The Different Fields of Physics

milky way at dawn and silhouette of a telescope
ClaudioVentrella / Getty Images

Physics is the branch of science which is concerned with the nature and properties of non-living matter and energy that are not dealt with by chemistry or biology, and the fundamental laws of the material universe. As such, it is a huge and diverse area of study.

In order to make sense of it, scientists have focused their attention on one or two smaller areas of the discipline. This allows them to become experts in that narrow field, without getting bogged down in the sheer volume of knowledge that exists regarding the natural world.

The Fields of Physics

Physics is sometimes broken into two broad categories, based on the history of the science: Classical Physics, which includes studies that arose from the Renaissance to the beginning of the 20th century; and Modern Physics, which includes those studies which have been begun since that period. Part of the division might be considered scale: modern physics focuses on tinier particles, more precise measurements, and broader laws that affect how we continue to study and understand the way the world works.

Another way to divide physics is applied or experimental physics (basically, the practical uses of materials) versus theoretical physics (the building of overarching laws as to how the universe works).

As you read through the different forms of physics, it should become obvious that there is some overlap. For example, the difference between astronomy, astrophysics, and cosmology can be virtually meaningless at times. To everyone, that is, except the astronomers, astrophysicists, and cosmologists, who can take the distinctions very seriously.

Classical Physics

Before the turn of the 19th century, physics concentrated on the study of mechanics, light, sound and wave motion, heat and thermodynamics, and electromagnetism. Classical physics fields that were studied before 1900 (and continue to develop and be taught today) include:

  • Acoustics: The study of sound and sound waves. In this field, you study mechanical waves in gases, liquids, and solids. Acoustics includes applications for seismic waves, shock and vibration, noise, music, communication, hearing, underwater sound, and atmospheric sound. In this way, it encompasses earth sciences, life sciences, engineering, and the arts.
  • Astronomy: The study of space, including the planets, stars, galaxies, deep space, and the universe. Astronomy is one of the oldest sciences, using mathematics, physics, and chemistry to understand everything outside of the Earth's atmosphere.
  • Chemical Physics: The study of physics in chemical systems. Chemical physics focuses on using physics to understand complex phenomena at a variety of scales from the molecule to a biological system. Topics include the study of nano-structures or chemical reaction dynamics.
  • Computational Physics: The application of numerical methods to solve physical problems for which a quantitative theory already exists.
  • Electromagnetism: The study of electrical and magnetic fields, which are two aspects of the same phenomenon.
  • Electronics: The study of the flow of electrons, generally in a circuit.
  • Fluid Dynamics / Fluid Mechanics: The study of the physical properties of "fluids," specifically defined in this case to be liquids and gases.
  • Geophysics: The study of the physical properties of the Earth.
  • Mathematical Physics: Applying mathematically rigorous methods to solving problems within physics.
  • Mechanics: The study of the motion of bodies in a frame of reference.
  • Meteorology / Weather Physics: The physics of the weather.
  • Optics / Light Physics: The study of the physical properties of light.
  • Statistical Mechanics: The study of large systems by statistically expanding the knowledge of smaller systems.
  • Thermodynamics: The physics of heat.

Modern Physics

Modern physics embraces the atom and its component parts, relativity and the interaction of high speeds, cosmology and space exploration, and mesoscopic physics, those pieces of the universe that fall in size between nanometers and micrometers. Some of the fields in modern physics are:

  • Astrophysics: The study of the physical properties of objects in space. Today, astrophysics is often used interchangeably with astronomy and many astronomers have physics degrees.
  • Atomic Physics: The study of atoms, specifically the electron properties of the atom, as distinct from nuclear physics which considers the nucleus alone. In practice, research groups usually study atomic, molecular, and optical physics.
  • Biophysics: The study of physics in living systems at all levels, from individual cells and microbes to animals, plants, and entire ecosystems. Biophysics overlaps with biochemistry, nanotechnology, and bio-engineering, such as the derivation of the structure of DNA from X-ray crystallography. Topics can include bio-electronics, nano-medicine, quantum biology, structural biology, enzyme kinetics, electrical conduction in neurons, radiology, and microscopy.
  • Chaos: The study of systems with a strong sensitivity to initial conditions, so a slight change at the beginning quickly become major changes in the system. Chaos theory is an element of quantum physics and useful in celestial mechanics.
  • Cosmology: The study of the universe as a whole, including its origins and evolution, including the Big Bang and how the universe will continue to change.
  • Cryophysics / Cryogenics /Low-Temperature Physics: The study of physical properties in low-temperature situations, far below the freezing point of water.
  • Crystallography: The study of crystals and crystalline structures.
  • High Energy Physics: The study of physics in extremely high energy systems, generally within particle physics.
  • High-Pressure Physics: The study of physics in extremely high-pressure systems, generally related to fluid dynamics.
  • Laser Physics: The study of the physical properties of lasers.
  • Molecular Physics: The study of the physical properties of molecules.
  • Nanotechnology: the science of building circuits and machines from single molecules and atoms.
  • Nuclear Physics: The study of the physical properties of the atomic nucleus.
  • Particle Physics: The study of fundamental particles and the forces of their interaction.
  • Plasma Physics: The study of matter in the plasma phase.
  • Quantum Electrodynamics: The study of how electrons and photons interact at the quantum mechanical level.
  • Quantum Mechanics / Quantum Physics: The study of science where the smallest discrete values, or quanta, of matter and energy become relevant.
  • Quantum Optics: The application of quantum physics to light.
  • Quantum Field Theory: The application of quantum physics to fields, including the fundamental forces of the universe.
  • Quantum Gravity: The application of quantum physics to gravity and unification of gravity with the other fundamental particle interactions.
  • Relativity: The study of systems displaying the properties of Einstein's theory of relativity, which generally involves moving at speeds very close to the speed of light.
  • String Theory / Superstring Theory: The study of the theory that all fundamental particles are vibrations of one-dimensional strings of energy, in a higher-dimensional universe.

Sources and Further Reading