09-02-2026, 10:04 PM
What Is a Computer?
Author: Lance Fortnow
Published: September 2, 2026
Topic: Theoretical computer science / foundations of computation
Lance Fortnow argues that computer science really is about computers—but only if we use a much broader definition of “computer.” Responding to a Quanta essay asking whether computer science needs computers, he challenges the famous saying attributed to Edsger Dijkstra that “computer science is no more about computers than astronomy is about telescopes.” Fortnow suggests that this analogy is backwards: computers are not merely the telescopes of computer science; they are more like its stars, the actual objects being studied. Historically, the word computer originally referred to a person who performed calculations, long before it came to mean an electronic machine.
For Fortnow, a computer is essentially any system or process that performs computation, regardless of whether it is electronic, mechanical, biological, social, or even human. A postal service routing a letter, an auction determining a price, or a person carrying out a mathematical procedure can all be viewed computationally. The Church–Turing thesis provides the theoretical foundation: any effectively computable process can, in principle, be represented by a Turing machine. Fortnow therefore argues that theoretical computer science must keep some notion of computation or process at its center; otherwise it simply becomes mathematics. Electronic computers are not strictly necessary for computer science, but computation itself is indispensable.
Key takeaways
ARTICLE
Author: Lance Fortnow
Published: September 2, 2026
Topic: Theoretical computer science / foundations of computation
Lance Fortnow argues that computer science really is about computers—but only if we use a much broader definition of “computer.” Responding to a Quanta essay asking whether computer science needs computers, he challenges the famous saying attributed to Edsger Dijkstra that “computer science is no more about computers than astronomy is about telescopes.” Fortnow suggests that this analogy is backwards: computers are not merely the telescopes of computer science; they are more like its stars, the actual objects being studied. Historically, the word computer originally referred to a person who performed calculations, long before it came to mean an electronic machine.
For Fortnow, a computer is essentially any system or process that performs computation, regardless of whether it is electronic, mechanical, biological, social, or even human. A postal service routing a letter, an auction determining a price, or a person carrying out a mathematical procedure can all be viewed computationally. The Church–Turing thesis provides the theoretical foundation: any effectively computable process can, in principle, be represented by a Turing machine. Fortnow therefore argues that theoretical computer science must keep some notion of computation or process at its center; otherwise it simply becomes mathematics. Electronic computers are not strictly necessary for computer science, but computation itself is indispensable.
Key takeaways
- A computer is broader than a digital machine: it can be any system carrying out a computational process.
- The central subject of computer science is therefore computation, not necessarily physical computers.
- The Church–Turing thesis connects these diverse computational processes to the abstract Turing-machine model.
- Fortnow draws a useful boundary: theoretical work that completely removes computation from the picture may be mathematics, but not necessarily computer science.
ARTICLE
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