"Gian Francesco Giudice: The Big Bang understood as the event that created the hot, dense gas of cosmic matter was not an explosion starting from a point in space. If it had been, we could detect traces of that initial point today. Instead, astronomical observations teach us that the primordial matter gas was incredibly uniform and homogeneous. This indicates that the universe in its infancy was like a giant pot of well-mixed soup. The Big Bang is the event in which this soup was created, not at any special point, but homogeneously everywhere in the pot. It is a uniform transition that involved a very large, perhaps even infinite, region of space that was suddenly filled with matter. Understanding the Big Bang means understanding what caused this transition. Journalist: And before the Big Bang, what was there? Gian Francesco Giudice: Today it is thought that before the Big Bang there was only empty space. A very special empty space, however. There was no matter, but the fabric of space was imbued with a form of energy called precisely vacuum energy capable of exerting repulsive gravity. The effect is quite amazing because it is the exact opposite of the force of gravity we are used to, which can only attract material bodies."