What is the main conflict in The Elegant Universe: Superstrings, Hidden Dimensions, and the Quest For' by Brian Greene?

This book is a search for perhaps the oldest question of humanity: Why are we here? In a very literal sense, the book examines the "whys" for the physical properties that surround people in everyday life. These things are mostly taken for granted because they are so commonplace—gravity, for example. Isaac Newton formulated the "how" for gravity, but not the "why," leaving room for Einstein's formulation of special relativity centuries later, and from there the quest for the ultimate theory to explain all: the T.O.E., or "theory of everything." This led physicists to string theory.