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Download Planet Detection - University of Washington
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Astronomy190 - Topics in Astronomy Astronomy and Astrobiology Lecture 21: Search for Extraterrestrial Intelligence Ty Robinson Questions of the Day • What is the Drake Equation, and why is it useful? • Even if life arises, will it inevitably evolve towards intelligence? • What are the methods SETI uses to search for intelligence today? Are We Alone? The Drake Equation Estimating the number of civilizations in the Milky Way with which we might hope to communicate Nc = Ns x fp x Ne x fl x fi x fc x L The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L number of stars in the galaxy (~200 billion) The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L fraction of stars that have planets (> 10%) QuickTime™ and a decompressor are needed to see this picture. The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L number of terrestrial planets per planetary system in the Habitable Zone QuickTime™ and a decompressor are needed to see this picture. The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L fraction of such planets on which life actually evolved QuickTime™ and a decompressor are needed to see this picture. The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L fraction of inhabited worlds that develop intelligent life The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L fraction of worlds with intelligent beings that produce a civilization capable of interstellar communication QuickTime™ and a decompressor are needed to see this picture. The Drake Equation Nc = Ns x fp x Ne x fl x fi x fc x L the lifetime of such civilizations (divided by the age of the galaxy) What if Nc is much larger than 1? Where are they? What if Nc is less than 1? Is anybody out there? Nc = Ns x fp x Ne x fl x fi x fc x L fi : the Question of Intelligence Is the evolution of intelligence inevitable? fi : the Question of Intelligence • two schools of thought 1. intelligent (radio telescope building) life is rare • we’ve had life for 3.5 Gyrs, but radio and TV signals for only the last 50 yrs. • intelligence evolved as the result of random chance • remember: evolution is not goal-oriented! fi : the Question of Intelligence • two schools of thought 2. there is evolutionary pressure for intelligence • natural selection promotes greater intellectual capability • if humans hadn’t developed technology-building intelligence, something else would have • maybe there is a widespread selection pressure for intelligence Convergent Evolution • organisms of different evolutionary backgrounds that occupy similar ecological niches will eventually come to resemble one another • maybe intelligence increases fitness so much that if that niche is not filled, species will be selected for intelligence via convergent evolution Is there an evolutionary trend favoring intelligence? Measuring Intelligence big brain small brain EQ= encephalization quotient Encephalization Quotient (EQ) Evolution to Higher Intelligence? Time (millions of years ago) Evolution to Higher Intelligence? Intelligence = Technology? The Search for Extraterrestrial Intelligence Radio SETI: Where to look? • a “hailing signal” would need to have a narrow bandwidth signal component – easier to see against “noise” from interstellar gas, distant galaxies, the radio receiver • first proposed to be tuned to 1420 MHz, the frequency of H gas in the interstellar medium – for comparison: NPR is at 94.9 MHz Categories of Signals • signals used for local communication where intelligent beings live • signals used for communication between a civilization’s home world and some other site • intentional signal beacons Finding and Decoding Signals • some things to look for: –broadcast in a strong, narrow wavelength –flashing on/off or switching frequencies –repetition –prime numbers? π? e? 1,679 bits 23 x 73 Where do we look? • targeted search – not all locations in space are equally probable for intelligent life • sky survey – no assumptions made about where they might be located Questions of the Day • What is the Drake Equation, and why is it useful? • Even if life arises, will it inevitably evolve towards intelligence? • What are the methods SETI uses to search for intelligence today? Quiz 1 - Explain why methane on Mars is a biosignature but methane on Titan is not. 2 - What term in the Drake Equation will NASA’s Kepler mission be the first to measure? 3 - What is one thing you did not understand from today’s lecture?
