The theory of general relativity is as relevant to us today as it was when it was formulated, as a discovery about space-time reveals. After working for half a century and spending £500m, scientists last week revealed that they have detected strange fluctuations in Earth's orbit. Space-time is bent and then twisted round our planet as it rotates, announced researchers with Nasa's Gravity Probe B project.
The effect is tiny but crucial, they added – and was predicted almost 100 years ago by Albert Einstein in his great theory of gravity, general relativity. According to Einstein, an apple falls to the ground not because it feels the force of Earth's gravity but because the apple is responding to the curvature of space-time near the Earth's surface caused by the planet's huge mass. In the same way, the Sun bends space in a manner that allows Earth to revolve around it.
Crucially, the theory raised a host of other predictions that scientists have been confirming for the past century. The findings of Gravity Probe B are the latest in a long list of these many vindications of Einstein's genius and reveal how his great theory touches our lives in unexpected ways.
"We have completed this landmark experiment of testing Einstein's universe," said project leader Francis Everitt, of Stanford University. "And Einstein survives."
Everitt began work on Gravity Probe B in 1962 and has worked on nothing else since, although he had many close shaves, with the satellite being cancelled and then revived on seven occasions before it was eventually launched in 2004. Then, after the probe reached orbit, spurious electrical signals were found to be distorting data that it had sent back. It took five years' study before scientists found how to extract clean data from it.
Results of the analyses of this data were revealed last week. They showed that Earth does indeed bend space-time. It was also found that, as our planet rotates, it drags space-time with it – a phenomenon known as frame-dragging. The effect is like spinning a spoon in a cup of tea, causing the liquid to start swirling round inside the cup. Read More
