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Eric Zencey:
I recall that as an undergrad, years and years ago, I had a prof who reported (with a chuckle, as in "could anything be more ridiculous?") that "there is even some evidence that stock market ups and downs correspond to sunspot activity."  Hmm...  Sunspots affect solar output, which affects agriculture, which is still one of the primary ways that valuable low entropy is brought into an economy (despite the fact that there has been an historical decline in the percentage of the workforce engaged in it.  Look for that trend to be reversed as we come off peak oil and are forced to practice sustainable agriculture.)
This reminds me of stochastic resonance. There need be no more than a very small effect of the sunspot cycle on economic activity, but since the sunspot cycle is (quasi)periodic it might be able to resonate with the nonlinear oscillator that is the economic system and get amplified in the response.
Strictly speaking, stochastic resonance occurs in bistable systems, when a small periodic (sinusoidal) force is applied together with a large wide band stochastic force (noise). The system response is driven by the combination of the two forces that compete/cooperate to make the system switch between the two stable states. The degree of order is related to the amount of periodic function that it shows in the system response. When the periodic force is chosen small enough in order to not make the system response switch, the presence of a non-negligible noise is required for it to happen. When the noise is small very few switches occur, mainly at random with no significant periodicity in the system response. When the noise is very strong a large number of switches occur for each period of the sinusoid and the system response does not show remarkable periodicity. Quite surprisingly, between these two conditions, there exists an optimal value of the noise that cooperatively concurs with the periodic forcing in order to make almost exactly one switch per period (a maximum in the signal-to-noise ratio).

Such a favorable condition is quantitatively determined by the matching of two time scales: the period of the sinusoid (the deterministic time scale) and the Kramers rate (i.e. the inverse of the average switch rate induced by the sole noise: the stochastic time scale). Thus the term "stochastic resonance".

Stochastic resonance was discovered and proposed for the first time in 1981 to explain the periodic recurrence of ice ages.[1] Since then the same principle has been applied in a wide variety of systems. Nowadays stochastic resonance is commonly invoked when noise and nonlinearity concur to determine an increase of order in the system response.

It'd be nice if the battle were only against the right wingers, not half of the left on top of that — François in Paris
by Carrie (migeru at eurotrib dot com) on Tue Mar 11th, 2008 at 07:01:56 PM EST
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