Experiments in particle physics usually proceed by smashing together particles so hard that one manages either to jiggle some of the substructure and maybe kick it out, or else to create entirely new particles from pure energy. For this one uses gigantic accelerators to make the particles collide with as high speeds as possible. Particle theorists work in two different ways. Either they attempt to explain particular experimental results with mathematical models, or they independently construct mathematical models guided by principles of naturalness and beauty. Such models can suggest new experiments to be done and have often been able to predict the outcome of experiments before they have been performed.
Cosmology is the study of the origin of the universe.
Particle Cosmology has developed as a science after it became clear in the 1960's that the universe originates from a Big Bang, and therefore that the very early universe must have been dense, hot and filled with particles that would, under such circumstances, collide at least as hard as in the collisions that we create in particle accelerators. Because of this correspondence, many aspects of the very early universe can be described with models of particle physics. Conversely, we are now beginning to learn things about particle physics through observations that use telescopes and other methods to look far into the universe and deep into its past. The recent abundance of results from such observations has made the subject of particle cosmology blossom. A field , or classical field, is a mathematical entity which can be thought of as a collection of numbers that tells you something about each point in space-time, such as the temperature at each point in a room.