Einstein's general theory of relativity can appear simple to some individuals due to several reasons:
Elegant and concise formulation: Einstein's general theory of relativity is expressed through a set of equations known as the Einstein field equations. These equations describe the relationship between the curvature of spacetime and the distribution of matter and energy within it. The mathematical form of these equations is elegant and concise, which can give the impression of simplicity to those familiar with advanced mathematical concepts.
Conceptual clarity: The core idea behind general relativity is relatively straightforward to grasp. It states that the presence of mass and energy curves the fabric of spacetime, and this curvature influences the motion of objects within it. The concept of spacetime curvature and its relationship to gravitational forces can be intuitively understood, making the theory seem simple at a conceptual level.
Familiarity with special relativity: General relativity builds upon Einstein's earlier theory of special relativity, which deals with the behavior of objects moving at constant speeds in the absence of gravitational forces. If one is already familiar with special relativity, the transition to general relativity becomes more accessible, as the concepts of spacetime, time dilation, and relativistic effects are already established.
Simplifying assumptions: In many practical applications, simplified versions of the general theory of relativity can be employed. For example, in weak gravitational fields or low velocities, the effects of general relativity are typically small compared to Newtonian gravity. By neglecting these small corrections, one can obtain results similar to those of Newtonian mechanics, making the theory seem less complex in certain contexts.
However, it's important to note that while the core ideas and equations of general relativity can be grasped at a basic level, the full scope and implications of the theory can be highly complex. General relativity involves advanced mathematical concepts, such as tensor calculus and differential geometry, which require in-depth study to fully understand and apply. Furthermore, the theory's implications for phenomena like black holes, gravitational waves, and the expansion of the universe can be highly intricate and challenging to comprehend fully.