Time comes in three different aspects, all of which are going to be important to us. 1. Time labels moments in the universe. Time is a coordinate; it helps us locate things. 2. Time measures the duration elapsed between events. Time is what clocks measure. 3. Time is a medium through which we move. Time is the agent of change. We move through it, or—equivalently—time flows past us, from the past, through the present, toward the future.
