Newtonian or Quantum physics ?

[space stuff]

Newton's laws are true for some extent only. I have read in book that these laws don't hold good at subatomic levels and levels of very high speeds. Here (at subatomic and high speeds) Quantum mechanics and Relativistic mechanics hold good. Why? Why, is it that newton's laws fail at these levels ?

There are some examples which are confusing. Our physics teacher says, there's no reality in quantum physics, it's only based on prediction, and nothing has been proved till now. He gives the example of the discharge tube experiment, in which the electrons move the light paddle wheel. Isn't it Newton's second law F=ma ? (There are some more examples he gave.)

This is what that creates mess in my mind. Is Newton true or Bohr, Heisenberg & Schrodinger (at quantum level)?

Anybody who clears this mess and provides a solid reason that I can counter throw on my teacher is appreciated.

Edited July 19, 2012 by space stuff

[alpha2cen]

Newton's laws are true for some extent only. I have read in book that these laws don't hold good at subatomic levels and levels of very high speeds. Here (at subatomic and high speeds) Quantum mechanics and Relativistic mechanics hold good. Why? Why, is it that newton's laws fail at these levels ?

There are some examples which are confusing. Our physics teacher says, there's no reality in quantum physics, it's only based on prediction, and nothing has been proved till now. He gives the example of the discharge tube experiment, in which the electrons move the light paddle wheel. Isn't it Newton's second law F=ma ? (There are some more examples he gave.)

This is what that creates mess in my mind. Is Newton true or Bohr, Heisenberg & Schrodinger (at quantum level)?

Anybody who clears this mess and provides a solid reason that I can counter throw on my teacher is appreciated.

 

There are many differences between two theories.

 

About energy level

 

Newton's low is a continuous energy level

_____________________________________________>

 

Quantum theory

quantized energy level; discontinuous energy level, and there is a gap between levels.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - ->

 

Newton's 1st law say "Inertia". It means there is a energy level. But, the level is not quantized.

[studiot]

Why do you want to throw anything at your teacher?

[D H]

Why, is it that newton's laws fail at these levels ?

Newtonian mechanics implicitly makes some assumptions about various physical behaviors that simply are not true. So what are these invalid assumptions? Just as a starter,

• Displacement is absolute. Newtonian mechanics assumes that a meter is a meter, which is not true. Length contraction is key consequence of special relativity.
   
  
• Time interval is absolute. Newton went into detail on absolute versus relative time in his scholium to his definitions, the portion of Newton's Principia that precedes his laws of motion. Newton's concept of relative time is still absolute. He assumes two observers equipped with ideal clocks will always agree on time intervals. They won't. The Hafele–Keating experiment demonstrated that this Newtonian assumption is false.
   
  
• Velocities are additive. That the speed of light is the same to all observers makes zero sense in the framework of Newtonian mechanics. Something had to give. That velocities add vectorially is one of the things that had to give.
   
  
• Mass can be broken into infinitesimally small pieces. Newton and Leibniz invented the calculus as an aid to advancing physics. The assumptions implicit in differentiation and integration don't jibe with the quantum nature of the universe.
   
  
• Position and velocity are knowable to infinite precision. You cannot know both position and velocity (momentum) to infinite precision. The Uncertainty Principle gets in your way.
   
  
• For each action, there is an equal but opposite reaction. Newton's third law fails subtlety with various electrodynamic forces, and fails miserably in the quantum domain. The very concept of "force" pretty much fails miserably in the quantum domain.

 

With all these problems, why is it that Newtonian mechanics does work so well in our mundane world? The answer is these assumptions are very close to correct in the limit of largish positions (so as to avoid quantum mechanics), smallish velocities (so as to avoid special relativity), and smallish masses (so as to avoid general relativity). We don't see the deviations between reality and Newtonian mechanics in our mundane, everyday world because these deviations are incredibly small in this domain. They're hidden in the noise.