Reality+ : Virtual Worlds and the Problems of Philosophy (9780393635812), page 44
There’s also the role of the computer in Sim Universe. In many computer architectures, interactions between digital objects will be mediated by a central processing unit. This means that while a proton and an electron may interact directly in Nonsim Universe, their counterparts in Sim Universe will interact indirectly, with a CPU serving as a go-between. That’s a structural difference. But there’s a version of Nonsim Universe with the same sort of structural difference. We need only imagine that God mediates every interaction among physical objects, as in occasionalist theories of causation that originated with al-Ghazali and other Islamic philosophers and were later taken up by the French philosopher Nicolas Malebranche. If God mediates all interactions, then causation will have a surprising structure, but atoms and other physical objects will still exist.
To sum up our discussion of the third premise: while universe simulations may have excess structure compared to nonsimulated universes, all the structure in Nonsim Universe is mirrored in Sim Universe, and that’s enough for our physical theories to be true there.
The conclusion is that if we’re in Sim Universe, our physical theories are true. At least, the physical objects in these theories—quarks, photons, atoms, and molecules—exist and are distributed through space and time much as those theories say. And once we’ve established this much, there’s little reason to doubt that cells, trees, rocks, planets, and other physical objects exist too.
There are some limits to the conclusion. It does not establish that beings in a simulation are conscious, so it does not address the problem of other minds. It also applies only to perfect simulations such as Sim Universe (I’ll discuss simulations more broadly in chapter 24). But the strategy does establish that if we’re in a perfect simulation such as Sim Universe, ordinary physical objects in the external world exist on a par with the existence of objects in Nonsim Universe. That’s a form of simulation realism.
What realizes the structure?
Suppose we’re in Sim Universe, a perfect simulation of Nonsim Universe. If I’m right, our universe contains quarks, atoms, and molecules, as our physics suggests. But if we’re in Sim Universe, our physics isn’t the bottom level. Underlying our physics is a computer in the next universe up. Let’s call that universe Meta Universe. Meta Universe may or may not itself be simulated. It has its own physics, which may be entirely different from the physics of Sim Universe. While Sim Universe and Nonsim Universe have a 4-dimensional spacetime, Meta Universe may be 26-dimensional and may be inhabited by beings we can barely conceive of.
What’s the relationship between the physics of Meta Universe and the physics of Sim Universe? It’s natural to say that the former realizes the latter. Biology in our world is realized by chemistry, and chemistry is realized by physics. If we’re in Sim Universe, physics is realized by what in chapter 14 we called meta-physics—the physics of Meta Universe.
If Sim Universe is a perfect simulation of Nonsim Universe, we’ll never learn about Meta Universe. Even if we’re in Sim Universe, all our evidence is consistent with our being in Nonsim Universe. We can speculate that our universe is a simulation in Meta Universe, but we won’t know unless the simulation is imperfect and some evidence leaks in.
All this brings out that the perfect simulation hypothesis is highly congenial to epistemic structural realism: the it-from-structure-from-X view. Recall that this view holds that whatever science tells us about the structure of physical reality, there’s an underlying nature, X, which science tells us nothing about. If we’re in a perfect simulation, our physics has the same structure as in Nonsim Universe but with the underlying nature of Meta Universe. We can know about the structure but not about its underlying nature.
Of course, the physics of Meta Universe has a structure of its own. So in this case, the structure in Sim Universe is realized by further structure in Meta Universe. This leaves open how the structure in Meta Universe is realized. Perhaps it’s realized by further structure, in a Meta Meta Universe. But that just defers the problem, so let’s just focus on the original top-level universe (the one that contains all the others), wherever it is.
How is structure realized in the top-level universe? There are two possibilities: First, the top-level universe may be a universe of pure structure. If so, we have the pure it-from-structure view at the top level (a version of ontological structural realism).
Alternatively, the top-level universe is a universe of impure structure; the structure is realized by something nonstructural. If so, we have the it-from-structure-from-it view at the top level—again, consistent with epistemic structural realism.
I don’t know which of these two possibilities is correct. The universe of pure structure is austere and elegant, but does it make sense? Recall the pure it-from-bit view. How could there be pure bits—that is, bits that aren’t differences in something more basic, such as voltages or charges, but instead are simply pure differences? The same issue arises more generally for the pure it-from-structure view. How could there be pure structure—logical and mathematical structure that isn’t structure in anything more basic? A conservative part of my mind wants to say that this is inconceivable, but a more open-minded part wants to say that we can learn to conceive of the previously inconceivable.
The universe of impure structure is more obviously coherent—but mysterious nonetheless. Recall the it-from-bit-from-it view (introduced in chapter 8). If there is a truly basic “it” that underlies all structure, then what is the nature of this “it”? It’s hard to see how we could ever know. So we’re threatened with a version of the it-from-structure-from-X view where the X is forever unknowable.
One hypothesis about the basic X is especially attractive, at least for someone with philosophical views like mine: Consciousness may well not be reducible to structure. Frank Jackson’s thought experiment about Mary the color scientist suggests that structure alone cannot capture the conscious experience of redness. Conscious experiences may have structure, but they seem to go beyond structure. So, could the basic reality underlying structure involve a fundamental sort of consciousness?
If we start from the it-from-bit-from-it view, this line of reasoning leads to the it-from-bit-from-consciousness view, also discussed in chapter 8. If we generalize the line of reasoning beyond digital structure, it leads to the it-from-structure-from-consciousness view. There are a few different versions of that view. Perhaps the structure of physics could be realized in a single cosmic mind, as in an idealist view—or by interactions among many tiny minds at the bottom level, as in a panpsychist view (which holds that everything is conscious).
The it-from-bit-from-consciousness view has the advantage of integrating consciousness with structure at a deep level, without trying to reduce consciousness to structure (as materialism does) and without separating consciousness entirely from physical structure (as dualism does). Of course, the view faces many problems of its own, not least the “combination problem” of how consciousness at the ground level of physics can somehow add up to the distinctive sort of consciousness that we experience. But I’ll leave the it-from-bit-from-consciousness view on the table at least as an interesting speculation.
Kantian humility
Immanuel Kant, whose moral theory we encountered in chapter 18, had a distinctive view of reality, too. He held that there’s a realm of appearances and a distinct, unknowable realm of things in themselves. We can know about appearances, but we have no knowledge of things in themselves.
Suppose you’re looking at a cup. The cup that you see is an appearance. However, underlying this appearance there is also a thing in itself—in German, a Ding an sich. Kant holds that we cannot know about the thing in itself underlying the cup. The thing in itself is an unknowable X.
Kant called his view transcendental idealism. He held that appearances—the ordinary objects we perceive in space and time—are deeply tied to the human mind. At the same time, he held that things in themselves are beyond our minds and transcend our knowledge. Our inability to know about things in themselves is often called Kantian humility.
My analysis of the perfect simulation hypothesis is interestingly reminiscent of Kant’s transcendental idealism. Suppose we’re in a perfect simulation. Then when I see a cup, I can know some of its properties: I know its color and its shape; more generally, I can know its structural properties. All these can be seen as aspects of the cup as an appearance. But I cannot know the cup’s underlying nature. In reality, behind the appearances, there is a digital object running on a computer in Meta Universe. In Sim Universe, the digital object is unknowable to me. We might think of the digital cup in Meta Universe as an unknowable thing in itself.
Of course, the analogy with Kant’s view is imperfect. Kant would have counted the digital cup in Meta Universe as just another appearance because people in the next universe up can perceive it in space and time. He’d hold that underlying this digital cup is a truly unknowable thing in itself. But then, we’ve seen that the same is true for the structure of physics in Meta Universe.
Still, there’s an interesting mapping from our picture to Kant’s. The structure of reality corresponds to Kant’s knowable realm of appearances. Whatever underlies this structure corresponds to Kant’s unknowable things in themselves.
An interpretation of Kant’s philosophy along roughly these lines was broached by the Australian philosopher Rae Langton in her 1998 book Kantian Humility. According to Langton, Kant’s realm of appearances is the realm of relations between things, including spatiotemporal relations and causal relations. Kant’s realm of things in themselves is the realm of intrinsic properties of things—properties they have independently of relations to other things. The relational properties of reality are knowable, but the intrinsic properties are unknowable.
Figure 54 Immanuel Kant, the apparent cup, and the digital cup in itself—with an unknowable thing in itself beyond that?
In effect, the realm of appearances is a vast network of relations, akin to the way we described the New York City subway as a network of relations. This network of relations yields a structural picture of reality. The realm of things in themselves is akin to the intrinsic nature of the stations in the network, except at the most fundamental level of reality. These intrinsic properties yield an intrinsic picture of reality. According to this interpretation, Kant holds a version of the it-from-structure-from-X view, holding that the structure involves a network of relations and X involves underlying intrinsic properties that we can never know.
In effect, Langton reads Kant as an epistemic structural realist, although he wrote 200 years before that view was named. Some experts on Kant object that this view does not do justice to Kant’s complex idealistic picture of reality. Still, it is a picture I can understand, and even a picture that might be true. It’s also a picture that helps us make sense of the simulation hypothesis. So I hope that something like this view might have been Kant’s.
Whatever one says about the fine details of interpreting Kant, my interpretation of the simulation hypothesis clearly has a Kantian flavor. You can read the views of many great philosophers into the simulation hypothesis, starting with Plato and Zhuangzi. Perhaps the most popular readings use it to illustrate Cartesian skepticism or Berkeleyan idealism. But if I’m right, the most apt reading is as an illustration of Kantian humility.
Chapter 23
Have we fallen from the Garden of Eden?
I LIKE TO THINK OF THE GARDEN OF EDEN AS A PLACE WHERE everything was exactly as it seemed to be, in our pre-theoretical picture of reality.
In Eden, everything was laid out in a three-dimensional Space. Space was Euclidean and was not relative to anything. Things in Eden changed with the passage of Time. Time flowed from moment to moment in one direction, with absolute simultaneity across the garden and across the universe.
The apple in the garden was gloriously, perfectly, and primitively Red. When we Perceived the apple, the apple and its Redness were simply revealed to us directly, without any mediation.
Rocks in Eden were Solid, full of matter all the way through without any empty space. They had an absolute Weight, which did not vary from place to place.
People in Eden had Free Will. They could act with complete autonomy, and their actions were not predetermined. Their actions were Right or Wrong. They either met the standards of Morality or they did not.
Then there was a Fall. We ate from the Tree of Science, and we were cast out of Eden.
We discovered that we didn’t live in an absolute three-dimensional Space in a world of absolute Time that passes. Instead, we live in a four-dimensional and non-Euclidean spacetime. Space and time are relative to reference frames, and there’s no absolute now.
We discovered that we didn’t live in a world where objects have intrinsic qualitative Colors that are revealed to us in Perception. Instead, colors are complex physical properties that affect our eyes and our brains in complicated ways. In perception, colors aren’t directly revealed to us but instead are inferred by the visual systems in our brains.
We discovered that rocks aren’t Solid. They consist of mostly empty space and are merely solid. They don’t have an absolute Weight: They have one weight on Earth, another on the Moon, and in outer space they’re weightless.
The jury is still out, but evidence suggests that we may not have Free Will. Our brains seem to be mechanical systems that determine our actions or at least strongly constrain them. However, we may still have free will—the ability to choose our own actions and mostly do what we choose to do. There may be no absolute standard of Morality by which our actions are Right or Wrong. Instead, there may simply be a system of morality that we construct and endorse, according to which our actions are right or wrong.
We no longer live in Eden. We’re growing accustomed to our non-Edenic world. But Eden still plays a powerful role in our picture of reality. Perception still presents us with a world of Colorful and Solid objects laid out in Space and changing with Time. We naturally think of people as acting Freely and doing things that are Right or Wrong.
All this helps to explain our intuitive reactions to the simulation hypothesis. Intuitively, if we are in a simulation, nothing is as it seems. We seem to be in a universe of solid and colorful objects laid out in a certain way in space. If we’re in a simulation, we’re not in such a universe.
I diagnose our intuitive reaction as follows. We seem to be in an Eden-like world of Solid and Colorful objects laid out in a certain way in Space. If we’re in a simulation, our world isn’t like this. The simulation doesn’t contain Solid and Colorful objects in Space.
But the same goes for our scientific world of quantum mechanics and relativity. Solidity, Color, and Space disappeared from the scientific world picture a long time ago. We reconceived Solidity, Color, and Space as solidity, color, and space. The simulation hypothesis is no worse off than the scientific worldview here. Neither contains Solidity, Color, or Space. But both contain solidity, color, and space.
What is the difference between Solidity and solidity, Color and color, between Space and space? That’s a story I’ll try to tell in this chapter.
The manifest image and the scientific image
In his 1962 article “Philosophy and the Scientific Image of Man,” the American philosopher Wilfrid Sellars distinguished two ways of looking at the world. The manifest image is the world as it appears in ordinary perception and thought. The scientific image is the world as it is characterized by science.
Sellars himself was especially concerned with the manifest and scientific images of human beings in the world. In the manifest image, we’re free and conscious beings whose actions result from reasons and decisions. In the scientific image, we’re biological organisms whose actions result from complex neural processes in our brain. How do we reconcile these two images of ourselves?
We can find manifest and scientific images for almost anything that we ordinarily think and talk about. In principle, we can distinguish the manifest image of the Sun (the Sun as we think of it in ordinary life) with the scientific image of the Sun (the Sun as science reveals it to be). The same goes for clouds and for trees. And we can certainly distinguish the manifest and the scientific images for color, space, solidity, and many of the other phenomena in the previous section.
The two images often clash. People seem one way in the manifest image and another way in the scientific image. If the images clash, what should we do? Throw out one of the images entirely? Or remake them so that they’re compatible?
The Canadian-American philosophers Patricia and Paul Churchland were both students of Sellars at the University of Pittsburgh in the 1960s. They have long argued that the scientific image has primacy over the manifest image. Where they clash, the manifest image should be discarded. Where human beings are concerned, this leads to Patricia Churchland’s program of neurophilosophy (discussed in the introduction), which holds that the science of the brain provides our best answers to traditional philosophical questions about the human mind. We should embrace a neuroscientific image of ourselves, with the brain and the nervous system at center stage.
Figure 55 The manifest and the scientific images: Patricia and Paul Churchland, in the Garden of Eden, eat from the Tree of Science.
Sellars himself thought that one of the tasks of the philosopher is to locate the manifest image within the scientific image. For any given part of the manifest image, there are a number of different things we can do with it:
(1) Elimination: We abandon the manifest image entirely in favor of the scientific image, as we abandon notions of witchhood and magic. The Churchlands have argued that much of our ordinary picture of the human mind should be eliminated in this way.
(2) Identification: We identify an aspect of the manifest image with an aspect of the scientific image, as when we identify water with H2O.
