Beyond the loka there is not nothing. There is space - infinite, empty, and unreachable, because the substance that makes motion possible ends at the line.
Alokākāśa is the part of space that holds none of the other five. No soul, no atom, no medium of motion or rest. Its points are anantānanta, infinitely infinite, against the loka's asaṃkhyāta; the whole occupied universe, fourteen rajju tall, is a finite figure in a field without end.
Nothing crosses into it, and the reason is exact: to move is to move through dharma, and dharma stops at the loka's edge. The freed soul rises to the last point and no further; the fastest atom does the same. The edge the atlas draws round every map is this line, and this chapter is the first place it says what the line is.
The six substances, as the overlap they are - Aloka highlighted