There are two characteristics of a bubble, says Rob Arnott, the investor often known as the godfather of smart beta. First, “we must make implausibly optimistic assumptions in order to justify prices”, he tells Bloomberg. Second, “the marginal buyer doesn’t care about valuation models”. By that metric, tech isn’t a bubble. Yes, the six big tech companies – Apple, Amazon, Alphabet, Facebook, Microsoft and Netflix – are worth $8.5trn, more than the entire Japanese market ($6trn). But for some stocks such as Apple, valuations aren’t detached from reality. “You just have to make moderately aggressive assumptions and you can easily justify the price.”
However, “micro-bubbles” abound. “When it comes to things like Tesla... and Netflix, you have to make very, very, very aggressive assumptions,” he says. And how many buyers…
