Gravitational Waves: Why Are Scientists Celebrating?

The entire planet shook on September 14th, 2015. The very fabric of space itself rippled and distorted. Your own body was repeatedly squashed and stretched.

But you can be forgiven for not noticing: the amount of stretching was around one billionth the diameter of an atom.

So what’s all the fuss about? What happened on September 14th, and why has it now got scientists so excited?

In 1915, Albert Einstein published his general theory of relativity, a visionary and revolutionary description of the nature of gravity. General relativity makes a host of bizarre but very specific predictions about how gravity affects matter and light. A huge number of these predictions have been exquisitely confirmed by experiments. So while we still don’t know whether Einstein’s theory is correct (and indeed we strongly suspect that general relativity isn’t the whole story), it seems to be an excellent description of how the Universe works under almost every circumstance we can currently examine.

But there’s always been one glaring gap in the story.

In 1916, Einstein pointed out that under many circumstances, a moving massive object will cause space itself to ripple, a little like the expanding ripples of water produced by a stone skipping over a pond. In particular, if two heavenly bodies are in orbit around each other, then the space around them will be filled with these “gravitational waves“, generated as the two objects bend the space around them with their mass. The waves that result then race away from the orbiting system at the speed of light, carrying away energy and thus causing the two objects to gradually but inexorably spiral in towards each other.

In 1916 this was completely esoteric. The two objects in orbit would have to be incredibly massive, and —> Read More