The beginning of time as we understand it is closely associated with the concept of the Big Bang theory, which is the leading scientific theory about the initiation and evolution of the cosmos. According to the Big Bang theory, the universe originated from an extremely hot and dense state approximately 13.8 billion years ago.

At this point, known as the Planck epoch, time, space, and matter all came into existence. This singular moment marked the beginning of the expansion of the universe, during which time and space stretched and matter formed into the galaxies and structures we observe today.

It's important to note that the notion of time as a beginning has philosophical implications and is still a topic of ongoing scientific research and discussion. Some theories suggest the possibility of multiple universes or a cyclic universe where time has no definite beginning or end.