Who would have believed, back when the movie E.T. the Extra-Terrestrial came out in 1982, that by 2003 we would have the technology to identify planets orbiting other stars, and in 10 years would locate 900 such exoplanets?
Some astronomers are now certain that in another ten years we will find ET, or some slavering-jawed variant thereof, in our interstellar back yard.
The cultural impact would be staggering. How does ET fit into having 72 virgins waiting for you when you croak, or going to Hell because you were hoping for 72 virgins?
More seriously, there’s something these scientists are not telling us. In the 12 billion year life span of our planet, our species is fully 200,000 years old. But ET wouldn’t hear us back when we were building Stonehenge. He needs us to be transmitting.
Let’s say humanity survives another 450 years, meaning that for 500 years we are sending I Love Lucy to the cosmos. That puts the odds of ET hearing us at 1 in 240 million. Since ET should be smart enough only to look at planets in the middle third of their life span, the chances improve to 1 in 80 million.
Of course I’m not really thinking about ET looking for us, my interest is in us looking for ET. Let’s say we look only at planets within the Goldilocks zone. We have found a few, for example Gliese 581g. From the thin information we have, just a fraction of a percent will be capable of sustaining life.
However, we are doubling the rate of exoplanet discovery every 3 years. Some predict that we will locate the first truly Earth-like planet in 2013. Great! By 2025 we will know of 63 Earths and I’ll be pushing up daisies. By 2068 we will achieve a 1% probability of hearing ET call home.
Probabilities can be debated, but the issue of scale remains. How likely is it that we will be lucky enough to be looking for ET during the fraction of a % of a planet’s life when ET might actually be transmitting?