Pure mathematics and physics are becoming ever more closely connected, though their methods remain different. One may describe the situation by saying that the mathematician plays a game in which he himself invents the rules while the physicist plays a game in which the rules are provided by Nature, but as time goes on it becomes increasingly evident that the rules which the mathematician finds interesting are the same as those which Nature has chosen. — 𝘗𝘢𝘶𝘭 𝘈. 𝘔. 𝘋𝘪𝘳𝘢𝘤, 𝘪𝘯 𝘩𝘪𝘴