If the Universe Is Teeming with Aliens ... WHERE IS EVERYBODY?: Seventy-Five Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life

by Stephen Webb

I mentioned the relevant timescales in chapter 1, but it’s worth repeating them here. We now know that the universe is 13.798 billion years old, give or take 37 million years. Astronomers still don’t have a full understanding of the formation of the first stars, but it seems reasonable to assume that the first Sun-like stars, and thus perhaps the first rocky planets, formed within a billion years after the Big Bang—in other words, about 12.8 billion years ago. If we take Earth as a guide, and assume intelligent life appears 4.5 billion years after a planet forms, then we could argue that the oldest civilizations appeared in the universe 8.3 billion years ago. The oldest stars in our Milky Way galaxy formed roughly 10–11 billion years ago so a similar argument suggests that the oldest neighboring civilizations could quite easily be 5 billion years old. Ray Norris, using an argument based upon stellar evolution, reasoned that the median age of an ETC would be 1.7 billion years. Different astronomers, using different arguments, have argued for a median age somewhere between the Norris figure of 1.7 billion years and the 8.3 billion years mentioned above. The specific age is hardly the point: whether you believe that extraterrestrial civilizations might be 1.7 billion years older than us, 8.3 billion years older or somewhere in between, the take-home message is the following. If ETCs survive natural and home-made catastrophes they are likely to be much, much older than us: the...