Fundamental interaction and the strong interaction. Their magnitude and behaviour vary greatly, as described in the table below. Modern physics attempts to explain every observed physical phenomenon by these fundamental interactions. Moreover, reducing the number of different interaction types is seen as desirable. Two cases in point are the unification of: Both magnitude ("relative strength") and "range", as given in the table, are meaningful only within a rather complex theoretical framework. It should also be noted that the table below lists properties of a conceptual scheme that is still the subject of ongoing research. The modern (perturbative) quantum mechanical view of the
Yukawa interaction explained by the fact that the Yukawa particle has spin zero and even spin always results in an attractive potential. The negative sign of the exponential gives the interaction an effectively finite range, so that particles at great distances will hardly interact any longer (interaction forces drop off exponentially with increasing separation). Now suppose that the potential formula_7 has a minimum not at formula_18 but at some non-zero value formula_19. This can happen, for example, with a potential form such as formula_20 with formula_9 set to an imaginary value. In this case, the Lagrangian exhibits spontaneous symmetry breaking. This is