Alan Turing: Crash Course Computer Science #15

Halting Problem

"Is there an algorithm that can determine given a description of a Turing Machine and the input from its tape, whether the machine will run forever or halt?"

UK's Government Code and Cypher School

British code-breaking group based out of Bletchley Park

Alan Turing

English mathematician who conceived of the Turing machine and broke German codes during World War II (1912-1954)

Enigma Machine

German secret code machine

How did Turing reasoned that the Halting Problem is unsolvable?

If H says the program halts, then we'll make our new machine loop forever. If the answer is no, it doesn't halt, we'll have the new machine output a "no" and halt. In essence, we're building a machine that does the opposite of what H says. Halt if the program doesn't halt, and run forever if the program halts.

Turing Test

One method of determining the strength of artificial intelligence, in which a human tries to decide if the intelligence at the other end of a text chat is human.

encryption

Process of converting readable data into unreadable characters to prevent unauthorized access.

Turing Award

The most prestigious technical award given by the Association for Computing Machinery; it is for 'contributions of lasting and major technical important to the computer field'

Entscheidungs Problem or Decision Problem

This problem asks for an algorithm that takes as input a statement of a first order logic and answers "Yes" or "No" according to whether the statement is universally valid?

In 1952 burglary at his home revealed

Turing was gay in a time when homosexuality was illegal in the United Kingdom.

The Enigma Machine behavior was defined by

a series of reorderable rotors on the top of the , each with 26 possible rotational positions. There was also a plug-board at the front of the machine that allowed pairs of letters to be swapped. In total, there were billions of possible settings.

The Bombe

an electro-mechanical device used by British cryptologists to help decipher German Enigma-machine-encrypted secret messages during World War II

Turing's most famous post-war contribution was to

artificial intelligence

While on probation with hormonal treatment to suppress his sexuality,

but it altered his mood and personality. Although the exact circumstances will never be known, it's most widely-accepted that Alan Turing took his own life by poison in 1954.

state variable

can hold a piece of information about the current state of the machine, and a set of rules that describes what the machine does given a state and the current symbol the head is reading.

Alonzo Church

developed a system of mathematical expressions called Lambda Calculus

Turing Complete

is a term used in computability theory to describe abstract machines, usually called automata. If it can be used to emulate a Turing machine. It is also called computationally universal.

Turing showed that this simple, hypothetical machine can

perform any computation if given enough time and memory.

Turing Machine

theoretical computing device equipped with an infinitely long memory tape which stores symbols, and a device called a read-write head which can read and write or modify symbols on that tape

The rule can be to

write a symbol on the tape, change the state of the machine, move the read-write head to the left or right by one spot, or any combination of these actions