Classical physics vs quantum physics

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SUMMARY

Classical physics and quantum physics are fundamentally interconnected, with classical laws emerging as approximations of quantum laws. The discussion clarifies that while all classical physics can be derived from quantum mechanics (QM), not all quantum phenomena can be explained through classical frameworks. The distinction lies in the mathematical representation and the scale at which these laws operate, emphasizing that classical physics describes average behaviors of quantum systems.

PREREQUISITES
  • Understanding of quantum mechanics principles
  • Familiarity with classical mechanics concepts
  • Knowledge of mathematical frameworks used in physics
  • Basic grasp of macroscopic vs. microscopic phenomena
NEXT STEPS
  • Explore the mathematical foundations of quantum mechanics
  • Study the implications of quantum mechanics on classical physics
  • Research the differences in behavior between macroscopic and microscopic systems
  • Investigate the role of approximation in deriving classical laws from quantum principles
USEFUL FOR

Students of physics, educators in science, and researchers interested in the foundational principles of physics and the relationship between classical and quantum theories.

jd12345
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Why do we say that classical physics is a lot different from quantum physics?

The laws that determine the macroscopic world should be derivable from quantum laws. So in a way the Newtonian or classical laws are basically quantum laws( maybe a bit approximated)
So why differentiate between macroscopic and microscopic world?
 
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Why do we say that classical physics is a lot different from quantum physics?
We don't (except by mistake). We say that quantum physics is different from classical physics :)

All dogs may be animals but not all animals are dogs.
All classical physics is a consequence of quantum - but not all quantum physics can be described classically.

Technically - classical physics is what QM does on average ... so the math is different.
 

Thread 'Two equivalent statements of time reversal symmetric Hamiltonian'

Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?
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