Soon after ChatGPT first captured the world’s attention four years ago, some investors began to fret that clever chatbots would upend one of the most lucrative businesses to have emerged in decades: Google search. For a time these concerns seemed unfounded, with the firm’s ad sales showing little sign of slowing. On October 29th, however, the fears returned with a vengeance, as Alphabet, Google’s parent company, shed $500bn of market value, 12% of its total, in a single trading session following disappointing quarterly earnings the previous day.