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Melvyn Bragg and guests discuss the physics of time. When writing the Principia Mathematica, Isaac Newton declared his hand on most of the big questions in physics. He outlined the nature of space, explained the motions of the planets and conceived the operation of gravity. He also laid down the law on time declaring: 鈥淎bsolute, true, and mathematical time, of itself and from its own nature, flows equably without relation to anything external.鈥� For Newton time was absolute and set apart from the universe, but with the theories of Albert Einstein time became more complicated; it could be squeezed and distorted and was different in different places.Time is integral to our experience of things but we find it very difficult to think about. It may not even exist and yet seems written into the existence of absolutely everything. With Jim Al-Khalili, Professor of Theoretical Physics and Chair in the Public Engagement in Science at the University of Surrey; Monica Grady, Professor of Planetary and Space Sciences at the Open University and Ian Stewart, Professor of Mathematics at the University of Warwick.