In the summer of 1774, the United Kingdom's Astronomer Royal, Nevil Maskelyne, stood on the side of a Scottish mountain contemplating something far more profound than the view. He was trying to work out exactly how much the Earth weighed.
Gravity (from Latin gravitas 'weight'), or gravitation, is a natural phenomenon by which all things with mass or energy, including planets, stars, galaxies and even light, are attracted to (or gravitate toward) one another.
There is a riddle at the heart of the renewable energy revolution. When the wind blows, the sun shines, and the waves roll, there is abundant green power to be generated. But when skies darken and conditions are calm, what do we do?
The veteran gravitational wave hunter from Glasgow University has come to the National Press Club in Washington DC to witness the announcement of the first direct detection of ripples in the fabric of space-time caused by the merger of two "intermediate-sized" black holes.
Imagine the energy of eight Suns released in an instant. This is the gravitational "shockwave" that spread out from the biggest merger yet observed between two black holes.