Not a belief I would say, but it was seriously considered. Many physicists, including some of the founding fathers of QM, thought about it, see e.g. https://en.

Not a belief I would say, but it was seriously considered. Many physicists, including some of the founding fathers of QM, thought about it, see e.g. https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_interpretation https://en.wikipedia.org/wiki/Von_Neumann%E2%80%93Wigner_int...