Relation between binding energy and inertial mass

cosmik debris

Can you explain why the binding energy of a nucleus is negative but positive in a nucleon? What I mean is, the sum of the mass of the components of a nucleus is more than that of a bound nucleus, but the sum of the quark masses is less than that of a bound nucleon. I think that is right. It seems the binding energy is opposite in sign.

Gulli

How about this: the Higgs mechanism gives rest mass to all particles except photons and gluons (that I know of). Particles that don't get rest mass from the Higgs mechanism always travel at the speed of light and don't have conventional inertial mass: they can't be made to move faster or slower, however they can change direction (which is also a form of acceleration), something they will resist as if they had inertial mass. A composite particle is being held together by a cloud of gluons or photons (composed of streams that are exchanged between those elementary particles with a rest mass) with zero net momentum in the rest frame of the composite particle. The composite particle as a whole has more inertial mass than the rest masses of all its elementary particles combined because the gluon or photon cloud has inertial mass because the speed of light is finite and hence gluons or photons that are "underway" between two elementary particles with rest mass, (while those particles with rest mass are being accelerated), will still favor an earlier equilibrium position, pushing the elementary particles with rest mass back a little. I think this is similar to having a closed box with on the inside perfect mirrors bouncing a lot of photons back and forth: moving the box away from you will cost more energy than you would expect based on the rest mass of the box alone, because you'll have more photons bouncing against the side nearest to you and less against the opposite side while the box is accelerating. So a single photon or gluon may not have any conventional inertial mass, but a cloud of photons or gluons does: accelerating the "barycenter" of the cloud requires an amount of energy that scales with the energy content of the cloud.