I often wonder about how little I understand vacuum, and only recently I've been paying attention to this "vacuum energy" hypothetical. I see it being associated with things as small as spontaneous emissions to things as large as the expansion of the universe. This is a huge range of length scales. I know of no other force (or energy or whatever) with that kind of reach. What could this potentially mean? As far as we can observe, is it reasonable to hypothesize that "vacuum energy" is scale invariant (does it make sense to say that energy or energy potential is scale invariant?), hereby enabling the coupling of physical phenomena from different length scales, and maybe even holding the key to the unification of QFT with GR? Or am I smoking crack? Have to say that it looks like a promising concept, even though I don't really understand what/how it is yet. Hence, I defer the title question to the experts.