In short what I like to say is that the Big Bang says nothing about what banged, why it banged, or what happened before it banged. It really has no b… - Alan Guth

The Big Bang theory says nothing about what banged, why it banged, or what happened before it banged.

What it takes to produce a gravitational repulsion is a negative pressure. According to general relativity, it turns out... both pressures and energy densities can produce gravitational fields, unlike Newtonian physics, where it's only mass densities that produce gravitational fields.

It becomes very tempting to ask whether, in principle, it's possible to create a universe in the laboratory—or a universe in your backyard—by man-made processes.

Inflation is a prequel to the conventional Big Bang theory. ...It does provide a theory of the propulsion that drove the universe into this humungous episode of expansion which we call the Big Bang.