September 2023



Stay safe + stay true, SFI!


A draft of an essay on Wheeler's famous it from bit paper to be published in 2024 by SFI Press in a forthcoming annotated volume, Foundational Papers in Complexity Science.


Information, physics, quantum: the search for links.
John A. Wheeler

And it is all one to me
Where I am to begin; for I shall return there again.

—PARMENIDES, Fragment 5 (trans. David Gallop)

In the contents of consciousness we recognize three sorts of elements, Firstness, Secondness, Thirdness. [—] What a Third is depends on two other things between which it mediates. Firstness is feeling-quality; secondness is brute reaction; thirdness is mediation.

--C.S. Peirce (1865-1909). The Logic Notebook.

John Archibald Wheeler, in this little understood but widely read and referenced essay—first presented as a paper at a Santa Fe Institute workshop in 1989—coins the phrase “it from bit” and argues that information is the natural language of the universe. Bits are its building blocks, preceding objects and matter. Order, meaning, and causality itself result from the simple act of registering a choice—an idea Wheeler encapsulates with the term “observer-participancy” (OP). Making a binary choice—yes or no—reduces uncertainty from an information-theoretic standpoint as the number of options (Haji-Akbari et al. 2009; Walchover 2017) before the question is answered—and hence the entropy—goes from two (one bit) to zero upon answering. The decrease in uncertainty also allows the OP to allocate its investments more efficiently, giving it access to new options and increasing entropy again (Flack 2017).

In my read of Wheeler, out of this cycle of symmetry-breaking come the sensations of space and time and, ultimately, with the concordant global increase in entropy, an arrow of time. The sensation that time passes is amplified by the mesoscale emergence of hierarchically structured physical and living systems. Further partitioning cause from effect by creating a separation of a scales, this hierarchy allows for feedback, reifying the loop created by the simple act of asking and answering questions, and also creating temporal and spatial heterogeneity and clustering. Reality—the universe—is a loop, but with complex internal structure. Wheeler’s essay is mostly an argument for the former with allusions to the latter.

To state this another way and connect with more familiar debates within complexity science, the determinism of fundamental physics—and to a lesser extent the determinism seeming implied by the emergent hierarchy of screened off organizational levels in biology—is an illusion in the deepest sense, although not necessarily in a proximal sense. Reality, Wheeler writes, is fundamentally circular: “physics gives rise to observer-participancy; observer-participancy gives rise to information; and information gives rise to physics.” If there is any inception point it is in the interaction of particles—initially the massless fundamental particles of quantum phenomena—and registration of these interactions by the changes they induce. In this simple Peircean quantum triad of particle interaction and registration, which Wheeler refers to as elementary observer-participancy, existence, the universe, and consciousness, have their origins.

There’s a tad more to unpack but for the moment it is worth highlighting that many essays have been written about Wheeler’s seductive yet initially perplexing idea, generally with the same conceptual formula. Most begin by reiterating the meaning of “it from bit,” discuss the double-slit and delayed-choice particle physics experiments—the surprising results of which helped Wheeler reach his conclusions—then wander on to the loosely woven connections he makes with adaptive systems and consciousness, and finally settle reluctantly into the conclusion that, while provocative, the paper is a failure, having not provided a satisfactory account of how observer-participants themselves arise. This formula follows Wheeler’s own conceptual line through his essay but only as it strikes surface.

I have now read the paper many times and must concede to having had these same thoughts as I struggled (always with enjoyment) through it. However, the more attention I give it the more convinced I am that although Wheeler characteristically creates many idea portals to untrodden intellectual territory that we readers could spend lifetimes exploring, he also creates efficient and creative paths through heavily trodden bogs, even if he also takes a few semantic and didactic liberties to get us to follow him.

Wheeler’s most intoxicating conclusion is that information precedes matter, rather than the other way around, as is typically the case in grand unified theories. Wheeler’s story turns not on objects like strings but on information-theoretic entities—decoders or registrants—his so-called observer-participants or choice-makers, as I call them.

Readers presumably assume, as I initially did, that an observer-participant needs to be an object with mass and, more egregiously, the capacity for computation. In other words, the universe could not come into existence without complex objects to start. This is both confusing (how could complexity be there from the beginning?) and a confusion. The confusion stems in part from human (perhaps Western) biases about what is required to perceive or register or pose a question. It also stems from Wheeler’s strategic decision to use several experiments in particle physics and cosmology to ground OP. In stressing the role of the measuring apparatus in these experiments as the registrant—the observer-participant—he immediately makes the concept of OP graspable, but the anthropomorphism also obscures.

The experiments that best distill the OP concept concern the nature of photons, whether they exist, where they are located, and whether they travel as particles or waves. To know a photon exists we must make measurements. Specifically, we can register the existence of a photon when it strikes and is absorbed by an electron in a photomultiplier that accepts its energy. The photon does not exist prior to emission or after detection—as it is destroyed when it is absorbed, meaning, importantly, it must be destroyed to confirm its existence, a point I will return to shortly.

For the moment, the key takeaway is the Peircean triadic nature of this experiment—there is a photon, an electron, and an observer-participant. In Wheeler’s telling, and in most descriptions of these experiments by others, the observer is the measurement device, or, if one backs up a step or two, the experiment-performing scientist. This gives the impression that observer-participants must be complex, but this is not generally assumed by physicists. And in this tiny modification to Wheeler’s presentation lies a key to averting the essay’s frequent but superficial dismissal—a third object with mass is not necessary—the triad can be simplified into two objects and two actions—the photon, electron, their collision, and the registration of the absorption of energy by the electron itself. In other words, the observer can be a third object with mass like a scientist, or it can be one of the interacting partners that in experiencing the event effectively registers it. The jump from first-person participancy to third-person participancy presumably entails an increase in complexity. Wheeler does not discuss this distinction or its implications but it potentially relates to the distinction between first- and third-person probabilities of what is observed vs. what occurs in quantum cosmology, as discussed in Hartle and Hertog (2017). I leave that thought to be explored by others.

The participancy part of observer-participancy is easier to understand. It comes from the fact that to register the photon an electron must absorb and consequently destroy it. The act of registering, or measuring, changes the nature of reality. Interestingly, when the electron absorbs the photon entropy in one sense decreases and in another increases. It decreases from the point of view of the photon’s existence—the absorption confirms that answer as “yes,” the photon existed. On the other hand, the absorption also pushes the electron into a higher energy state, increasing its options. Wheeler does not discuss this information transition, but recent work in biology on the information-theoretic conditions supporting macroscopic expansions suggests that it is an important factor in emergence (Flack 2017).

Wheeler follows his explanation of observer-participants and photons with a discussion of black holes, arguing that bits—via yes–no questions—not only bring objects into existence but give them their properties. In the case of black holes, their size—an “it”—is defined by the number of bits of information they contain. Through this example Wheeler gives substance to information as the language of the universe and bits as its building blocks. He is deriving physics from information—writing, “The quantum, h, in whatever correct physics formula it appears thus serves as a lamp. It lets us see the horizon area as information lost [measured as entropy], understand wave number of light as photon momentum, and think of field flux as bit-registered fringe shift.”

At this juncture, Wheeler begins to consider the implications of this new way of thinking for understanding how the universe is organized and what, besides the quantum, could be fundamental. Nothing, it turns out. He concludes there is no tower of turtles—existence is not in its most essential description a hierarchy but a loop. Laws and any hierarchical structure are consequences of self-synthesis that ultimately contribute to the loop. Space and time are emergent and additionally relative, with fluctuations at distances of the Planck length so great that space becomes lumpy and time nonsensical, emerging more meaningfully instead from convenient coarse-grainings over fluctuations that give rise to discreet rather than continuous objects.

Among the most important statements in the paper is, “Reality is a theory; the past has no evidence except as it is recorded in the present.” Registration is an act of amplification that screens off the quantum level but also produces bits that observer-participants use to do work (the electron enters a higher-energy state). This sounds very much like biology and like arguments I have made in my own papers! As the number of observer-participants grows, their joint interventions enrich the universe, the objective reality of which is defined by the degree of agreement among observer-participants in the answers to their yes–no questions. The objective reality resulting from this collective computation of consensus—from this collective intelligence—creates meaning, and observer-participants use the consolidated meaning map to communicate and work more efficiently, keeping the loop looping.

Wheeler is proposing that the universe comes into existence with a quantum triad of particle interaction and registration. This loop has no micro- and macroscale, no intrinsic spacetime, and no continuum. All of that is emergent—or, in the case of the continuum, an illusion, contributing to the loop lumpy, complex mesoscale phenomena that in cycling back on itself through feedback keeps the loop looping. OP requires no complexity to start. No mass and no resource intensive computation. Only quantum phenomena.

Abruptly with this insight comes the possibility that Wheeler’s essay is not, in fact, as so many have argued, ultimately a failure. Rather there is tremendous foresight in its reframing and refocusing, as well as actionable research directions. To understand the origins of the loop, we need to understand the origins of the quantum (perhaps the hardest part?). To understand looping, we need a theory of information (perhaps the most open-ended?). And for that, Wheeler writes, we should look to biology and the study of inference and perception.

A natural retort to this claim is that biology is measure zero given the scale of the universe and hence inconsequential. But that view, Wheeler wants us to understand, is surface. It privileges space and time, which, like biological systems, are emergent, not fundamental, and—more significantly—are to some extent a consequence of emergence, and, specifically, of coarse-graining by biological systems as they process the environment and distill regularities. The vastness of space and time is an illusion or at least a red herring; the vastness neither trivializes biology nor ensures biology’s contribution is negligible—as Wheeler points out, much can come from almost nothing (the boundary of a boundary is zero).

This concession to biology is a massive frameshift. Biological systems are not a consequence of physics, existing “above it” and largely screened off, but a core, causal set of sub-processes. Not in terms of their influence on particle physics, but in terms of their contribution to loop dynamics. Biological information processing contributes the mesoscale dynamics that keep the loop looping. Carlo Rovelli and colleagues (2018) make a similar point when they suggest that time may not be unitary, but a complex phenomenon with many layers, united only in their connection to entropy, and with each contributing unique properties to reality.

Wheeler, having opened an idea portal, leaves it to descendants to explore. Once one sits with this reframing for a while, the shock of the idea that biology could “contribute to physics” subsides and the natural teleological property of biology comes to the fore as holding the explanation of how.

Where Wheeler leaves off, Jim Hartle picks up. Jim was a student of Wheeler’s at Princeton and a collaborator of Santa Fe Institute cofounder and discoverer of the quark, Murray Gell-Mann. During Jim’s visits to SFI we discussed overlaps in our work—overlaps that Jim first perceived even as he worked largely in cosmology and I on computation in adaptive systems—an ideal Institute interaction. It was not, unfortunately, until just after he died this past year in 2023, upon re-reading some of his papers on time, coarse-graining, and information processing, that I realized just how extensively our ideas and interests overlapped.

Jim’s work further develops the idea that information should be central in any theory of the universe’s origins and structure. It also connects Wheeler’s incipient physics of information more concretely to fundamental physics as well as to the biology of information processing, contextualizing Wheeler and his essay within complexity science and pushing “it from bit” towards its conceptual center.

Hartle (2005) gives a form to Wheeler’s observer-participants that a biologist easily recognizes. Jim reformulates OPs as IGUSs (information gathering and utilizing systems)—a term Jim borrowed from Murray, who introduced it in The Quark & the Jaguar—and uses this more developed concept of information processing to show how human notions of past, present, and future can be sensible within the four-dimensional world of fundamental physics. Perhaps most significantly, Jim outlines the spacetime conditions supporting a common now—that is the capacity of entities separated in space to collectively experience approximately the same present. With this insight Jim provides another central detail to the “it from bit” story, as the capacity to experience or perceive approximately the same present is a key condition for the emergence of hierarchy and levels of organization in biology. I think Wheeler would like this generative trajectory. There is much to do!


Flack Jessica C. (2017). Coarse-graining as a downward causation mechanism. Phil. Trans. R. Soc. A.3752016033820160338

Gell-Mann, Murray (1994). The Quark and the Jaguar. Adventures in the Simple and the Complex. New York: W.H. Freeman.

Haji-Akbari, A., Engel, M., Keys, A. et al. (2009). Disordered, quasicrystalline and crystalline phases of densely packed tetrahedra. Nature 462, 773–777.

Hartle, James B. (2005). The physics of now. American Journal of Physics, 73, 101-109.

Hartle, James B. and Hertog, T. (2017). The Observer Strikes Back. In K. Chamcham, J. Silk, J. Barrow, & S. Saunders (Eds.), The Philosophy of Cosmology (pp. 181-205). Cambridge: Cambridge University Press.

Peirce, Charles Sanders (1865-1909). The Logic Notebook.

Rovelli, C., Segre, E., & Carnell, S. (2018). The order of time. New York, New York, Riverhead Books.

Walchover, Natalie (2017) Digital alchemist seeks rules of emergence. Quanta Magazine, March 8.

Wheeler, John Archibald (1989). Information, physics, quantum: the search for links. In Proceedings III International Symposium on Foundations