The Matrix
as Metaphysics
David J. Chalmers
The Matrix
In The Matrix
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Neo is hooked up to a giant computer simulation.
He has experiences of a normal reality in 1999.
In fact, it is 2199, and his body is floating in a tank.
A version of an old philosophical fable
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René Descartes’ evil genius
The brain in the vat
Brain in a Vat
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A brain in a vat, connected to a computer simulation of
the world, might have the same experiences that I do.
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The brain in a vat has beliefs corresponding to mine.
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I have hands
There is a table in front of me.
I am in Tucson.
These beliefs are massively false.
Envatment
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Let’s say:
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A matrix = an artificially-designed computer
simulation of a world.
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X is envatted (or X is in a matrix) = X has a
cognitive system which receives its inputs
from and sends its outputs to a matrix
The Matrix Hypothesis
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The Matrix Hypothesis: I am (and have always
been) in a matrix.
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For all I know, the Matrix Hypothesis is true!
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I can’t rule it out with certainty.
There may be many matrices developed in the
history of the universe.
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One “real” world, many “simulated” worlds.
More likely I’m in a simulated world?
Envatment as Delusion
Common view: If the Matrix Hypothesis is true,
then I have massively false beliefs:
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I do not have hands
There is no table in front of me
I am not in Tucson
I am completely deluded about reality.
Reality as a Hoax
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“Perception: Our day-in, day-out world is real.
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Reality: That world is a hoax, an elaborate
deception spun by all-powerful machines of
artificial intelligence that control us. Whoa.”
(from The Matrix DVD)
Skeptical Hypothesis
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If so: the Matrix Hypothesis is a skeptical hypothesis
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Its possibility suggests that we know very little about the world.
Skeptical argument
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I don’t know that I’m not envatted
If I’m envatted, most of my beliefs are false
 I don’t have hands, I’m not in Tucson, etc.
So I don’t know most of the things I believe
 I don’t know that I have hands, that I’m in Tucson, etc.
The Matrix Reconsidered
I’ll argue:
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The Matrix Hypothesis is not a skeptical hypothesis
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Even if I am envatted, I still have hands, there is still
a table in front of me, I am still in Tucson.
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Brains in vats have mostly true beliefs
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If I am in a matrix, things are perfectly real.
Appearance and Reality
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George Berkeley
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“Esse est percipi”
To exist is to be perceived
Idealism: reality = a set of appearances
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If so: the matrix yields reality.
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I don’t accept idealism
But will argue that nevertheless (for different reasons),
the matrix yields reality.
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Envatment as a Metaphysical
Hypothesis
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I’ll argue: the hypothesis that I am in a matrix is not a
skeptical hypothesis, but a metaphysical hypothesis.
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It is equivalent to a hypothesis about the underlying
metaphysical nature of the world.
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If accepted, this hypothesis might revise a few of our
beliefs, but it would leave most of them intact.
Three Metaphysical Hypotheses
I’ll present three metaphysical hypotheses
about the nature of our world, none of which is
a skeptical hypothesis.
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1. A Creation Hypothesis.
2. A Computational Hypothesis
3. A Dualistic Hypothesis
(We’ll then be considering their combination.)
Creation Hypothesis
Creation Hypothesis: Physical space-time and its
contents were created by agents outside physical
space-time.
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Cf. religious views of creation.
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The Creation Hypothesis could be true.
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The Creation Hypothesis is not a skeptical hypothesis:
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If the Creation Hypothesis is true, I still have hands, there is
still a table in front of me, I am still in Tucson.
Creation Hypothesis
Creator
Atoms
Computational Hypothesis
Computational Hypothesis: Physics is computational.
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I.e., microphysical processes throughout space-time are
constituted by underlying computational processes.
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Just as chemistry is constituted by physics, physics is
constituted by computations
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Underneath particles are patterns of bits
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E.g. Wolfram, A New Kind of Science
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An underlying cellular automaton?
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Perhaps: these computational processes are themselves
implemented by more basic processes.
Computational Hypothesis
Atoms
110101101011
011010000111
Computational Hypothesis II
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The Computational Hypothesis could be true.
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The Computational Hypothesis is not a skeptical
hypothesis:
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If it is true, there are still electrons and protons (they are just
implemented, as are molecules).
If it is true, I still have hands, and so on.
To accept it would involve revision to some of our
beliefs, but not massive revision.
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No more than quantum mechanics!
Dualistic Hypothesis
Dualistic Hypothesis: My mind is nonphysical and
interacts with the physical.
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My cognitive processes are outside physical space-time, and
receives their inputs from and send their outputs to processes
in physical space-time.
Cf. Descartes’ dualism.
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The Dualistic Hypothesis could be true.
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The Dualistic Hypothesis is not a skeptical hypothesis
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If it is true, I still have hands, and so on.
Dualistic Hypothesis
Mind
Atoms
Combination Hypothesis
Combination Hypothesis: A combination of the
Creation Hypothesis, the Computaional Hypothesis,
and the Dualistic Hypothesis.
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Physical processes were created by other beings, are
computationally implemented, and my nonphysical mind
interacts with them..
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The Combination Hypothesis could be true.
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The Combination Hypothesis is not a skeptical
hypothesis.
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If it is true, I still have hands, and so on.
Metaphysical Hypothesis
Metaphysical Hypothesis: The Combination
Hypothesis, plus
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The computational processes were designed by the creators
in order to simulate a world.
[and maybe: The implementing processes, my cognitive
processes, and the creators are all part of a broader domain.]
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The Metaphysical Hypothesis could be true.
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The Metaphysical Hypothesis is not a skeptical
hypothesis.
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If it is true, I still have hands, and so on.
Metaphysical Hypothesis
Atoms
Creator
110101101011
011010000111
Mind
Matrix/Metaphysics Equivalence
Matrix Hypothesis:
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‘My cognitive system receives its inputs from and sends its
outputs to an artificially-designed computer simulation of a
world’
Claim: The Matrix Hypothesis is equivalent to the
Metaphysical Hypothesis.
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If I accept the Metaphysical Hypothesis, I should accept the
Matrix Hypothesis.
If I accept the Matrix Hypothesis, I should accept the
Metaphysical Hypothesis.
Metaphysics  Matrix
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Dualistic Hypothesis  My cognitive system receives its inputs
from and sends its outputs to physical space-time.
Computational Hypothesis  My cognitive system receives inputs
from the computational processes implementing physical spacetime.
Creation Hypothesis  These computational processes were
artificially designed to simulate a world.
Jointly: My cognitive system receives its inputs from and sends its
outputs to an artifically-designed computer simulation of a world
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The Matrix Hypothesis!
Matrix Hypothesis
Creator
110101101011
011010000111
Mind
Matrix  Metaphysics
Matrix Hypothesis: Underlying reality is just as
Metaphysical Hypothesis specifies
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A computational implementation of physics, artificially
designed, interacting with my cognitive system.
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Things are the same at the underlying level, so things
are the same at all levels
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So the Matrix Hypothesis implies the Metaphysical
Hypothesis.
The Matrix: Not Skeptical
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The Matrix Hypothesis is equivalent to the Metaphysical
Hypothesis
The Metaphysical Hypothesis is not a skeptical hypothesis
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So: The Matrix Hypothesis is not a skeptical hypothesis
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Even if I am envatted
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I have hands
There is a table in front of me
I am in Tucson
The Matrix as Metaphysics
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If I discover that I am in a matrix, I should not
reject my ordinary beliefs about tables, etc.
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Instead, I have made a metaphysical discovery
about what tables are made of.
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The world is fundamentally made of bits!
Life in the Matrix
So: people in the Matrix have mostly true beliefs
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At least if the Matrix has been running for a long time.
A multi-vat matrix is needed for true beliefs about other minds.
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Brains in vats are not deluded.
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If we are in a matrix, things are perfectly real
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It’s just that the world is fundamentally computational.
No worse than the world being fundamentally quantummechanical!
Objection: Simulation is not reality
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Objection: The matrix is simulation, not reality
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Response: The Computational Hypothesis tells us
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Computation could underlie real physical processes
The computation must have all the detail of physics
The computation can itself be implemented.
The nature of the implementation doesn’t matter.
That it was designed as a simulation is irrelevant.
So a computer simulation could underlie reality
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If it is the basis of our experiences.
Objection: Deluded BIV?
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Objection: A brain in a vat might think “I’m out in the sun”, when it’s
in a dark lab. Deluded?
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Reply: The surroundings of the BIV in the brain’s domains are
irrelevant.
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Compare: A person with a Cartesian mind might think “I’m out in the
sun”, while the mind is really solitary ectoplasm. Deluded?
 Surroundings in the ectoplasmic domain are irrelevant,
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What matters is the causal basis of the cognitive system’s
experiences and beliefs, not the system’s surroundings.
Objection: Neo has hair?
Objection: Neo thinks ‘I have hair’.
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This thought will be true if the Neo has hair.
But Neo does not have hair!
So the Neo’s thought is false.
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Reply: ‘Hair’ means something different for a BIV.
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For BIV, ‘hair’ refers to virtual hair, constituted by
computational processes.
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BIV has virtual hair!
Same for virtual chairs, tables, etc.
Objection: BIV has world all wrong
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Objection: If we are envatted, the world is nothing like we think it
is.
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Reply: I deny this. Even if we are envatted, there are still people,
tables, football games, particles, arranged in space-time just as
we think they are.
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Deeper point: It’s just that the world has a further nature that goes
beyond our common sense conception. E.g.:
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quantum mechanics.
science reveals world’s structure, leaving intrinsic nature open
Residual Skepticism
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Matrix envatment is a non-skeptical hypothesis.
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But other skeptical hypotheses remain…
The Local Matrix
Local Matrix: Only my local environment is simulated,
not all of physical space-time.
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E.g. The Thirteenth Floor
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Akin to Truman Show skepticism: I still have hands, a
body, a house, but false beliefs about things further
from home.
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Moral: Being in the Truman Show is much worse than
being in the Matrix!
Other Skeptical Hypotheses
Recent Envatment: My mind was recently isolated and
connected to a computer simulation.
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Yields false beliefs about my present environment, although
past beliefs are OK.
Chaotic Envatment: My mind is isolated and receives
random stimulation from all sorts of sources that
coincidentally yield apparent regularity.
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Arguably: yields largely false or empty beliefs.
Tentative Moral
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If we assume there is some explanation for
the regularities in our experience, global
external-world skepticism is ruled out.
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Explanation yields reality?
Conclusion
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It’s not so bad to be a brain in a vat.
Next Time
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The mind-body problem
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DP, Chapter 2
Descartes, Meditations 1 and 2