The world is facing a perilous resurgence of the nuclear arms race. The United States and Russia, possessing roughly 90% of the world’s nuclear arsenal with over 5,000 warheads apiece, are modernizing their nuclear weapons and delivery systems, replacing their Cold War-era stocks. China’s nuclear warhead count is estimated at around 600. Meanwhile, the United Kingdom, France, and Israel are enhancing their nuclear capabilities, while India, Pakistan, and North Korea are actively developing and expanding theirs. Alarmingly, all nuclear-armed nations and NATO routinely practice their nuclear war strategies. Russia’s threats to use nuclear weapons during its war in Ukraine further heighten these anxieties.
This situation has led to a division among physicists. Some are now being employed to maintain, design, and advance nuclear weapons, a practice that originated with the Manhattan Project. Conversely, others are dedicated to reducing and eliminating nuclear threats, following the path of scientists like Hans Bethe, a Nobel laureate and former head of the Manhattan Project’s theoretical division, who urged a halt to the creation of new nuclear weapons in 1997. As founders of the Physicists Coalition for Nuclear Threat Reduction, we echo Bethe’s call.
This divergence within the physics community reflects a fundamental reality: physicists possess unique influence over public understanding and management of nuclear weapons. We possess both technical expertise regarding these weapons and a deep understanding of the catastrophic consequences of nuclear war. Therefore, public and policymakers tend to heed physicists’ warnings about nuclear dangers.
Historically, physicists have been at the forefront of efforts to promote nuclear restraint and disarmament. In 1946, in the aftermath of Hiroshima and Nagasaki, Albert Einstein established the Emergency Committee of Atomic Scientists, collaborating with various groups to raise public awareness of the nuclear threat and mobilize opposition. Starting in 1957, scientists, inspired by the Russell-Einstein Manifesto’s call to “remember your humanity,” convened the Pugwash Conferences to bridge Cold War mistrust and develop the technical basis for arms control treaties. That same year, Linus Pauling spearheaded a petition signed by 11,000 scientists advocating for an end to nuclear testing, contributing to agreements that banned testing in all environments except underground. In the late 1960s, physicists Richard Garwin and Hans Bethe elucidated how simple countermeasures could negate proposed missile defense systems, leading to the landmark 1972 treaty limiting missile defenses and capping U.S. and Soviet nuclear arsenals.
Beyond American scientists, figures like Andrei Sakharov in the Soviet Union, also a Nobel Peace Prize recipient, echoed Pauling’s fears and influenced Moscow’s decision to sign the 1963 Partial Nuclear Test Ban Treaty. Similarly, in Britain, Nobel laureate Patrick Maynard Stuart Blackett faced condemnation for opposing the development of nuclear weapons.
Today, the expertise of physicists is once again crucial. Despite significant reductions in U.S. and Russian warheads since the Cold War, the global nuclear landscape has deteriorated. U.S. nuclear planners and Congress are operating under the assumption that confrontations with Russia and China warrant an expanded U.S. nuclear arsenal with novel capabilities. This ignores the current arsenal’s already ample capacity to devastate both countries as functioning societies, with global environmental and economic repercussions. In fact, a 2013 Department of Defense review, confirmed by the White House, determined that the U.S. arsenal could effectively target all nuclear sites in both countries, plus North Korea, with a third fewer strategic warheads than the 1,550 permitted by the New START agreement.
Nevertheless, the U.S. is poised to spend $50 billion annually for decades to modernize its nuclear arsenal. This cycle began 15 years ago under the Obama administration, as a condition for securing Senate ratification of the New START treaty. Subsequently, the Trump administration accelerated the dismantling of nuclear arms control agreements, following a precedent set by President George W. Bush’s withdrawal from the Anti-Ballistic Missile Treaty in 2002. Further withdrawals included the 1987 Intermediate-Range Nuclear Forces Treaty, coupled with a refusal to extend the New START Treaty, rejection of the 1996 Comprehensive Nuclear Test Ban Treaty’s ratification, and contemplation of renewed nuclear weapons testing, thus threatening the moratorium adhered to by all nuclear-armed states except North Korea since 1998.
While the Biden administration extended New START for five years in 2021, just before its expiration, the treaty will expire without the possibility of further extension. Consequently, 2026 could mark the first year since 1972 without any treaty limitations on the world’s two largest nuclear arsenals.
The U.S. National Nuclear Security Administration’s Stockpile Stewardship Program aims to accelerate weapons development cycles and increase production output by expanding production infrastructure to accommodate a larger scope and volume of weapon systems. This includes designing new warheads for “anticipated future threats,” intended for deployment on land-based intercontinental ballistic missiles, bombers, and submarines. To support this expansion, the NNSA plans to recruit a “next generation of weapons designers and engineers” through increased academic fellowships, grant programs, and new academic alliances.
In light of these trends, independent physicists can serve as vital advocates for diplomacy and de-escalation. This is a challenging endeavor, however. Nuclear weapons development is deeply entrenched within well-funded laboratories, enjoying substantial support from Congress and industry, and managed by for-profit contractors. Conversely, those dedicated to mitigating the nuclear threat often operate within small university groups or nonprofits reliant on limited philanthropic resources.
Recognizing this disparity, we established the Physicists Coalition for Nuclear Threat Reduction in 2019, under the umbrella of Princeton University’s Program on Science and Global Security. Our goal was to create a network of physicists who would champion the reduction of nuclear threats through significant arsenal reductions, reforms to nuclear force postures and policies, and the fulfillment of international nuclear disarmament obligations. Initially supported by the American Physical Society’s Innovation Fund, and subsequently by the Carnegie Corporation of New York and individual donors, the coalition has partnered with the Arms Control Association since 2022.
Our team, comprised of 15 volunteer physicists, has visited over 170 institutions in the U.S. and Canada, primarily university physics departments, but also nuclear engineering departments and national laboratories. We deliver presentations on the technical and policy aspects of nuclear arms and facilitate discussions on policy changes aimed at reducing the risk of nuclear war. The technical topics covered range from warhead physics and the physical effects of nuclear war to verification science. Policy discussions address declaratory policies like no-first-use, nuclear weapon postures such as launch-on-warning, and the United Nations Treaty on the Prohibition of Nuclear Weapons.
Since its inception, the coalition has grown to include approximately 1,500 scientists, half of whom are early in their careers. We provide educational webinars, a monthly newsletter, and one-year, unpaid fellowships that enable early-career physicists and engineers to collaborate with senior experts on research projects, attend workshops, and participate in congressional briefings. In 2024, 36 coalition members traveled to Washington, D.C., to engage with members of Congress on safer nuclear weapons postures. The coalition has also initiated a program for members to connect with their congressional representatives at the local level.
The coalition now intends to broaden its efforts to include European NATO countries. The U.S. currently maintains an estimated 100 nuclear weapons deployed across six bases in Belgium, Germany, Italy, the Netherlands, and Turkey, and appears poised to resume deployments in the United Kingdom. France and the United Kingdom also possess their own nuclear warheads, with the latter leasing ballistic missiles from the U.S. Numerous policy questions warrant discussion, including whether NATO should adopt a no-first-use policy.
Physicists interested in joining and supporting the coalition can contribute in various ways. Those affiliated with academic institutions can host coalition speakers, organize courses and discussion groups for faculty and students, and contribute technical expertise on nuclear weapons to local peace organizations. Through the coalition, physicists can stay informed about critical developments and find opportunities to engage with like-minded colleagues in the scientific and arms control communities, members of Congress, and the public.
As nuclear restraint diminishes, arsenals are modernized and expanded, and governments adopt more aggressive nuclear postures, physicists have a crucial role to play in reminding policymakers and the public that these weapons diminish global safety. We must also prompt our scientific colleagues to consider whether contributing to the creation of weapons capable of ending civilization is a legacy worth pursuing.
Now, as in the past, we can strive to create a world free of nuclear weapons and a more peaceful future for all.
