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Castle Bravo had been built according to the “Teller-Ulam” scheme—named for its co-designers, Edward Teller and Stanislaw Ulam—which meant, unlike with the far less powerful atomic bomb, this hydrogen bomb had been designed to hold itself together for an extra hundred-millionth of a second, thereby allowing its hydrogen isotopes to fuse and create a chain reaction of nuclear energy, called fusion, producing a potentially infinite amount of power, or yield. “What this meant,” Freedman explains, was that there was “a one-in-one-million chance that, given how much hydrogen [is] in the earth’s atmosphere, when Castle Bravo exploded, it could catch the earth’s atmosphere on fire.