Anyone with a reasonable interest in astronomy will recognise the above image as containing the Drake Equation, sometimes referred to as “the second most famous equation after E=Mc2
It was first proposed in 1961 by American astronomer and astronomer and astrophysicist Dr. Frank Drake as a probabilistic argument to estimate the number of active, communicative extraterrestrial civilisations in the Milky Way Galaxy. Its values are defined as:
N = the number of civilisations in our galaxy with which communication might be possible (i.e. which are on our current past light cone);
R∗ = the average rate of star formation in our Galaxy.
fp = the fraction of those stars that have planets.
ne = the average number of planets that can potentially support life per star that has planets.
fl = the fraction of planets that could support life that actually develop life at some point.
fi = the fraction of planets with life that actually go on to develop intelligent life (civilisations).
fc = the fraction of civilisations that develop a technology that releases detectable signs of their existence into space.
L = the length of time for which such civilizations release detectable signals into space.
In the decades since its initial publication, the Drake Equation has been widely critiqued by astronomers and mathematicians because the estimated values for several of its factors are highly conjectural such being that the uncertainty associated with any of them so large, the equation cannot be used to draw firm conclusions.
However, these critiques actually miss the point behind Drake formulating the equation in the first place, because he was not attempting to quantify the number of extra-solar civilisations which might exist, but rather as a way to stimulate scientific dialogue about what had been very much looked upon as an outlier of research, and to help formulate constructive discussion on what is regarded on the first formalised discussion on the search for extra-terrestrial intelligence (SETI), as he noted in his memoirs:
As I planned the meeting, I realised a few day[s] ahead of time we needed an agenda. And so I wrote down all the things you needed to know to predict how hard it’s going to be to detect extra-terrestrial life. And looking at them it became pretty evident that if you multiplied all these together, you got a number, N, which is the number of detectable civilizations in our galaxy. This was aimed at the radio search, and not to search for primordial or primitive life forms.
– Frank Drake
Frank Drake not only hosted the first US meeting to discuss the potential for seeking signs of possible extra-terrestrial civilisations, he pioneered several of the earliest attempts to seek any such signals as demonstrating methods that might be used as a means to intentionally communicate our existence to other civilisations within the galaxy. As such, his work did much to put our speculative thinking about intelligences elsewhere in the galaxy on a solid foundation of scientific research, as will as being responsible for some for the foremost research in the field of modern radio astronomy.
This is his story.
Born in Chicago on May 28th, 1930, Frank Drake was drawn to the sciences and to electronics from an early age, and in order to further his education in both, he enlisted in the US Navy Reserve Officer Training Corps (ROTC). This allowed him to obtain a scholarship at the prestigious Cornell University, ostensibly to obtain qualifications in electronics, but also study astronomy.
While at Cornell, Drake’s astronomy class were able to attend a lecture by astrophysicist Otto Struve. While his name may not be instantly recognised, Struve was one of the most distinguished astronomers of the mid-20th century, a member of a generational family of astronomers stretching by to the 18th century and Friedrich Georg Wilhelm von Struve. He was also one of the first astronomers to openly promote radio astronomy as a key to determining whether there might be other intelligences living in our galaxy – an idea his contemporaries tolerated, rather than embraced.
Struve’s presentation positively affected Drake, and following his required 1-year military service following graduation in 1951 (served as the Electronics Officer aboard the cruiser USS Albany), Drake enrolled at Harvard University, where gained his doctorate in astronomy, with a focus on radio astronomy.
In 1956 Otto Struve was appointed as the first director of the National Radio Astronomy Observatory (NRAO)), and he started overseeing the establishment of a number of national radio astronomy centres across the United States. One of these was at Green Bank, Virginia, a facility Drake joined as a researcher in 1958. His initial work here started with the static arrays at Green Bank, carrying out the first ever mapping of the centre of the Milky Way galaxy, and the discovering that Jupiter has both an ionosphere and magnetosphere.
However, Struve was keen to enhance the facilities with steerable radio dishes, and to this end purchased an “off-the-shelf” 26 m dish and had engineer Edward Tatel (for whom it was later named) design a motorised mount for it so it could be pointed around the sky. This work was completed in 1959, and Struve turned to Drake to formulate the telescope’s first science mission.
At the time, Drake had just read an intriguing article in Nature magazine entitled Searching for Interstellar Communications. Within it, physicists Giuseppe Cocconi and Philip Morrison proposed using a large radio dish to monitor “incoming” radiation from stars along the 21-cm / 1,420.4 MHz wavelength – the radio frequency used by neutral hydrogen. Given this is the most common element in the universe, Cocconi and Morrison speculated it would be logical landmark in the radio spectrum to manipulate as a message carrier.
Taking this idea, Drake developed Project Ozma, a three-month programme run at the start of 1960 to listen for any signals coming from the vicinity of either Tau Ceti or Epsilon Eridani. At the time, no-one knew if either star fielded planets (although both were found have at least one planet orbiting them almost 50 years after Drake’s experiment).
Following Ozma, Drake was encouraged to formalise SETI research into a more co-ordinated effort (various programmes, such as Ohio State University’s work using the Big Ear telescope, were already in existence but without any real coordination). To this end, he helped put together the first small-scale meeting / conference on the subject in 1961 – the event at which he used his equation to stimulate the discussion.
Among those attending were Otto Struve (now retired), Phillip Morrison, astronomers Carl Sagan and Su-Shu Huang, chemist Melvin Calvin, neuroscientist John C. Lilly, and inventor Barney Oliver. Together they called themselves The Order of the Dolphin (due to Lilly’s work on dolphin communications), and together they laid the groundwork for a systematic approach to SETI research, which over the coming years would in turn give birth to numerous programmes, and more fully legitimise such research within scientific circles.
In the mid-1960s, and still based at Green Bank, Drake was nominated to spearhead converting the massive Arecibo Ionosphere Observatory – originally built as a project to study the Earth’s ionosphere as a means of detecting nuclear warheads inbound towards the United States – into what would become more famously known as the Arecibo Observatory, for several decades the largest radio telescope in the world.
This work finished in 1969 when the National Science Foundation formally took over the Arecibo faculties, and two years later Drake was approached by Carl Sagan with another intriguing proposal. Sagan had himself been approached English journalist Eric Burgess – who at the time was writing about the upcoming NASA Pioneer 10 and Pioneer 11 missions – about the idea of sending a physical message out to the stars.
Continue reading “Space Sunday: equations and launch scrubs”