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The Big Dig Test
Flyvbjerg's January 2025 experiment in which he asked two leading AI systems a factual question whose answer he had personally published — and received confident, fluent, catastrophically wrong responses that became the founding empirical artifact of the artificial ignorance diagnosis.
In January 2025, Bent Flyvbjerg sat down with ChatGPT and Perplexity and asked each a simple question: what was the cost overrun of Boston's Central Artery/Tunnel Project, known as the Big Dig? Flyvbjerg knew the answer. He had published it in peer-reviewed journals. The figure — 220 percent — had been cited hundreds of times in the academic literature on infrastructure failure. ChatGPT got it wrong. Perplexity got it worse, returning 478 percent, a figure with no grounding in any published source. Neither system hedged. Neither flagged uncertainty. Both delivered their errors with the grammatically impeccable, rhetorically persuasive confidence that large language models are engineered to produce. The experiment became the empirical core of Flyvbjerg's paper 'AI as Artificial Ignorance,' which circulated with a viral intensity unusual for an infrastructure scholar's academic work.
In The You On AI Field Guide
The test's diagnostic power derives from the nature of