How existence itself is possible does not seem explainable. Extremely difficult paradoxes, such as how the universe can expand and be consistent with spacetime curvature of general relativity, has been difficult to explain. Explanation is provided in this book along with explaining the cause of gravity itself. It includes a link connecting general relativity to special relativity and so forth for unification of theory. A historical development of theory is provided in terms of high-school algebra and geometry for easier understanding.