"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 our two-year-old computers to be rendered obsolete by Windows Vista when it comes out. We expect to upgrade to a new cell phone after our contract expires. And we expect that we'll be able to download any movie we want within the next year.

But this culture of constant expectations 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 microwaves -- would be downright perplexing to them.

And to think, all of these world-changing advances took place in just the 20th century. Heck, in just 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 six years of this century are any indication, 21st-century innovation will prove to be even more prolific than the 20th. Consider that more than 42 million Apple Computer (NASDAQ:AAPL) iPods have been sold since 2001 and have forever changed the way we listen to music, more than 300 million camera phones are in use since Vodafone (NYSE:VOD) introduced the first commercial model -- the J-Phone -- in 2000, and 12 million people have subscribed to satellite radio services XM Satellite Radio (NASDAQ:XMSR) and Sirius Satellite Radio (NASDAQ:SIRI) since 2001.

And those are just consumer products. Rapid technological advances are also being made in the health-care and renewable energy industries. This year, for instance, Gilead Sciences (NASDAQ:GILD) received FDA approval for its once-a-day HIV pill, Atripla, which stands to simplify dosing schedules and increase viral suppression of an affliction that affects some 38.6 million people worldwide.

A recurring topic that will be addressed and re-addressed in the 21st century is the need for renewable energy sources. Integrated oil companies, for example, are getting into the renewable energy game. In 2005, BP (NYSE:BP) said it would invest $1.8 billion over the next three years to research solar, wind, low carbon, and hydrogen power technology.

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 to solve our world's growing energy needs. At our Motley Fool Rule Breakers growth investing service, one company we've recommended is SuntechPower (NYSE:STP), 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 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 Rule Breakers 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 century combined. 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 are worthy of your investing dollars?

Motley Fool co-founder David Gardner and his Rule Breakers team are always keeping their eye out for ground-breaking companies that also happen to have great business models. For example, in April 2005, the team noticed Intuitive Surgical's tremendous sales growth and near-monopoly in robotic technology that allows for minimally invasive surgery. The pick has since returned 140% for Rule Breakers subscribers.

Interested? Full access to Rule Breakers is yours free for 30 days. It's easy to get started. Just follow this link for more information.

Todd Wenning owns call options on Sirius Satellite Radio. XM Satellite Radio is a Rule Breakers pick. Vodafone is an Inside Value recommendation. The Motley Fool is investors writing for investors.