Since Newtonian times, physicists have to talk of mass, a quantity having its origin a deep myth. In Newtonian mechanics, mass is impedes the change of velocity. In relativity, mass (in the conventional sense) is no more than the static energy. In non-relativistic quantum mechanics, mass plays to make the entity more of a particle. In relativistic quantum mechanics, mass is the energy required to generate a pair of electron and positron. In condensed matter physics, mass is the minimum energy to excite a system. Besides, mass also measures some correlation length.
Although we know many things about mass, we don't have a clear clue where mass comes from. In the standard model, all masses are produced by Higss mechanism: every mass-less particle moves in some kind of ether that is the Higgs clouds and acquires mass. Another idea is, mass can be generated by curved space, or more accurately, compactified dimension. Compactifying a dimension yields finite motion, one that is confined. According to quantum mechanics, finite motion implies discrete levels and finite gaps, so comes the mass. Yet, a clear regime is missing.
Graphene provides a playground for studying this regime. These authors roll the graphene and obtain a massive 1D system from a 2D massless Dirac system [http://arxiv.org/ftp/arxiv/papers/1010/1010.3437.pdf]. This is no surprising and actually was known before. But this is an example showing how mass might be generated this way. However, back to elementary particle physics, where is the hidden dimension in addition to the 4D space-time we are all used to ? Another question is, how the as-obtained masses interact in a gravitational way ? Anyway, mass should be gravitationally active !!!!
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