Paul responds above to Jochen:
"The real question at present is whether Planck is concerned with (for want of better phrases) the reality as occurred, or the reality as represented by light."
This question appears to be related to one of the basic issues of my essay on the collapse of causal theory in the philosophy of science, namely that believers in Biblical worldview which first inspired the development of the empirical sciences in the late middle ages became incapable of (or unwilling to) defend their own worldview based on the existence of God as the ultimate cause of the cosmos.
Western science was built, necessarily I think, on such a worldview with an Intelligent Designer. Not a popular idea today, but making a comeback (no, I am not a "young earther"). As the first scientists said, "We are thinking God's thoughts after Him." The secular view prevailed, but then the collapse of God as the causal explanation left us with no substantial explanation at all. We have been inventing substitutes ever since, but seem to have run out. That has led to the current essay question: "Its from Bits, or Bits from Its" Which causes which? My response to the title question is neither can cause either. Neither information nor things are adequate causal concepts.
All that seems to me relevant to the question of ultimate cause because boundary concepts, such as the speed of light, are favorite places to look for such a substitute.
"Reality as represented by light" is a phenomenal perception of reality. But that means that, as George Berkeley noted of Newtons' world of massey atoms, there is no possibility of observing those atoms other than via the sensory world. We never see the "actual" world of Newtons atoms any more than we actually see the "light" behind our visual perceptions. So there is no way to check whether our perceptions are accurate, or even whether those atoms (or light) actually exist to cause our perceptions. The "as it occurred" aspect of Paul's quote thus becomes metaphysically opaque.
Paul replies to Helmut...:
"c is not the speed of light, as in what is utilised in observation, when deployed by Einstein. It is just a constant, ie the theoretical speed of light in vacuo, used to calibrate distance and duration, nobody sees with it."
Is there an unseen thing called "light" by which we see? That has been the common sense assumption. Paul's reply to Helmut seems to support the notion that the speed of light is a boundary concept which helps define the nature of visually perceived reality. But I think that does not help solve the need for a causal concept by which to understand the existence of (or our perception of) a world which is contingent (not logically necessary), and thus in need of an explanation for its existence. At best, it only shifts the burden back to atoms or light or whatever.
I would be interested in whether anyone thinks my 9-page case on these issues (backed up by doctoral degree) has substance.