Tuesday, March 27, 2012

Geo-centric model and limit of Occam's razor.

I mentioned geo-centric model of the planetary motion a couple of times about how a sufficiently complex model can always be invented to fit the data.

In case you haven't seen a geo-centric model before, here is a Ptolemaic one

(see wikipedia entry for Occam's razor--another term I used in class about Nature's predilection for simplicity--which interestingly also uses helio-centric and geo-centric models as examples:  http://en.wikipedia.org/wiki/Occam's_razor


ps: interestingly, nature doesn't always seem to go for the "simplest" model--or at least not necessarily as we will model "simple". An interesting case in point is how the genes code the 20 amino acids. The original idea Crick had involved coming up with exactly 20 "unambiguous" triplets that can be placed next to each other and you will still be able to decode the sequence correctly even though there is no obvious delimiters between each amino acid code. This "comma free" version turned out not to be the one nature uses--which uses ambiguous triplets but ensures correct translation by using  specific starting/stopping  delimiters (see for example  http://www.emunix.emich.edu/~rwinning/genetics/code.htm).  The original Crick code was so compelling that it has been called the "greatest wrong theory". 

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