The stock market keeps hitting new highs. AI companies are valued in the trillions. Everyone seems to be winning. So why are the world’s top risk analysts quietly getting nervous?
The ten largest companies in the S&P 500 now account for roughly a third of the entire index by market value — higher than the peak of the dot-com bubble in 2000. Morgan Stanley’s chief investment officer has noted that the biggest stocks are currently as expensive relative to the rest of the market as they were at that peak. That kind of concentration doesn’t diversify risk — it multiplies it.
An asset bubble forms when the price of something — stocks, real estate, tech companies — rises far beyond what the underlying value can justify. In a Deutsche Bank survey of 400 asset managers, 57% identified a tech bubble bursting as their single biggest concern for 2026, the highest consensus on any risk factor in the history of those annual surveys. The top ten stocks in the S&P 500 now make up over 40% of its entire market cap. That kind of concentration doesn’t end quietly.
What inflates bubbles? Cheap money. When central banks hold interest rates low and inject liquidity into the system, that money has to go somewhere. It flows into assets, pushing prices up — not because the underlying businesses became more valuable, but because the currency chasing them lost value. This is the same cycle that has played out across every major empire in history: currency creation inflates asset prices until the math stops working.
The uncomfortable part is that nobody rings a bell at the top. The WSJ breaks down exactly how bubbles form — and what happens when they don’t.