Schrödinger's cat and the Copenhagen interpretation

Perhaps one of the most famous mental experiments in science, Schrödinger's cat is successful in illustrating the bizarre essence of quantum mechanics.

Schrödinger's cat experiment, proposed by Erwin Schrödinger himself, was created in order to criticize the interpretation that Niels Bohr and Werner Heisenberg had associated to the "quantum world".

By 1927 Bohr and Heisenberg were working together at the University of Copenhagen, at a time when quantum mechanics was at the peak of its development. The peculiar double-slit experiment (already described in detail in past articles), in which the addition of a detector to the experiment caused the electron to change its behavior entirely (from ondulatory to particle), motivated the two physicists to think that the introduction of an observer into a quantum system causes the system to fundamentally alter its state, in an act named "wave function collapse". If before the measurement the particle was described by a spread wave function in space, after the measurement, that is, after the "collapse", the particle is forced to demonstrate a specific position, in a region much more localized in space (thus a particle behavior; see photo 2). The observer agent is responsible for the collapse of the wave function. It is important to note that with "observer" we mean any entity (such as a measuring device) that requires the particle to show a specific result (this being random following the probabilities provided by quantum theory). Bohr and Heisenberg's thinking can be samarized as follows: a particle has no property (such as position, velocity, energy...) defined until a measurement is made; when executed, the particle chooses a single state within the conditions of superposition of states. This interpretation became known as "Copenhagen interpretation".

Schrödinger, in analyzing this new proposed interpretation, counter-argued using the Schrödinger's cat experiment . The experiment consists of a cat inside a closed box, which contains a device capable of releasing radioactive material. The radioactive material has a certain probability of being released, killing the cat, but has a probability of not being released, leaving the cat alive. Schrödinger pointed out that, following Copenhagen's interpretation, the cat would not be in any specific state (neither alive nor dead) until the box was opened. The condition of this "zombie cat", according to Schrödinger, evidenced a big lack of logic in Bohr and Heisenberg's proposal.

Despite the mental experiment proposed by Schrödinger, Copenhagen's interpretation remains one of the most accepted and widespread in the scientific world, even though there is no way to know if it is indeed the "correct look" of quantum mechanics.

Photo 1: The Schrödinger cat experiment

Photo 2: wave function before and after the "collapse" (photo obtained from the book "50 ideas of quantum physics you really need to know")