It is a mathematical framework in which it is convenient to describe objects and events. According to general relativity, gravity is not a force, but a property of space itself. It is a curvature in time-space caused by the presence of an object. It is generally regarded as going from simple to complex. Similarly, scientific theories undergo change to accommodate new data as they become available.
Amplification is an increase in magnitude of some detectable phenomenon.
Chemical equilibrium exhibits no change on the macroscopic level. A first class lever in a condition of static equilibrium remains at rest. The sum of all of the moments of the forces acting is zero. A gradient is a description of a pattern or variation. The description includes both the magnitude and the direction of the change.