Session S40: History of Physics

Development of ultra violet photoemission [UPS]: a history

UPS of solids investigations are summarized from the late 1940's through the very early 1960's which measured kinetic energy distributions [ EDC's ] of the emitted electrons. The experiments contributed to the opening of the photoemission spectroscopy fields. This era involved activities at G. E. Research Labs, Univ. of Missouri and W. E. Spicer's lab. The author knew most of the researchers.   

Magnetism in matter before the discovery of quantum spin: Bohr's less well-known contribution to the transition from classical to quantum physics.

How does one explain magnetic effects in matter when one views matter as a collection of classical charges in motion? The answer is: not at all! This is one of the points that Niels Bohr made in his doctoral dissertation in 1911, two years before addressing the issue of the stability of the hydrogen atom. The result, later rediscovered by H.J.van Leeuwen was amplified and formalized in Van Vleck's 1932 text on electric and magnetic susceptibilities and it is currently known as the Bohr-van Leeuwen theorem. We will review Bohr's two derivations, one statistical and one based on the motion of individual electrons. We will then propose reasons why this result, unlike that on the stability of hydrogen, did not lead to a major development in quantum theory but, instead, had to wait until after the introduction of spin and exchange forces in quantum mechanics to become generally known.   

Epistemological Dimensions in Niels Bohr's Conceptualization of Complementarity

Contemporary explications of quantum theory are uniformly ahistorical in their accounts of complementarity. Such accounts typically present complementarity as a physical principle that prohibits simultaneous measurements of certain dynamical quantities or behaviors, attributing this principle to Niels Bohr. This conceptualization of complementarity, however, is virtually devoid of content and is only marginally related to Bohr's actual writing on the topic. Instead, what Bohr presented was a subtle and complex epistemological argument in which complementarity is a shorthand way to refer to an inclusive framework for the logical analysis of ideas. The important point to notice, historically, is that Bohr's work involving complementarity is not intended to be an improvement or addition to a particular physical theory (quantum mechanics), which Bohr regarded as already complete. Bohr's work involving complementarity is actually an argument related to the goals, meaning, and limitations of physical theory itself, grounded in deep epistemological considerations stemming from the fundamental discontinuity of nature on a microscopic scale.   

Paradox, Natural Mathematics, Relativity and Twentieth-Century Ideas

We are enjoying a renaissance in the historiography of set theory which allows us to pinpoint the effect of Poincare's writing on the development of Einstein as an advocate of natural mathematics (what he called practical geometry). I will briefly describe the importance of Garciadiego's landmark work on Russell (1992), and Grattan-Guinness' epic recounting of the history of set theory (2000). I will present something for which historians of physics have searched but have not previously identified: the precise step at which Einstein incorporated practical geometry into his formulation of the relativitity of simultaneity. This leads to a troubling conclusion, at least for those who look to relativity for internal consistency. However, the trouble is not restricted to physics. We suggest that natural mathematics finds its way into the major twentieth-century ideas.