One of the paradoxes that Jim Al-Khalili chooses for his book Paradox: The Nine Greatest Enigmas in Physics (Broadway Books, 2012) is Fermi’s Paradox, which states that if the universe is as big as we think it is, and that there should be so many Earth-like planets in the universe, then there should be a lot of intelligent life out there, so where is everybody? Why have we not detected ET life yet, and why have they not contacted us?
In the 1960s, Frank Drake, organizer of the very first SETI conference, came up with the Drake Equation, a mathematical formula that tried to guess the number of civilizations in our galaxy whose radio signals would be detectable on Earth. Plugging in mostly wild guesses for figures regarding the number of planets per solar system with an environment suitable for life, the fraction of planets on which life actually appears, the fraction on which intelligent life appears, the fraction that would actually develop radio technology, and so on, Drake concluded there are roughly 50,000 civilizations in our galaxy whose radio signals should be detectable on Earth. So to Enrico Fermi’s question: why haven’t we detected any of them?
Well, first of all, the numbers Drake plugged in for his seven figures were, as I said, wild guesses. Secondly, as Michael Bodin points out in his book, Fermi’s Paradox: Cosmology and Life (Trafford Publishing, 2014), “The equation makes no allowance for relative importance, placing equal ‘weight’ on all factors, and it does not specify any particular life form.” So, maybe it is simply Drake’s equation and the numbers that he plugged in that are wrong.
Or there could be 75 other solutions to the Fermi Paradox.
In 2002, Stephen Webb wrote a book called If the Universe Is Teeming with Aliens… WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. Now that Springer has updated this publication to a second edition in 2015, I see this as the definitive book on the subject. Webb’s now 75 approaches to the question of why there is so much eerie silence in our skies can basically be broken down into 3 categories:
- They are (or were) here
- They exist, but we have yet to see or hear from them
- They don’t exist
The range of scenarios that Webb surveys include that Earth is part of a galactic quarantine, that the universe is an illusion created by intelligent beings, that as soon as sentience meets technology the civilization is fated to blow itself up, and that AI eventually supersedes all bio-life. Michael Hanlon, in his book The Science of The Hitchhiker’s Guide to the Galaxy (Macmillan, 2005), sums up this last one: “Deep Thought-like computers with brains the size of planets simply sit there pondering monumental thoughts from here to eternity. All this obsession with flitting around the cosmos could be just an adolescent fad that all intelligent races simply grow out of.”
Statistically, there are probably more mechanical civilizations out there than bio ones, because the bio lifeforms are more vulnerable and slower evolving than a society of robots that can keep upgrading themselves until they are immortal. Perhaps they are not encoded with the dreamer’s program that inspires them to look up at the stars and wonder who else is out there.
This week, one of Webb’s solutions is looking more plausible than his others. It falls into the category of, “They exist, but we have yet to see or hear from them.” The stars, Webb points out, are far away. If signals are sent, presuming they are radio waves at all, they will take a very long time to get here. By the time they do, will they be of any use?
On March 12, 2018, Science News reported that Claudio Grimaldi of École Polytechnique Fédérale de Lausanne and colleagues have written a paper that, using the Drake Equation calculations with the most recent figures that account for radiation shells, concludes that any alien broadcast that we receive will be from a civilization that is most likely already dead. Ghost signals.