The concept of time permeates our lives. We keep track of time throughout our day on our clocks, phones, or other devices. In the Olympic Games, we use time to dictate how long events are held and to measure how fast athletes perform. Time plays such a crucial role that we have developed many sayings involving time, like "time is running out" or it's "crunch time."
But how do you actually define time? Time can be defined as the measurement of repeating patterns. For millennia, the pattern was the rising and setting of the Sun to define the day, and then motion of the Sun across the sky to track a year. Today, we have many mechanical means to generate a repeating pattern from the swinging of a pendulum to the behavior of electrons in so-called atomic clocks.
We need very accurate measurements for the closely contested events in the Olympics, where the difference between gold and silver can be a fraction of a second. However, everyday technologies like GPS require even more precision.
Time and our ability to measure it accurately is also key for many frontiers of science, including astrophysics. The Chandra X-ray Observatory has instruments on board that measure the arrival time of every photon of X-ray light from the objects in space it observes. This timing information can be crucial in learning about cosmic phenomena like how quickly a neutron star spins or how material swirls around a black hole.
Let's look at some examples. Missy Franklin can cross 100 meters of a swimming pool doing the backstroke in less than 60 seconds. Gamma ray bursts that signal the birth of a black hole last about that long. In the race-walk event at the Olympics, the top athletes finish the 50-kilometer course in just over three and a half hours, or nearly 13,000 seconds. This is a little less time than it takes light from the Sun to reach Neptune. Of course, in the Universe, things can last much longer than that. Our Earth was formed about 4.5 billion years ago, while the Universe itself is thought to be a bout 13.8 billion years old. That's a lot of swings of a pendulum to be sure.
