thequantumlife: Gravity bends more than just...

Gravity bends more than just space. It bends time.

The early results from Gravity Probe B, one of Nasa’s most complicated satellites, confirmed yesterday ‘to a precision of better than 1 per cent’ the assertion Einstein made 90 years ago - that an object such as the Earth does indeed distort the fabric of space and time.

But this - what is referred to as the ‘geodetic’ effect - is only half of the theory. The other, ‘frame-dragging’, stated that as the world spins it drags the fabric of the universe behind it.

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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. Gravity, argued Einstein, was not an attractive force between bodies as had been previously thought.

That probably didn’t clarify it any. But there’s more!

When Einstein wrote his general theory of relativity in 1915, he found a new way to describe gravity. It was not a force, as Sir Isaac Newton had supposed, but a consequence of the distortion of space and time, conceived together in his theory as ‘space-time’. Any object distorts the fabric of space-time and the bigger it is, the greater the effect.

Just as a bowling ball placed on a trampoline stretches the fabric and causes it to sag, so planets and stars warp space-time - a phenomenon known as the ‘geodetic effect’. A marble moving along the trampoline will be drawn inexorably towards the ball.

Thus the planets orbiting the Sun are not being pulled by the Sun; they are following the curved space-time deformation caused by the Sun. The reason the planets never fall into the Sun is because of the speed at which they are travelling.

According to the theory, matter and energy distort space-time, curving it around themselves. ‘Frame dragging’ theoretically occurs when the rotation of a large body ‘twists’ nearby space and time. It is this second part of Einstein’s theory that the Nasa mission has yet to corroborate.

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