Einstein - Part II

Mass has an origin?

            That a question makes grammatical sense does not guarantee that it is answerable, or even coherent. The concept of mass is one of the first things we discuss in our freshman mechanics class. i.e., Engineering Mechanics. Classical mechanics, is , literally, unthinkable without it. Newton’s second law of motion says that the acceleration of a body is given by dividing the force acting upon it by its mass. So a body without mass would not know how to move, because you would be dividing by zero. Also, in Newton’s Law of Gravity, the mass of an object governs the strength of the force it exerts. One cannot build up an object that gravitates, out of material that does not , so you cannot get rid of mass without getting rid of gravity.

            Finally, the most basic feature of mass in classical mechanics is that it is conserved. For example, when you bring together two bodies, the total mass is just the sum of the individual masses. This assumption is so deeply ingrained that it was not even explicitly formulated as a law. Altogether, in the Newtonian framework it is difficult to imagine what would constitute an “origin of mass” , or even what this phrase could possibly mean. In that framework mass just is what it is – a primary concept.

            Later developments in Physics make the concept of mass seem less irreducible. Einstein’s famous equation for the inter convertibility of mass and energy, already mentioned was the watershed. In modern particle accelerators, this possibility comes to life. For example, in a large Electron Positron Collider (LEP), at the CERN laboratory near Geneva, beams of electrons and anti electrons (positrons) were accelerated to enormous energies. Powerful, specially designed magnets controlled the paths of the particles, and caused them to circulate in opposite directions around a big storage ring. The path of these beams intersected at a few interaction regions, where collisions could occur. When a collision between a high – energy electron and a high – energy positron occurs, we often observe that many particles emerge from the event. The total mass of these particles can be 1000’s of times the mass of the original electron and positron. Thus mass has been created, physically, from energy.

            Having convinced ourselves that the question of the origin of mass might make sense, let us now come to grips with it, in the concrete form that it takes for ordinary matter. Ordinary matter is made from atoms. The mass of atoms is overwhelmingly concentrated in their nuclei. The surrounding electron are of course crucial for discussing for discussing how atoms interact with each other – and thus for chemistry, biology and electronics. But they provide less than a part in a thousand of the mass! Nuclei, which provide the lion’s share of mass, are made up of protons and neutrons. All these are familiar, well established story dating back to 70 years or more. Newer and perhaps less familiar, but by now no less well- established, is the next step: protons and neutrons are made from quarks and gluons. So most of the mass of matter can be traced , ultimately, back to quarks and gluons.