Twenty years ago it appeared, for a moment, that all our energy problems could be solved. Cold fusion would end our dependence on the Middle East and stop those greenhouse gases blamed for global warming. It would change everything. But then, just as quickly as it was announced, it was discredited. Well, a funny thing happened on the way to oblivion - for many scientists today, cold fusion is hot again. "We can yield the power of nuclear physics on a tabletop. The potential is unlimited. That is the most powerful energy source known to man."    Clarification to the video, April 23, 2009: This story initially erred in describing how "60 Minutes" came to speak with Rob Duncan of the University of Missouri.   Duncan was not officially recommended by the American Physical Society but rather was recommended independently by the chairman of one of its divisions.    Discussion