Sep. 23--What do U.S. stocks, Asian stocks, Brazilian stocks, gold and other commodities and high-yield bonds all have in common?

Some would argue that they are all risky assets, driven higher in an attempt by the Federal Reserve and central banks worldwide to entice investors away from safe havens such as U.S. Treasurys.

In the vernacular of economists, the prices of the risky assets are being driven ever higher by "liquidity," or the huge amounts of money poured into the system by the central banks to pump life into a distressed economy.

In other words, central bankers haven't wanted investors to cower in the safety of assets such as U.S. Treasurys because they would fail to get the economy moving. Instead, the bankers have provided a nudge. They are essentially printing money, and through various policies making the interest in Treasurys almost nonexistent so that investors will venture further into riskier bonds and stocks in search of better money-making possibilities.

"They've made it painful for anyone who wants no risk," said strategist Ed Yardeni of Yardeni Research.

Now, with investors buying stocks and pushing prices higher, the Dow Jones industrial average finished Tuesday at 9829.87, the highest close since Oct. 6. And gold, though known as a safe haven in its own right, is attracting investors who are hoping to do better than they can in Treasurys. Gold closed Tuesday at $1,014, up more than 44 percent in less than a year.

Some analysts are growing increasingly fearful about what lies ahead. They know that prior liquidity-fests have ended badly, with a technology bubble bursting in 2000 and the stock market plunging 49 percent. Then came the housing bubble, fueled by liquidity flowing in to fight the tech-bubble recession. The 2007 bubble caused home prices to inflate, and a debt binge contaminated the health of the global economy.

"Now, they've created another risk bubble," said Howard Simons, a strategist for Bianco Research. "There is just too much paper out there."

That's paper in the form of stock certificates in global markets, shares of the gold exchange-traded funds and high-yield bonds. The money is flowing into paper assets, Simons said, because it's easy.

"It takes an effort to build a plant or buy equipment," he said.

Because so much money is available to invest, Simons notes, "You can't knock stock prices down for more than three hours in a day."

Meanwhile, the U.S. dollar looks troubled as it drops. But Michael Woolfolk, senior currency strategist at Bank of New York Mellon, said he doesn't believe the dollar is declining because investors think the U.S.