Cosmology Group Podcasts

Tim opens with a brief point about the postulation of a very low entropy past state. He contrasts the claim that, if this state is not the initial state of the world, that the entropy profile of the universe will be symmetric (intuitively, with a global minimum at the moment of the past hypothesis) and the claim that the macroscopic profile of the universe will be symmetric in the same way. David takes some time to respond to this point. David then turns the discussion to the inferential role of the past hypothesis. He starts by identifying two kinds of inferences that can be used to determine the state of the world at times other than the present: Inference by Prediction/Retrodiction (in which one takes facts about the present and applies the laws to determine facts about the past or future) and Inference by Measurement (in which one takes facts about the present plus facts about certain past events and determines facts about the past or future). Inference by Measurement is, David points out, much stron