The Four Fundamental Forces

Standards Know that there are four fundamental forces in nature: gravitation, electromagnetism, weak nuclear force and strong nuclear force

4 Fundamental Forces There are 4 fundamental forces within all atoms, which dictate interactions between individual particles, and the large-scale behavior of all matter in the universe. They are: Gravitational force Electromagnetic force Strong nuclear force Weak nuclear force

Gravitational Force Force of attraction between each and every particle in the universe. Always attractive: pulls matter together. Weakest of the forces. Very long ranged (furthest reach of all the forces, therefore of great importance in cosmology.

Gravitational Force Even though it’s weak, it always wins over cosmological distances. It is the most important force for understanding the large scale structure and evolution of the Universe.

Electromagnetic Force Determines how electrically charged particles interact with each other and with magnetic fields. Can be attractive or repulsive. Long-ranged, but weaker than the strong force. Holds electrons in their orbital shells around the nucleus of an atom

Weak Nuclear Force a.k.a., weak interaction Very powerful Very short-ranged: acts on scale of atomic nuclei

Weak Nuclear Force Causes radioactive decay in the form of beta decay Beta decay – a neutron spontaneously breaks up into a proton, an electron, and an antineutrino Responsible for synthesizing different chemical elements in stars and in supernova explosions

Strong Nuclear Force a.k.a. strong interaction Strongest of the forces Very short-ranged Is attractive Keeps protons and neutrons bound together in the nuclei of atoms (prevents protons from flying apart because of the repulsion between their like-charges)

Strong Nuclear Force Because it binds nuclear particles so tightly together, huge amounts of energy are released when nuclei are fused together (fusion) or broken apart (fission). It is the underlying source of the vast quantities of energy that are generated by the nuclear reactions that power the stars.

Unification of the Forces At the temperatures and energies in the universe today, the four forces are distinct from each other. Theoretical physicists think this was not always so.

Unification of the Forces In the very early universe, when temperatures were much higher, the weak, electromagnetic and strong forces were unified into a single force. Theories that would unify these 3 forces are called Grand Unified Theories, or GUTs

Unification of the Forces Superunified theories, or the Theory of Everything (TOE) unifies all 4 forces. It is thought that all 4 forces were unified during the first instants of the Big Bang.

Unification of the Forces Combining these forces is one of the biggest problems in physics today. It will take a unified theory to be able to understand what happened at the instant of the Big Bang, and for a fraction of a second after. Unification is also needed to understand what happens in the bottom of black holes, at the singularity.