雙語暢銷書《艾倫圖靈傳》第8章:水銀延時線(125)
The field of cryptography will perhaps be the most rewarding.
There is a remarkably close parallel between the problems of the physicist and those of the cryptographer.
這個問題對於物理學家來說，與對於密碼學家來說，有很多一致之處，但也有所不同。The system on which a message is enciphered corresponds to the laws of the universe, the intercepted messages to the evidence available, the keys for a day or a message to important constants which have to be determined.
對一條信息進行加密的過程，顯然是遵循物理定律的，被攔截的信息會提供線索，而密鑰則與日期或某些常數有關。
The correspondence is very close, but the subject matter of cryptography is very easily dealt with by discrete machinery, physics not so easily.
在這一點上是很有關係的，但用這種方法處理起來，卻非常之困難，相比之下，如果採用離散機器來處理，則要容易得多。There was more to Intelligent Machinery than this.
對於智能機器，這還沒有說完。One feature was that he laid down definitions of what was meant by 'machine', in such a way that it connected the 1936 Turing machine with the real world.
圖靈還爲"機器"做了一系列定義，這樣就把1936年的圖靈機與現實聯繫了起來。He distinguished first:
他首先區別出：'Discrete and 'Continuous' machinery.
"離散"機器和"連續"機器。We may call a machine 'discrete' when it is natural to describe its possible states as a discrete set.
我們稱一臺機器是"離散的"，當它所有的狀態可以被自然地描述爲一個離散的集合states of 'continuous' machinery on the other hand form a continuous manifold.
……而"連續"機器的狀態則是無窮而連續的machinery can be regarded as continuous, but when it is possible to regard it as discrete it is usually best to do so.
……微觀來看，所有的機器都是連續的，但是隻要有可能將其視爲離散的，我們就應當儘量把它視爲離散的。
