How much of the universe would you say is directly observable?
Well, anything more than 13.x billion light years away isn't observable, though it could be if you were that far away. In comparison, the color red isn't 'observable' unless you're the one observing it. Can you refine the question?
I was trying to understand people's stance on realism vis-a-vis anti-realism. If we can sense something with unaided perception (or not without), might that delineate what is empirically real?
Is observability a property of all physical entities and phenomena?
Hard to know exactly what you mean.. The visible spectrum of the electromagnetic radiation is usually what guides what we can see.
But observing need not be limited to vision, it can also be other senses.
So I guess the answer to your question is that the organism doing the observing guides what is observable or not. (Depending on what sensory systems the organism has - which does not need to be only the ones we find on earth..)
Physically speaking, some things are directly observable (EM phenomena), some gravitationally inferred (dark matter), some statistical (virtual particles) and some purely theoretical (tachyons).
You mean to ask: how much eludes us despite all our best efforts at detection?
Answer: I don't know. :)
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