Miracle on Probability Street

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Post on 25-Jul-2016




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<ul><li><p>32 S C I E N T I F I C A M E R I C A N A U G U S T 2 0 0 4</p><p>BR</p><p>AD H</p><p>INE</p><p>S</p><p>Skeptic</p><p>Because I am often introduced as a professional skeptic, peo-ple feel compelled to challenge me with stories about highly im-probable events. The implication is that if I cannot offer a satis-factory natural explanation for that particular event, the gen-eral principle of supernaturalism is preserved. A common storyis the one about having a dream or thought about the death ofa friend or relative and then receiving a phone call five minuteslater about the unexpected death of that very person.</p><p>I cannot always explain such specific incidents, but a princi-ple of probability called the Law of Large Numbers shows thatan event with a low probability of occur-rence in a small number of trials has a highprobability of occurrence in a large numberof trials. Events with million-to-one oddshappen 295 times a day in America.</p><p>In their delightful book Debunked!(Johns Hopkins University Press, 2004), CERN physicistGeorges Charpak and University of Nice physicist Henri Brochshow how the application of probability theory to such eventsis enlightening. In the case of death premonitions, suppose thatyou know of 10 people a year who die and that you think abouteach of those people once a year. One year contains 105,120 five-minute intervals during which you might think about each of the10 people, a probability of one out of 10,512certainly an im-probable event. Yet there are 295 million Americans. Assume,for the sake of our calculation, that they think like you. Thatmakes 110,512 295,000,000 = 28,063 people a year, or 77 peo-ple a day for whom this improbable premonition becomes prob-able. With the well-known cognitive phenomenon of confirma-tion bias firmly in force (where we notice the hits and ignore themisses in support of our favorite beliefs), if just a couple of thesepeople recount their miraculous tales in a public forum (next onOprah!), the paranormal seems vindicated. In fact, they aremerely demonstrating the laws of probability writ large.</p><p>Another form of this principle was suggested by physicistFreeman Dyson of the Institute for Advanced Study in Princeton,N.J. In a review of Debunked! (New York Review of Books,March 25), he invoked Littlewoods Law of Miracles (JohnLittlewood was a University of Cambridge mathematician): In</p><p>the course of any normal persons life, miracles happen at a rateof roughly one per month. Dyson explains that during the timethat we are awake and actively engaged in living our lives, rough-ly for eight hours each day, we see and hear things happening ata rate of about one per second. So the total number of events thathappen to us is about thirty thousand per day, or about a millionper month. With few exceptions, these events are not miracles be-cause they are insignificant. The chance of a miracle is about oneper million events. Therefore we should expect about one miracleto happen, on the average, every month.</p><p>Despite this cogent explanation, Dy-son concludes with a tenable hypothe-sis that paranormal phenomena may re-ally exist, because, he says, I am not areductionist. Further, Dyson attests, thatparanormal phenomena are real but lie</p><p>outside the limits of science is supported by a great mass of ev-idence. That evidence is entirely anecdotal, he admits. But be-cause his grandmother was a faith healer and his cousin was aformer editor of the Journal for Psychical Research and becauseanecdotes gathered by the Society for Psychical Research and oth-er organizations suggest that under certain conditions (for ex-ample, stress) some people sometimes exhibit paranormal pow-ers (unless experimental controls are employed, at which pointthe powers disappear), Dyson finds it plausible that a worldof mental phenomena should exist, too fluid and evanescentto be grasped with the cumbersome tools of science.</p><p>Freeman Dyson is one of the great minds of our time, and Iadmire him immensely. But even genius of this magnitude can-not override the cognitive biases that favor anecdotal thinking.The only way to find out if anecdotes represent real phenome-na is controlled tests. Either people can read other peoplesminds (or ESP cards), or they cant. Science has unequivocallydemonstrated that they cantQED. And being a holist insteadof a reductionist, being related to psychics, or reading aboutweird things that befall people does not change this fact.</p><p>Michael Shermer is publisher of Skeptic (www.skeptic.com)and author of The Science of Good and Evil.</p><p>Miracle on Probability StreetThe Law of Large Numbers guarantees that one-in-a-million miracles happen 295 times a day in America By MICHAEL SHERMER</p><p>In the course of anynormal persons life,</p><p>miracles happen roughlyonce a month.</p><p>COPYRIGHT 2004 SCIENTIFIC AMERICAN, INC.</p></li></ul>


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