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This question already has an answer here:

Why are we teaching an outdated theory when the math in general relativity isn't that hard? I really don't see a reason why we should teach a highly oversimplified theory in our schools. For me, it's like teaching that atoms are small balls that cannot be divided any further.

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marked as duplicate by Kyle Kanos, David Z Dec 24 '14 at 4:42

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    $\begingroup$ It's not false, it just doesn't describe the universe (as a whole) or deep gravitational wells. It works perfectly fine for our everyday life. In fact, GR, taken in the limit of weak fields leads to Newtonian mechanics. $\endgroup$ – Kyle Kanos Dec 24 '14 at 4:09
  • $\begingroup$ @KyleKanos why did you post that as a comment instead of an answer? $\endgroup$ – DanielSank Dec 24 '14 at 4:22
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    $\begingroup$ @DanielSank: I wasn't convinced we hadn't had this question before, so I posted it as a comment while I searched (and found) the duplicate. $\endgroup$ – Kyle Kanos Dec 24 '14 at 4:24
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Two reasons.

First, I strongly recommend Asimov's essay Relativity of Wrong that explains very concisely and clearly why questions such as this one are more wrong than Newtonian physics.

Second, the concepts of Newtonian physics are necessary for explaining pretty much anything in physics, including general relativity and quantum mechanics. These explanations usually go like this: "Take Newtonian physics and slightly modify this parameter (for GR) or that parameter (for QM)".

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    $\begingroup$ That's a great essay, Michael. I would put a short summary in your answer, something like " ... superseded theories are not so much wrong as incomplete". Also, I think the last sentence is a little misleading. It's not one single parameter that is tweaked but more like trying to imagine a more complete framework that fits with the former framework: GTR is very different in grounding than NG but part of the new theory has to be in explaining how the former arises. Likewise for QM. $\endgroup$ – WetSavannaAnimal Dec 24 '14 at 8:48
  • $\begingroup$ @WetSavannaAnimalakaRodVance: OK, my modify parameter comment was a bit simplistic. I was kind of hinting two things: first, Newtonian physics being a limit of GR and QM with $c\to\inf$ and $\hbar\to 0$ respectively, and second, deriving commutator relations in QM from Poisson bracket of classical mechanics. $\endgroup$ – Michael Dec 24 '14 at 18:00
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Classical mechanics are very important for everyday physics. For the energy scales, relative velocity differences, and mass scales that we experience is our everyday lives, Newtonian physics provide us with an extremely valuable tool of predicting outcomes of events. In other words Newtonian physics are an accurate enough approximation to the more precise theory, special relativity.

Lets not forget that Newtonian physics is accurate enough to take us to the moon!

Other than that some conservation laws from Newtonian physics carry on to the rest of physics, for example conservation of energy and momentum. A young physicist would therefore need a lot of experience with applying these laws, and the best way to do this is with the more 'intuitive' Newtonian physics.

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Because you dont need general relativistic (tensors ,differential geometry etc) calculation to send a rocket to the moon.

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    $\begingroup$ Assuming that the OP genuinely needs an answer, this answer will only prompt another "Why" question. It might be helpful for the OP if you include that answer here as well, elaborating a bit on this. No offense meant. :) $\endgroup$ – User Anonymous Dec 24 '14 at 5:38
  • $\begingroup$ Source on that? $\endgroup$ – Madde Anerson Dec 28 '14 at 4:36
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(1) We shall never have the right to affirm categorically of any one of the principles of the mechanical and physical theory, that it is true. (2) We are not allowed to affirm of any one of the principles on which the mechanical and physical theory rests, that it is false, so long as there has been no discovery of phenomena that disagree with the consequences of the deduction of which this principle constitutes one of the premises.

What I have just said applies particularly to the principle of inertia [or, in this case, the principles of GR]. The physicist has not the right no say it is certainly true; but still less has he the right to say it is false, since we have so far met with no phenomenon (if we leave out of consideration the circumstances in which the free will of man intervenes) that compels us to construe a physical theory from which this principle would be excluded.

Pierre Duhem, "Note on the Validity of the Principles of Inertia and Conservation of Energy"

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