This account would be improved with a few dates, even approximate ones (rich?) LOONY PLACE CONTAGION On Mon, Nov 24, 2008 at 6:55 PM, <rwg@sdf.lonestar.org> wrote:
Ed Pegg suggested jotting down some glider gun recollections. I'm a little fuzzy on the chronology of the period 46 guns and p32n and p20n puffers vs Corderman's switch engine and Schick's p12n puffers. Mike B, Mike S, RTW? Someone with a good set of LIFELINEs?
The glider gun shuttle appears during generations 774-791 of the r pentomino. I had glimpsed something suspicious thereabouts, and had made a mental note to investigate, but the software was so primitive that I procrastinated the long(!) search and manual copying.
Before I got around to it, Robert W. April, an analytical chemist friend of Schroeppel's, visited the (MIT) AI Lab, noodled on the teletype, and found that two rows of 15, separated by 1 blank line, promptly produce two shuttles which successfully bounce off each other before choking on their own eggs. I immediately built a (then record) p30 oscillator by arranging four shuttle pairs in a square. At dinner that evening (Joyce Chen's 500 Memorial Drive?), I expressed optimism for an imminent glider gun. (And got some scoffing.) But there were so many x, y, and time offets for both the corner and side collisions that one of them *had* to work. Exactly one did. I expected to make a large square with 8 shuttles, or even more if a glider came the wrong way out of a corner collision. But before the search even began, Richard P. Howell of the RLE PDP-1 project discovered that a block could eat shuttle eggs, reducing the hypothetical gun to two shuttles.
We hastily telegraphed "<28(?) coordinate pairs> is a glider gun" to Martin Gardner c/o Scientific American, fully expecting numerous other discoverers. Western Union (or we) garbled one coordinate, which Martin was able to correct by symmetry. It took a while for the telegram to reach Martin's then-unknown Hastings-on-Hudson address, and we were disappointed that he had not been able to test and confirm it, questioning whether we really understood that a gun must produce infinitely many gliders, not just a large number. (But we were also relieved at his failure to mention other discoverers.) Then out of nowhere we get a really excited congratulatory letter from an unknown guy named Robert T. Wainwright (soon to be editor and publisher of LIFELINE), to whom Martin apparently sent the pattern for confirmation.
Scientific American wrote the $50 check. Conway now claims that he phrased his conjecture in expectation of guns and puffertrains (his names) but I recall the opposite, suspecting him of purposely choosing the less plausible outcome to provoke refutation. --rwg Postlude: Noodling on that same teletype a few months later, Jan Kok, then in high school, found the period 8 galaxy Golly logo, starting with a fylfot of diagonal hooks.
Before "other discoverers" finally got into the act, I found puffers of period 32n and then 20n, and many guns of period 46n and 30n. Charles Corderman then found his switch engine puffers and Paul Schick found his p12n puffers, well before I found the period 900+200n (middleweight) spaceship guns.
Since then, people have built guns of true periods 22, 24, 36, 44, 48, 50, 54, 55, 56, and *all* periods >=60. By clever interlacing, these can produce glider streams of any period >=14, the theoretical density limit.
About two years ago, Nick Gotts found a *quadratically* growing pattern starting with only 26 dots, probably unbeatable.
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