Physics: What is the past? Why does the past exist?

Answer 1

The past is all events in your past light cone. There is no universal past. Every observer has a different set of events in his past light cone. 

Answer 2

The past is stuff you can remember. If you couldn't remember anything you would not survive to ask that question.

Answer 3

Before you read this - that was the past. Read it again - that was the past. Once more - that was the past.

Answer 4

past is when a person or object in motion surpasses the coordinate location of another person, place, or object. it exists in a transitory capacity to denote that an event of motion has occurred