Astronomy, acoustics, astrophysics, biophysics, chaos theory, chemical physics, computational physics, cosmology, cryophysics (cryogenics), crystallography, electromagnetism, electronics, fluid dynamics, geophysics, high energy physics and high pressure physics are a few of the different branches in the field of physics. Physics acts as a root in scientific study from which to branch into the scientific community.
Other branches of physics include: laser physics, mathematical physics, mechanics, meteorology, molecular physics, nanotechnology, nuclear physics, optics, particle physics, plasma physics, quantum electrodynamics, quantum mechanics, quantum optics, quantum gravity, relativity, statistical mechanics, string theory and thermodynamics.
Astrophysics is a subcategory of astronomy and focuses more on how objects in the universe interact with each other rather than simply on the chemistry and mathematics of celestial bodies. Similarly, cosmology studies the origins and future of the universe by examining black holes, dark matter and similar phenomena.
Quantum electrodynamics studies how matter and light interact and merges quantum mechanics and special relativity. Quantum mechanics is sometimes referred to as quantum theory and uses mathematical data that describes particle and wave behavior to gain insight to phenomena on a macroscopic scale. Quantum optics makes use of quantum mechanics to study how light interacts with matter on a universal scale. Quantum gravity, on the other hand, is a bit of a mystery and physicists seek to unify quantum mechanics and theory of relativity and explain it in mathematical formulas.