What is the Definition of Quantum Physics?

In summary, quantum physics is the field that studies the smallest quantities of physical entities and their interactions. It encompasses sub-fields such as quantum electrodynamics, quantum chromodynamics, and quantum field theory, and is the theoretical basis of the Standard Model of Particle Physics.
  • #36
My take is that what "quantum physics (QP)" is is mainly a semantics issue. The way I have sorted out this particular label for myself is that it is all the semi-classical stuff that came before the notion of a wave function arose; like black-body radiation, Bohr atom, Bohr-Sommerfeld atomic physics, Compton effect, photoelectric effect, deBroglie wave length, etc. Everything later I call quantum mechanics (QM). Once, for example, you start solving the Schrodinger equation you are doing QM, not QP. Again, that is just the way I compartmentalize. But the physics stands on its own, doesn't really need a label.
 
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  • #37
I think, today "old quantum theory", i.e., everything before the formulation of modern QT in three forms by Born, Jordan, and Heisenberg ("matrix mechanics" including field quantization of the em. field!), Schrödinger ("wave mechanics"), and Dirac ("transformation theory") is simply no longer part of quantum physics. You can forget about it completely (except that it is always good to know some of the historical development of our modern point of view).

Then I think usually one distinguishes quantum mechanics (QM) as the non-relativistic theory, which can be formulated in the "first-quantization formalism", as part of the general quantum theory (QT), which also includes quantum field theory. Relativistic QT cannot consistently formulated in the "first-quantization formalism" but most conveniently as a local relativistic quantum-field theory (although the old hole-theoretical formulation of QED by Dirac is in fact equivalent to modern QED but much less convenient).
 
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  • #38
f todd baker said:
My take is that what "quantum physics (QP)" is is mainly a semantics issue. The way I have sorted out this particular label for myself is that it is all the semi-classical stuff that came before the notion of a wave function arose; like black-body radiation, Bohr atom, Bohr-Sommerfeld atomic physics, Compton effect, photoelectric effect, deBroglie wave length, etc. Everything later I call quantum mechanics (QM). Once, for example, you start solving the Schrodinger equation you are doing QM, not QP. Again, that is just the way I compartmentalize. But the physics stands on its own, doesn't really need a label.
No. Quantum physics is the union of pre-1925 quantum physics, quantum mechanics, quantum field theory, quantum statistical mechanics, quantum optics, solid-state physics, etc., including all its approximation methods (in particular semiclassical models).
 
  • #39
So, is this an official naming, like a Newton is the unit of force in the SI system, or is it what you like to call it? I can understand it if you want to call it everything which, in any way, involves the quantum ideas, but I would still contend that the naming is semantic, not really right or wrong.
 
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  • #40
PeroK said:
Understanding what Quantum Mechanics is involves more than finding a soundbite. There are no prizes for describing quantum mechanics in thirty words or fewer.
I got one: Hard.
 
  • #41
f todd baker said:
So, is this an official naming, like a Newton is the unit of force in the SI system, or is it what you like to call it? I can understand it if you want to call it everything which, in any way, involves the quantum ideas, but I would still contend that the naming is semantic, not really right or wrong.
It is what everyone can pick up by looking at how physicists actually use the term. I never heard the term used it in your ideosyncratic sense.

If you trust Wikipedia to give the standard usage you find:
Wikipedia said:
Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles.  It is the foundation of all quantum physics including quantum chemistry, quantum field theory, quantum technology, and quantum information science.
According to this, quantum physics includes (not exclusively) quantum chemistry, quantum field theory, quantum technology, and quantum information science, and quantum mechanics is its foundation.
 
  • #42
A. Neumaier said:
If you trust Wikipedia to give the standard usage you find:
I think "standard usage" is one place where Wikipedia excels.
 
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