Submission to the 
Immortality Institute's book project.
the ultimate goal of an agent is positive experience
the only reason for choosing one course of action over another is the expectation (rational or not) that there is some significant chance that it will lead to a more positive experience than the alternatives (not necessarily a good experience, but better than the alternatives)
what counts as a positive experience varies widely in humans
however there is also a great deal of commonality due to our common genetic heritage generally people value (almost by definition) pleasure, satisfaction, mutual respect, joy, fun, ... over the respective opposites
rational choice theory decision theory
Imagine that some sufficiently advanced technology (indistiguishable from magic) allows you to monitor the quality of your subjective experience. Whenever you are curious you could glance at the display to see a quantative measure of how good (or bad) you felt at any given time, say a number from -10 to +10. If it happens to read +10 it means that you have never felt better and that you are having the best time of your life at that moment. A reading of zero means that whatever you are experiencing is equivalent (no better nor worse) than experiencing nothing at all, as you would in a dreamless sleep or a coma or death. Let's call that number the Q factor, for quality.
All other values that this hypothetical monitor could display are determined by these two reference points corresponding to maximum pleasure (+10) and oblivion (0). But first it will be necessary to distinguish between the Q factor at a given moment and the Q of an experience. The Q of an experience relates to the overall quality of a duration in time and is calculated as the product of the duration and the average Q during the duration. In this respect it is analogous to speed and distance covered. Say during the period between 2pm and 4pm you were in a car travelling on a highway and your speed varied between 60km/h and 100km/h. In order to calculate the distance covered you would need to know the average velocity during those two hours. If the average turned out to be 85 km/h, then the distance covered would be 170 km. Admittedly in the case of travelling in a car it is usually easier to calculate the average speed knowing the time and distance which are easier to measure, but the mathematical relation remains the same. The Q of an experience is defined as the average Q during the duration multiplied by the time period. If you experience an average Q of 3 for 2 hours, then the Q for that experience is 6 (units?) and if you experience an average Q of 2 for 3 hours, the Q for the experience is again 6.
Now it is possible to define the instantaneous Q factor, the number that the hypothetical monitor displays.
If the Q factor goes negative, it means that you would prefer to be unconscious at that moment. The Q factor for a particular experience is defined such that you would have no preference between two subjective experiences if