Richard, thanks for this.  I think you are being humble when you call it a layperson's understanding.  (Even if you aren't an astronomer or physicist by trade, the explanation is a good one, and very clearly written).

I have to admit, my simple brain is still somewhat confounded by a physical phenomenon that has no size or proportion, yet has mass.  This is not to say I think your explanation is baloney -- I don't -- it's just another example of theoretical physics that presents a conundrum to me.

String theory is another area that I like to (shallowly) dip into, solely as a challenge to my linear brain.