Time is the indefinite continued progress of existence and events that occur in apparently irreversible succession from the past through the present to the future.

Time is one of the seven fundamental physical quantities International System of Quantities

Time is not helpful without a Date and may be referred to as DateTime

Time is a fact of life that not all events in our universe happen concurrently - instead, there is a certain order. Defining a Time coordinate or defining Time, the way physicists do it, is to define a prescription to associate with each event a number so as to reflect that order - if event B happens after event A, then the number associated with B should be larger than that associated with A.

Proper Time#

Proper Time along a timelike world line is defined as the time as measured by a clock following that line and is thus independent of coordinates, and is a Lorentz scalar.

Proper Time could be described as the time on your wrist watch.

Perhaps of greater interest is the Proper Time Interval which is the interval between any two events.


now (or Simultaneity) is something we rarely think about - we just accept it as a fact of life. However, thinking matters through, it isn't obvious at all how one can determine whether or not two events at two different locations happen simultaneously, or not.

More Information#

There might be more information for this subject on one of the following:
  • [#1] - Time - based on information obtained 2018-04-23-