As the race to become the first company worth $1 trillion enters the final lap, technology monopolies are dominating the stock market. The five biggest companies by market value are U.S. tech stocks: Apple, Amazon, Alphabet, Microsoft and Facebook. Between them they accounted for more than a third of the $2.7 trillion increase in value of the S&P 500 in the past 12 months.
Worse, the top five now make up more than 15% of the S&P, the most for any top five since early 2000. Is it time to worry that the market is getting...