What is theoretical condensed matter physics, and why is it interesting?
Condensed Matter Physics is the study of the structure and behaviour of the matter that
makes up most of the usual (and unusual) stuff that surrounds us every day. It is not the
study of the very small (particle theory) or of the very large (astrophysics and cosmology)
but of the things in between. It takes for granted that most of these are made up of electrons
and nuclei interacting according to the well-established laws of electromagnetism and quantum
mechanics, and tries to explain their properties.
What makes it an interesting and fundamental branch of physics? It turns out that large
assemblies of electrons and nuclei in a condensed state
often exhibit so-called cooperative behaviour which is quite different from that of the
individual parts. Superconductivity, for example. And the study of this new behaviour requires
theoretical methods which can be every bit as sophisticated as those of particle theory or
relativity. In fact, mathematically they often have a lot in common. But while there is (we hope)
only one `theory of everything' which describes the building blocks of matter, at intermediate
scales there are any number of `effective' theories which account for the wealth of phenomena
which we observe. Thus the subject is very diverse.
In condensed matter physics, experiment and observation play a key role. As compared with
particle physics, most experiments are much easier to carry out, generally much more precise,
and take far less time. So the link between experiment and theory is that much stronger.
Condensed matter physics is both fast-moving and outward looking. Developments come from
fresh theoretical ideas, from ideas transplanted to a novel context, and from (sometimes
serendipitous) experimental discoveries. Some of these developments involve topics at the
interface between condensed matter physics and other fields - examples include atomic physics
Condensed matter physics is also very important because it often uncovers phenomena which
are technologically important. As well as solid state devices, the whole field of polymers,
complex fluids and other so-called `soft' condensed matter systems has all sorts of applications.
More recently, the methods which condensed matter theorists use to study interacting systems with
many degrees of freedom have been used to attack problems in such diverse fields as economics and
the life sciences.
As a study in itself, as well as being a sound basis for any career where quantitative skills
and problem-solving are at a premium, an apprenticeship in condensed matter theory is fascinating