Gravity and time dilation are related phenomena, but the statement that "gravity is caused by time dilation" is an oversimplification. In reality, gravity is described by Einstein's general theory of relativity, which is a geometric theory of gravity that incorporates both space and time.
According to general relativity, the presence of mass and energy curves the fabric of spacetime, causing objects to move on curved paths. This curvature of spacetime is what we perceive as gravity. Time dilation is a consequence of this curvature, as the presence of a massive object can affect the flow of time in its vicinity.
The need to reconcile gravity with quantum theory arises from the fact that general relativity and quantum theory are two fundamental theories of physics that describe the behavior of the universe at different scales. General relativity successfully explains gravity on large scales, such as the motion of planets, stars, and galaxies. On the other hand, quantum theory describes the behavior of matter and energy on the smallest scales, such as particles and their interactions.
At present, there is no widely accepted theory that fully combines gravity and quantum theory into a single framework, often referred to as a theory of quantum gravity. The challenge arises because the mathematical descriptions and principles of general relativity and quantum theory are fundamentally different and incompatible. Reconciling these theories is an active area of research in theoretical physics.
The reconciliation of gravity with quantum theory is important because it would allow us to understand the behavior of spacetime and gravity at the quantum level, such as the behavior of black holes or the early universe. It would also help resolve conceptual issues related to the nature of singularities and the information paradox associated with black holes.
In summary, while gravity and time dilation are connected, the need to reconcile gravity with quantum theory arises from the desire to understand the fundamental nature of gravity and its behavior at the smallest scales of the universe.