Electromagnetic fields. Be forewarned, this involves science...

It revolves around proving the existence of EMW, and how their presence can be predicted mathematically via some rather complex equations brought to light by "the silver hammer".

It helps to illustrate the effects of EMW on their surroundings. Helps to shed light on why things that measure the same, may not sound the same. Like, cables...

@artemus_5 

Wonder how many movies you have missed out on by abandoning early. From your experience, I gather science only exists in the now, and not in history...

@artemus_5

My apologies. Was out of order.

EMF - electromagnet waves.

Spend too much time texting w 14yr old daughter. Short form is king, and doesn’t always work. 
You can see in the movie how an ac signal generates waves in a predictable pattern along the conductor. With the complex waves being generated by an audio signal going through a wire, those waves are going to, in turn, have an impact on the signal passing through the wire. That “feedback loop”, is going to change the signal. Not measurable I suspect because we are not yet measuring the right parts of the signal.