Are humans alone in the universe? Three philosophers from Oxford University have studied the existing scientific literature to conclude that we probably are.
This seems to have upset some people. 鈥淚鈥檝e already got many emails from people who say I鈥檓 wrong because we鈥檝e already met aliens,鈥� says Anders Sandberg, who led the work.
Contrary to , however, Sandberg says scientists are quite optimistic that we have galactic neighbours. Of some 80 papers the team examined, 64 per cent estimated there were at least 100 extra-terrestrial civilisations out there.
Advertisement
At the crux of the discussion is the Fermi Paradox, which asks why, in a universe of near-infinite proportions, we have yet to spot aliens. Explanations range from a small likelihood of advanced life evolving to the idea that aliens are simply hiding from us.
Alien equation
Most discussions of the Fermi Paradox centre on the Drake equation, developed by alien-hunting astronomer Frank Drake. It requires educated guesses of the values of seven key variables, such as the rate at which stars form, the number of planets those stars produce and the fraction of planets which can support life.
Put all these together and you get an estimate for how many alien civilisations you can expect to see in the Milky Way. The trouble is, no one can agree on what numbers to use.
Some variables in the equation are well understood. Star formation in the Milky Way, for example, is around 1-10 solar-mass stars per year. But little is known about the conditions under which life develops, and how common they are. Published studies tend to lean toward the optimistic side, says Sandberg, because pessimists think it鈥檚 a waste of time to even entertain the question.
To get a more balanced view, Sandberg and his colleague combined variables from various published calculations of Drake鈥檚 equation to get a sense of how spread out these estimates are. They took聽one paper鈥檚 estimate of planet formation, another鈥檚 calculation of how frequently intelligent life develops, and so on.聽 鈥淭his is armchair astronomy, we haven鈥檛 even looked out the window,鈥� he says.
Galactic uncertainty
By repeating this over and over, they calculated a range of possible guesses for the number of alien civilisations. They estimate there is a 53 to 99.6 per cent chance we are alone in the galaxy, and a 39 to 85 per cent chance we are alone in the universe 鈥� most media reports have, of course, gone with the larger figures.
Sandberg says the main result of the paper is to illustrate that the Fermi Paradox is not paradoxical at all. While published estimates for the number of alien civilisations tend to paint an optimistic picture, the level of uncertainty among them means the overall picture is doubtful.
鈥淚f you want to argue there is certainly intelligent life, you need to argue some of these parameters are in a narrow range, which is a bold claim,鈥� says Sandberg. 鈥淏ut claiming that we are alone also takes a bold claim, as you have to cut off optimistic part of that range.鈥�
In other words, moving in either direction requires hard evidence, something alien-hunters are short on. It鈥檚 no surprise, then, that we can鈥檛 say for sure whether we are all alone.
Reference:
