The events of August were outliers, and they were of the quants' own making. To begin with, quants were indirectly responsible for the boom in housing loans offered to shaky candidates. Derivatives allow banks to trade their mortgages like bubble-gum cards, and the separation of the holder of a loan from the writer of a loan tended to create an overgenerous breed of loan officer. The banks, in turn, were attracted by the enormous market for derivatives like CDOs. That market was fueled by hedge funds' appetite for products that were a little riskier and would thus produce a higher return. And the quants who specialized in risk assessment abetted the decision to buy CDOs, because they assumed that the credit market would enjoy nine or so years of relatively benign volatility.
It was a perfectly rational assumption; it just happened to be wrong.
"The products are getting an order of magnitude more complex," says Berman. "Things change slightly, and get correlated where they weren't correlated before." Or, as he put it a little less gnomically, "You can't make it without understanding it, but you can buy it."
Beneath all this beats the great hope of the quants: namely, that the financial world can be understood through math. They have tried to discover the underlying structures of financial markets, much as academics have unlocked the mysteries of the physical world. The more quants learn, however, the farther away a unified theory of finance seems. Human behavior, as manifested in the financial markets, simply resists quantification, at least for now.
Emanuel Derman remembers dreaming of such a unified financial theory in the early 1990s, a little after he had made the leap from the university to the Street. But those dreams, he says, are dead. Quantitative finance "superficially resembles physics," he says, "but the efficacy is very different. In physics, you can do things to 10 significant figures and get the right answer. In finance, you're lucky if you can tell up from down."
