This is a standard way of thinking
about the vat scenario. It seems that this view is also endorsed by
the people who created The Matrix . On the DVD case for the movie, one
sees the following:
I think this view is not quite right. I think that even if I am in
a matrix, my world is perfectly real. A brain in a vat is not massively
deluded (at least if it has always been in the vat). Neo does not have
massively false beliefs about the external world. Instead, envatted
beings have largely correct beliefs about their world. If so,
the Matrix Hypothesis is not a skeptical hypothesis, and its possibility
does not undercut everything that I think I know.
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Philosophers have held this sort of view before. The 18th-century Irish
philosopher George Berkeley held, in effect, that appearance is reality.
(Recall Morpheus: "What is real? How do you define real? If you're
talking about what you can feel, what you can smell, what you can taste
and see, then real is simply electrical signals interpreted by your
brain.") If this is right, then the world perceived by envatted
beings is perfectly real: they have all the right appearances, and appearance
is reality. So on this view, even envatted beings have true beliefs
about the world.
I have recently found myself embracing a similar conclusion, though
for quite different reasons. I don't find the view that appearance is
reality plausible, so I don't endorse Berkeley's reasoning. And until
recently, it has seemed quite obvious to me that brains in vats would
have massively false beliefs. But I now think there is a line of reasoning
that shows that this is wrong.
I still think I cannot rule out the hypothesis that I am in a matrix.
But I think that even I am in a matrix, I am still in Tucson, I am still
sitting at my desk, and so on. So the hypothesis that I am in a matrix
is not a skeptical hypothesis. The same goes for Neo. At the beginning
of the film, if he thinks "I have hair", he is correct. If
he thinks "It is sunny outside", he is correct. And the same
goes, of course, for the original brain in a vat. When it thinks "I
have a body", it is correct. When it thinks "I am walking",
it is correct.
This view may seem very counterintuitive at first. Initially, it seemed
quite counterintuitive to me. So I'll now present the line of reasoning
that has convinced me that it is correct.
III. The Metaphysical Hypothesis
I will argue that the hypothesis that I am envatted is not a skeptical
hypothesis, but a metaphysical hypothesis. That is, it is a hypothesis
about the underlying nature of reality.
Where physics is concerned with the microscopic processes that underlie
macroscopic reality, metaphysics is concerned with the fundamental nature
of reality. A metaphysical hypothesis might make a claim about the reality
that underlies physics itself. Alternatively, it might say something
about the nature of our minds, or the creation of our world.
I think the Matrix Hypothesis should be regarded as a metaphysical hypothesis
with all three of these elements. It makes a claim about the reality
underlying physics, about the nature of our minds, and about the creation
of the world.
In particular, I think the Matrix Hypothesis is equivalent to a version
of the following three-part Metaphysical Hypothesis. First, physical
processes are fundamentally computational. Second, our cognitive systems
are separate from physical processes, but interact with these processes.
Third, physical reality was created by beings outside physical space-time.
Importantly, nothing about this Metaphysical Hypothesis is skeptical.
The Metaphysical Hypothesis here tells us about the processes underlying
our ordinary reality, but it does not entail that this reality does
not exist. We still have bodies, and there are still chairs and tables:
it's just that their fundamental nature is a bit different from what
we may have thought. In this manner, the Metaphysical Hypothesis is
analogous to a physical hypotheses, such as one involving quantum mechanics.
Both the physical hypothesis and the Metaphysical Hypothesis tells us
about the processes underlying chairs. They do not entail that there
are no chairs. Rather, they tell us what chairs are really like.
I will make the case by introducing each of the three parts of the Metaphysical
Hypothesis separately. I will suggest that each of them is coherent,
and cannot be conclusively ruled out. And I will suggest that none of
them is a skeptical hypothesis: even if they are true, most of our ordinary
beliefs are still correct. The same goes for a combination of all three
hypothesis. I will then argue that the Matrix Hypothesis hypothesis
is equivalent to this combination.
(1) The Creation Hypothesis
The Creation Hypothesis says: Physical space-time and its contents were
created by beings outside physical space-time.
This is a familiar hypothesis. A version of it is believed by many
people in our society, and perhaps by the majority of the people in
the world. If one believes that God created the world, and if one believes
that God is outside physical space-time, then one believes the Creation
Hypothesis. One needn't believe in God to believe the Creation Hypothesis,
though. Perhaps our world was created by a relatively ordinary being
in the "next universe up", using the latest world-making technology
in that universe. If so, the Creation Hypothesis is true.
I don't know whether the Creation Hypothesis is true. But I don't know
for certain that it is false. The hypothesis is clearly coherent, and
I cannot conclusively rule it out.
The Creation Hypothesis is not a skeptical hypothesis. Even if it is
true, most of my ordinary beliefs are still true. I still have hands,
I am still in Tucson, and so on. Perhaps a few of my beliefs will turn
out false: if I am an atheist, for example, or if I believe all reality
started with the Big Bang. But most of my everyday beliefs about the
external world will remain intact.
(2) The Computational Hypothesis
The Computational Hypothesis says: Microphysical processes throughout
space-time are constituted by underlying computational processes.
The Computational Hypothesis says that physics as we know it not the
fundamental level of reality. Just as chemical processes underlie biological
processes, and microphysical processes underlie chemical processes,
something underlies microphysical processes. Underneath the level of
quarks and electrons and photons is a further level: the level of bits.
These bits are governed by a computational algorithm, which at a higher-level
produces the processes that we think of as fundamental particles, forces,
and so on.
The Computational Hypothesis is not as widely believed as the Creation
Hypothesis, but some people take it seriously. Most famously, Ed Fredkin
has postulated that the universe is at bottom some sort of computer.
More recently, Stephen Wolfram has taken up the idea in his book A
New Kind of Science, suggesting that at the fundamental level,
physical reality may be a sort of cellular automata, with interacting
bits governed by simple rules. And some physicists have looked into
the possibility that the laws of physics might be formulated computationally,
or could be seen as the consequence of certain computational principles.
One might worry that pure bits could not be the fundamental level of
reality: a bit is just a 0 or a 1, and reality can't really be zeroes
and ones. Or perhaps a bit is just a "pure difference" between
two basic states, and there can't be a reality made up of pure differences.
Rather, bits always have to be implemented by more basic states, such
as voltages in a normal computer.
I don't know whether this objection is right. I don't think it's completely
out of the question that there could be a universe of "pure bits".
But this doesn't matter for present purposes. We can suppose that the
computational level is itself constituted by an even more fundamental
level, at which the computational processes are implemented. It doesn't
matter for present purposes what that more fundamental level is. All
that matters is that microphysical processes are constituted by computational
processes, which are themselves constituted by more basic processes.
From now on I will regard the Computational Hypothesis as saying this.
I don't know whether the Computational Hypothesis is correct. But again,
I don't know that it is false. The hypothesis is coherent, if speculative,
and I cannot conclusively rule it out.
The Computational Hypothesis is not a skeptical hypothesis. If it is
true, there are still electrons and protons. On this picture, electrons
and protons will be analogous to molecules: they are made up of something
more basic, but they still exist. Similarly, if the Computational Hypothesis
is true, there are still tables and chairs, and macroscopic reality
still exists. It just turns out that their fundamental reality is a
little different from what we thought.
The situation here is analogous to that with quantum mechanics or relativity.
These may lead us to revise a few "metaphysical" beliefs about
the external world: that the world is made of classical particles, or
that there is absolute time. But most of our ordinary beliefs are left
intact. Likewise, accepting the Computational Hypothesis may lead us
to revise a few metaphysical beliefs: that electrons and protons are
fundamental, for example. But most of our ordinary beliefs are unaffected.
(3) The Mind-Body Hypothesis
The Mind-Body Hypothesis says: My mind is (and has always been) constituted
by processes outside physical space-time, and receives its perceptual
inputs from and sends its outputs to processes in physical space-time.
The Mind-Body Hypothesis is also quite familiar, and quite widely
believed. Descartes believed something like this: on his view, we have
nonphysical minds that interact with our physical bodies. The hypothesis
is less widely believed today than in Descartes' time, but there are
still many people who accept the Mind-Body Hypothesis.
Whether or not the Mind-Body Hypothesis is true, it is certainly coherent.
Even if contemporary science tends to suggest that the hypothesis is
false, we cannot rule it out conclusively.
The Mind-Body Hypothesis is not a skeptical hypothesis. Even if my mind
is outside physical space-time, I still have a body, I am still in Tucson,
and so on. At most, accepting this hypothesis would make us revise a
few metaphysical beliefs about our minds. Our ordinary beliefs about
external reality will remain largely intact.
(4) The Metaphysical Hypothesis
We can now put these hypotheses together. First we can consider the
Combination Hypothesis, which combines all three. It says that physical
space-time and its contents were created by beings outside physical
space-time, that microphysical processes are constituted by computational
processes, and that our minds are outside physical space-time but interact
As with the hypotheses taken individually, the Combination Hypothesis
is coherent, and we cannot conclusively rule it out. And like the hypotheses
taken individually, it is not a skeptical hypothesis. Accepting it might
lead us to revise a few of our beliefs, but it would leave most of them
Finally, we can consider the Metaphysical Hypothesis (with a capital
M). Like the Combination Hypothesis, this combines the Creation Hypothesis,
the Computational Hypothesis, and the Mind-Body Hypothesis. It also
adds the following more specific claim: the computational processes
underlying physical space-time were designed by the creators as a computer
simulation of a world.
(It may also be useful to think of the Metaphysical Hypothesis as saying
that the computational processes constituting physical space-time are
part of a broader domain, and that the creators and my cognitive system
are also located within this domain. This addition is not strictly necessary
for what follows, but it matches up with the most common way of thinking
about the Matrix Hypothesis.)
The Metaphysical Hypothesis is a slightly more specific version of
the Combination Hypothesis, in that in specifies some relations between
the various parts of the hypothesis. Again, the Metaphysical Hypothesis
is a coherent hypothesis, and we cannot conclusively rule it out. And
again, it is not a skeptical hypothesis. Even if we accept it, most
of our ordinary beliefs about the external world will be left intact.
[ Top ]
IV. The Matrix Hypothesis as a Metaphysical
Recall that the Matrix Hypothesis says: I have (and have always had)
a cognitive system that receives its inputs from and sends its outputs
to an artificially-designed computer simulation of a world.
I will argue that the Matrix Hypothesis is equivalent to the Metaphysical
Hypothesis, in the following sense: if I accept the Metaphysical Hypothesis,
I should accept the Matrix Hypothesis, and if I accept the Matrix Hypothesis,
I should accept the Metaphysical Hypothesis. That is, the two hypotheses
imply each other, where this means that if one accepts the
one, one should accept the other.
Take the first direction first, from the Metaphysical Hypothesis to
the Matrix Hypothesis. The Mind-Body Hypothesis implies that I have
(and have always had) an isolated cognitive system which receives its
inputs from and sends its outputs to processes in physical space-time.
In conjunction with the Computational Hypothesis, this implies that
my cognitive system receives inputs from and sends outputs to the computational
processes that constitute physical space-time. The Creation Hypothesis
(along with the rest of the Metaphysical Hypothesis) implies that these
processes were artificially designed to simulate a world. It follows
that I have (and have always had) an isolated cognitive system that
receives its inputs from and sends its outputs to an artificially-designed
computer simulation of a world. This is just the Matrix Hypothesis.
So the Metaphysical Hypothesis implies the Matrix Hypothesis.
The other direction is closely related. To put it informally: If I accept
the Matrix Hypothesis, I accept that what underlies apparent reality
is just as the Metaphysical Hypothesis specifies. There is a domain
containing my cognitive system, causally interacting with a computer
simulation of physical-space time, which was created by other beings
in that domain. This is just what has to obtain in order for the Metaphysical
Hypothesis to obtain. If one accepts this, one should accept the Creation
Hypothesis, the Computational Hypothesis, the Mind-Body Hypothesis,
and the relevant relations among these.
This may be a little clearer through a picture. Here is the shape of
the world according to the Matrix Hypothesis.
At the fundamental level, this picture of the shape of the world is
exactly the same as the picture of the Metaphysical Hypothesis given
above. So if one accepts that the world is as it is according to the
Matrix Hypothesis, one should accept that it is as it is according to
the Metaphysical Hypothesis.
[ Top ]
One might make various objections. For example, one might object that
the Matrix Hypothesis implies that a computer simulation of physical
processes exists, but (unlike the Metaphysical Hypothesis) it does not
imply that the physical processes themselves exist. I will discuss this
and other objections in later sections. For now, though, I take it that
there is a strong case that the Matrix Hypothesis implies the Metaphysical
Hypothesis, and vice versa.
V. Life in the Matrix
If this is right, it follows that the Matrix Hypothesis is not a skeptical
hypothesis. If I accept it, I should not infer that the external world
does not exist, or that I have no body, or that there are no tables
and chairs, or that I am not in Tucson. Rather, I should infer that
the physical world is constituted by computations beneath the microphysical
level. There are still tables, chairs, and bodies: these are made up
fundamentally of bits, and of whatever constitutes these bits. This
world was created by other beings, but is still perfectly real. My mind
is separate from physical processes, and interacts with them. My mind
may not have been created by these beings, and it may not be made up
of bits, but it still interacts with these bits.
[ Top ]
The result is a complex picture of the fundamental nature of reality.
The picture is strange and surprising, perhaps, but it is a picture
of a full-blooded external world. If we are in a matrix, this is simply
the way that the world is.
We can think of the Matrix Hypothesis as a creation myth for the information
age. If it is correct, then the physical world was created, just not
necessarily by gods. Underlying the physical world is a giant computation,
and creators created this world by implementing this computation. And
our minds lie outside this physical structure, with an independent nature
that interacts with this structure.
Many of the same issues that arise with standard creation myths arise
here. When was the world created? Strictly speaking, it was not created
within our time at all. When did history begin? The creators
might have started the simulation in 4004 BC (or in 1999) with the fossil
record intact, but it would have been much easier for them to start
the simulation at the Big Bang and let things run their course from
there. When do our nonphysical minds start to exist? It depends on just
when new envatted cognitive systems are attached to the simulation (perhaps
at the time of conception within the matrix, or perhaps at time of birth?).
Is there life after death? It depends on just what happens to the envatted
systems once their simulated bodies die. How do mind and body interact?
By causal links that are outside physical space and time.
Even if we not in a matrix, we can extend a version of this reasoning
to other beings who are in a matrix. If they discover their situation,
and come to accept that they are in a matrix, they should not reject
their ordinary beliefs about the external world. At most, they should
come to revise their beliefs about the underlying nature of their world:
they should come to accept that external objects are made of bits, and
so on. These beings are not massively deluded: most of their ordinary
beliefs about their world are correct.
There are a few qualifications here. One may worry about beliefs about
other people's minds. I believe that my friends are conscious. If I
am in a matrix, is this correct? In the Matrix depicted in the movie,
these beliefs are mostly fine. This is a multi-vat matrix: for each
of my perceived friends, there is an envatted being in the external
reality, who is presumably conscious like me. The exception might be
beings such as Agent Smith, who are not envatted, but are entirely computational.
Whether these beings are conscious depends on whether computation is
enough for consciousness. I will remain neutral on that issue here.
We could circumvent this issue by building into the Matrix Hypothesis
the requirement that all the beings we perceive are envatted. But even
if we do not build in this requirement, we are not much worse off than
in the actual world, where there is a legitimate issue about whether
other beings are conscious, quite independently of whether we are in
One might also worry about beliefs about the distant past, and about
the far future. These will be unthreatened as long as the computer simulation
covers all of space-time, from the Big Bang until the end of the universe.
This is built into the Metaphysical Hypothesis, and we can stipulate
that it is built into the Matrix Hypothesis too, by requiring that the
computer simulation be a simulation of an entire world. There may be
other simulations that start in the recent past (perhaps the Matrix
in the movie is like this), and there may be others that only last for
a short while. In these cases, the envatted beings will have false beliefs
about the past and/or the future in their worlds. But as long as the
simulation covers the lifespan of these beings, it is plausible that
they will have mostly correct beliefs about the current state of their
There may be some respects in which the beings in a matrix are deceived.
It may be that the creators of the matrix control and interfere with
much of what happens in the simulated world. (The Matrix in the movie
may be like this, though the extent of the creators' control is not
quite clear.) If so, then these beings may have much less control over
what happens than they think. But the same goes if there is an interfering
god in a non-matrix world. And the Matrix Hypothesis does not imply
that the creators interfere with the world, though it leaves the possibility
open. At worst, the Matrix Hypothesis is no more skeptical in this respect
than the Creation Hypothesis in a non-matrix world.
The inhabitants of a matrix may also be deceived in that reality is
much bigger than they think. They might think their physical universe
is all there is, when in fact there is much more in the world, including
beings and objects that they can never possibly see. But again, this
sort of worry can arise equally in a non-matrix world. For example,
cosmologists seriously entertain the hypothesis that our universe may
stem from a black hole in the "next universe up", and that
in reality there may be a whole tree of universes. If so, the world
is also much bigger than we think, and there may be beings and objects
that we can never possibly see. But either way, the world that we see
is perfectly real.
Importantly, none of these sources of skepticism — about other
minds, the past and the future, about our control over the world, and
about the extent of the world — casts doubt on our belief in the
reality of the world that we perceive. None of them leads us to doubt
the existence of external objects such as tables and chairs, in the
way that the vat hypothesis is supposed to do. And none of these worries
is especially tied to the matrix scenario. One can raise doubts about
whether other minds exist, whether the past and the future exist, and
whether we have control over our worlds quite independently of whether
we are in a matrix. If this is right, then the Matrix Hypothesis does
not raise the distinctive skeptical issues that it is often taken to
I suggested before that it is not out of the question that we really
are in a matrix. One might have thought that this is a worrying conclusion.
But if I am right, it is not nearly as worrying as one might have thought.
Even if we are in such a matrix, our world is no less real than we thought
it was. It just has a surprising fundamental nature.
VI. Objection: Simulation is not Reality
(This slightly technical section can be skipped without too much loss.)
[ Top ]
A common line of objection is that a simulation is not the same as reality.
The Matrix Hypothesis implies only that a simulation of physical processes
exists. By contrast, the Metaphysical Hypothesis implies that physical
processes really exist (they are explicitly mentioned in the Computational
Hypothesis and elsewhere). If so, then the Matrix Hypothesis cannot
imply the Metaphysical Hypothesis. On this view, if I am in a matrix,
then physical processes do not really exist.
In response: My argument does not require the general assumption that
simulation is the same as reality. The argument works quite differently.
But the objection helps us to flesh out the informal argument that the
Matrix Hypothesis implies the Metaphysical Hypothesis.
Because the Computational Hypothesis is coherent, it is clearly possible
that a computational level underlies real physical processes, and it
is possible that the computations here are implemented by further processes
in turn. So there is some sort of computational system that
could yield reality here. But here, the objector will hold that not
all computational systems are created equal. To say that some computational
systems will yield real physical processes in this role is not to say
that they all do. Perhaps some of them are merely simulations. If so,
then the Matrix Hypothesis may not yield reality.
To rebut this objection, we can appeal to two principles. First, any
abstract computation that could be used to simulate physical space-time
is such that it could turn out to underlie real physical processes.
Second, given an abstract computation that could underlie physical
processes, the precise way in which it is implemented is irrelevant
to whether it does underlie physical processes. In particular,
the fact that the implementation was designed as a simulation is irrelevant.
The conclusion then follows directly.
On the first point: let us think of abstract computations in purely
formal terms, abstracting away from their manner of implementation.
For an abstract computation to qualify as a simulation of physical reality,
it must have computational elements that correspond to every particle
in reality (likewise for fields, waves, or whatever is fundamental),
dynamically evolving in a way that corresponds to the particle's evolution.
But then, it is guaranteed that the computation will have a rich enough
causal structure that it could in principle underlie physics
in our world. Any computation will do, as long as it has enough detail
to correspond to the fine details of physical processes.
On the second point: given an abstract computation that could underlie
physical reality, it does not matter how the computation is implemented.
We can imagine discovering that some computational level underlies the
level of atoms and electrons. Once we have discovered this, it is possible
that this computational level is implemented by more basic processes.
There are many hypotheses about what the underlying processes could
be, but none of them is especially privileged, and none of them would
lead us to reject the hypothesis that the computational level constitutes
physical processes. That is, the Computational Hypothesis is implementation-independent:
as long as we have the right sort of abstract computation, the manner
of implementation does not matter.
In particular, it is irrelevant whether or not these implementing processes
were artificially created, and it is irrelevant whether they were intended
as a simulation. What matters is the intrinsic nature of the processes,
not their origin. And what matters about this intrinsic nature is simply
that they are arranged in such a way to implement the right sort of
computation. If so, the fact that the implementation originated as a
simulation is irrelevant to whether it can constitute physical reality.
There is one further constraint on the implementing processes: they
must be connected to our experiences in the right sort of way. That
is when we have an experience of an object, the processes underlying
the simulation of that object must be causally connected in the right
sort of way to our experiences. If this is not the case, then there
will be no reason to think that these computational processes underlie
the physical processes that we perceive. If there is an isolated computer
simulation to which nobody is connected in this way, we should say that
it is simply a simulation. But an appropriate hook-up to our perceptual
experiences is built into the Matrix Hypothesis, on the most natural
understanding of that hypothesis. So the Matrix Hypothesis has no problems
Overall, then, we have seen that a computational process could
underlie physical reality, that any abstract computation that qualifies
as a simulation of physical reality could play this role, and that any
implementation of this computation could constitute physical reality,
as long as it is hooked up to our experiences in the relevant way. The
Matrix Hypothesis guarantees that we have an abstract computation of
the right sort, and it guarantees that it is hooked up to our experiences
in the relevant way. So the Matrix Hypothesis implies that the Computational
Hypothesis is correct, and that the computer simulation constitutes
genuine physical processes.
VII. Other Objections
When we look at a brain in a vat from the outside, it is hard to avoid
the sense that it is deluded. This sense manifests itself in a number
of related objections. These are not direct objections to the argument
above, but they are objections to its conclusion.
[ Top ]
1: A brain in a vat may think it is outside walking in the
sun, when in fact it is alone in a dark room. Surely it is deluded!
Response: The brain is alone in a dark room. But this does
not imply that the person is alone in a dark room. By analogy,
just say Descartes is right that we have disembodied minds outside space-time,
made of ectoplasm. When I think "I am outside in the sun",
an angel might look at my ectoplasmic mind and note that in fact it
is not exposed to any sun at all. Does it follow that my thought is
incorrect? Presumably not: I can be outside in the sun, even if my ectoplasmic
mind is not. The angel would be wrong to infer that I have an incorrect
belief. Likewise, we should not infer that envatted being has an incorrect
belief. At least, it is no more deluded than a Cartesian mind.
The moral is that the immediate surroundings of our minds may well be
irrelevant to the truth of most of our beliefs. What matters is the
processes that our minds are connected to, by perceptual inputs and
motor outputs. Once we recognize this, the objection falls away.
Objection 2: An envatted being may believe that it
is in Tucson, when in fact it is in New York, and has never been anywhere
near Tucson. Surely this belief is deluded.
Response: The envatted being's concept of "Tucson" does not
refer to what we call Tucson. Rather, it refers to something else entirely:
call this Tucson*, or "virtual Tucson". We might think of
this as a "virtual location" (more on this in a moment). When
the being says to itself "I am in Tucson", it really is thinking
that it is in Tucson*, and it may well in fact be in Tucson*. Because
Tucson is not Tucson*, the fact that the being has never been in Tucson
is irrelevant to whether its belief is true.
A rough analogy: I look at my colleague Terry, and think "that's
Terry". Elsewhere in the world, a duplicate of me looks at a duplicate
of Terry. It thinks "that's Terry", but it is not looking
at the real Terry. Is its belief false? It seems not: my duplicate's
"Terry" concept refers not to Terry, but to his duplicate
Terry*. My duplicate really is looking at Terry*, so its belief is true.
The same sort of thing is happening in the case above.
Objection 3: Before he leaves the Matrix, Neo believes
that he has hair. But in reality he has no hair (the body in the vat
is bald). Surely this belief is deluded.
Response: This case is like the last one. Neo's concept of "hair"
does not refer to real hair, but to something else that we might call
hair* ("virtual hair"). So the fact that Neo does not have
real hair is irrelevant to whether his belief is true. Neo really does
has virtual hair, so he is correct.
Objection 4: What sort of objects does an
envatted being refer to. What is virtual hair, virtual Tucson,
and so on?
Response: These are all entities constituted by computational processes.
If I am envatted, then the objects that I refer to (hair, Tucson, and
so on) are all made of bits. And if another being is envatted, the objects
that it refers to (hair*, Tucson*, and so on) are likewise made of bits.
If the envatted being is hooked up to a simulation in my computer, then
the objects it refers to are constituted by patterns of bits inside
my computer. We might call these things virtual objects. Virtual
hands are not hands (assuming I am not envatted), but they exist inside
the computer all the same. Virtual Tucson is not Tucson, but it exists
inside the computer all the same.
Objection 5: You just said that virtual hands are not
real hands. Does this mean that if we are in the matrix, we don't have
Response: No. If we are not in the matrix, but someone else
is, we should say that their term "hand" refers to virtual
hands, but our term does not. So in this case, our hands aren't virtual
hands. But if we are in the matrix, then our term "hand"
refers to something that's made of bits: virtual hands, or at least
something that would be regarded as virtual hands by people in the next
world up. That is, if we are in the matrix, real hands are
made of bits. Things look quite different, and our words refer to different
things, depending on whether our perspective is inside or outside the
This sort of perspective shift is common in thinking about the matrix
scenario. From the first-person perspective, we suppose that we are
in a matrix. Here, real things in our world are made of bits, though
the "next world up" might not be made of bits. From the third-person
perspective, we suppose that someone else is in a matrix but
we are not. Here, real things in our world are not made of bits, but
the "next world down" is made of bits. On the first way of
doing things, our words refer to computational entities. On the second
way of doing things, the envatted beings' words refer to computational
entities, but our words do not.
Objection 6: Just which pattern of bits is a given
virtual object? Surely it will be impossible to pick out a precise set.
Response: This question is like asking: just which part of the quantum
wavefunction is this chair, or is the University of Arizona? These objects
are all ultimately constituted by an underlying quantum wavefunction,
but there may be no precise part of the micro-level wavefunction that
we can say "is" the chair or the university. The chair and
the university exist at a higher level. Likewise, if we are envatted,
there may be no precise set of bits in the micro-level computational
process that is the chair or the university. These exist at a higher
level. And if someone else is envatted, there may be no precise sets
of bits in the computer simulation that "are" the objects
they refer to. But just as a chair exists without being any precise
part of the wavefunction, a virtual chair may exist without being any
precise set of bits.
Objection 7: An envatted being thinks it performs actions,
and it thinks it has friends. Are these beliefs correct?
Response: One might try to say that the being performs actions* and
that it has friends*. But for various reason I think it is not plausible
that words like "action" and "friend" can shift
their meanings as easily as words like like "Tucson" and "hair".
Instead, I think one can say truthfully (in our own language) that the
envatted being performs actions, and that it has friends. To be sure,
it performs actions in its environment, and its environment
is not our environment but the virtual environment. And its friends
likewise inhabit the virtual environment (assuming that we have a multi-vat
matrix, or that computation suffices for consciousness). But the envatted
being is not incorrect in this respect.
Objection 8: Set these technical points aside. Surely,
if we are in a matrix, the world is nothing like we think it is!
Response: I deny this. Even if we are in a matrix, there are still people,
football games, and particles, arranged in space-time just as we think
they are. It is just that the world has a further nature that
goes beyond our initial conception. In particular, things in the world
are realized computationally in a way that we might not have originally
imagined. But this does not contradict any of our ordinary beliefs.
At most, it will contradict a few of our more abstract metaphysical
beliefs. But exactly the same goes for quantum mechanics, relativity
theory, and so on.
If we are in a matrix, we may not have many false beliefs, but there
is much knowledge that we lack. For example, we do not know that the
universe is realized computationally. But this is exactly what one might
expect. Even if we are not in a matrix, there may well be much about
the fundamental nature of reality that we do not know. We are not omniscient
creatures, and our knowledge of the world is at best partial. This is
simply the condition of a creature living in a world.
VIII. Other Skeptical Hypotheses
The Matrix Hypothesis is one example of a traditional "skeptical"
hypothesis, but it is not the only example. Other skeptical hypotheses
are not quite as straightforward as the Matrix Hypothesis. Still, I
think that for many of them, a similar line of reasoning applies. In
particular, one can argue that most of these are not global skeptical
hypotheses: that is, their truth would not undercut all of our empirical
beliefs about the physical world. At worst, most of them are partial
skeptical hypotheses, undercutting some of our empirical beliefs, but
leaving many of these beliefs intact.
New Matrix Hypothesis: I was recently created, along
with all my memories, and was put in a newly-created matrix.
What if both the matrix and I have existed for only a short time? This
hypothesis is a computational version of Bertrand Russell's Recent Creation
Hypothesis: the physical world was created only recently (with fossil
record intact), and so was I (with memories intact). On that hypothesis,
the external world that I perceive really exists, and most of my beliefs
about its current states are plausibly true, but I have many false beliefs
about the past. I think the same should be said of the New Matrix Hypothesis.
One can argue, along the lines presented earlier, that the New Matrix
Hypothesis is equivalent to a combination of the Metaphysical Hypothesis
with the Recent Creation Hypothesis. This combination is not a global
skeptical hypothesis (though it is a partial skeptical hypothesis, where
beliefs about the past are concerned). So the same goes for the New
Recent Matrix Hypothesis: For most of my life I have not been
envatted, but I was recently hooked up to a matrix.
If I was recently put in a matrix without realizing it, it seems that
many of my beliefs about my current environment are false. Let's say
that just yesterday someone put me into a simulation, in which I fly
to Las Vegas and gamble at a casino. Then I may believe that I am in
Las Vegas now, and that I am in a casino, but these beliefs at false:
I am really in a laboratory in Tucson.
This result is quite different from the long-term matrix. The difference
lies in the fact that my conception of external reality is anchored
to the reality in which I have lived most of my life. If I have been
envatted all my life, my conception is anchored to the computationally
constituted reality. But if I was just envatted yesterday, my conception
is anchored to the external reality. So when I think that I am in Las
Vegas, I am thinking that I am in the external Las Vegas, and this thought
Still, this does not undercut all of my beliefs about the external world.
I believe that I was born in Sydney, that there is water in the oceans,
and so on, and all of these beliefs are correct. It is only my recently
acquired beliefs, stemming from perception of the simulated environment,
that will be false. So this is only a partial skeptical hypothesis:
its possibility casts doubt on a subset of our empirical beliefs, but
it does not cast doubt on all of them.
Interestingly, the Recent Matrix and the New Matrix hypothesis give
opposite results, despite their similar nature: the Recent Matrix Hypothesis
yields true beliefs about the past but false beliefs about the present,
while the New Matrix Hypothesis yields false beliefs about the past
and true beliefs about the present. The differences are tied to the
fact that in Recent Matrix Hypothesis, I really have a past existence
for my beliefs to be about, and that past reality has played a role
in anchoring the contents of my thoughts that has no parallel under
the New Matrix Hypothesis.
Local Matrix Hypothesis: I am hooked up to a computer
simulation of a fixed local environment in a world.
On one way of doing this, a computer simulates a small fixed environment
in a world, and the subjects in the simulation encounter some sort of
barrier when they try to leave that area. For example, in the movie
The Thirteenth Floor, just California is simulated, and when
the subject tries to drive to Nevada, the road says "Closed for
Repair" (with faint green electronic mountains in the distance!).
Of course this is not the best way to create a matrix, as subjects are
likely to discover the limits to their world.
This hypothesis is analogous to a Local Creation Hypothesis, on which
creators just created a local part of the physical world. Under this
hypothesis, we will have true beliefs about nearby matters, but false
beliefs about matters further from home. By the usual sort of reasoning,
the Local Matrix Hypothesis can be seen as a combination of the Metaphysical
Hypothesis with the Local Creation Hypothesis. So we should say the
same thing about this.
Extendible Local Matrix Hypothesis: I am hooked up
to a computer simulation of a local environment in a world, extended
when necessary depending on subject's movements.
This hypothesis avoids the obvious difficulties with a fixed local matrix.
Here the creators simulate a local environment and extend it when necessary.
For example, they might right now be concentrating on simulating a room
in my house in Tucson. If I walk into another room, or fly to another
city, they will simulate those. Of course they need to make sure that
when I go to these places, they match my memories and beliefs reasonably
well, with allowance for evolution in the meantime. The same goes for
when I encounter familiar people, or people I have only heard about.
Presumably the simulators keep up a database of the information about
the world that has been settled so far, updating this information whenever
necessary as time goes along, and making up new details when they need
This sort of simulation is quite unlike simulation in an ordinary matrix.
In a matrix, the whole world is simulated at once. There are high start-up
costs, but once the simulation is up and running, it will take care
of itself. By contrast, the extendible local matrix involves "just-in-time"
simulation. This has much lower start-up costs, but it requires much
more work and creativity as the simulation evolves.
This hypothesis is analogous to an Extendible Local Creation Hypothesis
about ordinary reality, under which creators create just a local physical
environment, and extend it when necessary. Here, external reality exists
and many local beliefs are true, but again beliefs about matters further
from home are false. If we combine that hypothesis with the Metaphysical
Hypothesis, the result is the Extendible Local Matrix Hypothesis. So
if we are in an extendible local matrix, external reality still exists,
but there is not as much of it as we thought. Of course if I travel
in the right direction, more of it may come into existence!
The situation is reminiscent of The Truman Show. Truman lives
in an artificial environment made up of actors and props, which behave
appropriately when he is around, but which may be completely different
when he is absent. Truman has many true beliefs about his current environment:
there really are tables and chairs in front of him, and so on. But he
is deeply mistaken about things outside his current environment, and
further from home.
It is common to think that while The Truman Show poses a disturbing
skeptical scenario, The Matrix is much worse. But if I am right,
things are reversed. If I am in a matrix, then most of my beliefs about
the external world are true. If I am in something like The Truman
Show, then a great number of my beliefs are false. On reflection,
it seems to me that this is the right conclusion. If we were to discover
that we were (and always had been) in a matrix, this would be surprising,
but we would quickly get used to it. If we were to discover that we
were (and always had been) in the Truman Show, we might well go insane.
Macroscopic Matrix Hypothesis: I am hooked up to a
computer simulation of macroscopic physical processes without microphysical
One can imagine that for ease of simulation, the makers of a matrix
might not both to simulate low-level physics. Instead, they might just
represent macroscopic objects in the world and their properties: e.g.
that there is a table with such-and-such shape, position, and color,
with a book on top of it with certain properties, and so on. They will
need to make some effort to make sure that these objects behave in a
physically reasonable way, and they will have to make special provisions
for handling microphysical measurements, but one can imagine that at
least a reasonable simulation could be created this way.
I think this hypothesis is analogous to a Macroscopic World Hypothesis:
there are no microphysical processes, and instead macroscopic physical
objects exist as fundamental objects in the world, with properties of
shape, color, position, and so on. This is a coherent way our world
could be, and it is not a global skeptical hypothesis, though it may
lead to false scientific beliefs about lower levels of reality. The
Macroscopic Matrix Hypothesis can be seen as a combination of this hypothesis
with a version of the Metaphysical Hypothesis. As such, it is not a
global skeptical hypothesis either.
One can also combine the various hypothesis above in various ways, yielding
hypotheses such as a New Local Macroscopic Matrix Hypothesis. For the
usual reasons, all of these can be seen as analogs of corresponding
hypotheses about the physical world. So all of them are compatible with
the existence of physical reality, and none is a global skeptical hypothesis.
The God Hypothesis: Physical reality is represented
in the mind of God, and our own thoughts and perceptions depend on God's
A hypothesis like this was put forward by George Berkeley as a view
about how our world might really be. Berkeley intended this as a sort
of metaphysical hypothesis about the nature of reality. Most other philosophers
have differed from Berkeley in regarding this as a sort of skeptical
hypothesis. If I am right, Berkeley is closer to the truth. The God
Hypothesis can be seen as a version of the Matrix Hypothesis, on which
the simulation of the world is implemented in the mind of God. If this
is right, we should say that physical processes really exist: it's just
that at the most fundamental level, they are constituted by processes
in the mind of God.
Evil Genius Hypothesis: I have a disembodied mind,
and an evil genius is feeding me sensory inputs to give the appearance
of an external world.
This is Rene Descartes's classical skeptical hypothesis. What should
we say about it? This depends on just how the evil genius works. If
the evil genius simulates an entire world in his head in order to determine
what inputs I should receive, then we have a version of the God Hypothesis.
Here we should say that physical reality exists and is constituted by
processes within the genius. If the evil genius is simulating only a
small part of the physical world, just enough to give me reasonably
consistent inputs, then we have an analog of the Local Matrix Hypothesis
(in either its fixed or flexible versions). Here we should say that
just a local part of external reality exists. If the evil genius is
not bothering to simulate the microphysical level, but just the macroscopic
level, then we have an analog of the Macroscopic Matrix Hypothesis.
Here we should say that local external macroscopic objects exist, but
our beliefs about their microphysical nature are incorrect.
The evil genius hypothesis is often taken to be a global skeptical hypothesis.
But if the reasoning above is right, this is incorrect. Even if the
Evil Genius Hypothesis is correct, some of the external reality that
we apparently perceive really exists, though we may have some false
beliefs about it, depending on details. It is just that this external
reality has an underlying nature that is quite different from what we
may have thought.
Dream Hypothesis: I am now and have always been dreaming.
Descartes raised the question: how do you know that you are not currently
dreaming? Morpheus raises a similar question:
Have you ever had a dream, Neo, that you were
so sure was real. What if you were unable to wake from that dream? How
would you know the difference between the dream world and the real world?
The hypothesis that I am currently
dreaming is analogous to a version of the Recent Matrix Hypothesis.
I cannot rule it out conclusively, and if it is correct, then many of
my beliefs about my current environment are incorrect. But presumably
I still have many true beliefs about the external world, anchored in
What if I have always been dreaming? That is, what if all of my apparent
perceptual inputs have been generated by my own cognitive system, without
my realizing this? I think this case is analogous to the Evil Genius
Hypothesis: it's just that the role of the "evil genius" is
played by a part of my own cognitive system! If my dream-generating
system simulates all of space-time, we have something like the original
Matrix Hypothesis. If it models just my local environment, or just some
macroscopic processes, we have analogs of the more local versions of
the Evil Genius Hypothesis above. In any of these cases, we should say
that the objects that I am currently perceiving really exist (although
objects farther from home may not). It is just that some of them are
constituted by my own cognitive processes.
Chaos Hypothesis: I do not receive inputs from anywhere
in the world. Instead, I have random uncaused experiences. Through a huge
coincidence, they are exactly the sort of regular, structured experiences
with which I am familiar.
The Chaos Hypothesis is an extraordinarily unlikely hypothesis, much more
unlikely than anything considered above. But it is still one that could
in principle obtain, even if it has miniscule probability. If I am chaotically
envatted, do physical processes obtain in the external world? I think
we should say that they do not. My experiences of external objects are
caused by nothing, and the set of experiences associated with my conception
of a given object will have no common source. Indeed, my experiences are
not caused by any reality external to them at all. So this is a genuine
skeptical hypothesis: if accepted, it would cause us to reject most of
our beliefs about the external world.
So far, the only clear case of a global skeptical hypothesis is the
Chaos Hypothesis. Unlike the previous hypothesis, accepting this hypothesis
would undercut all of our substantive beliefs about the external world.
Where does the difference come from?
Arguably, what is crucial is that on the Chaos Hypothesis, there is
no causal explanation of our experiences at all, and there is no explanation
for the regularities in our experience. In all the previous cases, there
is some explanation for these regularities, though perhaps not the explanation
that we expect. One might suggest that as long as a hypothesis involves
some reasonable explanation for the regularities in our experience,
then it will not be a global skeptical hypothesis.
If so, then if we are granted the assumption that there is some explanation
for the regularities in our experience, then it is safe to say that some
of our beliefs about the external world are correct. This is not much,
but it is something!
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Chalmers' website: www.consc.net
(Some philosophical notes on this article can be found here.)