In 1970s he postulated that the surface of a black hole can only stay the same or increase, but can never decrease. Later, Hawking has shown that black holes are not completely black - they give off thermal radiation known as Hawking radiation and will eventually explode. In 1981 Stephen Hawking and Jim Hartle proposed the No Boundary Condition -the space and time are finite in extent but are closed up on themselves without boundaries or edges. The quantum theory must be applied during the beginning of the universe in order to find the wave function of the universe. Hawking is using the idea of imaginary time to solve that problem.
Time is divided to two components, imaginary and real.
Imaginary time is continuous but the real time vanishes at singularity and becomes a spatial dimension . Time and space shrink together and become indistinguishable . Thus quantum physics can be applied during the imaginary time at singularity and Laws of physics are not broken. The No Boundary Condition theory predicts density variation in the beginning of the universe due to quantum fluctuations of the vacuum. Thanks to quantum state of the early universe, the positive energy was borrowed from the inflating gravitational field to create matter.