In his informative but somewhat hagiographic article on Alexander Friedmann’s contributions to modern cosmology (Physics Today, October 2012, page 38), Ari Belenkiy suggests that the Russian physicist should be recognized as the father of Big Bang cosmology. I believe the suggestion is unsupported by historical documentation and that Belenkiy misrepresents to some extent the work of the other pioneer of modern cosmology, Georges Lemaître. It seems to me that Belenkiy, when discussing priority, does not make a sufficiently clear distinction between expanding models and finite-age models of the Big Bang type. Of course, Lemaître’s 1927 paper proposing a universe expanding from a static Einstein state does not earn him credit for fathering Big Bang cosmology—but has anyone said that it does?

Friedmann’s 1922 paper was not an argument for the expanding universe, which appeared as a mathematical possibility only and not as the solution that corresponds to the actual universe. Although Friedmann wrote in his 1922 paper of a “beginning of the world” in connection with solutions that correspond to expanding world models, he did it in an uncommitted way and without referring to astronomical or physical data. Neither in the 1922 work nor in his companion paper of 1924 did he mention physical terms such as “energy” or “radiation,” not to mention “nebula” or “redshift.”

If later commentators have presented Friedmann’s cosmological papers as basically mathematical and unconcerned with physics and astronomy, it is because that is how the papers were. Belenkiy objects by referring to “Friedmann’s considerable achievements in meteorology and aerodynamics”—hardly a relevant argument with regard to his two cosmological papers. It was precisely in that respect that Lemaître went beyond Friedmann. The Belgian physicist did not “fail” to consider all the solutions that Friedmann had discussed. He focused on the expanding solution that seemed to correspond to the redshift data and thus to the real universe as studied by the astronomers.

At any rate, Lemaître’s candidacy for paternity of the Big Bang universe rests on his “primeval atom” hypothesis of 1931 in which he offered for the first time a physical picture of the nonsingular beginning of the universe.1 While one can perhaps call Friedmann the father of the Big Bang in an abstract, uncommitted, and mathematical sense—although that would stretch the notion of paternity—it was only with Lemaître that the physical Big Bang entered the history of science.

Finally, when Belenkiy deplores the lack of recognition of Friedmann and refers to Yakov Zeldovich and other Russian scientists as exceptions, one should keep in mind the context of the cold war in the 1960s and later: In the Soviet Union, there was a political need to credit Friedmann as the true and only founder of relativistic evolution cosmology.

This brief letter is in no way an attempt to belittle the great work of Friedmann, only to offer a more balanced view. Friedmann’s seminal contributions to cosmology are beyond question, but there is no need to exaggerate them or to read later advances into them.

Ann. Sci.