GRAVITATIONAL WAVES

Over 100 years ago, Albert Einstein predicted that space-time could be warped and stretched. It turns out, he was correct

Gravitational waves are ripples in the fabric of space- time. They were predicted to exist by Albert Einstein in 1916, although he then got cold feet and retracted his prediction the following year, only to re-make it in 1936.

Specifically, gravitational waves are a prediction of Einstein’s revolutionary theory of gravity, the ‘General Theory of Relativity’, which he presented in Berlin in November 1915, at the height of WWI. Whereas Isaac Newton had maintained that there was a ‘force’ of gravity between the Sun and Earth, like a piece the invisible elastic tethering the Earth to the Sun and keeping it forever in orbit, Einstein showed that this is an illusion. No such force exists. Instead, the Sun creates a ‘valley’ in the spacetime around it, and the Earth travels around the edge of the valley rather like a roulette bowl in a roulette wheel.

We cannot see the landscape of space-time because space-time – a seamless amalgam of three space dimensions and one of time – is a four- dimensional thing, and we are mere three-dimensional creatures. That is why it took a genius like Einstein to realise that what we think of as matter moving under the influence of the force of gravity is in fact matter moving through warped space-time. As the American physicist John Wheeler said: “Matter tells spacetime how to warp and warped space-time tells matter how to move.”

According to General Relativity, space-time is no mere passive backdrop to the events of the Universe. Instead it is ‘thing’, which can be bent and stretched and warped by the presence of matter. And, if it can be distorted in this way, argued Einstein, it can also be jiggled. When this happens, an undulation of space-time spreads outwards at the speed of light like concentric ripples on a pond: a gravitational wave.