Talks by Časlav Brukner
At the heart of the quantum measurement problem lies the ambiguity about exactly when to use the unitary evolution of the quantum state and when to use the state-update in dynamics of quantum mechanical systems. In the Wigner’s friend gedankenexperiment, different observers (one of whom is observed by the other) describe one and the same interaction differently. One – the friend – uses the state-update rule and the other – Wigner – chooses unitary evolution.
In general relativity causal relations between any pair of events is uniquely determined by locally predefined variables - the distribution of matter-energy degrees of freedom in the events' past light-cone. Under the assumption of locally predefined causal order, agents performing freely chosen local operations on an initially local quantum state cannot violate Bell inequalities. However, superposition of massive objects can effectively lead to "entanglement" in the temporal order between groups of local operations, enabling the violation of the inequalities.