The Matrix as Metaphysics

1. The Matrixas Metaphysics David J. Chalmers

2. The Matrix • In The Matrix • 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

3. 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.

7. 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

8. 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?

9. 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.

11. 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)

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.)

17. 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.

18. Creation Hypothesis Creator Atoms

19. 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.

20. Computational Hypothesis Atoms 110101101011011010000111

21. 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!

22. 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.

23. Dualistic Hypothesis Mind Atoms

24. 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.

25. 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.

26. Metaphysical Hypothesis Atoms 110101101011011010000111 Mind Creator

27. 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.

28. 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!

29. Matrix Hypothesis 110101101011011010000111 Mind Creator

30. 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.

31. 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

32. 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!

33. 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!

34. 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.

35. 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.

36. 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.

37. 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

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

39. 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!

40. Other Skeptical Hypotheses • RecentEnvatment: 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.

41. 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?

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

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