The Observer Strikes Back

Understand

In the modern quantum mechanics of cosmology observers are physical systems within the universe.

• They have no preferred role in the formulation of the theory nor in its predictions of third person probabilities of what occurs.
• However, observers return to importance for the prediction of first person probabilities for what we observe of the universe: What is most probable to be observed is not necessarily what is most probable to occur.
• This essay reviews the basic framework for the computation of first person probabilities in quantum cosmology starting with an analysis of very simple models.