It's one of the fundamental forces of nature which holds the universe together. Yet gravity is still a mystery to physicists. This week Adam visits Cardiff University's School of Physics and Astonomy to find out about the force which keeps us all on the ground.

Broadcast Tuesday 20th September at 7pm

Listen to the latest programme online

We all know the story of Isaac Newton and the apple. The idea that the famous fruit fell on Newton's head, causing him instantly to dream up the theory of gravity, may be a myth but what's certain is that Newton realised that the force which causes an apple to fall straight to the ground is the same force which governs the motion of the planets.

At Cardiff University's School of Physics and Astronomy Adam meets Dr. Mark Hannam and gets a crash course in gravity. Marks explains that the gravitational pull of matter distorts the Universe - the bigger the object the greater the distortion. You can picture it by imagining a bowling ball on a trampoline. This is one of the fundamentals of Einstein's Theory of General Relativity which can be summarised as "Matter tells space how to curve and space tells matter how to move".

Another of Einstein's predictions was gravitational waves. These are like the ripples created on the surface of that trampoline when you drop the bowling ball onto it. Gravitational waves make space expand and contract as they pass through it and scientists are trying to detect them by measuring tiny variations in the distance between objects in space. And by tiny, they mean really tiny - only a thousandth of the diameter of a proton. To detect them you need to shield your instruments extremely well from all background 'noise' and movement.

Cardiff University has recently hosted a major conference on gravitational waves Dr. Patrick Sutton, who organised the conference, plays Adam a recording of the tell-tale 'chirp' of gravitational waves produced by two black holes or neutron stars falling towards each other. Adan also meets Laura Nuttall, a postgraduate student who's analysing data from across the world and separating the background noise from the interesting stuff so that scientists can finally understand the pulling power of gravitational waves.

Links

Cardiff University School of Physics and Astronomy

Black Hole Hunter