Observation influences reality: John Wheeler and the “It from Bit”
“Wheeler became even more deeply convinced of the importance of information
after concocting a thought experiment that exposed the strangeness of the
quantum world for all to see. Wheeler’s delayed-choice experiment is a
variation on the classic (but not classical) two-slit experiment, which
demonstrates the schizophrenic nature of quantum phenomena. When
electrons are aimed at a barrier containing two slits, the electrons act
like waves; they go through both slits at once and form what is called an
interference pattern, created by the overlapping of the waves, when they
strike a detector on the far side of the barrier. If the physicist closes
off one slit at a time, however, the electrons pass through the open slit
like simple particles and the interference pattern disappears. In the
delayed-choice experiment, the experimenter decides whether to leave both
slits open or to close one off _after the electrons have already passed
through the barrier_–with the same results. The electrons seem to know
in advance how the physicist will choose to observe them. This experiment
was carried out in the early 1990s and confirmed Wheeler’s prediction.”
