As if these results weren’t strange enough, Wheeler introduced the element of time and made the prediction that even if we perform such a measurement after a photon has passed through one of the slits, we would still get the same effect, causing the photon to act like a particle retroactively.3 In other words, he predicted that a measurement in the present would mysteriously influence the past. This is the delayed-choice experiment, and it was finally conducted in 2007, confirming Wheeler’s prediction.
