Alan Turing

In October 1950 the philosophy journal Mind published a paper by Alan Turing, a mathematician at Manchester, that asked whether machines can think. Among the objections he set out to answer was one he called "The Theological Objection": that thinking is a function of the immortal soul, which God gives to every man and woman but not to animals or machines. Turing wrote that he could not accept any part of it, though he would try to answer it on its own terms. Then he did so, with some mischief. Would it not limit God's power, he asked, to say God could not give a soul to an elephant, or to a machine? Building thinking machines need be no more irreverent than having children. He added that he was not much impressed by theological arguments, whatever they were used to support.¹

Twenty years earlier the same man had written to his mother that he was sure he would meet his dead friend again. This chapter asks how the schoolboy who believed in the survival of the spirit became the scientist who answered the soul argument with a joke, and what can and cannot be known about that change.

Chapel at Sherborne

He was born in London on 23 June 1912, the second son of Julius Turing of the Indian Civil Service and Ethel Sara Stoney, and was baptised fifteen days later.²³ While his parents were in India, he and his brother were fostered with a family at St Leonards-on-Sea.⁴ In May 1926 he arrived at Sherborne School, which offered a liberal education "in accordance with the principles of the Church of England"; chapel was compulsory, with daily prayers and two services on Sundays.⁵⁶ For his first terms he sang treble in the chapel choir, and on 7 November 1927 he was confirmed in the chapel by the Bishop of Salisbury, with fifty-six other boys.⁷⁸ His biographer Andrew Hodges calls confirmation one of those duties for which everyone had to volunteer.⁸ On the belief timeline, that ordinary Anglican schooling is where his faith sits.

His masters found him difficult. His housemaster wrote that he was not a normal boy, and the headmaster that he was bound to be a problem in any community.⁹ One master complained of his attitude to discussion of the New Testament, though accounts differ on which report it came from and what prompted it.¹⁰

Christopher

In the sixth form, in 1928, he became friends with Christopher Morcom, a boy a year ahead who shared his passion for science and astronomy. In December 1929 both sat for scholarships at Trinity College, Cambridge; Morcom won one and Turing did not.¹¹¹²¹³ Two months later, on 13 February 1930, Morcom died in London of an illness brought on by tuberculosis, aged eighteen. He was buried at dawn two days later at Catshill in Worcestershire.¹⁴ That night Morcom's housemaster told the boys that no one could tell why he should have died like this, but that there was a reason, perhaps to help some of them, since a friend could sometimes influence others more by his death than by his life.¹⁵¹⁶

Within days Turing wrote to his mother that he felt sure he would meet Morcom again somewhere, and that there would be work for them to do together; now that he was left to do it alone, he must not let his friend down.¹⁷ He told Morcom's mother that he would put as much energy into his work as if Christopher were alive, because that was what he would want.¹⁸ The death did not, on this evidence, end his belief. It deepened his hope that the spirit survives. For at least three years, Hodges writes, drawing on his letters to Mrs Morcom, Turing's thoughts turned on how the mind, and Christopher's in particular, was embodied in matter, and whether death could release it.¹⁹ On his timeline, the loss and the hope belong together as one mark.

He had chosen, as the prize awarded to Morcom after his death, the astronomer Arthur Eddington's The Nature of the Physical World (1928).²⁰ Eddington, a Quaker, argued that the new quantum physics freed science from its old determinism: "science thereby withdraws its moral opposition to freewill."²¹ In his Swarthmore Lecture of 1929 Eddington wrote that "rejection of creed is not inconsistent with being possessed by a living belief," and that "we have no creed in science, but we are not lukewarm in our beliefs."²²²³

"Nature of Spirit"

Around April 1932, as a Cambridge undergraduate staying with the Morcoms at their house near Bromsgrove, he wrote a short essay for Christopher's mother called "Nature of Spirit."²⁴ Following Eddington, he argued that the new physics had broken the predestination of the old astronomy, and that we have a will able to act on the atoms of the brain. He cited the Cambridge philosopher McTaggart for the view that matter is meaningless without spirit. He had once believed, he wrote, that at death a spirit might go to a universe entirely separate from ours, but he now thought matter and spirit so connected that this was a contradiction; the spirit was eternally bound to matter, though not always to the same body, and when the body died the spirit found a new one, sooner or later, perhaps at once.²⁵²⁶ Hodges calls it a statement of belief in the survival of the spirit after death.²⁶

On the timeline, the essay is where his doubt begins, but it is a doubt of an unusual kind. It is the first place where he revises his belief in his own words: not giving up the spirit, but giving up a heaven apart from the physical world.

A later determinism

The documents then fall silent on belief for more than a decade. In 1932 and 1933 he read von Neumann's mathematics of quantum mechanics and Russell and Whitehead's Principia Mathematica, which, Hodges writes, helped turn an emotional enquiry into a rigorous one.²⁷ In 1936 he published the paper on computable numbers that described what is now called the Turing machine; Hodges suggests, marking it as his own reading, that it answered the fascination with the problem of mind that Morcom had sparked.²⁸ He took his doctorate at Princeton.²⁹

In the war he worked on breaking German codes at Bletchley Park, and named the first of his code-breaking machines "Agnus," which Hodges reads as a joke an atheist might make.³⁰ It was probably in 1941, Hodges writes, that he decided that intuition and originality must also be computable, and by 1945 he no longer thought anything uncomputable was needed to explain the mind.³¹ By then he had, in Hodges's words, long abandoned his youthful hope of finding free will or free spirits through quantum mechanics; his later thought was strongly determinist and atheistic.³² On the timeline, this is where his disbelief appears, and it is the weakest mark: Hodges gives no date and no document for the change, and the sources read for this chapter have none either. A popular account says that Morcom's death shattered his faith and led him into atheism. His own letters and essay of 1930 to 1933 show the opposite at first. Accounts differ.³³

The theological objection

The 1950 paper is the only public expression, and the timeline marks it as his expression. Besides the theological objection, Turing answered the neurosurgeon Sir Geoffrey Jefferson, who had argued in 1949 that no machine could equal a brain until it could write a sonnet because of thoughts and feelings felt, and know that it had written it. It was the secular cousin of the soul argument, and Turing took it more seriously.³⁴³⁵ He also poked fun at religion in passing, asking how Christians regarded the Muslim view, as he put it, that women had no souls; Hodges calls the fun somewhat superficial, and notes that Bertrand Russell wrote to say he had enjoyed the paper very much.³⁶ Yet in the same paper Turing wrote that the statistical evidence for telepathy was, unfortunately, overwhelming.³⁷ He was not a tidy materialist.

Messages from the unseen world

In March 1954 he sent his friend Robin Gandy four postcards headed "Messages from the Unseen World," a joke on the title of Eddington's 1929 lecture. One is a verse in the style of the school hymns of his childhood, about waves of wondrous light playing out God's holy pantomime. Hodges calls it the sort of mocking religious joke Turing shared with his friends, and yet perhaps also a serious return to his first wonderings about mind and matter.³⁸ It is the last mark on his timeline, an echo rather than a revision.

He died at his home in Wilmslow, Cheshire, on 7 June 1954, at forty-one.³⁹ No text read for this chapter shows him calling himself an atheist, an agnostic or a materialist; those are other people's words for him.⁴⁰ What the documents show is a boy who lost his closest friend and believed, for a time, that the friend's spirit lived on; a young man who tried to make that belief consistent with physics; and a scientist who, some time later, gave it up, and kept a joke about it to the end. Hodges wrote that the nature of spirit, as Turing had described it to Mrs Morcom, always remained for him a natural wonder.⁴¹

Bertrand Russell, who enjoyed Turing's paper on thinking machines and whose materialist philosophy Hodges sets beside it, has his own chapter in this book.