“Space is big. You just won’t believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it’s a long way down the road to the chemist’s, but that’s just peanuts to space.”
(Douglas Adams, The Hitchhiker’s Guide to the Galaxy)
The famous Drake Equation, first proposed by the astrophysics Frank Drake in 1961, is a interesting way to address the so-called Fermi Paradox: why, with all the existing stars and galaxies out there, nobody has, to date, ever got in touch with us – not that we have realised it, at least (http://news.discovery.com/space/do-we-overlook-alien-beacons.htm) – and there’s no sign of life, let alone intelligent?
The lasting utility of the Drake Equation is that it identifies the main factors playing a role in the development of a form of life, of whatever kind. It takes this simple form:
N = R* • fp • ne • fl • fi • fc • L
N = The number of civilizations in the Milky Way galaxy whose electromagnetic emissions are detectable.
Given by:
- R* =The rate of formation of stars suitable for the development of intelligent life. This is actually more complex than it seems at a first glance. We also know that life takes billion of years to emerge, or so we think judging from the only one case we know about, ours. Therefore blue supergiant stars that last “only” a few (hundred) million years before going supernovae don’t stand a lot of chance… (http://www.universetoday.com/24587/blue-giant-star)
- fp = The fraction of those stars with planetary systems. We recently had some luck with this one, thanks to Kepler and WISE discoveries. We now know those stars are far more than we initially thought (http://www.space.com/14200-160-billion-alien-planets-milky-galaxy.html)
- ne = The number of planets, per solar system, with an environment suitable for life. Same as the previous variable, this one looks increasingly positive, and we have even made some firm identifications out of 1106 planetary systems, 1786 planets, 460 multiple planet systems recorded as of May 2014 (http://exoplanet.eu/catalog). A Earth-twin has been found, too. (http://www.dnaindia.com/world/report-nasa-s-kepler-space-telescope-finds-earth-s-twin-where-life-can-exist-1979622). We may also add that exomoons can be suitable for life as well – without mentioning big asteroids or other similar celestial corps.
- fl = The fraction of suitable planets on which life actually appears. This variable, and the following ones, are where our troubles really start. We simply don’t know because we have never found any evidence for any of them, no matter the reason…
And, to make things, even more complicated, we finally have real question marks with not even one possible educated guess:
- fi = The fraction of life bearing planets on which intelligent life emerges.
- fc = The fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
- L = The length of time such civilizations release detectable signals into space
(Credit: NASA)
There have always been, since the onset, an easy criticism to this equation – the fact that, since there are no explicit or even likely values for those variables, the equation itself is, at best, a “guesstimation”. It’s true it can amount to any number, zero, low or sky-high, and, as Michael Crichton allegedly declared in a lecture given at Caltech in 2003 “an expression that can mean anything, means nothing.” (http://www.learningace.com/doc/5005023/cec179997dbc52b1b4174ef9d0cebe6c/lecture_by_crichton_at_caltech)
For much I do love Crichton (I have avidly read, and enjoyed, all his books) I have to disagree with this statement and any accusation of lack of meaning: the function of this equation is not to calculate the number of alien civilisations, nor Drake has ever thought it would. The idea was to stimulate dialogue in SETI (the Search for Extraterrestrial Life initiative) and outside, by offering elements for consideration. Asking the right questions is fundamental, and some of the recent discoveries have been providing clues for at least some of those factors. There are a few other methods we could hunt ET life with – e.g., checking for alien artifacts in space or for evidence of asteroid mining (http://www.space.com/20155-hunting-intelligent-aliens-extreme-seti.html). If they are out there, they would be doing something, wouldn’t they?
Something more far-fetched has even been hypothesized, like searching for absence of a star, for example: a “Type II” Kardashev’s civilisation would be able to use up all its energy, and literally “eat the star away” (http://news.discovery.com/space/galaxies/looking-for-alien-bubbles-in-other-galaxies-120731.htm). The same civilisation could use minuscule black holes, of an atom’s width but carrying the mass of a million tons and convert them in energy to power their spacecraft’s engines…(http://news.discovery.com/space/a-seti-search-for-black-hole-power-plants-121121.htm).
– In case you wonder if all this make any sense at all in real world physics, Michio Kaku has some answers, with his I-II-III types of impossibility. Check this out: https://www.youtube.com/watch?v=geBmlndUexA or read his fascinating book Physics of the Impossible (http://www.amazon.com/Physics-Impossible-Scientific-Exploration-Teleportation/dp/0307278824) –
Moreover, when considering the last variables of the equation, we could, for instance, observe that not all intelligent life communicates – just think about dolphins or mammals (http://news.discovery.com/space/do-the-meek-inherit-the-galaxy.htm) or that not all communications can be detected (http://news.discovery.com/space/do-aliens-go-invisible-by-going-green-120207.htm).
Whatever you may think about these methods, results so far have been less than dazzling. This is why the Drake Equation keeps being meaningful, and what’s more important, keeps us guessing. Incidentally, there is a final variable that has been added to the original formulation, fd, also called “the Dalek Variable” , proposed by Popular Science in 2013 (http://www.popsci.com/technology/article/2013-06/evil-alien-cyborg): namely, the fraction of those civilizations that can survive an alien attack. If this is correct, I am afraid the value of the Drake equation will be zero, after all. We certainly won’t.