However, the individual microstates of the black holes may also be viewed as “elementary particles”, something that can be localized just like the electron. So string theory i.e. quantum gravity tells you that there are many species of elementary particles. The light ones are well-described by the quantum field theories – an approximate, effective description. However, you may continuously try to increase the mass of the particles, look for ever heavier species, and when you get to very high particle species, they may be viewed as higher excited, “large” strings or branes and, when they’re even heavier, as black hole microstates!
Some of the previous steps in the unification – such as S-duality – have found rigorous maps between seemingly elementary objects (such as electrically charged “electrons”) – and the seemingly composite objects (such as “solitons”, e.g. magnetic monopoles). So it’s not quite a new insight that elementary and composite objects can’t be strictly separated – an aesthetically appealing intuition that was promoted by people such as Werner Heisenberg when he was older and the S-matrix school but that didn’t lead to any solid insights prior to the birth of string theory.
— Unification as a source of certainty
— Lubos Motl
2013.04.06 Saturday ACHK