Colloquia

Department of Physics Colloquia Schedule

FALL 2005

> > SPRING 2005

Thursday, September 8, 2005

SEAN CARROLL, Assistant Professor of Physics
University of Chicago

"Beyond Dark Energy"

General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, September 15, 2005

PIER ODDONE, Director
Fermi National Accelerator Laboratory

"The Future of Accelerator-based Particle Physics"

All major accelerator based facilities for particle physics in the US will end by the end of the decade. This will occur at the time when data from the Large Hadron Collider in Europe is likely to open wholly new horizons. Is this the end of the line for US accelerator based particle physics or a great opportunity to start new major initiatives? I will discuss the present state of the field and the decisions that need to be made to insure the future vitality of the field.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, September 22, 2005

WOLFGANG KETTERLE, John D. MacArthur Professor of Physics; 2001 Nobel Laureate
MIT

"Observation of High-Temperature Superfluidity in a Gas of Fermionic Atoms"

Ultracold quantum degenerate Fermi gases provide a remarkable opportunity to study strongly interacting fermions. In contrast to other Fermi systems, such as superconductors, neutron stars or the quark-gluon plasma of the early Universe, these gases have low densities and their interactions can be precisely controlled over an enormous range.

A major goal has been the realization of superfluidity in a gas of fermions. Our observation of vortex lattices in a strongly interacting rotating Fermi gas provides definitive evidence for superfluidity. By varying the binding energy between fermion pairs, we have studied the crossover from a Bose–Einstein condensate of molecules to a Bardeen–Cooper–Schrieffer superfluid of loosely bound pairs. The crossover is associated with a new form of superfluidity. The observed transition temperatures normalized for the density of the gas by far exceed the highest transition temperatures achieved in high-T_c superconductors.

I will also summarize recent accomplishments with Bose-Einstein condensates including quantum reflection and nonlinear atom optics.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, September 29, 2005

DAVID NELSON, Mallinckrodt Professor of Physics
Harvard University

"Spherical Crystallography: Virus Buckling and Grain Boundary Scars"

Ordered states on spheres require a minimum number of topological defects. The difficulty of constructing ordered states was recognized by J. J. Thomson, who discovered the electron and then attempted regular tilings of the sphere in an ill-fated attempt to explain the periodic table. One set of solutions to this "Thomson problem" requires that regular triangular lattices be interrupted by an array of at least 12 five-fold disclination defects, typically sitting at the vertices of an icosahedron. For R>>a, where R is the sphere radius and a is the particle spacing, the energy associated with these defects is very large. This energy can be lowered, however, either by buckling, as appears to be the case for large viruses, or by introducing unusual finite length grain boundary scars. The latter have been observed recently for colloidal particles adsorbed onto water droplets in oil. Examples of topography-induced defect configurations for
liquid crystals coating spheres and torroidal vesicles will be discussed as well.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, October 6, 2005

EDMUND BERTSCHINGER, Professor of Physics; Division Head, Astrophysics
MIT

"Brownian Motion of Dust, Stars, and Invisible Matter"

A century after Einstein's miraculous year of relativity, quantum theory and statistical mechanics, the cross-connections between these subjects (and Einstein's later contribution of general relativity) remain at the forefront of modern research. This talk will present some of the connections between Brownian motion and gravitation.

After reviewing Einstein's theory of Brownian motion, I will summarize its extensions by Fokker, Planck, and others to a kinetic theory of weakly collisional gases. When applied to self-gravitating systems, however, equilibrium statistical mechanics breaks down. For example, long-range gravitational encounters of stars in dense star clusters fail in their attempt to establish thermodynamic equilibrium because self-gravitating systems have a negative specific heat. Nevertheless, non-equilibrium kinetic theory can be applied to the dark matter that makes up most of the mass of the universe. I will discuss the effects of Brownian motion of dark matter particles both in the early universe (when the collisions are mediated by supersymmetry or the weak interaction) and in the more recent universe when gravity drew dark matter into galaxies like our own.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, October 13, 2005

ERIC ADELBERGER, Professor of Physics; Adjunct Professor of Astronomy
University of Washington

"Tests of the Gravitational Inverse-Square Law at the Dark Energy Length Scale"

It is remarkable that small-scale experiments can address important open issues in fundamental science such as: "why is gravity so weak compared to the other interactions?" and "why is the cosmological constant so small compared to the predictions of quantum mechanics?" String theory ideas (new scalar particles and extra dimensions) and other notions hint that Newton's Inverse-Square Law could break down at distances less than 1 mm. Furthermore, the observed dark enrgy density corresponds to a length scale of 85 microns that may have fundamental significance. I will review some motivations for testing the Inverse-Square Law, and discuss recent experiments with torsion balances, small oscillators, micro-cantilevers, and ultra-cold neutrons. Our torsion-balance experiments have probed for gravitational-strength interactions with length scales down to about 70 micrometers, which is approximately the diameter of a human hair.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, October 20, 2005

MASAHIRO MORRI , John L. Loeb Associate Professor of the Natural Sciences
Harvard University

"Cracking the Unitarity Triangle: A Quest in Flavor Physics"

The Standard Model of particle physics, despite its great successes, fails to give a compelling explanation for the pattern of masses and mixing of the particles found in Nature.  The problem is most evident in the quark-mixing matrix, which governs the interactions between different flavors of quarks.  In this talk, I will discuss why flavor physics is an attractive way of hunting for New Physics, and how the experimental constraints can be expressed concisely with the so-called Unitarity Triangle.  I will provide an overview of the recent progress, mainly from the B-Factory experiments, in constraining the Unitarity Triangle and discuss future prospects.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, October 27, 2005

The Pappalardo Lecture in Physics

CHARLES ALCOCK, Director, Harvard-Smithsonian Ctr for Astrophysics
Harvard University

"Shadows of Faint Objects:  The use of indirect search techniques in astronomy "

Many of the targets of contemporary astronomy are expected to be extremely faint, below the detection threshold of the largest telescopes we hope to build.  These objects span the range from small bodies in the outskirts of our solar system, through planets around other stars, out to neutron stars and black holes in the universe at large.  Indirect search techniques are essential to progress.  I will discuss the common features of indirect searches and outline possibilities for rapid progress in the coming decade: a survey of the outer solar system and the characterization of extra-solar planets.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, November 3, 2005

The David and Edith Harris Distinguished Lecture in Physics

ANDREI LINDE, Professor of Physics
Stanford University

"Inflation, Dark Energy, and String Cosmology"

For a long time scientists believed that our universe at the moment of its creation looked as an expanding ball of fire. This scenario dramatically changed during the last 25 years. Now we think that initially the universe experienced a stage of inflation, accelerated expansion in an unstable energetic vacuum-like state. It became hot only later, when the vacuum-like state decayed. According to the recent observational data, 5 billion years ago the universe entered a new stage of accelerated expansion driven by dark energy. In this talk I will describe the basic principles of inflationary cosmology and recent cosmological observations. Then I will concentrate on the recent progress in describing inflation and dark energy in the context of string theory.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, November 10, 2005

CHRISTOPH PAUS, Associate Professor of Physics
MIT

Title TBD

Abstract forthcoming.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, November 17, 2005

IAIN STEWART, Assistant Professor of Physics; Alfred P. Sloan Research Fellow
MIT

Title TBD

Abstract forthcoming.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, November 24, 2005

Thanksgiving Holiday: no colloquium

Thursday, December 1, 2005

Speaker TBD

Title TBD

Abstract forthcoming.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

Thursday, December 8, 2005

CATHERINE KALLIN, Professor
McMaster University

Title TBD

Abstract forthcoming.

Time: 4:15 pm
Place: Room 10-250 / MIT

Refreshments @ 3:45 pm in 8-314 (The Physics Common Room)

The Department of Physics Colloquium Series will resume on
Thursday, February 9, 2006.