Terminology for space and time, part 1

There are several senses of the words space and time that need to be carefully distinguished in order to avoid confusion. Let’s start with natural philosophy in the tradition of Aristotle:

Space is “the feature of physical being according to which each such being can be identified as occupying a place — and, as such, can be located and measured in relation to other such beings.” (John W. Carlson, Words of Wisdom: A Philosophical Dictionary for the Perennial Tradition)

The author notes that this conception of space is different from the idealized expanse of early modern science. It is a more relational conception of space, which fits better with the relativisitic manifolds of late modern physics.

The same author defines time this way: “a measure of the physically changing as such, numbered as to before and after.” This would be called a “B-series” in the philosopher John McTaggart’s terminology: a static, tenseless series of events in before-after relationship. An “A-series” is a time series from past events to what’s happening now, on to future events. This is a dynamic, tensed conception of time.

Either way, time is considered a series or a location in a series (as in a point in time), whereas space is considered a place or a locus of places (as in the definition of a circle as the locus of points equidistant from a point). However, this obscures how a route through space is a series of points that have a before and after, similar to time. It also obscures how places in time can be in different directions from one another.

To keep all this straight, I suggest speaking of a time series for a serial conception of time (whether A or B series). The corresponding term for space would be a place series, which is similar to a world line in spacetime. A locus of points in time, not necessarily in a single series, could be called a chronus of points in time. The corresponding term for spacetime is a manifold.

We think of physical objects as having spatial properties but they also have temporal properties — e.g., they are constructed, used, wear out, fall apart. So the word object should not be considered merely something with spatial extent. The length of an object in space corresponds to the length of time of an event (or the length of an event in time), and the distance between objects in space corresponds to the duration between events in time or between the beginning and ending of one or more events.

In a time series one may speak of going forward or back in time but this should not be considered as reversing the chain of causality. It is either considering a time series in the opposite direction (i.e., a change of perspective) or taking a return trip along the same route. The term “time travel” should be avoided.