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What does the Drake Equation teach us about extraterrestrial civilizations? What does it NOT teach us? What complexities does it hide? Is it even science? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPTION (AUTO-GENERATED)
So you're single and you're sick of it. You're ready to jump into the dating game and find that special someone, a life partner, a parent to your dozen children. But where to start? You don't really hang out at bars, you don't talk to the people at work, so you decide to start online. And so you make a dating profile.
And on the profile you start off with things about yourself, you know, what you look like, the things you like to do, your job. Maybe you illustrate book covers for romantic literature. You enjoy listening to the best astronomy podcast in the world. You are an amateur cheese enthusiast, etcetera, etcetera. That's the first half.
The second half is you describing what you want in a partner, and you start with the obvious. You'd prefer a human, someone that speaks your language, lives in or near your city, and is also single and looking for a partner. And then maybe you introduce some more specifics, some, you know, some qualities that you would enjoy in that life partner. Maybe a certain age range. Maybe someone who likes to be outdoors or play card games or go to the movies.
Maybe someone who isn't allergic to dogs because you have 14 dogs that you you have a lot of issues. But maybe there's reasons why you're single. I'm just I'm just saying. Anyway. But then you start thinking even deeper, imagining your ideal partner.
Like, you're really taking away. Like, man, if I could just have the one perfect person in my life, this is exactly what that person would look like. Like. Maybe they're exactly five foot seven. Maybe they have exactly brown hair and green eyes.
They must enjoy eating cheese three times a week minimum. They must be employed as a a piano tuner. They must know the third first thirty digits of pie. They must know how to bake an apple pie. Their second dough must be longer than the big dough.
Like, it just it gets really, really specific. So you come up with this list, for your ideal partner and you give it to a friend and ask for their opinion. And your friend is gonna ask a very simple question. With this many details, how many people do you think match this exact profile? So you start running the numbers.
You're gonna make a guess. At first, it's easy to calculate. You can you can look up the population of your city. You can guess that a certain fraction are in the right age range, speak the right language, are single. But then it starts to get a little bit harder.
Exactly how many piano tuners are in your city? How many match all the other requirements? Of those, how many of those know how to bake or let alone an apple pie? And let's not even try to guess the whole toe length thing. That's just weird.
The end result of all these calculations is you don't know. You don't know. So you give it a shot. You you post your profile online anyway, and you wait. And you wait.
And you wait. And you wait. Nothing. You get nothing. No response, no calls, no emails, no messages.
You start to wonder what's going on. Are you really alone in this city? Will you be single for the rest of your life? So after all the waiting, you ask your friend for some more advice because you even though you ignored them the first time, you ask them again, and they suggest maybe loosening up the rules. Like, are you sure you need to be this specific?
Do they really need to enjoy cheese three times a week? We bring it down to two or one? There's there's more possibilities for partners out there than your hyper specific list might suggest. But then you start thinking, you're wondering if maybe you actually forgot something. Maybe that's not the problem.
What if you met someone with all these qualities that had, you know, just the right height and hair color and attitude and everything, but they put the toilet paper roll on with the flap in the back instead of the front. This is they're obviously incompatible. So you're back to square one, which is you don't know if you'll ever find a soulmate. This is, of course, an extended metaphor for the Drake equation, a tool developed by Frank Drake, hence the name, in 1961. And it wasn't necessarily written on the back of a bar napkin, but it was sketched out in a hurry to give some conference attendees something to talk about.
And it attempts to answer the question, are we alone, in a scientific way, which is a pretty serious thing. This is a question we have asked for ever, especially once we began to realize that the distant stars were just like our own sun and probably had planets around them, and we started wondering about the worlds in our own solar system. We wanted to know, are we alone? But for a very long time, this was a very philosophical question, perhaps a theological question. It wasn't a scientific question, and the Drake equation is an attempt to approach this question with the tools of science.
It is humanity's galactic dating profile. You know, it starts at the top saying, oh, carbon based, water solvent, planet bound species hopes to forge open and honest relationship with extraterrestrial civilization that respects life. Just friends at first, but open to becoming more serious. The Drake equation is the second half of the profile. It's what we're looking for in a relationship.
It attempts to write down all the important things that make us us and led us to being us and try to get a handle on how many potential partners we might find out there in the galaxy. In principle, you should be able to go out there, make a bunch of observations, measurements, estimates, put all these together and out pops a single number. Or at worst, a range of numbers, the number of civilizations in our galaxy that we can talk to, that we can form a relationship with. And just like a dating profile, it starts off easy and obvious, but gets trickier as it goes. I'm not gonna read the equation itself to you because it's it's just a bunch of meaningless letters, but I will explain the terms as originally envisioned by Frank Drake.
The big number that we're after is n, what we're gonna call n. That's the big one, the big one, the number of civilizations in our galaxy with which communication might be possible. These are the people we can talk to in the galaxy. This depends, according to Frank Drake, on a number of individual parameters. It depends on the average star formation rate in our galaxy.
How how often and how quickly does our galaxy produce stars? Then, of those stars, what fraction of them have planets? Then, of those planets, how many of them can potentially support life? Then of the ones that can potentially support life, how many actually develop life at some point? Then the ones that eventually develop life, how many of those go on to develop intelligent life, AKA a civilization?
Then what fraction of those go on to develop a technology that we can use to communicate with them? Maybe radio signals, maybe morse code by covering up their star with a blank you know, whatever. And then what fraction of those contribute to Patreon? That's patreon.com/pmsutter. Your contributions keep this show going, and a certain fraction of the intelligent species in our galaxy help support this show.
That's patreon.com/pmsutter. That may not have appeared in Frank's original formulation. That may be a later addition, but I'll have to I'll have to fact check that. And then the final parameter is the length of time for which a civilization would be able to communicate. So they might develop radios and and all sorts of cool technology, and then they blow themselves up, and so there's a certain lifetime there.
And then you mush all these numbers together and out pops a number, the number of people we can talk to, the eligible singles in our galactic city. And on the surface, the Drake equation seems totally harmless. Either you take it seriously, which means you actually try to estimate all those individual numbers and guess as to how many potential galactic life partners are out there, or you don't take it seriously as a physics question and just use it to frame discussions and have a nice little fireside chat. And the rest of this episode is going to be my opinion because I think the Drake equation fails on both counts. I think it's useless both as a physics equation and as a philosophical tool.
So feel free to disagree because this is going to be my opinion, and feel free to voice your disagreements on the show website or on social media. I'm at Palma, etcetera on all channels. You can go to askaspaceman.com. But you ask the question, specifically Gary p on email, Seth l on YouTube, and Bob h on YouTube. You ask the questions, and this is my show, so I get to go first, and then you are free to rebut my arguments.
Let's start with taking it seriously. Let's start with the Drake equation as it's written, take it as equation in physics, and see how productive or fruitful it is. Where we actually want to make a legitimate prediction because that's what scientists do of how many intelligent species are in the galaxy that we can talk to. Critique number one, it's not an equation. It's not an equation.
Yes. I know that there's an equal sign in it, and I know that it's called the Drake equation. But you need more than an equal sign to be an equation. Equations are like a marriage. They unite multiple concepts into a single house.
They show the interconnectedness and relatedness between seemingly different things. Look at e equals mc squared. That's a very powerful equation That tells me something about the relationship between mass and energy, that they're just the same thing. Or the equations of general relativity, this tells me about the relationship between the geometry, the bending of space time, and the matter and energy embedded in it. There's a relationship there, a connection there.
The equations tell me how they're connected. Or Maxwell's equations, they tell me how charges and magnetic fields and electric fields are all related to each other. Or or or f equals ma, good old Newton's second law. This tells me that force, something I feel, is related to acceleration, something I do. These are very powerful concepts.
Equations have power to reveal these relationships, and they can be reshaped and rearranged. I can take an equation and shuffle around the parameters to to show new relationships. Just look at f equals m. I can say, okay. If I have a mass and it's accelerating, it will impart a certain force.
Or I could flip it around and say, if I apply a force to an object, then depending on its mass, it will have a certain acceleration. I can rearrange those parameters, and I can learn new things because it's all about relationships. The Drake equation is just a bunch of numbers multiplied together. It's not an equation, it's a definition. It only goes in one direction, not both.
I take a bunch of numbers, I multiply them together, and I get a number. There's no deeper concept that it reveals. It's just a breakdown of one large problem into smaller problems. That is not an equation. That is a definition.
Definitions are fine. We use definitions in physics, but they are not equations in the sense of something like Maxwell's equations or Newton's second law or the equations of thermodynamics. Critique number two. The uncertainties in these parameters are completely unknown. You have a much bigger problem than you realize.
It's more than just guessing the individual numbers. How what's the star formation rate? What fraction of stars carry planets? How long will a civilization last and make detectable signals? Those are all numbers that you can guess, but individual numbers carry with them baggage.
They carry with them some level of precision. This is called the uncertainty. And in science, knowing the uncertainty is more important than knowing the number itself. This is words of wisdom, tossing out pearls here, courtesy of Ask a Spaceman. What you know is less important than how well you know it.
So the problems are bigger than you might suspect. In order to pin down the big n, the big number of life partners in the galaxy, we don't have to just measure, say, the number of planets where life arises. We also have to understand the uncertainties, the range of possible values. And if you don't go get those exactly right, you're sunk. You've got nothing.
If your uncertainty tells you that you've really nailed one of these parameters, like, yes, oh, we are so precise about one of these numbers, like, that's so good, and you're wrong in that uncertainty, it's worse than just getting the wrong number because you'll stop caring about the value. You'll assume it's legit, and you'll move on. And in the end, you'll have a completely wrong answer because you misestimated your uncertainties. That is a critical mistake. You need to know how well you know something.
Even if you nail all the parameters, but just one of them has a big uncertainty, you haven't learned anything. Because all these numbers just multiply together, even if you know perfectly well every single one of the parameters in the Drake equation, but one of them has a big uncertainty, you haven't accomplished anything. How many piano tuners are in your city? Maybe you'll guess a hundred. But a hundred plus or minus one is a very different answer than a hundred plus or minus 50.
Right? If I say a hundred plus or minus one, that is a very confident prediction. And I better get that right because if I'm wrong, I'm being misled. But if I'm being honest, I say 100 plus or minus 50, then I basically don't know, do I? I basically don't know.
And it's more complicated than just a simple plus or minus. The uncertainties on each of these numbers is more than just a bell curve, a standard distribution that you might learn in statistics. You don't know the shape of that uncertainty. Is it 100 plus or minus 20? Is it a hundred plus 10 and minus 30?
A hundred plus 50 and minus 25? These are very, very different. And until you know, until you have some grasp of how these uncertainties shake out, you got nothing. Our problems are tripled. The Drake equation is three times more mysterious than you might expect.
One, we don't know the values. Two, we don't know the uncertainties on those values. And three, we don't know the form of the uncertainties. The lesson here, it's very, very easy to be led astray with the Drake equation because we have no intuition or experience with these essentially made up parameters. You think you might have a final answer, but you have no idea how well you know that number.
And if the final answer if you say, okay, there's there's a thousand aliens plus or minus a hundred. One, you don't know if you got the thousand right. And two, you don't know if you got the plus or minus a hundred right. Most of the parameters are impossible to measure, and their uncertainties are impossible to quantify. Just how many species will turn on their radios and start talking?
How do you even begin to estimate an uncertainty for that value? Critique number three. We could have the completely wrong parameterization and you have no way of knowing if you're right. Remember that the big goal here is n. That's the holy grail, the white whale, to choose your own metaphor for an impossible goal.
The Drake equation is one particular way of breaking down that big problem into a bunch of smaller, potentially more solvable problems. This is a tried and true method in physics. That's totally cool. That's no big deal. But this process of breaking down a big problem into smaller bits, which we call parameterization, can again lead you astray.
Remember, we have nothing to guide us. We're making somewhat educated guesses as to how to proceed to the big n, the big number. Your choice of how many parameters to use and what parameters to use affects how we think about it and how the statistics relate to each other. The individual parameters multiply together like it's just number times a number times a number times a number, but their uncertainties don't. Combining uncertainties with multiple parameters is not a very simple thing to do, especially if you don't know what those uncertainties look like.
The relationship between the parameters is more opaque than you might naively think. On the surface, it looks like a very simple equation. You just multiply a bunch of numbers. But under the surface, because so much is unknown, because so little is based on knowable things, physics things, we don't understand how these parameters relate to each other. We have an incomplete knowledge of the Milky Way galaxy.
We have incomplete surveys. We have incomplete data, incomplete maps. What fraction of stars lead to planets? What fraction of what kind of stars lead to planets, and does that matter? Does that matter for our estimates in the Drake equation?
Does that matter if we're trying to hunt for life and we have only so many dollars to spend on observational programs, we can only look at a certain small fraction of the stars in our galaxy to hunt for life or to listen for signals. Do we look at all small red stars? All stars like our sun? Just big stars? A little bit of columns a, b, and c, perhaps?
We don't know. Just trying to capture that with a single parameter in the Drake equation of just what fraction of stars lead to planets hides the true complexity. The choice of parameterization affects your final result, and it hides important considerations. Considerations that you can't just gloss over if you're trying to make a robust prediction. Critique number four.
The Drake equation doesn't capture all the possibilities. It assumes many things about life. And to be fair, those assumptions are pretty standard. As far as we know, intelligent creatures live on planets and have access to resources to make interstellar phone calls, you know, all the deal. But we're learning about a lot about life in the universe that we didn't know in 1961.
Like, I don't know, the huge reservoirs of liquid water in the outer solar system, or the past history of liquid water on Mars, or the methane seas on Titan. The Drake equation assumes that to get life, you need to follow a chain from a to b to c to d to e to have intelligent life. And while it's it's very general and very broad, it underscores the point that we don't fully understand these numbers. What fraction of stars host planets that could lead to life? Well, if you're just caring about liquid water on the surface of a rocky planet, that will give you one number.
But if you also include, say, planets that might have liquid water underneath an icy crust, that's a completely different number. And the Drake equation doesn't capture that nuance. It doesn't capture the possibility. We don't understand the numbers that go into the Drake equation. We don't understand their uncertainties at all.
We don't understand how the parameters connect to each other or how their uncertainties connect to each other. In essence, I'm arguing that we don't learn anything by solving, and I hope you can hear my air quotes here, the Drake equation. Have you ever heard the phrase garbage in, garbage out? Read any paper on the Drake equation. I dare you.
They always start with some numbers we know relatively well, like the star formation rate, some good guesses about planet formation around various kinds of stars, but then they start just making things up using all the appropriate scientific jargon. Like, how many how how common is it for a rocky world to generate life? How common is that life to develop intelligence? You you you'll have to make it up, folks, because we have no idea. And then you put in numbers into each of those parameters and out pops a big n, a big number.
The original prediction in that conference that Frank Drake was a part of, when they ran their numbers, they guessed anywhere between a thousand and a hundred million intelligent communicating species in our Milky Way galaxy. That's a difference of a hundred thousand. The latest paper I read on this, and there's a paper every few months on the Drake equation, came out with zero. Zero. There are huge variations in predictions over the decades in using the Drake equation.
All the Drake equation does is encode our assumptions. You could just say, hey, everyone. I think there's, 57 intelligent species in our galaxy. You could just do it. That could be the entirety of your paper.
Or you can run through the machinery of the Drake equation, breaking down each individual parameter, assigning a value to it and an uncertainty to it, assuming how those uncertainties and parameters connect to each other, and end up saying there are 57 intelligent civilizations in the galaxy. What did we learn? What did we accomplish? Did we actually make a prediction, or did we just make a very, very complicated guess? Look at this way.
Let's flip it around. Let's say we had a complete 100% total census of the Milky Way galaxy and we were in contact with all the alien civilizations in the Milky Way, all 57 of them. So now you know the answer, n equals 57. Could you flip that around? Could you flip the Drake equation around and learn about the individual parameters?
No. We would know the answer, but there's no connection between the final answer and the individual parameters. The Drake equation is in physics. Most of the terms do not depend on physics. It's not astronomy either because most of the parameters don't depend on things that we can observe.
I'm gonna go all the way here. I don't think the Drake equation is even science. Don't get me wrong. Don't get me wrong. The question are we alone is definitely something that can be answered using the scientific method.
But the Drake equation is the veneer of science because mathematics is involved, but science is more than math. Math is an essential component of science, but there's more to it. The Drake equation doesn't give me any scientific tools. Because so many of the parameters aren't directly measurable or even estimatable, I can't use the methods of science to give me something that I can rely on. I can't use the Drake equation to make a prediction because all I'm doing is replacing one big guess.
How many civilizations? You know, throw the dart at the dartboard, okay, there's my guess, or I just guess on a bunch of smaller numbers and then mush them together and out pops a number. So let's not take it seriously. So may it's not a physics equation. It's not an astronomy equation.
It may not even be a science equation. Let's not treat it like something real like general relativity or Maxwell's equations or or Newton's second law. Let's not try to estimate the parameters because it's just encoding our ignorance. Is it still useful? Well, a common defense here is it's just meant to spark discussion, try to help organize our thinking.
Well, the discussion has been sparked. Here I am discussing it, so I'll concede that point. But is our thinking about extraterrestrial life really more organized, thanks to the Drake equation? Have we advanced our understanding by taking this problem and putting it in terms of the Drake equation? Did the Drake equation help us learn anything?
Did we make our problems simpler or more easily solvable? Did the parametrization make the conversation about extraterrestrial life easier or did it just shift the discussion to things that don't matter? Because we spend all day arguing about the different parameterization and the importance of the various parameters and the relative levels of uncertainty of the various parameters. That's where the discussion in the Drake equation is, but that doesn't matter. What matters is how many intelligent civilizations are out there.
Because the parametrization is all made up. It's artificial. We don't understand 80% of the parameters. We don't understand their uncertainties or how they connect. And so that's where all the discussion is and not on the thing it's trying to solve, which is how many people can we talk to?
Are we gonna be single for the rest of our lives? Does the Drake equation give us a clear understanding of how intelligence arises in the galaxy? Did we learn about causes? No? Maybe?
I don't think so. All we have to go on is our example, and it's a very limited example of us here on Earth around our Sun. Trying to encode that in something like the Drake equation doesn't help us learn how other intelligent species might arise. It doesn't help. Are we really better off with the Drake equation?
I don't think so. In fact, in some ways I think we're worse off because the discussion is about stuff that doesn't matter. My response to the Drake equation? You want to know if we're alone in the galaxy? That's a great question.
That's a scientific question. Let's go out and measure. Skip the parameterization because we're so ignorant about the parameterization, it doesn't even make sense, and most of it is unknowable anyway. Just measure n, the number of intelligent galaxies. Start counting.
Just start counting. We already have some constraints on it. The chances of life appearing around any one star are somewhere between 0%, which is never, and 100%, which is always. It's obviously greater than zero because here we are. We've got one example.
It's most likely less than a hundred because we see stars all by their lonesome with nothing but dust around them. We're pretty dang sure there's no life around them. Every time we look at a star and don't see any planets, we can reduce the chances from a %. And the longer we listen with SETI and don't hear anything, the we can move the loneliness bubble out further and further within the galaxy and reduce the chances from a %. Every time we find signs of organic molecules or amino acids or liquid water, we can raise the chances from 0%.
The Drake equation tries to tell us how much to move those chances. Like, oh, okay. You see a cloud of organic molecules? Then you need to increase the chances of life appearing around anyone's star by point o o 2%. But we can't make that connection.
All we know is that organic molecules or amino acids or liquid water are nice, and so that emboldens our search. We can't quantify it. We can't quantify it. So just start looking. This is a question and answerable with science, but not through the Drake equation, but through direct observation.
Like I said, feel free to disagree with me. It's fine. I know this is a matter of debate, and I'm happy to engage in the discussion. Feel free to point out things I may have neglected or not thought about. I'm open, totally open to to having it out with you and proving you wrong.
No. No. To to having an open and honest discussion about this topic because I see the Drake equation a lot as representing our scientific inquiry into life outside the Earth, and I don't think the Drake equation is a faithful representative of how science actually operates. If you get a chance, I actually discussed the Drake equation as part of my book, pmsutter.com/book. It's coming out 11/20/2018.
Your Place in the Universe, Understanding Our Big Messy Existence, The Search for Life is a topic that I do discuss, and, yeah, I I basically make all the same points, but in word form. And, I if you wanna meet me and talk to me about this in one of our Astro Tours, that'd be really fun. Go to astrotours.co, going to all sorts of exotic destinations. And feel free to call me up on my radio show, spaceradioshow.com, and we can have a chat live on the air about this. Thanks to my top Patreon contributors this month, Justin g, Kevin o, Christy, and Helga b.
You can go to patreon.com/pmsutter and keep this show going. You can also follow me on all social media channels. My handle is at paul matt sutter. You can go to askaspaceman.com for links to this show, place where you can comment, the whole show archive. It's hilarious.
You can also follow the show on YouTube. That's youtube.com/paulmsudder. Leave a review on iTunes if you think we're alone. Five stars on iTunes, and I'll see you next time for more complete knowledge of time and space.