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Fundamental Forces of Nature

By Staff Writer

There are four fundamental forces in nature, Gravitational, Electromangtic, Weak and Strong, that are responsible for all the interaction between matter in the Universe.

Natural phenomena such as thunder, lightening, the twinkling of stars, falling objects and the spectacular aurorae, a few to mention, puzzled human beings from time immemorial. Attempts to explain the reason for these and many other phenomena led to the formulation of Electromagnetism and Gravity as fundamental forces of nature. However, many phenomena in the microworld, the realm of subatomic particles, such as radio active decay could not be explained using electromagnetic force or gravity. Further exploration and experiments with particle accelerators helped formulate two other forces acting in this realm, the Weak and the Strong forces. These four forces are the fundamental forces of nature. That is, these four forces come into play when matter interacts with other objects or particles. In the macroscopic level or in the visible world, gravity and electromagnetism dominates while in the microscopic or subatomic world the weak and the strong forces are the dominating ones with electromagnetism playing its own role in particle interactions.

Every object in the universe exerts a force on everything else, attracting them. This is the gravitational force that keeps human beings on Earth and planets around the Sun. There is a famous anecdot about an apple falling on to Newton’s head, that made him think about gravity and formulate the laws of gravitation. Galileo’s experiments in the 17th century to prove that gravity accelerates all objects equally without regard of its mass, paved the foundation for Newton’s theories of universal gravitation and the laws of planetary motion. Gravity depends on the masses of the objects and falls off inversely with the square of the distance between them. Gravitational force is an attractive force. This concept, gravity as a force, was replaced by spacetime curvature described by Albert Einstein 1917 in his general theory of relativity. According to this, gravity is the natural consequence of the presence of matter in spacetime. That is, gravity is the curvature of spacetime due to the presence of matter. Gravity has the longest range among the four fundamental forces, infinite, and is the weakest of all forces. Let us take the strength as 1 for a comparison with other forces discussed in the following paragraphs. A hypothetical particle graviton has been postulated to be mediating the gravitational interaction between objects but it is yet to be discovered.

Electromagnetism is the force acting between all electrically charged particles in the physical world as well as in the micro- world. It combined the electric and the magnetic forces that were considered distinct forces until the marvellous works of James Clerk Maxwell, William Gilbert, Michael Farady, Benjamin Franklin and others in the 16th and 17th centuries. The electromagnetic force, similar to gravity, depends on the charges on the two bodies and varies as the inverse sqare of the distance between them. The electromagnetic force is both attractive and repulsive, as in the cases of charges of like polarities and opposite polarities, respectively. Also, like and unlike charges, under favorable circumstances, get annihilated. The electromagnetic force is mediated by the exchange of photons, the constituents of light. They are massless particles that travel at the speed of light. It is 1036 times stronger than gravity. Electromagnetism also has infinite range.

The weak force was introduced to explain &beta decay. During this process a neutron is converted into a proton with the emission of an electron and an electron antineutrino. Going further down into the subatomic level, a neutrino is made up of two quarks of the type down and one up. During &beta decay one down quark gets converted into an up quark with emission of a virtual W boson which immediately undergoes decay producing an electron and an electron antineutrino. The weak force is also responsible for initiation of nuclear fusion in stellar interiors and the decay of unstable subatomic particles. The exchange particles in the weak interaction, the W-, W+ and Z bosons, are very massive, around 80 GeV and were discovered in particle accelerators in 1983. The weak force has very short range, 10-18 meters. This is about 0.1% of the size of a proton. The weak force has a strength of 1025 compared to gravity.

Strong force, also known as the nuclear force, is responsible for binding the protons and nutrons together in a nucleus, despite the electromagnetic repulsion between the protons. It is experienced only by quarks, leptons do not. The strong force is very short ranged, 10-15 meters, about the size of typical diameter of medium sized nuclei. It is the strongest force and is 1039 times stronger than gravity, 1011 times stronger than the weak force and is about 100 times stronger than the electromagnetic force. The strong force manifests through the exchange of gluons and holds quarks together, the constituents of nutrons and protons.

Ranges and Relative Strengths of Fundamental Forces

Force Relative strength Range (m) Exchange particle
Gravity 1 Infinite graviton
Week 1025 10-18 W, Z bosons
Electromagnetism 1036 Infinite photon
Strong 1038 10-15 gluon