Who judges Karma?

Kamma (action) & vipaka (results) is merely a neurological mechanism.

For example, you get angry or become violent towards another person. When you are self-righteously angry or violent in a survival instinct mode, adrenaline is pumping through your nervous system therefore there is a sense of euphoria when you are angry or violent. But when the social situation/circumstance ends and the adrenaline & euphoria also ends, the stress of the anger & violence inwardly remains. Then you suffer from stress & tension and possibly regret & remorse. This is merely a neurological mechanism following natural law.

For example, you have wrong view about sex and believe women are sexually equal to men. So you have sexual fantasies about imagined insatiable women (with equal insatiable sexual voyeurism as men) and watch p**nography, generating both feelings of pleasure & motivations of lust. But due to continued wrong view & repeated exposure, the sense of pleasure decreases but the unfulfillment of lust grows. Therefore, you suffer from frustration and are reborn as a hungry ghost because you can't get enough pleasure to satiate your building of frustration, restlessness & lust. You try to justify your wrong views with an attachment to a literal reading of the 3rd precept in Buddhism but you remain reborn as a hungry ghost. Eventually, you meet a very lusty woman who validates your delusions about sex but, soon after, this woman gets pregnant, enjoys having children, as has more children. Her natural reproductive lusts wane/ease but, due to your wrong view, you still believe women are sexually equal to men. Your wife, however, no longer desires much sex, you fight, yet divorced, you lose your money to the ex-wife & children, and you spend the rest of your life having sex with prostitutes, about who you continue to believe are sexually equal to men. The prostitutes tell you that your ex-wife was abnormal and you believe the prostitutes, believing they are Buddhas because they can have sex with an empty emotionless mind. This is natural law.

Opponent-process theory is a psychological and neurological model that accounts for a wide range of behaviors, Every process that has an affective balance, (i.e. is pleasant or unpleasant), is followed by a secondary, "opponent process". This opponent process sets in after the primary process is quieted. With repeated exposure, the primary process becomes weaker while the opponent process is strengthened. According to opponent-process theory, drug addiction is the result of an emotional pairing of pleasure and the emotional symptoms associated with withdrawal. At the beginning of drug or any substance use, there are high levels of pleasure and low levels of withdrawal. Over time, however, as the levels of pleasure from using the drug decrease, the levels of withdrawal symptoms increase.

Opponent-process theory

On the contrary, personal gods are quite the norm in Buddhism, and many of them interact with humans regularly. Read more Buddhist sutras and you may notice this as well.

If you drink poison or medicine, there is no need for an external agent to determine what effect it will have on you. Its effect will be determined by both its nature and the disposition of the one affected.

Lord Yama is the god that holds the office of judgement, but this role seems to be a play on the manifestation of karma that occurs by natural processes anyhow. He is an interlocutor. If a human teacher can inform you of what is right and wrong, and scold or praise you, certainly a deity can do the same, regardless of his or her position in the universe.

Karma works without a judge. It's as much cause and effect as the moon orbiting Earth because of gravity or the wind blows leaves. Karma is.

Karma also has effects on this life, even in the short term.

The answer to this really depends on what you are thinking of as judgment.

If you are speaking about the sensation that is experienced as a result of an intentional act of thought, word or deed, then you are the judge (before the fact). As you intend to create experience of pleasure, you will experience pleasure; as you intend to create experience of pain, you will experience pain; as you intend to end kamma, you will experience neither pain nor pleasure.

If you are speaking about the intensity of such experiences of sensations resulting from your own actions, then, I suggest that this too is a matter judged by yourself, but yourself at the highest perspective - that will be, from the Buddhist point of view, the view closest to the Four Truths, or, stated another way, it will depend on your degree of detachment - in your experience. Here you will find that a change in perspective also has the power to change the experience. So you not only judge, but you are in control of the sentence. The danger here, and you did not ask about the danger of judging, is that the further the foundation of your view is from the highest, the harsher will be your own judgment of yourself. The fully developed compassionate heart is very forgiving.

If you are speaking about the material manifestation, the 'form', (e.g., an eye for an eye, a tooth for a tooth) that results from your intentionally created pleasure or pain or experience without pleasure or pain, then this is something that is beyond the scope of most people to determine. I have a theory that it is the collective wisdom of all beings since the beginning of time, but that is just my view.

See: http://buddhadust.net/backmatter/indexes/sutta/an/idx_10_dasakanipata.htm#p75

For a warning concerning attempting to judge such matters before you have experienced the full maturity of awakening. One of the 'fruits' of arahantship is this ability.

No one judges karma, and karma does not require a judge for it to work.

It's a natural law: what you sow is what you reap. Your actions set up potential for future arising of either conflict and discord or peace and harmony. If you create causes of conflict, you reap (all or some of) their results. If you create causes of peace, likewise.