Scale separation: breaking down unsolvable problems into solvable ones

Markus Wallerberger and Anna Kauch Exact solutions are often impossible in materials physics. In an international research cooperation involving TU Wien and Saitama University in Japan a technique has now been developed to make unsolvable quantum calculations solvable on certain scales. In physics, one often has to deal with different scales that can be described separately from one another: For the earth's orbit around the sun, it makes absolutely no difference whether an elephant in the zoo walks to the left or to the right. And the movement of the elephant can be described without having to know anything about the properties of the electrons in its ear. The world can be divided into different scales. In materials research, too, it is important to describe the behavior of particles on the appropriate scales. However, you first have to find out which scales are the decisive ones - a difficult task for which there was previously no clear solution strategy.