It will take another eight months to determine whether he got the other correct say scientists analysing data from Nasa’s Gravity Probe B satellite. The spacecraft was launched into orbit from California, US, on 20 April 2004. The mission’s chief scientist presented details at a physics meeting in Jacksonville, Florida.
Gravity Probe B uses four ultra-precise gyroscopes to measure two effects of Einstein’s general relativity theory. One of these effects is called the geodesic effect, the other is called frame dragging. A common analogy is that of placing a heavy bowling ball on to a rubber sheet.
The bowling ball will sit in a dip, distorting the rubber sheet around itself in much the way a massive object such as the Earth distorts space and time around itself. If the bowling ball is then rotated, it will start to drag the rubber sheet around with it. In a similar way, the Earth drags local space and time around with it – ever so slightly – as it rotates.
Over the course of a year, these effects would cause the angle of spin of the gyroscopes to shift by minute amounts. The data from Gravity Probe B’s gyroscopes clearly confirm Einstein’s geodesic effect to a precision of better than 1%. The scientists from Stanford are still trying to extract its signature of frame-dragging from the data. They plan to announce the final results of the experiment in December 2007, following eight more months of data analysis.
Physicists have been unable to incorporate gravity into a unified theory to describe all that is known about the fundamental forces between elementary particles in nature. Modifications to general relativity could be important steps towards a unified theory. “There is an expectation that at some level we will expose a departure from pure general relativity as envisaged by Einstein,” Professor Sumner said.
“One of the areas of general relativity that is less well founded is when you get into very intense gravitational field interactions. Some astrophysical objects will be in very high field situations such as pairs of massive black holes orbiting one another.”
A joint mission between Nasa and the European Space Agency called Lisa (Laser Interferometer Space Antenna) will study gravitational waves coming from binary systems such as these.