It was a tough and scary day on Wall Street. Stocks fell fast and the Dow saw its worst day since 9/11.

The Dow’s drop was 504 points. The Standard and Poor's 500 fell almost 5 percent. Overall, it was the worst day on Wall Street in over seven years.

"It's sending a message that the stock value of financial companies is in a lot of trouble,” said Jeff Cooperstein, an Economist at the University of Arkansas.

Three big problems today on Wall Street:

1. The Lehman brothers filed for the biggest bankruptcy in history.
2. The Bank of America said it's planning on buying Merrill Lynch.
3. AIG will soon be announcing a major restructuring after accepting $20 billion from the state of New York.

"I think that the stock markets are just reacting to a series of bad financial news,” explains Cooperstein. “And also the fact that the feds didn’t bail out Lehman, unlike what they did for Fannie Mae and Freddie Mac."

But does one bad day mean bad news for investors? Cooperstein says these things actually tend to work themselves out.

"You're in the stock market for the long haul and a one-day drop isn't going to cause you to have to work another twenty years,” says Cooperstein.