Schrödinger found superposition so odd he tried to illustrate its absurdity by a thought experiment. He imagined his cat in a box, with a radioactive source that could randomly emit a photon to trigger a deadly poison gas. In quantum theory, that photon plus a detector is a quantum system that both detects and doesn’t detect a photon until it is observed. If the box is also a quantum system, it also superposes the poison being released and not, so the cat is in an alive-dead superposition until Schrödinger opens the box to observe it. 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?
Quantum theory doesn’t define observation, so if the superposition doesn’t stop until Schrödinger observes it, the cat will be both alive and dead before that, which doesn’t make sense. This assumes that only human observation triggers quantum collapse. In contrast, a processing model takes observation to mean any physical interaction, as any physical event will collapse a quantum wave. It follows that to observe a quantum wave means to interact with it in a physical event.
For Schrödinger’s cat, this means the photon superposition collapses when the detector observes it, so the poison that kills the cat is released regardless of Schrödinger’s observation. Before opening the box, Schrödinger doesn’t know if the gas was released but the cat does, or did! The quantum superposition is stopped by any observation, not just ours, so there is no alive-dead cat.
Schrödinger assumed the observation of quantum theory was human observation, but then physical events couldn’t occur until we saw them, which can’t be. After all, if the universe needs us to cause quantum collapse, physical history couldn’t begin until we evolved, which is silly. Hence, any observation causes quantum collapse, not just those that involve our eyes or instruments.
This also clarifies the concern that quantum theory means that observing the world creates it. It is true that observation formally causes it, but it isn’t a sufficient cause, because every observation is a mutual interaction, so it isn’t a dream. We are creating the physical world but so is everything else, so when we observe a photon, it also observes us. If every observation creates a physical event, we alone aren’t creating the universe, everything is. This might seem strange, but the strange logic of quantum theory, that observing quantum events creates physical events is, as usual, impeccable.
The Schrödinger’s cat example was meant to illustrate the absurdity of quantum theory but actually illustrates its depth. We think we see our world objectively, as it is, but quantum theory tells us that we only observe the view we generate, just as in a virtual reality.