Photonics Dictionary

Schrödinger's cat

Schrödinger's cat is a thought experiment devised by the physicist Erwin Schrödinger in 1935 to illustrate the paradoxical nature of quantum mechanics, particularly the concept of superposition and the interpretation of measurement in quantum theory.

In essence, Schrödinger's cat involves imagining a scenario where a cat is placed in a sealed box along with a radioactive atom, a Geiger counter, and a vial of poison. The setup is designed so that if the Geiger counter detects radiation (due to the decay of the radioactive atom), it triggers the release of the poison, which kills the cat. If no radiation is detected, the cat remains alive.

According to quantum mechanics, until the box is opened and an observation is made (i.e., until a measurement is performed), the system of the cat, atom, and poison exists in a superposition of states. This means the cat is considered to be simultaneously alive and dead.

Quantum measurement problem: The paradox highlights the challenge in understanding how quantum superposition (where a particle or system can exist in multiple states at once) relates to classical measurement, where an observation seems to force a definitive outcome.

Schrödinger's cat is often used to discuss interpretations of quantum mechanics, such as the Copenhagen interpretation (where measurement "collapses" the wave function to a definite state) or the Many-Worlds interpretation (where each outcome exists in a separate, branching universe).

While Schrödinger's cat is a theoretical construct and no actual cats are harmed, it serves as a thought-provoking illustration of the counterintuitive aspects of quantum theory and the challenges in reconciling quantum behavior with our classical understanding of reality. It remains a significant concept in discussions about the foundations and interpretations of quantum mechanics.
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