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Comment by nextaccountic | Hacker News Reader

What I'm asking is, everyday materials usually obey the Pauli exclusion principle

Why is the situation where an whole atom doesn't obey the Pauli exclusion principle much more exotic and unusual?

I mean, take a look at the wikipedia pages https://en.wikipedia.org/wiki/Composite_boson and https://en.wikipedia.org/wiki/Composite_fermion - when one talks about composite bosons, it's exotic materials like superfluid helium, bose-einstein condensates, cooper pairs.

Since it's only a even/odd difference, I would expect that roughly half materials form composite bosons, and the other half form composite fermions, but this doesn't seem to be the case.

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> everyday materials usually obey the Pauli exclusion principle

In the everyday case, this is pretty much always in reference to electrons (which are fermions). Even when we're talking about atoms or solids, the effects of the PEP are due to electrons: https://en.wikipedia.org/wiki/Pauli_exclusion_principle#Appl...

The quantum-mechanical wavelength of everyday whole atoms is much smaller than their physical size, so they behave as classical particles (and the PEP doesn't really apply). In contrast, electrons have wavelengths large enough that they exhibit macroscopic quantum mechanical effects in everyday scenarios.

> Since it's only a even/odd difference, I would expect that roughly half materials form composite bosons, and the other half form composite fermions, but this doesn't seem to be the case.

Every element has bosonic and fermionic isotopes. Neutral atoms have equal numbers of protons and electrons, so any neutral atom with an odd number of neutrons is a composite fermion, and any neutral atom with an even number of neutrons is a composite boson.

> when one talks about composite bosons, it's exotic materials like

Atoms with both even atomic and even mass numbers, nuclei with an even mass number.

I mean, both wikipedia articles you point to focus on exotic examples, but there are far more common mundane examples of both, too.

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