Michael
You do not have to have an opinion about the universe being closed. For us, it must be, because that is a necessary consequence of 'we exist'. Whether there 'is' something else is irrelevant, because we cannot have knowledge of it. We need to examine what it is possible for us to have knowledge of, not what it is possible for us to believe in. I am assuming that 'universe' really means entirety of physical existence as is knowable to us. There is nothing philosophical about my argument, it is based on 'we exist' and hence what physically existent feature enables knowledge, as opposed to belief. Which is the equivalent of only one definitive form of existence being knowable to us (the closed system). And the answer is, detectability. Which can involve validated direct experience, or properly validated indirect experience (aka hypothesis). But not belief.
The point about expansion is that if there is intrinsic evidence for this, then we need to include that, and the implied something else, as part of our knowable physical existence, ie what comprises the closed system is re-defined. But there is always a closed system, the differential being 'can have knowledge of', 'cannot have knowledge of'.
If we cannot measure, or whatever, because it is impossible for us to do so, that does not negate what actually occurs. This is the power of hypothesis, so long as it is properly effected, and does not become belief. If we cannot measure, or whatever, something because it does not physically exist, that is obviously a different circumstance.
As I said in my post above, measurement requiring a reference is not the underlying point of relativity. It is what measurement is, ie comparison against a common dominator to establish difference. But first, what is being measured must be established, and that too involves reference. However, since this is being effected within a closed system, at least that is possible. So we can measure your string by comparison with something else, or by comparison with a measuring device which is calibrated to be a physical representation of a conceptual constant known as length.
I particularly note: "What exists, and what is measured aren't necessarily the same, but it requires the relativity of measurement to resolve this difference, in order to be sure about what is constant in reality, and what just appears to be constant in relative measurement."
This is incorrect. Our inability to measure perfectly is just that, a failure. We cannot invoke some metaphysical conception to overcome this. Just get better rulers.
There is nothing inherently wrong with using light as a measurement tool, or approximating its actual speed to a constant. So long as it is understood what is being done, and it is done correctly. Einstein's logical postulate about the principle of relativity is correct. Indeed it is a statement of the blindingly obvious. His error is in the application of that, because he introduced duration into distance via x=vt and conflated the light representation of reality with reality. There is no observational light in relativity. The light he refers to is in fact time, which is a constant. And of course it is c, because there is only light reality, existent reality (for want of better labels) has been expunged. Look at his attempts with examples to explain it in 1905 & 1916, or indeed, Cox & Foreshaw's attempt, which is standard and readable. [I posted a paper on this on my blog, or send me a link to paulwhatsit@msn.com, if you wish].
Paul
