# Physics background for Quantum Mechanics

Very often on this site people ask what background in math is needed to be able to understand quantum mechanics (based on a short search of this site). So that question is answered. However, I want to know what background in PHYSICS itself is needed for QM. I can hardly imagine that a mathematician with no/very little knowledge of physics would be able to grasp QM. So, what background in Physics is needed to be able to understand and appreciate QM to the max?

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Related posts on Math.SE and Mathoverflow. – Qmechanic Feb 10 '13 at 20:34

Nobody should ever venture into QM without a working knowledge of Hamiltonian Mechanics: the meaning of the Poisson brackets with the Hamiltonian has a natural extension in QM Ehrenfest's theorem. Understand classical Liouville's theorem, and you won't be puzzled by the uncertainty relations in QM. Working with the Least Action Principle will prepare your mind for the path integral formulation, although they are not the same thing. The meaning of the Hamiltonian itself...

Of course, electromagnetism and any other branch of physics will help but, compared to Hamiltonian Mechanics, it is secondary.

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A solid understanding of the following is sufficient for much of elementary QM:

1. Classical Hamiltonian mechanics, in particular conservation of energy, momentum, and angular momentum, and the Kepler problem (planet and sun).

2. Some elementary optics: The wave equation, and how to solve it using the Fourier transform. Superposition principle and interference patterns. Perhaps the derivation of geometric optics from the wave equation.

As you proceed to more advanced QM topics, you need more and more physics, ultimately everything.

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A solid understanding of Classical Mechanics and Classical Thermodynamics would be adequate.

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What about classical electromagnetism? – SmellyCat Nov 18 '12 at 22:06
You are right; Pardon me. I would say it is not as critical as the first two, in my opinion and experience. It is nice to have seen a lot of classical electromagnetism before you get to the Hydrogen Atom and such ilk. In general, most results from books such as Griffiths and Shankar do not require an intense knowledge of Classical E&M. I would say it is nice, but not as necessary as the first two I listed – Dylan Sabulsky Nov 18 '12 at 22:10

This might be a restatement of some of the answers already given. In my opinion you can look at physics as a simple video game: completing a level unlocks the next. In this case after completing classical physics you can move onto modern physics. To fully grasp the concept of qm you have to have a good understanding of Hamiltonian mechanics, electromagnetic waves(optics), thermodynamics, electromagnetism and also relativity. In a nut shell, the bear minimum you need to know is the aspects of classical mechanics that are different for quantum mechanics. If particles behave as waves, you should know how waves function (geeky physics pun) or if you want to know how to violate the law of conservation of energy in a very short time frame you should know how to use the conservation of energy in classical mechanics and so on.

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