Other topics:
Emergence
Strings
Gravity and Cosmology
Condensed Matter Physics
Nanoscience
Quantum Mechanics
Elementary Particles
Quantum Fluids
CONDENSED MATTER PHYSICS
Most of the matter in the universe (except possibly the mysterious 'dark matter') is in a 'condensed' form, ie., collected together into assemblies of many 'elementary particles'. Condensed matter can exist in solid or liquid form, or as a 'plasma' of charged particles, or in more exotic forms like superfluids or superconductors- these latter are examples of 'quantum liquids'. We are surrounded by condensed matter- (indeed we ourselves are condensed matter); everything you can see, from flowers and clouds to distant stars and galaxies, is condensed matter. Most of it is in a highly structured form, despite the simplicity of the interactions between the building blocks (electrons, protons, atoms, molecules, etc.).
The
aim of condensed matter physics is to understand the
collective properties of assemblies of particles,
rather than the properties of the individual parts
(although a complicated assembly of particles like a
large molecule may have fascinating collective
properties of its own, but yet 
just be a building block for
some even bigger condensed matter system. These
collective properties can be extraordinary- as in the
properties of superfluids, or
of living matter. Phenomena such as superfluidity, or
life, are clearly not embodied in any way in the
original building blocks, but do arise when these
blocks operate together. To describe these, new
concepts like 'order parameters', or 'quasiparticles',
have been invented. These concepts have been crucial
throughout physics, and have also been behind the
development of much of chemistry and biology during the
20th century.
In recent years condensed matter physicists have been much concerned with inventing radically new structures, not existing in Nature. Some of this activity is now labelled as 'nanoscience', with speculations about new kinds of 'quantum device' very much in the air.
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