You've heard of Markov chains. But who was Markov?
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Calculating the stationary distribution is one of the main things people do with Markov chains. That's all that PageRank is -- the stationary distribution of the Markov chain constructed from the network of links on the web.
Markovs is a natural law, proven, is it not? Well then, it will be found in any system.
Ah, just like chess has 64 possible states. Except that chess has on the order 10^47 states.