Isaac Newton formulated laws of motion and universal gravitation, which describe the motion of objects under the influence of forces. His theory explained many phenomena- orbits of planets, tides, and the motion of projectiles.
James Maxwell combined the theories of electricity and magnetism, which describe how electric charges and currents produce electric and magnetic fields. His theory also predicted the existence of electromagnetic waves such as light, radio, waves and X-rays.
Thermodynamics defines concepts of temperature, entropy and free energy, which are useful for studying the efficiency of engines, the direction of spontaneous processes and the equilibrium state of systems. It was developed by William Thomson, Sadi Carnot, Rudolf Clausius and Ludwig Boltzmann.
Albert Einstein proposed the theory of special relativity, which describes how space and time are relative to the state of motion of an observer. The theory revolutionsed our understanding of space and time, and resolve some paradoxes that arose from Newton's theory to objects moving at very high speeds.
Physicists such as Max Planck, Niels Bohr, Werner Hisenberg and Erwin Schrodinger developed the theory of quantum mechanics. It describes how matter and energy behave at the smallest scales, which explains many phenomena like superconductivity and chemical bonding.
Cosmology is the study of the origin, structure, and evolution of the universe which was deduced by various physicists- Georges Lemaitre, Edwin Hubble, Stephen Hawking, Robert Herman among may others. The theory explain phenomena such as Big Bang, cosmic microwave background, expansion of universe, formation of galaxies, cosmic inflation, and dark matter.