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For example: Relativistic effects are only especially prominent when approaching speeds close to that of light. But, one can take into account these effects even at low speeds and still get a correct result. Solving basic high-school kinematics problems using relativistic models would be a bit ridiculous and unnecessary--but it works.

In an analog, Quantum mechanics is used to explain and model phenomenon at an extremely small scale. What I'm wondering is, can quantum mechanics be used to explain phenomenon on a larger scale, such as Coulombic or gravitational effects?

Forgive me for my ignorance if the answer is obvious.

God's Drunkest Driver
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  • Like relativity, nothing in the formulation of quantum mechanics limits it to "small" things. I'm not sure what exactly you are asking here. The quesiton of how do explain gravity quantumly is the study of quantum gravity, and still an active field of research. The emergence of the Coulomb force from QFT is well-understood, see e.g. this answer of mine. As written, this question seems too broad to receive useful, focused answers. – ACuriousMind Jan 28 '16 at 18:07
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    Usually a new theory or model merely extends the scope of an existing model - it doesn't only work for the new areas. It should be correct for all already known factors and then also work for the new additions. The usual Newtonian kinematics work for a certain range of speed. The relativistic equations you mention simply broadens this range. – Steeven Jan 28 '16 at 18:08
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    The answer is obvious, but many physicists tend to forget about it, too. The existence of matter and light, on any scale, is a quantum effect. You can't have either without it. If you are looking for a macroscopic quantum state... a superconducting magnet would be a good example. Whether one needs quantum mechanics to explain something is not just a matter of size. If energy gaps are involved, like in the case of a superconductor, quantum effects can persist at any size. – CuriousOne Jan 28 '16 at 18:08
  • @ACuriousMind: I think the OP simply needs a hands on example for QM at work in the macroscopic world. While I agree that the scope is very broad, we don't have to discuss things like the Sunyaev–Zel'dovich effect as part of it, which are completely meaningless for the OP's level of questioning. You have included electromagnetism yourself... that's the kind of thing that people need to understand as fundamentally quantum mechanical effects that also have a classical description for some, but not all, of their properties. – CuriousOne Jan 28 '16 at 18:13
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    Chemistry, by the way, is quantum mechanics redux... without QM even the periodic table is nothing but a phenomenological fact without anything but magic to explain its existence. – CuriousOne Jan 28 '16 at 18:39
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    bose einstein condensates –  Jan 28 '16 at 19:15
  • Superconducting qubits show a wide range of quantum effects, including entanglement. They are several hundreds of microns in size. – DanielSank Jan 30 '16 at 04:25

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Just like relativity, quantum mechanics does apply to large scale which classical mechanics applies, but it seems ridiculous as you tell what happend if we apply relativity to low speed object

Specifically,anything include frequency should have a quantum number n,where E=n*hf ,so the spring "lives"in our scale does have a quantum number n and thus get a quantized energy ,for a spring 0.1kg ,k=0.5N/m delta x =5cm ,we can find out that the frequecy is too small to get an observable energy change since the Planck constant is so small

Thus you can prove that Mawell's theory is true for Bohr model when the shell n becomes very large correspondent with the quantum physics,where Bohr also proposed a theory named correspondence priciple

And what for the object has no apparent frequecy like a moving car? Well depend on what value you desire ,maybe you can find out Ehrenfest's theorem for other thing such as potential But Bohr's correspondence principle still and as it should hold always

cindy50633
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  • Magnetic levitation is got from field but the effect is macroscopic. –  Jan 30 '16 at 04:01
  • polarization to get the cinema 3d effect. It Impacts directly our vision with toy-like glasses. More generally , all the polarization effects encountered in the everyday life. Else, the correspondance principle as you stated –  Jan 30 '16 at 04:12