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It would be very helpful if you can give a few examples that are at micrometer level or above, and include some explanations or insight on the causes of these behaviors.

wang1908
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    This post (v1) seems like a list question. – Qmechanic Jan 31 '18 at 15:52
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    https://en.wikipedia.org/wiki/Macroscopic_quantum_phenomena – sammy gerbil Jan 31 '18 at 16:03
  • Just the normal classical behavior of macroscopic objects is the result of decoherence which is due to entanglement with the environmental degrees of freedom. So, the absence of what is normally considered to be "typical quantum behavior" like e.g. interference, is actually a quantum mechanical effect. Entanglement is, after all, considered to be a non-classical effect. – Count Iblis Jan 31 '18 at 16:10
  • How about superconducting qubits? They are ~100 $\mu$m in size and exhibit all kinds of quantum effects, including violation of the Bell inequality. Is that the sort of thing you're talking about? – DanielSank Jan 31 '18 at 16:31
  • Magnets, lasers, masers, atomic clocks, Mossbauer effect, superconductivity, superfluidity, light diffraction and interference, electricity, and more. – safesphere Jan 31 '18 at 16:33
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    While I normally feel that a hard-line approach to list-based questions tends to be excessive, the obvious lack of detail in the responses this thread has accrued makes it pretty clear that the question falls on the wrong side of the site policy on list-based questions. Voting to close as Too Broad. – Emilio Pisanty Jan 31 '18 at 17:03
  • @Wang-X-Y No. This site used to have a blanket ban on list-based questions; we've relaxed the ban somewhat, but in its current form this question simply doesn't meet the requirements. It is conceivable that you might be able to edit the question to meet the letter and spirit of the guidelines (and similarly this blog post) in that the question needs to make it very clear that the expectation is for answers to contain much more detail than they do currently, but I'm not holding my breath for that. – Emilio Pisanty Jan 31 '18 at 18:54
  • Edited the question, hope that fixed it. – wang1908 Jan 31 '18 at 19:06
  • As the stability of matter is due in part to quantum effects (https://physics.stackexchange.com/questions/1077/how-can-i-stand-on-the-ground-em-or-and-pauli/1081#1081), you could answer this question with 'everything.' So it is important to be more specific about what you consider to be a macroscopic quantum effect. – Rococo Jan 31 '18 at 20:13

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Black body radiation. . It cannot be fitted classically. It needs quantum mechanics.

The atomic spectra can only be explained by quantum mechanics.

anna v
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Just two simple examples: (1) The decrease of specific heat with temperature. (2) Superconductivity.

freecharly
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The periodic table of elements. Explainable using Schrödinger's equation, electron spin and the exclusion principle.

Philip Wood
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This is an interesting question. Macroscopic instances of quantum phenomena are usually very dependent on how people interpret quantum mechanics. For some, quantum phenomena are exclusively microscopic so that the macroscopic effects that we see are mere consequence of microscopic quantum phenomena, but not quantum phenomena in and of themselves.

One clear example is that of semiconductors and transistors. In both cases, the underlying theory is manifestly quantum mechanical. Both systems are essential components of modern electronic devices. But would you say that a computer or a smartphone are quantum systems? Conventionally speaking, the answer would be no.

I do have a goodie for you, however. It consists of an experiment in fluid dynamics that exhibits such strong analogies to exclusively quantum phenomena that it has been cited as evidence for the Pilot Wave interpretation of QM. I'll let this Veritasium video paint the rest of the picture for you:

starseed_trooper
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    Bouncing fluid droplets, while possibly useful as a model system to understand QM, are not in any reasonable sense a macroscopic quantum effect. All they really show is that wave phenomena can occur in many different systems. – Rococo Jan 31 '18 at 20:13
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According to Seth Lloyd (MIT), the phenomenon of birds migrating, photosynthesis, and even smelling and sneezing might be explained by quantum physics in addition to chemistry.

Sajjad Nasir Imran
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line emission spectra of elements. lasers and masers.

niels nielsen
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