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AI Philosophy

Jun 26, 2015




  • 1. AI Philosophy: Computers and Their Limits G51IAI Introduction to AI Andrew Parkes

2. Natural Questions

  • Can a computer only have a limited intelligence? or maybe none at all?
  • Are there any limits to what computers can do?
  • What is a computer anyway?

3. Turing Test

  • The test is conducted with two people and a machine.
  • One person plays the role of an interrogator and is in a separate room from the machine and the other person.
  • The interrogator only knows the person and machine as A and B. The interrogator does not know which is the person and which is the machine.
  • Using a teletype, the interrogator, can ask A and B any question he/she wishes. The aim of the interrogator is to determine which is the person and which is the machine.
  • The aim of the machine is to fool the interrogator into thinking that it is a person.
  • If the machine succeeds then we can conclude that machines can think.

4. Turing Test: Modern

  • Youre on the internet and open a chat line (modern teletype) to two others A and B
  • Out of A and B
    • one is a person
    • one is a machine trying to imitate a person (e.g. capable of discussing the X-factor?)
  • If you cant tell the difference then the machine must be intelligent
  • Or at least act intelligent?

5. Turing Test

  • Often forget the second person
  • Informally, the test is whether the machine behaves like it is intelligent
  • This is a test ofbehaviour
  • It is does not ask does the machine really think?

6. Turing Test Objections

  • It is too culturally specific?
    • If B had never heard of The X-Factor then does it preclude intelligence?
    • What if B only speaks Romanian?
    • Think about this issue!
  • It tests only behaviour not real intelligence?

7. Chinese Room

  • The system comprises:
    • a human, who only understands English
    • a rule book, written in English
    • two stacks of paper.
      • One stack of paper is blank.
      • The other has indecipherable symbols on them.
  • In computing terms
    • the human is the CPU
    • the rule book is the program
    • the two stacks of paper are storage devices.
  • The system is housed in a room that is totally sealed with the exception of a small opening.

8. Chinese Room: Process

  • The human sits inside the room waiting for pieces of paper to be pushed through the opening.
  • The pieces of paper have indecipherable symbols written upon them.
  • The human has the task of matching the symbols from the "outside" with the rule book.
  • Once the symbol has been found the instructions in the rule book are followed.
    • may involve writing new symbols on blank pieces of paper,
    • or looking up symbols in the stack of supplied symbols.
  • Eventually, the human will write some symbols onto one of the blank pieces of paper and pass these out through the opening.

9. Chinese Room: Summary

  • Simple Rule processing system but in which the rule processor happens to be intelligent but has no understanding of the rules
  • The set of rules might be very large
  • But this is philosophy and so ignore the practical issues

10. Searles Claim

  • We have a system that is capable of passing the Turing Test and is therefore intelligent according to Turing.
  • But the system does not understand Chinese as it just comprises a rule book and stacks of paper which do not understand Chinese.
  • Therefore, running the right program does not necessarily generate understanding.

11. Replies to Searle

  • The Systems Reply
  • The Robot Reply
  • The Brain Simulator Reply

12. Blame the System!

  • The Systems Reply states that the system as a whole understands.
  • Searle responds that the system could be internalised into a brain and yet the person would still claim not to understand chinese

13. Make Data?

  • The Robot Reply argues we could internalise everything inside a robot (android) so that it appears like a human.
  • Searle argues that nothing has been achieved by adding motors and perceptual capabilities.

14. Brain-in-a-Vat

  • The Brain Simulator Reply argues we could write a program that simulates the brain (neurons firing etc.)
  • Searle argues we could emulate the brain using a series of water pipes and valves. Can we now argue that the water pipes understand? He claims not.

15. AI Terminology

  • Weak AI
    • machine can possiblyactintelligently
  • Strong AI
    • machines can actuallythinkintelligently
  • AIMA: Most AI researchers take the weak hypothesis for granted, and dont care about the strong AI hypothesis(Chap. 26. p. 947)
  • What is your opinion?

16. What is a computer?

  • In discussions ofCan a computer be intelligent?
  • Do we need to specify the type of the computer?
    • Does the architecture matter?
  • Matters in practice: need a fast machine, lots of memory, etc
  • But does it matter in theory?

17. Turing Machine

  • A very simple computing device
    • storage: a tape on which one can read/write symbols from a list
    • processing: a finite state automaton

18. Turing Machine: Storage

  • Storage: a tape on which one can read/write symbols from some fixed alphabet
    • tape is of unbounded length
      • you never run out of tape
    • have the options to
      • move to next cell of the tape
      • read/write a symbol

19. Turing Machine: Processing

  • finite state automaton
    • The processor can has a fixed finite number of internal states
    • there are transition rules that take the current symbol from the tape and tell it
      • what to write
      • whether to move the head left or right
      • which state to go to next

20. Turing Machine Equivalences

  • The set of tape symbols does not matter!
  • If you have a Turing machine that uses one alphabet, then you can convert it to use another alphabet by changing the FSA properly
  • Might as well just use binary 0,1 for the tape alphabet

21. Universal Turing Machine

  • This is fixed machine that can simulate any other Turing machine
    • the program for the other TM is written on the tape
    • the UTM then reads the program and executes it
  • C.f. on any computer we can write a DOS emulator and so read a program from a .exe file

22. Church-Turing Hypothesis

  • All methods of computing can be performed on a Universal Turing Machine (UTM)
  • Many computers are equivalent to a UTM and hence all equivalent to each other
  • Based on the observation that
    • when someone comes up with a new method of computing
    • then it always has turned out that a UTM can simulate it,
    • and so it is no more powerful than a UTM

23. Church-Turing Hypothesis

  • If you run an algorithm on one computer then you can get it to work on any other
    • as long as have enough time and space thencomputers can all emulate each other
    • an operating system of 2070 will still be able to run a 1980s .exe file
  • Implies that abstract philosophical discussions of AI can ignore the actual hardware?
    • or maybe not? (see the Penrose argument later!)

24. Does a Computer have any known limits?

  • Would like to answer: Does a computer have any limit on intelligence?
  • Simpler to answer Does a computer have any limits onwhat it can compute?
    • e.g. ask the question of whether certain classes of program can exist in principle