You can picture a beam of light setting off and travelling for a whole year without stopping. The length it covers is the light year — so large that stop being useful and the number stops feeling like a number. That is the quiet trick of the word: it names a gap too big to picture. Once a word carries that feeling, people borrow it for any gap they want to call enormous, whether the gap is in quality or in years.
可以想成一道光出發，不停地跑滿一整年。它跑過的長度就是一光年——大到公里已經不管用，數字也不再像數字。這個字最厲害的地方就在這裡：它替一個「大到想像不出來」的距離取了名字。一旦一個字帶著這種感覺，人就會把它借去講別的差距。不管那個差距是好壞上的落差，還是時間上的遙遠，借過來就都變得很大。