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Are the Androids Dreaming Yet?

The eye, hand and pencil of a human mathematician was modeled as the read-write head of a teletype. It allowed the machine to read input from the tape and write information back so as to keeping track of intermediate calculations or provide the final output. The operation of the machine was straightforward. At each moment in time the machine could read a symbol on the tape, move the tape forward or backwards, and write or erase a symbol. That’s all he needed to model a human doing something like long multiplication. Turing argued his model was exactly analogous to a human performing a computation.

Turing’s imaginary machine was now able to perform computations just like a human. You could write down the rules for a given procedure and the machine could, for example, do long multiplication. At each step of the calculation, the computer would examine the state machine, look up the state in the instruction book and put the machine into its new state. If you recall Searle’s Chinese Room, this is the same process the man in the room followed: get a symbol, look it up in a book, and reply with the corresponding symbol.

Universal Turing Machine
We have missed one important step from our explanation of the modern computer: the ability to run programs. Nowadays, we take for granted you can download a program from the Internet or buy one from a shop. In the 1930s adapting a single machine to multiple purposes was a radical idea. Machines were built to do one thing, and one thing only, and there was no concept of a general-purpose machine. Nowadays this is hard to comprehend, but there is a similar revolution going on in manufacturing today with the widespread adoption of 3D printing. Today most factories use tools – lathes, drills and saws – to fashion objects. Each machine does a specific job and is not ‘general purpose’. But innovative new machines can now be purchased relatively inexpensively called 3D fabricators, which print entire objects. The same happened for electronic logic in Turing’s time.

Before computers, logical tasks were performed by banks of relays. How these banks work can be illustrated by the workings of an old-fashioned elevator. If you pressed a button to call an elevator, you closed a switch coupled to a relay in the basement sending power to the car. Another switch was tripped automatically when the elevator reached the desired floor. All the functioning of the elevator system was fixed. Once you pressed a button to go up you could not change your mind and press

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