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Philosophical interpretation of classical physics


Classical Newtonian physics has, formally, been replaced by quantum mechanics on the small scale and relativity on the large scale. Because most humans continue to think in terms of the kind of events we perceive in the human scale of daily life, it became necessary to provide a new philosophical interpretation of classical physics. Classical mechanics worked extremely well within its domain of observation but made inaccurate predictions at very small scale - atomic scale systems - and when objects moved very fast or were very massive. Viewed through the lens of quantum mechanics or relativity, we can now see that classical physics, imported from the world of our everyday experience, includes notions for which there is no actual evidence. For example, one commonly held idea is that there exists one absolute time shared by all observers. Another is the idea that electrons are discrete entities like miniature planets that circle the nucleus in definite orbits.

The correspondence principle says that classical accounts are approximations to quantum mechanics that are for all practical purposes equivalent to quantum mechanics when dealing with macro-scale events.

Various problems occur if classical mechanics is used to describe quantum systems, such as the ultraviolet catastrophe in black body radiation, the Gibbs paradox, and the lack of a zero point for entropy.

Since classical physics corresponds more closely to ordinary language than modern physics does, this subject is also a part of the philosophical interpretation of ordinary language, which has other aspects, as well.

In classical mechanics it is assumed that given properties - speed or mass of a particle; temperature of a gas, etc. - can in principle be measured to any degree of accuracy desired.

Study of the problem of measurement in quantum mechanics has shown that measurement of any object involves interactions between the measuring apparatus and that object that inevitably affect it in some way; at the scale of particles this effect is necessarily large. On the everyday macroscopic scale the effect can be made small.

Furthermore, the classical idealization of a property simply being "measured" ignores the fact that measurement of a property - temperature of a gas by thermometer, say - involves a pre-existing account of the behavior of the measuring device. When effort was devoted to working out the operational definitions involved in precisely determining position and momentum of micro-scale entities, physicists were required perforce to provide such an account for measuring devices to be used at that scale. The key thought experiment in this regard is known as Heisenberg's microscope.


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