Full Idea
It is the existence of past objects that explains why the past is fixed, and why there are truths about the past, and it is the non-existence of future objects that explains why the future is malleable.
Gist of Idea
The past (unlike the future) is fixed, along with truths about it, by the existence of past objects
Source
Baron,S/Miller,K (Intro to the Philosophy of Time [2019], 1.3)
Book Reference
Baron,S/Miller,K: 'Introduction to the Philosophy of Time' [Polity 2019], p.15
A Reaction
The authors label this view 'EntityNowandThenism', and it comes in a section on the 'Temporal Ontology'.