Abstract
Why do physicists freeze matter to extremely low temperatures? Why is it worthwhile to cool to temperatures which are a billion times lower than that of interstellar space? In this talk, I will discuss new forms of matter, which only exist at extremely low temperatures. With the help of laser beams, gases of ultracold atoms can be transformed into crystals, insulators and magnetic materials, and recently into a supersolid which is gaseous, liquid and solid at the same time.