Hello friends here I propose another interesting question to think about.

**The principle of equivalence,** which Einstein used to build the Theory of General Relativity, **establishes the equality between gravity and inertia.**

As it is known, **the Gravity field equations are generally covariant,** and therefore invariant under any coordinate transformation. Any attempt to construct a theory of gravitation involving only Lorentz invariance is unfeasible.

Because of the aforementioned equality between gravity and inertia, **it ****seems plausible that the equations of mechanics are also generally covariant.** If this were not so, it could cause inconsistencies, as a theory of gravity only invariant under Lorentz transformations.

**Therefore, to properly study motion**, it is not enough considering special relativity, which is only Lorentz invariant, and **we must resort to general relativity with general covariance as** is done **in the section**** “ ****THE PHYSICS OF TIME TRAVEL****“.**