Note that in referring to gravity as a force, I am implicitly adopting
a Newtonian viewpoint. In physics, there are two useful ways of looking
at gravity – the Newtonian, or classical, viewpoint and the Einsteinian, or
general relativistic, viewpoint. In Isaac Newton’s view, as formulated by
his Laws of Motion and Law of Gravity, gravity is a force which causes
massive bodies to be accelerated. By contrast, in Einstein’s view, gravity
is a manifestation of the curvature of space-time. Although Newton’s view
and Einstein’s view are conceptually very different, in most cosmological
contexts they yield the same predictions. The Newtonian predictions differ
significantly from the predictions of general relativity only in the limit of deep
potential minima (to use Newtonian language) or strong spatial curvature (to use general relativistic language). In these limits, general relativity yields the
correct result.