Thus, there is a difference between something of matter and nothing of spacetime, but it is purely geometrical and there is nothing behind the geometry. Matter during this era is often called GUT matter to symbolize its difference from quarks and leptons and its existence under GUT forces. These black holes are not necessarily low mass, for example, it requires 1 billion tons of matter to make a black hole the size of a proton. But their small size means that their behavior is a mix of quantum mechanics rather than relativity. Before black holes were discovered it was know that the collision of two photons can cause pair production .
Pair production is one of the primary methods of forming matter in the early Universe.
In this case, the gravitational energy of the black hole is converted into particles. But, if the pair is produced above the event horizon, it is possible for one member to fall back into the black hole, the other to escape into space. Thus, the black hole can lose mass by a quantum mechanical process of pair production outside of the event horizon. The rate of pair production is stronger when the curvature of spacetime is high. Thus, Hawking was able to show that the mini or primordial black holes expected to form in the early Universe have since disintegrated, resolving the dilemma of where all such mini-black holes are today.