Does karma exist?

What do you think? Feel free to elaborate and justify how you came to your opinion.

I answered, "I'm not sure, but I don't think so."

If karma is causal, then its effects would, in principle, be detectable in the world, if only with very powerful data mining computers. If karma is combined with some doctrine about reincarnation, then it gets much messier, for how does one detect karmic relations between lives? That is, how does one ascertain the specific entity that one was in history? I don't know, and I think questions of these sorts are wholly speculative.

If karma is indeed a speculative theory, then on which grounds would one choose any given speculative theory when there are many other such speculative theories? Why not subscribe, for instance, to Nietzsche's doctrine of eternal recurrence, which says that one lives the same life over and over in all its particulars for eternity? For that matter, why not concoct some absurd arbitrary doctrine -- say, by rolling dice to pick propositions from a matrix -- and live according to that?

One is not born into this world with a doctrine. Doctrine is a tribal accretion upon the raw fact of one's birth, and one's birth tribe is a product of geography and biology. I don't care to submit myself to biogeography, nor to a set of alien biogeographical commitments in later life. My goal is to think for myself. In the course of experience, I have discovered that this goal necessitates me to pare down my doctrinal obligations. "Seek simplicity, and distrust it," as Bertrand Russell recommends. Speculative tribal theories (karma, eternal recurrence) require me to toss my goal and my principle for no good reason that I can discern. In the absence of such a reason, I'll stick with my non-tribal, anti-doctrinal point of view. Speculative theories don't hold a candle to the breadth and richness of thought and experience that rise up in their place.

It does exist but not in the traditionally understood manner. It is not a law of reciprocity but rather it is a sort of lesson plan. If you 'learn your lesson' then you move on to the next one. Sometimes this manifests through reciprocity but reciprocity is a different principle entirely with it's own workings.

Does anyone know of an online scholarly introduction to the concept of karma? I'm thinking of something along the lines of the Stanford Encyclopedia of Philosophy but for Indian philosophy.

Mostly because, as an immediate consequence of one's action, I would only consider it as a difficulty from separating one's self from the harmful act being done. Beside that, I never had any evidence of karma: when such separation is good I have never observed any bad feedback, unless one was actually convinced of its existence before anything happened.