Number 569, December 14, 2001
by Phil Schewe, James Riordon, and Ben Stein
Physics Stories of the Year for 2001
In cosmology, the observations of second and third peaks in the spectrum
of the cosmic microwave background (Update 537),
the detection of the "re-ionization" era in the early universe
(555),
and some tentative evidence that the fine structure constant is changing
(552);
in the physics of atoms, the effective stopping and storing of light
in a gas (521);
in particle physics the observation of CP violation in the decay of
B mesons (525,
547);
in condensed matter physics, the observation of superconductivity at
117 K in a crystal of carbon-60 (555)
and at 40 K in MgB (526,
530);
Bose-Einstein condensate on a chip (559),
in helium (532),
and the topic meriting the 2001 Nobel Prize (560);
in nuclear physics the first experimental formulation of a nuclear liquid-gas
phase diagram (upcoming Update). Other stories include the retraction
of the element 118 discovery (550);
further evidence for neutrino oscillations, at the new Sudbury detector
(544);
doubly strange nuclei (552);
chaos insights on weather (543);
crystallization using sound waves (541);
room-temperature spin injection for spintronics (543);
quantum entanglement of macroscopic gas clouds (558);
quantum holography (566);
attosecond pulses (567).
Oceans Might Be Common and Diverse
Oceans might be common and diverse in our solar system and in other
solar systems, according to David Stevenson of Caltech, who regards
the old notion of a narrow "habitable zone" (Venus too hot,
Mars too cold, Earth just right) for liquid water oceans as erroneous.
Stevenson spoke earlier this week in San Francisco at a meeting
of the American Geophysical Union at a session intended to bring together
two scientific communities that scrutinize very different realms--the
planets and the seafloor on Earth.
The connection? Observations from the bottom of the ocean show that
microbes thrive both in near-freezing seawater and in near-boiling effusions
from thermal vents. These conditions might turn up in many other planetary
environments.
For example, the Galileo spacecraft has provided evidence for watery
oceans on three of Jupiter's moons-Callisto, Ganymede, and Europa. Subsurface
oceans could be kept liquid by warmth from tidal forces (Jove wringing
its satellites) or from radioactivity. Torrance Johnson of JPL, also
speaking that the meeting, said that Europa's ocean might be 75-150
km thick and could thus harbor twice the water in Earth's oceans.
Stevenson added that observations also hint at oceans on Titan, Triton,
and Pluto. In the case of Titan (soon to get the Galileo treatment when
the Cassini spacecraft reaches Saturn in 2004) an ocean would be a mixture
of water and ammonia (acting as antifreeze). Under some circumstances
water might even be found inside Uranus and Neptune.
A Nano-Electron-Volt Neutral Atom Storage
Ring
A nano-electron-volt neutral atom storage ring, built and tested by
physicists at Georgia Tech, should help the development of atom fiber
optics.
Generally, storage rings not only store particles but also serve to
define an energy and trajectory insofar as the particles are guided
around a prescribed track by some kind of magnet system; particles with
the wrong energy would fly away. Normally the magnets exert themselves
by grabbing onto the particles' electric charge. Neutral atoms don't
have a net charge but they can possess a net dipole moment which, if
the atom is moving slowly enough, is sufficient for guidance (see figure).
The Georgia Tech experiment (Michael Chapman, michael.chapman@physics.gatech.edu,
404-894-5223, Jacob Sauer, jakesauer@mindspring.com, Murray Barrett,
m.barrett@mindspring.com) is much more modest than your typical particle
accelerator: it's only 2 cm across and corrals neutral rubidium atoms
moving at speeds of 1 meter/sec (equivalent energy=nano-eV, temperature=microkelvins).
So far swarms of one million atoms have made as many as seven circuits
around the ring. The same researchers produced the first all-optical
generation of a Bose-Einstein condensate (Update 545),
and they hope to load the atoms from a condensate with their new storage
ring (dubbed the "Nevatron"). Possible goals include ultra-sensitive
gyroscopes and atom lasers. (Sauer
et al., Physical Review Letters, 31 December 2001;
also see group website.)
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