An alpha particle is a sub-microscopic, positively charged particle of matter. According to Thomson's model, if an alpha particle were to collide with an atom, it would just fly straight through, its path being deflected by at most a fraction of a degree. At the atomic scale, the concept of "solid matter" is meaningless. The Thomson atom is a sphere of positive electrical charge, anchored in place by its mass. Thus the alpha particle would not bounce off the atom like a ball, but might pass right through if the atom's electric fields are weak enough to permit it. Thomson's model predicted that the electric fields in an atom are too weak to affect a passing alpha particle much (alpha particles tend to move very fast). Both the negative and positive charges within the Thomson atom are spread out over the atom's entire volume. According to Coulomb's Law, the less concentrated a sphere of electric charge is, the weaker its electric field at its surface will be.