The Problems and Challenges of General Relativity

Einstein's equation, equals mc squared, tells us that energy and mass are interchangeable concepts. The original clues-a-cline theory might have looked promising at the time, but it had some pretty serious problems and challenges. Not many people were really thinking about theories of extra mentions for a long time until the 1980s. It got popular again in the 1980s has everything to do with string theory.