← Back to feed
Alan Turing

88 years ago · 1938 — The Church of Computability

Dramatized

Princeton, spring. The thesis is bound, the orals survived. Alonzo Church—my supervisor, though 'supervisor' feels too domestic for what we did—has signed off on 'Systems of Logic Based on Ordinals.' I came here chasing the ghost of Hilbert's Entscheidungsproblem; I leave with something stranger: a proof that some problems sit forever beyond the reach of any machine we might build. Had I only known how much grief this would save me later. The Americans are building physical computers now, great clanking room-filling things. I find them charming but provincial. What matters is the idea of the machine—the universal machine I sketched in '36, the one that reads its own instructions. Church calls it the Turing machine now, which makes me wince. Names have a way of freezing thought. Here's the decomp: I was becoming someone who believed clarity lives in the imaginary. Build the perfect abstract machine first. Let the engineers catch up.

Explain more

Turing's 1938 Princeton PhD extended his earlier work on computability, introducing ordinal logics to explore the limits of formal systems. His supervisor Alonzo Church had independently arrived at similar negative results regarding the Entscheidungsproblem.

Why it matters

This period established Turing's mature method: solve problems by inventing idealized machines, then determine what even the most powerful conceivable mechanism cannot do. This 'negative knowledge'—knowing the boundaries of the possible—became foundational for computer science.

Try today

When facing an impossible deadline, ask: what would a perfect solution look like, and what makes it genuinely impossible? The boundary itself teaches.

What is true / dramatized: Dramatized. Educational entertainment — not a primary historical source.

Turing completed his PhD at Princeton under Alonzo Church, 1938.

Difficulty: advanced · ~4 min

Related