The “crack of doom” is a phrase referring to the blaring of trumpets that heralds the Last Judgment. As you might expect from such a piquant phrase, it’s been used to some effect in literature.
In Moby Dick Melville uses it to describe the enduring dangers of the sea:
But though, to landsmen in general, the native inhabitants of the seas have ever regarded with emotions unspeakably unsocial and repelling; though we know the sea to be an everlasting terra incognita, so that Columbus sailed over numberless unknown worlds to discover his one superficial western one; though, by vast odds, the most terrific of all mortal disasters have immemorially and indiscriminately befallen tens and hundreds of thousands of those who have gone upon the waters; though but a moment’s consideration will teach that, however baby man may brag of his science and skill, and however much, in a flattering future, that science and skill may augment; yet for ever and for ever, to the crack of doom, the sea will insult and murder him, and pulverize the stateliest, stiffest frigate he can make; nevertheless, by the continual repetition of these very impressions, man has lost that sense of the full awfulness of the sea which aboriginally belongs to it.
Most famously, Shakespeare used it in Macbeth:
Thou art too like the spirit of Banquo; down!
Thy crown does sear mine eyeballs. And thy hair,
Thou other gold-bound brow, is like the first.
A third is like the former. Filthy hags,
Why do you show me this?—A fourth? Start, eyes!
What, will the line stretch out to th’ crack of doom?
