The elite club keeps on growing. Google’s parent Alphabet last week became the fourth US company ever to achieve a $1tn market valuation, something that once seemed unthinkable. The search engine joined technology peers Apple, Amazon and Microsoft in crossing the prized market threshold, driven up by investors’ appetite for their shares.

The broader stock market too has hit a record as valuations responded to the truce between the US and China on trade and surging profits from Wall Street banks. The S&P 500 went over 3,300 for the first time last week. Yet the seemingly relentless march of the markets and the concentrated gains of these tech stocks raise some uncomfortable questions for investors. The tech giants now make up a significant chunk of the market. They account for more than 15 per cent of the S&P 500’s total value, according to Bespoke Investment, and provided one-fifth of the market’s growth in 2019.

For the wider economy and the market, this is a big deal. The growing dominance of passive funds has only exacerbated this trend; the money flowing into these stocks has forced passives to follow suit as their weighting in the index has increased. Apple, whose market cap of $1.3tn exceeds the total value of stocks on many exchanges, accounted for almost one-tenth of the 29 per cent rise of the S&P 500 last year, according to Bespoke. This level of dominance should give investors pause for thought.