Fundamental Interactions of Nature (English):

Since the beginning of mankind, humans always want to know about themselves or nature. Humans always want to know how all the universe, living, and nonliving things came into existence. To get answers to these questions, humans always keen to develop their brainpower. Due to this curiosity, today we have much-advanced science and technology. And we are doing many advanced experiments to know about ourselves, how our universe works?

In the last 200 years, Science has developed so much that, in the 18th-19th century we knew that we all are made up of matter. But due to the advancement of science, we came to know that matter has also its substructure i.e. matter is also made up of atoms and atoms has also its substructure which is consists of a nucleus and electron. In Physics we want to know what are the basic building blocks of life and our universe.

Elementary particles are those which have no substructure, as per our present studies we have 61 elementary particles which are basic building blocks of the universe. To understand the behavior of our universe we need to understand the behavior of elementary particles. To understand this behavior we have to understand the fundamental interactions which occur between matter and energy from subnuclear to cosmological level. We have the four fundamental interactions in nature which govern the whole of the universe. These four fundamental interactions are gravitational interaction, electromagnetic interaction, weak interaction, and strong interaction.

Gravitational Interaction: It was the first interaction known to humans. It was first discovered by Sir Isaac Newton in the year 1666. This gravitational interaction is responsible to keep macroscopic bodies like planets, galaxies in their definite motion. This interaction is universal in nature whether for massive objects or subatomic particles. This interaction is directly proportional to the product of masses of two objects in interaction or inversely proportional to the square of the distance between these two bodies. Graviton is a particle that is responsible for this interaction between two bodies. Graviton has not discovered experimentally till now. Gravitational interaction is the weakest force of nature. If we talk about effective earth’s gravity then its range is 3200km. Gravitational interactions are always attractive in nature, independent of medium, velocity, and orientation. On a microscopic level, the gravitational interaction between small masses is very much insignificant, so, on microscopic physics, we usually let gravitational interaction as negligible. After the development of Einstein’s general theory of relativity and quantum field theory, many attempts are going on to couple this gravitational interaction with the other three interaction forces.

Electromagnetic Interaction: It was first formulated on the basis of great empirical work. Its foundation stone laid by Coulomb and later on Faraday and Maxwell did great theoretical and experimental work on these interactions. These interactions happen between two charged particles. This interaction is directly proportional to the product of both charges and inversely proportional to the square of the distance between these two charges. This interaction is attractive as well as repulsive, dependent on medium or velocity, and independent of orientation. Photon is a carrier particle of this interaction between two bodies.

Weak Interaction: Weak interaction is unique from other interactions because it does not form any bound system of particles. It only comes into the picture when particle decay happens. It is also responsible for radioactive decay life beta-decay. It is a very short-range force of range about 10-18 m. In 1934, Fermi gave the first theory of weak interaction known as Fermi’s theory of beta decay. In the 1970s Abdus Salam gave a theory about weak interaction which told us about W+, W-, and Z0 which are carrier particles of this interaction.

Strong Interaction: This is the interaction that is responsible for the boundedness of the nucleus. The exact nature of this force is not known till now but many properties have been observed from the experiments. This force is dependent on the spin, orientation, and velocity of particles. This interaction is an exchange type of force. This force is charge-independent in nature. The range of this force is only about a dimension of the nucleus i.e. 10-15 m. Gluons are the carrier particles of this interaction. This is the strongest interaction of nature. To study this interaction we have a separate area of field theory known as quantum chromodynamics.

Till now we have a theory to define the unification of electromagnetic and weak interaction which is known as electroweak interaction. The theory which has discussed electromagnetic, weak, and strong interaction is known as the Grand unified theory. And many attempts are made by brilliant brains to unify gravitational interaction with the other three interactions and quantum gravity model, loop quantum gravity are some theories which are trying to do this.

With time our understanding of the universe is increasing and we should optimistically work on this problem of unification. And one day our hard work will give us positive returns. This is one of the areas in physics where young aspiring physicists can put their energy and skill and they will get a reward from this.