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PH1102E Weeks 12 and 13

Appearance and reality

I. Sims

II. Are Sims radically deceived?

III. Are we Sims?

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I. Sims

The papers you read by Nick Bostrom (“Do we live in a computer simulation?”) and David

Chalmers (“The Matrix as metaphysics”) complement, and in some respects duplicate, one

another. The take-home message from Bostrom’s paper is that it’s more likely than you

probably realize that you are “living in a computer simulation”; the take-home message from

Chalmers’ is that if you are living in a computer simulation, it makes no difference to the vast

majority of your beliefs (apart from any beliefs you may have about the ultimate origins and

constitution of the Universe).

What does Bostrom mean when he says we might be living in a computer simulation? He

means much the same thing as Chalmers means when he speaks of “being in a matrix.” And this

is much the same as what Nozick means when we talks about “living in an experience

machine.” What all these hypothetical (or maybe not so hypothetical) situations have in

common is that in all of them, our thoughts and experiences consist of, or arise from, the

operations of a large computing device -- or, more abstractly, a large network of interconnected

and interdependent nodes -- as a result of that device’s receiving input from another large

computing device. The first device is computationally equivalent to a human brain. The second

is computationally equivalent to a human brain’s environment, starting from its body (skin,

eyes, ears, and other sense-organs; muscles, fingernails, etc.) and extending outwards from

there.

What does “computationally equivalent” mean? Think of your life as a process. It involves the

generation and loss of cells, the conversion of chemical energy (in food) to mechanical energy

(motor behavior), and myriad forms of cell activity, including brain-cell activity. Another Process

is computationally equivalent to your life-process, provided that for every event that plays a

role in your life-process, there is a corresponding event in the other Process, and for every

relevant relationship between the events in your life-process, there is a corresponding

relationship between the corresponding events of the other Process.

Similarly, we can consider a storm as a process. Another process, P, is computationally

equivalent to a storm, provided that for every relevant event of the storm (e.g., every

movement of a water molecule, or every electrical discharge) there is a corresponding event of

P, and, for every relevant relationship among events of the storm (e.g., that one lightning-bolt

preceded another), there is a corresponding relationship between the corresponding events of

P.

In general, two processes are computationally equivalent if they have the same number of

parts (parts being counted separately accordingly as they play separate roles in the process),

and if the relationships among these parts in the one process mirror the relationships among

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the parts of the other process. A part can be an event that occurs during some stage of the

process, or an object that is involved in the process, or a state of such an object at some point

in the process. The relationships among a process’ parts might be anything, subject only to the

limitations imposed by the natures of the parts (e.g., what they are made of).

Two process that relate to one another this way are said to be isomorphic. The processes that

take place in one of Bostrom’s ancestor simulations, or one of Chalmers’ matrices, or a

particularly powerful model of one of Nozick’s experience machines, are isomorphic to the

processes that occur in our minds, bodies, and environment. In terms of structure, therefore, a

“simulated” life (a life that is part of an ancestor simulation) is indistinguishable from an non-

simulated life: the same network of interdependencies characterizes both a simulated and an

non-simulated universe.

This leaves an important question unanswered. According to some philosophers of mind --

dualists -- there is more to having conscious thoughts and experiences than merely possessing a

brain (or other physical system) that operates as a complex network of interdependent

elements. If these philosophers are correct, there is no logical or metaphysical guarantee that

reproducing all of the world’s networking will reproduce all -- or any -- of the conscious thought

or experience that takes place in our world. Chalmers himself takes this line, being a dualist.

However, Chalmers argues that even though there is no outright contradiction in the idea that a

system isomorphic to a normally functioning human brain might fail to produce any conscious

thoughts or experiences, we have good reasons to think that as a matter of fact, if you were to

reproduce the activity of a normal human brain in the form of some other kind of process -- an

isomorphic process -- the result would be normal thought and experience.

His main argument for this is the “fading qualia” argument. Suppose that as you’re watching TV,

some doctors are somehow secretly replacing the neurons in your visual cortex (the part of

your brain responsible for visual imagery) with computer-chips that perform the same function

as the neurons they replace. They “perform the same function,” in the sense that they have the

same effects on, and are affected in the same ways by, the neurons to which they are

connected. By the end of the procedure, the doctors have replaced all of your natural neurons

with silicon prostheses.

Question: when the procedure is over, do you have visual experiences? Or are you blind, and

for that matter incapable of having any sort of visual imagery? But remember that in terms of

function -- input and output -- nothing has changed in your brain (or mind). Your “wiring”

remains the same, just using different kinds of wires and circuits (synthetic instead of organic).

The unreplaced neurons to which your new prosthetic neurons are connected are none the

wiser, so to speak. So, when we ask you at the end of the procedure whether you can see,

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you’ll say “Yes.” And when you get up off the sofa to get a drink from the refrigerator, you’ll

navigate your way as smoothly as ever. In a word: all of your behavior will remain the same as it

was before the surgery. But how strange all this would be, if you were now completely without

conscious visual experience!

There are also more general, methodological reasons to suppose that any process isomorphic

to a given conscious process is itself conscious. If something more than isomorphism with a

conscious process is required to achieve conscious thought and experience, what more is this?

Unless we are prepared to attribute occult powers to flesh -- powers irreproducible in any other

medium -- it is hard to see how we can fail to take isomorphism with our own neural processes

as decisive evidence of conscious thought and experience like ours.

The upshot of which is that conscious lives just like our own could, in theory, be conjured up in

an immensely powerful computer, or network of computers, along with an isomorphic

reproduction of everything we encounter in the world (at least, down to the level of resolution

that the computers can achieve). Such a reproduction would, if Chalmers is right, contain

mental lives just like ours. But would it also contain trees, rain, human bodies, and streetlights

just like the ones that we encounter on a regular basis?

No, not just like ours. But the Sim’s trees (etc.) do have something important in common with

our trees. Our trees are disposed to bring about certain experiences when we encounter them

in certain ways, or under certain circumstances. Simulated trees are disposed to bring about

the same experiences when Sims encounter them (the simulated trees) in certain ways, or

under circumstances.

Does this mean that there are trees in an ancestor simulation, in the same sense of “trees” as

there are trees in Kent Ridge Park? Are the things the Sims use for shade one kind of tree, the

things we use for shade another? Or are the things the Sims use for shade are “trees” in a

different sense from that in which the things we use for shade are “trees” -- i.e., do the Sims do

not mean the same thing as we do by “tree”? Hard to say.

In support of the first option (two kinds of tree, rather than two senses of “tree”): if we were

somehow uploaded into a Bostrom-like Sim World that included simulations of trees, we would

have tree-form experiences just like those we have now. (I’m assuming that my Sim “avatar” is

ismorphic to my non-simulated form.) The fact that we don’t have such experiences if we peer

into the computer running the simulation just shows that we can’t see the trees that are in the

simulation with our present sense organs, or from our present point of view. Or, so one might

argue.

In support of the second option (two senses of “tree,” rather than two kinds of tree): if we

create a Bostrom-like Sim World, this World will not contain anything that we, the Simulators,

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can use as firewood, or make into a table, or rest under for shade -- at least, not as long as we

reside outside the simulation. Our Sims can and do use their trees in all these ways -- or rather,

they “use their trees as firewood,” and “make tables with their trees,” and “use their trees for

shade.” They do these things in a sense different from that in which we do them, but

importantly similar as well: the thoughts and experiences of our Sims are just like those that we

have when we sit under a shade tree, and the Sims themselves as well as their trees are

isomorphic to us and our trees. So it’s not an accident or coincidence that we use the word

“tree” to refer to various states or operations of the computer running the simulation. But the

things in the simulation are not trees in the same sense of the word “tree” as the things in Kent

Ridge Park are trees. Or, so one could argue.

II. Are Sims radically deceived?

Suppose that you are running one of Bostrom’s ancestor simulations on a powerful 23rd

century computer. While doing so, you ask yourself: Are my Sims deceived? They have all kinds

of beliefs, and say all kinds of things, but how many of these are true? For example, my Sims

think and assert that there are trees. Are they correct to do so?

Consider an individual Sim in your simulation -- call him Sim Jim. When Sim Jim says, “This is a

tree,” pointing (or, “pointing”) to what he takes to be a tree, does he speak truly? That depends

on what he means by “tree.” If by “tree” he means “a non-simulated such-and-such” (filling in

whatever you want for “such-and-such”), his statement is false. But simulation (or its absence)

is not usually at the forefront of our minds -- or our Sims’ minds -- when we are talking about

trees.

If Sim Jim is a normal, non-philosophical person, what does he mean by “tree”? One thing he

could mean by “tree,” after all is said and done, is: the kind of thing that gives me such-and-

such experiences -- e.g., leafy green visual experiences, or barky rough tactile experiences, or

sweet blossomy olfactory experiences, etc. That is, he might define a tree as the kind of thing

that is apt to produce these sorts of experiences in me, under suitable circumstances (I’m

looking at, or touching the tree, or breathing in through my nose, or whatever).

More generally, Sim Jim might define all kinds of things as powers to produce suitable

experiences in him, under suitable conditions. A tree is a power to produce tree-form

experiences in him; a chair is a power to produce chair-form experiences in him; a

thunderstorm is a power to produce thunderstorm-form experiences in him; etc.

If this is how Sim Jim conceptualizes things, he is what’s known as a “phenomenalist.” Stated

simply, albeit somewhat crudely, phenomenalism is the view that if it looks, sounds, feels,

smells, and tastes like an X, then it’s an X. (Less crudely: if it constantly looks, sounds, etc. like

an X, then it’s an X. A thing that looks like a tree one moment and a cow the next moment, and

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generally fails to produce any stable set of experiences in onlookers, is not a tree, even when it

looks like one.)

According to phenomenalists, macroscopic -- and also microscopic -- beings are, as John Stuart

Mill puts it, “permanent possibilities of sensation.” It would have been better to call them

“permanent possible causes of sensation,” or “permanent opportunities for sensation.” While it

might sound strange at first, phenomenalism has quite a bit to recommend it. You might think

that the theory puts too much emphasis on the nature of our experiences, and not enough on

the natures of the things that cause them. What if there is a race of aliens whose minds are so

structured that streetlights give them the sensations that trees give us, and trees the sensations

that we get from streetlights? Would that make streetlights trees and trees streetlights? Or do

we have to say that whether a thing is a streetlight or a tree depends on our point of view?

If the phenomenalist had to say either of these things, he might be in trouble. But it is not clear

that he has to. If there were such a race of aliens, they would misperceive trees and

streetlights. For there is no way to swap sense-impressions of streetlights for sense-impressions

of trees without having to make radical alterations all throughout one’s experience, including

ones that will wreck its orderly and realistic quality. (What sensations do the aliens have when

they visit a streetlight factory? Or a nursery? How do they account for “trees’” ability to give

light, and “streetlights” shade?)

But suppose that somehow all of the aliens’ experiences are coherent with one another: they

experience trees as we experience streetlights, but somehow, taking all of their experience

together, the aliens’ experiences present to them a world as intelligible and orderly as the one

that our own experiences present to us. (So it is like the situation that would obtain if half the

human race saw things the way I do, the other half in photographic negative: see Fig. 1.)

Figure 1: Two ways of seeing the same things

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We can even suppose that the aliens experience color the way we experience sound, and time

the way we experience space. As long as their sensations enable them to navigate their

environment as effectively as our sensations allow us to navigate ours, there is nothing better

about our way of having sensations as opposed to theirs, any more than a map that portrays

water with blue and land with green is better than one that uses blue for land and green for

sea. A “permanent possibility of sensation” is therefore best understood as a reliable producer

(or potential producer) of sensations that have a certain place in a coherent mental life -- some

coherent mental life, not necessarily one with the same sensations as ours (or even sensations

anything like ours -- remember the bat).

If we accept phenomenalism, how should we describe the relationship between us and our

Sims? It is like the difference between people who see the world according to color-inverted

schemes, only more extreme, and with one side -- us, the simulators -- having a wider field of

vision than the other (our Sims). Our Sims perceive a field of events as complex as any that we

ordinarily perceive. These events form only a small fraction of that part of the world that we

can perceive, but that does not make them any less real than the events that take place outside

the computer, and unrelated to its inner workings. Indeed, it may be that for all we know, the

part of the world that we can perceive is just a small fraction of a world that contains simulators

of our world.

Phenomenalism is subject to an important restriction. While it may be alright to equate tables

and chairs, clouds and trees, mountains and atoms with permanent potential causes of

sensations, we cannot equate conscious minds with permanent potential causes of sensations.

For minds are (or, are also) permanent potential havers of sensations. They are the things in

which the permanent potential causes produce sensations (when they do). But we have already

found reason to believe that any being that is isomorphic to a conscious being (in the sense that

its parts and processes perfectly parallel those that we find in a conscious being, or such a

being’s body) is itself a conscious being. So, our Sims are not deceived in taking themselves and

their co-Sims to be conscious. They are every bit as conscious as we are.

Our Sims are mistaken if they think that the limits of reality coincide with the limits of what

they can perceive. They are also mistaken if they believe that their lives are not the product of

intelligent design, or that it they are the product of an infinitely benevolent designer (unless,

indeed, our world -- the world of the simulators -- is the work of such a designer). (Here I’m

assuming that we, the simulators, are not infinitely benevolent.) If we want to, we can create a

Sim who is deceived on one or more of these points. But even he will not have grounds to

relinquish any of his everyday beliefs. This is what Chalmers means when he says that the

suggestion that we might be residing in a simulated reality -- a matrix, experience machine, or

ancestor simulation -- is a metaphysical hypothesis, rather than a skeptical hypothesis.

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III. The likelihood that we are Sims

So far, we have considered what would follow if we were Sims. But isn’t the possibility that

we’re Sims merely that: a possibility, yes, but not one we have any reason to think is realized?

Not according to Nick Bostrom. At least: not if we have reason to think that our descendants

will have the means and motive to run ancestor simulations. For, the likelihood that we are

living in a computer simulation is approximately the likelihood that they will. This comes of the

fact that a civilization that runs ancestor simulations generates many more people, and many

more “worlds” (spheres of perceivable reality) than there ever were, are, or will be non-

simulated people living in a non-simulated world.

A common objection to this is that whatever our descendants may do, the fact that we are

talking about our descendants shows that we are not in a computer simulation. But all it really

shows is that we are not in any simulation that our descendants run. The point is that any

evidence we have that our descendants will run ancestor simulations is at the same time

evidence that ancestor simulations do get run at some time or another in the history of the

world -- the non-simulated world. If you think of all the lives that get lived in simulated worlds,

and all the lives that get lived in non-simulated worlds, you see that the lives in simulated

worlds vastly outnumber the lives in non-simulated worlds (assuming that ancestor simulations

ever get run). Therefore, unless we have some specific reason to think that our world is not

among the simulated ones, we should consider it likely that we are living in a computer

simulation.

The fact that to our knowledge no computer has been built with the power required to run an

ancestor simulation is neither here nor there, from this point of view. After all, there may be

countless ancestor simulations in which the Sims have the exactly as much -- which is to say,

exactly as little -- reason as we to think that no ancestor simulations have ever been run. It

would different, maybe, if there were an infinite number of non-simulated lives, but we have

no reason to think that any more than a finite number non-simulated lives ever get lived:

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The circle filled with vertical lines represents all lives that ever exist -- simulated as well as non-

simulated lives. The small circle flled with horizontal lines (as well as vertical ones) represents

the subset of these lives that are not simulated. In other words, the part of the big circle that

the small circle doesn’t cover represents the simulated lives. Actually, the small circle in this

diagram is misleadingly large (or the large circle misleadingly small): to represent the actual

ratio of simulated to non-simulated lives (assuming that ancestor simulations do get run) would

require a sheet of paper larger by far than this.

So, the question comes to this: do we have any reason to think that our lives are not part of a

computer simulation (or, better: a computer process)? If not, we need to take the possibility

that we are part of such a simulation more seriously than we are ordinarily inclined to take it.

M.W.P.