"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 Microsoft Surface 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. 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 -- 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 of this century are any indication, 21st-century innovation will prove to be even more prolific than that in the 20th. Consider the social and cultural changes brought about by camera phones manufactured by Nokia (NYSE: NOK) and Sony's (NYSE: SNE) join venture with Ericsson, Sony Ericsson. Suddenly, everyone with a cell phone can be a freelance paparazzo or news reporter. Indeed, there are quite a few of them out there these days with mobile-phone sales topping 1.15 billion units in 2007.

Video conferencing has also taken off as a new mode of communication, and is much easier to use as video quality and sound have vastly improved. eBay's (Nasdaq: EBAY) Skype unit, for example, allows free video chat, so all you really need is a webcam to have face-to-face conversations with a friend in Mumbai.  

A recurring topic that will be addressed and readdressed in the 21st century is the need for renewable energy sources. Integrated oil companies are getting into the renewable energy game. BP has stakes in solar, geothermal, wind, and hydrogen power technology. Then there are the agricultural conglomerates like Bunge (NYSE: BG) and Archer Daniels Midland (NYSE: ADM) that are ramping up production to capitalize on the growing demand for ethanol-based products.

Clearly, whether the eventual 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 in solving 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 company that designs, manufactures, and sells photovoltaic cells, which are used to generate power in solar panels.

Currently, solar power accounts for a fractional percentage of 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 always keep their eyes 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 670% 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. Apple is a Stock Advisor choice. Suntech Power is a Motley Fool Rule Breakers pick, as is Intuitive Surgical. The Motley Fool is investors writing for investors.