Would relativity explain a lot of it? "Empty" space isn't always empty. You put a camera anywhere in the known universe and almost instantly it will get bombarded by particles.
All those particles in flight, albeit sparse, have mass or in the case of photons can collide turning their energy into mass.
TLDR. What is the mass of all in flight particles?
No, even empty space, where there is not even one particle or even the thought of anything aspiring to be a particle within the defined area, will have a tiny weight.
All those particles in flight, albeit sparse, have mass or in the case of photons can collide turning their energy into mass.
TLDR. What is the mass of all in flight particles?