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?

The environment needs to be Turing-complete.

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.

Cross reference with the 16-bit ALU:

http://news.ycombinator.com/item?id=1782327

http://news.ycombinator.com/item?id=1740482

http://news.ycombinator.com/item?id=1738013

http://news.ycombinator.com/item?id=1736805

http://news.ycombinator.com/item?id=1736694

The guy that made the 16-bit ALU is not the same guy that made this thing. FYI...

No, that's why I didn't call this a duplication. It's more of a "If you like that then you'll like this".

Once its done, someone should start down the path of implementing minecraft on it :)

That would be ultra-meta.

There is something beautiful about that level of meta. I would be impressed if someone built a active matrix display in it.

Like this? http://www.youtube.com/watch?v=jaoSzCfa9OM

a game within a game that's impresive. but going dipper then 2 level is quite impossible!!

Caution curious geeks, don't spend more than 10 minutes near Minecraft if you plan to get any serious work done over the next month ;-) (I hadn't played a game for more than a day or two since GTA4 and after thinking it was stupid at first, MC has sucked me in bad!)

To all those who question,"Why would you build such a thing?"

A. Because we can.

The relevant phrase I give is "ars gratia artis" which MGM's logo of "art of the sake of art"

the CPU seems to be 2.5D - 2D plan with vertical register/etc orientation. 3D anybody? Also, any chance somebody building/exploring non Von Neumann one?

3D wiring in Minecraft is an enormous pain in the ass. In fact, the whole thing is a big PITA. Want me to elaborate?

(I am sometimes working on a Minecraft CPU with a MOVE instruction set.)

I don't craft mines but it looks like the active 'wire' bits are not voxels like most other things in Minecraft, but instead are painted on 2d surfaces yea? Please elaborate!

They are voxels, they just have very specific placement rules. They take up a full block but can't be stacked.

There's also the fact that the wires transmit information only 15 tiles. It's possible to build repeaters though, but those repeaters have some lag and take up space.

The hardest part are the memory cells. A single bit, even in the optimal configuration, takes up 3x3x2 blocks.

Correct. They can only be placed on the top of voxels, but they can propagate forward and up. I.e. you can build "stair wires" but not "column wires".

Next step: build a Von Neumann Universal Constructor!

But can it play Crysis?