“I was sitting in a chair in the patent office at Bern when all of sudden a thought occurred to me: ‘If a person falls freely he will not feel his own weight.’ I was startled. This simple thought made a deep impression on me. It impelled me toward a theory of gravitation.” Albert Einstein, ‘How I Created the Theory of Relativity’, Kyoto Address, 14th December, 1922 (trans. Yoshimasa A. Ono, rpt. in Physics Today, August 1982, 35, p46).