Here, we prove thatarbitrarilyinhomo-geneous and anisotropic cosmologies with “flat” (includingtoroidal) and “open” (including compacthyperbolic) spatial topology that are initially expandingmust continue to expand forever at least insome region at a rate bounded from below by a positive number,despite the presence of arbitrarilylarge density fluctuations and/or the formation of black holes

We describethe minimal modification required for self-acceleration and show that its maximum likelihood yieldsa 2.4σpoorer fit to cosmological observations compared to a cosmological constant, which, althoughmarginally still possible, questions the concept of cosmicacceleration from a genuine scalar-tensormodification of gravity.