Session J15: History of Physics and Educational Topics

On the Late Invention of the Gyroscope

The invention of the gyroscope is usually attributed to the French physicist Jean-Bernard-Leon Foucault in 1852. He certainly invented the word and also used his gyroscope to demonstrate the rotation of the Earth. However, the gyroscope was actually invented around 1812 by German physicist Johann Bohnenberger who called his device simply the ``machine''. Several others, including American physicist Walter R. Johnson (who called his apparatus the ``rotascope''), independently invented the gyroscope in the 1830's. Each of these devices employed a central object (sphere or disc) that could spin freely on a shaft. This was placed between three independent gimbals, which could also move freely. Bohnenberger's ``machine'' has much the same appearance as an armillary sphere. Such devices had been produced for at least the preceding three centuries. They were used to display the movements of various celestial bodies. However, armillary spheres are only simulations of celestial appearances, not actual demonstrations of physical phenomena. Gimbal systems similar to those found in gyroscopes were used on ships to level oil lamps from at least the sixteenth century and the ideas behind armillary spheres date back at least a millennium before that. So why was the gyroscope invented so late? Some possible reasons will be presented for the long delay between the development of the individual underlying components and the eventual appearance of the gyroscope in its modern form.   

Sommerfeld's balancing act with Einstein: The geometry of relativistic velocity space

Minkowski's (M's) first paper (1908) on relativistic 4-space mentions that it made contact with nonEuclidean geometry, but he died in early 1909 before he could pursue that idea. Sommerfeld (S) saw that one of the known examples of that geometry, the sphere of imaginary radius, was a natural model for relativistic velocity space, and in 1909 he presented in 3 pages an illuminating geometrical proof of Einstein's (E's) theorem on relativistic velocity addition. Very different was his 79-page systematic development in 1910 of the 4-space vector algebra that had been invented by M. In a crucial footnote in it S had side-stepped the nonEuclidean idea, while still being true to what he believed, saying: ``It is possible, though hardly to be recommended, to translate all the following into corresponding nonEuclidean terminology.'' At a meeting in Salzburg in 1909 E and S had become friends. A 1910 letter of E's to S tells us that at Salzburg E must have let S know how strongly he disliked the 4-space view of relativity, but that he now really liked S's long paper. The importance of S's special geometric insights, and their relative neglect subsequently, will be discussed.   

Francis Perrin's 1939 Analysis of Uranium Criticality

In May 1939, French physicist Francis Perrin published the first numerical estimate of the fast-neutron critical mass of a uranium compound. While his estimate of about 40 metric tons (12 tons if tamped) pertained to uranium oxide of natural isotopic composition as opposed to the enriched uranium that would be required for a nuclear weapon, it is interesting to examine Perrin's physics and to explore the subsequent impact of his paper. In this presentation I will discuss Perrin's model, the likely provenance of his parameter values, and how his work compared to the approach taken by Robert Serber in his 1943 Los Alamos Primer.   

Babson, Bahnson, the DeWitts and the General Relativity Renaissance

During the 1950s the efforts of an unlikely group composed of two colorful businessmen, a handful of physicists, and Air Force representatives helped to create a renaissance in general relativity research. Industrialist Agnew Bahson was an air conditioning magnate with connections to leading scientists, and the Air Force. In addition to his contribution to ``respectable'' physics, his life and death are shrouded in a cloak of UFO and anti-gravity conspiracy theories. Business theorist Roger Babson was driven to search for a solution to anti-gravity after first his sister and later his grandson drowned tragically as children. This presentation tells of the globe spanning, harrowing adventure of mountainside crashes, an international love affair, physicists masquerading as secretaries, the founding of Les Houches, the development of the first radar defense system and how Bahnson and Babson became benefactors of mainstream physics, leading to the creation of the Institute of Field Physics at the University of North Carolina Chapel Hill led by Cecile and Bryce DeWitt and ultimately to the groundbreaking research that predicted the Higgs boson.   

Who was Christine Shack?

In the April 2009 issue of {\it Physics Today}, is an article on ``John Wheeler's work on particles, nuclei and weapons" written by Kenneth Ford. In Figure~4, among the twenty-one individuals in a group photo of the Project Matterhorn B team and support staff at Princeton University, there appears in the first row an African American woman, identified as Christine Shack. The major goals of this presentation are to give my findings on: Who was Christine Shack? What was her role(s) in Project Matterhorn? What was her career after leaving this project? My answers are based in part on several interviews with Shack.   

Black Holes: are they as real as we think?

The history of black holes is a bumpy one including long periods of time for which the topic was of little scientific interest. Today, black holes seem to have captured the imagination of the general public as well as cosmologists and astrophysicists. Researchers routinely make the claim that supermassive objects found at the center of galaxies are confirmed black holes and the general public has grasped onto this ``reality'' with fervor. However, it is interesting and perhaps beneficial to review these claims against the backdrop of historical perspective. This paper revisits the path taken in the development of the concept of the black hole with particular emphasis on its most unique property -- the event horizon.   

Online and Blended Climate Change Courses for Secondary School Educators from the American Museum of Natural History

The American Museum of Natural History (AMNH) has created both online and blended climate change education courses directed toward secondary school educators. The online course carries graduate credit and is authored by leading scientists at AMNH and at NASA's Goddard Institute for Space Studies. It focuses on weather and climate; sources of climate change; the response of the climate system to input; modeling, theory and observation; what we can learn from past climates; and potential consequences, risks and uncertainties. The blended course includes an abbreviated version of the online course along with additional activities, many suitable for classroom use. Both the online and blended course experiences will be reviewed, including the use of an educational version of NASA's Global Climate Model. Attendees will be provided with a DVD of Climate Change videos and data visualizations from the American Museum of Natural History.   

Learning Physics from the Real World by Direct Observation

It is axiomatic that hands-on experience provides many learning opportunities, which lectures and textbooks cannot match. Moreover, experiments involving the real world are beneficial in helping students to gain a level of understanding that they might not otherwise achieve. One practical limitation with the real world is that simplifications and approximations are sometimes necessary to make the material accessible; however, these types of adjustments can be viewed with misgiving when they appear arbitrary and/or convenience-based. The present work describes a very familiar feature of everyday life, whose underlying physics is examined without modifications to mitigate difficulties from the lack of control in a non-laboratory environment. In the absence of any immediate formula to process results, students are encouraged to reach ab initio answers with guidance provided by a structured series of worksheets. Many of the latter can be completed as homework assignments prior to activity in the field. This approach promotes thinking and inquiry as valuable attributes instead of unquestioningly following a prescribed path.   

Teaching the Maxwell and Dirac Equations in the Same Algebra

The geometric algebra of 3-D Euclidean space is sufficient to write and solve both Maxwell's equations and the Dirac equation. The formulations are fully relativistic and covariant. In this approach both the Maxwell electromagnetic field and the Dirac electron field are expressed as linear combinations of the algebraic basis elements of the tangent space at a given point in space. It is noteworthy that there are eight independent basis elements of the geometric algebra of the tangent space just as there are eight independent quantities in the four complex components of the standard Dirac spinor. Expressing the Dirac field as a linear combination of basis elements of the tangent space greatly facilitates visualization of solutions of the Dirac equation and provides insight into the nature of spin up vs. spin down states and the distinction between electron and positron states. Geometric algebra is quite intuitive, needing only standard associative and distributive rules coupled with the anticommutation of two orthogonal vectors as in the traditional cross product. A good understanding of geometric algebra could be developed as part of a one-semester, advanced algebra course. It would then be straightforward to illustrate solutions of both the Maxwell and Dirac equations in an undergraduate physics course on wave equations.