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Name: Pete
Status: student
Age: 60s
Location: N/A
Country: N/A
Date: 2000-2001

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.


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 say, "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.

Vince Calder

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 baseball.

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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