New York - The Dow Jones industrial average closed above 15,000 for the first time Tuesday. An improving outlook for the economy and record corporate earnings are persuading investors to buy stocks. Federal Reserve stimulus is also helping.

The Dow has gained 15 percent this year. It has more than doubled since hitting a bottom at 6,547 on March 9, 2009 during the Great Recession.

Now that stocks have scaled these heights, what's next? Four market experts give their views.

THE BULL: James Paulsen, chief investment strategist at Wells Capital Management.

Paulsen thinks stocks can go a lot higher. Paulsen says investors are shedding their fear following the stock market slump that accompanied the Great Recession. He keeps a close watch on a key figure called the price-earnings ratio, a measure of how much investors are paying for stocks relative to a company's earnings per share.

Investors are now paying an average of 15.7 times earnings over the past 12 months. Paulsen says that ratio could climb as high as 20 times, as long as the economy doesn't fall into recession.

THE SKEPTIC: Michael Lewitt, chief investment officer of Credit Strategy Advisory Group

Lewitt is optimistic in the short run but bearish over a longer period. He worries that investors are just buying stocks because they expect the Fed to keep stimulating the economy and that they don't have as much fear as they should. One sign: They are borrowing 28 percent more than they did a year ago to finance their stock trades, and now have a near-record amount of debt, according to Bank of America Merrill Lynch figures.

THE BEAR: Uri Landesman, president of Platinum Partners

Stocks are poised for a decline, having risen too far, too fast, says Landesman. Investors, encouraged by the ongoing stimulus efforts of the central bank, led by Fed Chairman Ben Bernanke, are starting to think that stocks are a one-way bet.

Landesman thinks investor confidence is more fragile than it appears. The catalysts for a sell-off, he says, could be anything from disappointing earnings news to weak economic data, either from the U.S. or overseas.

THE ORACLE: Warren Buffett, chief executive of Berkshire Hathaway and stock market guru.

Warren Buffett said Monday that he never knows where the stock market will go in the short term, but he remains confident stocks will continue moving higher in the long run.

"The retention of earnings by American industry, the growth of the country will cause stocks to go higher over time," Buffett said. "You're not getting everything out of stocks in terms of the dividends they pay compared to the earnings. That retention builds it up. It's exactly like if you had a savings account and you only took out part of your interest, your savings would grow."

Instead of paying attention to when stocks are rising to records, investors should pay attention to when stocks are falling past important milestones, Buffett says.

"That's when stocks are getting cheaper. That's when stocks are going on sale."