01
Definition and Scope
Physics is the quantitative study of the fundamental behavior of the natural world. It seeks mathematical descriptions that connect measurable quantities through general physical laws.
The subject spans enormous scales: quantum fields and elementary particles, atoms and molecules, condensed matter, biological systems, planets, stars, galaxies, and the large-scale structure of the Universe.
- Classical physics describes many macroscopic systems accurately.
- Quantum physics describes microscopic matter and radiation.
- Relativity describes spacetime, gravity, and high-speed phenomena.
- Statistical physics connects microscopic states to macroscopic thermodynamic behavior.
02
Measurement and Physical Laws
Physics is an empirical science. Models are constrained by observation and experiment, while mathematical theories provide precise predictions that can be tested.
Physical quantities are represented with units and dimensions. Dimensional analysis provides a basic consistency check for equations.
[velocity] = [length]/[time]
03
Symmetry and Conservation
Symmetry is one of the central organizing principles of modern physics. Continuous symmetries are deeply connected to conservation laws through Noether's theorem.
- Time-translation symmetry is associated with energy conservation.
- Spatial translation symmetry is associated with momentum conservation.
- Rotational symmetry is associated with angular-momentum conservation.
04
Scales of Physics
- Classical scale: mechanics, fluids, thermal systems, and electromagnetic devices.
- Atomic scale: electrons, atoms, molecules, and quantum states.
- Nuclear scale: nuclei and nuclear interactions.
- Particle scale: quarks, leptons, gauge bosons, and quantum fields.
- Cosmic scale: stars, galaxies, black holes, cosmology, and large-scale structure.
05
Modern Frontiers
- Quantum information and quantum computing.
- Dark matter and dark energy.
- Neutrino properties.
- Quantum gravity.
- High-energy particle physics.
- Gravitational-wave astronomy.
- Condensed-matter quantum phases.
- Fusion and plasma physics.
- Nonequilibrium and complex systems.