It’s a crystal…
Like sugar, or salt, or Copper Sulphate: playing its own shape through space.
Except it’s a crystal with a difference.
It repeats through the fourth dimension.
It plays on a never-ending loop, through time; over and over.
Once set up it could, in theory, outlive me, you, civilization; the world, the sun… and pulsate on, for ever, into empty space.
And yes, someone – two of them in fact – has built one.