# Quantum scale explanation.

## Main Question or Discussion Point

We all know that Quantum mechanics can be "ignored" when working with systems in which the typical distances and energies are big enough (compared to h, or other quantum constants).
However, when I try to think of an explanation for it I'm not sure I hit the right one.

Let's say I want to work out the Earth-sun System with Quantum Mechanics. That would mean I'd have to build a wave function for every atom in the system, or generally one terrible wave function describing the probabilities of all atoms to be found in certain positions.
Well - when I think about it like that, I imagine a terribly chaotic function.

Does the resolution has to do with the fact that probable deviations of the atoms from their most probable location are in the scale of 10-10[m]? Or is it something else?

Thanks a lot.

Tomer.

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Can you explain to me the quantum scale? Because I need to finish my physics essay, and I'm confused.. Thank you very much.

Well, since no one replyed, I'm probably not the best person to answer you, but as far as I know, Quantum scale is the the scale where quantum Phenomena start showing ;)

From what GRW theories says, it seems it is quantum all the way. As the macroscopic object is described by an equation that governs atomic particles, but just includes collapses more frequently at the macroscopic scale.

Hi Tomer,

I think a first sensible step could be to describe the earth-sun system by using only two particles: one particle with the mass of the sun, and another particle with the mass of the earth. You're actually doing the same in QM when you're describing the proton as one particle: at that level of description (i.e. assuming normal energies and such), it's irrelevant that it is made of quarks; its interior has no effect on its exterior behaviour. Likewise to a first approximation you can assume that the evolution of the earth around the sun is independent of the earth being populated by humans or not, or being made mainly out of protons or neutrons.

Once you're convinced that makes sense, you can realize that the description of sun-earth is identical to the description proton-electron in the hydrogen atom model; you just have to change some symbols and thus orders of magnitude.

But how to go from describing earth-sun as a quantum mechanical atom to the classical description, I don't really know, and I would suspect it depends on what interpretation of QM you're using. That being said, I don't know if every interpretation purports to explain the transition to the classical regime. I think the relation quantum-classical is not settled.