[qnleigh]

An interesting thing related to these questions in the context of physics: there was an interesting discussion on Scott Aaronson's blog a few years ago about why the universe should be quantum mechanical. One idea that was brought up is quite related to the open questions you name here.

Here's an excerpt from a comment of Daniel Harlow (a prof at MIT):

> In order for us to be having this discussion at all, the laws of physics need to have the ability to generate interesting complex structures in a reasonable amount of time starting from a simple initial state. Now I know that as a computer scientist you are trained to think that is a trivial problem because of Turing completeness, universality, blah blah blah, but really I don’t think it is so simple. Why should the laws of physics allow a Turing machine to be built? And even if a Turing machine is possible, why should one exist? I think the CS intuition that “most things are universal” comes with baked-in assumptions about the stability of matter and the existence of low-entropy objects, and I think it is not so easy to achieve these with arbitrary laws of physics.

Scott replies:

> Multiple people made the case to me that it’s far from obvious how well

(1) stable matter,

(2) complex chemistry,

(3) Lorentzian and other continuous symmetries,

(4) robustness against small perturbations,

(5) complex structures

being not just possible but likely from “generic” initial data,…can actually be achieved in simple Turing-universal classical cellular automaton models.

See comments 225 and 261

https://scottaaronson.blog/?p=6244