It's quite a departure from the original, but you can make absolutely gorgeous images with some simple instructions.
This is the best pattern I've been able to come up with so far:
It makes a cloth/napkin, and then slowly absorbs blood from the four corners.
Chris, if you're out there: Hi!
Here's what I consider his greatest work:
To give you one example: that paper is why I think Titan is the most likely world in the solar system where we might find present-day complex life. (Other than Earth of course.)
Why? There's no liquid water on the surface, and it's too cold!
Answer: phase boundaries everywhere. See Fig. 3 from paper.
Titan has a hydrocarbon-based "water cycle" with solid, liquid, and gas all existing at the same time, along with what appear to be seasons. Universal computation occurs in the vicinity of phase boundaries, so I would not be terribly surprised if we found "cryolife" there. It would be radically different from our own, but not really... I agree with people like Langton that life should be considered primarily an informatics phenomenon rather than a conventional chemical reaction or physical state.
If Titan life were intelligent, they'd regard us as hell-beasts with blood of molten water. :) We could never physically touch, as we would vaporize them and they would freeze us solid.
There's a contemporary scientist named Dr. Christoph Adami at Michigan State's new BEACON center who's probably the closest to following in Langton's footsteps.
Adami expounded upon these ideas by defining life as "a phase of matter in which the dynamics of information processing overcome those of ordinary matter and energy." I am paraphrasing, and possibly butchering it a little... can't find the original quote, but that's the basic idea. Life is a phase of matter -- one whose behavior is dominated by universal Turing-complete computation. You might call living matter "Turium" or something.
The fact that this whole line of reasoning hasn't been taken up more broadly is IMHO some kind of failure of the academic and scientific system.
Edit: adjusting the density of the initial map seems to result in different patterns appearing in the output
EDIT: Also, as the article that you link points out, while all definitions of Turing machines agree on their power as a class, minimality results like this are quite sensitive to the details of the definition. (In particular, the article seems to hedge its bets by saying that that machine may be the smallest universal machine.)
That's mostly just my intuition though; it is very possible that I am wrong.
(There's a textbook example where you can add auxiliary memory to a (1D) Turing machine, called a "multi-tape" Turing machine. And you can reduce that to a single-tape Turing machine, but at the cost of blowing up the number of states in the finite automaton).
If Langton's ant is capable of universal computation, wouldn't non-halting programs be a counterexample to this convergence?
Interestingly, multiple ants don't need conflict resolution, as two ants sharing the same cell will want to leave it at the same state.
(Imagine the ant as a space-ship, and every time it turns, it also changes its pitch/yaw, so the directions are based on its direction of travel.)
Current | Previous | Action
white | white | go starboard
white | black | go port
black | white | go down
black | black | go up