The atomic bomb was one of the first clues as to what was coming. We could blow up the planet. But atomic energy had other sinister implications. Assaults on boundaries. The easiest one to understand was radioactivity.
Radiation can penetrate objects.
Only the thickest of lead shielding could stop it. Maybe there would be some other form of radiation that not even lead could stop. Although reseach into atomic physics would discover other realities perhaps even more threatening to our boundaries than radiation, for the time being, its contamination was what we could appreciate. Contamination is an assault on purity. Something has come into where it doesn t belong.