Quantum physics vs. Quantum Mechanics

  • Thread starter WarrickF
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  • #1
WarrickF
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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?

Thanks
Warrick
 

Answers and Replies

  • #2
There really is none.
 
  • #3
Berislav
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AFAIK, quantum physics is usually used as the more general. It is quantum mechanics and quantum field theory.
 
  • #4
Pengwuino
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One of my professors said that theorizing about something is physics, putting equations to it is mechanics.
 
  • #5
WarrickF
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Great thanks - I thought I was going crazzy :)
 
  • #6
dextercioby
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Pengwuino said:
One of my professors said that theorizing about something is physics, putting equations to it is mechanics.

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

Daniel.
 
  • #7
Galileo
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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.
 
  • #8
dextercioby
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Galileo said:
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.

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

Daniel.
 
  • #9
vanesch
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Galileo said:
The way I see it is that quantum physics is more general than quantum mechanics.

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.

cheers,
Patrick.
 
  • #10
preet0283
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quantum mechanics deals with the algebra of the operators assigned to the observables.
 
  • #11
Telos
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From the current Wikipedia article on Quantum Mechanics.

We will use the term "quantum mechanics" to refer to both relativistic and non-relativistic quantum mechanics; the terms quantum physics and quantum theory are synonymous. It should be noted, however, that certain authors refer to "quantum mechanics" in the more restricted sense of non-relativistic quantum mechanics.
 
  • #12
Juan R.
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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?
 
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  • #13
Simonne
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: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?!
Help!
 
  • #14
Astronuc
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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.
 
  • #15
Simonne
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Thanks!!! :biggrin:
 
  • #16
Anonym
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I'm a Literature buff writing a health and diet book desperately trying to comprehend Quantum Physics so I can sum it up.

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.
 
  • #17
Simonne
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Ok! Will do!
Cheers,
Simonne
 
  • #18
Surrealist
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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)
 
  • #19
George Jones
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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)

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".
 
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  • #20
Anonym
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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.

Or that Quantum Mechanics is not a field theory.

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

Not yet.

Physics is ALWAYS based on clearly, underlying mathematical description. This is the only thing that makes a difference.
And considering we are talking about PHYSICS here and not how we SPELL a word, that is the criteria that *I* am using. What criteria did YOU use?

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.
 
  • #21
Asiadeep
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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.
 
  • #22
rewebster
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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.

I can be confused if I read this.
 
  • #23
Anonym
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I can be confused if I read this.

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.
 
  • #24
Anonym
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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.

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.
 
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  • #25
reilly
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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.

Regards,
Reilly Atkinson
 
  • #26
Anonym
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I guess you somehow did not get the gist of my comment (#9), which plainly says that all do not subscribe to treating all three names interchangeably. Perhaps the problem that my language is too subtle.

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.

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.

The problem is not with your language, the problem is with your attitude. You are not doing math-ph and therefore for you there is no difference. The three terms do not form an equivalence class, similarly as the Newtonian mechanics vs EM vs GR. The vector derivative (rot, curl) does not exist within the classical analysis. The vector analysis is a different math framework; GR curvature does not exist within the vector analysis. In QM the situation is very similar. You can’t describe spin (Pauli-Schrödinger) within complex Hilbert space framework, you need 4-dim C2 algebra of the Pauli matrices. The spin coupled with the magnetic field says that you are already in relativistic QM.

Of course it's all semantics; last I knew, semantics is the study of meanings, which is clearly what this thread is about (sorry about ending a sentence with a preposition, for which I apologize).

I do not agree that this thread is about semantics or meanings. It reminds me slightly the discussion in “Einstein and the Physics of the Future” (“Some Strangeness in the Proportions”, Addison-Wesley (1980)).

Your position seems to me close to S. Weinberg concluding comment (p.506):”I think the theoretical physicist is like the drunk in the story who has lost a quarter. He has no idea of where he lost it, but he’s looking under a lamp post because that is where the light is good.”

I was educated on other version of that story:”The man has lost a quarter and he’s looking under a lamp post. One would like to help him. “Where you lost it?” Over there, about 20m from here.” If so, why you are looking here?” “Because no light there!” (“Physicists jokes”; compare SU(5) and all GUT's).

Then S. Weinberg continues:”However, I always sympathize with the drunk. Because it is true. He doesn’t really know where he lost the quarter, but if he looks for it anywhere else but where the light is good, he is sure not going to find it.”

I do not sympathize with that man. He lost his quarter where the light was obscure; he never was in the area of the absolute darkness. He doesn’t need a good light, since the quarter always just in front of his eyes. As an example what I have in mind, I suggest reading two pages paper by F.J. Dyson “Feynman’s proof of the Maxwell equations”, Am. J. Phys., 58, 209 (1990).

Regards, Dany.
 
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  • #27
sarastar6
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  • #28
sarastar6
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hello everybody,



i wanna ask if anyone could help me in studying the hydrogen atom in high dimensions.

and am sorry as i am new here maybe i dont use this forum in the propper way.



thank u:smile::smile:
 

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