# Fundamental Interactions

There are four kinds of interaction between particles and are responsible for for all processes in the universe from atoms to interaction of the galaxies. The four fundamental interactions found in nature are Strong interaction, electromagnetic interaction, weak interaction and Gravitational interactions. These forces work from smallest scale to the scale of the universe. Strong and weak interaction are dominant on smaller scale and electromagnetic and gravitational are dominant on larger scale. Following table explains their nature in detail

Interaction Particles affected Range Relative strength Particles exchanged
Strong  Hadrons  $\sim 10^{-15}m$  1  Mesons
Electro  Charged particles  $\infty$  $\sim 10^{-2}$  Photons
Weak  Hadrons and leptons  $\sim 10^{-17}m$  $\sim 10^{-13}$  Intermediate bosons
Gravitational All  $\infty$  $\sim 10^{-40}$  Gravitons

1. Strong interaction: Strong interaction is responsible for holding the nucleons together in atomic nucleus and is independent of electric charge. This interaction works within a distance of $\sim 10^{-15}m$ and time for interaction is $\sim 10^{-23}s$

2. Electromagnetic interaction: It works on all charged particles and are charge dependent resulting in attractive as well as repulsive force. Its range is infinite and this interaction happens through photon.

3. Weak interaction: Weak interaction is responsible for decay of strange and non strange particles and for non leptonic decays of strange particles. The weak interaction is responsible for the radioactive decay of subatomic particles, and it plays an essential role in nuclear fission.

4. Gravitational interaction: It is the weakest among the four and has infinite range. This interaction is clearly visible on larger scale but in atomic scale its effect can be easily neglected. This interaction is explained in terms of ‘Gravitons’ with mass zero and travel with the speed of light. Gravitons are yet to be detected in lab.

It should be noted that gravitational force is universal as it effects all known particles.On the contrary, weak force affects all particles except photon. Electromagnetic force happens between charged particles.