Participatory Universe

What good is a universe without somebody around to look at it?
— Robert Dicke (1916-1997)
John A. Wheeler at Princeton University in 1967. (Image Credit: The NY Times).

John A. Wheeler at Princeton University in 1967. (Image Credit: The NY Times).

John Wheeler, who is mentor to many of today’s leading physicists, and the man who coined the term “black hole”, suggested that the nature of reality was revealed by the bizarre laws of quantum mechanics. According to the quantum theory, before the observation is made, a subatomic particle exists in several states, called a superposition (or, as Wheeler called it, a ‘smoky dragon’). Once the particle is observed, it instantaneously collapses into a single position (a process called ‘decoherence’).

Wheeler's hunch is 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 his idea, he devised what he calls his “delayed-choice experiment,” which was tested in a laboratory in 1984 (and 2007). This experiment was a variation on the famous “double-slit experiment” in which the dual nature of light was exposed depending on how the experiment was measured and observed, the light behaved like a particle (i.e., a photon) or like a wave.

Unlike the original “double-slit experiment”, in Wheeler’s version, the method of detection was changed after a photon had passed the double slit. The experiment showed that the path of the photon was not fixed until the physicists made their measurements. In other words, the outcome of the experiment depends on what the physicists try to measure: If they set up detectors beside the slits, the photons act like ordinary particles, always traversing one route or the other, not both at the same time. But if the physicists remove the detectors, each photon seems to travel both routes simultaneously like a tiny wave. When it comes to quantum systems, reality depends on how we interact with it.

Putting down her cup of tea, she asked in a timid voice, “Is light made of waves, or is it made of particles:” “Yes, exactly so,” replied the Mad Hatter. (Source: “Alice’s Adventures in Wonderland”).

Putting down her cup of tea, she asked in a timid voice, “Is light made of waves, or is it made of particles:” “Yes, exactly so,” replied the Mad Hatter. (Source: “Alice’s Adventures in Wonderland”).

These conclusions lead many scientists to speculate that the universe is fine-tuned for life. For example, this is how Robert Dicke, Wheeler’s colleague at Princeton, explained the existence of our universe:

If you want an observer around, you need life, and if you want life, you need heavy elements. To make heavy elements out of hydrogen, you need thermonuclear combustion. To have thermonuclear combustion, you need a time of cooking in a star of several billion years. In order to stretch out several billion years in its time dimension, the universe, according to general relativity, must be several billion years across in its space dimensions. So why is the universe as big as it is? Because we’re here!

Does this mean humans are necessary to the existence of the universe?

While conscious observers certainly partake in the creation of the participatory universe envisioned by Wheeler, they are not the only, or even primary, way by which quantum potentials become real. Ordinary matter and radiation play the dominant roles. Wheeler likes to use the example of a high-energy particle released by a radioactive element like radium in Earth's crust. The particle, as with the photons in the two-slit experiment, exists in many possible states at once, traveling in every possible direction, not quite real and solid until it interacts with something, say a piece of mica in Earth's crust. When that happens, one of those many different probable outcomes becomes real. In this case the mica, not a conscious being, is the object that transforms what might happen into what does happen. The trail of disrupted atoms left in the mica by the high-energy particle becomes part of the real world.

Erwin Schrödinger: “Until you observe the cat, it is both alive and dead at the same time.”

Erwin Schrödinger: “Until you observe the cat, it is both alive and dead at the same time.”

At every moment, in Wheeler's view, the entire universe is filled with such events, where the possible outcomes of countless interactions become real, where the infinite variety inherent in quantum mechanics manifests as a physical cosmos. And we see only a tiny portion of that cosmos. Wheeler suspects that most of the universe consists of huge clouds of uncertainty that have not yet interacted either with a conscious observer or even with some lump of inanimate matter. He sees the universe as a vast arena containing realms where the past is not yet fixed.

Wheeler had come to view quantum measurement, how it creates an actuality of what was mere potentiality, as the essential building block of reality. Quantum is the "crack in the armor" that covers the secret of existence, a clue that the mystery of creation may lie not in the distant past but in the living present. If the universe is a giant computer, the laws of nature will most likely be coded in a functional programming language based on “lazy evaluation”, or “call-by-need”, which is an evaluation strategy that delays the evaluation of an expression until its value is needed and which also avoids repeated evaluations. The benefits of lazy evaluation include: (i) the ability to construct potentially infinite data structures, (ii) the ability to define control flow structures as abstractions instead of primitives, and (iii) increase in performance by avoiding needless calculations. But most importantly, lazy evaluation can lead to reduction in memory footprint, since values are created when needed. It is thus consistent with Wheeler’s idea that the universe is designed under the advice of an “efficiency expert.

In fact, there is no obvious extravagance of scale in the construction of the universe, according to Wheeler. For the purpose of having somebody around to be aware of the universe, life on one planet only (i.e., the Earth) seems to be a reasonable design goal. The anthropic principle thus provides a new perspective on the question of life elsewhere in space: they are not essential because it is not economical. Put another way, the universe has to be such as to permit awareness of that universe itself; and to do so economically with life on just one planet. “This point of view is what gives me hope that the question — How come existence? — can be answered,” said Wheeler.

Faith is the number one element. It isn’t something that spreads itself uniformly. Faith is concentrated in a few people at particular times and places. If you can involve young people in an atmosphere of hope and faith, then I think they’ll figure out how to get the answer. Faith and hope are absolutely central to everything one does.
— John Archibald Wheeler (1911-2008)


  1. Interview with John Wheeler: From the Big Bang to the Big Crunch. Cosmic Search, Vol. 1, No. 4. Retrieved from:
  2. Folger, Tim (2002, June 1). Does the Universe Exist if We’re Not Looking? Discover. Retrieved from:
  3. Stenger, Victor J. (2007). The Anthropic Principle. In: The Encyclopedia of Nonbelief. Prometheus Books. Retrieved from: