If aliens are likely, where is everybody? A lunchtime question with no answer.
In 1950, walking to lunch at Los Alamos, the physicist Enrico Fermi suddenly asked his colleagues, 'Where is everybody?' Everyone knew he meant aliens. Billions of Sun-like stars, many far older than ours, and yet no sign of anyone. More than seventy years on, the silence is still unexplained.
The Fermi paradox is the clash between the apparent likelihood of extraterrestrial civilisations and the lack of any evidence for them. The reasoning runs like this: the Milky Way has billions of stars like the Sun; some probably have Earth-like planets; many are much older than the Sun, so life could have had a big head start; and even slow interstellar travel could cross the galaxy in a few million years. So why has no one turned up?
The question itself came out of a casual chat. Fermi, a Nobel laureate famous for posing simple but seemingly unanswerable questions, had been discussing flying saucer reports with Emil Konopinski, Edward Teller and Herbert York. After the talk moved on, he blurted out his question, remembered in slightly different words by each. Teller recalled general laughter, because everyone instantly understood. Fermi never published on it, and some scholars have questioned whether the paradox should carry his name at all. Similar ideas appear much earlier, in Bernard de Fontenelle in 1686 and in the writings of the rocket pioneer Konstantin Tsiolkovsky.
The term 'Fermi paradox' was coined in 1977, after Michael Hart argued in 1975 that the absence of visitors suggested 'we are the first civilization in our Galaxy'. Frank Tipler went further, arguing that alien self-replicating probes should already be here. The debate had real consequences: Senator William Proxmire cited Tipler when he pushed to end NASA's funded search for extraterrestrial intelligence in 1981.
Proposed answers fall into broad families. Perhaps intelligent life is extremely rare, blocked by some 'Great Filter', a term coined by Robin Hanson in 1996, with the origin of life itself a leading candidate. Perhaps civilisations do not last long. Perhaps they exist but choose not to be seen, as in the 'zoo hypothesis', which Tsiolkovsky anticipated. Several of these answers carry uncomfortable implications for our own future.
Source: Wikipedia — Fermi paradox · Text summarised from Wikipedia (CC BY-SA 4.0)
