Electromagnetism is electricity and magnetism merged together. This force is stronger than gravity. Electromagnetism is apart of quantum mechanics. The theory was developed by James Clerk Maxwell. The electromagnetic force also holds electrons in their orbit around the nucleus.
Strong nuclear force keeps atoms together like superglue. More specifically, it holds together the subatomic particles of the nucleus It is apart of quantum mechanics. it also has the shortest range, which means that particles have to be super close before its effects are felt.
Weak nuclear force is responsible for radioactivity. It is apart of quantum mechanics. The particles involved are big so their travel is limited only to short distances.
Gravitational force is apart of the theory of general relativity. Newton's law of gravity began to lead to unification. He wrote that the gravity force that acts on the sun and the planets depends on the quantity of matter that they contain.
General Relativity was developed by Albert Einstein. This theory only focuses on gravity for understanding the universe in regions of both large-scale and high-mass. It is smooth and makes sense.
Quantum mechanics deals with the movement of subatomic particles. It focuses on the universe in regions of both small scale and low mass. It is ruled by chance and scientists can only try to predict outcomes. It is crazy, bumpy, and constantly moving. Quantum mechanics involves 3 out of the 4 fundamental forces: weak nuclear, strong nuclear, and electromagnetism.
Unification started with Einstein's theory of general relativity trying to merge with the theory of quantum mechanics. The new particles that were being found was helping unify the forces. String theory was the key to unification.
String theory provides a unified description of the fundamental structure of our universe. It states that all forces are made from vibrating energy like strings. The strings vibrate in different ways for different objects. No experiment can prove this theory wrong. Scientists have used string theory to discover 6 extra dimensions.
To sum up the concept of Modern physics, there are four fundamental forces: strong nuclear, weak nuclear, electromagnetism, and gravitational, and the theories of general relativity and quantum mechanics were unified by string theory.