It took me a while to find out the description of this proof of space-time (and check whether it's satire or not), so to save you time here's the gist of it:

From the whitepaper:

Loosely speaking, the PoST consists of two phases: an initialization phase (executed once), in which miners “commit” to the data that fills the space S , and an execution phase (executed repeatedly), in which miners prove that they are still storing the data. The time component of the spacetime resource is the elapsed time between successive proofs—if the interval between initialization (or the previous execution phase) and the latest execution phase is T, this proves the miner expended S · T spacetime.

https://drive.google.com/file/d/18I9GPebWqgpvusI1kMnAB9nayBb...