Experiment #9 · Thought experiment

Schrödinger's Cat

Macroscopic superposition and the measurement problem

Erwin Schrödinger · 1935 · Quantum foundations

First published: E. Schrödinger, "Die gegenwärtige Situation in der Quantenmechanik", *Naturwissenschaften* 23 (1935): 807–812, 823–828, 844–849.

If quantum superposition is real, a cat in a sealed box can be both alive and dead until someone opens the lid.

Schrödinger devised the case as a *reductio* against the Copenhagen reading of quantum mechanics: a cat is sealed in a box with a vial of poison rigged to a radioactive atom whose decay (or non-decay) over an hour is a 50/50 quantum event. If quantum states evolve into superpositions, the entire system — atom, vial, cat — should end up in a superposition of (decayed-and-cat-dead) and (not-decayed-and-cat-alive) until measured. Schrödinger meant this as absurd; subsequent physics has been less sure. The case is the canonical pressure-test for how, where, and whether the quantum-to-classical transition occurs.

Formulation

Atom with 50% decay probability per unit time → Geiger counter → relay → poison release. After one half-life, the joint state is a superposition of |decayed⟩|dead⟩ and |undecayed⟩|alive⟩. Question: is the cat in fact in such a superposition prior to observation, and if not, where does the linearity of Schrödinger evolution fail?

Compare this experiment

Dimensions Engaged

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Matter

Forces Matter · Ontological Status: are macroscopic objects determinate between measurements, or are they inheritors of the same indeterminacy as the atoms that compose them?

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Observer

The canonical test case for Observer · Metaphysical Agency: does measurement (and if so, by what kind of observer) actualise outcomes, or are outcomes always already there and "measurement" merely informs?

Responses — How Schools Engage

Affirms / takes the bait 2

Quantum Realism

Take the superposition literally: the cat is in a genuinely indefinite state. Decoherence explains why we never *see* such states, but the formal superposition is real until something irreversibly correlates with it.

Idealism

A natural place for the von Neumann–Wigner reading: consciousness collapses the wave function, so the cat is in superposition only until a *mind* enters the causal chain. The thought experiment dramatises the role of subjectivity in physics.

Denies / rejects the premise 1

Logical Positivism

The question "is the cat alive or dead before opening the box" has no determinate answer because no observation is yet defined. Pretending otherwise reifies the wave function past its empirical content.

Reframes the question 2

Multiverse Theory

Everettian: both outcomes are real on different branches. There is no collapse, no paradox, and no special role for the experimenter — only the appearance of a single outcome from the perspective of any one observer.

Naturalism

Pilot-wave / Bohmian: the cat has a definite state throughout — guided by a wave function we cannot fully access. The apparent paradox is an artifact of identifying ψ with the totality of physical reality.

Holds it inconclusive 1

Analytic Metaphysics / Logical Atomism

A live debate: the case rules out naive realism about classical states without singling out a winner among collapse, hidden-variable, and many-worlds readings. Treat the choice as theory-relative.