If you’re a fan of Science Fiction, or just really keen for humans to find alien life, you might have heard of the Drake equation.

It was coined in 1961 by astronomer Frank Drake, and it provides an estimate for how many advanced alien civilizations there could be in our galaxy. But I hate to break it to you. 1961 was over 60 years ago.

And three decades before we discovered any planets beyond our solar system. In all that time, astronomers  have been able to learn a lot more about how the universe ticks. How abundant the ingredients of life are.

And what conditions may or may not be necessary to give rise to life. So, the question we have here at SciShow is this: Is there any value in going back to that equation? Or should we come up with  something entirely brand new? [intro jingle] For everyone who doesn’t have the original Drake equation etched into their memory… including me…it looks like this.

In some versions, the multiplication signs aren’t there, but remember that’s really the only kind of math this formula really makes you do. And I know that’s a lot of letters. But I am here to walk you through them.

N is the number of alien civilizations that live in a given galaxy. And that given galaxy is almost always ours, the Milky Way. For the terms on the right  side of that equals sign, you can think of each as belonging to one of three groups.

Astronomical, biological, and social. R* is the formation rate of stars in a galaxy. How many stars form every year, on average.

Fp is the fraction of stars in  that galaxy that have planets. Ne is the average number  of planets per solar system that are potentially habitable. Fl is the fraction of habitable  planets that actually develop life.

Fi is the fraction of those inhabited planets that manage to develop life  where that life is intelligent. And then Fc is the fraction of those planets where intelligent life has developed technology we can detect from Earth... And finally, L is the average time that technology is going to be broadcasting into space.

Not how long the civilization has been around… just how long they’ve been able  to “talk” with the universe. Like, even though anatomical humans have been around for a couple  hundred thousand years, give or take, our radio signals have been leaking into space for a lot closer to like a single century. And now you might be screaming, why does this even matter?

It’s not like it shows us where the rest of those N civilizations are, or puts us into contact with them or anything. Well, technically, the Drake Equation was always more of a conversation starter than a truly helpful equation. Which I say with all the love in the world.

Frank Drake created it to help  organize a radio astronomy conference. It was a way to get astronomers thinking about what things they’d need to  know to answer the question “How many aliens are out there?” And at the time, only R* had  any kind of estimated value. But Now we’ve got a little more to go on.

And over the decades, astronomers have learned enough to start debating whether the Drake equation needs a makeover, or just needs to retire. One revision from 2013 proposed simplifying  the entire Drake equation to just this: Well, simplifying in terms  of aesthetics, at least. This version basically  recognizes those three groups I mentioned before, but also smooshes most of the biological and social stuff together.

It’s not really less complex. In fact, when you peer under the hood, it’s probably even more complex because of  how complicated the universe turned out to be. First, we’ll take a look at what’s hiding in that deceptively simple Rastro term.

Over the past six decades,  astronomers have learned just how not-constant the original R* term is. Cause It turns out a galaxy’s star formation rate evolves over time. And when it comes to hosting planets, not all stars are equal.

Different kinds of stars are better or worse at forming different kinds of planets… especially habitable planets. For example, red dwarfs can go through a stellar version of the Terrible Twos that strips planets of their atmospheres. Meanwhile, stars that are similar in  mass to our Sun evolve pretty fast.

And shorter life spans mean  shorter amounts of time that a planet can host life. So according to many astronomers, it’s actually the stars  in-between red dwarfs and our Sun, called K stars, that are our best bet for habitable planets. But even three decades in, we’re still  in the early days for exoplanet research.

Astronomers have identified… like… 30 rocky worlds that could maybe, hypothetically, host life as we know it. And our search for these  worlds is still very biased. But not towards our own setup, like trying to find Earth 2.0 around Sun 2.0.

It’s actually biased toward  finding planetary systems where the planets orbit  really close to their stars, just because it’s a lot  easier to see those planets. So we’re still working out how many planets we’re really dealing with out there even before considering the lack of nuance brought to you by the Habitable Zone. What’s that, you ask?

A Habitable Zone attempts to predict where a planet could orbit a given star and maintain liquid water on its surface. Because liquid water is a critical ingredient for life as we know it. But a planet just being in the Habitable Zone doesn’t mean it’s actually habitable.

For example, red dwarfs are small and dim, so their habitable zones are super close. Not only close enough for a planet to get its atmosphere stripped away, but close enough for the star’s gravity to sometimes lock the planet into place… one half in perpetual day, and  the other half in perpetual night. In contrast, just because a planet isn’t  in its star’s Habitable Zone doesn’t mean it’s uninhabitable.

For one thing, a star’s Habitable Zone actually migrates as it ages. So when life first arose on  Earth 3.8-ish billion years ago, our planet wasn’t inside the Sun’s habitable zone. Supposedly, it was too far out, and any liquid surface water  should have been a bunch of ice.

But Earth had a thick atmosphere full of greenhouse gasses that kept it warm. Then, there’s the fact that planets are not the only worlds that  could potentially host life. They may not have appeared in any  part of Drake’s original equation, but any good conversation about  habitable worlds these days is eventually gonna turn to moons.

Moons like Europa, which thanks to its gravitational interaction with Jupiter and its lunar siblings, has a salty ocean buried  underneath kilometers of ice. And get this: the Europa Clipper mission, which is set to launch in October 2024, has a little silver plate engraved with, among other things… the original Drake Equation. So it’s clear that some NASA nerds  still hold it in their hearts, even if other astronomers want to re-work it.

And with that rework have come  attempts to actually calculate Rastro, or similar terms. For example, that 2013 paper estimates that one habitable planet forms  in our galaxy every 10 years. But that really is just a starting point for whatever the rest of the equation looks like.

So let’s move onto Fbiotec, which smooshes together all the terms from the original Drake equation that deal with life actually evolving on potentially habitable worlds, and also evolving enough to  produce signals we can detect. Unfortunately, here’s where  we run into a bit of a wall. Astronomers can try to use Earth as a proxy, but we don’t know how easy it is for a planet to produce life, let alone intelligent life, because we only know of one  place where it happened.

And everywhere else, we’ve only  found the ingredients for life, like water, carbon, and nitrogen. Although to be fair, certain ingredients seem to be, like, everywhere. We’ve found them on moons, on asteroids, there were even some complex organic molecules found floating loose in protoplanetary disks.

But it’s all a far cry from life itself. That being said, the Drake equation and its re-worked successor don’t seem to be accounting for  everything they might need to. Like… what about aliens  colonizing uninhabited planets?

Or what if some aliens are populating planets with robotic probes that can send signals implying there’s life on that planet, even though there isn’t? Or what if an alien civilization got wiped out, but the technology it left  behind kept transmitting? . Are we going to have to argue about alien AI before we figure out what  constitutes AI down here?

Well… maybe. One paper from 2020 used the Drake equation to estimate the number of potential  artificial civilizations in the galaxy, and compare it to the number of  potential biological civilizations the original Drake equation was focused on. AI civilizations often wound up  outnumbering the biological ones.

So our search for life may actually be more likely to turn up super  incredibly intelligent computers. Which is a… really wild concept. And also a super creative  use of the Drake equation.

But again… not really what Drake had in mind with the original. All those non-straightforward  ‘civilization’-establishing considerations are pretty new. And those are some pretty  big holes to fill in order to really feel like we’ve covered  all our extraterrestrial bases.

But maybe that’s more than you really need. If you think the 2013 version  is as simple as it gets, Drake himself is about to rock your world. The most important term in this equation is time, which Drake believed so much that he had a license plate that read NEQLSL.

And here’s the thing. We don’t have to limit our search to the kind of proverbial yelling that Drake originally had. The original formula was focused on aliens sending radio signals out into the universe, but we can try to hunt for other  signs of alien civilizations.

Or, we can focus on biosignatures that may tell us whether  there’s any life on a planet, like, at all. Now that we have more flexible and sensitive tech, we’re not limited to only listening for the  loudest signals of extraterrestrial life. For example, we can see if a planet has a significant amount of  oxygen gas in its atmosphere, perhaps maybe that’s an  alien form of photosynthesis.

And compared to a century of radio waves, life has been pumping oxygen  into Earth’s atmosphere for like two billion years. In other words, we’re not just chopping off some of those later terms based on intelligent life evolving and developing. We’re jacking up the values we can plug in for L. and ultimately, a  biosignature-based Drake equation requires a different kind of rewrite than a mere smooshing together of terms.

We have to reconceptualize what’s important. Will we really only be  satisfied once we find an alien that can tell us to live long and prosper? Or given how much our technology has progressed since Star Trek went on the air, maybe we lean in to finding any  definitive signs that life exists beyond this tiny blue dot  floating through the cosmos.

We can still etch the original Drake equation into our spacecraft plates, though. It’d be a solid conversation  starter for any aliens that want to hear the story of how we eventually found them. And if I had my way, I’d sneak into whatever factory they’re making those plates and carve a thank you to our patrons.

Because I want the aliens to know how much your support means to us as well. You’re awesome. Thanks for watching. [ OUTRO ]