Image credit (Large Helical Device project in Japan)
The Relative Truth is Objective article is one of my favorites. In that article there is a section subtitled “Why do we use the word relative?” where I use the example of electromagnetism to demonstrate the meaning of ‘relative truth is objective.’
What is the origin of magnetic field? We know that moving charges create a magnetic field. We know that the intrinsic spin of the charged particles create magnetic field too.
Motion – external or intrinsic – is necessary for the appearance of the magnetic field. When there is motion there is relativity. Physicists say that magnetic field is a relativistic effect as if it is completely understood. Magnetic field is more mysterious than people think. We have a beautiful theory of electromagnetism (Maxwell equations, Lorentz force, Theory of Relativity) which is very precise but we still don’t understand what electric charge is and what the origin of magnetic field is.
The article mentioned below (from 2010) shows that physicists are now taking the “origin” problem more seriously.
“magnetic fields are mathematically and physically equivalent to a vorticity, meaning they have a tendency to rotate. This is what makes it difficult to determine the origin of magnetic fields, since it means that magnetic fields have helicity, which is a kind of “topological charge.” However, helicity cannot change under the influence of an ideal force, forbidding the emergence of any vorticity from an initial zero value.”
“To generate magnetic fields (a vorticity) from a state of no magnetic field, we must break the topological invariant,” Mahajan told PhysOrg.com. “For that to happen, the effective force has to be so that it cannot be expressed as a perfect gradient. The baroclinic departure could do it, and special relativity does it (in ideal dynamics) by simply demanding that the equations of motion be Lorentz invariant.”