The scientists' warning can be reconciled with the DA, however. The Doomsday clock specifically estimates the proximity of atomic self-destruction—which has only been possible for about seventy years.[10] If doomsday requires nuclear weaponry then the Doomsday Argument 'reference class' is people contemporaneous with nuclear weapons. In this model, the number of people living through, or born after Hiroshima is n, and the number of people who ever will is N. Applying Gott's DA to these variable definitions gives a 50% chance of doomsday within 50 years.