2.4 Pure Definition
2.4.1 What is Time
Time is a subtle concept. In this section, we get a proper definition of time. We begin with Newton and Leibniz.
As the creators of Calculus, Newton and Leibniz are famous rivals to each other. On the nature of time, they had completely opposite views. For Newton, time (and space) is the stage for events to happen. Time is something real in itself.
For Leibniz, time is not a real substance. Time is just a bookkeeping system to relate different objects and different events. Time is a system of relations.3
For example, consider the statement “the cloud is higher than the ground.” The cloud is an object. The ground is another object. But “higher than” is not an object. Instead, it is a relation between objects.
3 The Elegant Universe Appendix