TURBOTECH@applelink.apple.com (Turbo Tech Int'l, Dave Kliman,PRT) (06/07/91)
From the New York Times 5/28/91, page C1: -------------------------------------------------------------- SLOWED ALMOST TO A STOP, ATOMS REVEAL SECRETS OF MATTER. -------------------------------------------------------------- By Malcolm W. Browne A device that cost only a few hundred dollars is yielding discoveries about the fundamental nature of matter that normally turn up only in giant particle accelerators with billion-dollar budgets. Experiments conducted with the device at the Joint Institute for Laboratory Astrophysics in Boulder, Colo., have confirmed some key predictions of a major theory of the structure of matter, and forthcoming experiments will investigate the possibility of subtle deviations from the theory that would reveal previously undetected relationships among the basic forces of nature. And, while operating their table-top apparatus, scientists at the institute have achieved a temperature only one-millionth of a degree Celsius above absolute zero, a world record for extreme cold. The astrophysics institute is operated jointly by the University of Colorado and the National Institute of Standards and Technology. Its director, Dr. Carl E. Wieman, said that modifications in the apparatus would soon bring its operating temperature to substantially less than one-millionth of a degree above absolute zero. The absolute zero, calculated using equations of the science of thermodynamics, is a temperature of approximately minus 273.16 degrees Celsius, or minus 459.69 degrees Fahrenheit. It is impossible to reach any temperature lower than the absolute zero, and even the sparce atoms and molecules drifting in intergalactic space have much higher temperatures. "We hope this summer to reach a temperature so close to the absolute zero," Dr. Wieman said, "that we will observe for the first time a weird condensation of matter," predicted by a theory of Albert Einstein and Satyendranath Bose, an Indian mathematician and theoretical physicist. By reducing the temperature of a substance to essentially absolute zero, the theory predicts, atoms can be made to lose their individual identities and merge as a kind of homogeneous atomic soup. The key to experiments at the astrophysics institute and similar investigations at Stanford University and the Ecole Normale Superieure in Paris is a technique called laser cooling. As the institute group has reported in a series of papers in Physical Review Letters and other major physics journals, carefully tuned and focused laser beams are used to halt flying atoms in their tracks, thereby reducing their temperatures to virtually nothing. NOT AN ORDINARY SWIRL A new technique for producing extreme cold was devised two decades ago, when physicists began to reach temperatures within 0.8 degrees Celsius of the absolute zero by diluting ordinary liquid helium (He-4) with a liquefied isotope of helium, He-3. At such temperatures, the startling behavior of ultrasmall particles obeying the rules of quantum mechanics becomes visible in the full-size world. When an ordinary liquid is made to swirl around in a jar, for example, it forms a single vortex that deepens as the swirling speed increases. But a jar of ultracold liquid helium behaves differently because it is "quantized"--that is, it obeys the laws of quantum physics rather than the laws that rule the everyday world. As swirling is increased, the central vortex does not deepen, but with increases in the speed of swirling, the liquid helium undergoes quantum jumps. First, the liquid abruptly forms two vortices (never seen in ordinary liquids), then three and more with each quantum leap. Such odd effects have given physicists a full-size window through which the microscopic quantum world of subatomic particles can be directly observed. Taking this a step further, the experiments at the Joint Institute for Laboratory Astrophysics have opened another window--one through which the Standard Model theory of matter can be explored. The device complements the experiments that huge particle accelerators can perform. The heart of the institute's apparatus is a glass chamber about the size of a fist, which is filled with a gas consisting of atoms of the metal cesium. A pump removes most of these atoms until a very high vacuum is established in the chamber. Despite the vacuum, some 100 million cesium atoms remain in the vessel, randomly colliding with each other and the walls of the container, and endlessly recoiling, as in any ordinary gas. This constant motion is better known as heat. THE EFFECT IS CUMULATIVE But by shining six infrared lasers (similar to lasers used in cd players) through the chamber from different angles, the team has succeeded in slowing down and virtually halting every atom--that is, in reducing each atom's temperature to almost zero. The lasers must be perfectly tuned to the resonances of the atoms, and must be positioned perfectly to avoid imparting momentum to them. Dr. Wieman explained that this method of slowing down flying atoms was achieved by hitting the atoms with photons of light from various directions, in such a way that each atom is robbed of its momentum and slowed down. "Each head-on impact of a photon with a cesium atom slows the atom down by about one-third of a centimeter per second," he said. "The overall effect is cumulative--something like slowing down a bowling ball by bombarding it with ping-pong balls." Within a second or two after the lasers are turned on, the cesium atoms become trapped at the intersection of the beams, and clump into a ball several millimeters thick, suspended in the middle of the glass chamber. As each atom is bombarded by photons it absorbs them and becomes excited to a higher energy state. The atom then spontaneously falls back to its earlier energy state, emitting a photon of its own. This photon has a higher energy than a photon absorbed by the atom from the laser beams, so the atom experiences a net loss of energy. The lost energy, representing an atom's heat, is carried off by emitted photons at the speed of light. By this mechanism, the laser device achieves ultracold refrigeration. "The atoms entrapped by the intersecting lasers are robbed of so much energy that they no longer bang into each other but instead, behave exactly like a bunch of little ball bearings sitting in a bowl," Dr. Wieman said. VERY PRECISE MEASUREMENTS "When we shut off the lasers, gravity draws them slowly to the bottom of the chamber, because they no longer have even the slight energy needed to counteract gravity. If we choose, we can hold the cooled atoms in place under the influence of electric and magnetic fields we impose on the chamber, using a few turns of strategically placed wire." Because the laser technique allows scientists to handle atoms almost as delicately as if they were using microscopic tweezers, very precise measurements of the atoms are possible. The group has been able to study the detailed structure of electron shells in the atoms by forcing them to resonate with laser light. Recent laser resonance experiments on ultracold cesium atoms at the institute have all but demolished one popular theory and lent support to another., Dr. Wieman said. A major mystery that has focused the efforts of particle physicists is the phenomenon of parity violation. In the everyday world, most things are "conserved"--that is, they balance out. In classical physics, every action has an equal and opposite reaction, and in classical optics, the angle of incidence at which a ray of light strikes a mirror precisely equals its angle of reflection. But a particularity of nuclear and subnuclear particles is that they exhibit a kind of uneven "handedness" that scientists call parity violation. The discovery in the 1970's that the electromagnetic force is directly related to the weak nuclear force through a carrier called weak neutral current involves just such a parity violation, and a very successful theory precisely predicts the size of this uneven handedness. Ordinarily, parity violation must be studied in the behavior of particles spawned by the collisions of ultra-high-energy protons or electrons in huge particle accelerators. But Dr. Wieman's group has discovered that some kinds of parity violation can be measured very precisely from the tiny distortions cesium atoms undergo in its laser traps. THE 'TECHNICOLOR' THEORY "So far," he said, "our experiments have confirmed the predictions of the Standard Model, but this summer our measurements will be sufficiently precise to detect subtle deviations from the Standard Model theory, if such exist. That would be a clue that all physicists yearn to see--that there are new physics out there beyond what we now know, ready for a new epoch of discovery. "Meanwhile, however, our results last summer appear to have weakened, if not destroyed, the theory known as 'technicolor.' Technicolor is the name of a theory that attempts to explain the mystery of parity violation in terms of some dynamical process. We expect that our experiments this summer will settle the technicolor question." But the most exciting prospect, Dr. Wieman said, is the possibility of creating a "Bose-Einstein condensate," in which cesium atoms "become totally coherent, in all senses." Physicists have long recognized that the fundamental building blocks of matter can be thought of as both particles and waves. If measured as a wave, any particle or atom has a set of mathematical properties called a "wave function," in which a number called Planck's Constant is a key feature. In a Bose-Einstein condensate at a temperature of essentially absolute zero, the wave function of all the condensed atoms would become identical, thereby creating a kind of super atom that would have very peculiar properties. Experiments at the institute have reached the point where creation of this substance now appears to be possible. Dr. Wieman said that most of his group's apparatus was assembled from such appliances as video recorders, compact-disk lasers and other devices sold in ordinary stores. "The philosophy underlying our work is the same as that of high energy experiments," he said, "but the difference is that our experiments are done on table tops, instead of the kind that cost $8.2 billion." The latter is the estimated cost of the Superconducting Supercollider, a giant particle accelerator planned for construction in Texas.
dietz@cs.rochester.edu (Paul Dietz) (06/11/91)
(This has nothing much to do with nanotechnology, but I'm posting the followup here because the original message was here.) This laser-cooling scheme sounds interesting, especially if they can produce Bose-condensed collections of atoms and/or ions. The rate of a transition that puts a boson into a state already occupied by n identical bosons is multiplied by a factor of (n+1). For example, the rate of decay of an electronically excited atom in a laser amplifier can be much faster than its rate of spontaneous emission. Similarly, radioactive decay should also be accelerated by this effect if the decayed atom were to be added to an already large bose-condensed collection of identical atoms or ions. This is true even for non-electromagnetic decays, since there is nothing that says the boson must be a photon. One would have to arrange it so that the addition of the decayed atom to the bose-condensed state is allowed kinematically; i.e., recoil would have to be countered or the decay would have to involve two or more particles (for example, beta decay with the electron and neutrino emitted with equal but opposite momenta). This is a serious problem, since the energy of the bose-condensed atoms will be extremely small, on the order 10^-10 eV or less. That will lead to a very large reduction in the rate of the transition, since most decays would send the decayed atom into some other state. However, "n" is potentially very large. It would be interesting indeed if a practical means could be found to accelerate radioactive decay. Paul F. Dietz dietz@cs.rochester.edu
toms@fcs260c2.ncifcrf.gov (Tom Schneider) (06/12/91)
In article <Jun.10.21.24.58.1991.17976@planchet.rutgers.edu) dietz@cs.rochester.edu (Paul Dietz) writes: ... ) Similarly, radioactive decay should also be accelerated by this effect ) if the decayed atom were to be added to an already large ) bose-condensed collection of identical atoms or ions. This is true ) even for non-electromagnetic decays, since there is nothing that says ) the boson must be a photon. ) One would have to arrange it so that the addition of the decayed atom ) to the bose-condensed state is allowed kinematically; i.e., recoil ) would have to be countered or the decay would have to involve two or ) more particles (for example, beta decay with the electron and neutrino ) emitted with equal but opposite momenta). This is a serious problem, ) since the energy of the bose-condensed atoms will be extremely small, ) on the order 10^-10 eV or less. That will lead to a very large ) reduction in the rate of the transition, since most decays would send ) the decayed atom into some other state. However, "n" is potentially ) very large. ) It would be interesting indeed if a practical means could be found to ) accelerate radioactive decay. ) ) Paul F. Dietz ) dietz@cs.rochester.edu There is a nice story about this possibility in the July 1991 issue of Analog, "Ode to Joy" by Dean McLaughlin. Tom Schneider National Cancer Institute Laboratory of Mathematical Biology Frederick, Maryland 21702-1201 toms@ncifcrf.gov
eachus@largo.mitre.org (Robert I. Eachus) (06/12/91)
The mechanism in the McLaughlin story is slightly different, but
it is another example of a disturbing phenomena often observed
recently in Analog. Wild-eyed theories that, by the time the story is
published, can be compared to what is appearing in technical journals
with about the same lead time. But if, right now, science fiction at
its wildest is having trouble anticipating the present, in a few years
ALL science fiction will be historical fantasy, and we will have lost
an important tool for dealing with future shock.
This shock is accelerating--and not just in science. One of my
favorite examples is the computer game Balance of Power 1990, which
was obsolete a few months after it was published, and well before
1990. In science right now, the rate of progress is staggering. I'm
just waiting for some (presumably on-line) magazine or newsgroup to
start publishing a list of the top ten scientific discoveries of the
month... Come to think of it, sometimes sci.nanotech comes pretty
close to doing just that.
--
Robert I. Eachus
with STANDARD_DISCLAIMER;
use STANDARD_DISCLAIMER;
function MESSAGE (TEXT: in CLEVER_IDEAS) return BETTER_IDEAS is...dietz@cs.rochester.edu (Paul Dietz) (06/12/91)
In article <Jun.11.18.04.16.1991.27731@planchet.rutgers.edu> toms@fcs260c2.ncifcrf.gov (Tom Schneider) writes: >> [ possibility of accelerating radioactive decay ] >There is a nice story about this possibility in the July 1991 issue of >Analog, "Ode to Joy" by Dean McLaughlin. Except that the physics in that story is utter nonsense... Paul F. Dietz dietz@cs.rochester.edu