John Wheeler, colleague of Albert Einstein and Niels Bohr, as well as the man who coined the term "black hole" has selected the question of "Why Existence?" as his last quest before he dies (he just turned 91 in July.) An early supporter of the anthropic principle (which states the universe is the way it is because we exist to see it) his new idea is known as genesis by observership. He suggests that our observations might actually contribute to the creation of physical reality. He believes that the universe is built like "an enormous feedback loop, a loop in which we contribute to the ongoing creation of not just the present and the future but the past as well." To illustrate the point he created a variation on the classic two-slit experiment.

The two-slit experiment is "a cornerstone of quantum mechanics" and is used to show how light can act as either a wave or as a particle. In the experiment, light-a stream of photons-shines through two parallel slits and hits a strip of photographic film behind the slits. The experiment can either be run with photon detectors right beside each slit to allow physicists to observe the photons as they pass, or with detectors removed so that the photons pass through unobserved. When the detectors are used, the photons pass through either one slit or the other, thus acting like particles. But without the detectors, instead of two distinct clusters of dots on the film showing where individual photons hit after passing through one slit or the other, a band of light and dark stripes appears. This pattern could only be produced if the photons are acting like waves, with each single photon spreading out and hitting both slits at once "like a breaker hitting a jetty." Alternating bright stripes on the film show where crests from those waves overlap; dark stripes indicate that a crest and a trough have cancelled out. The outcome of the experiment depends on what the physicists try to measure. If the detectors are set up, the photons behave like particles. If there are no detectors, the photons travel all possible routes. Wheeler's version of the experiment is similar but with greater implications by showing that observations in the present can affect how a photon behaved in the past.

Imagine a quasar-one of the most (if not the most) bright objects in the sky. Now picture two large galaxies between earth and the quasar. The gravity from massive objects like a galaxy can bend light much as a glass lens does. In Wheeler's experiment the galaxies substitute for the two slits, and the quasar is the light source. Photons from the quasar can follow one of two paths, past one galaxy or the other.

Now on earth, some astronomers decide to observe the quasar. Here the telescope plays the part of the photon detector from the experiment. If they look at one galaxy, they will see the photons deflected from that galaxy. If they look at the other galaxy, they would get the same results. "But by carefully aranging mirrors, they could make photons arriving from the routes around both galaxies strike a piece of photographic film simultaneously" which would "mimic the second part of the two-slit experiment." This would create the alternating light and dark bands appear on the film, identical to the pattern found in the two-slit experiment.

Even if light from the quasar was so faint that its photons hit the film one at a time the same results would still appear, meaning a lone photon not observed by the telescope traveled both paths towards earth, even if the paths were separated by light years. By the time the astronomers decided which measurement to make-"whether to pin down the phton to one definite route or to have it follow both paths simultaneously"-the photon could have already been travelling for billions of years, even before life appeared on earth. The measurements made now, would determine the photon's path. On the other hand, they could "retroactively force the photon onto one straight trail toward their detector, even though the photon began its jaunt long before any detectors existed."

One might think it possible to dismiss this idea offhand except for one thing: it was demonstrated in a laboratory. In 1984 physicists at the University of Maryland set up a tabletop version of the delayed choice scenario. "Using a light source and an arrangement of mirrors to provide a number of possible photon routes, the physicists were able to show that the paths the photons took were not fixed until the physicists made their measurements, even though those measurements were made after the photons had already left the light source and begun their circuit through the course of mirrors."

Wheeler believes that we are part of a universe that is a work in progress. "We are tiny patches of the universe looking at itself-and building itself. It's not only the future that is still undetermined but the past as well. And by peering back to the Big Bang, our present observations select one out of many possible quantum histories for the universe." While conscious observes play a role in this so-called participary universe, the dominant roles are played by ordinary matter and radiation.

Wheeler uses the example of a high-enery particle released by a radioactive element in earth's crust. The particle, like the photon in the experiments, exists in many possible states, travelling in every direction, until it interacts with something like a piece of mica in earth's crust. When that happens, one of the possible outcomes becomes real, so in this case it was an inanimate object, not a conscious observer that changed what could happen into what did happen. "The trail of disrupted atoms left in the mica by the high-energy particle becomes part of the real world." Wheeler believes that most of the universe consists of huge clouds of uncertainty that have not yet interacted with either an observer or inanimate matter. "He sees the universe as a vast arena containing realms where the past is not yet fixed."

This theory has addressed one of the "most confounding aspects of modern physics:" the relationship between the observations and outcomes of experiments on quantum systems. This problem was explemplified and made famous by the thought pardox known as Schrodinger's Cat. "The principles of quantum mechanics dictate severe limits on the certainty of our knowledge."

Andre Linde, a Stanford University physicist says "You may ask whether the universe really existed before you start looking at it. That's the same Schrodinger Cat question. My answer would be that the universe looks as if it existed before I started looking at it...when we look at the universe, the best we can say is that it looks as if it were there 10 billion years ago." Linde agrees with Wheeler's view of the participatory nature of reality except on one point: Linde believes that conscious observers are an essential component of the universe and cannot be replaced by inanimate objects. He claims the universe is like a recording device, and that people (or any other observer) are what you need to see what is on the recording device. He says "It's not enough for the information to be stored somewhere, completely inaccessible to anybody. It's necessary for somebody to look at it. You need an observer who looks at the universe. In the absence of observers, our universe is dead."

*Discover-June 2002 issue