Principle of Maximal Aging
Longevity derives from activity ...
There are infinitely many paths in
between two events. The proper time (aging) shown on a clock carried between events depends on which path is taken. In inertial reference frames the aging between events when the path taken is a straight line is greater than for any nearby alternative path. Straight line paths are those in which the velocity of an object through space remains constant. Nature guides objects along the path of maximal aging unless some outside influence changes the objects velocity. This is the foundation for Newton's first law of motion, an object moves with constant velocity unless a force is applied to it.
In non-inertial reference frames, for instance where spacetime is curved as in the vicinity of masive objects, the path of maximal aging will be a geodesic. A geodesic is the generalization of a straight line in curved spacetime and is the shortest curve connecting two spacetime events. An example of a geodesic that we can visualize is the shortest distance between two points on the surface of Earth. That is the path of a string stretched between those points on a globe. The curve the string forms is a segment of a great circle.
When an object undergoes acceleration its spacetime path departs from the path of maximal aging and it ages more slowly. The universe as a whole, not being subject to acceleration ages faster than anything in it.