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The big bang is often presented as the beginning not just of matter but also of space and time, a statement based on general relativity. The theory does not allow us to extrapolate to times before the big bang because it implies that the density and temperature of matter become infinite. Infinities, however, present a limitation to the equations and the theory used, not necessarily to the actual physical system (the universe). Modern attempts to amend the theory by quantum effects have led to alternative scenarios with the universe bouncing back after a phase of collapse before the big bang. The physics involved, combining ultra-high density with abstract space-time properties, remains poorly understood, and the story of misinterpretations of universe models has continued. Nevertheless, we are getting closer to a reliable picture of the beginning (or the end) of time.