李圆圆

Occam’s razor

Occam's (or Ockham's) razor is a principle attributed to the 14th century logician and Franciscan friar William of Ockham. Ockham was the village in the English county of Surrey where he was born. The principle states that \Entities should not be multiplied unnecessarily.\Sometimes it is quoted in one of its original Latin forms to give it an air of authenticity:

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In fact, only the first two of these forms appear in his surviving works and the third was written by a later scholar. William used the principle to justify many conclusions, including the statement that \existence cannot be deduced by reason

alone.\That one didn't make him very popular with the Pope.

Many scientists have adopted or reinvented Occam's Razor, as in Leibniz's \

observables\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

\exactly the same predictions, the simpler one is the better.\

In physics we use the razor to shave away metaphysical concepts. The canonical example is Einstein's theory of special relativity compared with Lorentz's theory that ruler's contract and clocks slow down when in motion through the ether. Einstein's equations for transforming spacetime are the same as Lorentz's equations for transforming rulers and clocks, but Einstein and Poincaré recognised that the ether could not be detected according to the

equations of Lorentz and Maxwell. By Occam's razor it had to be eliminated.

The principle has also been used to justify uncertainty in quantum mechanics. Heisenberg deduced his uncertainty principle from the quantum nature of light and the effect of measurement. Stephen Hawking writes in A Brief History of Time: \determines events completely for some

supernatural being, who could observe the present state of the universe without disturbing it. However, such models of the universe are not of much interest to us mortals. It seems better to employ the