Is Wigner's Friend Just Schrödinger's Cat?

Wigner's Friend thought experiment is largely considered equivalent to Schrödinger's Cat if the cat is viewed as an observer, though subtle differences exist regarding communication.

• Wigner's Friend and Schrödinger's Cat are conceptually similar if a cat is considered an observer.

• Schrödinger did not originally describe the cat as an observer.

• The ability to communicate with the observer is a distinguishing factor in some scenarios.

The Wigner's Friend thought experiment is essentially Schrödinger's Cat, replacing the cat with an observer, as both explore quantum superposition and observation. The key distinction lies in whether the 'observer' can communicate, which influences the experimental conditions and potential for quantum state collapse. While Schrödinger did not initially describe the cat as an observer, adopting this perspective makes the two experiments conceptually very similar.

Defining the Observer

• 00:00:06 If a cat is considered an observer of a quantum system, then Schrödinger's Cat becomes indistinguishable from Wigner's Friend. The quantum system, like a radioactive atomic nucleus in superposition, is observed by either the cat or a human friend. This perspective suggests that the primary difference between the two thought experiments is how one defines an 'observer' and their role in quantum measurement, rather than fundamental mechanics.

Differences in Communication

• 00:01:35 A key reason some separate Wigner's Friend from Schrödinger's Cat is the ability to interact with Wigner's friend, such as asking questions that could or could not cause a collapse of the quantum state. This level of communication is not possible with a cat, highlighting situations where a sentient, communicating observer is explicitly required for certain versions of the experiment. Despite this, the experiments remain broadly similar conceptually.