  Schwarzschild's 'interior solution' is a space-time metric that satisfies
Einstein's gravitational field equations with a source term that Einstein
created on the basis of an unjustified identification of the conceptually
distinct notions of the passive gravitational mass of matter and the active
gravitational mass of matter. Giving up that assumption allows deriving from a
variational principle new and better (because logically obtained) field
equations that more faithfully extend the Poisson equation for Newton's gravity
than do Einstein's, with an active gravitational mass density providing the
source term. Solving these equations for a nonrotating spherical ball of matter
with uniform mass density produces a new, improved interior metric matched at
the surface of the ball to Schwarzschild's 'exterior' solution metric. This new
metric can then be used to address questions about the flight times of photons
and neutrinos through such a ball of matter.
