America’s stock market, unconcerned by trade tensions or fiscal strain, sits near a record high. The exuberance is driven by a new generation of techno-optimism—this time, about artificial intelligence (AI). The 'Magnificent Seven' (Alphabet, Amazon, Apple, Meta, Microsoft, Nvidia and Tesla) now account for roughly 38% of the S&P 500’s market-capitalisation and about half of its profits. Their dominance, and the feverish faith in a new technology revolution, evoke memories of the late-1990s dotcom mania. The S&P’s cyclically adjusted price-earnings ratio (P/E) has breached 40 for the first time since 2000, when it reached 44—shortly before the benchmark plunged by nearly half, as the internet bubble burst. Then, as now, the conviction that a digital revolution would rewrite the rule

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