It is called the double slit experiment. In it an electron or any other particle flies toward a screen with a pair of slits. Past the screen is a physicist with a choice of two experiments. One will show that the electron was a particle and passed through one or another slit; the other will show that it was a wave and passed through both slits, producing an interference pattern. The electron will turn out to be one or the other depending on the experimenter's choice.
That was weird enough, but in 1978 Dr. Wheeler pointed out that the experimenter could wait until after the electron would have passed the slits before deciding which detector to employ and thus whether it had been a particle or wave. In effect, in this "delayed choice" experiment, the physicists would be participating in creating the past.
In a 1993 paper Dr. Wheeler likened such a particle to a "great smoky dragon," whose tail was at the entrance slits of the chamber and its teeth at the detector, but in between - before it had been "registered" in some detector as a phenomenon - was just a cloud, smoky probability.
Perhaps the past itself is such a smoky dragon awaiting our perception.
He wonders if the delayed choice experiment is a prescription for how the universe can be built up from information, as in a cosmic game of 20 questions, a series of yes-no decisions resulting from billions upon billions of quantum observations. It's a concept that has gone by many names over the last few decades from "genesis by observership" to "participatory universe" to the current fashion, "it from bit."
Typically there is a diagram, a cartoon actually, which consists of a giant U with an eyeball on top of one stem looking back at the other. The skinny unadorned end of the U is the Big Bang, he explained, tracing his finger along the loop.
"The model of the universe starts out all skinny and then gets bigger," he said. "Finally it gives rise to life and the mind and the power to observe, and by the act of observation of those first days, we give reality to those first days."
< http://www.nytimes.com/2002/03/12/science/physical/12WHEE.html >