““When an important change takes place in science, in which a new theory takes the stagw, the incoming theory is generally an extension of the old theory which has the property of becoming more and more like the old theory in some limiting situation. In effect, it reveals that the old theory was an approximation (usually a very good one) to the new one that holds under a particular range of conditions. Thus, Einstein's special theory of relativity becomes Newton's theory of motion when speeds are far less than that of light, Einstein's general theory of relativity becomes Newton's theory of gravity when gravitational fields are weak and bodies move at speeds less than that of light. In recent years we have even begun to map out what the successor to Einstein's theory may look like. It appears that Einstein's theory of general relativity is a limiting, low-energy case of a far deeper and wider theory, which has been dubbed M theory.””
