Until quite recently, letters were the most common way – and often the only way – for scientists to communicate informally with each other. It is not surprising therefore that science historians have long relied on letters as invaluable sources of information.

A dramatic illustration concerns the now-famous meeting between Werner Heisenberg and Niels Bohr in Nazi-occupied Denmark in September 1941 during which the two physicists, talking in private, sought to eke out the other’s view on progress towards a nuclear bomb. At first, the principal account of the mysterious visit came from a letter that Heisenberg sent in 1955 to the German science writer Robert Jungk. But among Bohr’s papers were several drafts of letters that Bohr wrote but never sent to Heisenberg after reading the latter’s account of the meeting. In 2002, when the Bohr family made the drafts public, the letters served as a corrective to Heisenberg’s version, showing it to be deceitful and self-serving.

Roles of letters

Now that e-mail has replaced letter writing as the principal means of informal communication, one has to feel sorry for future science historians, who will be unable to use letters and telegrams to establish facts and gauge reactions to events. In addition to the Copenhagen episode, another example of the role of letters is Stillman Drake’s startling conclusion, based on a careful reading of Galileo’s correspondence, that the Leaning Tower event actually happened. And of all the reactions to the discovery of parity violation in 1957, the simplest and most direct expression of shock came from Robert Oppenheimer. After receiving a telegram from Chen Ning Yang with the news, Oppenheimer cabled back: “Walked through door.”

Letters are also useful to historians because the character of scientists can often be revealed more clearly in informal communications than in official documents. Catherine Westfall, who has composed histories of both the Fermilab and Argonne national laboratories, likes to point out that letters often reveal leadership styles in striking ways. “[Former Fermilab director] Robert R Wilson knew he was making history and was ironically self-conscious,” she once told me. “Leon Lederman [another Fermilab director] told jokes, [while former Argonne director] Hermann Grunder wrote letters that were really never-ending to-do lists.”

Historians also use letters to reconstruct thought processes. We could not hope to understand the development of quantum mechanics, for instance, without studying the vigorous exchanges of letters between the likes of Bohr, Dirac, Heisenberg, Pauli and others as they thrashed out the theory in the 1920s. Indeed, the historian David Cassidy decided to write his biography of Heisenberg only after accompanying the physicist’s widow to her attic and seeing her drag out a trunk of Heisenberg’s personal letters, adding that he could not have completed the biography without them. Cassidy also said that the way to understand Heisenberg’s behaviour during the Third Reich is to study his nearly weekly letters to his mother.

Internet impact

Historians at the American Institute of Physics (AIP), who are working on a project to document the history of physics in industry, have encountered hints of how the Internet and computers are transforming scientific communication.

E-mail is, of course, cheaper and encourages quicker thought, and it introduces a peculiar blend of the personal and professional. The AIP historians have also detected a decline in the use of lab notebooks, finding that data are often stored directly into computer files. Finally, they have noted the influence of PowerPoint, which can stultify scientific discussion and make it less free-wheeling; information also tends to be dumbed down when scientists submit PowerPoint presentations in place of formal reports.

Generally, though, these new communications techniques are good for scientists, encouraging rapid communication and stripping out hierarchies. But for historians, they are a mixed blessing. It is not just that searching through a hard disk or database is less romantic than poring over a dusty box of old letters in an archive. Nor is it that the information in e-mails differs in kind from that in letters. Far more worrying is the question of whether e-mail and other electronic data will be preserved at all.

One can lose letters, of course, a classic case being much of Planck’s correspondence thanks to an Allied bomb in the Second World War. But the challenges of electronic preservation are more extensive and immediate. As AIP historian Spencer Weart notes: “We have paper from 2000 BC, but we can’t read the first e-mail ever sent. We have the data, and the magnetic tape – but the format is lost.” Weart is fond of quoting RAND researcher Jeff Rothenberg’s remark that “it is only slightly facetious to say that digital information lasts forever – or five years, whichever comes first”, meaning that information lasts only if regularly migrated to another format.

This problem has inspired various programmes to foster the preservation of electronic documentation. One is the Persistent Archives Testbed Project – a collaboration between several US institutions to develop a tool to archive electronic data (slac.stanford.edu/history/projects.shtml). Another is the Dibner–Sloan History of Recent Science and Technology Project (authors.library.caltech.edu/5456) that seeks not only to digitally archive important documents, but also to enlist the scientists involved to put these in a historical context.

The critical point

Technology, from pencils to computers, has transformed not only the nature and content of communication, but also the practices that rely on it. Electronic communication is changing not only science, but also science history. Historians of the future will have to rely on other kinds of data than their precursors, and tell the story of science differently.

There is no going back, as is illustrated once again by the Bohr–Heisenberg episode. Had the Web existed when Bohr wrote his invaluable draft letters to Heisenberg, his correspondence may well have not been preserved. Yet when the Bohr family decided to make the drafts publicly available, where did they put the material? On the Web.