Prediction and explanation in the multiverse

Understand

Probabilities in the multiverse can be calculated by assuming that we are typical representatives in a given reference class.

• But is this class well defined? What should be included in the ensemble in which we are supposed to be typical? There is a widespread belief that this question is inherently vague, and that there are various possible choices for the types of reference objects which should be counted in.
• Here we argue that the ``ideal'' reference class (for the purpose of making predictions) can be defined unambiguously in a rather precise way, as the set of all observers with identical information content.
• When the observers in a given class perform an experiment, the class branches into subclasses who learn different information from the outcome of that experiment.