  Three very different algorithms have been proposed for solution of the
Rayleigh-Taylor turbulent mixing problem. They are based upon three different
physical principles governing the Euler equations for fluid flow, which serve
to complete these underspecified equations by selection of the physically
relevant solution from among the many otherwise nonunique solutions of these
equations. The disputed physical principle is the admissibility condition which
selects the physically meaningful solution from among the myriad of nonphysical
solutions. The three different algorithms, expressing the three physical
admissibility principles, are formulated alternately in terms of the energy
dissipation rate or the entropy production rate. The three alternatives are
zero, minimal or maximal rates. The solutions are markedly different. We find
strong validation evidence that supports the solution with the maximum rate of
dissipated energy, based on a review of prior results and new results presented
here. Our verification reasoning, consisting of mathematical analysis based on
physics assumptions, also supports the maximum energy dissipation rate and
reasons against the other two. The zero dissipation solution is based on claims
of direct numerical simulation. We dispute these claims and introduce analysis
indicating that such simulations are far from direct numerical simulations.
  Recommendations for the numerical modeling of the deflagration to detonation
transition in type Ia supernova are discussed.
