Most science texts will tell you that matter exists in three states: solid, liquid and gas. Pressure plays a role in determining the state in which matter is found, but temperature is usually the deciding factor.

The conversions of solid ice to liquid water at its melting point and then to vapor or steam at the boiling point are so well known that the Celsius and Fahrenheit thermometers are based on these two points.

A few texts may mention a fourth state of matter called a plasma that is created when a gas is heated to such a high temperature that many of the electrons are stripped from the atoms, giving a mix of charged atoms or ions and free electrons.

Plasmas are relatively rare on Earth, although they exist momentarily around lightning bolts and are found in the ionosphere, but they are the most common state of matter in the universe. Stars, in essence, are huge balls of plasma.

Almost no text mentions a fifth state of matter that has been known only since 1995 and is known as a Bose-Einstein condensate (BEC). Its properties are unlike very few things ever seen before on Earth.

Albert Einstein first predicted the possibility of this state of matter in 1925 by extending work started by an Indian physicist, Satyendra Bose, writes Gary Taubes in the July 8, 1994, issue of Science. In the wave mechanical model of the atom, electrons are treated as standing waves surrounding the nucleus. Einstein said that if a group of atoms could be cooled to a sufficiently low temperature, their waves would merge.

In effect, says Taubes in a subsequent Science article published July 14, 1995, “The group of atoms lose their separate identities and become one.” No one could predict how a group of atoms acting as a single entity would behave, but matter at temperatures higher than those required for BECs to exist, a few millionths of a degree above absolute zero, acts strangely enough.

Liquid helium, at a steaming 2.18 degrees above absolute zero exhibits “superfluidity” which means that it loses all viscosity. Helium in this state defies the law of gravity by flowing up the vertical walls of its container.

Another feature of extremely cold materials is “superconductivity” or near zero resistance to electric current passage. When an electric current is applied to a superconductor, it tends to flow indefinitely. But before it could be determined if BECs had these, or other strange properties, a way to reach a temperature cold enough to create one had to be achieved.

Many physicists considered the creation of a BEC next to impossible, but Eric Cornell of the National Institute of Standards and Technology and University of Colorado physicist Carl Wieman reported the successful preparation of a BEC in the July 14, 1995, issue of Science.

They had cooled a small vapor of metallic rubidium to a few billionths of a degree above absolute zero using a combination of laser cooling followed by evaporative cooling in a magnetic trap. In the former, a stream of atoms slows and radiates heat as it is directed against a laser beam. The atoms were then funneled into a cone-shaped magnetic field where “hot” atoms escape leaving about 1,000 atoms of BEC colder than the deepest reaches of space.

The original BEC lasted for only about 15 seconds, but subsequent work has shown that they are liquid in nature. David Voss, in the March 23, 2001, issue of Science reported the presence of vortices when BECs are “stirred” with a laser beam, a sure sign of the liquid state. There is now some speculation that liquid helium may have been the first BEC.

Are BECs anything more than laboratory curiosities? Possible uses have been proposed ranging from atomic lasers to extremely accurate measuring devices for time and length.

The most fascinating discovery to date has been the slowing of light as it passes through a BEC. The velocity of light is constant in a vacuum but slows in materials such as water, glass and the like, causing it to bend and separate slightly. This is called the refractive index for a material and explains why white light separates into the colors of the spectrum when passing through a prism.

But the most refractive materials slow light only a miniscule amount from its standard 300 million meters per second.

Now, however, Lene Hau, a physicist at Harvard University and the Rowland Institute for Science, announced in the February 18, 1999, issue of Nature that she has slowed a light beam to a mere 17 meters per second by passing it through a BEC.

This feat already is causing some researchers to dream of one day achieving another impossibility, that of bringing a light photon to a complete halt.