Cold fusion refers to fusion reactions that occur at room temperature under normal pressure, using ordinary, simple devices.
Fusion happens when two atomic nuclei come together to form a new, heavier nuclei. This is not easily accomplished because of a basic scientific principle: oppositely charged particles attract while similarly-charged particles repel each other. Since atomic nuclei (as in hydrogen protons) are similar-charged particles, their natural tendency is to repel each other and thus prevent fusion reaction.
Scientists have discovered, however, that this natural repelling action turns into a powerful attracting force at very small scales – one millionth billionth of a meter. If the same-charge particles move any further apart than this, the natural repelling action takes place.
The sun uses brute gravitational force to achieve fusion reaction. With a mass 300,000 times that of Earth, there is sufficient gravitational force and pressure at the sun's core to push hydrogen nuclei together to form helium – and release the energy that reaches the earth as sunlight.
Man has replicated nuclear fusion in hydrogen bombs using an atomic bomb placed right beside a fusion fuel (such as deuterium or tritium) to emulate the heat and pressure at the sun's core as an initiator as well as in fusion reactors which try to mimic conditions at the sun's core by pushing hydrogen gas to extremely high temperatures or fusing atoms together with gigantic particle accelerators.
The term "cold fusion" became popular in 1989 when two scientists (Martin Fleischmann and Stanley Pons) announced that they were able to achieve a cold fusion reaction – something previously thought impossible given scientific theory.
The initial euphoria over the achievement of turned to controversy when other scientists claimed they were unable to replicate the test results. This led to charges that the two scientists had either doctored their data or became embroiled in wishful thinking. The controversy, which was widely reported in scientific publications and the media, ended with both scientists in disgrace.
In the years since, however, various scientists have achieved cold fusion reactions using a variety of approaches. Scientists at UCLA, for example, used a small lithium tantalite crystal (a pyroelectric substance that forms an electric charge when heated) placed within a hydrogen-filled chamber. When they warmed the crystal (from -30 F to 45 F), a 100,000-volt electrical field formed across the small crystal. A metal wire placed near the crystal discharged the electrical charge at a single point – and the hydrogen atoms in the chamber started smacking into other hydrogen atoms. The scientists noted the creation of helium nuclei, the release of high-energy radiation and free neutrons – all signs of fusion reaction. Similar results, using other methods, have been reported at various scientific installations.
Unfortunately, cold fusion as a cheap, reliable energy source is still currently unlikely. While the above experiments appear to prove the feasibility of fusion reactions without the need for gigantic equipment or massive amounts of energy, power output generated is still way below the amount of actual energy used.