Time is important to us. It seems that it always has been and always will be. Even in ancient times we always understood that the arrow of time moved forward. The sun rose and set every day. The phases of the moon guided us through the month. The first calenders were based on the phases of the moon. Thus, the days passed followed by the months and then the years as the daily background of the sun passed through the star constellations. When Newton described the underlying force of gravity and other forces that caused the motions we see in the world were explained by Newton. Time as a concept crystallized at that point as one of the basic physical quantities used to describe the behavior of the universe.
Centuries later Einstein turned things upside down with the concept of space-time. Time was not an absolute, but relative. People traveling at different speeds experience different time separations between different events. Both time and space can be changed (warped) by high speed motion. Two points on the timeline appear simultaneous at the same instant at a midpoint, but even the idea of simultaneity is relative. While it is clear we do not yet understand time, Einstein underlying idea that time was relative and not absolute made it more interesting.
The arrow of time still points away from the Big Bang though speculative physics’ views the universe after the Big Bang may be changing how we view the universe and altering our ideas about time. It is interesting to think about why when the ideas of relativity and quantum physics were merged in an attempt to determine if they would lead to a new and more unified theory of the universe, that time disappeared from the the new equations. One outcome is that events that play out in time are, in fact, illusions initially mapped onto the surface of the initially expanded universe; that all is written or predetermined at the start of the universe. We may perceive it as time, but it is all happening simultaneously.
Nevertheless, we all live in a civilization in which time passes and it is hard, if not impossible to deny the passage of time. This idea that it is an illusion doesn’t clearly settle with us at all. We are born, grow up and die knowing that we have lived and that time has passed from our beginning until our end.