I’ve heard it postulated that parallel universes could potentially interact with our own via gravitational forces only.

It occurred to me however that if they could interact gravitationally, then there is a way they could interact electromagnetically indirectly.

Here is my thought in a nutshell; in universe A, a strong radio source exists.  It causes an oscillation of electrons in a conductor of finite length such that the concentration of electrons in any one part of the conductor varies with time according to the electromagnetic field.

The electrons have mass, therefore their movement sets up a slight gravitational oscillation.

That gravitational oscillation effects matter in universe B, some of which consists of charged particles.  Those oscillating charged particles setup an electromagnetic field in universe B.

The net effect is some portion of an oscillating magnetic field makes it from universe A to B indirectly.  Whether it’s enough to be detectable remains a question.