Text 634, 121 rader
Skriven 2005-10-14 09:40:48 av Herman Trivilino (1:106/2000.7)
Ärende: PNU 749
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PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 749 October 13, 2005 by Phillip F. Schewe and Ben Stein
THE CAREER OF CHARLES TOWNES, filled with outstanding accomplishments in laser
science and radio astronomy, was celebrated at a meeting held last week at the
University of California at Berkeley. The gathering, called "Amazing Light:
Visions of Discovery," marked Townes's 90th birthday and was the occasion for a
series of talks by distinguished speakers (18 Nobel laureates were
present) on forefront topics in fundamental physics and the technological
innovations that arise from basic research (meeting website at
http://www.foundationalquestions.net/townes/). The following items represent
some of the interesting results and quips from the meeting.
To start with, this year's physics Nobel Prize
(http://www.aip.org/pnu/2005/split/748-1.html), announced only two days before
the start of the meeting, could not have been better aligned with Townes's
pioneering laser work and with recurrent themes expressed in several talks,
namely the ubiquity, versatility, and quantum nature of laser light. Two of
the 2005 laureates were actually in attendance: Roy Glauber (Harvard) and
Theodor Haensch (Max Planck Institute, Munich).
Haensch sounded an important precept by quoting Townes' former colleague,
Arthur Schawlow: "Never measure anything but frequency," meaning that signal
frequency can essentially be measured with higher precision than any other
physical quantity. For example, the frequency of light cast off by the
hydrogen atom in relaxing from its first excited state to its ground state is
known with an uncertainty of better than one part in 10^14. Haensch said that
this precision will improve further in coming years, with a corresponding
improvement in things like spectroscopy and readouts from the Global
Positioning System, an excellent example of turning a distance measurement into
a frequency measurement.
Who will be the next Charles Townes? We don't know, but to encourage and
recognize newcomers, a young scholars competition was held at the meeting. In
the technological innovation category, the first place award went to Jun Ye, a
JILA/NIST colleague of another of this year's Nobelists, John Hall. Ye also
spoke about the superb optical precision made possible by the advent of
femtosecond laser pulses. He reported on JILA/NIST's efforts to produce a
highly precise, stable laser output and its applications to various scientific
endeavors. Combining ultracold atoms, stable lasers, and coherent control
techniques, the JILA team is making advances in several areas including the
work on an optical atomic clock, where measurement precision has reached a
level of about 7 x10^-15. The precise measurement is made possible by a primary
frequency standard, NIST's fountain cesium atomic clock, which is accurate to
7 parts in 10^15.
What will be the next great invention on the order of the laser? We don't
know, but clever new ideas keep coming along. The second-place award in the
technological innovation competition went to Marin Soljacic (MIT) for his
concept of wireless, non-radiative energy transmission. Just as in the quantum
case in which the Schrodinger equation allows for a wave trapped in a box to
tunnel out, so Maxwell's equations allow for the leakage of electromagnetic
energy from an electromagnetic resonance object. If another such object were
placed not far from the first one, and the resonant frequencies of both were
the same, then the energy could be transferred between them with very little
energy lost to other objects in the nearby environmental that do not share the
same resonant frequency. The transmitted energy, although electromagnetic in
nature, would not be referred to as "radiation"
since it is bound to the resonant objects. It is rather an example of
"near-field" physics. Soljacic avoids words like "antenna," since the process
does not involve broadcasts of energy in the usual sense. In contrast, the
vast majority of energy radiated by antennas is typically wasted and lost into
free space, while only a small portion is picked up by the eventual receivers.
Instead, Soljacic uses terms like "source" and "drain" in analogy with
transistors to describe the movement of energy. An exemplary setup might
consist of a transmitter in a ceiling and devices in that room (e.g robots, or
computers) being powered wirelessly by this energy. (For a list of other young
scholar winners, see http://www.foundationalquestions.net/townes/pressroom.asp)
Steven Chu (LBL), speaking of measurements made in the biological physics
realm, said that Isaac Newton's worldview applied largely to a frictionless
world. If Newton had been the size of a bacterium, Chu suggested, the famous
force laws would we very different: (1) an object in motion will very shortly
come to a rest; (2) an object nominally at rest will jiggle around a lot; and
(3) the force an object feels is proportional to surface area and velocity.
Wolfgang Ketterle (MIT), speaking of trapped vapors at nano-kelvin
temperatures, said that unlike the early history of the study of coherent light
in the 1960s, the current study of coherent matter (atoms held in static BEC
clouds or released as "atom laser" beams) was not a "solution in search of a
problem." BEC-based matter-wave sensors, he said, would most likely find
useful applications in geology (as gravity sensors) and in navigation (rotation
sensors). Furthermore, molecular BECs made from paired fermi atoms and
partaking of strong tunable interactions, would likely serve as an arena for
studying two of the most important issues in all of condensed matter physics,
high-temperature superconductivity and the quantum properties of spin liquids
(ensembles of magnetic particles).
Anthony Leggett (Univ Illinois) addressed one of the meeting's
principal themes, grappling with quantum reality. We don't really
know the past, Leggett asserted. Our knowledge of macroscopic matter is
"thermodynamic" (meaning that what we know pertains to averages over large
numbers of particles) and not microscopic. Quantum uncertainty and chaotic
dynamics are also often invoked in denying the realization of longterm
predictability. Therefore we could never, as Pierre-Simon Laplace held, employ
deterministic equations to calculate the subsequent extended history of the
universe. (The issues of causality, the knowability of the past, and of free
will came up in several talks at the meeting.)
Where will science go next? We don't know, but Peter Galison (Harvard) spoke
of the intellectual climate in which past technological and scientific
discoveries have been made. He sees the historical and philosophical view of
physics over the past century or so as oscillating between two poles---the
positivist view (typified by Ernst Mach), according to which only experimental
observations are considered satisfactory and reliable, and the anti-positivist
view (typified by Thomas Kuhn), which is much more willing to credit
theoretical ideas in advancing and altering the general consensus. Meanwhile,
Freeman Dyson (Institute for Advanced Study) carved up physics history in a
different way. Borrowing Isaiah Berlin's famous dichotomy between "foxes"
(which know many things) and "hedgehogs" (which know one big thing), Dyson said
that the great hedgehogs and foxes of physics seemed to come in waves.
Einstein and Newton, said Dyson, were hedgehogs; they're the deep thinkers.
Enrico Fermi, and the guest of honor, Charles Townes, were foxes; with agility
they moved from topic to topic. Dyson's nominal topic was the future of
science. He claimed no method for predicting coming achievements. "The best
way to learn about the future of science," he concluded in his elegantly gruff
manner, "is to stay alive as long as you can and see what happens."
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* Origin: Big Bang (1:106/2000.7)
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