Exploring links between physics and information theory

Just as physics builds on an elementary, indivisible entity (the quantum: which is defined by the act of observation), so does information theory. Its quantum is the binary unit (the bit). While exploring links between physics and information theory, John Archibald Wheeler became convinced of the importance of information. Reality might not be wholly physical, but a participatory phenomenon, requiring the act of observation, and thus consciousness itself.

Beginning in the 1950s, Wheeler had grown increasingly intrigued by the philosophical implications of quantum physics. The most widely accepted interpretation of quantum mechanics was the orthodox interpretation - also called the Copenhagen interpretation. It held that subatomic entities such as electrons have no real existence; they exist in a probabilistic limbo of many possible super imposed states until forced into a single state by the act of observation. The electrons or photons may act like waves or like particles, depending on how they are experimentally observed.

In the 1960s Wheeler helped to popularize the notorius anthropic principle. It held that the universe must be as it is, because, if it were otherwise, we might not be here to observe it.
While exploring links between physics and information theory, Wheeler became 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 avariation 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 slitlike simple particles and the interference pattern disappears. In the delayed-choice experiment, the experimenter decides whether to leave bothslits 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. Wheeler accounted for this conundrum with yet another analogy. He likened the job of a physicist to that of someone playing 20 questions in its surprise version. In this variant of the old game, one person leaves the room while the rest of the group, or so the excluded person thinks, selects some person, place, or thing. The single player then reenters the room and tries to guess what the others have in mind by asking a series of questions that can only be answered yes or no. Unbeknownst to the guesser, the group has decided to play a trick. The first person to be queried will think of an object (only after the questioner asks the question). Each person will do the same, giving a response that is consistent not only with the immediate question but also with all previous questions. "The word wasn't in the room when I came in even though I thought it was," Wheeler explained. In some ways, the electron, before the physicist chooses to observe it, is neither a wave nor a particle. It is in somesense unreal; it exists in an indeterminate limbo. "Not until you start asking a question, do you get something," Wheeler said. "The situation cannot declare itself until you've asked your question. But the asking of one question precludes the asking of another."

Wheeler has condensed these ideas into The it from bit:

Every it, every particle, every field of force, even the spacetime continuum itself, derives its function, its meaning, its very existence entirely, even if in some contexts indirectly, from the apparatus-elicited answers to yes-or-no questions, binary choices, bits."

According to the it from bit, we create not only 'truth', but even reality (the "it") itself, with the questions we ask.

The irony is that Wheeler's own ideas suggest that - along the search for the ultimate theory of phycics - a final theory will always be a mirage. The 'truth' is imagined rather than objectively apprehended. This view comes close to relativism. The world is a figment of the imagination.

Wheeler offers us a paradox: at the heart of everything is a question, not an answer. When we peer down into the deepest recesses of matter or at the farthest edge of the universe, we see, finally, our own puzzled faces looking back at us.