Dear Mr. President:

Recent articles in the New Yorker and Washington Post report that the use of tactical nuclear weapons against Iran is being actively considered by Pentagon planners and by the White House. As members of the profession that brought nuclear weapons into
existence, we urge you to refrain from such an action that would have grave consequences for America and for the world.

1800 of our fellow physicists have joined in a petition opposing new US nuclear weapons policies that open the door to the use of nuclear weapons in situations such as Iran's. These policies represent a "radical departure from the past", in the words of Linton
Brooks, National Nuclear Security Administration director. Indeed, since the end of World War II, US policy has considered nuclear weapons "weapons of last resort", to be used only when the very survival of the nation or of an allied nation was at stake, or at
most in cases of extreme military necessity. Instead, the new US nuclear weapons policies have significantly lowered the threshold for the potential use of nuclear weapons, as clearly evidenced by the fact that they are being considered as another tool in the
toolbox to destroy underground installations that are "too deep" to be destroyed by conventional weapons. This is a major and dangerous shift in the rationale for nuclear weapons. In the words of the late Joseph Rotblat, Nobel Peace Prize recipient for his
efforts to prevent nuclear war, "the danger of this policy can hardly be over-emphasized". Nuclear weapons are unique among weapons of mass destruction: they unleash the enormous energy stored in the tiny nucleus of an atom, an energy that is a million times
larger than that stored in the rest of the atom. The nuclear explosion releases an immense amount of blast energy and thermal and nuclear radiation, with deadly immediate and
delayed effects on the human body. Over 100,000 human beings died in the Hiroshima blast, and nuclear weapons in today's arsenals have a total yield of over 200,000 Hiroshima bombs.
Using or even merely threatening to use a nuclear weapon preemptively against a nonnuclear adversary tells the 182 non-nuclear-weapon countries signatories of the Nuclear
Non-Proliferation Treaty that their adherence to the treaty offers them no protection against a nuclear attack by a nuclear nation. Many are thus likely to abandon the treaty, and the nuclear non-proliferation framework will be damaged even further than it already has, with disastrous consequences for the security of the United States and the world.

There are no sharp lines between small "tactical" nuclear weapons and large ones, nor between nuclear weapons targeting facilities and those targeting armies or cities. Nuclear weapons have not been used for 60 years. Once the US uses a nuclear weapon again, it will heighten the probability that others will too. In a world with many more nuclear nations and no longer a "taboo" against the use of nuclear weapons, there will be a greatly enhanced risk that regional conflicts could expand into global nuclear war, with the potential to destroy our civilization. It is gravely irresponsible for the U.S. as the greatest superpower to consider courses of
action that could eventually lead to the widespread destruction of life on the planet.

We urge you to announce publicly that the U.S. is taking the nuclear option off the table in the case of all nonnuclear adversaries, present or future, and we urge the American people to make their voices heard on this matter.

Sincerely,

Philip Anderson, Michael Fisher, David Gross, Jorge Hirsch, Leo Kadanoff, Joel Lebowitz, Anthony Leggett, Eugen Merzbacher, Douglas Osheroff, Andrew Sessler
George Trilling, Frank Wilczek, Edward Witten