5. What is time?
Although the concept of time is one of the easiest things to learn that almost everybody understands, no one knows exactly why it exists and where it came from. Physicists define time as the progression of events. It only moves in one direction. It is possible to move forward in time, but never backward.
Time is something that we cannot touch, see, taste, but we can measure its passage and we can feel it. We can’t know if time will ever end, because if the Universe continues to expand, time will continue, but if a new Big Bang occurs, our time line would end and a new one would start over.