大爆炸(big bang)
宇宙起源的一种模型，主张宇宙是从温度和密度都极高的状态中由一次爆炸性的膨胀而产生的，发生在100～150亿年前。它有两个基本假设︰第一是爱因斯坦提出的，能正确描述所有物质的引力相互作用的广义相对论；第二是观察者所看到的宇宙既同观测的方向无关，又同所处的位置无关。有了这两个假设，就能计算出宇宙在很早时候（称普朗克时间）的物理条件。按照1940年代伽莫夫所提出的模型，宇宙从早期高度压缩的状态迅速膨胀，同时其密度和温度稳定地降低。在数秒钟之内，物质远多於反物质，形成某些原子核。再经过数百万年原子就可以形成，且辐射可以在空间自由地传播。氢、氦和锂的丰度以及宇宙背景辐射的发现支持了这种模型理论，它还解释了星系的红移是空间膨胀的结果。
English version：
big bang
Model of the origin of the universe, which holds that it emerged from a state of extremely high temperature and density in an explosive expansion 10-15 billion years ago. Its two basic assumptions—that Albert Einstein's general theory of relativity correctly describes the gravitational interaction of all matter and that an observer's view of the universe does not depend on direction of observation or on location—make it possible to calculate physical conditions in the universe back to a very early time called the Planck time (after Max Planck). According to the model proposed by George Gamow in the 1940s, the universe expanded rapidly from a highly compressed early state, with a steady decrease in density and temperature. Within seconds, matter predominated over antimatter and certain nuclei formed. It took another million years before atoms could form and radiation could travel through space unimpeded. The abundances of hydrogen, helium, and lithium and the discovery of cosmic background radiation support the model, which also explains the red shifts of galaxies as resulting from the expansion of space.
