lecture_31 - The Search for Extraterrestrial...

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-1 The Search for Extraterrestrial Life (Lectures #31-32) Astronomers have been making all sorts of mind-boggling discoveries over the past century – black holes, quasars, the leftover radiation from the Big Bang, just to name a few. What we have not yet found with any certainty is alien life that evolved somewhere other than the Earth. And yet clearly this would be the most stunning discovery the human race could ever make. The public may be fascinated with black holes and the Big Bang in an academic sense, but the discovery that we are not alone in the universe would have profound social, political, and possibly economic implications for our entire planet. The possibility of extraterrestrial life is the subject of practically all science fiction, and it is hard to imagine a universe with only one inhabited planet out of trillions. Given the number of planets that must exist in our galaxy (the Milky Way) alone, it seems a virtual certainty that life must have evolved somewhere else – possibly even within our own solar system. If this is so, why haven’t we yet detected it? To answer this question, and the question of whether there might be intelligent, technologically advanced civilizations out there, we need to delve in some detail into the nature of life on Earth itself. Only once we understand how life came about on our own planet will we be able to speculate meaningfully about the possibility that it might have arisen elsewhere, and about the forms that life might take in other environments. What is life? There is no single, widely-accepted answer to the question “What is life?”. How do we distinguish between animate and inanimate matter? Does it have to do with the chemical composition, or perhaps with the complexity of the physical structures and chemical reactions that take place in a particular lump of material? Or is there some mysterious “essence” that lies outside the physical realm that renders matter “alive”? Obviously, people have been trying to answer this question for a long time. As far as we are concerned, we’re going to take a pragmatic, descriptive approach. For our purposes, for something to be considered alive, it must satisfy two characteristics: The ability to reproduce The ability to evolve into other forms Note that a flame on a matchstick satisfies the first criterion – it can reproduce itself by starting other fires and creating “copies” of itself. But it fails on the second criterion – fire by itself cannot change form into something essentially different. All it can do is flicker and change its shape. On the other hand, since Darwin we have realized that a distinguishing feature of living organisms on Earth is that they not only reproduce from generation to generation, but they also change over time, with one species changing slowly into another through the joint processes of genetic mutation and natural selection. It is clear from the fossil record
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This note was uploaded on 04/29/2008 for the course APHY 103 taught by Professor Woods during the Fall '08 term at SUNY Albany.

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lecture_31 - The Search for Extraterrestrial...

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