The original ekpyrotic models relied on string theory, branes and extra dimensions, but most contemporary ekpyrotic and cyclic models use the same physical ingredients as inflationary models (quantum fields evolving in ordinary space-time). Like Big Bang cosmology, the ekpyrotic theory has accurately described essential features of our universe. It predicts a uniform, flat universe with patterns of hot spots and cold spots, in agreement with observations of the cosmic microwave background (CMB), observations confirmed to higher precision by the WMAP and Planck satellite experiments. Observation of a CMB has long been considered evidence of the Big Bang, but proponents of the ekpyrotic and cyclic theories contend that the CMB is also consistent with a Big Bounce as posited in those models. Other researchers argue that data from the Planck observations of the CMB "significantly limit the viable parameter space of the ekpyrotic/cyclic scenarios." Primordial gravitational waves, if ever observed, may help scientists distinguish between various theories about the origin of the universe.