There exist heavier particle species which are relevant for shorter distance scales. Most of the matter around us is composed of electrons, protons, and neutrons, or – using the more elementary description – electrons, up-quarks, and down-quarks (which are attracted by forces mediated by photons and gluons). However, there exist many other particle species similar to electrons – the so-called leptons – and many other quarks. Many of those particles are unstable, and therefore unimportant in the composition of stable materials.

But even if heavier particles are stable, they are less important than the light ones because it is hard to create them and because their potential existence only affects the phenomena at ever shorter distances. Elementary particles heavier than the Planck mass or so – \(10^{-8}\) kilograms or so – also exist and there are many of them. However, they may be interpreted as black hole microstates and their description in terms of Einstein’s general theory of relativity becomes more natural than their description in terms of quantum field theory.

String/M-theory provides us with many detailed interpolations between the regular light particle species and the black holes – e.g. Kaluza-Klein modes i.e. particles moving in extra dimensions; excited string states and branes, and others.

— Ten new things that science has learned about matter

— Lubos Motl

2012.05.09 Tuesday ACHK