The Schroedinger’s Cat Gedankenexperiment helped us appreciate the measurement problem by bringing superposition up from the microscopic world to the more familiar macroscopic scale. But it raised the problem of what we would see if we could see inside the closed box. If the very act of seeing always and immediately gets rid of the superposition of multiple states, then there is no experimental way to refute the Copenhagen interpretation and its weird alive/dead superposition state. But several questions remain: where or when does the superposition state cease to exist? Is it only real in the microscopic realm? Where is the boundary between micro- and macro-worlds?
Hungarian-American mathematician John von Neumann took on the question of whether consciousness was essential to the so-called collapse of the wave function. As we’ve already mentioned, some physicists have suggested that the collapse might actually occur as the instant the Geiger counter detected the radioactive decay. This was one way to keep the weirdness down at the microscopic scale, and diminish the role of consciousness.
In 1932, von Neumann presented a convincing argument that as long as the Geiger counter was isolated from observation, it would have to be considered to also exist in a superposition state. Assuming the device itself to be a physical system subject to the laws of quantum mechanics, it would have to join the state of the radioactive nucleus, which has a 50-50 chance of being decayed at 60 minutes.
Before being observed, the Geiger counter would be in a state in which it simultaneously registered and did not register a decay event. Any other device connected with the counter, like a recorder or the mechanism to release the poison would also have to share the same kind of superposition. The “chain” linking the microscopic to the macroscopic could only end when a conscious observer opened the box and saw one result or the other.
Once again, a holistic view of the universe is favored. The microscopic world differs in scale from the things we deal with every day, as we have seen many times. The difference in scale is quite large, and the behavior of matter seems qualitatively different between the macroscopic and microscopic worlds. But in reality it is one continuum, and the same laws apply. There is no sharp boundary between what is too small for common sense or too large for quantum physics. There is, alas, no way to keep the quantum world separate from the one we are comfortable with.
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