A Common Student Question: Are There Aliens? This question can launch a discussion of the possibility of life in the universe. The UFO Phenomenon ~50% of the US public believe intelligent ETs have visited the Earth. Many scientists readily accept a high probability of life somewhere in the universe. Good science does not accept UFO and alien visitation stories. Why? Photographs are not enough to support the extraordinary claim that aliens have visited Anecdotal stories Evidence more logically explained by known earthly phenomena No one has provided strong positive evidence Explanations are used to account for weak evidence -- the government is hiding the bodies --conspiracy/cover-up --scientists are biased/cant be trusted --ETs have modified peoples mind --witnesses abducted and no longer exist. Published: Nov 25, 2009 The Estacada News For three weeks in a row in January 1980, UFO sightings in Barton and Eagle Creek claimed the lead headlines on the front page of the newspaper. The headlines included Low flying UFO spotted in Barton flats, More UFO sightings reported here, and Hovering UFO photographed here. A retired pilot who witnessed one of the UFOs said that its flying properties were unlike any other aircraft or helicopter hes ever seen. The pilot said he saw a craft with six red lights in a v-formation descend rapidly, stop abruptly in mid-air, hover briefly and then commence traveling at a high rate of speed in another direction. source & references:0000 Vocabulary &pid=15.1 Green Bank Telescope Thank You Robert C. Byrd Drake Equation Plaque at NRAO Green Bank Conference Room N = R* f p n e f l f i f c L So the Drake Equation gives us an estimate of N, the number of civilization in our galaxy that are capable of communication. Lets see how what each of these number mean. R* is rate of star formation. 10 stars/year ~200 billion stars Estimates may be as high as 400 billion stars. Confident estimate. f p = fraction of stars that have planets. 0.5 ( conservative estimate ) Half of all stars form planets of some type. We have discovered over 1000 exoplanets to dat Recent survey suggests ALL do initially ( although they might not all develop real planets) We have only searched this much of the Milky Way using the Kepler Space Telescope. n e = number of planet per star that can support life. ~2 habitable planets per star. Can include habitable moons around large planets. f = fraction of habitable planets that actually develop life. 1.0 The fraction is 1 because life is believed to have arisen on Earth many time. f i = fraction of planets with life that actually develop intelligent life This fraction could be much lower since intelligence has been on Earth VERY RECENTLY occurring about half way through the total lifetime of our Sun. Probably the hardest parameter to estimate and the most uncertain. f c = fraction of civilizations that develop communication This fraction could be high, probably 1.0. L = length of time that civilization communicates. 10,000 years. Or until civilization destroys itself. Maybe 10 years (remember the Cold War). Maybe indefinitely. What Does All This Mean? Using Drakes original estimates for the factors (1961), N = 10 x 0.5 x 2 x 1 x 0.01 x 0.01 x 10,000 the Equation gives 10 communicating civilizations in the galaxy at any moment. But other reasonable estimates suggest values from 1 to 5000! fp, the fraction of stars that have planets around them n e, the number of suitable planets in each planetary system f l the fraction of suitable planets which develop life f i the fraction of life-bearing planets which develop intelligent life f t the fraction of intelligent life bearing planets which develop technology L, the length of time the civilisation releases signals into space What if theyve already tried to contact us and we missed the call? Works Cited Microsoft Encarta, Exobiologye.htmlhttp://www.pbs.org/wgbh/nova/origins/drak e.html nhttp://en.wikipedia.org/wiki/Drake_equatio n