According to loop quantum cosmology, quantum gravity effects resolve the big-bang singularity and replace it with a cosmic bounce. Furthermore, loop quantum cosmology can change the shape of primordial cosmological perturbations, such as reducing power at large scales in inflationary models or suppressing the tensor-to-scalar ratio in the matter bounce scenario; these two effects are potential observational tests for loop quantum cosmology. In this article, I discuss these and other predictions, as well as three open problems in loop quantum cosmology: its relationship to loop quantum gravity, the trans-Planckian problem, and a possible transition from a Lorentzian to a Euclidean space-time around the bounce point.
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