Confronting the bomb

A dangerous acceleration in the nuclear arms race is underway. The United States and Russia — which together hold almost 90% of the world’s nuclear weapons, at more than 5,000 warheads each — are building a new generation of nuclear weapons and delivery systems to replace their Cold War-era arsenals. China may now possess about 600 nuclear warheads. The United Kingdom, France, and Israel are upgrading their arsenals, while India, Pakistan, and North Korea are developing and growing theirs — and all the nuclear armed states and NATO regularly rehearse their nuclear war plans. Russia, amid its war on Ukraine, has repeatedly threatened to use its nuclear weapons.

Two different roles for physicists have re-emerged. Some are being recruited to maintain, design, and develop nuclear weapons, continuing a practice that began with the Manhattan Project 80 years ago. Others are working to reduce and end nuclear dangers, following in the footsteps of scientists like Hans Bethe, Nobel laureate and former head of the Manhattan Project’s theoretical division, who in 1997 urged President Bill Clinton and “atomic scientists in the laboratories” to "cease and desist from work creating, developing, improving and manufacturing further nuclear weapons." As the founders of the Physicists Coalition for Nuclear Threat Reduction, we agree with Bethe.

This split within our community also reflects a deeper truth: Physicists have unique influence over how society thinks about and manages nuclear weapons. We understand both their technical realities and the catastrophic consequences of nuclear war. When physicists speak about nuclear dangers, the public and policymakers tend to listen.

Physicists have long organized and pushed for nuclear restraint and disarmament. In 1946, in the shadows of Hiroshima and Nagasaki, Albert Einstein founded the Emergency Committee of the Atomic Scientists, which worked with unions, women’s groups, media organizations, and others to alert the public about the danger, and to mobilize people against the weapons. Starting in 1957, scientists — inspired by the Bertrand Russell–Albert Einstein Manifesto’s call to “remember your humanity, and forget the rest” — convened in the “Pugwash Conferences” to break down Cold War mistrust and develop the technical foundations for nuclear arms control agreements. That same year, physical chemist Linus Pauling rallied 11,000 scientists to petition for an end to nuclear testing, contributing to agreements to ban testing everywhere except underground. In the late 1960s, physicists Richard Garwin and Hans Bethe helped the public and Congress understand that simple countermeasures could neutralize proposed missile defense systems, contributing to the landmark 1972 treaty limiting missile defenses and making it possible to cap Soviet and U.S. nuclear build-ups.

It was not just American physicists. In the Soviet Union, Andrei Sakharov, who shared Pauling’s concerns, helped convince Moscow to agree to the 1963 Partial Nuclear Test Ban Treaty (both he and Pauling received Nobel Peace Prizes). In Britain, Patrick Maynard Stuart Blackett, a physics Nobel laureate, opposed the development of nuclear weapons there, a position for which he was condemned.

Today, physicists’ voices are needed again. Despite the deep cuts in the number of U.S. and Russian warheads since the Cold War, the nuclear world order has taken a turn for the worse. U.S. nuclear arsenal managers and Congress assume that confrontations with Russia and China require an expanded U.S. nuclear arsenal with new capabilities. This disregards the fact that the current U.S. arsenal is already more than capable of threatening both countries as functioning societies, with devastating environmental and economic effects that would ripple across the world. Indeed, in 2013, after a comprehensive review by the Department of Defense, the White House determined that the U.S. nuclear arsenal could cover all nuclear targets in both countries, plus North Korea, with one-third fewer deployed strategic warheads than the 1,550 weapons permitted by the current U.S.-Russia New START agreement.

Nevertheless, the U.S. plans to spend $50 billion or more per year for decades on a new nuclear arsenal. How did we get here? The current cycle of U.S. nuclear “modernization” was launched 15 years ago by the Obama administration, in exchange for the required two-thirds vote of the Senate to ratify the New START treaty. Then the first Trump administration began to dismantle nuclear arms control agreements, continuing a practice started by President George W. Bush, who in 2002 pulled the U.S. from the Anti-Ballistic Missile Treaty. The Trump administration also withdrew from the 1987 Intermediate-Range Nuclear Forces Treaty, refused to extend the New START Treaty, ruled out ratification of the 1996 Comprehensive Nuclear Test Ban Treaty, and discussed renewed nuclear weapons testing — threatening the moratorium under which no nuclear-armed state other than North Korea has tested since 1998.

In 2021, just before New START expired, the incoming Biden administration agreed with Russia to extend the treaty for five years, but that extension will run out in a year and the treaty cannot be extended again. If it is not replaced, 2026 will be the first year since 1972 in which there are no treaty constraints on the two largest nuclear arsenals in the world.

In its current nuclear weapons Stockpile Stewardship Program, the U.S. National Nuclear Security Administration has called for “shortened development cycles” for weapons, and “enhancing production throughput” through “expansion of production infrastructure to support increased production scope and increased number of weapon system builds.” The plan includes new-design warheads for “anticipated future threats,” including for land-based intercontinental ballistic missiles, bombers, and submarines. To support this expansion, the NNSA plan proposes to recruit a “next generation of weapons designers and engineers” by providing “new opportunities for students through increased academic fellowships and grant programs" and "[building] new academic alliances.”

This appears to go well beyond the original nuclear warhead Stockpile Stewardship Program, which was founded with the intention, in the words of President Clinton, to ensure “existing nuclear weapons remain safe and reliable” [emphasis added].

In the face of these developments, independent physicists can provide a crucial voice for diplomacy and restraint. This is not easy: While the work to build nuclear weapons has been institutionalized in laboratories that receive billions of federal dollars each year, have ample congressional and industrial support, and are operated by for-profit private contractors, those working full-time to reduce the threat are based in small groups in universities, or in nonprofits dependent on scarce philanthropic funding.

With these concerns in mind, we founded the Physicists Coalition for Nuclear Threat Reduction in 2019 as a project of Princeton University's Program on Science and Global Security. Our aim was to develop a network of physicists to advocate for reducing the threats from nuclear weapons through deep cuts in nuclear arsenals, reforms in nuclear force postures and policies, and fulfillment of the international obligation to achieve nuclear disarmament. Supported for its first two years by the American Physical Society's Innovation Fund and continuing funding from the Carnegie Corporation of New York and individual donors, it has partnered since 2022 with the Arms Control Association.

Our team of 15 volunteer physicists have visited over 170 institutions across the U.S. and Canada — mostly university physics departments, but also nuclear engineering departments and national labs — giving colloquia on technical and policy aspects of nuclear arms and engaging in discussions about policy changes to mitigate the dangers of nuclear war. Technical topics are wide-ranging, from warhead physics to the physical effects of nuclear war to verification science. Policy discussions have touched on declaratory policies, such as a no-first-nuclear use; nuclear weapon postures, such as launch on warning; and the new United Nations Treaty on the Prohibition of Nuclear Weapons.

Since the coalition’s founding, about 1,500 scientists have joined; half of them are early in their careers. The coalition offers educational webinars, a monthly newsletter, and one-year, unsalaried fellowships that let early-career physicists and engineers work with senior experts on a research project, attend workshops, and participate in congressional briefings. In 2024, 36 coalition members visited Washington over two days to engage members of Congress on less dangerous nuclear weapons postures. The coalition also launched a program for members to reach out to congressional representatives in their districts.

The coalition now aims to expand efforts to European NATO countries. The U.S. has an estimated 100 nuclear weapons deployed across six bases in Belgium, Germany, Italy, the Netherlands, and Turkey, and appears poised to resume basing in the United Kingdom. France has nuclear warheads of its own, as does the United Kingdom, which also leases ballistic missiles from the U.S. There are many policy issues worth discussing, such as whether NATO should adopt a no-first-nuclear-use posture.

Physicists interested in joining and supporting the coalition can contribute in several ways. Those in academia can host coalition speakers on their campus, organize courses and discussion groups for faculty and students, and contribute technical expertise on nuclear weapons to local peace groups. Through the coalition, physicists can also receive news about key developments and opportunities for engagement with like-minded peers in the scientific and arms control community, members of Congress, and the public.

As nuclear restraint is cast aside, arsenals are modernized and expanded, and governments adopt more belligerent nuclear postures, we physicists can play a key role in reminding policymakers and the public that these weapons make the world less safe — and raising the question to our scientific colleagues whether building civilization-ending weapons is a worthy legacy.

Now, as in the past, we can work to create a nuclear weapon-free world, and a more peaceful future for humanity.

The authors co-founded the Physicists Coalition for Nuclear Threat Reduction in 2019. To learn more about the coalition or join, visit physicistscoalition.org.

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