Our knowledge of time’s arrow comes from the ordinary run of human affairs. So for EthnoPhysics, the direction of time is derived from the historical record of human events; our collective experience, as recorded in the newspapers. Arbitrary sequences of events can be compared with such mundane proceedings, and a binary description of their relationship made as follows. The historical record is introduced via the reference sensation of touching the Earth. And the very common human experience of keeping in touch with some selection of terrestrial events is assumed to provide an ordered set of sensations that we note by . Consider comparing these terrestrial-events with another chain-of-events associated with particle P, written as
Make the comparison using their temporal orientation, to define as the direction-of-time for P’s events
When P is like the Earth both particles have the same temporal-orientation, so . If this condition obtains, then
and we say that P’s events are in historical order. The historical-order is locked into the numerical-order of event-index using the following nomenclature. Let and be an arbitrary pair of events in . If and , then we call the initial event, and the final event of the pair.
When we call a chain-of-events a history we imply it is historically ordered. The ice cubes in a summer drink melt away. Fires burn-out. People are born, and then they die. These event chains are understood as going forward in history. To label initial and final events consistently within this collective grasp of order, consider using a thermal reference provided by the absorption of a tepid particle. Let so that P has the same temporal orientation as the Earth. Then the temperature , of both P and the Earth are on the same side of tepid. Both are either higher or lower. So they both describe the absorption in the same way; as either a warming process or a cooling process. But not one of each. The terms initial and final can therefore be used uniformly for describing both P and the Earth. This agreement applies to any thermally-similar particle. And the similarity only needs to be a crude, binary distinction. So, the events happening to most particles are automatically described as going forward in history because almost all of our experience happens in Earth-like conditions.
We refer back to later to make a formal definition of time. But next we discuss the prehistorical foundation for all timekeeping, solar clocks.