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Quantum physics vs. Quantum Mechanics

  1. Jul 15, 2005 #1
    Hi All,

    I’m sorry if this is a silly question, but can someone please tell me what the difference between Quantum physics and Quantum Mechanics is?

  2. jcsd
  3. Jul 15, 2005 #2
    There really is none.
  4. Jul 15, 2005 #3
    AFAIK, quantum physics is usually used as the more general. It is quantum mechanics and quantum field theory.
  5. Jul 15, 2005 #4


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    One of my professors said that theorizing about something is physics, putting equations to it is mechanics.
  6. Jul 15, 2005 #5
    Great thanks - I thought I was going crazzy :)
  7. Jul 15, 2005 #6


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    No, no, "mechanics" in "Quantum Mechanics" stands for the science's name. :wink:

  8. Jul 15, 2005 #7


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    The way I see it is that quantum physics is more general than quantum mechanics.
    Quantum physics is the name for a collection of quantum theories: (non)relativistic quantum mechanics (also including quantum optics) and quantum field theory.
    Just like classical physics is a collective name for classical mechanics, electromagnetism and relativity.
  9. Jul 15, 2005 #8


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    I partly agree. Of course, you forgot classical statistics and (non)relativistic thermodynamics. And quantum statistics :wink:

  10. Jul 15, 2005 #9


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    Indeed ; I thought quantum theory is the conceptual framework of Hilbert spaces, operators, and all that, which you can then apply to different, more concrete, models.
    One such model is non-relativistic mechanics of point particles, and the result is then quantum mechanics.
    Another such model is relativistic fields (or relativistic point particles, which turns out to give the same result), and the result is then quantum field theory.
    Still another model are relativistic strings, and the result is string theory.

  11. Aug 5, 2005 #10
    quantum mechanics deals with the algebra of the operators assigned to the observables.
  12. Aug 6, 2005 #11
    From the current Wikipedia article on Quantum Mechanics.

  13. Aug 6, 2005 #12
    I see many confussion here.

    No the Wiki is not correct.

    There is no relativistic quantum mechanics. Both Dirac equations and Klein/Gordon wave equations are wrong equations, when examinated in detail. The only consistent relativistic quantum formulation is relativistic quantum mechanics which is not a quantum mechanics in original sense and does not use original Dirac and Klein/Gordon.

    As perfectly explaned by Galileo above, classical electrodynamics, thermodynamics, and mechanics build classical physics.

    For instance, Electrodynamics is that part of science does not reduced to mechanics that explain electromagnetic phenomena.

    At quantum level, things are similar. Quantum physics is not a synonym for quantum mechanics. Mechanics is only about movement, electromagnetic phenomena cannot be reduced to mechanics alone, and thus there exists quantum electrodynamics.

    Also there is a quantum thermodynamics, that, of course, cannot be explained in pure mechanical terms. In fact, quantum thermodynamics cannot be constructed from usual Hilbert space formulation and one needs of more general formalisms, e.g. Liouville space and supermatrices.

    As a final note, of course, quantum physics and quantum theory are not synonimous. Quantum physics is the collection of quantum theory more quantum experimentation. Or physics is not one of experimental sciences?
    Last edited: Aug 6, 2005
  14. May 28, 2007 #13
    :bugeye: Wow! I feel like an spy in a strange new land! I'm a Literature buff writing a health and diet book desperately trying to comprehend Quantum Physics so I can sum it up and googled Quantum Physics Vs Quantum Mechanics and most of this is going over my head! Most? Who am I kidding?! All of it! Can I ask someone - in Penrose's book 'Shadows of the Mind' - he talks about Quantum mechanics showing that our concept of matter has suffered a similar fate to that of our old concepts of the nature of time and space since Einstein's general relativity discovery. (*big breath in*) Can I use the term Quantum Physics here, or does it have to be quantum mechanics? And is the lay person going to know/care?!
  15. May 28, 2007 #14


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    Some people, even some teaching physics, apparently use quantum physics interchangeably with quantum mechanics, which is not correct.

    Quantum mechanics is a subset of quantum phyiscs, which includes quantum electrodynamics, . . .

    If one is concerned about particles and particle (matter) interaction, then referring to QM is appropriate.

    I don't believe a lay person will care, or even be aware of a distinction, unless that person has researched the fields of QM and QP.
  16. May 28, 2007 #15
    Thanks!!! :biggrin:
  17. May 28, 2007 #16
    It will be great fun to read cooking prescriptions based on methods of QFT. Please provide ref when you will finish writing. I will be happy if it will be also practical but it is only sufficient and not necessary condition.

    Regards, Dany.
  18. May 29, 2007 #17
    Ok! Will do!
  19. May 29, 2007 #18
    at most Universities,
    quantum physics = intermediate level, (for college seniors, e.g. Griffiths)
    quantum mechanics = semi-advanced level, (for first year graduate student, e.g. Sakurai's MQM)
  20. May 30, 2007 #19

    George Jones

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    Yes, most universities do this, but often it occurs a year earlier - between third year and fourth year of undergrad.

    I don't really agree with this labeling. I gave my opinion in this https://www.physicsforums.com/showthread.php?t=90002".
    Last edited by a moderator: Apr 22, 2017
  21. May 30, 2007 #20
    Or that Quantum Mechanics is not a field theory.

    Wikipedia:” the terms quantum physics and quantum theory are synonymous”

    Not yet.

    I suggest the following criteria: the quantum physics is everything that satisfy delta(x)*delta(p)>h/2; the QM = non-relativistic version of QT(completed); the relativistic QM=unified theory of strong and electroweak interactions (not completed yet) and general QM= unified theory of electroweak, strong and gravitational interactions (not formulated yet).

    Regards, Dany.
  22. Jun 2, 2007 #21
    I'm not a professional physicist or anything but as far as I understand quantum physics is the whole science to it including all the maths and such however transforming it to something more practical tends towards quantum mechanics.
  23. Jun 3, 2007 #22
    I can be confused if I read this.
  24. Jun 4, 2007 #23
    My impression also that Juan R. statement is logically inconsistent. Both Dirac and Klein-Gordon equations are certainly not wrong and it is not clear what he mean QM in original sense.

    However, don’t present yourself as the Schrödinger’s Cat. If you are the macroscopic system then you may be confused or not and not in the superposition of that states.

    Regards, Dany.
  25. Jun 5, 2007 #24
    I would like to add how I understand word “wrong”. Consider Galilean world vs SR. Is it wrong? I think the answer should be no. However, it is not adequate. The process of knowledge acquisition takes time. The average time required for the adequate formulation of the physical theory is of order 100 years.

    The relativistic equations of motion are not adequate but the Dirac equation, for example, is outstanding approximation. Dirac equation does not predict the existence of quarks, but it have to. You want something better? Write it. Dirac tried to improve it all his life. However, in order to reach it, you should move. QED leads to divergences. Clearly it is artifact. But you should move forward. Renormalization allowed to leave EM and to move into the physics of weak and strong interactions. Then C.N. Yang and R. Mills established the connection with the classical EM and gravitation (W. Pauli sleeped away it). Now you may perform examination in details since you know the details.

    One should comprehend that there is no final theory and never will be. To any new generation of physicists will remain what to do, more than before, more difficult than before and more sophisticated than before. The Weinberg’s dream is nonsense. But the Hamilton’s and Schrödinger’s dream is what you will see in your lifetime: the entire reformulation (generalization) of all of the classical physics in terms of wave mechanics.

    What about QG? I consider the present experimental techniques (CW) obsolete. The theorists should wait for the opportunities that the optical pulse compression will open. I expect that it will allow the intentional experiments in cosmology performed on the laboratory table of the average university. Then we will know. And obviously it is not the end of the story.

    Regards, Dany.
    Last edited: Jun 5, 2007
  26. Jun 5, 2007 #25


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    In a similar, earlier post in a similar thread i noted that many physicists use quantum theory and quantum mechanics quite interchangeably. I always have, as have many physicists far more celebrated than I. This can be demonstrated simply by looking at different texts and books. It's no big deal.

    juan r -- How do you explain 50 or so more years of the triumphs of relativistic QM. What's the problem with say computing the lifetime of the pi-0 meson, or the photoproduction of muons, ..... To say there is no relativistic QM is completely at odds with the past 70 or 80 years of experience.

    Reilly Atkinson
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