Wednesday, February 09, 2011

Schrödinger's camera

kw: observations, physics, quantum theory

OK, I reckon most folks know the thought experiment called Schrödinger's cat: A cat is put in a box with a glass jar of cyanide and a hammer that will be dropped on the jar if a signal is received by a Geiger counter. A radioactive source is used that has a 50% chance of emitting a particle into the receiving window of the Geiger counter within the next hour. After one hour the radioactive source is removed and the box is opened. Is the cat alive or dead? Before you opened the box, was the cat either alive or dead, or in some combination of states?

Schrödinger intended this as a bitter joke, but it has deep philosophical implications, according to physicists. It emphasizes the rôle of the "observer" in quantum events. According to the dogma I was taught, until a quantum event, or an event governed by a quantum event, is "observed", all possibilities exist in some superposition of states, and only when an observation is made does this superposition "collapse" upon one of the possible final states, in a random fashion. Does that mean that the cat in the box doesn't either live or die until an observer opens the box? More to the point, is the cat an observer? Or does observation require human intelligence, or that very loosely defined quality, "sentience"? (or the equally fuzzy "consciousness" … I think cats are conscious, but …)

Let's go further. Suppose the box is to be opened automatically, and a camera takes a picture of the inside. Hours later the experimenter develops the camera's film (or, if it is digital, puts the picture in a computer to look at it). Does the dead/alive superposition persist until the experimenter (or any other conscious being) looks at the picture?

I resolve the dilemma this way. Consider diffraction. When light passes an edge, some is scattered into the shadowed area. By using a laser beam and a razor blade you can verify this for yourself. Not only that, with a sensitive detector, you can determine that some tiny amount of light is diffracted even if the visible beam entirely misses the edge of the blade. The amount depends on the magnitude of the "miss". Now consider the diffraction pattern itself. Perhaps it is just seen on a screen, or a scan by a detector yields a string of numbers representing the brightness of the beam at various points. Is the same diffraction pattern there if the detector, and you, are absent? If a specific small area is seen to receive 0.001% of the laser beam, does it continue to do so when you and your detector are absent? I happen to think it does.

This shows that the "observer" rôle must be conferred upon any object that is capable of affecting the path of the photons of the light beam. Since the quantum wave function is typically nowhere zero, that means that every particle in the universe is an observer. The universe doesn't need us or other "conscious" or "sentient" observers. It observes itself, and it does what it does whether we exist or not.

Thus I contend that there is no superposition of states to collapse. Every particle, whether lepton or boson (or mysterious dark matter particle), is continually influenced by every other particle in existence, and not just by its gravitational force. The probability that a particular influence will make a measurable effect on the particle's position and velocity at some future time is proportional to the distance between them, and to the sensitivity of the measurement, with the understanding that the measuring apparatus also influences the particle. For example, when you move a razor blade closer to or farther from a laser beam, the blade is part of the measurement, and so are you. Your position in the room influences things, though your detector may not be sensitive enough to record it. And just by the way, the laser "beam" is simply the brightest part of a photonic phenomenon that fills all space, or will if given time enough.

Going further than this leads to madness. I'm glad I got that off my mind.

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