1. The Core Insight: Postselection “Mimics” Self-Consistency
Imagine you have a time loop. The Novikov self‑consistency principle says: only histories that are internally consistent can happen. If you try to send a message back that would create a paradox, the universe simply doesn’t allow that branch.

Now think of a postselected experiment:

You run a quantum circuit many times.

At the end, you measure a certain qubit. You look only at the runs where that qubit is, say, |1⟩. You discard all runs where it’s |0⟩.

By doing this, you are artificially selecting only those branches of the quantum state that meet a specific condition. The other branches – which would lead to logical paradoxes – are thrown away.

Thus, postselection enforces a consistency condition from the outside. The mathematics of that condition turns out to be identical to the consistency condition required for a CTC. So, for the purpose of correlations and computational outcomes, the postselected circuit behaves as if a time loop existed.