Scientists from the University of Pennsylvania (USA) have developed a model of the universe before the Big Bang explosion that occurred 13.7 billion years ago, which led to the formation of the current universe. 
According to Einstein’s Theory of Relativity, the Big Bang was the beginning of the current universe, where not only matter but also space and time were born.
However, Einstein was unable to explain what happened before the explosion.
By combining quantum physics and relativity to trace evidence in today’s universe, American scientists discovered that the pre-Big Bang universe was one with physical conditions similar to the current universe but was contracting, reaching a state of super-dense matter that could collapse. This collapse then caused a massive explosion that created the universe we see today.
American scientists believe that in the contracting universe model before the Big Bang, space and time were similar to those in the current universe, but gravity was directed inward, reaching a point where the quantum properties of space and time transformed gravity into a repulsive force instead of the attractive force observed in today’s universe.
It is this repulsive force that triggered the Big Bang, leading to the formation of the current universe and causing it to continue expanding.
