Anisotropy of the Cosmic Background Radiation implies the Violation of the Strong Energy Condition in Bianchi type I Universe

We consider the horizon problem in a homogeneous but anisotropic universe (Bianchi type I). We show that the problem cannot be solved if (1) the matter obeys the strong energy condition with the positive energy density and (2) the Einstein equations hold. The strong energy condition is violated during cosmological inflation.