What would you want from an unbounded utility function that you couldn't get if the math turned out so that only bounded utility functions can be used in a decision procedure?
An actual description of my preferences. I am unsure whether my utility function is actually unbounded but I find it probable that, for example, my utility function is linear in people. I don't want to rule this out just because that current framework is insufficient for it.
Predicting your preferences requires specifying both the utility function and the framework, so offering a utility function without the framework as an explanation for your preferences does not actually explain them. I actually don't know if my question was hypothetical or not. Do we have a decision procedure that gives reasonable results for an unbounded utility function?
The phrase "rule this out" seems interesting here. At any given time, you'll have a set of explanations for your behavior. That doesn't rule out coming up with better explanations later. Does the best explanation you have for your preferences that works with a known decision theory have bounded utility?
Perhaps I see what's going on here -- people who want unbounded utility are feeling loss when they imagine giving that up that unbounded goodness in order to avoid bugs like the one described in the OP. I, on the other hand, feel loss when people dither over difficult math problems when the actual issues confronting us have nothing to do with difficult math. Specifically, dealing effectively with the default future, in which one or more corporations make AI's that optimize for something having no connection to the preferences of any individual human.
Do we have a decision procedure that gives reasonable results for an unbounded utility function?
Not one compatible with a Solomonoff prior. I agree that a utility function alone is not a full description of preferences.
Does the best explanation you have for your preferences that works with a known decision theory have bounded utility?
The best explanation that I have for my preferences does not, AFAICT, work with any known decision theory. However, I know enough of what such a decision theory would look like if it were possible to say that it would n...
This post describes an infinite gamble that, under some reasonable assumptions, will motivate people who act to maximize an unbounded utility function to send me all their money. In other words, if you understand this post and it doesn't motivate you to send me all your money, then you have a bounded utility function, or perhaps even upon reflection you are not choosing your actions to maximize expected utility, or perhaps you found a flaw in this post.
Briefly, we do this with The St. Petersburg Paradox, converted to a mugging along the lines of Pascal's Mugging. I then tweaked it to extract all of the money instead of just a fixed sum.
I have always wondered if any actual payments have resulted from Pascal's Mugging, so I intend to track payments received for this variation. If anyone does have unbounded utility and wants to prove me wrong by sending money, send it with Paypal to tim at fungible dot com. Annotate the transfer with the phrase "St. Petersburg Mugging", and I'll edit this article periodically to say how much money I received. In order to avoid confusing the experiment, and to exercise my spite, I promise I will not spend the money on anything you will find especially valuable. SIAI would be better charity, if you want to do charity, but don't send that money to me.
Here's the hypothetical (that is, false) offer to persons with unbounded utility:
If I am lying and the offer is real, and I am a god, what utility will you receive from sending me a dollar? Well, the probability of me seeing N Tails followed by a Head is (1/2)**(N + 1), and your utility for the resulting universe is UTILITY(UN(N)) >= DUT * 2**N, so your expected utility if I see N tails is (1/2)**(N + 1) * UTILITY(UN(N)) >= (1/2)**(N + 1) * DUT * 2 ** N = DUT/2. There are infinitely many possible values for N, so your total expected utility is positive infinity * DUT/2, which is positive infinity.
I hope we agree that it is unlikely that I am a god, but it's consistent with what you have observed so far, so unless you were born with certain knowledge that I am not a god, you have to assign positive probability to it. Similarly, the probability that I'm lying and the above offer is real is also positive. The product of two positive numbers is positive. Combining this with the result from the previous paragraph, your expected utility from sending me a dollar is infinitely positive.
If you send me one dollar, there will probably be no result. Perhaps I am a god, and the above offer is real, but I didn't do anything beyond flipping the first coin because it came out Tails. In that case, nothing happens. Your expected utility for the next dollar is also infinitely positive, so you should send the next dollar too. By induction you should send me all your dollars.
If you don't send money because you have bounded utility, that's my desired outcome. If you do feel motivated to send me money, well, I suppose I lost the argument. Remember to send all of it, and remember that you can always send me more later.
As of 7 June 2011, nobody has sent me any money for this.
ETA: Some interesting issues keep coming up. I'll put them here to decrease the redundancy: