Undecidability and the problem of outcomes in quantum measurements

Understand

We argue that it is fundamentally impossible to recover information about quantum superpositions when a system has interacted with a sufficiently large number of degrees of freedom of the environment.

• This is due to the fact that gravity imposes fundamental limitations on how accurate measurements can be.
• This leads to the notion of undecidability: there is no way to tell, due to fundamental limitations, if a quantum system evolved unitarily or suffered wavefunction collapse.
• This in turn provides a solution to the problem of outcomes in quantum measurement by providing a sharp criterion for defining when an event has taken place.