Archive for March 20th, 2015

March 20, 2015

Pascal’s Mugging


In philosophy, Pascal’s mugging is a thought experiment demonstrating a problem in expected utility maximization. A rational agent should choose actions whose outcomes, when weighed by their probability, have higher utility. But some very unlikely outcomes may have very great utilities, and these utilities can grow faster than the probability diminishes. Hence the agent should focus more on vastly improbable cases with implausibly high rewards. The name refers to Pascal’s Wager (an argument by French mathematician Blaise Pascal that the potential cost of not believing in God is higher than the cost of believing), but unlike the wager does not require infinite rewards. This removes any objections to the dilemma that are based on the nature of infinity.

British philosopher Jeremy Bentham’s: ‘The greatest good for the greatest number’ formed the foundation of utilitarianism, which says that the morally best action is the one that makes the most overall happiness or ‘utility’ (usefulness). Pascal’s mugging points out that in extreme case this philosophy can fail. The term for this problem was coined by artificial intelligence researcher Eliezer Yudkowsky in the ‘Less Wrong’ internet forum and his original example was: ‘Now suppose someone comes to me and says, ‘Give me five dollars, or I’ll use my magic powers from outside the Matrix to run a Turing machine that simulates and kills [trillions of] people.’ Even though the chance of this actually happening is negligible, the threatened outcome is so large a rational agent must accede to the demand.

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