"There has been more material progress in the United States in the 20th century than there was in the entire world in all the previous centuries combined."
-- Stephen Moore and Julian Simon, Cato Institute, December 1999

Given the success of the 20th century, those of us living in the 21st century have come to expect constant improvements in technology. We expect to upgrade to a high-definition TV within a few years. We expect that our cell phones will soon also be our cameras, personal organizers, and portable music players. And if you've seen the previews on YouTube, you expect to own a MicrosoftSurface once it becomes available.

But this culture of constant expectation is a relatively new phenomenon in human history. In terms of technology, your great-great-grandfather's life in the 19th century wasn't that much different than his great-great-grandfather's before him. In fact, the two could have switched times and places and still functioned with relative ease. But try putting one of them here in the 21st century. Talk about a fish out of water! Things we accept as commonplace today -- commercial airplanes, television, and microwave ovens -- would be downright perplexing to them.

And to think, all of these world-changing advances took place in just the 20th century. Heck, in a mere 66 years, we went from the Wright Brothers' first flight to Neil Armstrong setting foot on the moon. That's absolutely incredible when you think about it in the context of human history.

So what's next?
If the first eight years are any indication, innovation will prove even more prolific this century than it was in the 20th century. Consider the social and cultural changes brought about by YouTube, which was acquired by Google (NASDAQ:GOOG) late in 2006. Suddenly, everyone with a video camera could be Woodward and Bernstein. Heck, Virginia Sen. George Allen's reelection campaign was effectively derailed after his "macaca" remark appeared on YouTube.

A recurring topic that will be addressed and readdressed in the 21st century is the need for renewable energy sources. Integrated oil companies, for example, are getting into the renewable-energy game. Royal Dutch Shell (NYSE:RDS-A) has stakes in solar, geothermal, wind, and hydrogen power technology. Then there's the surge of hybrid vehicle sales. Auto manufacturers such as Toyota (NYSE:TM), Ford (NYSE:F), and Honda (NYSE:HMC) are ramping up production to capitalize on the growing demand for fuel-efficient vehicles.

Clearly, whether the solution is wind energy, ethanol, nuclear energy, a more efficient use of current fossil fuels, or solar energy, a lot of money will be spent and made to solve our world's growing energy needs. At our Motley Fool Rule Breakers growth investing service, one company we've recommended is Suntech Power, a Chinese business that designs, manufactures, and sells photovoltaic cells used to generate power in solar panels. Currently, solar power accounts for a small percentage of current energy use, so there's huge growth potential here. Moreover, because Suntech is aiming to be the world's low-cost producer of solar technology, our team thinks the company is in a good position to meet both consumer and environmental demands.

How to profit from change
More world-changing technology will come about in the 21st century than in any previous one. The Cato Institute's report noted that "the progress of the 20th century is not a mere historical blip but rather the start of a long-term trend of improved life on earth." Indeed, science and engineering have already reshaped the world we knew just 10 years ago.

This is great news for investors. Such innovation presents unparalleled opportunities to capitalize on the pioneering companies that will change our world -- but which of these companies is worthy of your investing dollars?

Fool co-founder David Gardner and his Rule Breakers team are always keeping their eye out for groundbreaking companies that also happen to have great business models. For example, in April 2005, the team noticed Intuitive Surgical's tremendous sales growth, and its near-monopoly in the robotic technology that enables minimally invasive surgery. The pick has returned 574% for subscribers since then.

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This article was originally published Oct. 16, 2006. It has been updated.

Fool contributor Todd Wenning does not own shares of any company mentioned. Microsoft is a Motley Fool Inside Value pick. Suntech power is aMotley Fool Rule Breakers pick. The Motley Fool is investors writing for investors.