AST 115 1st Edition Lecture 37 Outline of Last Lecture I. The Big Banga. Chronologyb. Comments on the Big Bang TheoryII. The Forces of NatureIII. The Big Bang Theory (plus inflation)a. Cosmic Horizon ProblemIV. The Future of the UniverseOutline of Current Lecture I. The Future of the Universe continuedII. Resolutions of Olbers’ ParadoxIII. Introduction to Chapter 15 – Astrobiologya. Life Beyond Earthb. Probability of Extra – Terrestrial LifeCurrent Lecture The Future of the Universe continued…o We think our universe is an open universeo Measures of luminous mass indicate that the average density is too low and thus an open universe. But dark matter pushes value near the critical density.o More recently, the observation of the acceleration of the expansion rate confirmsthat the universe is open (but curiously close to being flat).o 2 – dimensional analogs: Closed Flat OpenThese 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. Resolutions of Olbers’ Paradoxo 1) The Paradox implicitly assumes a static universe, but we now have evidence that the universe is expanding. Light from distant stars can be reshifted to invisibility in the infrared and radio part of spectrum.o 2) The Paradox implicitly assumes an infinitely old universe in which light from infinitely far away has had time to get here. The Big Bang theory says the universe began 13.8 BY ago, so light from stars, say 200 BLY away, hasn’t had timeto get here yet. These are beyond our “Cosmic horizon”. Note: the cosmic horizon represents the ultimate limit of detectability of objects in the universe. This is determined by the speed of light and the age of the universe. The radius of the cosmic horizon is now 13.8 BLY. A billion years from now,it will be 14.8 BLY. The radium of the “observable universe” is how far we can “see” with current technology. Before 1609, this was 2.5 MLY. Now, using modern telescopes, the radius of the observable universe is about 13.2 BLY. Introduction to Chapter 15 – Astrobiologyo Life Beyond Earth Life = carbon-based, water-based, “life as we know it”. Carbon can join with up to three other atoms in long molecules that have strong, yet flexible bonds. Organic molecules are plentiful on Earth. “Life” would seem to require: planets like the Earth, orbiting stars like the Sun. Such planets would have to be far enough from its star to have water be liquid, yet not so far that it would be ice. “Habitable zone” or “Goldilocks zone” should exist around any star. In our solar system: Venus is too close to the Sun and is too hot for “life”. Mars is near the outer edge of the habitable zone.o Probability of Extra – Terrestrial Life Drake Equation = an estimate of the current number, N, of intelligent, communicative civilizations in the Galaxy. We consider only our Galaxy because extra-galactic distances are so great that communication with any intelligent beings would be essentially impossible. N is the product of several
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