What On Earth Is Wrong with Gravity?

Of the four fundamental forces in nature, gravity is the one with which everyone is most familiar, and yet it is the least understood scientifically.

Sir Isaac Newton, apocryphal apple story or not, was the first to propose a workable model that would explain and predict the motion of objects throughout the universe. The power of his physics is attested by its use in the successful space program of the twentieth century.

It would take the genius of Einstein in the early 1900's to notice that Newton's model could not account for the observed motion of Mercury around the sun, for the motion of objects close to the speed of light, and for the effects of unimaginably massive objects. Instead of a static background of space upon which physical events took place, Einstein proposed that space-time is a fabric which interacts with physical objects, affects them and is affected by them. One of the implications of this theory was that the direction of light could be affected by the curvature of space-time around a massively large object. This insight was beautifully confirmed in 1919, when a solar eclipse bore out the prediction with uncanny precision, to the surprise of the entire world. Einstein became an overnight celebrity.

Yet for all his genius, Einstein's model failed to account for gravitational effects on the subatomic level, and physicists have been scratching their heads ever since. In today's documentary, Brian Cox travels to meet with physicists and astronomers who are doing what they can to try to explain the mystery of gravity.

Related videos:

Documentary on the Large Hadron Collider

Brian Greene's first episode of The Elegant Universe, describing the differences between Newtonian mechanics and Einstein's relativity.

LIGO and how to measure gravitational waves.
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