Why Isn't Newtonian Physics Wrong??

[Akul]

Well, it's being said that theories and properties being done in Quantum physics proves the hypothesis and lemmas of Astrophysics. So scientifically, micro-molecules and femto-molecules actually resemble Mega-molecules and Zeta molecules. In contrary, quantum physics disapproves the laws of Newtonian physics which are vastly applicable to Macro-molecules (i.e; from milli to kilo). What I would say is that, may be Newtonian physics is wrong and quantum physics is right; may be quantum physics holds good for molecules of all sizes; and the fact that newtonian physics is obeyed by the macro-molecules may be because of practical aberrations. Any comments??

[pzkpfw]

Everything has an area of applicability. Different models are "better" or "worse" in different contexts.

 

Say you are asked how fast you'd be running - with relation to the ground - if a train was going South at 10 km/h and you are running South along the top of the train at 10 km/h. Probably you'd say 20 km/h.

 

You'd be wrong, but at those low speeds you'd be close enough, and there's no need to bring relativity into it.

 

Newtonian physics is still plenty good in plenty of areas of applicability. Sure it's "wrong". But it's "good enough".

[ajb]

...and the fact that newtonian physics is obeyed by the macro-molecules may be because of practical aberrations. Any comments??

You might be interested in Ehrenfest's theorem, which loosely says that in quantum mechanics Newton's laws on average hold. You might also be interested in Bohr's correspondence principle which says that when we have a large number of constituents quantum and classical mechanics give the same answer. (Making that more mathematically precise is hard). Also Dirac's minimal canonical quantisation procedure springs to mind here, which is loosely "replace Poisson brackets with commutators".

[pwagen]

Sure it's "wrong". But it's "good enough".

Very strongly reminds me of Asimov's "The Relativity of Wrong", which I believe can be applied here.

 

http://chem.tufts.edu/answersinscience/relativityofwrong.htm

[spocktorwho]

We use Newtonian equations when quantum effects can be ignored because they are so small. So technically it would be wrong, but it's good enough for that certain problem.