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Do concepts in Newtonian Mechanics such as Normal force, etc. still hold true? I don’t mean if you use newtonian mechanics, will it still chunk out the correct computation. What i mean is that does the equations of Newton accurately describe the universe? Im also pointing to Newton’s concept of gravity where objects pull, whereas Einstein’s predictions says that gravity pushes via waves in space-time.

John Smith
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    See also Did relativity make Newtonian mechanics obsolete? – sammy gerbil Dec 18 '17 at 14:21
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    Does general relativity accurately describe the Universe? If so, how do I use it to predict the Super Bowl winner? – WillO Dec 18 '17 at 14:23
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    One of the signs of the "rightness" of a modern new theory, is that it successfully encompasses and returns to the old theory, with the right values in it's equations. So whatever theory supersedes GR, one of the first checks of it is to see can we get GR back out of it, given the appropriate conditions. A line in a textbook that sticks with me is: "some of the material presented here is wrong, but if we are really, really lucky, most of it is wrong" –  Dec 18 '17 at 15:04

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As of today, there's one thing we know: no currently existing theory "describes the universe entirely correctly". The best theories we have are KNOWN to be "wrong" somewhere, in the sense that we know of physically possible situations where we know that the theory doesn't work. In general, we don't have any working theory of which we know that it doesn't break down at Planck scales. General relativity is known to break down ; but our quantum theories don't know how to include gravity in extreme circumstances (in fact, the standard model breaks down long before we are at Planck scales). There are tentative suggestions of what should be done (that's the job of theorists after all), but none has come out as a mature, working theory.

This is in fact not a bad situation, because it avoids hubris...

entrop-x
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  • So how about the most correct theory then? Newton vs Relativity i mean – John Smith Dec 18 '17 at 14:43
  • Well, obviously, General Relativity is "better" than Newton in principle, because Newton's gravity can be derived as an approximation to General Relativity in weak fields and slow motions. For every situation where Newton gives results close to "reality", General Relativity will do so too... at least, if we can solve the mathematical problem. The mathematical problems in GR are way, way harder than in Newtonian gravity, which is why, if Newtonian dynamics is "good enough" we prefer it: the calculations are WAY WAY easier. – entrop-x Dec 18 '17 at 14:47
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General relativity describes gravitation; the normal force is at the microscopic level a combination of electromagnetic force with the Pauli principle (see [this nice question and related answers])(How can I stand on the ground? EM or/and Pauli?), neither of which are incorporated in GR.

ZeroTheHero
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