The Thermodynamics of Relativistic Multi-Fluid Systems

  • Bob Osano University of Cape Town
Keywords: Relativistic, Thermodynamics, Particles, Single-Fluid, Multi-Fluid, Cosmology


This article extends the single-fluid relativistic irreversible thermodynamics theory of Müller, Israel and
Stewart (hereafter the MIS theory) to a multi-fluid system with inherent species interactions. This is illustrated
in a two-fluid toy-model where an effective complex 4-velocity plays the role of a primary dynamical
parameter. We find that an observer who resides in the real-part of this universe will notice that their
knowledge of the universe parametrized using real, rather than imaginary, quantities are insufficient to fully
determine properties such as the total energy density, pressure or entropy, In fact, such an observer will
deduce the existence of some negative energy that affects the expansion of their perceived real universe.