Of the five states matter can be in, the Bose-Einstein condensate is perhaps the most mysterious. Gases, liquids, solids and plasmas were all well studied for decades, if not centuries; Bose-Einstein condensates weren't created in the laboratory until the 1990s. A Bose-Einstein condensate is a group of atoms cooled to within a hair of absolute zero. When they reach that temperature the atoms are hardly moving relative to each other; they have almost no free energy to do so. At that point, the atoms begin to clump together, and enter the same energy states. They become identical, from a physical point of view, and the whole group starts behaving as though it were a single atom. To make a Bose-Einstein condensate, you start with a cloud of diffuse gas. Many experiments start with atoms of rubidium. Then you cool it with lasers, using the beams to take energy away from the atoms. After that, to cool them further, scientists use evaporative cooling. "With a [Bose-Einstein condensate], you start from a disordered state, where kinetic energy is greater than potential energy," said Xuedong Hu, a professor of physics at the University at Buffalo. "You cool it down, but it doesn't form a lattice like a solid." Instead, the atoms fall into the same quantum states, and can't be distinguished from one another. At that point the atoms start obeying what are called Bose-Einstein statistics, which are usually applied to particles you can't tell apart, such as photons.