What the Doomsday Clock actually measures

Where it comes from

The Bulletin of the Atomic Scientists was founded in 1945 by scientists who had worked on the Manhattan Project. The clock first appeared on the cover of the Bulletin in 1947 as a graphic device — a way to communicate risk to people who were not going to read a technical paper about it.

The setting is decided by the Bulletin's Science and Security Board, in consultation with its Board of Sponsors, which has long included Nobel laureates. It is announced periodically rather than continuously, and the reasoning is published alongside it. Reading that statement is the entire point; the number by itself is a headline, not information.

What it covers

The clock started as a nuclear indicator and has widened over the decades. The Bulletin's stated scope now includes nuclear risk, climate change, biological threats, and disruptive technologies — the categories of danger that are made by people and could, in principle, be unmade by them.

What it is not

It is not a probability. It is not a forecast. It is not derived from a model that anyone can run, and it does not tick forward on its own between announcements. It has moved away from midnight as well as toward it, which is the clearest evidence that it is an assessment rather than a countdown.

It also says nothing about asteroids, supernovae, or any other hazard that is not of human origin. Those are somebody else's department, and that department has telescopes.

• Not a prediction of when anything will happen.
• Not a measurement with units — 'minutes' are rhetorical.
• Not automatic; a human board decides each setting.
• Not concerned with natural hazards such as near-Earth objects.

How to read a clock-move headline

When the setting changes, open the Bulletin's own statement before anything else. It names the specific developments the board weighed. Almost every viral version of the story omits them, which is how a considered risk assessment becomes a screenshot with an alarmed caption.

For the current setting and the reasoning behind it, go to the Bulletin directly. We deliberately don't reprint a number here that could quietly go out of date on a page you found eighteen months from now.