Physics Colloquia WINTER QUARTER 2004

Michael Nauenberg
Physics Department, UC Santa Cruz

January 8, 2004

Newton, Hooke and the early development of orbital dynamics

During the second half of the 17th century the outstanding problem in astronomy was to discover the physical basis for Kepler's three empirical laws which describe the motion of planets orbiting around the Sun. The answer to this fundamental problem is generally credited solely to Isaac Newton who described its solution in his masterpiece, the Principia, first published in 1687. But how Newton reached this solution has been the subject of much confusion and debate during the past half century, particularly concerning the seminal role played by Robert Hooke, who corresponded with Newton on this subject in the Fall of 1679. In this lecture I will discuss this correspondence and related historical documents which shows Newton's profound but still incomplete understanding of the physics of orbital dynamics at that time. I also will exhibit two experiments which led Hooke to his insights into the physics of planetary motion. This historical analysis reveals that the solution of this orbital problem was actually a joint achievement of Newton and Hooke.

David Hafemeister
Physics Department
Cal Poly University

January 15, 2004

The Energy Situation in 2004

The conclusions of the American Physical Society--Panel on Public Affairs (APS-POPA) energy study of 1996* are still relevant today, and they will be briefly discussed in terms of recent trends. Cars, refrigerators and houses have greatly improved, but yet energy use continues to climb. The best news on the supply side is the Combined Cycle Gas Turbine. The talk will use basic models to cover the following:

M. King Hubbert's model for petroleum resources will be extended to include economics

Combined cycle gas turbine efficiency will be shown to be 60%

A proposal to stabilize electrical grids and improve on Adam Smith will be presented

Cost-of-conserved energy & life-cycle-costs will be applied to energy efficient refrigerators

Scaling model for a cubic building will give: linearized heat transfer, free temperature and balance point, and drastic savings for super-insulated houses.

Stephen Libby
Lawrence Livermore National Laboratory

January 22, 2003

Entropy Flow and Atomic Radiation in Near Equilibrium Plasmas

Plasmas in "Local Thermal Equilibrium" (LTE) have locally well-defined free electron temperatures Te controlling the distribution of atomic ionization states. The solar interior is a typical example. Non-local thermal equilibrium (NLTE) occurs when electron collisions and/or Planckian radiation are insufficient to force LTE. Examples range from low density stellar atmospheres to dense plasma inertial fusion hohlraums and x-ray lasers.

NLTE phenomena are far more complex than LTE. In LTE, the rates controlling the absorption and emission of radiation are a unique function of Te, density, and composition. In NLTE, the analogous rates depend not only on Te, and the material composition, but also crucially on the full electron and photon distribution functions.

While analysis of general NTLE behaviors remains difficult, the practical case of quasi-steady-state NLTE systems is amenable to simplification. We have developed a general theory and computational framework to treat atomic radiation responses to non-Planckian or hot electron perturbations. Atomic radiation in the neighborhood of equilibrium is described by a linear response matrix giving the net emission (absorption) at a given frequency caused by deviations from the black-body radiation spectrum at a second frequency. The response matrix is calculated by solving the usual kinetic rate equations with special boundary conditions. According to Onsager, the matrix must be symmetric, yielding a powerful test for NLTE codes. We prove that the principle of minimum entropy production characterizes steady-state near-LTE excited-state populations and derive the exact response matrix in terms of the underlying kinetics. Applications include the "factorization" of the equations of NLTE radiative transfer resulting in large increases in computational efficiency, and the "automated" discovery of tailored x-ray (including x-ray laser) schemes.

Michael Thorpe
Physics Department, Arizona State University

January 29, 2004

Protein Flexibility and Folding

We apply a novel approach to the exploration of energy landscapes of macromolecules, network glasses and proteins that uses constraint theory. Constraints fix the bond lengths and bond angles and allow the use of theorems from graph theory to accomplish a rigid region decomposition of the network of atoms, which identifies the rigid regions, the flexible joints between them and also the stressed regions.

Protein folding is an example of a phase transition in which rigidity percolates as the protein proceeds from a floppy to a rigid state. We show how the folding pathway can be determined from the three- dimensional native state structure of the protein.

In designing new drugs in the pharmaceutical industry, it is important to take account of the flexibility of both the target protein and the ligand (drug) that is to be attached. We will show a movie of the motion of a protein-ligand complex.

Douglas D. Osheroff
Physics Department, Stanford University

February 5, 2004

Understanding The Columbia Shuttle Accident

On February 1, 2003 NASA's Space Shuttle Columbia broke apart on re-entry at an altitude of 200,000 feet and a velocity in excess of 12,000 mph. All aboard perished. Within hours Hal Gehman was asked to chair a board investigating that accident, which was charged with determining the physical cause of the accident, but also considered the underlying causes. The physical cause was determined to have been a piece of insulating foam, with a density only 1/30th that of water, that struck the leading edge of the left wing 82 seconds into launch. Such foam had fallen off the cryogenic fuel tank on virtually every flight, but NASA did not consider it a safety risk. The speaker will describe the accident, his role in the investigation, and discuss the the circumstances that allowed this accident to occur.

Peter Littlewood
National High Magnetic Field Laboratory/
Los Alamos National Laboratory
and Theory of Condensed Matter Group,
Cavendish Laboratory, Department of Physics,
Cambridge, UK

February 12, 2004

Coherent Excitonic Matter

By shining light on a semiconductor, one creates pairs of electron and holes that bind together with the Coulomb interaction to make a neutral "atom" called an exciton--the solid state analog of positronium. This combined entity is a composite boson. The possibility that a gas of excitons might undergo Bose-Einstein condensation was raised over 40 years ago, but despite considerable effort and many beautiful experiments, no unequivocal observation has been made.

I will discuss some theoretical ideas and experiments in semiconductor systems, and in particular some novel approaches with optical microcavities that make use of the decay of excitons into photons. In this case, the exciton condensate is a special kind of laser.

Joseph Lykken

February 19, 2004

The Search for Extra Dimensions

String theory predicts extra dimensions of space, and suggests a number of physical mechanisms to hide them from our everyday experience. Some of these mechanisms are so efficient that even extra dimensions of macroscopic size could have eluded detection. Experiments are already underway, using a variety of techniques, aimed at the direct or indirect discovery of extra dimensions.

Aharon Kapitulnik
Stanford University

February 26, 2004

Measurements of Gravity-like Forces at sub-100 microns distances

Until recently, it was believed that quantum gravitation effect will be impossible to verify experimentally, due to the impossibly short distance scale over which they are known to be important. However, recent developments in string theory predict supersymmetry with six or seven new dimensions and many new types of fields and extended objects. In addition, new phenomenologies of extra dimensions have been constructed suggesting that new, dramatic effects may be discovered in experiments; in particular the violation of the gravitational inverse square law at length scales below 1 mm.

We will describe a set of experiments that involve the utilization of micro-cantilevers as force sensors to measure gravity-like forces at length scales between 15 and 100 microns [1]. In all schemes an alternating mass scheme is designed to excite a test mass which is placed on a sensitive cantilever with force resolution exceeding 10$^{-18}$ N. We will discuss the current limits of our experiments and their future extensions.

Matthias Steinmetz
Astrophysics Institute Potsdam
Potsdam, Germany

March 4, 2004

Galactic Archeology: the formation history of the galaxy revealed

How have the Milky Way and other galaxies in the universe been formed? In a monolithic giant collapse about 10 billion years ago or due to the successive merging of smaller protogalactic clumps as envisioned by the current cosmological "concordance model"? In the latter case, signatures of this formation history should be locked up in the kinematic and chemical properties of stellar populations awaiting discovery. The newest generation of computer simulations are now making quite specific predictions on how to trace these signatures and new observational campaigns from the ground and in space have been started to search for them. Indeed, the first couple of examples have been clearly identified. Together observations and simulations will soon enable us to reconstruct the formation history of the Milky Way and, possibly, of other galaxies in the Local Group.

Burton Richter
Stanford Linear Accelerator Lab

March 11, 2004

Gambling with the Future: Energy, Environment, & Economics in the 21st Century

In the late 1950s measurements of the concentration on carbon dioxide in the atmosphere began at Mauna Loa in Hawaii. It soon became clear that atmospheric CO-2 was increasing and the scientific community began to try to understand why, and what the consequences might be. It was not until the “Earth Summit” at Rio de Janeiro in 1992 that governments began to support a world-wide effort to understand what is now called Global Climate Change. Today, it is generally accepted that human activity is affecting the heat balance of the planet and that the greenhouse effect from increased CO-2 will increase the global temperature with uncertain consequences. We are already in a regime that has no precedent in the last 400,000 years, and these consequences are almost certainly bad if greenhouse gas concentrations increase unabated. The driving force is the increase in global population and the economic development, coupled to energy use that everyone wants so as to increase their standard of living. I will summarize the evidence, the projections for the next 50-100 years, and outline what our options are. The problem can be brought under control without miraculous intervention if we have the will, something that is not at all clear.