Erwin Schrodinger was a physicist and one of the founders of quantum mechanics, which predicts the probabilities of measurements taken in the observation of matter at microscopic scales. His thought experiment, known as Schrodinger's Cat, was a hypothetical experiment that exposed the problems with the Copenhagen Interpretation of the superposition theory of quantum mechanics.
The wave-particle duality
The idea of wave-particle duality originated from the debate over the nature of light in the 17th Century. Christiaan Huygens believed light consisted of waves, while Isaac Newton argued it was made up of particles. Several scientists, including Albert Einstein and Niels Bohr, established the current scientific theory that all particles also have wave properties, and vice versa. The theory holds that all microscopic particles, including compound particles such as atoms and molecules, exhibit this dual nature, but the wave properties of macroscopic particles are undetectable because the wavelengths are so small.
While the theory of wave-particle duality has proved robust under scientific observation, no single explanation for why microscopic particles behave the way they do that has so far emerged has gained universal acceptance. While interpretations of quantum mechanics argue this is a fundamental universal property, others argue it only appears that way as a limitation of the observer. The Copenhagen interpretation of superposition is one popular theory.
The Copenhagen Interpretation of superposition
Superposition refers to the concept that, at atomic and subatomic levels, particles of matter such as electrons are able to exist simultaneously at least partly in all of their theoretically possible states. Superposition is observable as interference peaks that show electrons being in multiple locations simultaneously. However, when measured, they give a result that corresponds to only one of these possible states. The Copenhagen Interpretation provides the explanation that it is the act of measuring that collapses the system into a single observable state.
The Schrodinger's Cat problem
Schrodinger postulated the cat problem to highlight the issues with superposition, in particular, the difficulty of determining at what point a physical system capable of existing in multiple states simultaneously loses that capacity and takes on the singular state.
Schrodinger's Cat experiment hypothetically sets up a situation where a cat is closed into a steel chamber, along with a device that is secured against interference from the cat. The device contains a Geiger counter with a tiny piece of radioactive material, set up so that if even one atom decays, a relay will cause a hammer to be released, shattering a small vial of poison and killing the cat. It is as equally likely that a single atom of radioactive material will decay as that none will. The paradox postulates that, until the box is opened and the state of the cat can be observed, according to the Copenhagen Interpretation, the cat can, for the duration of the experiment, be considered to exist in both its living and dead states simultaneously.