I could not think of anything more abstract than...
TIME
Click on a photo to enlarge
This is a composite image. I have shot the hourglass myself.

Nikon D3s Nikkor 50mm 1.4G @ f/5.6 1/100 iso 640
This is a composite image. I have shot the hourglass myself.
And added these images to the composition after gray-scale conversion.
Source
You probably will not be able to see the clouds very well :) Source
Source
MonoMad Photographic Contest
https://steemit.com/monomad/@brumest/monomad-photographic-contest-week-4-topic-abstract-please-read-the-rules
Cheers,
David