I'm trying my best to learn particle physics and cosmology for the last year or so. One of the concepts I'm trying to understand is how the 95% figure humanino quotes above is arrived at. I've seen this figure (or something close to it) a few times here. I read the paper http://arxiv.org/abs/0906.3599" [Broken], and it indicates that they were able to compute the masses of all hadrons using Lattice QCD. It seems that they (S.Durr et al.) were able to develop a table of mass ratios and then by plugging in one experimental value, they were able to compute the masses for the other particles. This implies that physicists must understand a lot about how the glue mechanism contributes to mass if they can compute mass using QCD theory. Or am I missing something? How do scientists know that 95% of the mass is attributable to glue while 5% is attributable to the Higgs mechanism? What it is about the glue that gives particles mass? I've seen descriptions of how the Higgs field is supposed to do this but I haven't seen a discussion of how the glue does this, at least not in terms I could understand. Does anyone know of an accessible text or article on this? I've also seen some posts from some of the forums better posters (from my personal observation) that say we don't really know what mass is? Is this a widely held opinion? How can we compute it if we don't know what it is?