Hugh
thank you for reading and commenting on my essay! I am reading yours and will comment in your blog shortly.
You ask in the context of Wheeler comparing the workings of the universe with a computer (which struck me as limiting and impractical): "But is it possible?"
Short answer: yes, but! Longer answer: I do see the universe as a computer, but I did not like Wheeler's idea of implementation in terms of binary yes-no questions, even though, having read many essays, now I think that perhaps he did not quite mean it that way. In your essay you offer a far more sophisticated version of such implementation. The problem I have with both is that either way implies a pre-existing extensive knowledge about the universe, which you then... well, implement. However, I believe the idea is invaluable in testing out our predictions and probing proposed models.
I rather liked Wheeler's idea, which you quote, that a very simple principle lies at the heart of reality, waiting to be discovered. And so I envision the computer modeling of the universe based on cellular automata- like 'pixels', which, despite their inherent simplicity, can give rise to great complexity. This is the sort of computer I envision for the universe. In this regard, have you read the beautiful essay by Prof. D'Ariano? What is your opinion on it?
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You ask: "These threads of causality (could you call them observers?)"
No, they are not the 'observers' but the chains of events as seen from various 'observers' points of view (here the 'observers' are the later events). Say, *now* you have 2 events/processes about to interact with each other. Each is the output of a set of previous events/processes = a set of preceding events in a particular order. These 2 ordered sets are 'the threads of causality' for each of the 2 events in question.
Now you can do a union of both sets and discover that the 2 processes in question share some of the past events. The 2 subsets that result from the Union operator may be ordered differently in each of the 2 'causality sets'.
In a graphical representation, one can imagine a set of events like beads on a plane. In the above example of only 2 'threads of causality', imagine a wavy thread connecting some of the beads. Now, if the 2 events in question have the same thread of causality, say, red and green, then the two threads simply follow the same beads. But, if they differ, the 2 threads interweave in some localities -- it happens where the order is different. If you imagine lots of such threads of causality connecting beads/events, you get an intricate tapestry. That's a good analogy/graphical representation of spacetime on quantum level. no? :)
I very much liked your essay and even saved a copy on my machine. The breaths of your knowledge in this area is astounding. Definitely, yours is a very interesting, stimulating and deserving a high rank essay.
Off to your blog,
-Marina