. We tend to have a good opinion of ourselves, what all the bad things we do, we’re kind of very tribal and violent and there’s some not very palatable things about humanity. But we still have a pretty exalted opinion of ourselves and let’s just hope at least that the aliens don’t think of us this way. So let me give you, again, just to pose this, because it’s hard not to think about it, the analogy of the technology in biology development. Because I’ve talked about the real estate in space, the 20 billion habitable worlds times 100 billion galaxies, incredible number. But what about the real estate of time? So you could have an earth clone, a fully identical twin of the Earth that formed 8 billion years before the Earth formed, because there’s plenty of carbon in the universe and water half a billion years after the Big Bang. And the Earth formed quite long in the history of our universe. So you could have a planet, like the Earth, with biology that got started like it did on the Earth, that has an 8 billion year headstart on us. What is that even like? Can we even imagine that? I don’t think so. But let’s just look at two final analogies. Try and imagine the progression of technology from arrowheads to a smartphone, that’s 50,000 years. So can you conceivably imagine what technology we might have 50,000 years from now, when this is what we have now? I don’t think so. I don’t think we can do it 10 years ahead. But you have to do that because out there in the universe that could be what we’re dealing with. And in biology terms, it was a few billion years to go from microbes to humans. And again, you could have biology that has been playing out for billions of years beyond. And so what is to us as we are to a microbe? We don’t know. So this is a subject as you know, as you can tell, that’s ripe with possibility. So as a final thought, let’s just imagine that there is an Earth-like planet and it’s fairly close and maybe we send some nanobots there, we’re not gonna go there, it’s too far, it’s too expensive in energy to send people there. But let’s just imagine something interesting is happening. (gentle music) That’s it, thank you. (audience applauds) – [Host] Fantastic.