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Are the Androids Dreaming Yet?

Half silvered
Mirror

Light

Detector

Interferometer

if only one photon is traveling at a time, still no light comes out in one direction and all the photons come out the other. The wave functions of each photon interfere with each other constructively or destructively. The only conclusion available is the photon must be traveling along both paths! They are said to be in ‘superposition’. If you introduce a measuring device half way around the experiment, it will destroy the superposition and the photons behave in the common sense way. Remove the measuring device and, once again, the photons seem to take both paths. Richard Feynman pointed out that you really have to imagine that the photons take every possible path, not only the straight line paths. He received his Nobel Prize for demonstrating how to add up these infinite paths to get a finite answer with his ‘sum over histories method’. Superposition is a strange idea when limited to the realm of small particles but what about larger things? – cats for example.
Erwin Schrödinger’s unfortunate cat is trotted out to demonstrate the paradox so often that Stephen Hawking is on record for wanting to reach for a gun every time he hears mention of it.
The thought experiment works like this. A cat is put in a box with a radioactive substance, a Geiger counter and a vial of poison. If the counter detects a radioactive decay it breaks the bottle and the cat dies, if no decay is detected the cat lives.

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