Copenhagen interpretation (Wigner)
Explanation
Quantum mechanics describes physical systems by means of wave functions that contain all possibilities until something forces the system to adopt a definite value. That "something" is called measurement or collapse, and its nature has been one of the central mysteries of 20th-century physics. In the 1930s, the mathematician John von Neumann showed mathematically that, however far we follow the causal chain — apparatus, cable, eye, retina, optic nerve, cortical neuron — collapse never appears spontaneously in the formalism. It has to be introduced by convention at some point.
Eugene Wigner, the Hungarian Nobel-prize physicist, took this observation very seriously in 1939. If the Schrödinger equation is universal and governs any physical system, then any purely physical process (including eyes and neurons) can be described as a quantum process without collapse. Where, then, does the quantum superposition break and a definite fact occur? Wigner's provocative answer was: in the consciousness of the observer. Only when a conscious mind takes notice of the result does the wave function collapse.
To make the argument intuitive, Wigner proposed the thought experiment known as "Wigner's friend". Imagine that a friend performs a measurement inside a laboratory and writes down the result. You are outside. For you, before your friend tells you anything, the entire system (atom + apparatus + friend + notebook) would be in a superposition: friend-who-saw-up plus friend-who-saw-down. Only when he informs you does your epistemic state update. But Wigner did not read it merely as an update of knowledge: for him, the friend's consciousness had already collapsed the system from within.
The philosophical consequence is enormous. If consciousness collapses wave functions, then it is not an epiphenomenon produced by matter, but a constitutive factor of physical reality. Fundamental physics would, in a sense, be incomplete without mind. Some interpreted this idea in an idealist key (reality actualizes itself before the gaze of mind), others in a dualist key (there is an ontological distinction between the mental and the physical), and others as an invitation to think of mind as part of the basic furniture of the universe, as in certain panpsychist lines.
The interpretation has serious problems. The most important is decoherence: when a quantum system interacts with a large and warm environment (such as a measuring apparatus or a brain), superpositions are dispersed so quickly that, for practical purposes, there is collapse without any need to invoke a conscious observer. Furthermore, the idea is uncomfortably anthropocentric: do cats collapse?, insects?, computers?, did anything collapse before the appearance of life in the universe? These questions have pushed most physicists toward interpretations without consciousness.
Even though it is a minority view today, Wigner's interpretation left a lasting mark. It encouraged physicists such as Henry Stapp, Roger Penrose or Stuart Hameroff to seek deep connections between consciousness and quantum mechanics, gave rise to contemporary idealist interpretations (QBism, Rovelli on one reading) and brought back to the table the old question about the place of mind in nature. Even for those who reject it, it served a valuable function: reminding us that the measurement problem is still open and that it is not clear that a purely physical description can account for everything that is real.
Strengths
- Takes the measurement problem seriously.
- Recognizes the role of the observer in fundamental physics.
- Inspiration for quantum theories of consciousness.
- Articulated by first-rate physicists.
Main critiques
- Decoherence explains apparent collapse without the need for consciousness.
- Problematic anthropocentrism.
- Largely abandoned in contemporary physics.
- Conflates epistemology with ontology, according to critics.