A short history of nearly everything - Bill Bryson [14]
What an interesting and exciting thought. We may be only one of millions of advanced civilizations. Unfortunately, space being spacious, the average distance between any two of these civilizations is reckoned to be at least two hundred light-years, which is a great deal more than merely saying it makes it sound. It means for a start that even if these beings know we are here and are somehow able to see us in their telescopes, they're watching light that left Earth two hundred years ago. So they're not seeing you and me. They're watching the French Revolution and Thomas Jefferson and people in silk stockings and powdered wigs—people who don't know what an atom is, or a gene, and who make their electricity by rubbing a rod of amber with a piece of fur and think that's quite a trick. Any message we receive from them is likely to begin “Dear Sire,” and congratulate us on the handsomeness of our horses and our mastery of whale oil. Two hundred light-years is a distance so far beyond us as to be, well, just beyond us.
So even if we are not really alone, in all practical terms we are. Carl Sagan calculated the number of probable planets in the universe at large at 10 billion trillion—a number vastly beyond imagining. But what is equally beyond imagining is the amount of space through which they are lightly scattered. “If we were randomly inserted into the universe,” Sagan wrote, “the chances that you would be on or near a planet would be less than one in a billion trillion trillion.” (That's 1033, or a one followed by thirty-three zeroes.) “Worlds are precious.”
Which is why perhaps it is good news that in February 1999 the International Astronomical Union ruled officially that Pluto is a planet. The universe is a big and lonely place. We can do with all the neighbors we can get.
3 THE REVEREND EVANS'S UNIVERSE
WHEN THE SKIES are clear and the Moon is not too bright, the Reverend Robert Evans, a quiet and cheerful man, lugs a bulky telescope onto the back deck of his home in the Blue Mountains of Australia, about fifty miles west of Sydney, and does an extraordinary thing. He looks deep into the past and finds dying stars.
Looking into the past is of course the easy part. Glance at the night sky and what you see is history and lots of it—the stars not as they are now but as they were when their light left them. For all we know, the North Star, our faithful companion, might actually have burned out last January or in 1854 or at any time since the early fourteenth century and news of it just hasn't reached us yet. The best we can say—can ever say—is that it was still burning on this date 680 years ago. Stars die all the time. What Bob Evans does better than anyone else who has ever tried is spot these moments of celestial farewell.
By day, Evans is a kindly and now semiretired minister in the Uniting Church in Australia, who does a bit of freelance work and researches the history of nineteenth-century religious movements. But by night he is, in his unassuming way, a titan of the skies. He hunts supernovae.
Supernovae occur when a giant star, one much bigger than our own Sun, collapses and then spectacularly explodes, releasing in an instant the energy of a hundred billion suns, burning for a time brighter than all the stars in its galaxy. “It's like a trillion hydrogen bombs going off at once,” says Evans. If a supernova explosion happened within five hundred light-years of us, we would be goners, according to Evans—“it would wreck the show,” as he cheerfully puts it. But the universe is vast, and supernovae