A negative spaceship (or agar crawler, or bubble) is a finite signal pattern traveling ("crawling") through a periodic agar such as zebra stripes, and thus comparable to a spaceship. The leading edge of the signal removes the agar, and the trailing edge rebuilds the agar some time later. The distance between the two edges is sometimes adjustable, as shown in a lightspeed bubble. The central part of the "spaceship" may consist of dying sparks or even simple empty space.
All agar crawlers currently known are faster than c/2, so it is not currently possible to put one in a greyship without it eventually crashing into the front.
x = 180, y = 60, rule = B3/S23:T100,58
$180o2$180o2$180o2$180o2$180o2$180o2$74o2b3o2b3o2b94o$75b2o3b2o3b2o8b
o$74o3b2o3b2o3bob2obo4b83o$89b2o5bo$74o17b89o$92bo$74o19b87o$93bo4bo$
74o19b2o4b81o$93bo5bo4bo$74o19b2o4b2o4b75o$93bo5bo5bo4bo$74o19b2o4b2o
4b2o4b69o$93bo5bo5bo5bo4bo$74o19b2o4b2o4b2o4b2o4b63o$93bo5bo5bo5bo5bo
$74o19b2o4b2o4b2o4b2o4b63o$93bo5bo5bo5bo4bo$74o19b2o4b2o4b2o4b69o$93b
o5bo5bo4bo$74o19b2o4b2o4b75o$93bo5bo4bo$74o19b2o4b81o$93bo4bo$74o19b87o
$92bo$74o17b89o$89b2o5bo$74o3b2o3b2o3bob2obo4b83o$75b2o3b2o3b2o8bo$74o
2b3o2b3o2b94o2$180o2$180o2$180o2$180o2$180o2$180o2$180o!
#C [[ THUMBSIZE 2 THEME 6 GRID GRIDMAJOR 0 SUPPRESS THUMBLAUNCH ]]
#C [[ THUMBSIZE 2 ZOOM 9.2
HEIGHT 500 GPS 15 ]]
#C Will it be better if people can see the sides of the torus?