6.3.pdf

The Matrix as Metaphysics
Final Lecture of the Year!

Two Senses of ‘Physical’

• Recall the notions of ‘substrate’ and ‘phenomenal aspect’
• Phenomenal aspect of a world = The parts of a world you can (potentially)

experience

• Substrate = The most fundamental level, that which underlies the
phenomenal aspect

• ‘Physical’ can be used in the context of the phenomenal aspect of a
world or its substrate
• Physical substrate = the most fundamental level of a world is microphysical

particles, not code, Cartesian immaterial substance, etc.

• Physical space-time = Physical objects that we can experience, thus a part of
(or maybe even the entire) the phenomenal aspect of a world

Physical Space-Time in The Matrix

• The Matrix has physical space-time
• It has objects you can see—otherwise, what were we watching?

• But not a physical substrate—that is code

Review: Conceptions of Reality

• Intuitive picture or conception of reality:
• Reality is mind-independent
• The substrate of reality is matter and energy
• Reality is the (absolute) base world

• When we are presented with a challenge to any of the premises of the ‘intuitive picture’ we have
a choice:
• Concede that the world we are in is not the real world
• Or re-define reality

• Chalmers really makes two claims
• The first, The Metaphysical, or Matrix, Hypothesis is a claim of what being in a virtual reality (Matrix) world

would amount to
• Remember, it’s different from the movie (not glitchy, evil, etc.)

• The second claim is the Metaphysical reading of The Metaphysical/Matrix Hypothesis.
• The Metaphysical Reading is: if The Metaphysical Hypothesis is true, our world would still be the real world.
• We would just need to re-define the substrate
• It contrasts with the skeptical reading, which says we would not be in the real world if the Metaphysical Hypothesis were true

• Metaphysical reading → Re-define reality
• Skeptical reading → Keep Intuitive conception of reality

The Matrix Hypothesis

• The Combination Hypothesis consists in three separate hypotheses all
being true. The Matrix Hypothesis is a version of the Combination
Hypothesis.

• First Hypothesis = Creation Hypothesis.
• Creation Hypothesis: “Physical space-time and its contents were created by beings

outside physical space-time” (Chalmers, 39).
• One version of the Creation Hypothesis is the belief that a God (or gods) outside the physical

universe created the physical universe. Most people probably believe something like this.

• Another version of the Creation Hypothesis is that “our world was created by a relatively
ordinary being in the ‘next universe up’” (Chalmers, 39).

• Another way of putting this: our world is not the base level, and something in the base level (or at
least a level closer to the base level than ours) created our world.

• It is not (yet) saying we are in a Sim world. For that requires…

The Matrix Hypothesis

• The Combination Hypothesis consists in three separate hypotheses all being true. The Matrix
Hypothesis is a version of the Combination Hypothesis.

• Second Hypothesis = The Computational Hypothesis
• Computational Hypothesis: “Metaphysical processes throughout space-time are constituted by underlying

computational processes” (Chalmers, 40).
• Does not deny that there are physical particles. Just adds that there is something underlying even the smallest physical

particles, and says that this thing is computational.

• Restated more formally: our substrate is made up of computational processes.
• Physical objects exist, but are not at substrate level.
• Further, facts about substrate do not change the truth of our beliefs about the phenomenal world.

• Whether I am in Tucson = fact about world at my level, not fact about world at some other level.
• If Computational Hypothesis is true for my (level) world, then whether I am in Tucson = fact about computational processes or

‘code’ underlying my world.
• Different from appearance = reality: I can be mistaken about being in Tucson, even if the Computational Hypothesis is true.

• Suppose I thought I got on a plane to Tucson, but I really got on a plane to Phoenix. Then my belief that I am in Tucson would be
false.

• What would not make my belief false is if I am an envatted being at some base (or more basic) level in Phoenix at that level, but
am in Tucson in my world.

• The Computational Hypothesis added to the Creation Hypothesis gets you a Sim World. But not yet the
Matrix, which needs…

The Matrix Hypothesis

• The Combination Hypothesis consists in three separate hypotheses all being true. The Matrix
Hypothesis is a version of the Combination Hypothesis.

• Third Hypothesis = The Mind-Body Hypothesis
• Mind-Body Hypothesis: “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”
(Chalmers, 41).

• Refers to realization basis/substrate of minds.
• If computational and mind-body hypotheses are true then substrate of world = code, substrate of mind = (potentially) matter

• Helpful to think of ‘physical space-time’ as relative to a world.

• Key difference between envatted beings and Sims:
• If you are a Sim, then only Computational Hypothesis must be true.

• Your mind is not outside of ‘physical space-time’ relative to that world.

• If you are an envatted being, then both Computational and Mind-Body hypotheses must be true.
• Your mind is outside ‘physical space-time’ relative to that world.
• Not to be confused with Computational Theory of Mind. If the Computational Hypothesis is true, then the world is made up of

computational processes (code). But, if you are an envatted being, then your mind is made up of a different kind of
computational process.

• Counterintuitive claim: even if the world you are in is computational, and the world more basic than yours is physical at the
lowest level (i.e. has a substrate of matter rather than computations), if you are an envatted being, then your mind is outside
‘physical space-time.’

Let’s Visualize All This

Sim/Virtual World
Base World

01010111111000000001111100 101011010

Sim Chalmers

Envatted Chalmers

Brain of Envatted Chalmers

Substrate of
Sim/Virtual World

‘Physical’ objects in Sim/Virtual World

Note:
‘Physical
space-time’
refers to what
is inside the
Sim/Virtual
world, even if
it is based in
code and the
base world is
not.

The Matrix Hypothesis

• Call the combination of Creation, Computational, and Mind-Body
hypotheses the Combination Hypothesis.

• The Matrix Hypothesis is the Combination Hypothesis plus the claim that
“the computational processes underlying physical space-time were
designed by the creators as a computer simulation of a world” (Chalmers,
42).
• In other words, the standard (theistic) interpretation of the Creation hypothesis is

ruled out.

• Metaphysical Hypothesis = Matrix Hypothesis
• If Matrix Hypothesis is true, then “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” (Chalmers, 43).

Readings of the Matrix Hypothesis

• The Skeptical Reading of the Matrix Hypothesis
• Brain in vat in Phoenix, Body in VR world in Tucson-in-VR

• You are in Phoenix

• All of your perceptual beliefs are false
• C.f. Descartes’ Evil Demon

• The Metaphysical Reading of the Matrix Hypothesis
• Same details: Brain in Phoenix, Body in VR world in Tucson-in-VR

• You are in Tucson

• All of your perceptual beliefs are true

• Only beliefs that change truth value are beliefs (of theoretical physicists and
metaphysicians) about nature of substrate

Replies to Objections

• Objection 1: “A brain in a vat may think it is outside walking in the
sun…surely it is deluded!” (Chalmers, 46).
• Reply, the brain is not in the sun, but the person is. Person is where body is.

• Compare to Dennett:
• Dennett: Chalmers:

Location of
Person

Physical
Distance

Location of Person

World Boundary

Replies to Objections

• Objection 2: A brain cannot truly believe it is in Tucson if the brain is in Phoenix.
• Reply: First, the person believes, not the brain. Second, there are two Tucsons, Tucson-in-the-

base-world and Tucson-in-the-sim-world. The person’s belief refers to whichever world the
person is in.

• Objection 3: Neo believes he has hair (before leaving the Matrix).
• There are two referents of hair, hair-in-the-base-world, and hair-in-the-Matrix. A person’s

belief is indexed to the world they are in.

• Objection 4: What sort of objects are there in a VR world?
• There are the same sorts of objects we always thought there were: chairs, tables, etc. It is

just their noumenal basis is computational, not physical.

• Other objections are answered by these answers.
• Chalmers talks about the difference between the city Tucson and the concept hair, on the

one hand, and other concepts like friend and action that don’t have –in-a-world distinctions,
but we can ignore this for our purposes.

Other Skeptical Hypotheses

• New Matrix Hypothesis: I am an envatted brain in a sim world that
was recently created.
• Upshot:

• My present beliefs are true and false in the same way as the basic Matrix Hypothesis
• I am still in Tucson if I am in Tucson-in-the-Matrix

• But my past beliefs (e.g. about what I was doing 5 years ago) are all false.

• Recent Matrix Hypothesis: I was just unknowingly put in the Matrix.
• Now most of my beliefs are false, as they would be on the skeptical reading of

the Matrix (or Sim, etc.).
• “The difference lies in the fact that my conception of external reality is anchored to the

realm in which I have lived most of my life” (Chalmers, 50).

Other Skeptical Hypotheses

• One other scenario Chalmers compares to the Matrix (Metaphysical)
Hypothesis is the Local Matrix Hypothesis.
• Local Matrix Hypothesis: I am in a Matrix that only simulates part of the world, e.g.

California.
• Same as Matrix about beliefs (I am in Riverside for the same reasons I would be in basic

Matrix), but imperfect, i.e. easy to figure out if you are in a sim.

• Extendible Local Matrix Hypothesis: The world is simulated as needed; it
follows subjects around.
• Upshot depends:

• If Matrix is infinitely extendible, then basically the same as Matrix from inside, but with lower
start-up and higher maintenance costs than Matrix from base world.

• If Matrix is not infinitely extendible, then like Local Matrix Hypothesis.
• Chalmers: “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” (Chalmers, 52).

Other Skeptical Scenarios

• Macroscopic Matrix Hypothesis: Simulation only bothers with
ordinary-object-level and above simulations.
• Chalmers: “This is a coherent way our world could be, and is not a … skeptical

hypothesis” (Chalmers, 52).
• I disagree: we can observe microphysical objects with the right instruments (e.g. Electron

Microscopes), so if only macroscopic things were simulated, we could find out we
weren’t in the world with microscopic things; this would be an imperfect simulation.

• God Hypothesis: Physical Reality is represented in the mind of God.
Like Berkeley.
• Chalmers thinks this is not skeptical but metaphysical, just a different kind of

simulation.
• We’ll hold off until we read Schwitzgebel before we decide.

Other Skeptical Scenarios

• Descartes’s Evil Genius (Demon) Scenario:
• This has a metaphysical as well as a skeptical reading, according to Chalmers.

• We already know the skeptical reading—it’s the one Descartes gave! None of our beliefs are (necessarily) true.
• Chalmers: “Here we should say that physical reality exists and is constituted by processes within the genius”

(Chalmers, 53).

• Dream Hypothesis:
• Chalmers says it depends:

• If you’re just dreaming now, then it’s like New Matrix.
• If you’ve always been dreaming, then it’s like evil genius scenario “it’s just that the role of ‘evil genius’ is played

by a part of my own cognitive system!” (Chalmers, 53)
• But he is wrong for reasons we have covered.
• As Descartes notes, you can only dream about what you’ve already perceived. So, if Descartes is right, you can’t

always have been dreaming!

• Chaos Hypothesis:
• I do not receive inputs from any world, instead “I have random uncaused experiences” (Chalmers

54).
• There are no external objects, there is no external world.