Nuclear weapons are different from every other type of weapons technology. Their awesome destructive potential and the unparalleled consequences of their use oblige us to think critically about the ethics of nuclear possession, planning, and use. Joe Nye has given the ethics of nuclear weapons deep consideration. He posits that we have a basic moral obligation to future generations to preserve roughly equal access to important values, including equal chances of survival, and proposes criteria for achieving conditional or “just deterrence” to minimize the risk of nuclear use and help preserve these values. While Nye's conditions are laudable, they are not achievable. They rely on flawed assumptions about the nature of nuclear weapons and the inherent risks of the nuclear deterrence system. Since the Cold War ended, the strategy and practice of nuclear deterrence has grown riskier, more urgent, more dangerous, and less stable. It is time to rethink how we manage nuclear risks. A new nuclear security system must be built on the design principle that the consequences of system failure cannot threaten to end or fundamentally disrupt civilization. We owe the future a new nuclear security strategy that can prevent an existential global nuclear event.

Using a simple, coarse-grained Poisson process model, we calculate – for seven types of astrophysical catastrophe – both their individual and combined threat to complex lifeforms (extraterrestrial intelligences (ETIs)) throughout the Milky Way Galaxy. In terms of cumulative effects, we calculate that ETIs are likely to be astrophysically driven extinct on timescales of roughly once every 100 million years. In terms of comparative effects, large bolide impactors represent the most significant type of astrophysical contribution to the galaxy-wide debilitation of hypothesized ETI civilizations. Nonetheless, we conclude that astrophysical existential threats – whether taken singly or in combination – are likely insufficient, alone, to explain the Fermi Paradox. Astrophysical catastrophes, while both deadly and ubiquitous, do not appear to be frequent enough to wipe out every species in the Galaxy before they can attain or utilize spacefaring status.