u/Far-Presence-3810

My wife was reading over my shoulder while I was reading a physics post and asked what the Unruh effect was. I often explain to them a rough idea of different science concepts but trying to explain both quantum field theory and special relativity overlapping in a particularly weird way was beyond me.

Just had me wondering what other concepts in physics that people can think of which are just extremely difficult to explain to someone who doesn't already have a background in physics. What do you think would be the hardest concept to explain?