Are we the only civilization-building intelligent species that has ever occurred in the universe?
It’s one of science’s oldest questions.
Earlier this year, my colleague Woody Sullivan and I published a paper in the journal Astrobiology (A New Empirical Constraint on the Prevalence of Technological Species in the Universe) presenting new results that, I believe, throw new light on the ancient question.
And, based on that work, last month I wrote an OpEd in The New York Times that ran with provocative title “Yes, There Were Aliens.”
The Times piece found a large audience and generated strong responses running from agreement to dissent to folks telling me I really should look into UFOs (sorry, not my thing).
Today, I would like, once again, to present our argument and dive a little deeper into its meaning and its limits. In particular, I want to address two excellent rebuttals written by Ross Andersen in The Atlantic and Ethan Siegel in Forbes.
Neither Andersen or Siegel was buying some of my contentions and they both made good points. The thing about science (take note climate deniers) is that it’s really a call and response.
Both Andersen and Siegel are great writers. Their skepticism made me think even harder about the ideas in our paper and that was really helpful.
One note before we begin. This piece is a tad long because I need to introduce some of the background for the rest of my argument to make sense. Those familiar with the “Drake equation” and its history can skip the next section.
In 1961, astronomer Frank Drake was asked to convene a meeting to hash out the possibilities of interstellar communication.
Drake decided to frame the question in terms of one simple one:
What is the number of alien civilizations (let’s call them exo-civilizations) existing now in the galaxy?
To foster discussion at his meeting, Drake broke the problem up into seven pieces.
Each piece represented a different aspect of the problem and each could be expressed as a factor in an equation for the total number of existing exo-civilizations (which we will refer to as N).
Drake’s equation looks like this:
University of Rochester
Courtesy of Adam Frank
In Drake’s equation,
- R* is number of stars born each year
- fp is the fraction of stars that have planets
- ne is number of planets per star living on orbits in the right place for life to form (the so-called “Goldilocks” zone)
- fe is the fraction of planets where life gets started
- fi is the fraction of life-bearing planets on which intelligence evolves
- fc is the fraction that go on to develop advanced technological civilizations
The final factor ‘L’ is the most haunting, representing the average lifetime of a technological civilization.
The Drake equation has been hugely important for thinking about life in the universe. For the past 50 years, it’s served as a critical guide for astronomers in organizing their thinking and their investigations of the subject.
What’s important to note is that when Drake wrote his equation in 1961, only the first term, the number of stars forming per year, was even close to being known. Every other term was “data free.”
That meant through most of its history, scientists using the Drake equation could only provide educated guesses about the other terms.
- If you where optimistic, you argued for values that led to a large value of N.
- If you were pessimistic, you argued for values that led to tiny values of N.
It was a free-for-all…
But that was before the exo-planet revolution. In the past 20 years, astronomical discoveries have transformed our understanding of planets orbiting other stars. In the process, they have nailed the second two terms in the Drake equation (fp and ne).
What we found was that there were planets everywhere…
Pretty much every star in the sky hosts at least one planet.