Schrödinger found superposition so odd that he illustrated its absurdity by a thought experiment. He imagined his cat in a box with a device that would release poison gas if it detected a photon of light, then added a radioactive source that randomly emitted photons. The box is closed, so no-one knows when the gas is released, but according to quantum theory, the source and device are a system that superposes a photon being detected and not detected, until it is observed. Hence, that the poison is released and not released also superposes, so the cat is in an alive-dead superposition until Schrödinger opens the box! But how can a cat be alive and dead? Or if cats can’t be alive and dead, how can a photon exist and not exist? Or if a photon can do this but a cat can’t, when does the superposition stop?
Schrödinger’s example illustrates that quantum-scale events make no sense at the macro-scale because that a cat can be both physically alive and dead is ludicrous. Yet quantum theory doesn’t actually predict this because it doesn’t require the observation that stops a superposition to be human. In this model, every physical event is an observation, so the photon superposition stops when the detector observes it, regardless of what Schrödinger sees. It then releases the poison and the cat dies. Before opening the box, Schrödinger doesn’t know if his cat is alive or dead, but the cat does (or did). If quantum superposition is stopped by any observation, not just ours, there is no alive-dead cat.
Quantum theory requires every physical event to be an observation by what causes it, and as usual, its logic is impeccable. Every entity that interacts physically then also observes that event, so this rule is universal. In contrast if only humans observed, we would be necessary for physical history to occur, which is unlikely. In quantum theory, our universe began as a superposition that only an observation could stop, but we didn’t exist then. It follows that just Schrödinger wasn’t needed to stop the superposition in his cat’s box, we weren’t needed to stop the superpositions that led to past physical events, as quantum waves have been collapsing into physical events since the beginning of time.
In quantum theory, observation formally causes physical events, so is our world a dream? The observer alone causes a dream but the world we see isn’t only caused by us, so it isn’t a dream in this sense. If every physical event is a mutual observation, as it seems to be, then we aren’t creating the universe alone, everything is, as the photon we observe is also observing us. That every physical event is an observation implies a virtual world but not a dream world.
Schrödinger’s alive-dead cat then doesn’t illustrate the absurdity of quantum theory but its depth. That every active entity in our universe observes to stop superpositions allows physical history to emerge from quantum possibilities.