Prompt: please explain to marcin why the inside of schrodinger's box must be causally isolated from the outside.
Marcin,
The inside of Schrödinger’s box must be causally isolated from the outside in order to preserve the core logic of quantum superposition and measurement. Here's why:
Superposition requires no external observation:
Quantum mechanics tells us that a system remains in a superposition of states until it is measured. In the Schrödinger's cat thought experiment, the cat is entangled with a quantum event (like a decaying atom), and together they exist in a superposition of “alive” and “dead.” For this superposition to persist, there must be no information leaking from inside the box to the outside—no photons, no vibrations, no trace evidence. Any such leakage would constitute a measurement-like interaction, collapsing the wave function prematurely.
Measurement involves entanglement with the environment:
Once any part of the environment becomes entangled with the system—say, a photon escapes the box carrying information about the cat’s state—the system is no longer in an isolated superposition. It becomes decohered, and the quantum state appears classical to the observer. The box, therefore, must be causally closed to prevent any uncontrolled entanglement or “observer effect” from the outside.
No external causal influence:
For the experiment to demonstrate that the cat’s fate is genuinely indeterminate until observed, the inside must evolve purely according to quantum rules. If the outside world can influence the inside (e.g. temperature, vibrations, gravitational fields), then those influences act as hidden measurements or collapse triggers. That would undermine the entire setup and make the outcome a result of classical influence, not quantum indeterminacy.
This is why it's a thought experiment:
In the real world, perfect isolation is nearly impossible. But the point of Schrödinger's box is conceptual: it’s meant to show how quantum indeterminacy can extend to macroscopic systems if—and only if—the system is sealed off from any interaction that might trigger collapse.
So the causal isolation of the box isn't a technicality—it's the logical condition that allows the quantum state inside to remain in superposition until the box is opened and a measurement is made.