Everything that happens in the universe—from planets orbiting stars to atoms forming molecules—is governed by just four fundamental forces of nature. Understanding these forces helps us explain how matter behaves on every scale, from the smallest particles to the largest galaxies.
Gravity
Gravity is a force that pulls objects together and is the easiest force to notice. Ancient Greek and Indian philosophers have questioned it for a long time, and it was not until recently that a famous scientist, whom you have probably heard about, realized something very important. This scientist is Isaac Newton, who in 1687 published “Philosophiae Naturalis Principia Mathematica”. He realized that every object in the universe attracts every other object in the universe and that the strength of the gravitational force is stronger the more mass an object has. Not only this, but he also discovered how the strength of gravity decreases with the square of the distance between the two objects. This idea now unified both events that occurred on Earth, like an apple falling, and that of the moon orbiting around the Earth. This is known as the Law of Universal Gravitation.
After a while, Albert Einstein came along and, through his General Theory of Relativity, described how gravity can be described as the bending of the fabric of space-time. This bending affects things in the universe, like planets, galaxies, and also light. Everything that has mass creates a dent in space-time, which is what causes objects to be attracted to each other.
Although it might be hard to believe that gravity is the weakest force of the four, just think about how a simple small magnet can completely counteract the force of gravity of the entire planet. Although it is weak, gravity acts across an infinite distance!
Electromagnetism
The Electromagnetic force includes both electricity and magnetism.
Light carries the electromagnetic force
Electromagnetism is responsible for keeping electrons orbiting around the nucleus of an atom, and it makes it possible for chemical compounds to form.
Electromagnetism is similar to gravity in the way that its strength drops with the square of the distance between the two objects, and it also works at infinite distances. A big difference between them is that electromagnetism only affects charged objects, attracting like charges and repelling opposite charges.
Strong Nuclear
The strong nuclear force is the strongest force, as you might expect. It is 100 times stronger than electromagnetism, and 100 trillion trillion trillion times stronger than gravity (yes, that number is right…).
Although it is extremely strong, it only affects distances smaller than an atom. The strong nuclear force holds together the building blocks of atoms and works at two different scales:
At the level of the nucleus, it holds the protons and neutrons together.
At the level smaller than the protons and neutrons, holding quarks that hold the protons and neutrons themselves.
Weak Nuclear
The weak nuclear force is responsible for interactions between subatomic particles, which are the particles that make up matter.
The main function of the weak force is that it allows neutrons to turn into protons and vice versa. If a neutron is changed into a proton in an atom, the electric charge of the atom becomes positive. The fact that the neutron became a proton means that the type of element has been changed because the number of protons in an atom tells us which element it is.
The weak force only works on the smallest of scales, a thousand times smaller than that of the strong force. Although it is a million times weaker than the strong force.
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