Aristotle (384-322 BC) was one of a few philosophers who introduced the concept of time for the very first time. He defined time as:**“A movement that is referenced with respect to change”**

In actuality, Aristotle entailed that time is infinite and it will never end just like the Universe. But this theory was later questioned by most well-known scientists.

Later on, Sir Isaac Newton and Leibniz wrote their research-based hypothesis.

Newton’s Point of View:

According to Newton’s theory which is** Philosophiæ Naturalis Principia Mathematica**, he clearly described two different types of time that are as follows:

**Absolute Time:**Understandable with the help of mathematical laws but is undetectable perfectly.**Relative Time:**This is considered a change in motion of objects (Sun & Moon) with respect to some duration.

This clear distinction between the two times gave a clear picture of the realistic time concept.

This is why Newton’s theory was named** “Newtonian Time”**

According to Leibniz, time is relational. It means that you can not measure time accurately. He entailed in his theory that time you can only consider time to compare and schedule your daily life events.

Ancient scientist Albert Einstein came up with his own theory of relativity in which he clearly declared the relationship between time and space. Contrary to Newtonian time, Einstein stated that time is different for different people and depends on the speed of their movement.

In his theory, he also mentioned that the speed of light is the same for all. It means if someone travels very fast through space, his motion will be slower through time and vice versa. It is assumed that maybe one day, Einstein’s theory would open all gates towards traveling through time.

The concept of 24 hours in a day was first given by Ancient Egyptians who used sundials to calculate time. Due to their use, Egyptians were successful in dividing the daytime into 12 equal parts. But as the sundials were able to work only in Sunlight, there was a difficulty in dividing the nighttime into equal parts.

For this purpose, Egyptians conducted deep research and unveiled a theory that was enriched with the study of stars. The philosophers examined a thorough scheme of stars and highlighted the 12 most prominent of them. These 12 stars were changing their positions in the sky after equal intervals of time.

And analyzing their respective movements, Babylonians divided the night into 12 equal intervals. And this is the 24-hour/day concept that was introduced in the world for the very first time.

In history, there have been a lot of ways that were used to calculate time. But the following are the most precise considerations in this regard:

The systems for time calculations are based on the sexagesimal system that has a base numeral of 60. Babylonians were the first people who adopt this time calculation system.

This system is preferred because its base has a lot of possible factors. These factors make the calculations of time even more accurate when taken into account.

**For example:**

- Base 60 can be divided into hours and minutes
- 1 hour is equal to exactly 60 minutes
- These 60 minutes can be split into 30, 20, 15, 12, 10, 6, 5, 4, 3, 2, and 1-minute intervals

In System International, this is the most accurate way to calculate time. These clocks use two types of atoms for time calculations that include:

- Cesium
- Strontium

The time depends upon the atomic motions of these two atoms.

In ancient times, people were used to calculating time with the relative motion of the Sun. Solar time is calculated using sundials, where the position of the shadow cast by the Sun on a dial indicates the time.