Success or failure, for Einstein it\'s all relative

Poor old Einstein has had a rough few days.It all began with an experiment last week that bizarrely found sub-atomic particles called neutrinos appear to move faster than the speed of light.The finding was a shock. The speed of light was enshrined in 1905 by Einstein as the Universe\'s speed limit. Today, physicists almost everywhere accept it as such. Could the great man have got it terribly wrong? But soon after this shadow fell across Einstein\'s reputation, another experiment came along which has validated -- magnificently and on a cosmological scale -- another of his landmark ideas. According to Einstein\'s general theory of relativity, light emitted from stars and galaxies is slightly tugged by gravity from celestial bodies. Danish astronomers have put the theory to the test in measuring light emitted by galactic \"clusters. These are sectors of deep space which are packed with thousands of galaxies, held together by their own gravity. Their density and mass should thus have a perceptible gravitational effect on the light they emit. University of Copenhagen cosmologist Radek Wojtak and colleagues analysed light from around 8,000 of these clusters. They were looking for variations in \"redshift,\" a measurement of the shift in light. As the Universe expands, light from a star becomes slightly redder as its wavelength lengthens, indicating a widening distance between the star and Earth. Wojtak\'s team measured the wavelength of light from galaxies lying in the middle of the galactic clusters, where the densest gravitational pull prevailed, and those lying on the more sparsely-populated periphery. \"We could measure small differences in the redshift of the galaxies and see that the light from galaxies in the middle of a cluster had to \'crawl\' out through the gravitational field, while it was easier for the light from the outlying galaxies,\" said Wojtak. They then measured the galaxy cluster\'s total mass to get a fix on its gravitational potential. \"The redshift of light is proportionately offset in relation to the gravitational influence from the galaxy cluster\'s gravity,\" said Wojtak. \"In that way, our observations confirm the theory of relativity.\" The findings do not negate popular theories about dark matter and dark energy, the enigmatic phenomena that account for almost all over the matter in the Universe. Until now, Einstein\'s theory of the impact of gravity on light had only been tested from within the Solar System itself -- essentially by measuring light from the Sun that was \"redshifted\" by the gravitational pull of Mercury. On September 22, physicists reported that neutrinos can travel faster than light, a finding that -- if verified -- would blast a hole in Einstein\'s theory of special relativity. In experiments conducted between the European Centre for Nuclear Research (CERN) in Switzerland and a laboratory in Italy, the particles were clocked at 300,006 kilometres per second, about six km/sec faster than the speed of light, the researchers said. The physicists themselves admitted they were quite flummoxed by the findings and other experts are skeptical, suggesting a problem in measurement techniques or equipment. Wojtak\'s research is released on Wednesday by Nature, the British scientific journal.