in 1989, a couple of scientists in a small university created headlines by demonstrating a simple chemical reaction that led to cold fusion of nuclei. However, the claim was later found to be false and the whole incident remains a sad example of shoddy science. But now, another group of scientists has reportedly demonstrated a different table-top experiment where they claim to have observed nuclear fusion. If this claim is true, it could be amongst the biggest discoveries in science.

When nuclear fusion was first discovered in the 1940s, there was a lot of talk about it being a virtually limitless and free source of energy. But this promise of cheap, clean fusion energy has remained a dream. The technology for generating controlled nuclear fusion has not delivered.

The extreme conditions that are ordinarily needed for achieving the fusion of two light nuclei (like hydrogen or its heavy isotopes) are found in the core of stars like our Sun. The high temperatures and pressures in the cores allow the nuclei to fuse together to produce helium and a lot of energy. It is this energy that we receive from the Sun. In fact, the Sun and billions of other stars have been shining for billions of years because of this energy.

R Talyerkhan and his collaborators at the Oak Ridge National Laboratory in usa, together with scientists in Russia have reported a simple experiment where they claim to have seen nuclear fusion. This fusion, unlike the older "cold fusion' needs only some liquid and sound waves. The key to the whole experiment is a process called cavitation in which bubbles of a liquid are forced to collapse very quickly by high frequency sound waves. This implosion of the bubbles causes extremely high temperatures and pressures (like those in the core of the Sun) allowing the nuclei to fuse together.

The experiment uses the phenomenon of sonoluminescence where light flashes are emitted when ultrasonic waves travel in a liquid. The light is emitted because the energy is concentrated in a very small region during the cavitation and this concentration causes the molecules to emit light. Estimating this energy leads the researchers to conclude that it is large enough to induce nuclear fusion in the liquid.

The liquid used in the experiment is acetone, the stuff of which paint thinners are made. What the researchers did was to replace all the hydrogen in acetone (which is an organic solvent) with deuterium atoms. Deuterium is a heavy isotope of hydrogen in which there is a proton and a neutron inside the nucleus as opposed to hydrogen where there is only a proton. When high frequency acoustic waves were shone on the liquid, light flashes were seen. The researchers even detected neutrons and tiny amounts of tritium, a heavier isotope of hydrogen. When this same experiment was repeated with ordinary acetone, there were no neutrons or tritium. This supports the finding that the sonoluminescence produces enough energy to fuse deuterium nuclei but not for hydrogen nuclei.

The scientific community is obviously treating this claim with a lot of skepticism, especially after the cold fusion fiasco. Most scientists believe that the experiment has to be repeated by other scientists for it to be confirmed. In any case, many steps are needed for transforming the nuclear fusion on a table-top to a viable energy source. If the experimental findings are confirmed and the technology for cheap generation of fusion energy is worked out, then of course, it could provide the long sought limitless, clean source of energy for all humanity.