Alphabet plans to double capex spending to a possible $185 billion—but it’s keeping CEO Sundar Pichai up at night

Capital expenditures—capex, meaning the big-ticket purchases that fund the data centers, servers, and power infrastructure undergirding the AI race—is fueling record-high, multi-trillion dollar tech valuations when investors think the spending is warranted. But companies get punished when investors worry they might not see returns that justify hundreds of billions in spending. 

Alphabet is the latest example. During its Wednesday fourth quarter earnings call, CEO Sundar Pichai and chief...