Why are there different laws of physics if you look at a
problem from the quantum level?
When one starts to do interpret the results of experiments and
measurements involving molecules, atoms, and things smaller. One finds that
these results do not obey the laws of classical mechanics, which work so
well in our macroscopic world. Newtonian mechanics [classical mechanics]
simply makes incorrect predictions. Some early examples are: the heat
capacity of substances at low temperatures, the photoelectric effect, the
electronic spectrum of the hydrogen atom. This is just a few examples from a
long list of failures of classical mechanics on the atomic/molecular level.
CLASSICAL MECHANICS SIMPLY DOES NOT WORK FOR ATOMS AND MOLECULES.
So one is forced to seek a theory that DOES WORK, that makes the proper
predictions of EXPERIMENTAL RESULTS. Quantum mechanics, with its arcane
rules DOES WORK. It makes predictions that DO AGREE with experimental
results, hence it is accepted.
The understandable difficulty people have with quantum mechanics is that it
is not possible to "get a feel for it" in our macroscopic world, like you
can with classical mechanics. We have no direct experience with the rules or
the results it predicts. One has to set aside our macroscopic intuition and
"Does quantum mechanics make the correct prediction of the results of such
and such experiment?" If it does, then we accept the theory as correct, even
though we have no experience at our macroscopic level with the experimental
results or their explanation at the atomic level.
The laws of physics at the quantum level are more accurate. The laws of
physics as Isaac Newton developed them are approximations that are much
easier to work with. So long as you don't get down to the size of
individual particles, Newton's laws work just fine. The error is too small
to notice. Newton's laws are essentially the total effect of all the
molecules of the baseball combined into one object. What one molecule does
isn't going to matter at that level. Quantum mechanics would refer to what
each molecule does, including the forces holding the molecules together. In
the end, it would give the same result as Newton's law for the flight of a
If you are looking at individual particles, you need the precision of
quantum mechanics. If you are looking at something moving close to the
speed of light, you need relativity. If size scale is larger than particles
and atoms, and if speed scale is much smaller than that of light, Newton's
simplified version of physics laws can be used successfully.
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Update: June 2012