Planck era | 0 s after Big Bang | The Big Bang era, prior to which Einstein's theory of gravitation breaks down and a quantized theory of gravity is needed. Density was so high that gravitational force acted as strongly as the other fundamental forces on the sub-atomic scale. | Big Bang | hadron era, inflation era | Big Bang era | 10-43 s or the time at which the size of the universe was roughly the Planck length (the time it takes light to travel the Planck length; G h bar / c5)1/2 where G is Newton's constant of gravitation, h bar is Planck's constant, and c is the speed of light |