Special relativity is well-known for having the least prerequisites of any modern physics subject. Yes, you can explain it with just calculus and vectors. That'

Special relativity is well-known for having the least prerequisites of any modern physics subject. Yes, you can explain it with just calculus and vectors. That's precisely what we already do in university courses. But the complaint that started this whole thread is "why can't physicists explain why it's hard to add in extra neutrinos to the Standard Model?" Understanding the reason requires 2-3 semesters of relativistic quantum field theory, a subject which in turn requires relativity, quantum mechanics, and classical field theory. Seriously, any resource that legitimately explains all of this, without bad analogies, and assuming no prerequisites, would end up precisely as hard to read (or likely harder) than the ~10,000 pages of textbook people currently study. The textbooks have already been optimized for ease of learning, there is no magic way to make a hard thing easy.