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A back-of-the-envelope calculation is a rough calculation, typically jotted down on any available scrap of paper such as the actual back of an envelope. It is more than a guess but less than an accurate calculation or mathematical proof. The defining characteristic of back-of-the-envelope calculations is the use of simplified assumptions. A similar phrase is "back of a napkin", which is also used in the business world to describe sketching out a quick, rough idea of a business or product.〔(NetworkWorld.com: Ethernet, Compaq, Facebook and napkins )〕 In British English, a similar idiom is "back of a fag packet". == History == In the hard sciences, ''back-of-the-envelope calculation'' is often associated with physicist Enrico Fermi,〔(Where Fermi stood. - Bulletin of the Atomic Scientists | Encyclopedia.com )〕 who was well known for emphasizing ways that complex scientific equations could be approximated within an order of magnitude using simple calculations. He went on to develop a series of sample calculations, which are called "Fermi Questions" or "Back-of-the-Envelope Calculations" and used to solve Fermi problems.〔( Back of the Envelope Calculations )〕〔(High School Mathematics at Work: Essays and Examples for the Education of All Students )〕 Fermi was known for getting quick and accurate answers to problems that would stump other people. The most famous instance came during the first atomic bomb test in New Mexico on 16 July 1945. As the blast wave reached him, Fermi dropped bits of paper. By measuring the distance they were blown, he could compare to a previously computed table and thus estimate the bomb energy yield. He estimated 10 kilotons of TNT; the measured result was 18.6.〔(Nuclear Weapons Journal, Los Alamos National Laboratory, Issue 2 2005. )〕 A story is told about how Albert Einstein and his wife visited the Mount Wilson Observatory in 1931. When she heard that the 100-inch telescope there is used to determine the shape of the universe, Elsa Einstein stated "Well, my husband does that on the back of an old envelope."〔()〕 Another example is Victor Weisskopf's pamphlet ''Modern Physics from an Elementary Point of View''.〔(Lectures given in the 1969 Summer Lecture Programme, CERN (European Organization for Nuclear Research), CERN 70-8, 17 March 1970. )〕 In these notes Weisskopf used back-of-the-envelope calculations to calculate the size of a hydrogen atom, a star, and a mountain, all using elementary physics. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Back-of-the-envelope calculation」の詳細全文を読む スポンサード リンク
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