Scientists prove Einstein's gravity theory is right
SEATTLE - In a test critical to theories of cosmology, scientists have for the first time measured the speed at which the force of gravity moves.
And, once again, it appears that physicist Albert Einstein has been proved right, scientists announced on Tuesday at a meeting here of the American Astronomical Society.
'Newton thought that gravity's force was instantaneous,' said Dr Sergei Kopeikin, a physicist at the University of Missouri. 'Einstein assumed that it moved at the speed of light but, until now, no one had measured it.'
By observing a slight 'bending' of radio waves when the planet Jupiter passed nearly in front of a more distant cosmic object, scientists said they determined that gravity's propagation speed is equal to the speed of light.
They said their finding was within an accuracy of 20 per cent, which they considered good enough to conclude that gravity's velocity probably is, indeed, equal to the speed of light.
The result came as no surprise to other scientists. But it was a relief to have confirmation that an important assumption about the property of gravity rested on a firm foundation.
The speed of gravity was one of the last unmeasured fundamental constants of physics.
No one had tried before, Dr Kopeikin explained, because most physicists had assumed it could not be done with current technology. They were waiting until a system of new observing instruments, the Laser Interferometry Gravitational Observatory, was in full operation to detect gravitational waves in space.
The measurement was made on Sept 8 using radio telescopes of the Very Long Baseline Array in the United States in conjunction with one in Germany. The simultaneous observations of Jupiter by such a broad system of telescopes were unusually sensitive to the slightest deflection of radio waves caused by the planet's gravity.
When light from a bright quasar, an object nine billion light-years away, passed near Jupiter, the planet's gravity shifted the quasar's radio signals. This resulted in a small change in the quasar's apparent position in the sky.
Einstein was confirmed, scientists said, by the equivalent width of five human hairs seen at 400 km. --The New York Times |
