From the scientific view, the theory of karma may be a metaphysical assumption -- but it is no more so than the assumption that all of life is material and originated out of pure chance
For, owners of their deeds (karma) are the beings, heirs of their deeds; their deeds are the womb from which they sprang; with their deeds they are bound up; their deeds are their refuge. Whatever deeds they do-good or evil-of such they will be the heirs. And wherever the beings spring into existence, there their deeds will ripen; and wherever their deeds ripen, there they will earn the fruits of those deeds, be it in this life, or be it in the next life, or be it in any other future life.
The present moment, though, is outside of time, it’s Eternity. In India they use the word “karma” for lack of any better term. But it’s a concept that’s rarely given a proper explanation. It isn’t what you did in the past that will affect the present. It’s what you do in the present that will redeem the past and thereby change the future.