Colloquia
Department of Physics Colloquia Schedule
SPRING
2004
>
> FALL 2003
Thursday, February 5, 2004
MICHAEL PESKIN
Stanford University
"Linear Collider: the Next Step in High-Energy
Electron Physics"
There is now a consensus in the world-wide particle
physics community that the next great accelerator after the LHC
should be an electron-positron collider, operating at 500 GeV
in the center of mass. In this colloquium, I would like to introduce
the prospects and promise of this facility. I will begin by reviewing
some results of the precision study of electroweak interactions
carried out in the 1990's, discussing both what we have learned
and how the special experimental techniques of e+e- colliders
have helped us learn it. I will then explain how these same techniques
will allow us, at the next stage, to gain insight into new models
of elementary particle physics and the origin of cosmic dark matter.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room)
Thursday, February 12, 2004
DEEPTO CHAKRABARTY
MIT
"Clocking Millisecond X-Ray Pulsars: A Speed
Limit for the Fastest Spinning Stars in the Universe"
Pulsars are highly-magnetized spinning neutron stars
formed in the supernova collapse of massive stars at the end of
their nuclear-burning lifetime. They are somewhat like giant atomic
nuclei, with roughly the Sun's mass compressed into a radius of
only 10 kilometers. Some pulsars are spun up to millisecond periods
by torques exerted by a binary companion star. These millisecond
pulsars are spinning near their centrifugal breakup limit, with
surface velocities nearly 20 percent the speed of light.
However, recent X-ray timing measurements indicate
that the pulsar spin frequency distribution cuts off sharply at
the fast end, well before the predicted centrifugal break-up limit
is reached. Although the braking mechanism that halts further
spin-up is not yet known, these data support theoretical predictions
that gravitational radiation losses may be responsible. If so,
then these gravitational waves may eventually be detectable by
LIGO.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, February 19, 2004
KATHRYN MOLER
Stanford University
"Mesoscopic Magnetic Imaging"
Collective electron effects often create magnetic
signatures on mesoscopic length scales. In principle, under carefully
chosen conditions, these magnetic signatures can help us to understand
both the mechanisms of quantum decoherence in electronic materials
and the correct theoretical description of strongly correlated
electron systems in reduced dimensions. I will describe recent
progress in sensitive and high-resolution magnetic imaging techniques
for materials physics. The local imaging capability is important
for studying both devices and materials: the most fundamental
effects are those that occur on the natural length scales associated
with many electrons, and many materials are inhomogeneous. I will
conclude with examples of work during the past few years that
have begun to demonstrate the usefulness of local probes for basic
condensed matter studies by testing theories of the mechanism
of superconductivity in high-Tc superconductors.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, February 26, 2004
DAVID KAISER
MIT
"Teaching Feynman's Tools: The Dispersion of
Feynman Diagrams in Postwar Physics"
Feynman diagrams have revolutionized nearly every
aspect of theoretical physics since the middle of the 20th century.
Introduced first as a bookkeeping device for simplifying lengthy
calculations in one branch of quantum physics, the diagrams soon
gained adherents throughout the fields of nuclear and particle
physics, condensed matter physics, and even gravitational physics.
By following how physicists learned about and used
Feynman diagrams from the late 1940s through the late 1960s, broader
changes in the infrastructure and intellectual development of
postwar physics come into focus. Everything about physicists'
patterns of work came in for re-evaluation after the war, from
the methods of training young theorists, to the methods of communicating
new results and techniques, to decisions about what topics merited
study, and with what means. Following Feynman diagrams around
thus helps us to make sense of theoretical physicists' changing
world during the middle decades of the 20th century.
Time: 4:15 pm
Place: Room 10-250
/ MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 4, 2004
PAUL McEUEN
Cornell University
“Carbon Nanotubes: Electrons in a 1D World”
Carbon nanotubes—nanometer diameter cylinders
made from rolling up single graphene sheets—offer an unprecedented
opportunity to explore the physics of electrons in one dimension.
The electrons in the nanotube occupy one-dimensional subbands
that result from the quantization of the electron motion around
the circumference of the tube. The mathematics of this is reminiscent
of early versions of string theory. The tubes can be metals or
semiconductors, depending on the detailed structure of the tube.
The mean free path for electron scattering in metallic tubes can
be extremely long, and semiconducting tubes can be fashioned into
field-effect transistors with significantly better intrinsic properties
than Si MOSFETs.
This talk will review measurements by our group
of the electronic and electromechanical properties of nanotubes.
I will address both the basic properties of electrons confined
to these tiny cylinders and also discuss a few potential applications.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 11, 2004
MICHAEL TURNER
University of Chicago
"Cosmic Acceleration: New Gravitational Physics
or Mysterious Dark Energy?"
The riddle of the speed up of the expansion of the
Universe is one of the most profound puzzles in all of science.
It touches upon a number of deep questions: What caused inflation,
is there a boson for every fermion, what is our cosmic destiny,
how will Einstein's theory be extended to include quantum mechanics,
and what has repulsive gravity?
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, March 18, 2004
WOLFGANG KETTERLE, John D. MacArthur Professor of
Physics;
2001 Nobel Laureate
MIT
"New Frontiers with Ultracold Gases"
Quantum degenerate ultracold gases are used to
explore new phenomena in condensed matter physics and to advance
atom optics. I will present recent results including a new low-temperature
record of 500 picokelvin, and experiments with atom chips where
the magnetic field of miniaturized wires traps and manipulates
ultracold atoms close to a surface.
Ultracold molecules were created from ultracold
atoms in a chemical reaction without heat release. This technique
led to the first observations of Bose-Einstein condensation of
molecules. A condensate of molecules consisting of two fermionic
lithium atoms realizes the strong coupling limit of superfluidity
of fermion pairs. This is the starting point for exploring the
BEC–BCS crossover in a strongly interacting gas of fermions.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in
4-339 (Physics Common Room).
Thursday, April 1, 2004
ALEXANDAR VAN OUDENAARDEN, Keck Career Development
Professor in Biomedical Engineering and Assistant Professor of
Physics
MIT
“Information Storage and Propagation in Genetic
Networks”
The ability of a living cell to grow and divide,
and to sense and respond to its environment is determined by a
complex web of intracellular, and sometimes intercellular, protein
and gene networks. During the last decade, new technologies such
as high-throughput genome sequencing and gene arrays have enabled
a large-scale identification of these interaction networks. Although
many of these networks have already been mapped, surprisingly
little is known about the function of specific network architectures.
Rather than taking a genome-wide approach, our lab focuses on
the smaller, recurring network motifs buried in the larger networks.
These motifs are built from a handful of genes and proteins and
display a network structure that appears over and over again in
different networks and different organisms. The underlying idea
is that these motifs define autonomous functional modules that
are the building blocks for the entire cellular network.
In this talk I will focus on two elementary motifs:
positive feedback loops that can be used to store information
and generate steep switches; and feed-forward loops that are used
to propagate signals and the concomitant noise through the network.
I will present both theoretical models and experiments on natural
and synthetic genetic networks in the bacterium Escherichia
coli and the budding yeast Saccharomyces cerevisiae.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 8, 2004
AHARON KAPITULNIK
Stanford University
“Measurements of Gravity-like Forces at Sub-mm
Distances”
Until recently, it was believed that quantum gravitation
effect would 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.
I 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.
In all schemes an alternating mass scheme is designed to excite
a test mass that is placed on a sensitive cantilever with force
resolution exceeding 10^{-18} N. I will also discuss the current
limits of our experiments and their future extensions.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 15, 2004
STANISLAS LEIBLER
Rockefeller University
"Are Bacteria Individuals?"
I will try to answer this simple question, together
with another one:
"Why should we care (as physicists or/and as humans)?"
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 22, 2004
CHARLES HOLBROW
Colgate University
“Sex, Lies, and Videotape: Essentials of Physics
Teaching”
Over the last eighty years, a half-dozen notable
MIT physics professors powerfully influenced the teaching of introductory
physics to undergraduates in America. In deciding how to teach
introductory physics each had to consider "sex, lies, and
videotape." "Sex," because the essence of sex is
attraction, and if you want to attract more students to take more
physics, you must work to make learning it more attractive. "Lies,"
because teaching depends on carefully selected, carefully crafted
lies—heuristics, myths, and stories we use to hide our shortcomings
from ourselves. "Videotape," representing technology
in general, because physicists always try to enhance instruction
by using available technology.
Along with some account of MIT's contributions,
I will describe the sex, the lies, and the videotape of today's
nationwide efforts to improve physics teaching.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, April 29, 2004
DAN AKERIB
Case Western Reserve University
"Looking for WIMPs in the Galactic Halo: The
Search for Dark Matter
Using Ultra-Cold Particle Detectors and Other Techniques"
Overwhelming observational evidence indicates that
most of the matter in the Universe consists of non-baryonic dark
matter. One possibility is that the dark matter is Weakly-Interacting
Massive Particles (WIMPs) that were produced in the early Universe.
These relics could comprise the Milky Way's dark halo and provide
evidence for new particle physics, such as supersymmetry.
After reviewing some of the evidence for dark matter
and the WIMP hypothesis, I will describe the search we are conducting
to detect these particles using phonon-mediated particle detectors
housed in a low-radioactive 20-milli-Kelvin environment 2,000
feet below ground. I will also describe some of the other experiments
that are part of the broad world-wide program to search for WIMPs.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, May 6, 2004
NORA VOLKOW
National Institute on Drug Abuse; Brookhaven National Laboratory
"Imaging the Addicted Brain: from Molecules
to Behavior"
Abstract forthcoming.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, May 13, 2004
FRANK WILCZEK, Herman Feshbach Professor of Physics
MIT
"The Origin of Mass and the Feebleness of Gravity"
I will discuss how most of the mass of protons and
neutrons, and therefore of matter, arises out of a theory which
contains only massless building-blocks. My discussion will be
quantitative and it will be based on well-established experimental
results, not speculation and wishful thinking. I will then discuss
how, with a modest infusion of speculation and wishful thinking,
an elaboration of these ideas provides a fundamental explanation
of why gravity appears so feeble compared to the other basic forces
of Nature.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
