So I just want to preface this by saying that this will be a long post, broken up into multiple parts. But if someone with greater physics understanding than me could explain these questions for me, I'd be grateful.

I am a MD who did a biology undergrad, so obviously most of my formal education has been based around that. However, I’ve always been fascinated by physics, and want to get a more thorough understanding than what typical pop science sources can give me. One of my favorite youtube channels is PBS Spacetime. I’ve watched most of their videos, and like that they go into more depth than most other sources that I can find, other than those aimed at people who are already in the related fields. I’ve taken up to Calc 2, but would be lying if I said I remember much other than the very basics. I took multiple physics classes in college, but they were not the same classes the physics majors took, and thus were mostly not calculus based. My point is that I am looking for sources and explanations that are around the level that Spacetime uses – deeper than the pop sci explanation, but not so deep that it requires having taken dif eq., linear algebra, etc. Although I particularly enjoy when a source goes through the actual equation, but breaks it down into components and kind of explains what each variable does. Anyway, with that background finished, I’ll finally get to my questions now, both of which revolve around the idea of virtual particles.