John Wheeler's plan to understand reality may be gaining traction
The It-from-Bit program to derive all of quantum reality, including space and time, from information has seen some of its greatest leaps in the last few years.
Quantum information is one of the hottest topics in quantum since cat meets box and one of the most exciting areas of study right now is how space and time emerge. You may have heard of connections between quantum information and spacetime, like ER=EPR, the dubious connection between entanglement and wormholes that made headlines a couple of years ago, but this is not that. There is a clear program, going back at least to the 1970s, originating with John A. Wheeler, Feynman’s and Everett’s (of Many-Worlds fame) PhD advisor, that the geometry that defines space and time must be emergent from bits.
This It-from-Bit program is more than just a philosophical aphorism. It is a research program that argues that the spacetime geometry that Einstein developed into his theory of general relativity, when you get down to its microscopic description, becomes a collection of quantum bits (qubits) and that what we know as space and time emerge from their entanglement or increasing information.
In the 1980s, Page and Wootters showed how time could emerge from the entanglement of stationary quantum systems with other systems that act as clocks. Now, researchers have added space to the mix as well. The best review of this I have found is a PhD thesis by Favalli that came out only last year, where he generalizes previous work on time and a single space dimension (hence eliminating rotations) to the usual four dimensions.
If quantum gravity ever becomes a viable theory, I think it must move beyond geometry, which, unfortunately, many theories such as string theory are stuck in. Admittedly, string theory has different goals than emergent space-time protocols, but nevertheless, if treated as fundamental, it goes against Wheeler’s belief that all physical reality must be reducible to information.
The program to do that rests on a few pieces. The first is John A. Wheeler’s It-from-Bit philosophy. The second is a relativity mechanism for quantum mechanics called Quantum Reference Frames. And the third is how we get emergent space and time from quantum entanglement. Bring all this together and we find perhaps the strongest direction to achieving a genuine understanding of microscopic reality: space, time, and matter all at once. And all of this is a hot topic right now with a lot of progress made only in the last few years.
The Wheeler It-from-Bit Philosophy
Wheeler often indulged in flowery language that was often misinterpreted, but he had clear ideas about what he believed constituted reality. From this essay by Wheeler:
It from bit symbolizes the idea that every itme of the physical world has at bottom — at a very deep bottom, in most instance — an immaterial source and explanation; that what we call reality arises in the last analysis from the posing of yes-no questions and the registering of equipment-evoked responses; in short, that all things physical are information-theoretic in origin and this is a participatory universe. The Search for Links — John Archibald Wheeler
Let’s unpack that.
Wheeler is saying that everything we regard as physical reality is a string of answers to yes or no questions that arise from the interaction between what we think of as reality- electrons, protons, atoms, buildings, planets, black holes, and so on, -and our measurement apparati.
Thus, we participate in the universe via an information exchange with it.
Perhaps, you wonder, however, why we would want to do away with geometry as fundamental. Why is information so much more critical?
Wheeler has a point in this case that we perceive the world as information. Geometry is something we infer about the world. We cannot perceive a continuum.
Wheeler’s program, therefore, has three questions, four no’s, and five clues:
The questions:
Why existence?
Why quantum?
Why “one world” from many observers?
The Nos
No tower of turtles
No laws
No continuum
No space, no time
The Five Clues
The boundary of a boundary is zero
No question? No answer!
The super-Copernican principle
“Consciousness”
More is different
Bear with me as I go through all this because, without it, you won’t understand the progress that is being made right now.
The Questions
The questions are sensible at least, and they are the ones that motivated Wheeler in his quest to understand reality. We all want to know why we exist. Some of us say God, but I’m not sure that Wheeler is referring to the Almighty. He’s talking about how existence comes into being, which goes hand-in-hand with his participatory universe.
Asking why quantum is shorthand for asking why, at the microscopic level, the universe is quantum when at our level of the everyday it is not. Wheeler believes that if we understand existence and how it comes into being, we could understand why it has to be quantum.
The last one might be disputed by Many-Worlds adherents. Wheeler argued there was a single world. This also goes into the participatory universe model. We are part of the same universe, but each of us is granted our own POV.
Wheeler answered the why quantum question with the answer “Because what we call existence is an information-theoretic entity” thus quantum mechanics encodes that information theoretic reality and classical physics emerges when information and communication become so dense that it appears to be a continuum.
To answer existence, however, he needed to answer the third question: how do we get a single world out of information that many participants share?
To answer this, we have to get to the no’s and the clues.
The Nos
No tower of turtles, a reference to William James (although James didn’t say turtles; he said “rocks”), means that we cannot allow for an infinite regress. We cannot simply have a set of physical laws that has under it another set of physical laws ad infinitum. At some point the structure must stop.
To avoid infinite regress, Wheeler suggested a loop instead:
“Physics gives rise to observer-participancy; observer-participancy gives rise to information.”
In other words, the universe is like a distributed computer program that runs on its observers, which could be computers or people.
No laws: Wheeler rejected the idea that the universe was, in fact, a machine, however. A machine has laws and rules it follows. Where do those laws come from? No, the universe must be in some sense self-referencing. It must induce laws upon itself. It must be self-organising. He compared it to a piece of music that observers were all playing together on a great piano-with the notes being bits.
No continuum: Wheeler suggests that mathematics has made it clear that the continuum doesn’t exist. I’m not sure what the heck he’s talking about here, possibly the axiom of choice, which is a weird mathematical rule that defies physical logic. The continuum indeed causes a lot of problems in physical laws that would be resolved with a discrete approach. He points to one, which is that quantum theory creates such large fluctuations at the tiniest scales that if a continuum did exist, it would break causality apart. Thus he says, “This circumstance reminds us anew that no account of existence can ever hope to rate as fundamental which does not translate all of continuum physics into the language of bits”.
No space, no time: Wheeler suggests, following Leibniz, that space and time are not real but inventions that we use to order things. There are strong reasons to believe that time is not fundamental. For one thing, it breaks when we try to weld quantum physics with general relativity. The equation that bears his name, the Wheeler-DeWitt equation, has no time in it at all. In any case, this no is a corollary of the third no since space and time are continuous.
The Clues
The Clues give us a direction to what the answers to the questions are, given the no’s.
The boundary of a boundary is zero: this is just a principle from the mathematics of topology. More correctly, the boundary of a boundary is empty because a boundary is necessarily closed in on itself. If you think of it, suppose I have a sphere enclosing a space. The sphere is the boundary of the space, but what is the boundary of the sphere? It has none because the sphere is closed. Wheeler hoped that this principle would lead us to all physical laws from no laws at all in the same way. In other words, can we “bound” physical law in something that itself has no boundary, no laws?
No question? No answer! Quantum physics tells us that we can’t have an answer about any physical object unless we measure it. Thus, all of reality as we perceive it is the result of interrogation. In Wheeler’s conception of quantum physics, when the question is not asked, the answer doesn’t exist. We can’t ascribe an answer, such as a position or momentum to an electron, unless we make a measurement. It makes no sense. If you ask where an arbitrary electron is in a room, the only sensible answer, as British physicist Brian Cox correctly points out, is that it fills the room. Ask the electron where it is using some kind of measurement aparatus, however, and it will localize. It will give you an answer.
The super-Copernican principle: The idea here is that not only are human beings not in a special location in the universe, which is the Copernican principle, but we are also not living at a special time. In particular, Wheeler is rejecting the concept that the beginning of the universe has a special status because it is unobserved. Indeed, he rejects any aspect of reality that is unobserved. The universe only has meaning for those who observe and participate in it in the here and now. History only has information as it is measured and interpreted by those living now. We need not, therefore, account for the bits to construct unobserved universe at all. It-from-bit means observed bits, not imagined ones. Existence across time is built by the inhabitants, the observer-participants who engender reality. As Wheeler frequently repeats: “Meaning is the joint product of all the evidence that is available to those who communicate.”
“Consciousness”: People often say (even Wikipedia gasp) that Wheeler believed consciousness to be the organizing principle, the ground of the participatory universe. But that’s not true. In fact, in an article in The New York Review of Books in 1979, Wheeler and Martin Gardner (who presented wonderful mathematical puzzles in Scientific American for many years) claimed that Wheeler found attempts to connect his name with the involvement of consciousness in quantum mechanics “increasingly irritating”. He tried and failed to clear his name with a talk to the AAAS called “Not Consciousness But the Distinction Between the Probe and the Probed as Central to the Elemental Quantum Act of Observation” where Wheeler emphasized his “agreement with Niels Bohr that acts of QM measurement are made by devices which can be monitored by computers, and thus disassociate himself from those who argue that human consciousness is essential to QM observation.” This is why Wheeler places “consciousness” in quotes. He says that while some consider thought essential to physical reality, “we, however, steer clear of the issues connected with consciousness.” He did not consider consciousness necessary to be an observer-participant of reality. Thus, the clue isn’t the existence or requirement of consciousness but its irrelevance. His view of observer-participation is not traditionally anti-realist but rather has a strictly information theoretic viewpoint. Hence it would be better to call Wheeler an information-realist.
Note: Wheeler considers an observer to be something that makes an irreversible act of registration or acquisition of information. Thus, it is the irreversibility and registration of information that matters, not consciousness.
More is different: This is the observation that emergent properties exist and therefore, time and space likewise may simply be the different that emerges from more information.
That is the Wheeler program. You see that Wheeler didn’t really see the bits from which it comes as being “down there” at the bottom of existence somehow. No, they are all there is. Everything else is emergent. Likewise, he was skeptical of those who sought to place consciousness front and center in quantum interpretation. He considered it pseudoscience. The bits aren’t necessarily in our thoughts.
Nevertheless, how the emergent reality, Newton’s laws, Maxwell’s equations, and Einstein’s relativity, comes about is important because it isn’t as if we just saw a bunch of binary numbers and decided that was space and time. We experienced space and time first. Our brains interpret the reality of our senses that way. We have to know how that experience rises up from bits.
