Discussion piece about Lock’s Law:
For a virtual environment to qualify as ‘a sandbox’, your users must be able to create turing machines, out of stuff the found lying around. - Locks Law (which I just made up :).
I wonder if it is possible to mathematically model what characteristics of an environment are relevant to be able to build an effectively Turing-complete mechanism?
All the ones that I’ve seen (minecraft, dwarf fortress, little big planet) are 100% mechanical, so I guess all you need is the ability to move things around, plus some kind of basic physics, so that moving things around can have knock-on effects. Most of the DF ones are fluidic computers (http://en.wikipedia.org/wiki/MONIAC_Computer) and the rest are mostly falling blocks style. Quite Pratchett-esque.
I think Second Life is cheating though, because you can attach scripting code to objects.