Time
When you are a child, one year feels like a lifetime because it is your lifetime. When you are five years old, waiting one year for something means waiting a period of time equal to 20% of your entire life thus far. As we get older, this fraction shrinks. When you're twenty, waiting a year means waiting another 5% of your life so far. When you're forty, waiting another year means waiting another 2.5% of your life so far. Suddenly, the years seem to be whizzing by, and you wonder where all the time went. This simple mathematical thought process provides only a partial explanation for the common feeling among humans that time seems to be speeding up as we grow older. Another factor is memory. Children are constantly learning new things about the world they live in: how to talk, how to make friends, how to play games, how the world works. Our developing brains process all of this information and store it in the form of memories. When we become adults, we start to settle into a ro...