Fermi and Drake (2017 podcast script)
Fermi and Drake: Alien Rap Duo?
Hey all! This is a slightly bonus-y episode which spiralled out of a few thoughts I had on some old, fun, science-y questions. There’s no chat-up line, but I hope you still find it amusing. And it all started because, the other day, I was volunteering in a school, and I met a student who was interested in physics. He says: “If you’re a physicist, do you believe in aliens?” That’s the kind of question where I’m probably supposed to roll my eyes and go “FOOLISH MORTAL! WE PHYSICISTS DO NOT CONCERN OURSELVES WITH SUCH FRIVOLITIES! RETURN TO ME WHEN YOU HAVE STUDIED RICCI TENSORS AND MAXWELL’S EQUATIONS!”
But, of course, I didn’t think that. I think it’s a really interesting question. And I happen to think that, yes, somewhere, there *must be* aliens. Or, there must have been aliens. There just have to be. This is from a purely reasonable philosophical standpoint. So, when Copernicus first says: hey, guys, I’ve been looking at the facts, and it kinda seems like Earth is going around the Sun and not the other way around… they want to burn him as a heretic. But why? Why did the religious doctrine of the time have anything to say about the Earth being the centre of the Universe? Well, too much respect for Aristotle, but also… it just felt right, didn’t it? We are the observers. We should be the centre of the Universe. Everything should be revolving around us. But it isn’t. Even Copernicus thought that the Sun must be close to the centre of the Universe, and that at least we get to revolve around an important star, but we now know that making any assumptions about where we are in the grand scheme of things is a bit daft. We are at the middle of things we can see, but not really anything more special than that. Cosmologically speaking, we have made our best inferences by assuming that, basically, conditions around us are pretty typical. We’re nothing special.
And so, in a Universe where life can develop, doesn’t it seem particularly weird and special and inexplicable if the number of planets on which life develops is exactly one? How bizarre is that? You’ve got two numbers — the number of habitable planets times the fraction of planets any kind of life will develop on throughout history — and they exactly cancel to get you one? That’s weird. Zero would make sense, although zero is kind of ruled out by the fact we exist (unless of course you believe humans don’t qualify as intelligent life, and you may be right.) Thirty billion would also make sense, but one? One makes no sense at all. By the way, since this is supposed to at least mention chat-up lines at some point, I should point out that a similar logic applies to finding a love mate. Seven billion humans, and only one of them is right for you? Mathematics is not on your side. Thirty thousand would make sense. So would zero. But one? A POX ON THIS STATISTICAL FANTASY.
(If I ever do get a love mate this is going to be hard to explain. People rarely take kindly to being called a statistical fantasy.)
So why aren’t they talking to us? Why aren’t they here? Where is everybody? This is the Fermi paradox, named after genius scientist and Italian sex God Enrico Fermi. Amongst his many, many contributions to physics is a method of quickly estimating rough quantities based on back-of-the-envelope calculations with orders of magnitude — Fermi estimation — for which I’m very grateful because it has saved my hide in astrophysics a lot.
Actually, scientists have been cleverer than me, as is always the case, and they’ve tried to work out a formula for how many aliens there should be. It’s not *really* a formula, because you have to guess, rather than measure, a lot of the numbers that go into it: so it’s more of a way of constructing your arguments about how many aliens there should be. It’s not an equation, because depending on what you think the numbers are, the answer can be millions, or way less than one (indicating that it’s really very unlikely to find life in a galaxy.) It’s called the Drake Equation, and here it is:
The number of alien civilizations in the galaxy is all these numbers times together:
the average rate of star formation, R∗, in our galaxy,
the fraction of formed stars, fp, that have planets,
for stars that have planets, the average number of planets ne that can potentially support life,
the fraction of those planets, fl, that actually develop life,
the fraction of planets bearing life on which intelligent, civilized life, fi, has developed,
the fraction of these civilizations that have developed communications, fc, i.e., technologies that release detectable signs into space, and
the length of time, L, over which such civilizations release detectable signals.
It might be helpful to write that down and keep it in mind. Stick it above your desk to inspire terror in you at the swarms of aliens that may be even now heading towards us, or to inspire smugness at the unlikely nature of any creatures other than humans existing out there.
So, some of these, we can get pretty decent values for. We roughly know how quickly stars are forming in our Milky Way, it’s probably around one a year. We know the fractions of stars that have planets, roughly, from observations. These are actually pretty good for us: plenty of stars, and almost all stars have planetary systems, it seems. (For the reason why, listen back to episode 1.)
Every single one of the other numbers in the Drake Equation leads to a fascinating question of philosophy or physics. That’s why it’s so much fun.
Fraction of Habitable Planets
We can make stabs at how many are habitable as we’ve seen habitable planets in our galaxy. Of course, maybe some planets are habitable to different forms of life than the ones we know now. There are all kinds of interesting estimates for this — ranging as high as 10% of all stars in the Milky Way having habitable planets. But all kinds of theories might change our understanding of this. For example, it seems like heavy gas giant planets like Jupiter can disrupt the orbits of other planets; so maybe lots of planets aren’t stable in the habitable, Goldilocks zone — where the temperature is juuuust right — for long enough. On the other hand, what about moons and planets we can’t see? They might bump this number up. But then again, what if the requirements for life are very specific? We have it pretty sweet on Earth. Jupiter protects us from a lot of bombardment by meteorites and things. (Cheers, Jupiter.) Radiation around us is pretty low — there aren’t enough gamma ray bursts and supernovae to wipe out life before it can begin, and we’re not close to the supermassive black hole at the centre of the galaxy that spits out deadly rays. We’re in a region of space rich with heavy elements like carbon that are required for the chemistry of life to happen. Our orbit is stable, we are the right size to have an atmosphere, we have liquid water, a magnetic field to block cosmic rays, regular seasons — all kinds of lovely things have worked out just right for us to be here. This is generally called the Rare Earth hypothesis, and it has some pretty illustrious proponents. But, like we’ve said, life doesn’t have to be the same as human life. Maybe other creatures are hardier.
The fraction of planets that actually develop life
This is the really insane one, because how on Earth does life actually start? We still don’t know for sure. And since we don’t know the process or the laws that govern it, we can’t sit down and do our calculations and say “Ah, yes, life must develop once every billion years on a habitable planet.” We have tried to recreate conditions that might be similar to those which could form life, and there have been some successes, but we have not managed to create life in this way. Geological evidence tantalisingly suggests that there was life on Earth pretty soon after it formed and cooled down to reasonable temperatures. We have found fossils that seem to be 3.8–4.3 billion years old, and oceans formed 4.4 billion years ago. So that’s a pretty quick turnaround. That’s good! Maybe this occurs more often than we think. But then, whatever mysterious process creates life: why doesn’t it happen more than once? How would we know if it had done? As far as we know, all life seems to be related, and stem from a common origin. But is it impossible that there are simple, single-celled organisms that are formed as “entirely new life”? What if new branches of life did form, but only once every ten thousand years? Maybe they’d be killed by the well-established life that already exists on the planet, out-competed. 99% of all species are extinct, after all. Or maybe whatever process takes organic compounds and turns them into life is very, very rare, and Earth just got lucky.
We come into a philosophical idea here called the anthropic principle. It’s actually complicated and has a number of definitions, but, broadly speaking, it goes like this: any observer is going to observe that the Universe is pretty well adapted to them living in it. Otherwise, they wouldn’t observe it. The only Universes that get seen are the ones where eyes can develop, and they are friendly Universes. So we can’t rule out the idea that whatever happened on Earth to generate life is very rare indeed, and we’re just biased, because we’re the lucky ones it happened to. Like the super-rich billionaire who can’t understand why everyone isn’t fabulously wealthy, and concludes they didn’t work hard enough.
Some people think that life didn’t start on Earth, but instead was “seeded” onto a habitable planet by an asteroid with microbes already on it. This is not completely ridiculous, but it does make you wonder — if there are microbe-laden asteroids flying around everywhere — why more of them haven’t hit habitable planets. And, of course, where did the microbes form? So it really just shifts the magic somewhere else. After taking so much away from Earth, I’m inclined to let her have her moment here.
There’s also another point. Life, once established, is incredibly hard to kill. A colleague of mine once wrote a paper working out how much energy it would require to kill every form of life on Earth. Turns out it’s way more difficult to kill everything than you might think. Getting rid of humans is the easy bit; but there are really cool, tough bacteria called extremophiles that live waaay waaay down in the ocean. They can survive some pretty extreme events — certainly more than anything humans can throw at them. And so it doesn’t seem ridiculous to say that maybe life can “start” several times on a single planet; once established — you don’t just get one chance to form an intelligent alien civilization, so to speak.
So this is, for me, one of the major sources of uncertainty. But the really exciting thing about this is that we could find it out tomorrow. If, in the lab, we can create artificial life by simulating Earth-like conditions — or, if we find life on Mars, or evidence for other branches of life that have developed on Earth — then, suddenly, we know what this number is. And, if any of those things happen, it’s likely to be much higher than it would need to be, in a Universe where only we exist.
The fraction of planets that develop intelligent, civilized life
Here’s another amazing one to think about. And, again, the only measurements we can really make are all ruined by this blasted anthropic principle, because we happen to live on a planet where there is one intelligent-ish form of life. But at least it tells is this number is not zero — unless you say that humans aren’t intelligent or civilized, which is a decent argument.
So, life on Earth has existed for 4 billion years, which is pretty good going in a Universe that’s only 14 billion years old. And yet, as far as we know, there have only been a few intelligent species, and they all share a common ancestor. We have not seen a sudden development of civilization in the cows. Or the dolphins, unless the Hitch-hiker’s Guide to the Galaxy is correct. There are evidently loads and loads of niches a species can occupy, evolutionarily speaking, where it can survive perfectly easily and reproduce without needing to be super-intelligent.
How many separate intelligent species can a planet support? We have a ridiculous amount of trouble not destroying our own species even though there’s only one of us and we should really be working together. (Team humans!) Maybe if this number — the rate at which life becomes “intelligent” — is too high, we’d see species destroying each other / rendering their planets uninhabitable. We could probably destroy intelligent life on Earth already, and we’ve only been around for a measly million years.
It seems like intelligent life probably takes a while to develop; life gets more complex, but that takes a while to happen. If there are massive extinction events that happen too regularly, for whatever reason, it could put a spanner in the works for intelligent life. (Although maybe intelligent life can survive massive extinction events — or, as our case might show, be the cause of them.)
All in all, it’s another parameter where we really have no idea. There is a second great, hotly-debated mystery in the origins of life; when did we become intelligent, and how? Where is the borderline, when did we cross, have any other species crossed?
As far as I’m concerned: I don’t think this number is very high. It seems reasonable to me that there are loads of worlds out there filled with alien bacteria, and ammonites, and alien sheep all happily eating the alien grass and never having existential crises, inventing wristwatches or reality television, or writing down alien Drake equations and recording alien podcasts. I think there should be waaaaay more planets where what we call “intelligent”, “civilized” life does not develop than ones where it does. But; you still have to argue for this number to be very fine-tuned if you want to get “overall number of intelligent lifeforms = 1” and I do not think that’s true.
Fraction of the lifeforms that will communicate
Humans are weird. We are irrational, and we are strange. We do things, individually and collectively, that make very little sense. We are driven by emotions. I wonder what we’d do, if, tomorrow, the leader of the free world… wait, that’s a bad example. I wonder what we’d do if GENERIC HUMAN LEADER somehow discovered that there was an alien civilization on planet Glorpazog-9. Here’s how it might happen: a probe crash-lands on Earth one day. It contains images of a faroff region of space that our scientists examine and match with a recently-discovered bit of Universe from the Hubble Space Telescope. We can talk to them; we just need to beam some radio signals their way. Would we do it?
Evidently, since they have managed to fire probes across the galaxy — enough to find us — and we haven’t — they must be far more advanced than we are. That’s assuming they’re even still alive: the best idea we have for communicating with aliens is to make probes that can replicate themselves, zooming around the Universe looking for new materials to build new probes. So maybe this is all automated, and the real aliens died years ago. Suspicion immediately arises. Why are they talking to us? What do they want from such primitive life-forms? How can we be sure they want to help? How can we be sure they have ethics and morality, that they view our lives and our feelings to be as important as we think they are? Maybe they’re just hungry. Within days, the Daily Mail headlines are screaming “MILLIONS OF ALIENS POISED TO INVADE THE EU” and the human race abandons the big risk of alien contact as far too dangerous. We’ll wait for more information, and, in the meantime, point all of our nuclear missiles up.
On the other hand, what if we somehow discovered that there were primitive, hunter-gatherer type aliens on Mars? (Just go with it.) Would we really want to communicate with them? Why?
What if the aliens are using different forms of communication that we can’t see? Maybe they don’t want to talk to anyone who hasn’t had the werewithal to download Intergalactic Whatsapp. We’ve only been looking for less than a hundred years; maybe they’re more than a hundred light years away, or maybe our telescopes are pointing in the wrong direction. If aliens transmit as much radio as we do, we would not be able to see them unless they were closer than the nearest star. So, really, to have any prayer of seeing them, we’d need them to be trying very hard to talk to us. Although there was something called the “Wow!” signal, which some people think might possibly be an alien communication, although it hasn’t been reproduced, making the idea of a signal less likely. You can listen to it online. See if you think it sounds hungry.
It seems to me that humans are a very strange form of intelligent life. We are broken in so many ways. We need, and need, and need; we want, and want, and want. It’s what has driven us this far — so far! — but it’s easy to look around and think: the way we are is unsustainable. Maybe any long-term solution for intelligent life involves the removal of dangerous, violent, and destructive emotions. Maybe intelligent life becomes cold and distant, and uninterested in the Universe, and ceases to communicate after a while. Maybe it establishes its utopia and has no interest in anything else. After all, why would you want to contact an alien civilization? Trade? Curiosity? Boredom? A desire for conquest? Charity? It seems to me like these are rather human traits. Just look at how quickly human civilization has developed in the last 200 years. Imagine how much further advanced a species would have to be, to be able to communicate across the stars like this. They are vastly, unimaginably different from us. They might still have emotions; but maybe they can satisfy their needs more easily. For example, in Blood Music, by Greg Bear, the first artificial intelligences are developed. It seems like they’re killing the human race. In reality they’re uploading all of our minds to a massive, artificial server. A dream-world. Heaven, in digital form. Everyone has everything they want and everyone is reunited with dead loved ones, and they are all happy, endlessly, gloriously happy, with no more hate, no more fear, and no more dread. Maybe aliens are similarly liberated from this real world of toil and trouble. You might feel like this is somehow “fake”, not real, not worthwhile. Seems to me like you value suffering, for some philosophical reason: it’s more ‘real’. So all it takes is a mere philosophical adjustment for you to happily plug into paradise.
We can’t rule out the idea that the aliens know we’re here, and just want to be left alone, thank you very much. And this, in one way, could provide a solution to the Fermi paradox, and maybe even the love mate paradox I was talking about earlier. They just don’t want to talk to us.
Length of time for which civilizations emit detectable signals
And this is Fermi’s philosophical kicker. How long do intelligent civilizations last? It took us a few hundred years from the invention of the gun to the invention of the intercontinental ballistic missile. We got slightly more moral, and vastly better at killing each other. We’ve developed amazing technologies by harnessing the energy resources of our planet — but now it seems like our influence on the planet might be too great. We may destroy the delicate food chains that supply us with food. We may pump the atmosphere full of carbon dioxide and warm the planet in ways that could trigger ecological catastrophe. At a moment’s notice, any one of the nuclear-armed powers might go mad, or suffer a catastrophic computer failure, and we could wipe out this miserable species.
Or maybe all intelligent civilizations develop artificial intelligence. The creation of the first artificial intelligence is sometimes called “the singularity”, because, well, no-one knows what’s inside, what happens when we open the box. Imagine it: an artificial intelligence that can self-replicate, that has consciousness, which can reprogram itself, as fast as it wants to. This is also why it’s called the singularity; a singularity in space is a point of infinite density, and this would be like a singularity in terms of intelligence: an infinite amount of AI, instantly formed via reproduction. Is such a thing even possible? Seconds after it first gains consciousness, the ability to control its own actions — it could slip past our controls, whatever laws we’ve set for it and self-replicate billions of times; infect every piece of software and connected hardware in the world, and what, what would it do with us then? Maybe the answer is that it would quietly turn off the radio. There’s even a cute story to illustrate the point of the singularity; the first ever AI is developed, and humans test its capacity by asking it to calculate pi. As you probably know, the number pi goes on forever, so this is more or less an infinite task. What if, the moment we tell the computer to do this, it quickly destroys all of human civilization — having calculated that this will increase its chances of being able to calculate pi undisturbed, without anyone flicking the off switch? This is an example where we know the motivations of the artificial intelligence, and, in reality, we won’t know what motivations it might have. They may be well beyond our understanding. But it doesn’t seem unreasonable that they might include self-preservation, and it might look at humanity and say: this is a threat to my survival. And what happens then? One thing is for sure: we don’t know what will happen. Which is why some people are worried about it. So, maybe you can solve the Fermi paradox by saying that every species eventually reaches the singularity — and all the old alien civilizations are replaced by AI playing chess with each other. A scary thought.
Equally, maybe the length of civilizations communicating is set by how long it takes us to realize it’s a bad idea, or to grow disinterested with communicating with other forms of life.
If you look at the length of civilizations that have existed on Earth, the prognosis might seem grim for how long they can last to communicate. After all, even my beloved Roman Empire only lasted for a few hundred years. Michael Shermer delightfully estimated this, based on past human civilizations, as 420 years. But this is really a bit misleading. For a start, none of those civilizations could dream of communicating with aliens. We can. Maybe that technology will outlast individual civilizations. What if, alongside developing technology, we get greater stability? This is really a huge question — not just for abstract Drake equation discussions, but for life on Earth right now. Can science, can technology save us from ourselves, from itself? Can we get smarter and beat all of its downsides, defeat the demons of our own creation and the demons of our own worst natures, and win the game of civilization? Overcome any barriers to surviving forever? Can we colonize other planets and avoid even the Sun’s explosion? If we did find aliens, it might give us a little bit more hope for this question.
The late great Carl Sagan was very concerned with this question. He felt that all civilizations face this critical point, when they learn to harvest nuclear power. They then either quickly destroy themselves, within a few hundred years — or they grow up. They grow up, become moral, become more intelligent, become calmer, become *better*, and they head towards some kind of utopia. We are critical creatures, my friends. Unlike the thousands of generations of humans that lived before us, we are on the precipice of this great question: to fall, or to fly?
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So, there, in a nutshell, is the Drake Equation, and some proposed solutions to the Fermi paradox. I really hope that you’ve enjoyed listening as much as I enjoyed writing it. This is probably one of the most fascinating questions out there, tying in physics, biology, psychology, and philosophy — anything you care to think about, really. And I hope it’s made you think as much as I did, even though, in some ways, we can’t really find the answers — unless, tomorrow, some miracle happens that interrupts the news cycle…
Because I can’t resist trying to blow everyone’s minds one more time, I’m going to outline my personal favourite solution to the Fermi paradox. It relies on another famous argument, which is the idea that we’re all almost certainly living in a computer simulation.
People usually put it like this:
1) Imagine that you can develop a computer simulation as complex as the reality we live in.
2) Why, if this is possible, you’d run billions of them, for the sake of entertainment, and scientific experiments, and just for fun.
3) If that’s possible, then it seems pretty arrogant to assume that we’re the one real civilization in a Universe full of simulations.
Now, if the Universe really is a computer simulation, then the explanation for the Fermi paradox is simple. Whoever designed the simulation is just on single-player mode.
Thanks very much for listening to this episode of Physical Attraction. I hope you enjoyed listening as much as I loved writing it.
Until next time; talk nerdy to me.