How is it that subatomic particles which continually pop in and out of existence don't end up blocking photons that journey millions of light years through space?

 

Photons also have to contend with space dust, plasma and whatnot, for that matter.*

 

*pun

They do.

 

When we measure intensity of stars we take the dust and stuff into account (it's called guessing... ok so it's a bit more complicated than that but...)

 

IIRC the vacuum fluctuations do impede photons, but what normally happens is a pair creation and annihilation resulting in a photon in the same direction at the same wavelength (no energy loss) I seem to recall that someone measured this with a small energy change in the virtual photon in some atoms... but I can't remember much more than that right now... sleep is probably a good plan!