The problems scientists confront today are actually much harder than they were at the dawn of the nuclear age, and their successes more heartily earned. This is why it is so distressing that even Stephen Hawking, perhaps the world’s most famous living scientist, gets more attention for his views on space aliens than his views on nuclear weapons.Scientists’ voices are crucial in the debates over the global challenges of climate change, nuclear proliferation and the potential creation of new and deadly pathogens. But unlike in the past, their voices aren’t being heard.

Indeed, it was Albert Einstein’s letter to President Franklin D. Roosevelt in 1939, warning of the possibility that Hitler might develop a nuclear weapon, that quickly prompted the start of the Manhattan Project, the largest scientific wartime project in history. Then, in 1945, the same group of physicists who had created the atomic bomb founded the Bulletin of the Atomic Scientists to warn of the dangers of nuclear weapons, and to promote international cooperation to avoid nuclear war. As Einstein said in May 1946, “The unleashed power of the atom has changed everything save our modes of thinking, and thus we drift toward unparalleled catastrophe.”

The men who built the bomb had enormous prestige as the greatest physics minds of the time. They included Nobel laureates, past and future, like Hans A. Bethe, Richard P. Feynman, Enrico Fermi, Ernest O. Lawrence and Isidor Isaac Rabi.

In June 1946, for instance, J. Robert Oppenheimer, who had helped lead the Manhattan Project in Los Alamos, N.M., argued that atomic energy should be placed under civilian rather than military control. Within two months President Harry S. Truman signed a law doing so, effective January 1947.

Today, nine nuclear states have stockpiled perhaps 20,000 nuclear weapons, many of which dwarf the weapons dropped on Hiroshima and Nagasaki. Yet proliferation is as alarming as ever, even though President Obama signed, and Congress ratified, the new strategic arms-reduction treaty in 2010. Iran’s nuclear program could lead to conflict. So could the animosity between India and Pakistan, which both have nuclear weapons.

The United States is complicit, because whatever our leaders may say, our actions suggest that we have no real intention to disarm. The United Nations adopted the Comprehensive Test Ban Treaty, which would ban countries from testing nuclear weapons, in 1996. But it has not come into force; the Senate rejected ratification in 1999, and while President Obama has promised to obtain ratification, he has not shown enough urgency in doing so.