Histories Without Collapse

This paper is a comparison of two theories the probability history in quantum mechanics. One derived from Copenhagen mechanics using projection postulate and basis "consistent histories" interpretation; other based on proposal by Bell, originally for "pilot state" theory but here applied to pure unitary The first can be used wider class histories depends postulate, or "collapse", which widely held an unsatisfactory feature theory; second universal state vector without collapse. We examine simple model Wigner's friend, Bell's give different probabilities sentient system. also Frauchiger-Renner extension this model, calculations throws light contradiction found Frauchiger Renner. By extending equip observer with memory, we reduce use Born rule at single time, show that rule, gives same result as applying course history, because entanglement memory: implements discuss implications cosmology.