BlinkerSpawn wrote:Just out of curiosity, what would a two-arm constructor using modern technology look like?
It's not entirely clear yet, but it looks like we'd need two separate streams of single-channel gliders from somewhere. It would be nice to be able to encode them in a single stream, since Snarks can reflect gliders down to 43-tick separation and we're stuck with 90-tick separation for syringes anyway. But that would turn out to be awkward for several reasons, not just the obvious one that we don't have a G-to-2G splitter that works at 43-tick separation.
So -- two streams of gliders going into the constructor, and two streams coming out, with as little signal crossing as possible. Maybe two diamond-shaped loops next to each other, each made with three Snarks and one of Scorbie's G-to-2Gs?
Constructor vs. Self-Constructor
A lot is going to depend on the application. If we're just building something simple, like say a spaceship gun along the lines of the HBK gun for example, then that's all the structure that's needed. For something self-constructing like a quadratic replicator, it seems like a lot of extra circuitry will be needed to synchronize the replication of the two separate loops.
Any extra circuitry tends into eat into the efficiency advantage that two-arm self-constructors have over slow-salvo single channel. It looks like the advantage only adds up to a factor of two or so, in the best case. So it's very tempting to stick with the single-arm designs that we already have some experience with.
A Sneaky Workaround?
If we want to build something that's really difficult with a unidirectional slow salvo and a lot easier with slow pairs, it may now be possible to have the best of both worlds -- a single recipe loop storing slow-pair constructions. It takes a significant investment, though:
1) build a Cordership seed and launch a Cordership;
2) after a long time, use 0-degree gliders to send a signal to stop the Cordership and make a faraway elbow;
3) the Cordership-stopper recipe should also return a glider toward the recipe source;
4) knock out the 0-degree elbow and send a recipe to use the faraway elbow to build a Snark and a new elbow;
5) follow that with a recipe that sends half of a slow-pair recipe back from the faraway elbow;
6) use the return-glider signal from #3 plus a strategic piece of local junk to get a new local elbow;
7) use the local elbow to build a Snark;
send the other half of the glider-pair recipe to meet the first half coming back from far away.
9) construct whatever difficult thing it is that can't be done without slow glider pairs.
10) ... profit?
It almost seems like we might as well develop freeze-dried synchronized salvos instead. With those, we wouldn't be limited to slow pairs.
Given enough room around the construction site, we could directly create any classic synchronized recipe, with gliders and *WSSes coming in from any direction. In some cases it might even be cheaper, all things considered, than all that messing around with Corderships.