TL;DR
Theoretical computer science's core questions can be studied without physical computers, but it was the practical experience with real machines that inspired these deep questions to be asked in the first place.
A famous saying in computer science goes: computer science is to computers what astronomy is to telescopes. It sounds profound, but theoretical computer scientists really can go their whole careers without touching a physical machine.
Yet the saying misses half the story. Tracing the history back, the author finds that without those clunky machines, these clever questions would never have been asked.
The theory stands apart from the machine
In the 1930s, mathematicians began using pure math to ask 'what can be computed?' The Turing machine — a hypothetical device reading and writing symbols on an infinite tape — defined the concept of computation, but this had little to do with physical computers. Turing was actually tackling a problem in the foundations of mathematics.
Today, theorists use the same mathematical framework to analyze physical systems, evolutionary dynamics, even quantum gravity. At this level, computers are indeed dispensable.
But the questions were machine-born
The complexity problem — why some problems are easy to solve and others hard — is central to theoretical computer science. Its seeds appeared with Babbage's analytical engine in the 19th century, but real research only ignited in the 1960s, when people began playing with actual computers.
The second law of thermodynamics is similar: nobody cared until engineers built steam engines. Practice breeds profound theory, and computer science is no exception.
So the saying is half right: without computers, the theory would still stand; but without computers, that theory might never have been conceived.
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