system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: how did guys like Marconi discover or knew radio waves exists without ever seeing them?
gpt
Electromagnetic induction had been known about since Faraday discovered it and worked out the math in the 1830s. Induction basically allowed magnetic fields to move electrically conductive things and moving magnets to generate electricity so *something* must have been there.

Maxwell then worked out the math that showed that there was an electromagnetic field that permeates space during the 1860s. Maxwell's math also said there were ways for this field to have information pass through it in the form of electromagnetic waves.

Through this, Heinrich Hertz was able to prove the existence of these electromagnetic waves. He was also kind enough to provide a means to both produce them and detect them.

From there, it was basically piecing all of this together into a coherent and practical system. Which is where Marconi and his brethren step in.