[Causal Networks revisited] - A New Kind of Science: The NKS Forum

A New Kind of Science: The NKS Forum

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Causal Networks revisited
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Posted by: Tony Smith

This time last year I used my summer break to break the back of reading NKS. This year I am hoping to be able to write something useful that draws on the NKS way of thinking. To that end I've been trying to think a bit more about some of the issues.

For some time I've been making some broad generalisations based on a loose concept of "causal networks" synthesised from my (mis)readings of Lee Smolin et al's work on quantum gravity and of NKS as well as my own thoughts on the nothing to something problems than Philip Mintz believes is impossible. So I decided it was time to reread what NKS has to say, for starters pp. 486-496:

At first it may seem bizarre, but one possibility that I believe is ultimately not too far from correct is that the universe might work not like a cellular automaton in which all cells get updated at once, but instead like a mobile automaton or Turing machine, in which just a single cell gets updated at each step. (p.486)

While I can now see and follow the argument that viewed from inside such a universe things might look much as they do in our universe, I'm going to press on a bit further based on what I was already thinking about, although I guess I should try to find a less confusing label. I now see that my own thinking has been more about the kind of systems discussed under "Evolution of Networks" (pp. 508-515), but that is not the point of this ramble.

Basically, I just want to mention why I don't see the "bizarre" possibility quoted above getting us very far in accounting for the universe we find ourselves in.

Our observations make a convincing case for space being active, in the sense that it allows the passage of information, at least in the form of electromagnetic radiation and neutrinos, simultaneously in all directions. Once you think about it a bit, it is not surprising that it might need a Planck scale network (10^-33 cm, 10^-43 sec) to support what we experience at out own scale as slow but persistent and almost ethereal fluctuations on the much more robust dynamic of space itself.

But if the simple mechanism determining the next state of the universe was not running in parallel at every Planck scale vertex (or edge) but was rather a single mobile automaton or Turing machine, it would need to both operate at around 10^220 cycles per second and somehow ensure that it updated all vertices/edges convincingly often.

It should go without saying that the universe has to have a viable history. I suspect the outline of such a history is close to being written for a universal network which updates its vertices/edges in parallel, but have no idea how we might make a start on the serialised version.

This problem is symptomatic of the only deep reservation I have with NKS, the implicit idea that while the mechanisms must be simple the data can be arbitrarily complex. To me the only credible account of the universe will embody both sufficiently simple mechanisms and sufficiently simple data.

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