The Matrix as Metaphysics David J. Chalmers

The Matrix In The Matrix A version of an old philosophical fable 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 René Descartes’ evil genius The brain in the vat

Brain in a Vat A brain in a vat, connected to a computer simulation of the world, might have the same experiences that I do. The brain in a vat has beliefs corresponding to mine. I have hands There is a table in front of me. I am in Tucson. These beliefs are massively false.

Envatment Let’s say: A matrix = an artificially-designed computer simulation of a world. 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 The Matrix Hypothesis: I am (and have always been) in a matrix. For all I know, the Matrix Hypothesis is true! I can’t rule it out with certainty. There may be many matrices developed in the history of the universe. 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: 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 “Perception: Our day-in, day-out world is real. 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 If so: the Matrix Hypothesis is a skeptical hypothesis Its possibility suggests that we know very little about the world. Skeptical argument 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: The Matrix Hypothesis is not a skeptical hypothesis Even if I am envatted, I still have hands, there is still a table in front of me, I am still in Tucson. Brains in vats have mostly true beliefs If I am in a matrix, things are perfectly real.

Appearance and Reality George Berkeley “Esse est percipi” To exist is to be perceived Idealism: reality = a set of appearances If so: the matrix yields reality. I don’t accept idealism But will argue that nevertheless (for different reasons), the matrix yields reality.

Envatment as a Metaphysical Hypothesis I’ll argue: the hypothesis that I am in a matrix is not a skeptical hypothesis, but a metaphysical hypothesis. It is equivalent to a hypothesis about the underlying metaphysical nature of the world. 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. 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. Cf. religious views of creation. The Creation Hypothesis could be true. The Creation Hypothesis is not a skeptical hypothesis: 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. I.e., microphysical processes throughout space-time are constituted by underlying computational processes. Just as chemistry is constituted by physics, physics is constituted by computations Underneath particles are patterns of bits E.g. Wolfram, A New Kind of Science An underlying cellular automaton? Perhaps: these computational processes are themselves implemented by more basic processes.

Computational Hypothesis Atoms 110101101011011010000111

Computational Hypothesis II The Computational Hypothesis could be true. The Computational Hypothesis is not a skeptical hypothesis: 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. No more than quantum mechanics!

Dualistic Hypothesis Dualistic Hypothesis: My mind is nonphysical and interacts with the physical. 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. The Dualistic Hypothesis could be true. The Dualistic Hypothesis is not a skeptical hypothesis 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. Physical processes were created by other beings, are computationally implemented, and my nonphysical mind interacts with them.. The Combination Hypothesis could be true. The Combination Hypothesis is not a skeptical hypothesis. If it is true, I still have hands, and so on.

Metaphysical Hypothesis Metaphysical Hypothesis: The Combination Hypothesis, plus 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.] The Metaphysical Hypothesis could be true. The Metaphysical Hypothesis is not a skeptical hypothesis. If it is true, I still have hands, and so on.

Metaphysical Hypothesis Atoms 110101101011011010000111 Mind Creator

Matrix/Metaphysics Equivalence Matrix Hypothesis: ‘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. 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 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 space-time. 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 The Matrix Hypothesis!

Matrix Hypothesis 110101101011011010000111 Mind Creator

Matrix  Metaphysics Matrix Hypothesis: Underlying reality is just as Metaphysical Hypothesis specifies A computational implementation of physics, artificially designed, interacting with my cognitive system. Things are the same at the underlying level, so things are the same at all levels So the Matrix Hypothesis implies the Metaphysical Hypothesis.

The Matrix: Not Skeptical The Matrix Hypothesis is equivalent to the Metaphysical Hypothesis The Metaphysical Hypothesis is not a skeptical hypothesis So: The Matrix Hypothesis is not a skeptical hypothesis Even if I am envatted I have hands There is a table in front of me I am in Tucson

The Matrix as Metaphysics If I discover that I am in a matrix, I should not reject my ordinary beliefs about tables, etc. Instead, I have made a metaphysical discovery about what tables are made of. The world is fundamentally made of bits!

Life in the Matrix So: people in the Matrix have mostly true beliefs At least if the Matrix has been running for a long time. A multi-vat matrix is needed for true beliefs about other minds. Brains in vats are not deluded. If we are in a matrix, things are perfectly real It’s just that the world is fundamentally computational. No worse than the world being fundamentally quantum-mechanical!

Objection: Simulation is not reality Objection: The matrix is simulation, not reality Response: The Computational Hypothesis tells us 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 If it is the basis of our experiences.

Objection: Deluded BIV? Objection: A brain in a vat might think “I’m out in the sun”, when it’s in a dark lab. Deluded? Reply: The surroundings of the BIV in the brain’s domains are irrelevant. 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, 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’. This thought will be true if the Neo has hair. But Neo does not have hair! So the Neo’s thought is false. Reply: ‘Hair’ means something different for a BIV. For BIV, ‘hair’ refers to virtual hair, constituted by computational processes. BIV has virtual hair! Same for virtual chairs, tables, etc.

Objection: BIV has world all wrong Objection: If we are envatted, the world is nothing like we think it is. 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. Deeper point: It’s just that the world has a further nature that goes beyond our common sense conception. E.g.: quantum mechanics. science reveals world’s structure, leaving intrinsic nature open

Residual Skepticism Matrix envatment is a non-skeptical hypothesis. But other skeptical hypotheses remain…

The Local Matrix Local Matrix: Only my local environment is simulated, not all of physical space-time. E.g. The Thirteenth Floor Akin to Truman Show skepticism: I still have hands, a body, a house, but false beliefs about things further from home. 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. 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. Arguably: yields largely false or empty beliefs.

Tentative Moral If we assume there is some explanation for the regularities in our experience, global external-world skepticism is ruled out. Explanation yields reality?

Conclusion It’s not so bad to be a brain in a vat.

Next Time The mind-body problem DP, Chapter 2 Descartes, Meditations 1 and 2