The Aliens Are Coming!

by Ben Miller

  Drake needed to set the pace for the conference, and—much in the mould of Fermi a decade earlier—decided the best way to do that would be to estimate the number of civilizations in the galaxy, N, that we might be able to receive signals from. The equation he came up with has become a landmark in the quest to communicate with alien intelligence, and here it is in all its glory:

  N = R* × fp × ne × fl × fi × fc × L

  Trust me, it looks a lot more ferocious than it is. And as a way of breaking it down, I want to take you to a Dire Straits gig.

  BROTHERS IN ARMS

  Specifically, I want to take you to Wembley Arena in the UK for the British leg of Dire Straits’ famous 1985–6 world tour. Their latest album, Brothers in Arms, has gone multi-platinum, and the 12,500-seat venue is packed to the rafters. The band close the show with their monster hit “Money for Nothing.” Tired but happy, the army of fans make for the exit. But wait. The band come back onstage for an encore. Mark Knopfler strikes up the opening chords of the album’s title track. Out in the corridors and turnstiles, the crowd hear that there is more to come, and about-turn.

  Back in the auditorium, the seats start to fill. “These mist-covered mountains . . . “ sings Mark. And one by one, they appear; cigarette lighters, held silently aloft. Human souls share the tender beauty of the song. Mark adjusts his sweatband and looks out into the darkness. It’s a deeply affecting sight, but let’s put our practical hats on for a moment. How many lit lighters does he see?

  You might think it depends on how much of the song Mark plays before he looks up. Surely, you say, the number of lit lighters will slowly build up during the song as more fans enter the auditorium. If Mr. Knopfler looks up after a minute, he’ll see fewer lighters than if he looks up during the final few bars. But that’s not necessarily the case.

  It all depends on how long the lighters shine for. To see what I mean, let’s imagine only one fan has a lighter, and that he can only keep it alight for thirty seconds before he burns his fingers. On average, will Mark see the light? Instinct will tell you he probably won’t. For a start, he might look up before the fan has even entered. Or he might look up after the fan has entered, but after the light has gone out.

  OK. So how many fans with lighters do we need to enter the auditorium during the four-minute song in order for Mark to see at least one light? This is where math comes in handy. Because to get the average number of lit lighters that Mark sees, we just need to multiply the rate at which fans with lighters enter the stadium by the length of time that they can keep them alight.8 For example, let’s say that eight fans with lighters enter the stadium during the song. In that case, the rate is 8/(4x60) fans per second, and the average number of lit lighters at any one time is

  Rate × length of time alight = 8/(4×60) × 30 = 1

  Interesting, eh? In other words, even if eight fans enter with lighters during the encore, on average when Mark looks up he will see only a single light.

  MONEY FOR NOTHING

  Right, now we know the principle of how this works, let’s get down to some gritty detail. Obviously with a capacity crowd of 12,500 fans, our current figure of eight fans with lighters entering during the course of the song is way out. How can we more accurately estimate the true number?

  There’s going to have to be a bit of guesswork here. Could all of the fans make it back into the arena during the four-minute encore? Based on the recent Bill Bailey gig I attended, I’m going to say “yes.” There will inevitably be a bit of a bottleneck at the entrances, but Wembley Arena is well served by generously proportioned walkways with exemplary signage. In fact, I am going to be so bold as to say that 10,000 of the fans make it back into the auditorium during the course of the four-minute song. That’s a rate of 10,000/4×60 = 42 fans per second.

  But wait. Not all of those fans will be carrying lighters. For a start, not all Dire Straits fans are smokers; in fact I would say quite the reverse. Given the band’s demographic, everyone attending is liable to be quite clean-living. Nevertheless, this is 1985, when menthol-flavored cigarettes are considered to be a healthy option. Let’s put the fraction that are smokers at 50 percent. And, of course, not all of the smokers will be carrying a lighter. For the sake of illustration, let’s say that 50 percent of them are carrying two lighters apiece; their favorite Zippo, and a backup.

  OK. So to estimate how many lighters Mark Knopfler sees, we need to multiply the rate at which fan-operated lighters enter the stadium by the length of time they are alight. In other words, if R is the rate at which the audience reenters the arena, fs is the fraction that are smokers, fl is the fraction of smokers that have lighters, nl is the number of lighters that each lighter-owning smoker carries, and L is the length of time in seconds that it is possible to hold a lighter without burning your fingers, then—big breath—the number of lit lighters Mark Knopfler sees during the encore is:

  N = R × fs × fl × nl × L

  Let’s plug in the numbers. In which case we get

  N = 42 × 50/100 × 50/100 × 2 × 30 = 630

  So on average, at any one time, Mark sees roughly 630 flames twinkling all around him in the darkened arena. He knows he is loved and no longer feels alone.

  SO FAR AWAY FROM ME

  As with pretty lights at an eighties stadium rock gig, of course, so with detectable alien civilizations. More or less, anyway. To figure out how many alien civilizations a radio astronomer might be able to see with his telescope, there are two things we need to get a handle on: the rate at which detectable alien civilizations emerge, and how long they are detectable for.

  OK, so at what rate do detectable alien civilizations emerge? Let’s assume that the kind of intelligent civilization we are going to be able to communicate with is a lot like us; inhabiting a rocky planet in orbit around a Sun-like star. Then we can start with the rate of formation of Sun-like stars, R*, and whittle it down just like we did in the case of the Dire Straits gig.

  First, let’s work on the rate at which Earthlike planets form. If R* is the rate of formation of Sun-like stars, and fp is the fraction of those stars with Earthlike planets, then their rate of formation is simply

  R* × fp

  That’s about as hard as it’s going to get. Of course some solar systems will have more than one Earthlike planet, such as our own, where arguably the Earth, Moon, and Mars—and maybe even Venus—have been habitable to life at some point. This is a bit like our example of smoking Dire Straits fans who have more than one lighter, so if ne is the number of Earthlike planets per solar system, then our running tally for the rate of formation of Earthlike planets is

  R* × fp × ne

  Right. I’m sure you’re getting the hang of this, so if fl is the fraction of Earthlike planets that support life, the rate of formation of life-supporting planets is

  R* × fp × ne × fl

  And if fi is the fraction of life-supporting planets that have intelligence, the rate of formation of intelligent life is

  R* × fp × ne × fl × fi

  We’re so nearly there. We have found the rate at which intelligent life appears in the galaxy. All we need to do now is multiply by the fraction of alien intelligences fc that have radio communication, and we will—at last—have the rate of formation of detectable alien civilizations. Here we go:

  R* × fp × ne × fl × fi × fc

  Good. Now, just as in the case of cigarette lighters at a Dire Straits gig, the number of detectable alien civilizations will be equal to the rate at which they appear, multiplied by the length of time they last for. So let’s put the cherry on top by multiplying by the length of time that an alien civilization is detectable, L. And, lo and behold, we have derived the Drake Equation:

  N = R* × fp × ne × fl × fi × fc × L

  Satisfying, eh?9

  NARROWING THE ODDS

  Back in the day, Drake and his colleagues at the first SETI conference judged the various factors of the Drake Equation to be as follows:

  R* = 1 (One
Sun-like star forms per year)

  fp = 0.2–0.5 (Between a fifth and half of all Sun-like stars have planets)

  ne = 1–5 (Such stars will have between one and five planets in their habitable zone)

  fl = 1 (All such planets will develop life)

  fi = 1 (All planets that develop life will also develop intelligence)

  fc = 0.1–0.2 (Between 10 and 20 percent will develop radio communication)

  L = 1,000–100,000,000 years (The length of time for which signals are transmitted is between one thousand and one hundred million years)

  Let’s take all the lower limits:

  N = 1 × 0.2 × 1 × 1 × 1 × 0.1 × 1000 = 20

  In other words, on any given day, when we point our radio telescopes up into the sky there are twenty stars, spread throughout the galaxy, from which we might detect alien signals.10

  Now let’s take the upper limits:

  N = 1 × 0.5 × 5 × 1 × 1 × 0.2 × 100,000,000 = 50,000,000

  Meaning that there are fifty million stars from which we might pick up a signal. Simplifying things even further, we can see that, very roughly speaking, most of the factors are approximately 1 apart from L, the number of years that a civilization is detectable.11 We can then write the Drake Equation in a stunningly simple form, like so:

  N ≈ L

  IS THERE ANYBODY OUT THERE?

  Equations are like poems. There’s what they seem to be about, and what they are really about. On the face of it, the Drake Equation simply tells us how to crunch the numbers to find out how many detectable alien civilizations might be out there in the galaxy, but of course there’s something much more important going on. The real power of the equation is in the assumptions it forces us to make.

  The deepest assumption is that the aliens will be just like us. We are presuming that the aliens will have technology like ours, societies like ours, and planets like ours. Now I don’t think for a second that Frank Drake is being naive; rather, his equation says, “hey, we’ve got to start somewhere, so we may as well start here.” If it provides anything, the Drake Equation gives us a lower limit on what we might expect to find out there in the galaxy. After all, who’s to say that aliens don’t inhabit dust clouds in deep space as well as rocky metal-rich planets like our own?

  The Drake Equation shows us that in considering the problem—namely, are we alone?—we need to think deeply about the very nature of life, intelligence, civilization, and technology. What do we mean by these things? And once we have made our assumptions, what data do we have that can turn them into bona fide estimates? For example, if we assume that biology is as universal as chemistry, how can our knowledge of how life evolved on Earth help us to make a guess about its abundance throughout the galaxy?

  As you can imagine, these are some of the most fascinating questions a human mind can ponder. To find answers, we will be foraging on the very fringes of scientific knowledge. What do the latest telescopes tell us about the abundance of Earthlike planets? What do the latest advances in biology tell us about the nature of life, and the chance of it being commonplace in the cosmos? What is intelligence, and how might we communicate with an alien intelligence that is vastly different from our own? What do we want to say? And why do we want to say it?

  LONG-DISTANCE RELATIONSHIP

  So why do scientists believe in radio contact with alien civilizations, but not in flying saucers? On a simple level, you might say it’s because of a lack of evidence. Given the fact that everyone now carries a mobile phone with a camera on it, you might think that there would be some really good footage of alien contact, but there isn’t. What’s more, no alien artifacts are on display in any of our museums, and no alien spaceship has landed on the White House lawn. What we do have is eyewitness reports.

  One of the fun things about this book is that, in examining aliens, we really get to think about what it means to be human. And it is time to face one of the more unpalatable truths about our species: When it comes to the world around us, we apes are not the most reliable of witnesses.

  As young children, we are bathed in imagination. We truly believe that we can fly, that we can see monsters in the wardrobe, and that a fat, bearded Latvian man delivers all the world’s Christmas presents on a fifteen-foot sleigh pulled by magic reindeer. We see a mixture of the world as it is, and the world as we imagine it to be. For children, wishing makes it so.

  As adults, on the other hand, we pride ourselves on our impartiality. We are certain that the wild dreams that we have at night never intrude into our waking hours. We believe we see the world as it truly is, and consider ourselves the masters of our own imagination. By this logic, when an otherwise upstanding member of the community—a policeman, say, or a magistrate—sees a ghost in the middle of the night, his anecdote is all the proof that we need. Chris is a company director, Chris saw a ghost, therefore ghosts exist. But are our minds really as reliable as we think they are?

  Your average scientist would say not. In fact you could say that one of the aims of science is to remove the so-called “human factor” from our observations of the world; to try and describe the universe in an objective, logical, self-consistent way that can be tested by experiment. Thus evolution is taken to be true not because it’s a great story and Darwin was a really steady guy, but because it predicted the existence of certain fossils before those fossils were ever found. Any given scientific theory stands only for so long as it is supported by experiment. It doesn’t matter how many Nobel Prize–winning biologists believe in evolution; if a fossilized dolphin suddenly turns up among the trilobites in a piece of Cambrian sedimentary rock then we’ll all be back to the drawing board.

  Compelling as the stories about flying saucers are, and as much as I for one would like to believe that they are true, the evidence is of poor quality. Kenneth Arnold was, no doubt, a reliable man not given to exaggeration. He truly believed that he saw a fleet of strange craft that summer, flying across the snowline of Mount Rainier, and was as puzzled by what he saw as anyone else. As an amateur pilot, he had additional credibility; he had the skills to tell a fleet of spaceships from a flock of geese, for example, or from a formation of conventional aircraft.

  Yet, harsh as it may seem, in scientific terms the reliability of Kenneth Arnold is neither here nor there. Science doesn’t care who you are or what you think you saw, it simply demands evidence. You saw a flying saucer? Show me the footage on your smartphone. An alien spaceship crash-landed in New Mexico? Show me a piece of the ship. You were abducted by aliens and subjected to an internal examination? Show me . . . actually never mind.

  “Ah,” I hear you say. “But scientists are people, too. Why should I believe some hippy with a test tube over a model citizen like Kenneth Arnold?” And you’d be right. Trusting a scientist purely because of his or her name and reputation is a dangerous game. Scientists make all the mistakes that everyone else makes. Their imaginations play tricks on them, they cherry-pick data that supports their pet theories, and they have a biased view of their own talents and abilities. But experiment saves the day time and time again. For a scientific hypothesis to gain weight, it has to be testable by experiment, and that experiment has to be repeatable. Scientists do make mistakes, but every time they do experiment puts them back on the right track. Without hard evidence to back them up, despite seven decades of sightings, crash landings, and abductions, the scientific case for alien artifacts is always going to be hard to make.

  LITTLE GREEN MEN

  Which brings us neatly back to Jocelyn Bell Burnell. Bell Burnell, you will recall, has picked up a series of pulses 1⅓ seconds apart, coming from within the constellation Vulpecula (“Little Fox”), which is itself smack dab in the middle of the so-called “Summer Triangle” of bright stars Deneb, Vega, and Altair. She has a dilemma. No serious astronomy graduate wants to tell their supervisor they have intercepted an alien signal; on the other hand, no serious astronomy graduate doubts that as far as aliens are concerned, they are on the front l
ine. If anyone’s going to take the call, it’s probably them.

  Summoning all her courage, Bell Burnell telephoned her supervisor, Anthony Hewish, who was teaching in one of the undergraduate laboratories, and told him what she had seen. “Must be man-made,” said Hewish, and came out to the telescope the next day to see the string of pulses for himself. Sure enough, there they were. He decided that there must be something wrong with the equipment, and for the next month he and Bell Burnell tried to eliminate as many sources of error as they could.

  First, they confirmed that the source was keeping pace with the stars rather than with the Sun. Astronomers refer to this as keeping sidereal time.12 That implied that the signal wasn’t coming from Earth, ruling out man-made interference. Except, of course, that produced by other astronomers, who also keep sidereal time. Could it be that some neighboring observatory was transmitting the signal as part of one of their research projects?

  A letter from Hewish to all the neighboring observatories drew a blank. What other straightforward explanations could there be? The team eliminated radar reflected off the Moon, signals from satellites, and effects due to a large corrugated metal building just to the south of the telescope. They then checked all the wiring, which to Bell Burnell’s considerable relief turned out to be sound. She had helped wire it, after all.

  They made a thorough analysis of the pulses. The pulses were 1⅓ seconds apart, and each one lasted less than 0.016 seconds. That meant that whatever was producing them had to be small. Basic physics says that nothing travels faster than the speed of light, so the object producing them had to be, at most, about three thousand miles across.13 That’s less than the radius of the Earth (3,959 miles), which in astronomical terms is on the tidy side.