By Emily Levesque, University of Washington
What does it mean to search for intelligent life on other planets? Where should we even start? How do we know if a distant civilization is trying to talk to us, or if there even are any distant civilizations at all? How can we separate science from science fiction when we imagine intelligent alien life? Astrophysicist Frank Drake famously tried to tackle these questions from a probability standpoint.
Frank Drake grew up in Chicago, in the 1930s, and began studying astronomy in college at Cornell University. While there, he attended a lecture by Otto Struve, an eminent astronomer who was, at the time, seen as quite unusual for his vocal belief that extraterrestrial intelligence was real, common, and worth searching for! This was in 1951—years before the space race began—but ideas that might have seemed fanciful to most listeners caught Frank Drake’s attention.
Drake’s early research focused on radio astronomy, studying everything from Jupiter to pulsars. His choice of research wasn’t by accident, even if he wasn’t focusing on extraterrestrial intelligence at the time. Radio signals had long been seen as a compelling potential means of detecting signals from other worlds.
Back in 1924, Mars made its closest pass to Earth in nearly a century and astronomers encouraged what was called a ‘National Radio Silence Day’, encouraging people to cease radio transmissions at regular intervals. The United States Naval Observatory sent a dirigible aloft with a radio receiver attached in the hopes of picking up a Martian message. Such was the optimism that the research team even had a cryptographer at hand in case translations were needed.
This campaign happened before we knew much about Mars, and years before Karl Jansky first detected radio signals from space, in 1931, launching the study of radio astronomy. Still, it set an early standard for trying to hunt for extraterrestrial signals in the radio regime.
The Drake Equation
In 1960, Drake took the opportunity to study two nearby stars at West Virginia’s Green Bank Radio Observatory, one Sun-like and the other just a bit cooler, in the hopes of spotting signs of life from imagined planets. During the following year Drake helped organize a small informal conference at the observatory. The group included a Nobel laureate, a member of the US National Academy of Sciences, and a young up-and-coming researcher named, Carl Sagan.
In preparation for the conference, Drake assembled what is now famously referred to as the ‘Drake equation’. It’s a bit different than other equations one might have come across in the field of science. For one, it looks nice and simple—just a series of numbers that we multiple together. The equation is meant to give us a value for N: the number of civilizations in our own galaxy that we could potentially detect.
To get that value, we multiply several important numbers. We start with R-star, the average rate at which stars form in our galaxy. We then multiply by the fraction of those stars that have planets, and by how many of those planets can potentially support life.
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An Unusual Equation
To keep going, we consider what fraction of those planets actually develop life, how many of those developed life forms evolve into intelligent civilizations, how many of those civilizations build technology that releases some sign of their existence into space, and how long those civilizations and technological capabilities last. The Drake equation is also unusual in that we can’t yet easily measure most of these numbers, and the scientific implications of the equation change dramatically depending on what numbers one plugs in.
In this manner, Drake’s math is less of a perfect computational equation and more of a statistical exercise or thought experiment quantifying how we should think about extraterrestrial intelligence, and how we might evaluate scientific ways of searching for it.
The Search for Extra-Terrestrial Intelligence, commonly abbreviated as SETI, has long struggled to get serious scientific report and funding. For a time, NASA earmarked funding for SETI, and one project, in 1971 funded a report. Authored by Bernard Oliver and John Billingham, it proposed the construction of a spectacular 1500 dish radio array nicknamed, Project Cyclops. The array was never built, but the report caught the attention of a young astronomer named, Jill Tarter.
Tarter had grown up in New York state and expressed an early interest in engineering, which she studied at Cornell University before continuing on to graduate school in astronomy at the University of California at Berkeley. After reading the Cyclops report she began working on other SETI radio projects, ultimately dedicating her career to the science of searching for extraterrestrial intelligence. This included spearheading tireless efforts to secure funding for supporting SETI research and building cutting-edge radio observatories.
The ‘Wow!’ Signal
To conclude, unfortunately, so far, we haven’t had much luck with detecting signals from intelligent life beyond our own planet. Although, there was the famous ‘Wow!’ signal, a signal detected by an Ohio radio telescope on August 15, 1977.
The signal lasted 72 seconds and was incredibly bright and resembled a radio transmission far more than any astronomical phenomenon, but it was never picked up again. To date, there’s no widely accepted explanation for it.
Common Questions about the Drake Equation
Otto Struve was an eminent astronomer who was, at the time, seen as quite unusual for his vocal belief that extraterrestrial intelligence was real, common, and worth searching for!
The Drake equation is meant to give us a value for N: the number of civilizations in our own galaxy that we could potentially detect.
NASA earmarked funding for SETI, and one project, in 1971 funded a report. Authored by Bernard Oliver and John Billingham, it proposed the construction of a spectacular 1500 dish radio array, nicknamed Project Cyclops.