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Is Quantum Mechanics and Quantum Physics the same?

  1. Sep 20, 2005 #1
    I have this debate with my colleges several times and I cant stress how much I would like to get this settled. Quantum Mechanics is STRICTLY done by math. While quantum physics could be any where from the general therios which you experiment and debate and do all kinds of scientist like stuff. Am I wrong or right?
     
  2. jcsd
  3. Sep 20, 2005 #2

    reilly

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    For all practical purposes, the two names are interchangeable.
    Regards,
    Reilly Atkinson
     
  4. Sep 20, 2005 #3

    chroot

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    Quantum physics is a branch of physics which includes several theories, such as quantum mechanics, quantum electrodynamics, and quantum chromodynamics.

    - Warren
     
  5. Sep 21, 2005 #4

    dextercioby

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    Erase the word "quantum". Is "mechanics" equal to "physics" ? My guess is no. :wink: As "mechanics" is a part of "physics", so is "quantum mechanics" a part of "quantum physics.

    Daniel.
     
  6. Sep 21, 2005 #5

    George Jones

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    I, too, think that the term "quantum physics" refers to the very general application of quantum principles. Often, when someone uses "quantum mechanics" in a very general context, I would prefer the use of "quantum physics" or "quantum theory."

    I think the titles of university courses have had an effect on which terms are used. A typical sequence of courses is: Quantum Physics; Quantum Mechanics; Quantum Field Theory. This gives the (false) impression that quantum physics is less advanced than the others.

    As others have said, all this comes under the umbrella of quantum physics.

    Regards,
    George
     
  7. Sep 21, 2005 #6

    reilly

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    In some instances, physicists are careless with language. Try the following, do a Google search with quantum, and any of the words, theory, mechanics, physics. You will see that all three are sometimes used interchangeably.
    Regards,
    Reilly Atkinson
     
  8. Sep 22, 2005 #7
    But ultimatly are they the same which I highl dought is no I figured you people would have a simple answer for me and sorry to say as far as I know i dont think they could be used interchangeably. Ill explain when you reply with how?
     
  9. Sep 22, 2005 #8
    NO this follows the Historical order of what came first and what is more fundamental. 1900/1905 to 1925 was the start and growth of Quantum Theory (or Physics if you like). To answer many questions not yet answered by QT, there came in 1926/27 Quantum Mechanics, a mathematical theory that could be there without QT first. As a response to problems some had with QM, came the growth of QFT. I believe at its core Field Theories are also “statistical problematic” (Throwing Dice), so it’s probably fair to say that QM uncertainty is fundamentally needed first for field theories.

    Where Einstein would have preferred to keep Quantum Theory “deterministic” or ‘local’ (not throwing dice) the only currently active theories under Quantum Theory are non-deterministic ones like QM, QFT, etc.

    Thus QM is the root for all current theories, Strings, Standard Model, MWT, etc. And through QM therefore rooted in the original Quantum Theory. I don't believe we have any serious current theories (advanced or not) rooted in Quantum Theory without an element of the uncertainty principal of QM. But there could be, so no the names are not interchangable.
     
    Last edited: Sep 22, 2005
  10. Sep 26, 2005 #9

    reilly

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    As the philosophers have noted: a name is not the same thing as the thing named. If you look through the literature you will indeed find many instances of quantum theory, quantum mechanics, and quantum physics used interchangeably. (Note; that does not mean that some do not attempt to be more precise than others.) And, for goodness sake, what's the big deal if the three terms form an equivalence class? It's the subject matter, that to which the name is applied that is important.

    Regards,
    Reilly Atkinson
     
  11. Sep 26, 2005 #10
    tuche.......................
     
  12. Sep 29, 2005 #11
    Einstein would say it’s the different subjects that makes naming them correctly a big deal.

    He never had a problem with Quantum Theory, just the narrower subject area of Quantum Mechanics providing one possible answer to the questions of Quantum Theory. There is plenty of room within Quantum Theory for additional ideas that do not include the uncertainty of the Theory of Quantum Mechanics. But you shouldn’t expect to hear much about those ideas unless one merits being described as a theory by showing at least a little of the success that QM has shown.
    Einstein never gave up on that. If he would have been successful, it would not have been QM anymore, but still a part of the Quantum Theory he’d original started with Planck etc.
    RB
     
  13. Sep 30, 2005 #12

    reilly

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    RandallB-- Your take, I would suggest, differs from that presented by A. Pais in his wonderful biography of Einstein, "Subtle is the Lord....The Science and Life of Albert Einstein. Pais in his own words, and in quotes from Einstein uses the three terms quite interchangeably -- particularly, see pp.440-449 in the Chapter entitled Einstein's Response to the New Dynamics. There's a good discussion in this chapter on Einstein's troubled with Quantum X, and some of his debates with Bohr -- all of which is discussed elsewhere in the book.

    I will grant you that historically there is the Old Quantum Theory of Bohr-Sommerfeld orbits, particulate photons and so on; and the New Quantum Theory of Heisenberg, Schrodinger, Born and Dirac. But the Old theory had lots of problems, so it's only of historical interest, one that is, I suspect in decline.

    And, note QFT can easily be fit in to what you call the "narrower subject area of Quantum mechanics" It's all about the choice of Hamiltonian, and the representation of states -- like Fock Space for systems with indefinite numbers of particles.; the formal dynamical properties of QFT are well described by traditional QM/QT/QP-- see Dirac's book, many of the early papers by Heisenberg, Pauli, Dirac, Weisskopf on QFT and QED written in the 1930s.
    Regards,
    Reilly Atkinson
     
  14. Oct 1, 2005 #13
    Reilly

    I suspect you may have missed my point, that QM is a subset of theories within the larger set of theories contained within Quantum Theories.
    I didn’t find any real conflicts in the reference you gave, just be sure to interpret statements like Einstein’s complaint about the “new quantum theory” as a complaint about “A theory” that is trying to interpret the whole of Quantum Theory correctly. That is, if you were to somehow invalidate QM though some falsifiable experiment it would not invalidate QT as there are several other non-QM approaches that might be useful to greater investigation.

    Maybe part of the problem in the term “narrower”. Consider other sets of theories 1)Classical or 2)Mystical or 3)Canonic (Bible) Theories all three could be built within Quantum Theory. All 4 when we include QM are each ‘narrower’ than Quantum Theory, logical as they do not include each other. But “narrower” does not mean small. But due to not providing adequate real scientific results all above all are quite small, with the exception of QM. In fact QM is huge, because it has produced productive scientific results. But still a subset of QT.

    I understand this may seem like semantics, but to scientists that should be important. You see it all the time in the popular press that Einstein didn’t: get, understand, was spooked by, had a problem with, never agreed with, Quantum Theory. It’s simply not true, he helped invent it and would have been excited by any interpretation of QT that might disagree with QM and help define what he considered “unknown variables”. It was QM not Quantum Theory in whole he had problems with. For a little more insight on the distinction try Louis de Broglie book “New Perspectives in Physics” (1962) as he reflects on his own history with QM vs. Quantum Theory.

    RB
     
  15. Oct 1, 2005 #14
    So is Quantum defined by the definition of "Foo Fighters" (see Will 'O Wisp post here and at abcnews.com), Such reports given by Aircraft Pilots, the two "Theorys of Lights", for which should come together in the name of Quantum. Well, I think my brain is too charged here to communicate efficiently, and I am only a high school grad. And I love to ask questions. Take a break and go into abcnews.com message boards. I know, I'm just trying to link your great minds to the great minds under Science and Technology. Anyway, I would love to understand the definition of Quantum....is it that of "matter" turning into another form of "matter"?
     
  16. Oct 1, 2005 #15

    reilly

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    RandallB -- Why not just say Physics? Granted, I've got a small brain full of linguistic and semantic contabulations, but I fail to see what in "Quantum Theory" would stay if, somehow, mainstream QP/T/M were shown not to be true. Precision of language is not always nor necessarily a hallmark of physics -- note the conditionals.

    Leah -- Do a Google. Quanum physics is what quantum physicists do.

    Regards,
    Reilly Atkinson
     
  17. Oct 2, 2005 #16
    all semantics
     
  18. Oct 3, 2005 #17
    I did (see post #8); I don’t see much problem using Quantum Theory or Quantum Physics interchangeably, at least not as bad as using Quantum Mechanics as being the same as either one.

    I don’t see the logic in your other question. Taking your “QP/T/M” as meaning Quantum Theory and Quantum Physics and Quantum Mechanics all being shown not to be true, then of course nothing in Quantum Theory “would stay”.

    The point is QM vs. QP/QT. QP/QT comes from Planck/Einstein 1900/1905 defining energy and even light as integer multiples of some smallest “packet or quantum of energy”. Later named a photon for light. The whole idea of light and energy coming in quantum steps, rather than a continuously measurable (dividable in ever smaller quantities) begs the question. How does that work?
    All the theory of Quantum Mechanics (1925+) does is attempt to answer that question.
    If QM is somehow shown to be wrong, it would not invalidate the premise or questions established by the original wider area of QP/QT.

    Now QM has done an impressive job at predicting statistical results by creating mathematical models that match observations. It has not been able to directly answer the question “How does that work”. Which is why there are so many additional theories within QM that are attempting to do so; Strings, M theory, 4D Strings etc.

    The question QP/QT vs. QM deserves a better answer than “it’s all semantics”.

    RB
     
  19. Oct 3, 2005 #18
    Name a theory in physics that can tell how anything really works. One can ask "but how does that work then?" just like a 3 year old can keep asking "why?" until his/her parent can't help to do anything but to admit defeat.
     
  20. Oct 3, 2005 #19

    ZapperZ

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    Can you please cite for me any credible source where such an exercise in this dichotomy is actually done? Even from the philosophy aspect, I have never of no one spending time differentiating such a thing. When you open a "Quantum Physics" text, does it clearly say where quantum physics end, and quantum mechanics starts? Would you consider Schrodinger Equation to be in quantum physics, or quantum mechanics? Under what authority are you able to claim that there is such a distinction?

    This is like saying MRI is different than NMR. For a person who has no clue what those two are, the difference in semantics is everything. But for anyone who understands the PHYSICS of those two, there's no difference! Luckily, this is physics, and human language that is filled with unforseen connotations is often irrelevant. Physics is ALWAYS based on clearly, underlying mathematical description (look at the String theory that you were touting). This is the only thing that makes a difference. It is why I claim that QM (or quantum physics) cannot be understood if one is ignorant of the mathematics.

    Zz.
     
  21. Oct 3, 2005 #20

    selfAdjoint

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    MRI and NMR are different beasties. NMR is Nuclear Magnetic Resonance, an experimental analytical technique. MRI is Magnetic Resonance Imaging, an exploitation of NMR plus other techniques to achieve biological imaging. To say they're the same is like saying television and electromagnetism are just the same.

    Aside from that, any history that presumes to relate quantum history to some proposed distinction between quantum physics and quantum mechanics must also treat the "Old Quantum Theory" of Bohr. I do believe "quantum mechanics" was introduced when they could actually do Hamiltonians and such.
     
    Last edited: Oct 3, 2005
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