The planets orbiting the sun are not being pulled by the sun.
Falling rocks are not being pulled by gravity.
In 1915, Einstein found a new way to describe gravity.
Gravity is not a force, as Sir Isaac Newton had supposed.
Gravity is what happens when space and time is bending the way a ball bends a blanket.
According to Einstein, in the same way that a large ball placed on a elasticated cloth stretches the fabric and causes it to sag, so planets and stars warp space-time. A marble moving along the sagging cloth will be drawn towards the ball, as the Earth is to the Sun, but not fall into it as long as it keeps moving at speed.
Ninety years after he expounded his famous theory, a $700m Nasa probe has proved that the universe behaves as he said. Now the race is on to show that the other half of relativity also works. [story]
The Nasa and Stanford Gravity Probe B project uses four ultra precise gyroscopes to detect minute distortions in the fabric of the universe to prove to the highest precision yet if Einstein was correct in the way he described gravity.
The wobble-free gyroscopes use the world’s most perfect spheres. Enlarged to the size of the Earth, the spheres would have mountains no more than 8 feet high.
With the gyroscopes spinning at 4,000 rpm, their suspension system used electrostatic fields to hold each rotor in a vacuum a mere paper’s width from the walls of its housing.
The satellite is a minivan-sized thermos filled with liquid helium keeping the gyroscopes near absolute zero.
The width of a human hair viewed from a quarter of a mile away are the miniscule angles used to measure space-time around the Earth.
The project studies the geodetic effect – the amount by which the mass of the Earth warps the local space-time in which it resides. Scientists are waiting for calculations to review frame-dragging – the amount by which the rotating Earth drags local space-time around with it.
Gravity Probe B required improvements in tracking which has led to new GPS receivers that measure position down to the centimeter level.
This video clip from Nova explains how gravity works.