Crossing Borders and Fostering Collaborations**

Since 2011, the Center for History of Physics at the American Institute of Physics (AIP) has sponsored five international conferences for early career scholars in the history of the physical sciences. As scholars who have greatly benefited from the early-career series, both as participants and organizers, we are deeply grateful to AIP for its generous and unwavering support. Thanks to funding from the AIP and other sponsors, the costs of travel and accommodation can be mostly or completely covered for all attendees. Their support has transformed the Early-Career Conference into an increasingly global event. After hosting the first three installments, AIP encouraged, fully supported, and sponsored the organization of additional conferences in San Sebastián/Donostia in 2018 and Copenhagen in 2023. Appropriately, the theme of the Copenhagen conference was “Crossing Borders and Fostering Collaborations.”

The Copenhagen Early-Career Conference was hosted by the Niels Bohr Archive, and the speakers gave their talks in the historic Auditorium A of the Niels Bohr Institute. In addition to the AIP, the conference was sponsored by the Inter-Union Commission for the History and Philosophy of Physics and the International Union of Pure and Applied Physics, which awarded the first Early Career Prize for the History of Physics. We are proud to present a paper by the inaugural prize-winner, Jean-Philippe Martinez, in this issue.

Martinez examines how and why the concept of virtual particles, formulated by Feynman in the 1940s, became a matter of debate only in the 1970s. Discussing the phenomenological basis that Feynman disposed of for the formulation of the concept and the emergence of the first criticism in the 1970s, he argues that the concept of virtual particles came under scrutiny in the context of increasing opposition to quantum electrodynamics rather than as a result of a reassessment of the unusual characteristics ascribed to them.

This circulation of knowledge, and the factors that promote, facilitate, or hinder circulation, emerged as a central theme of the conference and thus of the articles featured in this volume. In particular, transnational transfers, which are processes through which elements, norms, or representations from one nation emerge in another, appear repeatedly. These processes involve not only the translation of texts but also the movement of people, objects, and practices. Scientists traveling to international conferences, exchange visits, the dispersal of specialized instruments and materials, and the adaptation of experimental methods all illustrate this concept.

Perhaps no other objects embody the complex, multilayered nature of knowledge circulation more than the Babylonian tablets. The paper by Erica L. Meszaros illustrates how there is no such thing as a simple translation of knowledge. Exploring the interaction between astronomical procedures on Babylonian tablets through the lens of algorithms, Meszaros critically analyzes the concept of “algorithm” in the historical Mesopotamian context and uses it as a framework to examine the relationship between procedures, data, and methodological representations on the tablets. A case study from planetary procedure texts demonstrates how algorithm-based analysis can offer new insights into the interaction of individual procedures. The study aims to enhance understanding of how the authors and users of these ancient astronomical tablets engaged with their content.

The process that enabled Meszaros's sophisticated analysis of a tablet produced almost four thousand years ago reminds us that exchanges of knowledge across time and space do not occur automatically; they require considerable effort and resources, much like the Early Career Conferences. At the same time, this process transforms knowledge itself, not just through linguistic translation. When scientific ideas cross cultural and institutional boundaries, they are interpreted, adapted, and often further developed. Translation is, therefore, not merely a tool for disseminating knowledge but also a creative act that reshapes our understanding and expression of scientific knowledge. In this way, the history of the physical sciences, like that of other systems of knowledge production, has been profoundly influenced by translation and transnational communications, which have enabled scientific knowledge to traverse linguistic and cultural boundaries.

Among the lessons we learn from the articles in this issue is that the importance of translation goes far beyond communication through time and space. As science became larger and more expensive, the very success of its endeavors rested on scientists’ ability to translate their science into a language accessible to nonexperts. Elena Schaa's article explores how aesthetic themes in Werner Heisenberg's writings, particularly the Romantic motifs of mountaineering and the experience of knowledge, shape his scientific persona in biographies. It argues that these motifs, rooted in German Romanticism and the Bildungsbürgertum, present Heisenberg as both a Romantic genius and an average citizen, influencing contemporary ideals of physicists. In a similar vein, Thijs Latten explores the impact of Indian philosophy on Erwin Schrödinger's thoughts and works. Latten argues that Śaṅkara's Advaita Vedānta reading of the Upaniṣads greatly impacted Schrödinger's metaphysics, as well as providing him with personal spiritual consolation.

The translation of scientific knowledge takes on increased importance when it is used to emphasize a strategic alignment between scientific and national priorities, justifying the substantial investments of material and human resources. For example, while the most prominent motor for the impressive expansion of the physical sciences in the postwar is undoubtedly the symbiosis between physics and the military-industrial complex, Masahiro Inohana's article adds to a recent literature, which trailed the emergence of global, transnational, and diplomatic histories, helping to unveil how physicists effectively mobilized internationalism, humanitarianism, soft power, and the need to promote peace and understanding between nations as discursive tropes for promoting their disciplinary ambitions.

Several articles in this volume suggest that to fully understand the global postwar expansion of the physical sciences, it is essential to consider the complex connections between physics and the realm of global development. Throughout the 20th century, particularly in its latter half, linking scientific endeavors to the increasingly global narrative of modernization and development became an effective strategy for advancing their professions. The articles by Inohana and Michiel Bron highlight that the physical sciences played a central role in energy industries, proving crucial for countries like Japan and India, which needed to develop their energy matrix to support their development programs. But Bron can convincingly show that this connection is also visible in Europe when early interactions between geophysicists and the oil industry led to the emergence of the subfield of applied geophysics and the development of geophysical knowledge about radioactivity. This significantly influenced both the later oil and nuclear industries. By using oil fields as research sites for radioactive measurement techniques, oil firms established a knowledge base before World War II that facilitated the transition to nuclear energy and the close interconnection between the oil and nuclear industries in the 20th century. Christina Roberts's article further illustrates that these sciences were also integral to the strategies employed by great powers to attract developing countries into their spheres of influence, helping to convince them to adopt specific models of development and social organization. By exploring NASA's Spacemobile program—initially a domestic science education initiative—Roberts demonstrates how it transformed into a tool of Cold War diplomacy that promoted U.S. political interests and showcased NASA's technological achievements on an international stage.

Similar dynamics are evident in the United States’ involvement with the International Atomic Energy Agency (IAEA). In this context, mobile laboratories mounted on truck chassis exemplified the US goal of promoting its research institutions and practices to further diplomatic and political objectives. Loukas Freris's article highlights the significant role this mobile laboratory played in Alfred Maddock's 1959 mission, which resulted in the introduction of radiation protection practices in Greece. Maddock's mission included the introduction of dosimetry devices, the revision of architectural plans for radiochemical laboratories, and the alignment of Greek practices with IAEA radiation protection standards. This mission was crucial in establishing the IAEA as the global authority on radiation protection. Consequently, the agency evolved into one of the key institutions within the transnational network of organizations, such as the United Nations and the World Health Organization, which shaped the postcolonial development agenda.

However, Nithyanand Rao's article reviews yet another dimension of the expansion of the physical sciences in postcolonial spaces. Rao examines how the detection of atmospheric neutrinos at the Kolar Gold Fields in India was made possible by the often-overlooked labor of miners, primarily from lower castes. Engaging with the notion of verticality in physics, the article argues that the dominant lab-field framework in the history of science obscures the conditions that enabled such experiments, particularly the colonial, racial, and caste-based systems that supported deep mining and enabled the operation of the experiments. In other words, the interdependent nature of the gold political economy and labor relations forged at the intersection between colonialism, race, and caste resulted in a regime of labor, predicated on colonial and imperial violence, which not only enabled mining at extremely dangerous and difficult conditions at depths above 3 km—making the mine an ideal site for neutrino experiment—but also kept the physics experiment running. Rao's inquiry into what made underground spaces available for neutrino experiments offers a compelling example of how conversation with different historiographies can lead to innovative studies that bring to view elements that are usually absent in our narratives.

On the other hand, the history and philosophy of the physical sciences are also well-positioned to contribute to the historiography of development. Ambitious development projects require the training or importation of specialists, the acquisition of materials that embody advanced knowledge, standardization, and the implementation of evaluation practices and metrics. The articles in this issue address all of these points. In light of the current issue, this suggests that if we want to understand the history of physics from a global perspective, engaging with the historiography of development, its long roots in colonialism, and the prominent role it assumed in international relations in the last decades of the 20th century offers a promising path ahead.

Urko Gorriñobeaskoa concludes this issue with a thoughtful philosophical and historiographical analysis that displays the value of integrating the history and philosophy of science to address the ontological dimension of science. Beginning with a comparative analysis of “epistemic things” and “epistemic objects,” neologisms to define entities that embody concepts, Gorriñobeaskoa suggests a refined framework that combines biographical and genealogical approaches to study the history of these epistemic entities. The effectiveness of this framework is illustrated by its ability to stimulate novel ways of looking at the various entities discussed in the articles, ranging from small and elusive neutrinos and virtual particles to concrete dosimetry devices and nuclear reactors.

The 2023 conference was also remarkable because it only came to fruition after more than five years of planning and three years of delays. Originally scheduled for August 2020, the conference had to be postponed multiple times due to the pandemic and related factors. Over the years, some individuals involved in the conference organizing had to step back before they could see the results of their labor, while others stepped forward to take on their burden. The four guest editors of this issue were involved in the organization of the conference, but we would also like to recognize the other individuals who made the conference (and thus also this special issue) possible. We therefore thank (in alphabetical order): Jenifer Barton, Magnus Bøe, Nathan Cromer, Freja Ganderup, Gregory Good, Stephanie Jankowski, Christian Joas, Melanie Mueller, Jaume Navarro, Martin Speirs, Signe Strecker, Rob Sunderland, and William Thomas.

From their first iteration, these early career conferences have focused on bringing together attendees from around the world to connect with their peers and meet senior scholars who can help nurture their careers. AIP looks forward to continuing its collaboration with partners to support future conferences. The next conference will be held later this year in Salvador, Brazil, in conjunction with the Fifth International Conference on the History of Quantum Mechanics.¹ By fostering a global community of young scholars, AIP significantly contributes to the increasing internationality and thematic diversity of the history of physics community.