Editing Vacuum (section)

=== Gravity ===
{{more citations needed|subsection|date=April 2014}}
In [[general relativity]], a vanishing stress–energy tensor implies, through [[Einstein field equations]], the vanishing of all the components of the [[Ricci tensor]]. Vacuum does not mean that the curvature of [[space-time]] is necessarily flat: the gravitational field can still produce curvature in a vacuum in the form of tidal forces and [[gravitational wave]]s (technically, these phenomena are the components of the [[Weyl tensor]]). The [[black hole]] (with zero electric charge) is an elegant example of a region completely "filled" with vacuum, but still showing a strong curvature.