The Doomsday Clock isn't a clock and it doesn't keep time. It's a metaphor introduced by The Bulletin of the Atomic Scientists to gauge public safety.

末日时钟并不是真正的计时钟表，而是一面虚构的钟面，由芝加哥大学的《原子科学家公报》杂志于1947年设立，以标示出世界受核武威胁的程度。

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The doomsday clock in these stories indicates danger and the possibility of avoidance.

WSJ: Word Craft: Benjamin Percy, Author of Red Moon, on the Ticking Clock

In Japan, the demographic clock is already ticking toward a kind of demographic doomsday.

FORBES: Decline Of The Asian Family: Drop In Marriages, Births, Threatens Economic Ascendancy