Gravity: Why what goes up must come down

Of the four forces that control the universe gravity may be the most obvious, but it is also the most mysterious. Newton managed to predict the force of gravity, but couldn t explain how it worked at a distance. Then Einstein recognised that gravity and acceleration are interchangeable to devise his mind-bending general relativity, showing how matter warps space and time. Not only did this explain how gravity worked, but it predicted everything from black holes to gravity's effect on time. Whether it's the reality of anti-gravity or the discovery that a ball and a laser beam drop at the same rate, gravity is the force that fascinates.