Why Do Fermion and Boson Operators Commute?

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Boson and fermion operators commute because they operate in distinct Hilbert spaces, allowing them to act independently on their respective states. Bosonic states are defined with symmetrization, while fermionic states require antisymmetrization, leading to different mathematical treatments. When combining these states, a bosonic operator acts on the boson space, while a fermionic operator acts on the fermion space, resulting in a tensor product structure. This separation ensures that the order of operations does not affect the outcome. Understanding this distinction clarifies why fermion and boson operators commute in quantum mechanics.
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For bosons we define states as eg.

ln> = l1 0 1 ... >

where the numbers denote how many particles belong to the j'th orbital.

And similarly for fermions. We then define creation and anihillation operators which raise and lower the number of particles in the j'th orbital:

c_j, c_j^(dagger)

Now in many problems I have to commute bosons and fermion operators. I actually asked this question before, but I didn't completely understand the answer. My question is:
Why does fermion and boson operators commute? starting from the wavefunction symmetrization and antisymmetrization requirement
 
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Is it possible that one only acts on bosons and one only acts on fermions so it doesn't matter which one you do first. (Just a guess as I know zero about this. But hey it's Friday night, why not look a bit silly!)
 
It's been a while so I hope someone won't come along and tell me this is nonsense. But if I recall correctly, the reason is they live in different spaces. If you have a boson state ##|b\rangle## and a fermion state ##|f\rangle## then a combined state would be ##|b, f\rangle = |b\rangle \otimes |f\rangle##. A bosonic operator would look like ##\hat B \otimes 1## on this combined space, and a fermionic operator similarly like ##1 \otimes \hat F##.

Typing math on a smartphone is a bit of a pain, so I'll leave it at this, but hopefully you can work it out from there.
 
Time reversal invariant Hamiltonians must satisfy ##[H,\Theta]=0## where ##\Theta## is time reversal operator. However, in some texts (for example see Many-body Quantum Theory in Condensed Matter Physics an introduction, HENRIK BRUUS and KARSTEN FLENSBERG, Corrected version: 14 January 2016, section 7.1.4) the time reversal invariant condition is introduced as ##H=H^*##. How these two conditions are identical?

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