Conscious: A Brief Guide to the Fundamental Mystery of the Mind

by Annaka Harris

In an interview with the author Rob Reid, Donald Hoffman, a cognitive scientist at the University of California, Irvine, explains what would happen if we measured a single photon in Wheeler’s cosmological thought experiment: You can now ask, for each photon that comes to me, whether it came from the left [or the right] side of the gravitational lens. [Let’s say] I decide to measure which side it came from, and I find out that it went on the left side. That means I can say that for the last ten billion years, that photon has been on a path that started from the quasar and went around the left side of the gravitational lens. But if, instead, I had chosen not to make that measurement and just measure the interference pattern, it would not be true that for the last ten billion years that photon had gone [down a path] around the left side. So the choice I make today determines the ten-billion-year-history of that photon.