How does the existence of life relate to scale in the physical world?

Life happens as a result of certain complex formants. Certain quanta, although necessary for life, cannot by themselves be “alive”. I would say that life cannot exist at the sub-atomic level. At the quantum level, the rules that govern the macro universe in which life occurs are different. Those constructs within which life works up here, are not available down there, so to speak.

You can’t prove a negative, but it seems very unlikely to me. Still, with quantum uncertainty, it seems to me that there is room for self-organizing activity—i.e., organizations that are not totally determined by initial states. Where there is uncertainty, it seems to me there is the possibility of choice, and where there is choice, then it seems to me there is a possibility of self-directed organism.

But that’s just me. Hard scientists don’t seem to believe that probabilities play a significant role in the world.

Hard scientists understand probablilty very well. The problems arise when quantum scientists begin saying things like, “It’s not there until you look at it.”

Well, this might not be an answer you’re looking for, but:
There are theories of life and existence, without listing them out properly, I think it would be hard to answer this:

Scientific Realism

Scientific theories offer accurate reference to or portrayal of independent reality.
Matter is still believed to exist. Physical matter is seen on an Atomic level.

Phenomenalism

The view that no physical objects exist, but only the senses we receive exist.
Sense bundles in a void.

Common-sense realism

An individual’s common sense offers an accurate portrayal of independent reality.
What we see, is what it is, is physically there. (contradictions: moon – flat disc)

I think if reality was truly in the scientific model, our lives would be pretty… insignificant.
I personally like to think that Phenomenalism is true? It seems to place our feelings and existence in a higher value than the scientific view.

Sorry if this isn’t a very good answer :(

I have heard that, in terms of orders of magnitude, humans and most other multicellular life exists right in the middle, between galaxy clusters and quanta. I think we are the perfect size for what we are.

Life as we know it cannot exist at subatomic level. As basis of all known life is DNA and RNA, as you said, molecular scale is the smallest where you can find life. That said, existence of that life depends on chemical interactions that are quantum in nature and proceed at atomic/subatomic scale.