N = R* fp * ne * fl * fi * fc * L, the Drake Equation:
* N = The number of communicative civilizations
* R* = The rate of formation of suitable stars (stars such as our Sun)
* fp = The fraction of those stars with planets. (Current evidence indicates that planetary systems may be common for stars like the Sun.)
* ne = The number of Earth-like worlds per planetary system
* fl = The fraction of those Earth-like planets where life actually develops
* fi = The fraction of life sites where intelligence develops
* fc = The fraction of communicative planets (those on which electromagnetic communications technology develops)
* L = The "lifetime" of communicating civilizations
It's the L, "lifetime" that worries me.
The following paragraphs are from page 9 of the document "Nuclear Forensics: A Capability At Risk": the Preface. Click on the "read" link below and a page embed PDF will open in either another tab or browser window, depending on your settings.
"Leaders of the United States for more than a decade have believed that nuclear terrorism is among the gravest threats to our nation. Beyond the terrible loss of life, which in itself is difficult to appreciate fully, the successful detonation of one or more nuclear explosives in a U.S. city and the potential for more detonations could transform our nation into a national security state, focused on common defense to the detriment of the justice, general welfare, and blessings of liberty envisioned by our nation's founders. The nation's responses to the attacks on the United States on September 11, 2001, hint at this danger. America has proven resilient, but a nuclear detonation would cause far more death and destruction than were seen on 9/11.
"Our nation's ability to conduct forensic analysis of nuclear materials, nuclear explosions, and debris from radiological dispersion devices can contribute substantially to deterring, limiting, and responding to nuclear terrorist—complementing and enhancing efforts to secure nuclear materials and detect theft, diversion, and clandestine production. The capability to identify or exclude possible origins of nuclear material could, most importantly, enhance U.S. diplomatic and investigative efforts to prevent nuclear terrorism."