My question is more specific about time. Say what is time -time is a measure of changed(rate of change) but how do you measure time - by measuring something which is changing (movement of clocks or movement of celestial bodies). Do you find any loop in definition?

  • 1
    Decades ago I thought my Optics professor was a math and physics genius. Over coffee, in the basement cafeteria of the engineering (studies) building, he told me that God is the Universe. This is because God is timeless. Time is the comparison of one open system (the clock) to another open system where energy arrives at the observer from both open systems. This type of logic means God and/or Reality are timeless. The loop which generates human experience of time is human memory capacity. We imagine the past, present, and future states of clocks or other quantities map to imaginary timeline. Oct 14, 2023 at 19:44
  • There is no loop in the definition because this is not the definition. Time is not a rate of change, nor even a measure of change. It is measured by regular kinds of change, as in clocks, but that is not its definition either. Like so many other things we directly experience, it neither has nor needs a definition.
    – Conifold
    Oct 15, 2023 at 8:10
  • "What then is time? If no one asks me, I know what it is. If I wish to explain it to him who asks, I do not know." - Saint Augustine
    – CriglCragl
    Oct 15, 2023 at 8:34
  • @Conifold so without properly defining something how are we using it in maths and sciences
    – quanity
    Oct 15, 2023 at 19:57
  • By surmising their properties and relations to each other. To reason about things in math or to predict them in science, we do not need to know what they "are" or how they are "defined", we only need need to know what inferences can be drawn about them. We observe those that are consistently valid and surmise them as laws or axioms. Since one always defines something in terms of something else, defining ultimately fails anyway. Fundamental concepts are never really defined, only labeled, interrelated and logically manipulated.
    – Conifold
    Oct 15, 2023 at 20:07

3 Answers 3


There are many fundamental ideas that cannot be expressed without some degree of circularity. Take length, for example. If you try to explain what length is, you will find that it is impossible without referring to other words that implicitly or explicitly mean length.

The point is that complicated ideas can be explained in terms of simpler ones, but ultimately you reach a point at which a basic idea cannot be explained in simpler terms.


It takes time for a change to occur. Change can not happen at infinite speed. Had it been so ,no time would have been required for a change to occur. Where there is a sense of time , there is a change. Where there is a change , there is a sense of time.

Periodic or cyclic motion has been found ,and is required ,to express the notion of time. Had it been not so , we would have had no measure of time because a constant sense of change is required to measure time. On the other hand space has no such requirement.

  • "Where there is a change , there is a sense of time". Which came first ?
    – quanity
    Oct 14, 2023 at 13:14
  • @quanity sense of time and change are synonymous and understood simultaneously because speed of change can not be infinite. Change plus act of observation takes time. Oct 14, 2023 at 13:19

time is a measure of change but how do you measure time - by measuring something which is changing (movement of clocks or movement of celestial bodies). Do you find any loop in definition?

If this is the definition of time, then (1) five minutes, (2) 24 hours and five minutes, and (3) 2000 years and five minutes, all refer to the same time.

Surely not.

We use the change in clocks to measure the change in other things, just like we use a length of some material to measure the lengths of other things. Time and space are irrelevant in this process.

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .