This year, the International Year of Light, marks 100 years since Einstein’s theory of General Relativity—which showed how light was at the centre of the very structure of space and time.
2015 marks an important milestone in the history of physics: one hundred years ago, in November 1915, Albert Einstein wrote down the famous field equations of General Relativity. General Relativity is the theory that explains all gravitational phenomena we know (falling apples, orbiting planets, escaping galaxies...) and it survived one century of continuous tests of its validity. After 100 years it should be considered by now a classic textbook theory, but General Relativity remains young in spirit: its central idea, the fact that space and time are dynamical and influenced by the presence of matter, is still mind-boggling and difficult to accept as a well-tested fact of life.
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