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Quantum mechanical effect such as quantum mechanical tunneling, quantum mechanical confinement, quantum entanglement, or any other quantum mechanical effect to which I may not be aware, what is the largest scale that we have seen/verified these effects to have taken place at? Is it at the sub-atomic scale, at the atomic scale? At the molecular scale? At the complex molecular scale? At what scale do these effects drop off?

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    $\begingroup$ There are at least two meanings this could have: do you want scale in terms of number of atoms involved, or scale in terms of actual size of the system (i.e., one photon or something that is in a superposition of being in two places that are km apart)? $\endgroup$ – Rococo Sep 24 '16 at 18:15
  • $\begingroup$ Related: physics.stackexchange.com/q/10283 physics.stackexchange.com/q/23405 and possibly others. $\endgroup$ – dmckee Sep 24 '16 at 18:47
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    $\begingroup$ @Rococo In this case, an explanation like "there is no such largest scale" could be also an acceptable answer, particularly if it happens with an explanation of why. And, this is the accepted answer - because there is no size limit for a superconducting or superfluid system. $\endgroup$ – user259412 Sep 25 '16 at 13:18
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Quantum effects such as a wave like behavior are relevant until a measurment of the vector state occurs. At a complex molecular scale the particles are constantly measured by each other and the wave function collapses. Therefore the quantum effects remain at atomic scales and below.

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  • $\begingroup$ this is flipping amazing, so what your telling me is that not only does the @VictorVMotti, wave function collapse when we measure a particle but that at the molecular level or perhaps the complex molecular level the particles measure each other and cause the wave function to collapse. this completely expands my idea of what was possible of the Uncertainty Principle. Thanks for your input. $\endgroup$ – Brando Sep 26 '16 at 1:18
  • $\begingroup$ Also see the book Quantum Biology by Jim Al Khalili. $\endgroup$ – user56963 Sep 26 '16 at 9:30
  • $\begingroup$ That isn't true. Quantum superposition has been observed in a device around 50 microns in size, which is 50,000 times bigger than a typical molecule. $\endgroup$ – John Rennie Oct 11 '16 at 15:38
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Super-Conductivity and Super-Fluidity are macroscopic quantum phenomena.

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    $\begingroup$ This is true of course, but the OP's question is worded vaguely enough that many other examples are potentially possible. The heat capacity of a normal metal at low temperature cannot be explained with quantum mechanics, should we take the largest piece of metal that has been cooled sufficiently? Does the entire sun count due to the QM involved in fusion? $\endgroup$ – Rococo Sep 24 '16 at 18:20
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    $\begingroup$ Indeed, Brando, the stability of matter itself cannot be explained classically: physics.stackexchange.com/questions/126512/… . $\endgroup$ – Rococo Sep 24 '16 at 18:24
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    $\begingroup$ Supconductors are macroscopic in a sense, but there's another sense in which they're not. A superconductor is in its ground state. It's interesting to ask (although I don't think OP meant to ask this) how large of a Hilbert space can we make a quantum system occupy. For example, what's the largest GHZ state we can make? $\endgroup$ – DanielSank Sep 24 '16 at 18:41
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    $\begingroup$ @DanielSank thank you very much for your input, I had know idea what a Hilbert space was, what a GHZ state was or that a quantum system was different then an effect. Not that I understand any of those now, but at least now I have a direction to grow in. This site is turning out to be a great resource for me, and I am grateful to people like you and others to point novices like me into new and interesting ideas. $\endgroup$ – Brando Sep 26 '16 at 0:58

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