Today’s factismal: It is World UFO day.
There is no doubt that UFOs exist; there are objects that are flying around that are not identified. But a far more interesting question is “Are there other planets with intelligent life?” And the answer to that is still not known.
But that doesn’t mean that we can’t try to know the answer. One of the most famous attempts to resolve the question was made by Drake, who put together an equation estimating the number of intelligent civilizations in the universe:
Number of civilizations = Galaxies * Stars * Planets * habitable * life * intelligence * civilization
In order to solve Drake’s equation, all you have to do is know how many galaxies there are and the number of stars in each galaxy and the number of planets orbiting each star, along with the fraction of those planets in the “habitable zone”, the fraction of habitable planets that go on to develop life and the fraction of planets with life that develop intelligent life and the fraction of planets with intelligent life that go on to develop civilization. Of these factors, we have a good handle on the first two, and are getting some interesting information on the next two.
We know that there are about 500 billion galaxies in the universe (G=500,000,000,000). And we know that there are about 100 billion stars in a typical galaxy (S=100,000,000,000). Based on our observations of exoplanets, it appears that nearly every star will develop planets, so we can arbitrary put P at 0.9. Also based on our exoplanet work, we know that about 10% (h=.1) of those will be in the habitable zone; i.e., neither so close to their sun that the planet is too hot for life, nor so far out that it is too cold.
What we don’t know yet is how inevitable life is. Some exobiologists think that life is inevitable; others think that it is exceedingly rare. If we assume that life is very rare and happens in one out of every billion habitable systems and that intelligent life is even rarer and happens once on a trillion planets with life and that civilization is inevitable, we get:
N = 500,000,000,000 * 100,000,000,000 * 0.9 * 0.1 * 0.000000001 * 0.000000000001 * 1 = 4.5
So there should be about three other civilizations out there (remember that we count as one of those 4.5). Using different values for intelligence and life give different results; reasonable values range from 2 to 20,000.
And that leads to the Fermi Paradox: “Hey! Where is everybody?” After all, if all of these civilizations existed, then there should be some evidence of them, right? Well, maybe not. You can argue (and many have) that the ETI are there but space is so big that we haven’t had time to get their signals. You can argue (and many have) that they exist but will not communicate with us due to some “Prime Directive”. Or you can argue (and many have) that the act of communication is so fraught with assumptions that they are shouting at us, but we simply cannot understand them.
If you’d like to do more than just toss numbers at the problem, then do I have a citizen science opportunity for you! The SETILive community is gathering radio signals from stars that we know have planets in the habitable zone and they need volunteers to look at the signals to see if there’s communication buried in it. To get in on the search, set your coordinates for