Vedas are the repositories of knowledge. This knowledge was revealed to the Rishis or the ascended masters in their heightened state of self-awareness. Since it was heard from the source it is called Shruti in Sanskrit. (Shruti = heard).
Time destroys everything. Indeed in Sanskrit language, time and death are synonyms. They are both known as Kaal. Various civilizations have tried to leave their mark on the shifting sands of time. Some built huge pyramids, some built gigantic temples in order to leave their knowledge and culture for posterity. Today we see them only as ruins. The civilizations stand vanquished by time. Their message lost in the mists of ages gone by.
The Rishis or ascended masters knew the nature of time and took steps to prevent the knowledge from decaying with passing age. Knowledge has always been graded. All knowledge is not for everyone. In the wrong hands, it can be disastrous for the society. The know-how of making a weapon of mass destruction in the hands of terrorists is not acceptable.
Since time destroys everything, the only way to keep the knowledge intact is to pass it on from generation to generation. This is exactly what they proceeded to do.
Written records can fall into wrong hands so the first step was to pass it on from generation to generation as memorized word. The easiest way to commit something to memory is by developing it into a rhyme or ditty. These rhymes were called Richas and Sutras.
The language and selection of these Richas is such that each one can be correctly interpreted in a number of ways. Generally every important Richa can have as many as six meanings. A person with gross intelligence will get only the literal meaning which is often unimportant. A realized master on the other hand will be able to explain the real, intellectual and spiritual meaning.
This had to be done as some portions of this knowledge were meant for only those who had reached the appropriate state of maturity and enlightenment.
The knowledge was thus handed down from generation to successive generation. People of exceptional mental caliber were chosen to remember Richas and Sutras. In this way, the ascended masters negated the negative impact of time on available knowledge. It is because of this that Indian civilization and Vedic philosophy has emerged unscathed across a gaping chasm of time lasting twenty-four thousand years.
To make the less sensitive information available to masses, Upanishads and Bhashyas (commentary) were written.
For people with still lower mental caliber, the Upanishads were further simplified into Puranas. Two epics Ramayana and Maha Bharata were penned by the Rishis and these condense the wisdom of the Vedas into simple, easy to understand stories and parables.
There are a total of four Vedas and four Up-Vedas. The four Vedas are
Rig Ved, Sam Ved, Yajur Ved, and Atharva Ved.
The four up-Vedas are
Ayurved: The knowledge of physical and mental health.
Gandharvaved: The knowledge of music and fine arts, paintings and sculpture.
Dhanurved: Knowledge pertaining to offensive and defensive missiles and all kinds of warfare including the use of spacecrafts, high energy particle and beam weapons, defensive shields etc.
Sthapatyaved: The science of architecture and its relation to the flow of energies through a building.
In addition, there are six Vedangas (Limbs of Vedas.)
The Vedic view of time
Vedic philosophy construes time as a nonlinear entity. It believes that time is cyclical in nature. What has risen must fall. What is fallen must rise. The validity of this view proven by the history of our planet.
The limited modern view of time believes that time is a straight line and stretches endlessly. In reality, the time has no existence at all and is merely an illusion. It totally depends on the external influences acting upon a given system.
We all know that moons revolve around some of the planets (Earth, Jupiter, and Saturn) and all planets move around the sun. Sun is a dual star and moves around another star. This dual system, in turn, moves in the vastness of space around a fixed point called Vishnu Nabhi or grand center. Vishnu Nabhi is the seat of creative power for the visible universe. Sun takes about twenty-four thousand years to make a complete orbit around this seat of creative power.
The following Shloka from Manu Smriti explains it beautifully
Four thousand years is said to be the duration of the Sat Yuga. Its morning and evening twilight has just as many hundreds. So 400 years of morning twilight and 400 years of evening twilight when added together come to 400+4000+400 or 4800 years of the Sat Yuga. In the other three Yugas too, we get 300+3000+300 or 3600 years, 2400 years and 1200 years respectively. When the sun in its orbit comes closest to the grand center, the mental virtue increase to such an extent that humans can grasp all the subtle principles of creation, its magnetisms, and electricities. When Sun reaches a point farthest from the grand center, the mental virtue declines to such an extent that humans do not understand anything beyond the gross principles of creation.