Maxwell says that electric and magnetic fields are correlated with each other. Einstein hopes to unite these two together. I see people use special relativity to explain the magnetic field from moving charges.
But how about we assume that there is no electric field only magnetic field in the entire universe? Photons are tiny magnets that have north and south poles absorbing and emitting photons with lower frequencies/energies.
Matters are curled-up photons whose magnetic poles are rotating with each other forming chiral structures and producing chiral radiative vibrational fields that emit all directions. Some structures are positive and others are negative, or neutral if two photons rotate with each other. This can explain the mass and inertia. Moving faster across space at the same time increases the rotational frequency and thus needs energy. Appling energy to matter distributes it in both kinetic and rotational freedom thus it gains mass and inertia. Mass is a consequence of energy conservation and inertia is a consequence of momentum conservation.