Byron Wien, the 82-year-old vice chairman of Blackstone Advisory Partners, is one of the wise old men of Wall Street.

But for each of the last 15 years, he has written up an interview for Barron's about a person he calls "the smartest man in Europe," another octogenarian. This man has "built his reputation by identifying important trend changes early and putting serious money behind his conclusions," Wien writes.

So what does the smartest man in Europe have to say about what's happening now?

"The whole world is suffering from too much debt," he says. "As a result, growth almost everywhere is going to be slow."

And what about the U.S. stock market? "If you want to make real money investing, you will have to do it by picking stocks in technology and biotechnology, and I would emphasize the latter," the smartest man says.

The S&P 500 Information Technology Index has barely changed so far this year, while the S&P S&P Biotechnology Select Industry Index has soared 35.4 percent.

Among tech stocks, he likes Facebook, Salesforce.com, Apple, Alibaba and Palo Alto Networks. Mr. Smarts says he exited Google.

Meanwhile, the S&P 500 index dropped 2.1 percent Monday, as Greece's debt crisis intensified, before stabilizing. But it's not Greece that stands as the biggest danger for stocks, says MarketWatch columnist Mark Hulbert.

"There are many legitimate reasons why the stock market is vulnerable to a serious decline. But the Greek debt crisis is not one of them," Hulbert writes. "After all, investors can hardly be surprised by Greece’s debt difficulties, which have dominated the news for over five years now."

And Greece accounts for less than 2 percent of eurozone GDP.

So what's the real worry?

"We have a stock market that, depending on the metric, is either significantly or extremely overvalued, coupled with an already anemic earnings growth rate that is dangerously dependent on an unsustainably high corporate profit margin," Hulbert says.

The S&P 500 carries a 26.63 price-earnings ratio, based on a measure formulated by Nobel laureate economist Robert Shiller that encompasses 10 years of earnings. In recent months, the index has stood at its highest level outside of the pre-cash peaks of 1929, 2000 and 2007.

S&P 500 company earnings are expected to show a drop of 4.5 percent for the second quarter, according to FactSet.

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