Back in the summer of 1950, famed physicist Enrico Fermi visited Los Alamos National Laboratory and discussed the possibility of interstellar travel with his colleagues as they walked to have lunch. In the brief exchange, some thought faster-than-light (FTL) travel was possible while others thought not. During lunch Fermi posed his now legendary question: “Where is everybody?” Remarkably, although the question came out of the blue, everyone understood its implications.
At least one impetus for the conversation involved a query about how to explain a rash of UFO sightings. If aliens pervade the universe, some of them should have visited Earth already. However, all the observations at the time provided no substantial evidence for alien visitors (a conclusion still true today). Assuming the possibility of FTL travel, the existence of alien life and the lack of any evidence became known as the Fermi paradox.
The Drake Equation
Roughly a decade later, astronomer Frank Drake developed an equation that helps organize the scientific process by which we might determine the number of advanced alien civilizations in our galaxy. Known as the Drake Equation, it has 7 factors that break the huge problem of finding alien life into smaller, more manageable categories.
N = R* • fp • ne • fl • fi • fc • L
N: number of detectable civilizations throughout the Milky Way Galaxy
R*: rate of formation of stars suitable for intelligent life
fp: fraction of stars suitable for intelligent life that have planetary systems
ne: number of planets in those planetary systems
fl: fraction of those planets that develop life
fi: fraction of those life-forms that develop intelligence
fc: fraction of those intelligent life-forms that send signals into space
L: length of time those civilizations emit the signals into space
To determine all these factors will require research in disciplines including astronomy, physics, planetary science, geology, biology, biochemistry, and many others. In fact, scientists have formed a discipline called astrobiology that encompasses the specific aspects of all these other disciplines that pertain to life’s existence. A major component of astrobiology research entails the search for other planets that might host life. Until the discovery of the first exoplanet in the 1990s, this was a largely “data-free” endeavor. Research since then indicates that as many as 20% of stars might have habitable planets. We have no hard data driving the values of the last four factors and any one of these could easily be zero (meaning no civilization exists beyond Earth). Some research even suggests that as many as 22% of Sun-like stars harbor Earth-sized planets in some sort of habitable zone.1 However, scientists are likely underestimating the difficulty of making a truly habitable planet.
Resolving the Paradox?
Some people see that the number of civilizations predicted by the Drake Equation is zero (because the last four factors are really small). Others predict really large numbers by assuming, for example, that all the factors are around 0.1. These really large numbers lead to the paradox. According to the authors of a recent paper, replacing specific probabilities normally used for each factor with ranges that account for the uncertainty in each factor resolves (or rather “dissolves”) the issue.2 If one uses a uniform range between 0 and 0.2 for each number, the Drake equation predicts that we are alone in the galaxy over 21% of the time. With this relatively large probability that no other civilizations exist in the galaxy, Fermi’s paradox disappears.
I would point out that this analysis glosses over a more fundamental point: we have no idea what the values for the last four factors should be. And we have good reason to think some, like fl, are probably zero! In reality, most scientists consider the Drake equation, not as a tool to predict the number of detectable civilizations, but as a way to organize our approach to the search for life in the universe. We don’t know the answer we will find, but we can bear in mind that maybe life exists here on Earth (and anywhere else we might find it) because God created it to reflect his glory!
- Erik A. Petigura, Andrew W. Howard, and Geoffrey W. Marcy, “Prevalence of Earth-Size Planets Orbiting Sun-Like Star,” Proceedings of the National Academy of Sciences 110 (November 26, 2013): 19273–78, https://doi.org/10.1073/pnas.1319909110.
- Anders Sandberg, Eric Drexler, and Toby Ord, “Dissolving the Fermi Paradox,” Future of Humanity Institute, Oxford University (June 8, 2018): https://arxiv.org/pdf/1806.02404.pdf.