Today, researchers use huge lasers or powerful magnetic fields to trigger limited fusion reactions among deuterium and other hydrogen isotopes. Results are promising but still modest. Billions of dollars spent on research has yet to identify an economically viable fusion technology that can steadily produce more energy than it consumes.

But three years ago, nuclear engineers Rusi P. Taleyarkhan of Purdue University and Richard T. Lahey Jr. of Rensselaer Polytechnic Institute announced that they had produced thermonuclear fusion by imploding tiny deuterium-rich gas bubbles with sound waves and neutrons. The bubbles' violent collapse can cause some of the deuterium nuclei to undergo fusion, a claim that researchers say new experiments reinforce. Five groups — three in the U.S. and two in Europe — are working to reproduce the "sonofusion" results, and some apparently have succeeded and are preparing to publish their findings.