We think the Big Bang was the beginning of time and space itself. But there are problems with this story. The energy of empty space – known as the cosmological constant – poses one major problem. The cosmological constant is 120 orders of magnitude smaller than the standard Big Bang theory suggests it should be, a finding that scientists have called "the largest discrepancy between theory and experiment in all of science”. A solution is found in the idea of the cyclical universe. The cosmological constant has been winding down over a cycle of multiple Big Bangs and Big Crunches.