We are all bound to time and time scale due to which we live in our past, present and future.  Nobody knows the beginning or end of time and its scale.  Questions like beginning of time, end of time, only forward direction movement of time, relative time scale on our planet or on other planets or in our solar system as well as in other solar systems i.e., universe or universes are still beyond the understanding of human. Science is also backing on big bang theory to find the origin of time but still have not reached to time zero.  Time has different meanings or scales on our planet earth also and we synchronize our clocks’ and minds with those variations as we do it with our physical body changes due to passing time period. We know that time is governed on the basis of earth’s rotation about its own axis as well as its revolution about sun. Speed of rotation and revolution of not only earth but of all other planets in our solar system has been experimentally measured, verified and postulated in terms of famous laws known as Kepler’s laws of planetary motion as:

1. The orbit of a planet is an ellipse with the Sun at one of the two foci.
2. A line segment joining a planet and the Sun sweeps out equal areas during equal intervals of time.
3. The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit.

Without going much into the details of astronomy, here point is that we feel concerned about the time scale for which we are on the planet earth even though we cannot stop physical changes taking place in our body with time. We make a comparison of our time scale with that of other planets in our solar system and in others to see that how long life will be possible there. In this context, scientifically we can look for extraterrestrial life span and mythologically we can justify our scriptures time scale which they mention in terms of yugas, maha yugas, kalpas and many more leading towards the infinite time concept. The following table mention about the parameters like mass, radius, density, gravity, temperature, rotation time and revolution time of all nine planets of our solar system.   These parameters are very much related to each other and consequences of planet’s rotation and revolution. From the table it is very clear that Venus is the slowest and Jupiter is the fastest planets of our solar system in terms of time scale compared with earth. One day earth takes to rotate about its axis is equivalent to 247 days of rotation Venus takes about its own axis. That is one day on Venus is equivalent to almost a year on the earth. About hundred years of human life span on planet earth will correspond to only 100 days i.e. ¼ of year on Venus.  Going further, in a time scale of about 100 years on Venus, a life (with 100 years life span) will take roughly four turns of life on earth. This all seems to be scientifically justified.

If there exist any place in the solar system (our or other), moving very slowly as compared to earth then the time scale on that place will totally be different to time scale on planet earth. According to modern science, to mention the current age (and total age) of universe as described by Vedas (sacred books of Hinduism) there are two theories:

• The Steady State theory, which says the universe is never born, never dies, and is always like what it is.
• The Big bang theory, which says the universe and so time, began with a point of energy exploding in a "big-bang".

Since the universe is expanding and evolving, 1st theory is not 100% correct automatically. Big Bang theory says that the current age of universe is 11-20 billion years. But according to new observations, i.e. clusters of galaxies, super-clusters, Great Wall (Tully's complexes), it is quite evident that our universe is much much older than that. Lots of cosmologists believe that big-bang theory is not correct although it is most widely accepted. In short, modern man is not aware of forces and science which are needed to explain the creation of universe as well as to understand the amazing time scales of nature. 

Time scale as per scriptures

Let us see what the vedic science says about the time scale and age of universe:

• Total age of universe is 311.04 trillion years (human years).
• Current age is around 155.521972944 trillion years.

It is calculated as:

There are 4 ages on earth which keeps circulating:

Satya Yuga - 1.728 million years

Treta Yuga - 1.296 million years

Dwapara Yuga - 0.864 million years

Kali Yuga - 0.432 million years

Total: 4.32 million human years.

This yuga cycle is called maha (in english, it means great/big) or divya (divine) yuga. One thousand such cycles forms one day of Brahma (Hindu god who governs the universe). So one day of Brahma is 4.32 million * 1000 = 4.32 billion human years. Each such day of Brahma is called a "kalpa". His night also constitutes 4.32 billion human years. During his day, life exists in universe. In nighttime, no form of life exists. So one complete day and night has 8.64 billion human years. Age of Brahma is 100 years. Each year of Brahma has 360 days and same number of nights. Thus, total age of Brahma is 360 * 100 * 8.64 billion = 311,040 billion human years. i.e. 311.04 trillion years. This period is called "maha kalpa". The life span of the universe is one "maha kalpa". i.e. 311.04 trillion human years. This time span is also the duration of one breath of "Vishnu" (the ultimate god in Hindu religion). When he exhales, thousands of universes emerge and one "Brahma" is born in each universe. When "Vishnu" inhales, all universes get sucked and Brahma dies. This cycle is non-ending and eternal and "Vishnu" is considered eternal in Vedic Science (or religion).

Time scale of universe

Note that the period of Satya Yuga is 0.4x, Treta Yuga is 0.3x, Dwapara Yuga is 0.2x and Kali Yuga is 0.1x where x is the time-span of one maha-yuga cycle. In 1 day of Brahma, there are 14 "manvantara" and Each "manvantara" is divided into 71 "maha-yuga" cycles. So total make 14*71 = 994x (mahayuga cycles).  Remaining cycles (1 day of Brahma contains 1000 maha-yuga cycles) are used to fill gaps between manvantara. Before and after each manvantara (called as "sandhya" and "sandhyamsa" respectively), there is a junction of 1.728 million (age of Satya Yuga, or 0.4x) human years. Total number of junctions are 15 (since there are 14 manvantaras). So total gap period is = 0.4 * 15 = 6x. Hence total makes 1000 maha-yuga cycles or 1 Brahma day.

According to the Vedic texts, current age of Brahma is 50 Brahma years and 1 Brahma day (we are in the 1st day of 2nd half of Brahma)and we are in the seventh "manvantara", in the 28th turnover of its 71 yuga cycles. In this cycle, we are in the start of Kali Yuga. Age of kali yuga is not known perfectly but it is around 5000-10000 years. For calculation, lets assume 8000 human years. So current age of our universe (in terms of maha-yuga cycles) = (50 * 720 * 1000) -- 50 years * (360 days + 360 nights) * total no. of cycles in one day/night + (6 * 71) -- 6 manvantara each of 71 maha-yuga cycle + (7 * 0.4) -- 7 junctions or gaps for 6 manvantara+ (27 * 1) -- we are in 28th cycle of 71+ (0.4+0.3+0.2+0.1) -- In this cycle, we are in Kali Yuga. Satya Yuga, Treat Yuga and Dwapara yuga are 0.4x, 0.3x and 0.2x respectively. + around 8000 human years very small, so ignoring it. Thus total age = (36,000,000 + 456.7)x = 36,000,456.7 * 4.32 million = 155,521,972.944 million years = 155.521972944 trillion human years. Now adding the age of Kaliyuga i.e. around 8000 human years gives the current age of our universe..

Measureless universe

In other solar systems there are tidally locked planets whose day is effectively infinite. It is presumed to be in the order of 10’s of minutes, if it small enough and the slowest could indefinite, eternal day, and night, if it’s tidily locked with it’s host star. It's not at all at calling distance. Even highest planetary system in this material universe i.e Satyaloka is not at calling distance. The Vaikuntha planets begin 26,200,000 yojanas (209,600,000 miles) above Satyaloka (abode of Brahma). Thus the Visnu Purana describes that the covering of the universe is 260,000,000 yojanas (2,080,000,000 miles) away from the sun.