The arrow of time—the fundamental asymmetry between past and future that makes the universe evolve from lower entropy states toward higher entropy states—appears to require explanation in cosmology, yet Lambda-CDM offers no satisfying physical origin for this asymmetry. The Big Bang singularity itself is time-symmetric under the microscopic laws of physics, so the emergence of a preferred temporal direction from such a state lacks a clear mechanism. The initial conditions of the universe must be assumed to be in a state of extraordinarily low entropy, but Lambda-CDM provides no explanation for why this boundary condition should obtain (Penrose 2010; Carroll & Chen 2004).