I am quite new to this subject. I am just repeating in a few words, what I have learned so far: There are 4 fundamental forces of nature: strong, weak, electromagnetism and gravity. Physicists are trying to re-generate a condition, a very high temperature during the Big Bang, to find out which force actually works during that time. The Weinberg-Glashow and Abdus Salam model unified weak and electromagnetism to electro-weak force. Gravity still lays undefined in the Standard Model. At Planck's scale, physicists observe that the 4 forces of nature unify to one single force. We have not yet been able to define that force as yet but the quest is on.
Now the U(1), SU(2), SU(3)........What are these? Can anyone please help me understand, sequentially how the theories evolved? The Grand Unified theory is one which is SU(5)? Does SU stand for special unitary group?