Richard Schlegel

Comments on the Hafele-Keating Experiment.

Salient features of the Hafele-Keating test of relativistic clock-rate changes are presented; these changes were for cesium atomic clocks which had been flown around the world, once eastward and once westward, on approximately equatorial paths. An inconsistency for an earth observer, between equal energy but different time rates for eastward and westward moving clocks, is shown to be removed if the Sagnac effect is taken into account in the synchronization of clocks in the earth reference system. Also, it is shown that an atomic clocks directional relativistic loss (gain) for an eastward (westward) circumpolar journey is velocity independent. The observed relativistic time effects may be derived as general-relativistic changes, leaving the question of special-relativistic kinetic effects on a macroscopic clock an open one empirically.

Radiation Pressure on a Rapidly Moving Surface

The radiation pressure is calculated for a surface which is moving in an electromagnetic radiation field that is isotropic to a rest observer. In the limit where the velocity of the surface is that of light, the pressure is found to reach a maximum value 2u, where u is the isotropic electromagnetic energy density for the observer at rest. The finite value comes with an integration over radiation incident at all angles, even though radiation from a source which is directly approaching the surface has infinite momentum when the surface velocity reaches the speed of light. Estimates of radiation pressure in interstellar space lead to the result that the energy expended by a space-traveling vehicle in moving against electromagnetic radiation, at any possible speed, would be negligible.

Wave and Inertial Properties of Matter

The inertial properties of matter as expressed in Newtons second law, and the mass-energy equivalence, are derived as consequences of the deBroglie equation, the Lorentz transformations, and the energy-frequency relation, E = hv. Inertia is then presented as an effect resulting from the frequency and hence energy changes with motion that result from the special relativistic time transformation and apply to mass because of the energy-mass equivalence. The deBroglie wave equation and Newtons second law are shown to be equivalent with respect to a postulate set for the deductive presentation of wave and inertial properties of matter; the deBroglie equation and Newtons second law may therefore be regarded as having the same physical content.

Space at Mid-Century

The concepts of space which are used in contemporary physics are discussed, and are contrasted with the older concepts associated with Newtonian physics. The effects of uniform motion on space and the simplest currently accepted relations between space and time are stated. Deviations from three-dimensional orthogonal space as demanded by the general theory of relativity are discussed, with attention to the relative roles of space and time terms in the space-time curvature associated with gravitational fields. The development of cosmo-logical theory, on the basis of general relativity concepts, is briefly indicated. Machs suggestion for the relation of matter and space is described; more recent speculations relating over-all space and local properties, and the possibility of discontinuity in microscopic space, are noted. The emphasis in the current conception of space on interdependence between space and matter is pointed out.

Bohr and Einstein: A Course for Nonscience Students.

A course that has been given at Michigan State University for nonscience upper‐class students is described. Its aim is to present the salient ideas of relativity and quantum physics in association with the lives of Albert Einstein and Niels Bohr. Generally qualitative arguments and discussions of key experiments are used to convey the scientific content. The controversy between Bohr and Einstein on quantum theory is included, and serves to point up a basic philosophical innovation in twentieth century physics. Some attention is also given to the attempts of both Einstein and Bohr to influence political events.