Editing Wigner's friend (section)

===De Broglie–Bohm theory===
The [[De Broglie-Bohm theory]], also known as Bohmian mechanics or [[pilot wave theory]], postulates, in addition to the wave function, an actual configuration of particles that exists even when unobserved. This particle configuration evolves in time according to a deterministic law, with the wave function guiding the motion of the particles. The particle configuration determines the actual measurement outcome —e.g., whether Schrödinger's cat is dead or alive or whether Wigner's friend has measured 0 or 1— even if the wave function is a superposition. Indeed, according to the De Broglie-Bohm theory, the wave function never collapses on the fundamental level. There is, however, a concept of ''effective collapse'', based on the fact that, in many situations, "empty branches" of the wave function, which do not guide the actual particle configuration, can be ignored for all practical purposes.<ref>{{cite book |last1=Dürr |first1=Detlef  |last2=Teufel |first2=Stefan |title=Bohmian Mechanics: The Physics and Mathematics of Quantum Theory |year=2009 |publisher=Springer |isbn=978-3-540-89343-1}}</ref>

The De Broglie-Bohm theory does not assign any special status to conscious observers. In the Wigner's-friend situation, the first measurement would lead to an effective collapse. But even if Wigner describes the state of his friend as a superposition, there is no contradiction with this friend having observed a definite measurement outcome as described by the particle configuration. Thus, according to the De Broglie-Bohm theory, there is no paradox because the wave function alone is not a complete description of the physical state.