Daniel Yergin, the chairman of IHS Cambridge Energy Research Associates, says fossil fuels will continue to dominate U.S. energy consumption for decades to come. Vinod Khosla, a longtime Silicon Valley investor who runs the venture-capital fund Khosla Ventures, is betting alternative energy will play a bigger role much sooner. Who is right? The Wall Street Journal's Kimberley Strassel sat down to discuss the issue with Mr. Khosla and Mr. Yergin. . .