One loud moment, and after it nothing is arranged the way it was before. There is no slow build-up and no half-way stage: the change is finished in an instant, and everything that follows dates itself from that instant. That is why people reach for this name whenever a whole system turns over on a single day.
From the word’s history
Wiktionary records that the name was coined by the English astronomer Fred Hoyle on a BBC Third Programme broadcast on 28 March 1949, and notes that the popular belief that Hoyle meant it as a put-down has been rejected by Hoyle himself.
Wiktionary 記載這個名字是英國天文學家 Fred Hoyle 在 1949 年 3 月 28 日的 BBC 廣播節目上講出來的。它也特別指出一個常見的誤會：很多人以為 Hoyle 是拿這個詞在嘲笑這套理論（他支持的是另一套說法），但 Hoyle 本人否認過。換句話說，這個名字一開始就是個好記、好唸的形容，而「一聲巨響、一瞬間全變」正是後來各種借用都留著的部分。
Wiktionary, "Big Bang"
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