The mystery surrounding the Pioneer anomaly has deepened. The unexplained changes in acceleration seen in NASA’s Pioneer 10 and 11 probes could be related to similarly odd shifts in the speed of other space probes, possibly pointing towards new physics.

In the 1980s, researchers at NASA noticed that the Pioneer 11 spacecraft was slowing down more quickly than expected as it neared the edge of the solar system. The effect persisted until NASA lost touch with the spacecraft in 1995. A similar effect showed up in the Pioneer 10 spacecraft, which was sent in the opposite direction. Finally, in 1998, John Anderson, then at the Jet Propulsion Laboratory (JPL) in Pasadena, California, and his colleagues made their finding public.

Since then, other space probes have exhibited unexplained changes in speed. When NASA’s Galileo and NEAR spacecraft and ESA’s Rosetta flew past Earth, they showed bigger than expected boosts in speed. The largest anomaly was recorded for NEAR, whose velocity changed 13 millimetres per second more than it should have. This excess is much larger than the expected errors in measurement. Anderson, who is now with Global Aerospace Corporation in Altadena, California, and his team think that the two effects might be related. They have re-analysed the Pioneer data and say that Pioneer 11’s odd acceleration patterns seem to have begun right after its fly-by of Saturn in September 1979 (www.arxiv.org/ astro-ph/0608087).

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August 16th, 2006 | Physics, Space | 1 comment

Oxford University, the Lawrence Berkeley Laboratory in California, and the Massachusetts Institute of Technology have together made the first ‘molecular movie’ of the elementary interaction between light and matter, measuring what happens on a microscopic level when light travels though a medium.

The lead author of the study to be published in Nature, Dr Andrea Cavalleri at the Oxford University Department of Physics, said: ‘We’ve all seen how a stick in a pond appears to be at a different angle depending on whether we look at it from outside or inside the water. At a microscopic level, this effect depends on how stiff atomic bonds are and with how much delay atoms and electrons respond when they are placed in the rapidly wiggling electric field of light.

‘If you want to understand the propagation of light at microscopic level, especially in some the complex materials that are of interest for modern opto-electronic applications, you need to make a ‘molecular movie’ of how the atoms and electrons wiggle in the light field. To do so, you need to find a camera with an extremely quick shutter speed – that of a handful of femtoseconds (which is less than one thousandth of a billionth of a second).

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August 12th, 2006 | Physics | No comments