Plain Nonsense

You Can't Write Off Alien Intelligence

POPULAR books about science, even those written by scientists, do not usually make front page newspaper stories. But this happened recently with a book called Rare Earth: Why Complex Life is Uncommon in the Universe, by an astronomer and a geologist, Peter D. Ward and Donald Brownlee, and it has been given far more praise by other scientists than I feel it actually deserves. The book's thesis is that the chances of advanced technological life elsewhere in the Universe (not just in our galaxy) are extremely low. According to the New York Times, this book, written with such apparent authority, could endanger financing

Are there other intelligences in our galaxy?

of the privately-funded search for alien intelligence that currently runs at about £6 million a year. But ought the book to have this effect? In my opinion it makes a feeble case. While the geological side of its argument is excellent - describing the billions of years during which Earth was uninhabitable - its astronomical side is very weak. The book points out correctly that most stars, unlike the Sun, are double or multiple star systems. It then goes on to assert that in most cases, if not in all, this would inhibit the formation of habitable worlds in their orbits - a claim that is plainly nonsense. It would indeed be true in cases where two stars are very close to each other, say at the distance between the Sun and Mars. Whether an Earth-like world lay between them or outside them, its orbit would be chaotic and the radiation it received would be lethal. Yet many double stars are not like this at all. The pair are often further apart than Uranus is from the Sun, so that creatures on an Earth-like world circling one of them would see the other as just a bright star. I do not believe it would affect their lives in the least. This is the case with the two stars of alpha Centauri, the nearest stellar system to ours. Its two stars never approach each other more closely than eleven times the Earth-Sun distance, so that either might be a suitable abode for life. A more extreme case, but just as typical, is Mizar in the Plough. There are two Mizars circling one another, separated by 37 billion miles, nearly 400 times the Earth-Sun distance! And what of multiple stars? Again there need be no problem. Take epsilon Lyrae, the famous "double double", where two pairs of widely separated stars circle two others at a still greater distance. Plenty of room there for some healthy worlds. I do not myself believe there are other intelligences in our galaxy. If there were, they would surely have visited us (a point the book does not even make). But the number of galaxies in the Universe is so huge, perhaps 100 billion, equal to the approximate number of stars in our own galaxy. Square this number, and you have an estimate of the total number of stars in the entire cosmos of one followed by 22 noughts. To say that none of them are likely to nourish an advanced species is to make a very arrogant statement. Let the search for intelligent extraterrestrials continue.