If one imagines running the clock backward in time , any given region of the universe shrinks and all galaxies in it get closer and closer until they smash together in a cosmic traffic jam ? the big bang 不妨想像一下，将时间的流向倒转，于是宇宙中的每块区域都越缩越小，所有星系越来越靠近，直到挤在一起，造成宇宙大塞车这就回到了大霹雳。
