A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made (particle physics) to the behavior of the material Universe as a whole (cosmology).
Many positions, especially in research, require a doctoral degree. At the Master's level and higher, students tend to specialize in a particular field. Fields of specialisation include experimental and theoretical astrophysics, atomic physics, molecular physics, biophysics, chemical physics, condensed matter physics, cosmology, geophysics, material science, nuclear physics, optics, particle physics, and plasma physics. Post-doctoral experience may be required for certain positions.
The three major employers of career physicists are academic institutions, government laboratories, and private industry, with the largest employer being the last. Many people who are trained as physicists, however, use their skills in other parts of the economy, in particular in engineering, computing, and finance. Some physicists take up careers where their knowledge of physics can be combined with further training in other disciplines, such as patent law in industry or private practice. In the United States, a majority of those in the private sector with a physics degree work outside physics, astronomy and engineering altogether.