In the early 20th century, Madras was under the British Empire's rule. An Oxford history graduate, Julius, worked in the Indian Civil Service as a colonial administrative clerk. His wife Sara, a native of Madras and an engineer's daughter, was expecting their second child. Amid the era's political unrest, they chose to return to England for their child's birth. On June 23, 1912, in North London's Maida Vale neighborhood, their son Alan Mathison Turing entered the world. After relocating to South England and then returning to India, the couple left their sons, John and Alan, in London foster care due to baby Alan's ill health.
Alan Turing's Foster Care Experience
Alan was diagnosed with rickets, a bone disorder common in childhood. To prevent any travel stress, his parents left him with a retired couple in East Sussex. Later, back in England, his mother discovered his mental health issues, including sudden mood swings. Regardless of these issues, she found him sociable, intelligent, and endearing.
Alan Turing's Personality Traits
Alan demonstrated a fascination for numbers and an active mind even before he could read. His love for science and geography led him to experiment and invent. Besides academics, Alan enjoyed cycling and running, interests that stayed with him as an adult. He maintained a childlike personality and had little concern for his appearance. At 22, he bought a teddy bear-shaped stuffed toy and could recite the wicked witch's spell from Snow White. His eccentricities included hiding his teacup or chaining it to prevent theft.
Alan Turing's Academic Journey
At age thirteen, he joined Sherborne School, which later had Jeremy Irons and John le Carré as students. Alan's exceptional mathematical abilities and mental calculation skills were evident during his studies. He experienced his first love with a fellow student who tragically died of tuberculosis. In 1931, he enrolled at King's College, Cambridge, on a scholarship to study mathematics, graduating with honors in 1934.
In 1936, he published "On Computable Numbers," introducing the algorithm and the Turing machine concept. This paper demonstrated a category of problems without an algorithmic solution, significantly influencing computation theory. In 1936, Turing joined Princeton University (USA) and earned a mathematics doctorate in 1938. His paper caught the attention of acclaimed scientist John von Neumann.
The Turing Machine: A Pillar of Theoretical Computer Science
The Turing machine serves as a mathematical model that acts as the cornerstone for studying the basics of theoretical computer science. As an abstract operator, it performs fundamental operations. The abstraction of this machine signifies an infinite memory capacity and zero execution or computation time, thereby separating it from the physical constraints of a real computer.
This conceptual operator is technically termed a computational model. By abstracting from the physical computer, we transition from a tangible environment to a mathematical one. Although the Turing machine is a classic computational model, it isn't the only one, yet it's arguably the most recognized. The characteristics of this abstract model, however, might not align with what one would expect from a contemporary computer.
Decoding Complexity and Computability
The Turing machine, despite seeming oversimplified, forms the basis for explaining the concepts and properties of Complexity Theory and Computability Theory. These theories examine which problems can and cannot be automatically resolved. Essentially, Computability Theory helps us identify solvable problems and the potential existence of their solving algorithms. On the other hand, Complexity Theory aids in understanding the inherent complexity of problems—how intricate is the solution, and how much computational resources are needed for solving a specific problem?
Understanding the Turing Machine
A Turing Machine is comprised of an infinite tape divided into cells, which can essentially be considered as memory units. Each cell can hold symbols from the machine's alphabet. Each cell's information is finite—a single symbol, letter, or number, but not an arbitrarily long string. This magnetic tape serves as the input data receiver and the intermediate calculation data writer.
A mobile head, akin to a processor, reads, writes, or erases symbols from the cell it's positioned on. Governed by a program, it instructs the machine on how to behave based on its current configuration and the symbol it encounters—it can read, write, erase, or move one position at a time, either to the right or left.
In summary, a Turing machine is composed of an infinite tape, a mobile head, and a sequence of instructions. Interestingly, this simple conceptual model is theoretically capable of executing any mathematical operation. The latest and fastest computers, in theory, can't exceed this simple conceptual entity's capabilities—they can only perform the operations faster.
The Genesis of Theoretical Computer Science
Alan Turing is renowned for developing a formalism that systematically structures the concept of an algorithm utilizing the machines he designed. While algorithms weren't a new concept, their rigorous formalization certainly was. Turing, alongside American mathematician Alonzo Church, independently tackled the problem of arithmetic decidability, introducing two distinct concepts of computability - Turing's machines and Church's Lambda calculus, a formalism widely used later in the semantics of programming languages.
Thus, the Church-Turing thesis was birthed. It postulates the development of an algorithm concept not only through the Turing Machine and Lambda calculus but also through other formalisms. However, this new algorithm should possess computational power that is at most equivalent to the abstract machines. It's fascinating to see how such basic theoretical structures harbor immense computational power, evident in all programming languages developed in the 1900s. Turing, leveraging the computational prowess of his machines, provides a solution to David Hilbert's decidability question.
The War Era
The outbreak of World War II in 1939 led to Turing's recruitment by the British Army as a cryptanalyst at Bletchley Park, cracking German codes. The first electronic computer, named Colossus, was constructed under Turing's supervision. By 1944, Turing was tasked to develop a computer - the Automatic Computing Engine (ACE) - capable of rivaling von Neumann's American EDVAC project. In 1947, Turing conceptualized the idea of computer networks, software subroutines, and outlined the fundamental ideas of neural networks.
Alan Turing's Post-War Years and Legacy
Post-war, Alan Turing continued to design computers following von Neumann's architecture. His Mark I was completed in 1948, even before EDVAC, and he designed its programming language. Turing also explored artificial intelligence, a discipline that evolved from his 1950 article "Computing Machinery and Intelligence."
Turing's paper famously began with the question, "Can machines think?" Later, he proposed the Turing test, a method to ascertain if a machine can exhibit intelligent behavior. Turing's illustrious career was abruptly halted following his indictment and conviction for behavior that contradicted the morals of the era.
Two years post-conviction, Turing tragically took his own life by consuming a cyanide-laced apple, a chilling echo of the Snow White saga he knew so well as a child.
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