Mass, Light, Metaphysics

According to Newton, Mass is resistance to Acceleration, and is the Matter that is the inherent substratum of any change of an object, knowable only by its effects.  Thus, in some Metaphysical systems, it has the status of Substance.  In contrast, according to Einstein, as an object approaches the Speed of Light, that substratum is transformed into Energy, which conforms with the Mass-lessness of Acceleration-resistant Light, the existence of which is only inferrable from the visibility of objects. Thus, conversely, as an object slows down, Energy is transformed into Matter, just as it is according to Bergson.  In other words, Einstein's variation of Newton's Physics has at least some of the fundamental characteristics of Bergson's inversion of a Materialist Metaphysics.