IT GETS EVEN FUNNIER WHEN THEY ADD UNIVERSES:

Are we alone?: There could be more than 200 extraterrestrial civilisations humming away in our galaxy right now. Cosmos wonders where they are (Tim Dean, April 2007, Cosmos)

WHICH IS THE more shocking proposition: that our galactic neighbourhood is riddled with advanced alien civilisations? Or that we humans are a solitary beacon of intelligent life in a silent universe of almost incomprehensible vastness?

Either prospect is enough to keep you awake at night. Yet one of these two statements is likely true. We just don't know which one.

Of course we know, as witness the proviso folks have to add to option 1: "Despite the plethora of advanced civilizations, none can communicate with us."

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A grim reckoning: What has a 16th-century astronomer got to do with the defeat of governments and the possible extinction of the human race? Answers in fractions please (J. Richard Gott III, 11/15/97, New Scientist)

Early this century, when astronomer Edwin Hubble observed approximately the same number of galaxies receding from Earth in all directions, it looked as if our Galaxy was at the exact centre of a great explosion. But reasoning with the Copernican principle, scientists concluded instead that the Universe must look that way to observers in every galaxy - it would be presumptuous to think that our galaxy is special. As a working hypothesis, the Copernican principle has been enormously successful because, out of all the places intelligent observers could be, there are only a few special places and many nonspecial places. A person is simply more likely to be in one of the many nonspecial places. But the Copernican principle doesn't apply only to placement of galaxies in space - it works for the placement of moments in time as well.

What does it imply for "Homo sapiens ?"We have been around for about 200 000 years. If there is nothing special about the present moment, then it is 95 per cent certain that the future duration of our species is between 1/39 and 39 times 200 000 years. That is, we should last for at least another 5100 years but less than 7.8 million years.

Since we have no actuarial data on other intelligent species, this Copernican estimate may be the best we can find. It gives our species a likely total longevity of between 0.205 million and 8 million years, which is quite in line with those for other hominids and mammals. The Earth is littered with the bones of extinct species and it doesn't take much to see that we could meet the same fate. Our ancestor "H. erectus" lasted 1.6 million years, while "H. neanderthalensis" lasted 0.3 million years. The mean duration of mammal species is 2 million years, and even the great "Tyrannosaurus rex" lasted only 2.5 million years.

For us, the end might come from a drastic climate change, nuclear war, a wandering asteroid or comet, or some other catastrophe that catches us by surprise, such as a bad epidemic. If we remain a one-planet species, we are exposed to the same risks as other species, and are likely to perish on a similar timescale.

Some people might think that the discoveries of our age - space travel, genetic engineering and electronic computers - place us in a special position. These breakthroughs, they might say, could lead us to spawn new intelligent species, including intelligent machine species, enhancing our chances of survival. But such thinking may raise false hopes. For, according to the Copernican principle, you are likely to be living in a century when the population is high because most people will be born during such periods. And since it is people who make discoveries, it is not surprising that you will live in a century when many interesting discoveries are being made. But your chance of being born 200 000 years after the beginning of your intelligent lineage, in the very century when a discovery is made that guarantees it a billion-year future, is very small, because a billion years of intelligent observers would be born after such a discovery, and you would be more likely to be one of them. If you believe that any current discovery will dramatically increase our longevity, you must ask yourself: why am I not already one of its products ? Why am I not an intelligent machine or genetically engineered ?

Posted by Orrin Judd at August 10, 2009 11:47 AM