Funny thing happened on the way to stock market disaster...

The Dow had its best week this year, gaining 435.63 points, or 3.59 percent, to 12,554. (It was up 93 points today.) Good luck trying to figure out why - the news out of Europe and Washington hasn't been especially encouraging (a NYT headline reads, "Nobody is happy"). WSJ columnist Jason Zweig reminds us that so much of Wall Street these days is based on the vagaries of computer trading.

Ten or 15 years ago, most U.S. stocks changed hands on either the New York Stock Exchange or the Nasdaq market. Today, stocks fly across dozens of different exchanges and alternative trading facilities. A trade can be executed in less than 200 millionths of a second--about 1,500 times faster than you can blink your eye. During Facebook's first day of trading, more than 570 million shares turned over--or 10% more than the average daily volume of all NYSE stocks combined in 1997. All this activity has dramatically lowered the overall cost of trading. It has also generated a chaotic ocean of data in which it can be tough to tell who traded what, when or where. "There are certainly inefficiencies [in the existing system]," says Stephen Luparello, vice chairman at the Financial Industry Regulatory Authority, which oversees brokers and dealers. "By seeing only a portion of the trading, you run the risk of finding a lot more false positives and false negatives."

So do fundamentals like earnings and economic reports really matter anymore? Probably, but only in the context of how the computers respond to those fundamentals.