Hello All, I am quiet new to the subject, so if anybody can help me. The four fundamental forces of nature, gravity, strong, weak,electromagnetism. Through weak force, all the electrons, protons and neutrons interact with each other. An attempt was made late in the 20th.century to unify all those 4 forces together. Sheldon, Abdus Salam and Steven Weinberg unified the electromagnetic force and the weak interaction showing them as a single force the electro-weak force. Please correct me if I am wrong with anything. My questions: (a) Has there been any theory to unite electromagnetism with strong force? (b) Is Standard Model developed in an attempt to unify all the forces together? (c) Other than the electro-weak force has there been any other unified theory? (d) Quantum chromodynamics is a field of study of strong force? Is it a part of the standard model?