Nathan Taylor over at Praxtime (via Sean Carroll):
A new paper using data from NASA’s Kepler telescope came out recently, estimating that 22% of Sun-like stars harbor Earth-sized planets. This is a big increase over previous estimates. It’s very cool work. Love it. But the news spin was predictable:
You get the idea. Aliens under every rock. The existence of extraterrestrial intelligence (henceforth ETIs, or just ETs) is normally discussed in the context of the Fermi Paradox, which Wikipedia describes as “the apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilization and humanity’s lack of contact with, or evidence for, such civilizations.” Now I’m a strong advocate for there being no ETs in our galaxy, as explained in this recent post. In fact I’ve gotten so tired of hearing about ETs I’ve started thinking of it as “Carl Sagan Syndrome.” Name checking the deservedly well regarded astronomer and advocate for the Search for Extraterrestrial Intelligence (SETI). With this latest news cycle I got to wondering. Why so much Sagan Syndrome? What am I missing?
A good starting point is Stephen Webb’s book “If the Universe Is Teeming with Aliens … WHERE IS EVERYBODY?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life.” It’s a fun romp through the history of the Fermi Paradox. From page 23: “it was a 1975 paper by Michael Hart in the Quarterly Journal of the Royal Astronomical Society that sparked an explosion of interest in the paradox. Hart demanded an explanation for one key fact: there are no intelligent beings from outer space on Earth at the present time.” Hart’s explanation was “we are the ﬁrst civilization in our Galaxy.“
Hart’s 1975 paper is short and clear, and worth a quick read. Hart runs various scenarios, but for me the key insight is one of time scale. It takes (only) millions of years for intelligent life to completely fill the galaxy, but billions of years for it to evolve. So first out the gate should be everywhere before second out the gate. Logically if ETs exist they should be here. And they aren’t. So case closed.The Fermi Paradox literature since Hart could arguably be characterized as nonstop special pleading to avoid a common sense conclusion. Besides myrecent posts, you can find similar views from Robin Hanson, Ian Crawford,Leonard Ornstein. And in particular I want to cite Stephen Ashworth, both for his article “Alien Civilisations: Two Competing Models“, plus an email exchange where he was generous enough to spend time answering questions. Finally of course we have Stephen Webb himself (spoiler alert) finishing his book of 50 explanations by concluding ETs aren’t there. So while this is a minority view, it’s not uncommon.