A photon leaving a 10 billion light-year distant quasar has two possible (diverging and then converging) paths around a gravitational lens and a two paths are equally possible.
"Classical" quantum mechanics says that neither path is chosen until the probabilities are collapsed by observation.
Our act of observing causes the photon to "have taken" one path or another.
This is not conjecture or speculation, but well confirmed.
Hence, Wheeler's speculation about the past being changed once observations are made.