Letter writer J. Richard Gott III (PHYSICS TODAY, November 2010, page 12) and PHYSICS TODAY readers should be relieved to learn that Albert Einstein’s h-index as given by the Institute for Scientific Information (ISI) is 50, not 27 as Gott reported; hence it is higher than Gott’s 46. Although Einstein’s h-index is substantially lower than Edward Witten’s 125, remember that Einstein published between 1901 and 1955, when the entire body of scientific literature was very much smaller than in Witten’s publishing lifetime, 1976–present. To get an idea of the scaling involved, in the first six months of 1948, Physical Review had a total of 1476 pages, whereas in the first six months of 1998, Physical Review A–E had 39 141 pages—many more papers with many more references. Werner Marx, Lutz Bornmann, and Manuel Cardona have published an exhaustive analysis that clearly illustrates the point about different citation impacts of papers published in different time periods.1
I cannot think of any other physicist publishing in Einstein’s lifetime who would have an h-index comparable to his 50. For example, ISI gives an h-index of 26 for Erwin Schrödinger (1914–61), 30 for Werner Heisenberg (1921–76), 32 for Enrico Fermi (1922–55), and 44 for Paul Dirac (1924–85). Cardona and Marx give an h-index of 41 for Max Born (1900–70) and 45 for Heisenberg, corrected for some ISI omissions.2 I know of no physicist publishing before 1956 who has an h-index higher than 50. Thus Einstein’s h-index today properly reflects his stature relative to his contemporaries, and comparing h-indices of physicists living in vastly different time periods, as Gott does in his letter, doesn’t make sense.1
Of course, the h-indices of Einstein and of his eminent contemporaries have increased because of many posthumous citations. Einstein’s h-index at the time of his death in 1955 was a “measly” 20. I would not be surprised if some of his physicist contemporaries whom we know little about today had higher h-indices than Einstein’s then and much lower ones than his today. Similarly, some physicists today with h-indices higher than those of their contemporaries may have their fortunes reversed decades after they are gone. Just as with good wine, the h-index’s reflection of merit, when properly used, gets better with time.