A photo of an impish Richard Feynman playing the bongos appears in Ray Monk's biography of Oppenheimer. It is accompanied by the caption "Richard Feynman, Julian Schwinger's main rival for the title of greatest American physicist in history". That got me thinking; who is the greatest American physicist in history? What would your choice be?
The question is interesting because it's not as simple as asking who's the "greatest physicist in history". The answer to that question tends to usually settle on Isaac Newton or Albert Einstein; in fact few American physicists if any would show up on the top ten list of greatest physicists ever. But limit the question to American physicists and the matter becomes more complicated. Contrast this to asking who's the greatest American chemist in history; there the answer - Linus Pauling - appears much more unambiguous and widely agreed upon.
Any discussion of "greatest scientist" is always harder than it sounds. By what measure do you judge greatness?: A single, monumental discovery? Contributions to diverse fields? Theory or experiment? Creation of an influential school of physics? Or by looking at lifetime achievement which, rather than focusing on one fundamental discovery, involves many important ones? There are contenders for "greatest American physicist" who encompass all these metrics of achievement.
Here's what's concerning: Even a generous, expansive list of contenders for "greatest American physicist" in history is embarrassingly thin compared to a comparable list of European physicists. For instance, let's consider the last three hundred years or so and think up a selection which includes both Nobel Laureates and non-Nobel Laureates. The condition is to only include American-born physicists, otherwise the list will start becoming absurd.
Here's my personal list for the title of greatest American physicist in history, in no particular order: Joseph Henry, J. Willard Gibbs, Albert Michelson, Robert Millikan, Robert Oppenheimer, Richard Feynman, Murray Gell-Mann, Julian Schwinger, Ernest Lawrence, Edward Witten, John Bardeen, John Slater, John Wheeler and Steven Weinberg. I am sure I am leaving someone out but I suspect other lists would be similar in length. It's pretty obvious that this list pales in comparison with an equivalent list of European physicists which would include names like Einstein, Dirac, Rutherford, Bohr, Pauli and Heisenberg; and this is just if we include twentieth-century physicists. Not only are the European physicists greater in number but their ideas are also more foundational; as brilliant as the American physicists are, almost none of them made a contribution comparable in importance to the exclusion principle or general relativity.
Note that I said "almost none". If you ask who's my personal favorite for "greatest American physicist in history", it would not be Feynman or Schwinger or Witten; instead it would be Josiah Willard Gibbs, a man who seems destined to remain one of the most underappreciated scientists of all time but who Einstein called "the greatest mind in American history". Feynman and Schwinger may have invented quantum electrodynamics, but Gibbs invented the foundations of thermodynamics and statistical mechanics, a truly seminal contribution that was key to the development of both physics and chemistry. It's hard to overestimate the importance of concepts like free energy, chemical potential, enthalpy and the phase rule for physics, chemistry, biology, engineering and everything in between. In fact, so influential was Gibbs's work that it inspired that of Paul Samuelson, who unlike physicists, is actually agreed upon as the greatest American economist in history. If you really want to throw around lists of great American physicists (or even scientists in general), you simply cannot exclude Gibbs. In my dictionary Gibbs's contributions are comparable to that of any famous relativist or atomic physicist.
More importantly though, the sparse list of great homegrown American physicists makes two things clear. Firstly, that America is truly a land of immigrants; it's only by including foreign-born physicists like Fermi, Bethe, Einstein, Chandrasekhar, Wigner, Yang and Ulam can the list of American physicists even start to compete with the European list. Secondly and even more importantly, the selection demonstrates that even in 2013, physics in America is a very young science compared to European physics. Consider that even into the 1920s or so, the Physical Review which is now regarded as the top physics journal in the world was considered a backwater publication, if not a joke in Europe (Rhodes, 1987). Until the 1930s American physicists had to go to Cambridge, Gottingen and Copenhagen to study at the frontiers of physics. It was only in the 30s that, partly due to heavy investment in science by both private foundations and the government and partly due to the immigration of European physicists from totalitarian countries, American physics started on the road to the preeminence that it enjoys today. Thus as far as cutting-edge physics goes, America is not even a hundred years old. The Europeans had a head start of three hundred years; no wonder their physicists feature in top ten lists. And considering the very short time that this country has enjoyed at the forefront of science, we have to admit that America has done pretty well.
The embarrassingly thin list of famous American physicists is good news. It means that the greatest American physicist is yet to be born. Now that's an event we can all look forward to.