Time holds a unique place in science and the human consciousness.  However, defining or describing what it is extremely difficult.  Some define it only in the abstract saying that is an invention of the human consciousness that gives us a sense of order, a before and after so to speak.  However many physicists define it in terms of the physical properties of a space-time dimension.

What is time

However, the observable properties of time are something that most of us can agree upon.

One of the most persistent observations regarding time is that it is not directly perceive as matter or space but as an irreversible physical, chemical, and biological change in physical space.

This indicates a unit of time may only be a measurement of the sequential ordering of a physical, chemical, or biological change in space similar how a unit of length is a measure of the ordering of a position of an object in space.  This is because similar to time, length is not directly perceived as matter or space but as measurement of where in space an object is located.

However, as mentioned earlier many physicists view time in terms of the physical properties of a space-time dimension.  For example, a physical curvature in space-time is viewed by many physicists to be the causality of gravity.

This appears to contradict the fact that most of us do not perceived time as having the physical properties of matter or space.

Additionally our perception of irreversibly of time or that it always moves in one direction forward also appears to contradict the concept of time or a space-time dimension has physical properties because it is possible to physically reverse the position of an object in space.  For example, one can move an object to a different position, reverse the process and move it back to its original position.

Therefore, defining it in terms of its physical properties does not appear to be consistent with the observation that time is irreversible.

However, these same observations suggest that time may be only a measure of the sequential ordering of the casualty of events.  This would make it consistent with our perception of the irreversibility of time because one cannot reverse the causality of an event without creating a new event.  Therefore, time could never be reversed or moved back to a previous event because the sequential ordering of the causality of all events in the universe is unique.  This would be true in both the physical and mathematical perceptions of time.

This also provides the reason why events always move forward in time even thought the laws physics indicate that they should be reversible because the act of reversing an event would be the next event in that sequence. 

Therefore, defining time only in terms of a measure of the sequential ordering of the causality of an event would seem to provide an unambiguous definition of time that is more consistent with both physical and mathematical observations than defining it in terms of the physical properties of a dimension.

However, it would also free physicists from the constraints imposed by defining it in terms of its physical properties and allow them to consider the possibility the laws of nature are a result the existence of four *spatial* dimensions instead of four dimensional space-time as we have done in the article "Why four spatial dimensions?"

Later Jeff

The "Shadows" of four spatial dimensions

Copyright 2007 Jeffrey O’Callaghan

(In a PDF format)



1 Comment to “Defining what is time?”


  1. amrit — 06/01/2010 @ 2:25 pm

    Universe is timeless. With clocks we measure numerical order of material change running in space that itself is timeless.
    Cosmic space is 4D.



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