Atoms consist of smaller subatomic particles called elementary particles. Protons are the most basic unit of an atom, determining element identity. Neutrons are electrically neutral particles about same size as protons. Electrons orbit atomic nuclei, affecting chemical reactions
Physical cosmology has achieved consensus on the Standard Model (SM). Universe evolved from high temperature state through expansion and cooling. SM extends gravity theory to describe universe's overall structure. FLRW models provide simplest solution within decade of Einstein's discovery
Subatomic particles are smaller than atoms and can be composite or elementary. Composite particles contain multiple quarks, while elementary particles are fundamental. Hadrons contain ≤ 5 quarks and are divided into baryons (3 quarks) and mesons (2 quarks)
There are four fundamental forces: gravity, electromagnetism, weak, and strong. These forces are not reducible to more basic interactions. Matter consists of fermions that exchange virtual particles called gauge bosons
Fermions follow Fermi-Dirac statistics with half-odd-integer spin. They obey Pauli exclusion principle and possess conserved quantum numbers. Only one fermion can occupy a quantum state at a time. Fermions differ from bosons, which obey Bose-Einstein statistics
Force is a push or pull that can change an object's velocity unless balanced. Force is a vector quantity with magnitude and direction. SI unit of force is newton (N), represented by symbol F