What is time?

Actually there are two theories related to born of the universe. First is well known big bang which tells that universe was a sphere at start and after big bang it started expanding and will keep expanding till its end. And another is Bounce back theory, according to which there are such infinite big bangs till now. At starting of big bang it starts expanding, and at a certain point it starts contracting again. And again it converts in a small sphere. And this cycle keeps on going. If first theory is correct than mine definition is correct and if second theory is correct then your definition is correct.

We state that Big-bang occurred during so n so years ago. Millions and trillion years ago may be then we are actually pointing out to time then how come time evolved with big bang?

We measure time through earth’s rotation but if we imagine ourselves floating above the Milky Way . Can we measure time or space? We still can’t figure out. What actually is time and space? It requires deep analysis and thinking.

Time is not absolute. It’s relative. it cannot be measured, it can only be compared. we compare our clocks to rightly running clock. That is compared to clock of station or some authentic clock. Finally, we all compare our clocks with the position of sun. That is we are comparing with sun's motion. Years are compared to revolutionary motion of sun.

Newton's 1 hr is same throughout the day, months and years. But Einstein’s hour keeps on changing. Similarly for scale/distance/space. According to biology, time is a brain's idea. it has no real meaning. It is difference between 2 events perceived to occur one after the other, the perceived distance being felt as time. it has link with memories. If you sleep, and don't watch any dreams, there are no memories stored in your brain during that interval. So if you wake up even after 6 hrs, you feel you had just gone to sleep. Time perceived is zero. But when you do some work, let’s say cooking, you remember cleaning objects, collecting things, washing, cutting, cooking, serving, etc. these memories make you perceive your time. The memories of events occurring in serial order make you feel the length of time taken.

Proof 4 this: you don't remember your childhood's first 3 yrs, so you feel you were born directly at three. Time perceived for those 3 long and tedious years just zero. One more interesting thing? What is the earliest time you remember of your childhood? are you sure that one was earliest. The more you go back to past memories, the more they are randomly arranged. You cannot say from those random bits that which occurred before what, whether A was before B or B before A. you just can say that A and B both happened, which occurred earlier can't say.