Wednesday, March 03, 2010

Switching in less than a jiffy

kw: observations, science, physics, light, quantum theory

I'm reading a book about the historical development of quantum mechanics and entanglement. A review will appear in a couple more days; science histories take a while to read. I found fascinating the passionate debates engaged in by Bohr, Einstein, Schrodinger, Born, Ehrenfest, Heisenberg and others about what is really going on with quanta such as photons or electrons. Until deBroglie showed that the electron had a wave nature, it was not even considered a quantum.

As an objectivist (but not of the Rand variety), I am most compelled by things that actually happen. At root, a quantum behaves according to the kind of observation made upon it. The wave nature of photons, for example, is responsible for their ability to diffract when passing near an edge, to produce interference patterns, and to be refracted at the interface between differing media. The particle nature of photons is responsible for their ability to be detected by a photocell, a grain of silver chloride in photographic film, or even the retina of the eye.

The photons of light that form an image in your eye are focused as they enter the eye through the cornea, diffracted more or less by passing through a pupil of variable size, and focused more by the lens in the eye. For all these interactions, their wave nature prevails. Then, the energy of each photon is deposited in a dye molecule in a rod or cone cell, where it causes an electron to change its energy level. The electron then releases this energy into a nerve cell, which is now in a form that the brain can detect. The interaction with the electron depends on the photon's particle nature.

At one spot, the photon is behaving as a wave; at another less than 20mm away, it is behaving as a particle. At the speed photons travel through the eye (about 3/4 of their speed in vacuum), the "wave" interaction happens about 90 trillionths of a second before the "particle" interaction.

But that is from our point of view. What about the photon's "experience"? According to the theory of relativity, since a photon always travels at the speed of light, it experiences no passage of time; its "clock" is always stopped. From the time it is emitted, through its travels that possibly include reflections and refractions, until it is absorbed and moves one or more electrons about, the photon cannot experience anything but a timeless instant…speaking with gross anthropomorphism, of course! No matter "where" the points of emission and absorption may be, however far they may be separated, emission and absorption plus everything between are a single event.

There are several mysteries here, and though Heisenberg, Schrodinger and others developed ways of describing them mathematically, mysteries they remain. Yet the vision of every sighted creature (plus many other phenomena) depend on them, particularly on the dual nature of the photons.

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