For physics, the first half of the twentieth century was a time of profound transformation, bringing about the transition from what we now call 'classical' to 'modern' physics. With the new concepts and fields of study there emerged a global physics community, an ever-growing network of collaboration and scientific exchange. Yves Gingras has analysed hundreds of thousands of scientific papers published between 1900 and 1945, and identified several trends that characterize this transformative period (Phys. Perspect. 12, 248–265; 2010).

Credit: AIP SEGRÈ VISUAL ARCHIVE/GE RESEARCH AND DEVELOPMENT CENTER

In the early years of the twentieth century, the sensation of there being a mountain to climb in exploring and understanding the emerging concepts of quantum mechanics and relativity (among others) must have been overwhelming. That such a challenge can be met only through collaborative effort is beautifully captured in the words of Paul Drude, who delivered his inaugural address as a member of the Prussian Academy of Sciences on 28 June 1906 (and committed suicide only one week later): “In these times of rapid progress, when for each physicist there are plenty of tasks on offer, worries also arise that the skill and capacity of an individual permits the achievement of merely a small fraction of what is desired. In fact, this fraction would in general be vanishingly small if it weren't for the support, through the institution of our universities, from, on the one hand, the collaboration with colleagues, who advise where one's own abilities fail; and, on the other hand, from the education of a young workforce for scientific collaboration.”

Drude was indeed a central figure in the network of physicists of his time. According to the 'co-citation networks' constructed by Gingras, which capture how often a given author is cited with another, in the periods 1900–1904 and 1905–1910 Drude was one of the most centrally placed physicists, second only to J. J. Thomson (pictured here with Irving Langmuir, left, and William Coolidge, right). Thomson maintained his centre position until the mid-1920s, when others, including Arnold Sommerfeld, Werner Heisenberg, Arthur Compton and Hans Bethe, started to take over.

These changes reflect a shift in 'mainstream' topics, from electron and atomic physics, to quantum mechanics, to nuclear and solid-state physics. Indeed, no single physicist remained in a central position in the co-citation network for more than 15 or 20 years.

But the first half of the last century was also a time of radical political upheaval. Among the consequences were a decrease of German influence in physics and rapid growth in American physics research after the 1920s, as Gingras's detailed data show. On top of these changes, his study reveals a steady increase in the number of physicists and the subdivision of physics into ever more subfields, together with a trend towards publications with several authors, rather than single-author papers.

“Little drops of water, / Little grains of sand, / Make the mighty ocean / And the pleasant land”, says the poem commonly attributed to the American Julia Fletcher Carney. It holds some truth for physics as well.