What is the current status of Newton's Theory of Motion? Is it still a valid theory?

Question

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Answer 1

Newton's laws of motion are known to be false in the general sense. They don't explain motion on a cosmological scale. They don't explain quantum effects.

However they are true within a limited field. They are true when applied to macroscopic entities operating within flat space (not bent as per Einstein's laws). They work very well within normal human experience. Throw a ball, it does as Newton's laws suggest it will.

Einstein's laws and quantum laws can be seen as a refinement of Newton's laws that come into play in the places where Newton's laws break down.

Similar issues apply to relativity and quantum mechanics. They both work spectacularly well in their own scale (large and small respectively) but they are mutually incompatible and so in the strict sense are wrong. They don't explain all the observed behaviors of the universe.

A lot of physics work is directed at resolving this conundrum and coming up with a single theory of everything that explaines all observed phenomena. This hypothetical theory would give the same results as Newtons laws in the places Newton's laws work. The same results for Einstein's laws where they work and similarly for quantum mechanics. But we would then be able to see all observed behaviors in the framework of a single, integrated set of laws. How this will turn out, nobody knows.

So to answer your question directly. Yes, Newton's laws motion are still a very valid theory and are the appropriate laws to describe most of the motion you or I might encounter. You wouldn't want to try and solve a basic trajectory problem with the equations of relativity. You might end up with an answer that is more accurate, but only by a margin that is so small that you couldn't measure it, unless you were in the space business, or super accurate clock business.

Answer 2

For v << c his equations are valid. NASA still uses them for rocket launches and space navigation.

http://exploration.grc.nasa.gov/educatio...