= Microcausality
{title2=$[\phi(x),\phi(y)]=0$ for spacelike $x-y$}
<Microcausality> requires local bosonic observables at spacelike separation to commute. For a free <real scalar field>, the field <commutator> is the difference of its two <Wightman functions>; it vanishes at equal time and, by <Lorentz invariance>, at every spacelike separation. Nonzero spacelike vacuum correlations do not violate this condition, since a correlation is different from the response to a local intervention. Odd fermionic fields satisfy a corresponding spacelike anticommutation condition, while physical even local observables commute.
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