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Monday, January 29, 2007

OCCAM'S RAZOR

Occam's (or Ockham's) razor is a principle attributed to the 14th century logician and Franciscan friar; William of Occam. Ockham was the village in the English county of Surrey where he was born.

The principle states that "Entities should not be multiplied unnecessarily."

Many scientists have adopted or reinvented Occam's Razor as in Leibniz's "identity of observables" and Isaac Newton stated the rule: "We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances."

The most useful statement of the principle for scientists is,

"when you have two competing theories which make exactly the same predictions, the one that is simpler is the better."

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For those who are wondering why the words of a medieval theologian are important the answer is that he had put his finger on the final rule of the scientific method.

The main rules are
Observe, experiment & measure
Think up a theory that covers observations
Test the theory with further measurements, observations & experiments
If new measurements don't, at some point fit, amend the theory
Repeat until it fits.

Where this falls down is that sometimes 2 or more theories fit. Not only in evolution but in almost everything you can use the theory that God dunnit. Galileo's theory that the Earth moved round the sun fitted only marginally better than the previous theory that Rarth moved round the sun & all the planets moved round us too but also moved in epicycles within epicycles ad nauseam but it was simpler (incidentally this is a case where the original simple Sun round Earth theory had quite properly been modified with these endless cycles but eventually had to be junked). Global warming is a theory that requires a number of assumptions about the future which are more complicated than the one that things will go on pretty much as before.

In all these cases the proper response is to go with Occam. It doesn't prove Darwin right but it does prove this to be the most sensible & thus only reasonable working hypothesis. Politics is full of people trying to sell their own theory (conspiracy or economic or 'ism) which within their own terms cannot be disproved (eg all the countries which called themselves socialist weren't & if I get to establish real socialism here everything will be wonderful & nobody can prove it won't work - perhaps not but the simplest assumption is that the 99th person selling this line isn't going to do much better than the previous 98).

Maybe someday somebody will come direct to the right conclusion by making a whole bunch of assumptions/guesses & being right but even then those who use science will get there a bit latter by making a few more experiments & ruling out the wrong guesses.

Then sometimes you get the disagreement as to which is the simpler assumption. I have mentioned before that I tend to treat the Everett Many Universe Theory as probable. There are reasons for this - the 2 slit experiment, i am informed cosmologists say it fits better - but it does not create a simpler universe. However it does not involve more assumptions which is the point (since it explains 2 slit & nothing else does, it involves, in my view, slightly less unknown assumptions than the classic position. However I accept it is not clearcut & I don't know everything but William of Ockham makes a very good guide.

Comments:
Goodness me. My school carol concert was held in Ockham parish church every year. I've never once made the connection with William of Occam.
 
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