Colloquia
Department of Physics Colloquia Schedule
FALL
2003
>
> SPRING 2004
Thursday, September 11, 2003
NICHOLAS GIORDANO
Purdue University
"The Physics of the Piano"
While a piano is a complicated mechanical device,
it can presumably be described by physics at the level of freshman
mechanics, i.e. field theory should not be required. In
spite of this apparent simplicity, it is very difficult to use
Newton's laws to calculate the sound produced by a piano. In this
talk I will give a brief introduction to the physics of the piano,
and describe a few of the interesting problems involved in constructing
such a physical model of the instrument. I will then describe
our attempts to calculate the sound produced by a piano from first
principles, i.e. using F=ma.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room)
Thursday, September 18, 2003
FRANKLIN CHANG-DIAZ
Advanced Space Propulsion Laboratory, NASA Johnson Space Center
"The Physics of the VASIMR Engine"
Future high-speed space transportation will hinge
on the development of rockets whose performance far exceeds that
of chemical engines. The metric of interest is the rocket’s
Specific Impulse (Isp), which is given in units
of seconds and is quantitatively the ratio of the rocket-relative
exhaust speed and the acceleration of gravity at sea level. From
the highest Isp value of 500 sec., associated
with our best chemical engine, we wish to push to ranges of 5,000
to 30,000 sec. In doing so, we depart the field of chemistry and
enter the realm of plasma physics.
The Variable Specific Impulse Magnetoplasma Rocket
(VASIMR) is a new member in the small family of advanced electric
propulsion devices currently under study. Its salient features
include three magnetically linked stages where plasma is respectively
created, energized and subsequently accelerated to produce useful
thrust at high Isp. The plasma in VASIMR is
both produced and energized by radio waves, eliminating the materials
problems associated with physical electrodes in direct contact
with hot plasma. This leads to a much higher power density, as
compared with other plasma rockets. Plasma production is done
in the first stage by an integrated helicon type discharge, while
the bulk of the plasma energy is typically added in the second
stage by Ion Cyclotron Resonance Heating (ICRH.) Axial
momentum is obtained by the adiabatic expansion of the plasma
in a magnetic nozzle.
VASIMR is also capable of varying, under constant
power, the Isp and hence the thrust over a wide
operational regime, a feature called Constant Power Throttling
(CPT,) offering useful mission optimization flexibility. The
CPT technique primarily involves the selective partitioning
of the RF power to the helicon and ICRH systems, with the proper
adjustment of the propellant flow; however, other complementary
approaches are also being considered. While there are multiple
propellant options, operational and performance considerations
favor the light gases.
The physics and engineering of this device have
been under study since 1980 with considerable progress on all
fronts. A NASA-led, research effort, involving several teams in
the United States and abroad, continues to explore the potential
of this technology to meet the mission requirements of our next
generation of interplanetary spacecraft. This talk will review
the physics principles of this concept, discuss some of the main
technological challenges and present the latest status of the
research.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, September 25, 2003
SEAMUS DAVIS
Cornell University
"Ripples in a D-wave Sea: Quasiparticle Interference
Imaging in Cuprate Superconductors"
High temperature superconductivity in the cuprates
emerges when the localized electrons of a Mott-insulator become
itinerant due to carrier-doping. Understanding both the electronic
ground state and the excited states of these systems are key challenges
in CM physics today. Angle-resolved photoemission (ARPES) studies
have been remarkably successful in mapping the momentum-space
characteristics of the cuprate excited states. However, since
cuprate superconductivity develops from atomically localized electrons
and exhibits nanoscale disorder, a pure momentum-space description
may not be sufficient. Instead, simultaneous information on electronic
structure in both the real-space and momentum-space may be required.
I will describe a combination of several novel scanning
tunneling microscopy (STM) techniques which achieves these apparently
contradictory aims. I will describe STM experiments designed to
detect and identify the electronic ground state in other regions
of the cuprate phase diagram including FT-STS studies of the vortex
core and doping-dependent FTSTS studies.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, October 2, 2003
DIANDRA LESLIE-PELECKY
University of Nebraska
"Scientists and K-12 Education: Can We Make
a Difference?"
The National Science Foundation has focused of lot
of attention and resources on the integration of research and
education. An education component is specifically required for
most NSF proposals, including CAREER and all of the large “center”
grants. Activities range from designing courses for pre-service
teachers, to involving teachers in research labs, to putting scientists
in K-12 schools. What if any impact can research scientists realistically
have on K-12 education? The NSF-funded Project Fulcrum at the
University of Nebraska investigates how (and whether) scientists
can have a positive effect on science education in grades 3-8.
Project Fulcrum is a collaboration between the College of Education
and Human Sciences and the College of Arts and Sciences that places
10 math, science and engineering graduate students in elementary
and middle schools in the Lincoln Public School system. Each “Resident
Scientist” works in the same school for the entire year,
serving as a school-wide resource and being mentored by a Lead
Teacher. In addition to effects on the Resident Scientist’s
communication skills and awareness of K-12 science education issues,
data are collected to monitor student attitudes toward science,
student confidence in their ability to learn science, teacher
content knowledge, time spent teaching science, and teacher comfort
level with inquiry-based learning. This information is being used
to develop models for the most effective (and efficient) ways
that research scientists can be involved with K-12 education.
Time: 4:15 pm
Place: Room 10-250
/ MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, October 9, 2003
The Pappalardo Distinguished
Lecture in Physics
ROBERT P. KIRSHNER
Clowes Professor of Science, Harvard University
"The Extravagant Universe—Exploding Stars,
Dark Energy, and the Accelerating Cosmos"
Supernova explosions taking place halfway across
the Universe indicate we live in a Universe whose expansion is
speeding up. This suggests that space is suffused with a "dark
energy" that comprises most of the Universe, which causes
the cosmic acceleration we observe. This strange new picture of
the Universe appears to fit well with other observations of galaxy
clustering and of the glow from the Big Bang. This talk will review
the observational evidence, sketch the theoretical puzzles posed
by the data, and outline ways forward to uncover the nature of
the dark energy.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, October 16, 2003
JAMES BERGQUIST
NIST
"The Mercury-ion Optical Clock and a Test of
the Stability of the Fundamental Constants"
For modern-day physicists, the pursuit of better
clocks provides a natural means for studying various aspects of
nature, including the fundamental constants and the interaction
of radiation and matter. Those of us who measure time are mindful
of the practical applications, but we are also strongly driven
by scientific considerations and the desire to apply clocks to
other interesting measurements. One day, we may even find that
clocks, whose frequencies depend differently on the basic forces,
diverge in time, signaling a fundamental change in how we perceive
nature.
Perhaps the most promising route to better clocks
is to use optical frequencies, simply because clock stability
is proportional to frequency v0. We will describe the first all
optical, atomic clock, which is based on a laser-cooled, single
mercury (199Hg+) ion that is tightly, but benignly confined in
a small RF trap. We will describe the *clockwork* that has made
keeping time with an optical oscillator possible by means of phase-coherent
division of optical frequencies to microwave and rf frequencies.
Finally, we will discuss the implications of our work as a constraint
to present-day variation of the constants that determine atomic
transition frequencies.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, October 23, 2003
NATALIE ROE
Lawrence Berkeley National Laboratory
"Looking for a New Angle on CP Violation"
Four very successful years of data-taking at the
PEP-II asymmetric B factory have taught us much about the matter-antimatter
asymmetry in electroweak interactions. However, we still cannot
explain how a matter-dominated Universe came into being after
the Big Bang. After reviewing some recent results from the BaBar
experiment, I will discuss other mechanisms that could be responsible
for the baryon dominance, and hence for our existence.
Time: 4:15 pm
Place: Room 6-120 / MIT
Refreshments @ 3:45 pm
in the Lobby of Building 6.
Thursday, October 30, 2003
JOHN SCHWARZ
California Institute of Technology
"Superstring Theory: Past, Present, and Future"
String theory arose in the late 1960s as a candidate
theory of the strong nuclear force, but in 1974 the goal of the
program was changed to one that is much more ambitious: the construction
of a unified quantum theory containing gravity and all other fundamental
forces. If successful, it should account for all the properties
of elementary particles as well as the physics that controls the
big bang and all of cosmology. Major advances in understanding
aspects of superstring theory that apply when quantum effects
are small were made in 1984-85 (the first superstring revolution).
In 1995-97 (the second superstring revolution) and subsequent
years there has been dramatic progress in understanding superstring
theory when quantum effects are large. Despite all that has been
achieved, superstring theory is still a work in progress that
is far from completion.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, November 6, 2003
The David & Edith Harris
Distinguished Lecture in Physics
DAVID
GROSS
Director, Kavli Institute for Theoretical Physics, University
of California, Santa Barbara
"The Coming Revolutions in Fundamental Physics"
I shall review the present state of string theory
and speculate on its prospects for the future.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, November 13, 2003
PETER LEPAGE
Cornell University
"The Fall and Rise of Lattice QCD: High-precision
Lattice QCD Confronts Experiment"
By 1990, lattice QCD, the fundamental theory of
subnuclear structure, was on the verge of failure. A decade of
large-scale numerical simulations, consuming a large fraction
of the cycles on the world's largest supercomputers, had failed
even to produce reliable values for the proton mass. A series
of theoretical breakthroughs in the 1990s, culminating in late
1999 with a new discretization of the quark action, have finally
made high-precision (few percent) nonperturbative QCD possible
for the first time.
This seminar is a non-technical review of the conceptual
ideas behind these revolutionary developments in strong-interaction
physics, together with a survey of the current impact on theoretical
and experimental particle physics, and prospects for the future.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, November 20, 2003
ANDREA GHEZ
University of California, Los Angeles
"Unveiling a Galactic Black Hole at the Center
of Our Galaxy"
After almost a decade of astrometry from diffraction-limited
speckle imaging at the W. M. Keck 10m telescope, we have moved
the case for a super-massive black hole at the Galactic Center
from a possibility to a certainty. Thanks to our recent ability
to determine the orbits of individual stars, which confines the
central dark mass of 4 million times the mass of the sun to within
90 AU (1 AU = the Earth-Sun distance), or equivalently, 1,000
Schwarzchild radii. With the advent of adaptive optics, we have
significantly expanded our studies of the Galaxy's central black
hole, through the addition of diffraction-limited spectroscopy
and deep imaging at wavelengths other than 2.2 microns.
Spectroscopy has revealed that the stars orbiting
in such close proximity are apparently massive and young; the
origin of these stars is difficult to explain, given the strong
tidal forces, and may provide key insight into the growth of the
central black hole. Thermal infrared imaging (3.8 microns) has
led to the direct detection of plasma associated with the central
black hole. This source is variable on time scales as short as
40 min, implying that the emission arises quite close to the black
hole; within 5 AU, or 80 Schwarzchild radii and providing a new,
constantly accessible, window into the physical conditions of
the plasma in close proximity to the central black hole.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, December 4, 2003
GERARD 'T HOOFT, 1999 Nobel Laureate
University of Utrecht, Spinoza Institute
"Black Holes and Particle Physics"
Arguments from quantum field theory, thermodynamics,
and now also from superstring theory, all indicate that black
holes have a well-defined quantum structure, in a Hilbert space
of states that are defined by variables spread out evenly over
the black hole horizon. Yet, there are deep and fundamental problems
when we try to reconcile these findings with locality and Lorentz
invariance and general coordinate invariance of the laws of physics.
Questions addressed include: What does an observer,
falling into a black hole, see? Does the holographic nature of
the laws of physics point towards the necessity to revise our
notion of "reality"? Are black holes classical or quantum
particles?
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
Thursday, December 11, 2003
DONALD MONROE
Agere Systems
"The Schön Affair: Investigating Scientific
Misconduct"
In the spring of 2002, Hendrik Schön appeared
to be on a fast track to a Nobel Prize for his experiments in
electrically conducting organic materials (although others were
having difficulty reproducing his results). A few months later,
his career was over and his work largely discredited, after an
investigation panel found him guilty of scientific misconduct.
I will describe my experiences as a member of that
panel, the procedures we followed, and the detailed evidence that
compelled us to conclude that pervasive misconduct occurred.
Time: 4:15 pm
Place: Room 10-250 / MIT
Refreshments @ 3:45 pm in 4-339 (Physics Common
Room).
