NATURE|Vol 446|19 April 2007 NEWS

BIG CITIES NEED A FAST- PACED LIFE TO GROW Huge urban centres are fed by rapid innovation. www.nature.com/news Interim view from NASA relativity probe

Gravity Probe B (GP-B) seems like electrostatic effects on the spheres the experiment that never ends. at the core of the gyroscopes cause The spacecraft set records for misalignments and wobbles that the longest-running development vary unexpectedly over time. The project at NASA — 40 years — and data were also recorded in chunks data analysis is stretching into because solar flares required the its second year. The GP-B team system to be rebooted. may one day announce the most Physicist Clifford Will, who precise measurements yet of chairs NASA’s scientific advisory a long-sought effect of general committee for the project, says relativity. But that didn’t happen such errors are a real headache: on 14 April, when project scientists “There’s art involved — it’s a slightly presented an interim report to the nebulous business; that’s why they American Physical Society meeting are being careful.” Still, the team in Jacksonville, Florida. remains bullish about the remaining CORP. MARTIN LOCKHEED UNIV., STANFORD K. STEPHENSON, Team members promise a final data analysis. “I’m not interested in report by December, when money being disappointed,” says Francis for the $760-million experiment Everitt of Stanford University, the runs out. But it is clear that project’s principal investigator. unexpected systematic errors will NASA’s Gravity Probe B aims to confirm two predictions of general relativity. Meanwhile, the LAGEOS findings make it a real challenge to reach could be further improved before the original mission goals. For and called ‘frame-dragging’. The first experimental measurement the end of the year by incorporating the most subtle effect measured, mission survived every NASA of geodetic precession, another a new model of Earth’s gravitational the GP-B team needs to make the attempt to cancel it (see Nature 426, small distortion of space-time. The field, as gathered by the GRACE experiment’s uncertainty 100 380–381; 2003) and was finally geodetic precession of the Moon spacecraft. Erricos Pavlis of the times lower. launched in April 2004. around the Earth has previously University of Maryland in Baltimore GP-B is a simple concept that in The main goal was to measure been verified to an accuracy of about County, who works with the reality proved overwhelming. The frame-dragging to within 1% 0.7%. GP-B has now measured LAGEOS data, says that it would be experiment, proposed in 1964, accuracy. That would be ten times the effect on their probe to within nice to beat GP-B, but even so he required four perfect spinning better than the best measurements 1.5%. The team hopes to reduce this doesn’t want to see it fail. gyroscopes in Earth orbit to measure so far, which were taken by further — but it is the much smaller “After all these millions spent how the spinning planet drags the bouncing laser signals off the Earth- frame-dragging effect that everyone and decades of people’s work,” he fabric of space-time around with orbiting LAGEOS satellites. cares about. says, “it’s only fair that they get it — a phenomenon predicted by GP-B has had one success. At the The problems plaguing the something out of this project.” ■ Einstein’s general theory of relativity meeting, the team announced the analysis are systematic errors: Sarah Tomlin

Evidence for fourth neutrino fades A nine-year effort to resolve a mystery about at how one type of neutrino could turn into working on the data and can’t be so sure. the behaviour of neutrinos — particles that another, or ‘oscillate’. The LSND findings At low neutrino energies the detector saw interact only weakly with matter — has suggested that a fourth kind of neutrino more electron neutrinos in the experiment’s thrown up an unexpected signal. The existed — a sterile neutrino. But many beam of muon neutrinos than expected. findings, announced on 11 April, leave open scientists were sceptical of the result. The team can’t yet explain the observation the possibility that new physics hides within Using a 12-metre sphere filled with and the community’s curiosity is piqued. the observations, but winnows the options 800 tonnes of mineral oil to catch neutrinos, “Already theorists are sending us their for what that might be. the MiniBooNE team found no evidence, papers and saying look, we fit you,” says “The plot keeps thickening,” says Bill at high neutrino energies, for the sort project co-spokesperson Janet Conrad. Louis, co-spokesperson for the MiniBooNE of oscillation that workers at LSND had Meanwhile, MiniBooNE has switched neutrino detector based at Fermilab in reported (A. A. Aguilar-Arevalo et al. to observing antineutrinos, which is what Batavia, Illinois. preprint at http://arxiv.org/abs/0704.1500; LSND studied, to find out whether the MiniBooNE aimed to settle controversy 2007). “My view is that there is no longer variations between the two experiments’ raised by the Liquid Scintillator Neutrino any credible evidence for sterile neutrinos,” results are due to surprising differences in Detector (LSND) at Los Alamos National says Gary Feldman, a physicist at Harvard the behaviour of matter and antimatter. ■ Laboratory in New Mexico, which looked University. Team members say they are still Jenny Hogan

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