The concept of (seemingly) smooth Einsteinian spacetime (three physical dimensions inextricably bound together with time as the fourth) has not yet been unified with the theoretical and observable 'granulality' of quantum physics.
As a means of integrating these two seemingly incompatible paradigms, the idea of Spacetime Atoms (i.e. discrete particles of spacetime) was introduced in the early 2000s.
“We do not have a successful theory of spacetime that coherently incorporates the quantum nature of the physical world, so we do not yet know the nature of the deep structure of spacetime. Some of the observational facts on which the new theory will be built may, therefore, now be only roughly communicable and our sense-experience of the passage of time may be an example of such a fact.
In the last decades, however, progress on one approach to finding a theory of quantum spacetime – or quantum gravity as it is usually called – affords us a forward look at how the passage of time may eventually find a place in science.”
see:'The birth of spacetime atoms as the passage of time' (2014) by professor Fay Dowker, Blackett Laboratory, Imperial College, UK.
Note that the spacetime atom theory, along with causal set theory (see paper above) supports a cosmological effect analogous to so-called dark energy, and also asserts that it had a negative value at the 'beginning' of the universe - thus accounting for the (measured) acceleration of the expansion of the universe.
Further info: A BBC radio (podcast) interview with professor Dowker, 2107.
Also see: Arrow of Time