Space and Time

These notions are both puzzling and very interesting. To begin, let us define space as the ordered totality of concrete extensions and time as the ordered totality of concrete durations. (Space, time, causality and substance are fundamental categories of knowledge. That is why a thing is defined as a substance existing somewhere in space and at a certain point of time having the power to produce changes in other things.)

Space
It is characterised by relations like above, below, inside, outside, near, far, distance, here, there, right, left, in front, behind, etc. Space which is perceived is perceptual space; portions of space are perceived by means of vision, active touch, or movement. For example, our experience of the horizon of the sky as touching the ocean or the sea, or the convergence of a road or a highway are all perceptions of space. From the many perceptual spaces we may gradually frame a concept of space. It is perceived as shape, size, distance, etc. It is the ground of co-existence of things.

Therefore, we can say that the notion of space has the following characteristics:
(1) Space is one: particular spaces are all parts of one space.
(2) It is infinite.
(3) It is infinitely divisible.
(4) It is continuous.
(5) It has three dimensions: length, breadth, and depth or distance.
(6) Things exist in space.

Descartes identifies space with extension. It is not a real substance, but an attribute of matter. According to him, extension is the essence of matter.

Time
Now, let us discuss the notion of time. It is characterised by relations like now, then, soon, recently, long ago, today, after, etc. One can also think of time in connection with such questions as what is the time, what is the date, how soon, how long ago. On that basis one arrives at the Aristotelian definition that time is the number or measure determined by the successive equal stages of a local movement. It is a number when one answers three o'clock or January 26, 1969. It is a measure when one answers three years or 1969 years. One can push this line of thought further by asking whether there is just one time for the universe, or, on the other hand, there are many distinct times as there are distinct local movements. According to Einstein, there are as many standard times as there are inertial reference frames that are in relative motion.

Besides the above, there are other questions concerned with "now." Aristotle asked whether there is a succession of "nows" or just a single "now." It may be described as the meeting point of the immediate past and the immediate future; it emerges from the immediate past and grows/flows into the immediate future. It is not a mathematical instant but a duration filled with an event. There results what is called the psychological present, which is not an instant, a mathematical point, but a time-span, so that our experience of time is sometimes a "leisurely" now and sometimes a rapid succession of overlapping time-spans. The past is known by memory and the future is known by expectation. Only from such a perceptual time can we move to notion of time which is an ordered totality of concrete extensions.

The notion of time thus can be said to have the following characteristics:
(1) Time is one: particular times are all parts of one time.
(2) It is infinite.
(3) Time is also infinitely divisible.
(4) It is continuous.
(5) It has only one dimension. It is irreversible. The flow of time cannot be reversed.
(6) Time is filled with events. We cannot think of time apart from succession of events, outer or inner.

According to Henri Bergson, time is duration, or change, the continuous progress of the past which gnaws into the future. It is the vehicle of perceptual novelty. It is very heart of reality.