It is perfectly possible for a Conway's-Life universe to contain a glider without containing anything that can identify a glider, either within it or within its fundamental physics (i.e. source code). Despite this, if the pattern

XX
X X
X

should appear in the grid on one particular generation, if no other live cells intrude, the pattern will appear again one square northwest from before four generations later.

Likewise, a tree falling in the forest with noone around will create acoustic vibrations, even if it creates no auditory experience.