The Fermi Paradox: Drake's Equation
This video is sponsored by CuriosityStream. Get access to my streaming video service, Nebula, when you sign up for CuriosityStream using the link in the description. Our world represents but one tiny pale blue dot in a sea of darkness, the only bastion of life in the ocean of the night we know of, and yet there seem to be billions of billions of stars and planets, what are the odds our pale blue dot is the only such bastion? Today we'll be looking at the Fermi Paradox and Drake’s Equation. The first of these looks at the probability of other aliens existing, based on the size and age of our universe, while the second highlights the immensity of that scale in space and time. The Drake Equation is essentially a formula for calculating how many alien civilizations there ought to be in our galaxy right now. Today, we’ll be looking at that equation, and plugging in some of the known numbers to see what our estimates might look like.
But we’ll also be highlighting some of the problems with the equation, and the assumptions it can lead to. Dr. Frank Drake, who posited the equation in the form we’ll be considering here, is an accomplished astronomer, astrophysicist, and pioneer in the search for extraterrestrial intelligence. He was actually part of founding the SETI program, and was the creator of the Arecibo message, our own first attempt to say ‘Hello’ on the Galactic scale. So where did this idea come from? Well, the Universe is huge and old, really huge and really old, and by the 1960s it was getting pretty clear just how big our own galaxy was and how likely it was that a lot of those other stars were going to have planets. I’ve heard folks say we were surprised by just how many exoplanets there were, once we’d actually started discovering them, but to be honest I don’t remember anyone thinking otherwise.
Even as a kid in the 1980s first exploring astronomy and science fiction, the usual sentiment was that planets would be fairly common, and it was just a question of how common. Nobody was thinking that a galaxy of billions of stars was going to have anything less than many millions of planets, unless they were thinking it would have effectively none, in case our solar system was a bizarre fluke. The bigger question seemed to be how many of those millions or billions of planets might plausibly be Earth-like, or put another way, how many might conceivably make a home for us in the future. The next question, heavily related, was how many of those same planets might already be home to another civilization.
This is where the Drake equation comes in. In 1961, astronomer Frank Drake proposed a Probabilistic Argument to estimate how many such civilizations there might be. The equation itself is pretty non-controversial, since it’s a very solid basic approach to discussing the notion of alien civilizations in terms of frequency.
But what the factors are, how we determine them, and whether they warp our perspective for discussion, are all factors for debate. I tend to take that latter view, that they warp our perspective, and will get to that in a moment. But first, let’s discuss those factors. Before we even start into the equation itself, we should take a moment to consider that this equation is only discussing the Milky Way Galaxy, which is one issue I have with it, and is something we’ll revisit later.
Secondly, it aims to calculate the number of active civilizations in this galaxy at the moment which we can detect, not which have ever existed. Because of these issues, the equation is often restated with slightly different variables. But for today, we’re focusing on the basics and the original framing. With all that being said, the factors of the Equation are as follows: The Rate at which stars form in our galaxy. The Fraction of stars that have planets, The average number of those planets with potential habitability. The fraction of habitable planets on which life actually develops at some point, The fraction of planets which develop life which is also intelligent, The fraction of intelligent life which develop technology which is detectable to us by its signature, And lastly, the length of time for which that technology is releasing said detectable signature.
As we mentioned earlier, this is often stated differently, but the original notion was about detecting alien civilizations by radio from here on Earth, which is reflected in the way the equation is phrased. Were we to consider it in a more modern context, it's not just that we could speak about some of these factors with tighter constraints, but also that we’d probably rephrase the variables based on what we now know. For example, looking for oxygen absorption lines in an exoplanet’s atmosphere might indicate an ecology existed on that planet, and is another approach to looking for aliens, but it is not in any way dependent on the last three variables of the Drake equation. And there are many other such bio- and techno-signatures which we might reasonably include today, based on the knowledge and technologies we’ve developed in the last 60 years. So too, an alien civilization might abandon a given techno-signature, such as no longer using a power source that generated that signature in favor of a better one, rendering that means of detection a bad one or at least one only good for detecting civilizations in a very short window of usage. People often figure radio signatures themselves are one such short-term techno-signature in favor of some hypothetical faster than light, or FTL, communication system.
Bio-signatures are potentially handier as detection methods, because we know nothing about those last three variables, the ones relating to alien life. On the other hand, we have the first and second ones, star formation rate and planets-per-star, pinned down pretty well at this point, to at least an order of magnitude. Truth be told, we wouldn’t really care about star formation rates these days. If you’re a channel regular, you’ve probably heard me talk about why certain terms and phrases, like ‘our sun is a yellow dwarf star’, are rather outdated. This is because when we came up with these terms, we were still missing large pieces of information we now know: the number of different sized stars, for instance, or how long they live.
We also hadn’t really locked on the Age of the Universe by then, the Big Bang model had only been proposed a generation before, and I’m not even sure if we had switched to calling it the- Big Bang yet. It was originally used as a derogatory reference to the theory - we may have still been calling it the Primeval Atom Hypothesis, the original name proposed for the Big Bang. Even with the original variables, we can apply some knowledge from today: very few of the stars which have formed, and which could plausibly have had life like ours evolve around them, are likely to have expired by the present day.
The big giant stars that represent the lionshare of visibly-dying stars don’t stick around long enough for the likely evolution of complex life, and very nearly every star has planets, so we can probably safely just assume there are at least 100 billion stars in this galaxy with at least one planet, probably more. There are likely trillions of planets. The rate of formation has more to do with the assumption that civilizations pop up on a life-bearing planet after 4 billion years or so, then disappear at some point.
I really do think that suffers from both assuming that life arrives at complex intelligence at the same rate as Earth, and that civilizations inevitably wipe themselves out. This seemed to be a very common view of scientists and academics during the days of the Cold War. I’m sure it will come as no surprise that I disagree with both of those assumptions. The first one is overly simplistic, and overlooks all of the variables involved in the story of life and civilization, as though it should be exactly the same in every case, regardless of factors such as elemental abundance, ecological relationships, and important events.
As for the second, I’d personally caution folks about being overly fatalistic or pessimistic about their fellow humans, and have never thought it very likely you could have a doomsday scenario that got everybody, without replacing them with other folks of a different type. In considering the Drake equation, we have to imagine this as being almost insignificant, since it would only generate a pause in detectability. Even if you nuke yourselves, some folks will generally survive, and nobody in the Cold War was aiming for ‘wipe out humanity’ as their end-goal, nor were any of our weapons capable of doing so at the time. Fallout does not last forever, and humans breed pretty quickly on galactic timelines.
Even if you kill off 99% of the population, a couple of centuries later everything is rebuilt and your numbers are restored. Alternatively, if you get replaced by some killer machine intelligence, it doesn't really matter to the Fermi Paradox anymore than us replacing the Neaderthals would: for our purposes, it’s still an intelligence. And that’s a good example too, because we really didn’t replace the Neanderthals, and any artificial intelligence or other civilization replacing us is likely to be at least part-human in some fashion, even if it’s a metaphorical kinship as in the case of AI or uplifted animals, like super-intelligent humanoid cats, dogs, or dolphins. A lot of times the future doesn’t belong to A or B, but some hybrid of both. An individual or group which replaces another generally has some superior array of traits, though that might mean they are more coordinated and generous or more hyper-aggressive or very good at being sneaky and stabbing folks in the back.
Most of these options actually make a replacement species more likely to be detected, not because they are necessarily more likely to be broadcasting hello signals into space, but because we generally see signatures of civilizations. In general the more successful something is, the more noticeable it is. It is often suggested that they might hide, and we’ll come back to that point later too, but I would point out for now that civilizations hiding themselves is not a tactic that seems common in our own history. Cities and nations don’t hide themselves, but are far more likely to spend tons of money on various monuments and attractions to advertise themselves, and building roads and infrastructure to connect with other peoples and places. While there are numerous reasons a group may or may not advertise itself in some form or another, either directly or indirectly so, it seems fair to say that we observe this behaviour as a general rule.
Conversely, groups which choose to hide themselves are typically doing so to deliberately avoid a larger, potentially dangerous civilization, which by necessity they must be aware of in order to know there’s something to avoid. With the Fermi Paradox, we’re not talking about trying to find a specific hidden alien civilization, but any of them at all, so while we might miss one civilization hiding from another, it’s extremely unlikely that we’d miss who they were hiding from. Some civilizations might attempt to hide, while others might blow themselves up, or fail to recover from another sort of doomsday event. But with a bit of reflection, it seems like this group might be the minority. Let’s take an example: still assuming that at least 100 billion stars in our galaxy have planets, we’re left with five remaining factors to consider. If we assume that only 10% of stars have planets, and that of those only a further 10% are potentially able to support life, and only 10% of those actually developed life at some point, and only 10% of those developed intelligent life, and finally, that only a tenth of all such civilizations ever released detectable signature into space, we would still have had 10 million such detectable civilizations throughout our galactic history.
I’d argue that if even 10 million civilizations reached our technological level, it’s likely that at least one of them would not be self-destructive or replaced by something which was, especially since it seems more probable that such cases should be the majority, rather than some freak minority. Let’s discuss that more, though. Drake’s Equation, the Fermi Paradox, and SETI - the Search for Extraterrestrial Intelligence, principally by radio signals - all suffer from being a bit outdated, conceptually speaking.
Outside of Science Fiction, nobody was realistically expecting galactic empires to exist when these ideas were developed, and that hasn’t really changed. Such a civilization would need to rely on faster than light travel and communication, and current science says that probably is not in the cards for the future, if it’s possible at all. But historically, it was less about FTL, and more about materials and energy. It merits consideration that when Drake first posited his equation, we hadn’t even been to the Moon. And while nuclear designs for spaceships were being considered as a basic concept, even then, the notion of sending a crewed mission on a centuries-long voyage to another star seemed like a long shot, the sort of thing a civilization might only do once or twice over their entire collective existence, perhaps in order to save themselves from an extinction event.
If radio communications are a consideration, as the Drake equation originally assumed, then on the scale of interstellar empires they are likely to be extremely loud and fairly easy to see, due to various issues involved. But if we’re looking at anything smaller than that, where we’re trying to hear from a single planet or solar system among billions of duds, it’s a proverbial needle in a haystack, trying to find maybe a handful of planets transmitting faint, undirected radio sources. For the sake of context, let’s consider ourselves: even if we were looking directly at ourselves, we likely wouldn’t be able to hear our own civilization from beyond a very small pocket of the galaxy, much less from significantly further away. Civilization has existed here for thousands of years, but our transmissions haven’t reached out very far, and probably blend into the larger background on the galactic scale, so if we’re still assuming others would follow the model of life on Earth, why would we expect them to be any different? There’s also no real reason to assume alien civilizations would broadcast louder in the future unless they decided to stick with omnidirectional radio signals. Rather, it’s more likely that more advanced technology would make such broadcasts more difficult to find, since technology tends to favor weaker signals with higher compression rates that make them look like noise.
In fact, that’s the whole point of compression: to remove patterns by replacing them with a short note describing that pattern, effectively removing parts of the message to the point that it would be difficult to understand even if it were somehow picked up and determined to be alien in origin. Also, given the fall-off of radio signals, dropping as an inverse square to the broadcast distance, it would seem like interplanetary and interstellar communication would most likely use directed signals. Laser beams broaden with distance too, but using one to send a message to a distant location avoids using a lot of power and significantly extends your range. But in terms of detection, unless these beams were using significant amounts of energy, spotting them might be more difficult than the sort of idealized, symmetrically-transmitting civilization the Drake equation seems to assume. So if we could see only a millionth of the Milky Way Galaxy by radio, and only 10 million civilizations had ever existed in the galaxy, we’d only expect to ever see around 10 of them.
If they didn’t really spread out, but maybe colonized a few other neighboring systems to avoid having all their eggs in one basket, then it is still basically ten. And if they didn’t last for billions of years, but only a few millennia or centuries, then the odds that any would still be around at the same time as us for our instruments to hear them would be parallel to winning the lottery. And this makes a lot of sense too, considering the context. A lot of folks thought that giving us coin-flip odds of surviving the Cold War was being generous, and if we assume such generosity could be stated as having a 50/50 chance of surviving a given century, then our odds of surviving two centuries would be 1 in 4, our odds of surviving 3 centuries would be 1 in 8, our odds of surviving 4 centuries, 1 in 16, and our odds of surviving 10 centuries would be 1 in 1024. Of surviving 10,000 years, just 1 in a million. And ten thousand years is a very short detection period on the galactic scale.
Now, there are a ton of flaws in those assumptions, which we’ve discussed in more detail throughout our series on the Fermi Paradox and Alien Civilizations, but I wanted to restate them here for context. It’s important to understand that in the 1960s when these concepts were new, the assumption that alien signals would be hard to detect actually made a lot of sense. Of course, on this show we have a few counters to that argument, including the Hart Conjecture, the Hart-Tipler Argument, the Dyson Dilemma, and finally the general notion that even Intergalactic Colonization should be possible without resorting to FTL. Without going into depth, Michael Hart is an Astrophysicist who in 1975 did a detailed analysis of the Fermi Paradox, which is when it got its name, and who essentially argues that interstellar colonization should be possible and that life, which he argues evolves to be pro-growth, would make efforts toward furthering its expansion.
We can imagine this to mean that if a civilization settles their neighboring star systems, it follows that they should eventually continue to do the same, exponentially spreading outward. The analogy I like for this is that early humans spread over the whole planet without needing to coordinate with each other or sending out colonists from a single origin point, presumably somewhere in Africa. Instead, we established new regions, new economies, and new bases for expansion along the way. Each successive group has a motive to split and send out new colonies, dividing to produce more, and so on. Cosmologist Frank Tipler essentially added on the notion that this could be done through the assistance of machines, as a way of getting around the various issues with conventional Generation Ships, namely that the original colonists would have long since died off before they arrived at the colony world, not too mention the difficulty of maintaining a closed ecology in a spaceship in deep space, then setting one up on a new planet when you finally arrive.
We tend to take that ability for granted on this show not because it is easy but because we have discussed the challenges and problems in depth, see our Generation Ships Series for details on that. Some folks feel that the Fermi Paradox should be renamed the Fermi-Hart Paradox, or the Fermi-Hart-Tipler Paradox, in part because Fermi himself didn’t regard it as a paradox, he just figured aliens were rare, that civilizations are probably short-lived compared to galaxies, and that interstellar travel wasn’t viable, which, as we noted earlier, would solve the problem entirely if true. I doubt we will ever see it renamed though, as sadly both Hart and Tipler have unenviable reputations unrelated to the Paradox which we won’t delve into here. The Dyson Dilemma, which I’ve often regretted naming such myself, basically argues that civilizations don’t really colonize planets, anymore than we colonized mountain caves, but instead would tend to build up artificial structures from available raw materials. Things like the O’Neill Cylinder, vast artificial habitats which make use of regionally-available raw materials to create an artificial living area. Just as your average house or apartment complex is significantly more efficient and useful by comparison to a cave, a space habitat with around a million times more efficiency than a planet has a similar analogy.
Continuing with the idea that it makes sense on such a scale to eventually build a house in space, we can imagine that larger civilizations would continue to build such habitats, creating the analogy to a city, if we’re still thinking of the planet like a cave. Even well before that point, a civilization is likely going to want other resources in space, with energy being a primary concern. Since our Sun puts out a couple billion times more sunlight than what lands on Earth and powers our ecosystem, it might be a reasonable assumption that home stars gradually become wrapped up by such artificial habitats and power collecting structures, until they either englobe the thing completely - what is called a Dyson Sphere or Dyson Swarm - or until they run out of raw materials.
Such a process, even partially complete, would alter a star’s visible spectrum and brightness, with anything approaching total englobement effectively dimming the star into the waste heat frequencies of the infrared range. In an ideal form, such constructs would appear mostly dark, being visible only in that they would still be warmed by the starlight as they use it. Finding these objects is what’s referred to as Dysonian SETI, and we would solidly classify such a civilization as being “type 2” on the Kardashev Scale. While perhaps not as well known, this represents another major type of SETI, hunting for the infrared emission or techno-signature of such objects rather than radio signals. Civilizations which would be capable of even small-scale structures on this level would represent populations millions, if not billions of times greater than our own, but rather than spread out, they’re packed into a single star system.
No FTL, advanced communications, or loud noises required for this model. And with a few modifications, those O‘Neil Cylinders and similar constructs also present the basic framework for ideal generation ships, if you were to strap an engine on the back. More importantly though, the sheer power available to such civilizations makes sending such ships to other systems possible, and not at a slow crawl either, but at an appreciable fraction of light speed.
What’s more, those civilizations are not limited to finding only rare ideal planets around rare G-types stars: since they’re working with the raw resources of planets and other objects, they can essentially build copies of their civilization around any star with enough components in its neighbourhood. Like a pioneer building a cabin in the woods, as long as they have trees to make logs - in this case, asteroids, planets, and even the star itself - they can build their home anywhere they please, not where they find a comfortable cave. Given that this would make colonization comparatively easy after a certain point, the Dyson Dilemma, is essentially the argument that unless some factor prevents or dissuades a civilization from participating in this type of expansion, it seems implausible that they wouldn’t eventually do so. Once they’ve spread out a bit, they shouldn’t really be subject to extinction events, and since each new colony would have the capacity to continue the expansion, it should self-perpetuate across the whole galaxy, and even beyond.
If we consider the possibility that this could be the case, if even a single such civilization ever arose in the galaxy and successfully pursued that policy, they should have colonized the whole place by now to an extent that we couldn’t possibly miss them. And considering the time scale we’re dealing with, it most likely wouldn’t be just our own galaxy, but probably the whole supercluster of thousands of galaxies by now. Again, see our Dyson Dilemma episodes and Generation Ships series for more detailed discussion of that concept and the methods that should make it possible. Back to Drake’s Equation. This intergalactic issue is one of the big flaws, since you can’t just run your numbers on our own galaxy. If you’re not contemplating massive self-perpetuating interstellar colonization, with or without FTL travel, then other galaxies don’t matter, so leaving it out of the equation at the time made perfect sense, and was necessary in any case since we had no idea how big the Universe was in terms of galaxies at the time.
That first factor then, the rate of star formation in our galaxy, is not enough from the perspective of an intergalactic scale. But this is something folks often seem to skip over anyway. Even when I mentioned it earlier, it was to say how many stars were in the galaxy, not a discussion of the rate at which they form. This is because a precise formation rate is hard to pin down, since we still don’t know how many stars there are, or exactly what their breakdown is in terms of type and lifespan.
They also tend to form in clumps of space and time from events that cause lots of them to be birthed, like nebulae and supernovae. But if it’s around a hundred stars per year in our galaxy, on average, it would seem pretty solid to say that probably at least 10 stars per year are likely to have both the lifespan to support planetary evolution, and some form of rocky planet or moon that falls into the loose range of being life-plausible. That factor, the average number of life-potential planets per star that has planets, is a total wild card. And it only gets worse, since it’s actually the only factor we can really even guess about, with all the remaining factors being complete unknowns. Folks often talk about how we have pinned Drake’s Equation down a lot more these days, but we really haven’t. Rather, all we have is a better understanding of some of the data for the first variable, and some better-informed ideas about how the others might look.
All we really know, in the context of the equation, is that most stars probably have planets, and that the galaxy has about half a trillion stars. We also now know that there are billions of galaxies, and indeed a lot of stars in between those galaxies as well. But again, all this really does is change the educated guess we make about that first factor. It lets us go from guesses about 1 in 10 stars having planets, to talking about 1 in 100 or 9 in 10 having them, an uncertainty of a couple orders of magnitude dropped to less than one, and while that’s certainly helpful, it ultimately changes very little. It also has the downside of introducing a mental bias, because we start by talking about that first factor of planets around stars, and tend to frame it as somewhere between 1% and 99%, which frequently gets simplified to 1 in 10, and we seem to tend toward assuming that the other factors are probably in that range as well. We did that earlier in this episode, specifically saying 1 in 10, and still ending up with 10 million civilizations having existed in our galaxy at some point.
Even if we decided that each of those factors was only 1 in 100, it would only have dropped down to 10,000 civilizations. What’s crucially missing here is that final factor, how long they exist and are detectable, and if they can and do expand into the galaxy, which isn’t considered in the 10,000 we’ve arrived at, and it matters a lot. A civilization that’s spread throughout the galaxy is probably detectable forever, or at least on fairly arbitrary timescales, whereas one that lasts a mere million years still represents less than a thousandth of the period the galaxy could plausibly have had intelligent life in it. In this case, it gets a lot more believable that we just aren’t in the one-millionth of the galaxy where their radio signals could be heard during the tiny fraction of time their civilization was around out of a few billion years civilizations could have been around. And for perspective, we should probably consider that such a civilization, lasting for a mere million years, would still have existed for over one hundred times longer than our own.
If a civilization sticks to one planet, it’s a lot more plausible they’ll die off eventually, but you don’t really need them to do so in order to solve the Paradox, because you just have to find values for the other 4 factors which add up to one in a million or less. All that’s needed is for each of them to be 1% or less. Indeed, given that 100 cubed is a million, if one of those factors was 100% the others could still be 1% and still make hearing a civilization less likely than not. Another big flaw though is not with the equation itself, but with how it’s framed. Probabilistic arguments are only meant as loose setups until you can get better data, and people have a tendency to assume each term is in the same general region of likelihood.
All those factors might be 1 in 10 except 1 of them, and the probability could end up being 1 in 10 quintillion, rather than a smaller number we might be expecting based on intuition. The probability of the others doesn’t matter. As an example, if we did a version of Drake’s Equation to calculate your odds of winning the state lottery, I might set that up as saying it was the product of your odds of living in a country that has states, the probability those states can have a lottery, the probability you live in one that does, the probability you regular visit a place that sells tickets, the probability you ever buy one, and the probability a ticket is a winner. All those early factors were somewhere in the 1 in 10 or better region, but that last one is very low. Indeed knowing the last one is low might discourage people from buying tickets, lowering the second to last factor’s probability, because it is a bad idea, lowering the odds further of winning. That’s an important thing to remember about probabilistic arguments, such as the Doomsday Argument, people often get locked into viewing them as immovable and not subject to intelligent critters contemplating them and altering their behavior.
Many probabilistic arguments can seem very convincing once considered mathematically even when intuition on first hearing them says they’re wrong, and often that is quite true. What’s more, the number of factors is arbitrary, so if you have one that has eight factors and one that has six, and you’re estimating loosely by assuming it’s all 1 in 10 per factor. With six, you’re looking at 1 in a million, while eight gets you 1 in 100 million. And unfortunately, that’s easy to do with Drake’s Equation.
Factors 3 and 4, the probability of planets that can potentially support life and the probability that life actually develops, could easily be rolled into one factor, or split into another to include complex life that develops Eukaryotic life, biological cells with nuclei, one of the more popularly suggested Great Filters life must evolve through before it can get to that final status as a detectable alien civilization. Now, all this just represents a tendency toward mental bias in folks considering the Fermi Paradox and Drake’s Equation, and it’s not actually a flaw in the math or in the equation itself. But over many years of discussing the Fermi Paradox with thousands of people, I would rate that as probably one of the most significant problems it encounters. Folks just look at it, hear the first coupled factors, and say “Well surely, even if it’s 1 in a million, if there are billions of worlds, there must be life”, but nothing about the equation itself implies only 1 in a million, or even 1 in a quintillion.
Another missing factor relates to zones of detectability. Again, if we’re assuming that we’re just listening for copies of ourselves, of other folks broadcasting terrestrial radio and TV and occasionally a louder or more deliberate shout, then we would have problems hearing that outside of a radius of some hundreds of light years. That area would not contain even a million stars, let alone a million plausible stars for Earth-like worlds, and would represent only around a millionth of the stars in the galaxy.
The odds of hearing, or being heard, could be fairly low indeed. Of course, you can build much bigger transmitters, and much bigger receivers, see our Mega Telescopes episode, but we can say with pretty decent certainty what that factor should be for us looking for our analogue,and it cuts nearly all of the galaxy out except for a tiny little volume of space some hundreds of light years around, with the galaxy being a hundred thousand light years across. To be fair, aliens might be much louder, but there’s no reason to assume they would be if they’re only transmitting within their home system, and maybe to some nearby neighbors with tight beam signals. Alternatively, if they didn’t, then the entire final factor of civilization duration can be removed or treated as a value of 1. Let’s dwell on that a little more, because that final factor, where a world has made it through all of the filters to having technologically advanced life emitting radio could have existed for only a millionth of the time the galaxy has been around, and was detectable to only those nearest stars occupying a millionth of that galaxy, or they could have spread out across the galaxy and endured in various forms since they first invented rockets, potentially for billions of years.
The difference between those two scenarios is a factor of a trillion. That’s the difference between a single star, and an entire large galaxy, the difference between one small shack that existed for a few days, and every structure on this planet that we have ever built in the history of our existence. It is the difference between running into intelligent life on a planet that’s been inhabited for centuries with vast empires and civilizations, or bumping into one random alien survey team that just happens to be investigating the same planet as you. And that’s just the impact of that one final factor meant for contemplating our odds of detecting them if they ever even existed at all. So yes, we can nail down that first factor, stars having planets, as being very high, and we can probably nail down the second factor of planets with the right size and temperature as being decently common - though those two likely don’t include all the options for letting a planet potentially support life. But we have no idea about the odds of life actually emerging, much less all the factors which might be involved, and getting to intelligence is another matter entirely, with a myriad of other factors varying in probability to consider.
Even if we get through all of that, we still have the final factor for longevity and detectability to consider, which can be anywhere between 1-in-a-trillion, and near certainty. Every time we have a new discovery relating to exoplanets, or a solution to some astronomical or geological phenomena which adds new insight to our origins, folks ask if we can finally pin down Drake’s Equation. The answer, as we’ve seen today, is no. There’s just too many unknowns involved, and clearing some up only changes things in a Bayesian sense. If we don’t know how probable something is, we can still have a discovery that tells us that it’s twice as likely or unlikely as before, but it really doesn’t help us. We still wouldn’t know if it was near certain, or worse than the odds of winning the lottery ten times in a row.
Fundamentally, 60 years after its been proposed, I think it is worth asking not whether Drake’s Equation is right or wrong, but rather if discussing it really helps us solve the Fermi Paradox. Truth be told, we won’t actually know the answer to those variables until we have discovered hundreds of worlds with alien life and had the chance to examine them, and even then all that will really tell us is that it is possible for intelligent life - our own species- to arise on a planet, and journey to hundreds of others with life, thus implying that final factor of longevity and detectability is high, and that the other factors about the potential for life to arise might be based on how many planets we find where life hasn’t been found, versus where it has. But we still wouldn’t know about the rest, and could still only arrive at educated guesses at best.
The implication of searching a million star systems and finding life on a hundred of them, but no highly intelligent life, would be that life probably evolves often enough, 1 in 10,000 systems, or 40 million in the galaxy, but that technology develops very rarely, since we could only find one example and could show that one example - us - had the ability to spread throughout the galaxy by investigating all those worlds in person. It’s the Catch-22 of the Fermi Paradox. Since we’ve already done a lot of astronomy looking for radio signals and for the infrared signatures of Dyson Swarms, unless someone stops by to tell us they exist, we’ll probably only get the answer by going out there and investigating in detail. And that act of investigating itself will ultimately answer as many questions about the Fermi Paradox as the results of the investigations. In the end, the only way to prove if anybody else is out there, unless they come to us, is to go to them, and that’s just one more reason why we should head out into space, in case avoiding being wiped out by misfortune by staying on our one lone world, our pale blue dot, wasn’t enough reason to venture into the galaxy. Our episode ran rather long today, as it often does with Fermi Paradox episodes, so I cut out some discussion of human population growth rates and why they are not declining, as that’s a popular objection to the notion of galactic expansion.
It also tends to be a touchy topic that might cause a stir with Youtube’s Algorithms, so it’s doubly ideal for a Nebula Extended Edition, and if you’d like to catch that discussion or any of our other extended editions on Nebula, they do replace our sponsor reads. Our episodes come out on Nebula early and ad free, and we do have some exclusive episodes, like our Coexistence with Alien Series as well as these new Nebula Plus Extended editions. Now you can subscribe to Nebula all by itself but we have partnered up with CuriosityStream, the home of thousands of great educational videos, to offer Nebula for free as a bonus if you sign up for CuriosityStream using the link in our episode description. This means you can watch all the amazing content on Curiositystream, like the “Is Anybody Out There” which delves into the SETI Project of looking for alien signals and habitable exoplanets, but also all the great content over on Nebula from myself and many others.
And you can get all that for less than $15 by using the link in the episode’s description. I mentioned us discussing population growth or a lack thereof as a reason civilizations might not colonize the galaxy, and a missing chunk of that is that we have good reason to think Lifespans will keep going up, potentially radically so, and especially if that included an extension in fertility which would have massive impact on population. You can have a lot of kids in a few centuries if you’re so inclined, and that is one of the Effects of Longer Lifespans and this weekend we’ll have our monthly SciFi Sunday Bonus episode to look at other effects.
Then next Thursday, April 15, we’ll look at another challenge future civilizations might have in terms of creating a sense of purpose in a post-scarcity near-utopian world, one which may not be populated by modern humans in the biological or psychological sense, and something we’ll look at in two weeks as we examine Transhumanism and Post-humans. Then we’ll wrap April up with another Fermi Paradox Episode, where we will ask what the impact and changes to our discussion of the topic are when we contemplate concepts like Multiverses and the Many Worlds Interpretation of Quantum Mechanics. If you want alerts when those and other episodes come out, make sure to subscribe to the channel, and if you’d like to help support future episodes, you can donate to us on Patreon, or our website, IsaacArthur.net, which are linked in the episode description below, along
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