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Can computers think

May 18, 2015




  • 1. Can computers think ? Krishnan GTC talk Sept. 18,2011

2. Classic book on the subject 3. Machines vs. Humans

  • Machinery outperforms us in physical ways
    • Cars outrun us
    • Planes can fly, we cant
  • This doesnt disturb us
  • Is thinking a human prerogative ?
    • Can mechanical devices out think us

4. What can computers do better ?

  • Computations on large numbers
    • E.g. Multiplying two 100 digit numbers
  • Play chess (and other games)
  • Answer natural language questions
    • IBM Watson
  • House cleaning robots ?
  • But does this mean they are intelligent ?

5. Advertisement Will you buy ? Thinking Computer : Rs. 100,000 6. What is intelligence ?

  • Newell and Simon - the use and manipulation of various symbol systems, such as those featured in mathematics or logic
  • Large debate in the AI, Psychology, Philosophy community

7. Alan Turing

  • British scientist
    • Helped solved the Enigma Machine (WWII)
    • Advances in Probability Theory
  • Invented the theory behind computers
    • Turing Machine
    • Turing Test

8. The imitation game

  • Proposed by Alan Turing in 1950
  • It is played with three people, a man (A), a woman (B), and an interrogator (C) who may be of either sex. The interrogator stays in a room apart from the other two.
  • The object of the game for the interrogator is to determine which of the other two is the man and which is the woman. He knows them by labels X and Y, and at the end of the game he says either X is A and Y is B or X is B and Y is A.

9. Turing test: Distinguish man and machine What would it take for a computers thoughts to be indistinguishable from a humans? 10. 11. 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.

12. 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.

13. 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

14. 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.

15. Strong AI

  • Strong AIis artificial intelligence that matches or exceeds human intelligence
  • The intelligence of a machine can successfully perform any intellectual task that a human being can
  • Advocates of "Strong AI" believe that computers are capable of true intelligence
  • They argue that what intelligence is strictly algorithmic, i.e., a program running in a complex, but predictable, system of electro-chemical components (neurons).

16. Strong AI

  • Many supporters of strong AI believe thatthe computer and the brainhave equivalent computing power
  • With sufficient technology, it will someday be possible to create machines that have the same type of capabilities as humans
  • However, Strong AI's reduction of consciousness into an algorithm is difficult for many to accept
  • Proponents are: Ray Kurzweil, Marvin Minsky etc.

17. Weak AI

  • TheWeak AIthesis claims that machines, even if theyappearintelligent, can onlysimulateintelligence
  • They will never actually be aware of what they are doing
  • Some weak AI proponents believe that human intelligence results from a superior computing mechanism which, while exercised in the brain, will never be present in a Turing-equivalent computer
  • Roger Penrose is a proponent of Weak AI

18. What can a computer compute ?

  • Hardware circuits, gates, wires
  • Software Program that runs on the hardware
  • Turings remarkable discovery All computing machines are equivalent in what they can do
    • Though speeds may differ
  • All computers are equivalent to a Universal Turing machine

19. Algorithms

  • The word comes from the Persian mathematician Abu Jafar Mohammed ibn Musa al Khowarizm
  • He wrote a book
    • Kitab Al-jabr wal-muqabala
  • Example algorithm
    • Euclids algorithm for highest common factor of two numbers

20. Euclids algorithm This is a systematic procedure that will work for any two positive integers 21. David Hilbert (1862-1943)

  • Hilbert's programme:
  • To establish the foundations of mathematics, in particular by clarifying and justifying use of the infinite:

``The definitive clarification of the nature of the infinite has become necessary, not merely for the special interests of the individual sciences but for the honour of human understanding itself.''

  • Aimed to reconstitute infinitistic mathematics in terms of a formal system which could be proved (finitistically)consistent ,completeanddecidable .


  • Consistent : It should be impossible to derive a contradiction (such as 1=2).
  • Complete : All true statements should be provable.
  • Decidable : There should be a (definite, finitary, terminating) procedure for deciding whether or not an arbitrary statement is provable. (TheEntscheidungsproblem )

There is the problem. Seek its solution. You can find it by pure reason, for in mathematics there is no ignorabimus. Wir mssen wissen, wir werden wissen 23. Bertrand Russell (1872-1970) Alfred Whitehead (1861-1947)

  • Russell's paradox showed inconsistency of naive foundations such as Frege's: {X | X X}
    • "The set of sets which are not members of themselves"
  • Theory of Types andPrincipia Mathematica(1910,1912,1913)

24. Kurt Gdel (1906-1978)

  • Uber formal unentscheidbare Stze der Principia Mathematica und verwandter Systeme(1931)
  • Any sufficiently strong, consistent formal system must be
    • Incomplete
    • Unable to prove its own consistency

25. Alan Turing (1912-1954)

  • On computable numbers with an application to the Entscheidungsproblem(1936)
  • Church, Kleene, Post

26. 27. Turing machine

  • Imagine a device for carrying out a computational procedure (like Euclids algorithm)
  • What is the general form such a machine can take ?
    • Machine should have discrete states (large but finite in number)
    • Input/Output of unrestricted size
    • Finite number of states implies cannot internalize the data

28. A Turing Machine ...... ...... Tape Read-Write head Control Unit 29. The Tape ...... ...... Read-Write head No boundaries -- infinite length The head moves Left or Right 30. ...... ...... Read-Write head The head at each time step: 1.Reads a symbol 2.Writes a symbol 3.Moves Left or Right 31. ...... ...... Example: Time 0 ...... ...... Time 1 1.Reads 2.Writes3.Moves Left 32. The Input String ...... ...... Blank symbol head Head starts at the leftmost position of the input string Input string 33. States & Transi