宇宙開始的那一瞬間
這一支是名字原本指的事件，其他用法都是從它借過去的。
noun · B1
The huge explosion at the beginning of time that most scientists believe started the universe. Space, time and everything in them began expanding from one tiny, very hot point at that moment.
大霹靂／宇宙大爆炸
核心畫面
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.
可以想成一聲巨響：響完之後，原本的擺法就全變了。沒有慢慢醞釀，也沒有過渡階段——改變在一瞬間就完成，之後的一切都從那…更多收起
可以想成一聲巨響：響完之後，原本的擺法就全變了。沒有慢慢醞釀，也沒有過渡階段——改變在一瞬間就完成，之後的一切都從那一瞬間開始算時間。這個畫面最關鍵的不是「很大聲」，而是「一次到位」。所以只要一整套東西是在同一天全部換掉，英文就很容易借這個名字來用。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 entry for Big Bang (packet evidence kaikki:3f6f69a190036ae4:739021673), etymology_text.
Two branches
一次到位的大改變
借的不是宇宙，是那個「一瞬間全部換掉」的形狀：舊的當天停，新的當天起。
noun · C1
The name given to the sudden change in the system and rules of the London stock exchange in 1986, which took effect on one day and opened the market up after years of tight restrictions.
大改革（倫敦股市，1986）