Dear Ken,
This is miles better!
First of all, I'm glad that you don't think acceleration resolves the twins paradox. But I do wonder why you would use 'acceleration' rather than saying something like 'the boosted twin', especially since acceleration has been wrongly thought by many to resolve the paradox.
But now to important stuff. I was talking with someone yesterday about my concerns with using verbs to describe space-time points, events, all of space-time, etc. What I learned was that a B-theorist uses the word "exist" non-existentially. Personally, I consider it nonsense to use language that doesn't actually apply to things by redefining words in such a convoluted way. Moreover, I think it leads to a lot of confusion, especially because it's so hard to not fall into the trap of thinking of these non-existential things that 'exist' as *existing*. (As an example, when you read what you wrote, don't you find it hard to not think of a *static* block? I think it's really hard to think of the block as a temporally singular, non-existential thing. I honestly can't make sense of "a thing that doesn't exist." Then I also have a tough time not thinking of existence *and* motion along the block when you write "updating is performed by a 3D agent over time"). And finally, I think if what's being proposed is so nonsensical that it can't even be properly described because the language comes to mean something else entirely, that's a pretty good indicator that it really is just nonsense.
So what's my point: I do understand what you've written here, insofar as every time you say "I'm" you're really speaking non-existentially about what you "are". I'm actually pretty okay with the description until the last paragraph, because I don't think you're being too cavalier with your use of non-existential verbs until that point. But in the last paragraph, I think you're getting a bit carried away when you use three in a row ("updating is performed") in a way that tends to give the impression that you're not only talking of the block as something that 'exists' but doesn't really exist, but also of a sequence of updates that move up the world line.
Alternatively, you could say (with the use of single quotation marks to indicate non-existential use of verbs) "The whole 4D block 'exists'. My world-line 'exists' in it. At each point along my world-line, I 'have' some knowledge of the entire 4D block; i.e., as I may 'know' something about past, present, and future events at each point of my world-line. At 'later' times, my knowledge of the block is more complete than at 'earlier' times." (I know "earlier" and "later" are adjectives, but I think it's good to still use the single quotes there). Maybe you could sum that up by saying, "one's incomplete knowledge of the 4D block 'is' a monotonically increasing function of one's worldline, where at each point along the worldline, that incomplete knowledge 'is' 4D".
I think we're now on the same wavelength about what you want to describe, and I think the description of 'subjective updating', if stated carefully in this way, making sure to note the non-existential meaning of 'exist', etc., is about the best you can do. But then I simply have to wonder why you want it to be that way anyway. One reason, from our discussion above, might be that you don't like quantum non-locality. But I have a tough time seeing how a fear of existence in a world in which magic happens, can lead one to want to 'live' in a world where one doesn't actually *live* at all; where one doesn't actually *exist*. I think it's better to try to sort out our problems than just give in to unrealistic implications--and I honestly think a realistic version of quantum theory, or really quantum gravity, will come about after we've taken the more immediately necessary step of properly interpreting and understanding relativity.
I guess that brings the discussion back to the one we were having above. Would it be at all possible to take that up again now? I think I've shown an ability to really understand this position that I think needs to be rejected, being very open to thoughtful consideration of its meaning and implications. I think you'll find if you do read what I wrote there, that I've given the same thoughtful consideration in coming to my own position on the matter.
One more thing I wanted to say before I quit, in relation to the point you made early on about symmetry, is this: last night at the summer school on physics and philosophy of time that I'm attending, Stephan Hartmann gave a talk about the No-Alternatives Argument, which basically runs as, "Physicists have identified certain constraints, C, and have a set of data, D, that they want to use to construct a quantum gravity. To date, only string theory seems to meet all of C and D. Given the amount of effort that's been put into the construction of an alternative, we can be optimistic to some extent that there reall are no alternatives." The "some extent" is evaluated using Bayesian analysis.
My objection to this entire line of reasoning comes in at the very beginning. It's true that having identified C, the usual goal is to try to construct a theory that adds C explicitly into the framework. But we know of cases in history, where ideas have been rejected for a long time just because they were naively thought to be at-odds with some constraint or other that people thought necessary to hold onto. For instance, given a butterfly's ability to easily flutter about, or even the fact that the Earth retains its atmosphere, people felt quite strongly for a long time that the Earth has to be fixed at the centre of the solar system, and this constraint was violently held onto (e.g., Bruno). But then Galileo showed (with a simple thought experiment that didn't even need to be conducted) that butterflies can flutter around just as well in the cabin of a ship, as they can when it's back at harbour, and it was realised that this constraint wasn't necessary to the realisation of the data, and the Solar System could, for all that constraint had mattered, be heliocentric. In light of what I've written about symmetry above, I would like you to consider that perhaps the standard symmetry constraint of modern physics maybe is being made too explicitly, for all the observed symmetries that must be reconciled.
Cheers,
Daryl