Imaginary time
= Imaginary time
{title2=$t=-i\tau$}
Analytic continuation from real <time> to $t=-i\tau$ turns unitary evolution into $e^{-\tau H/\hbar}$. A <thermal trace> has extent $\beta\hbar$, or $\beta$ when $\hbar=1$. This converts oscillatory <action> phases into an <Euclidean path integral> where convergence permits it; it is not the actual laboratory <time> of a dissipative process.