Schrodinger's Cat is a thought experiment dealing with which type of mechanics?

Schrödinger's Cat is a thought experiment, sometimes described as a paradox, devised by Austrian physicist Erwin Schrödinger in 1935. It illustrates what he saw as the problem of the Copenhagen interpretation of quantum mechanics applied to everyday objects.

The experiment itself concerned the following. A cat is placed in a steel box along with a Geiger counter, a vial of poison, a hammer, and a radioactive substance. When the radioactive substance decays, the Geiger detects it and triggers the hammer to release the poison, which subsequently kills the cat. The radioactive decay is a random process; there is no way to predict when it will happen. Physicists say the atom exists in a state known as a superposition—both decayed and not decayed at the same time.

Until the box is opened, an observer does not know whether the cat is alive or dead. Because the cat's fate is intrinsically tied to whether or not the atom has decayed, the cat would, as Schrödinger put it, be "living and dead ... in equal parts" until it is observed. The cat is considered to be both alive and dead at the same time until it is observed.