From a scientific point of view, there is no conclusive definition of the idea of time. However, everything that happens can be placed within a time dimension. In an everyday sense, the idea of time refers to the duration of something (the life of a person or the measurement of any event with a beginning and an end).
The human being has the need to measure time in some kind of magnitude, since he observes that everything that surrounds him is subject to change. Thus, the intuitive idea of time refers to the succession of events from the past, through the present and towards the future.
Measuring time in the past
In ancient civilizations, sand, water and fire were used as indicators of the passage of time, but these elements functioned as chronometers and not as clocks. In this sense, the hourglasses invented by the ancient Egyptians were containers filled with water with different time scales marked inside and when the water level dropped, the exact elapsed time was known.
It was the ancient Romans who popularized sundials
One thousand years before Christ, the Chinese invented the water clock (a giant wheel moved by water indicated the passage of time every 15 minutes).
The first mechanical clocks began to be built in England in the 13th century and in the Renaissance Galileo discovered the isochrony of the pendulum, an aspect that made possible an advance in the understanding of time and in the manufacture of clocks.
Different ways of understanding the same idea
For Newton the idea of time is homogeneous, absolute and eternal. Thus, everything that happens happens in a uniform way. This conception is known as absolute time. For Newton, time and space are independent, since events happen and things move without any relationship.
For Einstein, the magnitude of time and the magnitude of space are closely related. According to the theory of relativity, the measurement of time depends on what conditions an observer has. This conception is explained in the theory of relativity.
The ancient Greek philosophers realized its paradoxical dimension. In fact, Aristotle claimed that time is an era that is no longer. On the other hand, they observed that time is not something external to us but is perceived internally, since it is undeniable that the memory of what has happened remains in our spirit. In this sense, the ancients differentiated between cosmic time and lived time.
For Kant, the idea of time is what allows us to order perceptions and experiences. Thanks to the idea of time we are able to structure everything that surrounds us. According to Kantian terminology, space and time are a priori forms of sensibility.
At present it is known that all living beings have biological clocks that allow them to regulate their vital functions and this discipline is known as chronobiology.
In the world of fiction and theoretical physics, the possibility of time travel has been contemplated, a circumstance that would imply all kinds of paradoxes (for example, if a person could go into the past, there would be the possibility of avoiding their own birth).