AST 115 1st Edition Lecture 38 Outline of Last Lecture I. The Future of the Universe continuedII. Resolutions of Olbers’ ParadoxIII. Introduction to Chapter 15 – Astrobiologya. Life Beyond Earthb. Probability of Extra – Terrestrial LifeOutline of Current Lecture I. Drake Equation ContinuedII. Communication with Extra-Terrestrial IntelligenceCurrent Lecture Factors of the Drake Equation:o The first two factors are astronomical in nature and are reasonable well-known. One is the rate at which solar-type stars form in the Galaxy.o Next is the fraction of solar-type stars that have planets. We have discovered hundreds of massive Jovian-like planets orbiting nearby yellow stars.o This evidence strongly suggests that other smaller, terrestrial-like planets might also exist.o The next several factors are biological in scope and not well-known. What is the probability that “life” will emerge on a planet just like Earth in some solar-type star’s habitable zone?o No one knows yet. All we can do is make estimates of such factors.o The last factor is the longevity (lifetime) of technologically advanced civilizations. It is the most important factor and the one for which we have only one known case.o Optimistic Ncc:= (1)(0.5)(0.1)(1)(1)(0.5)(4 × 106) ~ 1 milliono Pessimistic Ncc:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.= (1)(0.5)(0.1)(0.1)(0.1)(0.1)(4 × 103) ~ 1 The Pessimistic Ncc suggests that we could be unique. In the Optimistic case, the typical separation between civilizations would be: ~ 250 LY- Radio waves would take 250 years to travel to extra-terrestrial life. How could we hope to communicate with any such beings? Radio waves. Communication with Extra-Terrestrial Intelligence (CETI)o By actual travel (outgoing) Best current speed: ~ 22 km/sec (~47,000 mph). Achieved at the launch of the New Horizon probe to Pluto. How long to get to Alpha Centauri at our best possible current speed?- About 80,000 yrs. Best theoretical speed: relativistic v → c. (Velocity = speed of light).- According to special relativity theory, no object with mass can achieve the speed of light.- There is no objection, however, to getting closer and closer to the speed of light by expending more and more energy.- Assuming that we could somehow accomplish relativistic travel, we find a very strange result. - Ex: Trip at 99.5% of c to Alpha Centauri. Round distance ~ 8 LY. But a moving clock runs slow at this speed by a factor of ~ 10. Thus, the travelers would experience 8/10 yr or ~ 10 months. They would return on Earth 8 yrs after departure.o By sending artifacts Pioneers 10 and 11 each have pictographs to indicate who sent them and when. And Voyagers 1 and 2 each have gold-plated records with sights and sounds of Earth encoded. Voyager 2 should pass in the vicinity of Sirius (9 LY away) in ~ 80,000 yrs.o By traveling (incoming/they visit us) UFOs (Unidentified Flying Objects): term has come to imply “flying saucers”. However, this is incorrect. IFOs (Identified Flying Objects): Most UFOs are explainable as astronomical, meteorological, biological, or other natural phenomena in which case they become IFOs.o By messages Radio messages (as opposed to lasers; lasers could be seen as a threat) Outgoing: - Unintentionally (strong radio and TV broadcasts since 1930s; powerful defense Radar since the 1950s).- Intentionally (in 1974, the Arecibo radio telescope sent a coded message toward the Great Globular Star Cluster in Hercules, M13). We have not yet received a reply. Incoming (most efficient)- SETI = Search for Extra-Terrestrial Intelligence- “Listen” with radio
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