A physicist is a Scientist trained in Physics. Physicists study a wide range of physical phenomena spanning all length scales: from the sub-atomic particles from which all ordinary matter is made (Particle physics) to the behavior of the material Universe as a whole (Cosmology). There are numerous different branches of physics and each has its corresponding specialists, such as astrophysicists, geophysicists, or biophysicists.
Employment as a professional physicist generally requires a doctoral degree. Physicists are employed by universities as professors, lecturers, and researchers, and by laboratories in Industry. Many people who are trained as physicists, however, use their skills in other parts of the economy, in particular in Engineering, Computing, and Finance.
Traditional tools of the astronomer include the Telescope, and a device such as the quadrant or sextant to measure elevation. In the 20th century, the Radio telescope extended the range of astronomical observation. This expanded range of observation led to the development of Physical cosmology, the study of the structure, beginnings, and fate of the Cosmos. Two of the more celebrated physicists of the modern age are Edwin Hubble and Steven Hawking.
Despite enormous advances in the technology used to make observations of the universe, the majority of astrophysical observation is still a slow and painstaking job.
It was soon found that the atom could be split (Fission) or combined (Fusion). Each process resulted in behavior that could not be explained by Bohr's model of the atom. In the atomic age, Werner Heisenberg and Erwin Schrödinger developed a theory of Quantum mechanics to explain the behavior of matter at the smallest scale. Modern physicists are still trying to cope with difficulties introduced by this theory. In particular, it does not fit well with our view of Gravity and the universe at the large scale, although it explains the small scale very well. Today's physicists hope to reconcile the two view of the universe some day soon.