CHICAGO — Two different words leapt to mind yesterday upon hearing the news that Google's share price surpassed $500.

Juggernaut, and bubble.

Maybe a third word, too: Wow.

One of America's new bellwether companies, Google Inc. closed at $509.65. Having gone public just two years ago at $85 a share, it's a remarkable run up in price for an eight-year-old California firm that searches the Internet for information on everything from how to fix a PB&J sandwich to the discography of Jelly Roll Morton. It makes its money by selling advertisers that millions of eyeballs see each day.

"People don't want to be left behind with a stock like this," said Scott Kessler, an equity analyst who follows Google for Standard & Poor's. "They don't want to tell their friends they weren't smart enough not to take part. That momentum is part of the story."

The question is whether Google's market performance accurately reflects the achievement of an extraordinarily innovative company dominating its field, or is a product of unrealistic and unsustainable hype.

It was just six years ago that a similar frenzy of technological innovation and investor excitement came to a crushing end as numerous speculative and risky bets on nascent technology firms proved overly optimistic.

If there is something different this time, Allen Weiner, an analyst for technology research firm Gartner Inc. said that technology has become a greater part of "the fabric of our country."

Where GM and Ford were once at the heart of the national economy and identity, companies like Google that specialize in technology applications have taken on that role.

"Even if people don't understand Google, they see it as a watershed company that represents where we are headed," he said.

There are just a handful of U.S. stocks that trade at prices north of $500. Those include the Chicago Mercantile Exchange, another high-flying relatively new issue, and legendary Wall Street darling Berkshire Hathaway, where Class A shares trade for more than $100,000.

Google has reached its plateau because of its technological prowess as a search engine and because it is a social phenomenon.

"There is this enthusiasm and emotional connection certain stocks have with users," Kessler said. "That means many people are employing the Peter Lynch method of investing, 'Buy what you know.' "

With Google, "people around the world can get answers to most anything they are seeking for free in a very easy fashion and that helps in their day-to-day lives," he continued. "What could be better than that?"

Then there's the crucial fact that, unlike the last time tech stocks reached what appeared to be unreasonable levels, Google is making money.

In its third-quarter report released last month, Google's revenues nearly doubled from the year-earlier period. It also beat estimates by 20 cents a share as its revenue jumped by 70 percent to $2.69 billion for the quarter.

Those numbers are growing due to Google's dominance in Internet search.

"Google accounts for 61.6 percent of all U.S. searches," said Bill Tancer, general manager of global research for Hitwise, a Web tracking firm. "The next biggest competitor is Yahoo, with 22.4 percent of the market."

Through search, Google sells advertising, dominating with small text ads that accompany the results. Its newer products include video searches and an e-mail service that comes with attached ads. It bought YouTube last month for $1.65 billion in stock and is pushing other products like Google Maps as vehicles to reach an audience and sell advertising. None of that is likely to surpass its search business.

"The one thing that's going for them is that the amount of information that is on the Internet keeps growing at leaps and bounds," he said. "As that trend continues to grow, search will continue to be the key to Internet use."