Robots don't take bathroom breaks, and that's one reason why, all else being equal, they may make better factory workers than the human version. But all else is getting less equal. New generations of super "smart" robots are doing more and more complex tasks, their needle arms going into tiny spaces the most delicate human hand can't reach. And just as the machines leap forward in sophistication, their price is coming down.

Another industrial revolution bangs at the doors, and as other industrial revolutions have done, this one will change everything. For one thing, factories that moved to Asia for low-wage workers may return to the United States. After all, if machines can do the labor-intensive jobs, it may not matter whether the factory is in Cleveland, Hartford, Nashville or Guangzhou.

In truth, while factory jobs have left the United States, factories never quite did. America still makes lots of stuff that can be produced with a handful of people running computerized equipment. What's different now is that the machines are getting more clever.

There were always some advantages to manufacturing locally, and they remain. For example, the Flextronics solar-panel plant in Milpitas, Calif., can ship a solar panel to Phoenix more quickly and cheaply than a factory in Jiangsu province can. Courtesy of robots, it can now also compete with the Chinese solar-panel giants on manufacturing costs. Furthermore, the company's creative secrets are safer at home than in China, where protections for intellectual property are notoriously lax.

This trend helps workers in other high-wage countries. In Drachten, Netherlands, a Philips Electronics factory now employs one-tenth as many people as its sister plant in Zhuhai, China, according to a report in The New York Times.

Companies operating here won't care as much whether their employees are unionized or not. For one thing, they'll employ relatively few humans. For another, the people who run the robots will have high-level skills that automatically command good pay. Local cost of living and the price of energy may still play a role. But to attract the factories, a community will have to offer a tech-savvy workforce able to keep the robots on task.

Won't displacing vast numbers of factory workers with plug-in substitutes set off a social revolt? Probably not here, because the kinds of workers who simply glued one part on another were laid off long ago. Today, 9 percent of working Americans are directly employed in manufacturing, way down from 30 percent in 1950.

China is another matter. Its economic miracle has relied on having lots of low-wage people do low-skilled things. They have the jobs to lose. True, China is rapidly educating engineers and other tech workers. But it remains a developing nation where impoverished masses hold high expectations for a cushier tomorrow. Apple is still building factories in China to make the iPhone, but even those plants will have more robots and fewer people than in the past.

The wild card is how robots may threaten other kinds of jobs. These new machines can move around and perform multiple operations. They'll do farm chores, cooking and housecleaning. They're already packing boxes for shipment, using video cameras for eyes.

So here are the big-picture questions: What will happen to those replaced by mechanical arms? Will they be dropped into shiftless poverty? Or will they share in the productivity miracle and suddenly find themselves freed to write poetry? What about new occupations this revolution may open?

All bets are off about who will be the industrial superpower of the 21st century. But here's a hint: It may not be China, after all.