There is a famous question by Einstein which was reported by his biographer, the physicist Abraham Pais, and which expresses his concern with quantum physics:
We often discussed his notions on objective reality. I recall that during one walk Einstein suddenly stopped, turned to me and asked whether I really believed that the moon exists only when I look at it.
However, it is interesting that Einstein's intuition is problematic in Special Relativity as well.
When we look at the moon we see it one second into the past, so to speak.
But what do we mean when we ask if the moon exists or assert that it does?
We may mean that it exists as an idea in our minds, or as an object in a so called block universe in which past and future and present all exist in some unintelligible way.
But we naturally and intuitively mean that it exists Now!
But alas, special relativity does away with the concept of absolute simultaneity, and as a result it renders physically meaningless the idea of a metaphysical or "real" Now-somewhere-else.
1) In what sense can we ask if the moon exists, if it is 1 light second away?
2) Is there a notable discussion of this problem in philosophy?
Note 1 - I am aware of the Andromeda paradox and the block universe view, but I believe that they fail to resolve the problem — if past, present, and future, all have the same status of existence, then that kind of existence is doubly unintelligible and cannot correspond to our intuition of existence as in a thing that exists-Now.
Note 2 - this question is a "response" to @ChrisDegnen's take on this problem. I believe he got SR wrong, but nevertheless his take (which I do not subscribe to) seems prima facie valid — that there exists an absolute plane of simultaneity even if this plane has no place in science and physics.