The cumulative part of spacetime is time.
It is the cumulative nature of time [for an macroscopic scale] that makes the time a minus in the spacetime interval formula?
Space cannot be cumulative, for two things at two different places at the same time cannot be labelled as “the same thing”.
— Me@2013-06-12 11:41 am
There is probably no directly relationship between the minus sign and the cumulative nature of time.
Instead, the minus sign is related to fact that the larger the time distance between two events, the causally-closer they are.
— Me@2018-10-13 12:46 am
— Distance and Special Relativity: How far away is tomorrow?
2018.10.13 Saturday (c) All rights reserved by ACHK