Abstract
Probably the most dramatic historical challenge to scientific realism concerns Arnold Sommerfeld’s ([1916]) derivation of the fine structure energy levels of hydrogen. Not only were his predictions good, he derived exactly the same formula that would later drop out of Dirac’s 1928 treatment (something not possible using 1925 Schrödinger–Heisenberg quantum mechanics). And yet the most central elements of Sommerfeld’s theory were not even approximately true: his derivation leans heavily on a classical approach to elliptical orbits, including the necessary adjustments to these orbits demanded by relativity. Even physicists call Sommerfeld’s success a ‘miracle’, which rather makes a joke of the so-called ‘no miracles argument’. However, this can all be turned around. Here I argue that the realist has a story to tell vis-à-vis the discontinuities between the old and the new theory, leading to a realist defence based on sufficient continuity of relevant structure. 1Introduction2No Realist Commitment Required?3Enter the Physicists4A New Approach to the Non-relativistic Success5Relativity and Spin6Structure and Realist Commitment7Conclusion
Highlights
2 No Realist Commitment Required? 3 Enter the Physicists 4 A New Approach to the Non-relativistic Success 5 Relativity and Spin 6 Structure and Realist Commitment 7 Conclusion
Realism is how it apparently overcomes the usual realist defences. When it comes to the success-to-truth inference at the core of scientific realism, modern realists set a high bar for the level of success required
Sommerfeld’s ‘fine structure formula’ was perfect, since it is exactly the same formula that later resulted from the relativistic Dirac quantum mechanics (QM) of 1928
Summary
The historical challenge to scientific realism widely considered the most serious and problematic concerns Sommerfeld’s ([1916]) derivation of the fine structure spectral lines of hydrogen. What makes the case so powerful against. In addition most contemporary realists insist that such success only justifies a realist commitment to the ‘success-fuelling’ or ‘working’ parts of the theory in question; the wider theory might well be radically false, without any threat to realism These popular defences do not seem remotely helpful when it comes to the Sommerfeld case. One can see why some have been tempted to refer to the Sommerfeld case as a ‘counterexample’, at least loosely speaking: the quantitative accuracy of Sommerfeld’s fine structure formula is extremely impressive, and highly motivating for the realist. It seems especially hard in this case for the realist to shrug her shoulders and say ‘Well, this is just one case, and my inference is defeasible’.
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