E.T. Won't Be Phoning Anytime Soon
News that astronomers using NASA's Kepler Space Telescope had discovered anwhere liquid water can exist certainly deserves the attention it has received. In fact, evidence of life surviving--and even thriving--in tempts one to believe that, given billions of years and a decent supply of organic molecules, life (albeit simple bacterial life) will eventually develop just about anywhere liquid water exists.
All that said, even absolute evidence of bacteria or non-sentient animals on an alien world would offer plenty of grist for scientists in certain fields but little that would change the life for most people in the short term.
On the other hand, contact with an alien civilization would, obviously, have enormous impacts in every area of human endeavor ranging from science to religion. That's why a fair number of people--some of them kooks, some of them--have devoted time to various methods of searching for extraterrestrial intelligence.
I was, at one time, very enthusiastic about these efforts and even thought I might make it a career: I pursued a fair amount of upper-level coursework in planetary astronomy, edited a science magazine, took a first job as a science writer, and even interviewed for a job on a SETI project once. I still believe, personally, that SETI efforts are worthwhile and deserving of private support.
But, as I've looked at the data, I'm increasingly convinced that SETI is very unlikely to succeed in my lifetime or even my son's.
The fundamental problem lies with the final variable of the famous " " that SETI researchers use to estimate the number of communicating extraterrestrial civilizations in the galaxy.
The first two parameters deal with things that observational science clearly can answer in due time: the rate of star formation in the galaxy (somewhere between 7 to 10 a year), and the percentage of stars that have planets (the latest data from Kepler indicates that it's at least 40 percent). Next, scientists jump into slightly more speculative categories that science can still help explain: the fraction of those planets that go on to develop life and the fraction fo that life that becomes intelligent. There's no way to answer these questions for sure but worthwhile-for-other-reasons research in our own solar system (Mars in particular) can shed light on the first variable and a better understanding of human evolution can provide some evidence on the second.
The final two variables--the percentage of those civilizations that transmit radio signals and the average life of a civilization that transmits them--seem to me beyond science's ability to answer until we actually contact a number of other alien civilizations.
And, when one runs the equation, the final variable turns out to be the most important: even if one selects unrealistically low values for every other variable, an assumption that civilizations last billions of years would results in a galaxy teaming with intelligent life. Even if one selects high values for the other variables, on the other hand, picking a short lifespan for "transmitting civilizations" means that the universe is either devoid of intelligent life beyond Earth or that (provided that nothing can travel faster than light) any civilization we communicate with will likely be gone by the time before we receive its messages.
I'm hardly the first to notice this: Astronomer Carl Sagan devoted so much time to left-wing environmental causes in part because the Drake equation convinced him that the final variable was the one part of the equation humankind could control.
Given that humanity has been sending signals into space for nearly a century, listening for them for about 40 years, and still hasn't found anything indicates to me that the universe isn't teeming with intelligent life. Since everything else we know seems to suggest relatively high values for the other variables, every passing year without alien contact indicates that either intelligent life rarely develops or that civilizations which develop the ability to communicate don't last very long.
It's too soon to know much for certain but, despite my fondest hopes, I don't expect to talk with E.T. anytime soon.