## Nature’s Four Fundamental Forces

After having read The Grand Design, written by renowned physicist Stephen Hawking, I am totally amazed that the universe so complex is derived from only four fundamental forces: gravitational, electromagnetic, weak nuclear, and strong nuclear forces.

Each time when humans discovered one such force, history began to change. In fact, history is being transformed radically as people try to harness these forces. Every historian will tell you that during the last 400 years, the world has changed so much more than all the previous years combined. It all began with Isaac Newton’s masterpiece, Principia Mathematica, published in 1687, in which he described the natural gravitational force and the three laws of motion.

Gravitational Force
You will appreciate the strength of this force when something heavy falls onto your head, or when you fall from a height. The fact that you see the sun everyday is due to the gravitational pull between the sun and the earth that prevents the earth from spinning away. High or low tide is another subtle exhibition of the gravitational interactions between the sun, moon, and earth. Gravitation is an attractive force between two objects. The magnitude of the force depends on the masses of the objects and the distance between them.

How important is this force? Well, where would you be if not for the gravitational force? Everything would be floating around aimlessly in space. Most important of all, life could not have developed without gravitation that made the earth an anchor for everything to coalesce so that chemical and other reactions vital to life can take place.

Electromagnetic Force
This force was largely discovered by Michael Faraday (1791-1867), who experimented with magnets and metallic conductors. Unlike gravity, this force can be either attractive or repulsive depending on the charge (positive or negative). Faraday discovered the relationship between magnetism and electricity, thus establishing the basic concept of electromagnetic theory.

A generation later, James Maxwell (1831-1879) further advanced the electromagnetic theory with higher mathematics. The result was Maxwell’s equations demonstrating that magnetism, electricity, and even light, are manifestations of the same phenomenon. Maxwell also demonstrated that electric and magnetic forces travel through space in the form of waves, and at the constant speed of light. This sets the stage for the development of a new theory known as quantum mechanics that explains the third and fourth forces of nature.

How important is this force? Academically, Maxwell’s electromagnetic theory is considered the second “unification” in physics after the first one, Newtonian mechanics, achieved by Isaac Newton. In practice, we can easily see the great impacts of its applications such as: electric motor and generator, light bulb, telephone, television, computer, and so on. Electromagnetic energy is now on its way to substitute oil and coal especially in transportation and energy generation.

Weak and Strong Nuclear Forces
These are the forces that power the sun and all other stars of the universe. To understand these forces, we have to go down to the invisible level of atoms and molecules that are the basic constituents of all matters. How important are these forces? Well, do you think sunlight is important? Sunlight is the ultimate source of energy and life. Do you think nuclear bombs are powerful? Humans are now capable of destroying the earth several times over if all the nuclear bombs in stock are detonated.

The destructive power of the nuclear forces is seen in the explosion of an atomic bomb over Hiroshima in 1945. For peaceful purpose, nuclear applications include: X-ray, MRI, carbon dating, and nuclear reactor for ship propulsion or electricity generation. History will radically change again when nanotechnology, genetics, and fusion energy, all based on nuclear forces, begin to mature and commercialize its products currently under development.

What is the weak nuclear force? This force is responsible for the spontaneous radioactive decay (radioactivity) of certain substances. In addition, this force is able to initiate the process of hydrogen fusion taking place in the sun and other stars.

What is the strong nuclear force? It’s the attractive force that binds protons and neutrons together to form the nucleus of an atom. If this force is broken via fission or fusion, an incredible amount of energy will be released. How much? The well-known Einstein’s equation gives you some idea: Energy equals mass times the square of the velocity of light. The extreme velocity of light is the factor that produces the incredible amount of energy.

Although it sounds like fiction, Einstein’s elegant equation accurately depicts the simple relationship of nature where matter, energy and light are interchangeable. They are the same thing but exist in different forms only. Does that mean everything has the same origin and is derived from nature’s four fundamental forces? It sounds simple but perhaps true as scientific discovery is pointing toward that direction. After all, we know that everything is made up of atoms and molecules with different arrangements, each of which gives a special property, texture, weight, look, smell, and taste.

What is nuclear fission? Fission is a reaction where the nucleus of an atom splits into lighter nuclei, releasing a tremendous amount of heat, and also free neutrons and photons in the form of gamma rays. In the case of uranium-235, nuclear fission is induced by bombardment with a neutron. The nucleus first absorbs the neutron to form uranium-236. Then it breaks down into two lighter elements, Krypton-92 and Barium-141, and releases 3 free neutrons. These neutrons will hit other uranium nuclei, thus causing a chain reaction. The fission process can be controlled to proceed slowly in a nuclear reactor. In an atomic bomb, the process is uncontrolled fission.

What is nuclear fusion? Fusion is a reaction where two or more nuclei fuse together to form a heavier nucleus, releasing a proton (or neutron) and tremendous heat. For nuclei heavier than the iron nucleus, heat will be absorbed rather than released. Fusion must occur in an environment of very high temperature and pressure to overcome the repulsive force of the positively charged protons present in the reacting nuclei. The sun and all other stars are vivid examples of nuclear fusion producing extreme heat and light. Uncontrolled fusion has been achieved in the early 1950s with the explosion of the hydrogen bomb. Controlled fusion to harness its energy for peaceful purpose is being developed in the laboratory for decades. The result is not yet complete despite some progress made.

In the simplest case of nuclear fusion, two isotopes of hydrogen, H-2 (deuterium) and H-3 (tritium), fuse together to form H-4 (helium) with the release of a neutron and tremendous heat. This is largely the nuclear fusion occurring at the sun for billions of years. Have you wondered how can this go on for so long? First, the sun is a very big star with plenty of hydrogen to burn. Second, its size produces great gravitational pull toward the center, hence an extreme pressure environment for nuclear fusion to take place. Third, the sun also has an extremely hot environment due to nuclear fusion, which in turn sustains continuous fusion into the future. When will the sun burn out? Someday, billions of years later according to the scientists, something we don’t have to worry about.

(June 2011)