Density Matrix & Subsystem Correlations (ρ_clock)
4x4 Pure Entangled
In the Page-Wootters model, the total universe wavefunction |Ψ> is static (H|Ψ> = 0). Time is born solely from entanglement between the internal Clock System (C) and Rest of Universe (R). Conditioning R on clock state |t>_C yields a time-dependent state |ψ(t)>_R.