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/sci/ - Science & Math

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12004203 No.12004203 [Reply] [Original]

How can a composite system be a boson if it is constituted of fermions?

For example, the He-4 nucleus is considered a boson (https://en.wikipedia.org/wiki/Helium-4).). But in what way is it a boson? I doesn't seem possible for a bunch of He-4 nuclei to pile up on each other in the same quantum state because protons and neutrons are fermions (made up of quarks which are also fermions).

>> No.12004244

The total spin of helium is 0, so goes for angular momentum. It does have properties of boson with spin 0.
For example, helium has property of superfluidity, which can occur only in bose condensate.

>> No.12004269
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12004269

>>12004203

>> No.12004503

>>12004203
More is different.

>> No.12004803

>>12004203
Spin 0, integer isospin

>> No.12006467

>>12004203
i'll show you a hadron *unzips throbbing hard dick and cooms on you*

>> No.12006518

>>12006467
i appreciate the bump, butt...

anyway, sure the total spin is 0, i recognize that's an integer spin. i have a physics ugrad degree, and maybe it's been too long since i studied (simplified) multiparticle QM, but it's not jumping out at me how that would make He-4 a boson (integer spin) since it's made up fermions (half integer).

Furthermore, my understanding of the difference between these classes of particles is that bosons can occupy the same quantum state, while fermions cannot. I am having a hard time understanding what it means for several He-4 nuclei to occupy the same quantum state. Would that be like more than one electron occupying the same quantum state in, say, a hydrogen atom or an infinite square well? And that you could dump as many electrons as you want into that quantum state?

>>12004244
understanding this would help me appreciate bose-einstein condensates a lot more

>> No.12006927

>>12006518
It's just addition of angular momentum. If you want an answer that isn't just handwavy "half-integer plus half-integer equals integer", then you'll need to brush up on the representation theory of SU(2).