A failure to understand quantum time
In which, through no fault of my own, a religion is invented.
Topic: quantum physics
Thesis: given quantum mechanics and its problematic implications for the subjective experience of time, it is no less strange than the alternatives to suppose that the universe has only one eternal consciousness that experiences all beings.
Previously we asked the following question. Imagine you are a researcher about to carry out the second case of the double-slit experiment. That is, you are about to send a single photon toward a wall with two slits, where a measuring device scans each slit to determine which one the photon will pass through. You know the result can be one of two possibilities: either Slit A or Slit B.
Your question is: suppose the many-worlds/many-islands interpretation is true. Thus, there is a world where I view the measuring device and determine the answer to be Slit A. And there is a world where I do the same, but for an outcome of Slit B. Which world is the one that I will inhabit?
There are two ways to make the question trivial. The first is if we switch to the third person: which world will the Researcher inhabit? In this case we can say: both. In each world there is an identical version of the researcher, identical except for her response to observing the true answer in her version of reality.
The second way to make the question trivial is to ask it only after the experiment has been performed. In that case, which world do I inhabit? The answer is determined by looking at the experimental readout. And which world did I inhabit, prior to the experiment? That answer, again, is trivial; it’s the same regardless of the experiment’s outcome.
Inching toward the more difficult question—from this after-the-fact perspective, we can also ask: “Why do I inhabit the world of Slit A, and not the world of Slit B?” We notice that this question is parallel to what Benj Hellie called the “vertiginous question” [wiki]. I prefer to call it the “Squirrel in Dallas problem”—that is: “Why am I me, and not a squirrel in Dallas?” That is, what is special about this body, the body of Mattias Martens, such that I experience its sensations in particular, and feel nothing of the longing for nuts of that squirrel in Dallas?
The best one can do with this question, it seems, is to take it on its own terms and respond tautologically. You are you, by the principle of identity. If you were someone else, you would be someone else. There is no possible world where you are not you; that is a contradiction.
To all appearances, this is also the best one can do about the “Researcher of World-Slit-A” problem. You are the one who experienced outcome A (or B): if you were the other one, you would be the other one.
Importantly, the identity of Researcher World-Slit-A and the identity of Researcher World-Slit-B are understood to be separate. It may be difficult to define exactly which bits of matter are truly constitutive of any given person at any given time—that is, which particles are me and which particles are merely attached or in contact with me—but few would claim that they are some particles on Earth, plus some motes of dust in a far-off galaxy.
Point being, a clear condition of some matter being part of a certain body is that it physically interacts with other particles of that body. Once the worlds decohere, the particles of Researcher World-Slit-A do not interact with the particles of Researcher World-Slit-B: that is no more and no less than what we mean by decoherence. And sure enough, quantum physicists do not report “phantom experiences” or anything of the kind from parallel versions of themselves. To all possible appearances, the Researchers of the two worlds are distinct people.
That brings us back to the original question, posed in a new way. Which of the two researchers shares an identity with the researcher prior to the experiment? Which is “her”? Or is it both? Or neither?
If it is one or the other, then we arrive at Zeh’s “many-minds” interpretation [wiki], which is that the researcher—and by extension, all of us, constantly—actually chooses, in some preconscious or metaphysical way, which world to inhabit.
This idea is worth entertaining, if only to see what it leads to. As Zeh stresses, the “choice”—Zeh does not imply an act of will, but no other word seems to suffice here—is made at the level of each individual subject. The researcher goes into World-Slit-B, her colleague into World-Slit-A. From the perspective of each, it makes no difference whether the other subjectivity came into the same world. Her colleague continues to behave in the same way as before. It is only from the perspective of that colleague that things may have turned out differently.
If we really follow this idea to its conclusion, the results are interesting. When we are born, we occupy some position in the branching structure of the multiverse. Given the constant, manifold nature of world-splitting, it is statistically very unlikely that the subjectivity of any given person actually shares that world with me. From the moment of conception, every subject is surrounded by Philosophical Zombies [wiki], who act just like humans, who are humans from a physical perspective, but whose actual self is almost certainly off experiencing some parallel reality.
Then there is the issue of choice. Again, Zeh does not assert that minds can willfully choose which world to inhabit. But neither is there anything to rule it out. The most obvious case is the well-known thought experiment of quantum immortality, where the choice seems forced: if a quantum outcome is arranged such that I might experience being alive, or I might die and have no experience, how can my mind enter the latter universe? How can the experiencer experience non-experience?
Thus, we end up imagining a world where no human body inhabited by a genuine subject—that is to say, you—can ever die, no matter the unlikelihood of the quantum branches required to keep you alive. But it is also a world where, even though the multiverse is full of subjects, any given subject can take it as a statistical certainty that she is permanently alone.
It seems to me that Zeh did not intend to suggest these conclusions. All he wanted to do was solve the measurement problem by cleanly separating the subjective and objective accounts of observers. But the result is a metaphysical mess—and, it would seem, an empirical mess as well, since it could imply that the laws of probability break down as a subject approaches death. But anyone who believes that only one of the two worlds holds the “real” researcher from the experiment has to contend with these implications.
What are the remaining options? Either the researcher before the split is both versions of herself, or the researcher before the split is neither version of herself. What are the arguments for these options, precisely?
Let’s start by supposing that she is both of her future selves. In a certain naive way, this is trivially true: we tend to imagine ourselves as bodies moving through time, and whatever logic it may be that links us in one instant to ourselves in the next instant, that logic would still apply in both timelines. The only reason we earlier rejected this is because, from an outside view of both branches considered together, it violates our understanding of the idea of “person” to suppose that they can be multiple non-interacting bodies.
What would be the argument to suppose she is neither? This argument is made in one simple step: to reject the idea that a person is a body moving through time. Instead, a person is a body at a certain instant. There is no continuity in time: with each new instant there is a new population of the world.
This would fit hand-in-glove with presentism [wiki], the view that “now” is all there is. It avoids the surprising metaphysical idea that in the next universal instant, this body will be inhabited by a stranger. In its pure form it seems to also avoid a great deal else that seems useful, like the idea that one ought to plan for the future or learn from the past. Still, some may settle into a satisfying view of consciousness and quantum effects based on presentism and the non-continuity of the self.
There is another way to bring things together into a coherent picture. Let’s again consider the idea that the answer to the question is both: both researchers have the identity of the original researcher.
This also requires us to drop the common-sense idea that a person is a body moving through time—more precisely, along a single timeline. Instead, from the outside view, a person would have to be a body on a branching time-tree of possible states. At any given instant, this person is in a certain state: reacting to past experiences, anticipating future possibilities, experiencing their now. But at any given instant there may not be a particular “next” instant. The tree of selves may be linked by the family resemblance of this person through time and across branches of possibility, but the idea of a self “traveling through time” no longer works. There is only a tree of versions of the same person, each one individually experiencing its own now. (The best known advocate of this idea is the physicist Julian Barbour [wiki], who takes the idea considerably farther than I take it here.)
Is this really distinct from presentism? I say yes, because presentism is the view that the future and the past are not real. Using the outside view I describe here, the future and the past are clearly real: from the subject’s perspective at any given point in the tree, “now” is the point itself, “the past” is the limb leading from the birth of the cosmos to that point, and “the future” is the sub-branch of the overall tree that begins at now. But we can’t recover the common-sense idea of a single future path that will be the one that I experience.
Earlier we said that the researcher cannot both be the researcher of World-Slit-A and the researcher of World-Slit-B because a person cannot be made of disparate sets of non-interacting particles. But really, there was a fallacy in that. Instants in classical time are separated from each other in just the same way that parallel worlds are separated from each other. They, too, do not “interact”; that is, they do not interact in the way that the neurons in my brain interact. They have a relationship with one another, but that relationship is static by definition, a relationship of physical-logical-mathematical implication.
What this means is that, fundamentally, there is no difference in kind between, in one case, the strangeness of the researcher of World-Slit-A being unable to experience the subjectivity of the researcher of World-Slit-B, despite being the same person; and the strangeness of me being unable to experience the subjectivity of myself ten seconds ago. So, at this point, the phenomenological (what-is-it-like) question raised by many-worlds seems to be solved.
And yet, a surprising implication of this chain of reasoning remains open for consideration. If there is no difference in kind between the separation of a subject from her counterparts in parallel worlds, and the separation of a subject from versions of herself in past instants, then why suppose a new, separate kind of difference, a relationship of non-identity, between a subject and an entirely different subject?
In the understanding put forth so far, my identity is preserved across instants because I change only gradually: the person I am now is recognizable and distinguishable in instants in the near-past and near-future. But considered along the full path, these changes accumulate. At the extents, there is a “me” who is just a fetus, a “me” who is a shrivelled old man—very possibly, a “me” who is just at the moment of disintegration in a nuclear blast. All these “mes” seem to have very little physically in common with each other.
Accordingly, it’s fair to ask: how do I know that you, reading this now, are not also an instance of me?
It’s useful to consider this surprising question from the perspective of Buddhist doctrine, in particular the concept of Anattā or “no-self” and the concept of the “five aggregates” [wiki]. According to Buddhist practice, when we ask ourselves what we are, five possible answers come forward:
Our material form (rupa);
Our feelings (vedana);
Our perceptions (samjna);
Our thoughts, beliefs, and ideas (sankhara);
Our consciousness, in the sense of our foundational capacity for awareness (vijñāna)
Here the accounts may diverge slightly depending on the school, but the general idea is that enlightenment consists in fully realizing the fact that I am none of these things, by virtue of the fact that I observe them: I cannot be something and simultaneously be what observes it. In addition, each of these candidate aspects of the self can be broken down into parts that do not add up to the whole, and each of them fluctuates in time, failing to provide a true foundation for self. Accordingly, self is void, and the full acceptance of this truth corresponds to final enlightenment and liberation from all being.
The idea is restated in the book On Having No Head by Douglas Harding. As my friend Stephen Arthur put it to me, in reference to that book: “My void is your void.” The void of self, when distinguished from all the attributes of any one being at any one instant, is the same in all cases: by definition, there is only one void, one thing that is entirely without attributes.
Following this idea, the void of self is the void of all selves. Put another way, the void is the experiencer of all that can be experienced. Experience is unitary; it only appears fragmentary to a given subject because a subject is a special case of experience: experience as it applies to a certain being.
Of course, we can debate how much this idea is an interpretation of quantum mechanics, and how much it is an independent philosophical notion. Some interpreters of physics argue that we should resist attempting to answer philosophical questions in quantum mechanical terms, not least because quantum mechanics itself is still in flux: it has yet to be unified with general relativity.
Yet, let us permit ourselves to entertain this idea. And let us permit ourselves to extend it a bit further. Let us imagine that in the set of all possible experiences in the universe, there is an ordering. Let us imagine that the experience of this instant has an end, and when it ends, I wink out of existence as Mattias Martens at 9:41 PM on August 23, 2021; and I wink back in, not necessarily as me in the next instant (for I may not exist in the next instant), but as some other being in the tree of possibility and time—perhaps, indeed, as you.
We can think of this as an unnecessarily overloaded way of understanding consciousness in the multiverse, or perhaps as a poetic interpretation of something that can’t quite be directly accessed by the mind. Either way, we imagine ourselves as the Wandering Consciousness, experiencing all there is to experience: experiencing me, writing this, and you, reading this; experiencing life as a factory owner and life as a worker, life as a caribou and life as a wolf, life as an insect, as a bacterium, as every pair of ragged claws scuttling across the floors of silent seas.
We can imagine a church of this wandering consciousness. In this church, as we greet one another, we hold in our minds the certainty that the experience that seems inaccessible to the senses, the experience of life from behind one another’s eyes, is open to us: not in this moment, for all I have in this moment are the senses and memories and apprehensions of one body, but somewhere in the chain of experience, in the unknown and possibly infinite path of the Wandering Consciousness that experiences all things. And we greet each other with the holy phrase: “I look forward to being you.”
I look forward to being you.