Time to Learn!

Time seems inconsistent sometimes: one moment it’s flying by and the next moment the world seems to have stopped. That’s why we rely on clocks to keep track of the time. It allows people to schedule countless events and synchronize their lives. Clocks have been around for a long time. Sundials (shown below) are considered the first clocks ever invented. Over 5,000 years, people would observe the Sun’s position by looking at the shadow of an object. However, this method could not be super accurate and didn’t work when the Sun wasn’t visible in the sky (when it was cloudy or during the night). Nowadays, our clocks are super accurate and easy to interpret at any time. So how did we get from sundials to atomic clocks (don’t worry, they aren’t radioactive!)?

Fun Fact: Although they didn’t last too long, some historical clocks didn’t follow the 24-hour system, including a 10-hour clock used during the French revolution and a 6-hour clock used in the 18th century!

People were measuring time way before clocks were invented. Different cultures varied in their methods of keeping track of time. In fact, the calendar we use today (the Gregorian calendar) borrows aspects from the Babylonian, Egyptian, Jewish, and Roman calendars. Eventually, the sundial came along, allowing people to note the time of day. In ancient times, people also utilized simple water clocks to keep track of time, but it wasn't easy to use and could be inconsistent.

The first mechanical clocks emerged in the 1300s. They used the weights and verge escapements to control the increments of time. If you want to learn more about verge escapements, you can watch this video: https://www.youtube.com/watch?v=BoeP0adbDKg (credit to Croix Rousse Watchmaker). Verge escapements were ingenious mechanisms, but they were often inaccurate because it was difficult to regulate the factors that they depended on: the amount of driving force and the amount of friction.

Once they were invented, spring-driven clocks were heavily favored over the weighted mechanical clocks due to its small size and portability. This device involved the uncoiling of a wound spring; its constant unwinding controlled the speed of the hour hands (and later on, minute hands too). Although slightly more accurate than the weighted mechanical clocks, spring-driven clocks were still inaccurate; they also had to be rewound after a certain amount of time.

The first clock that was considered accurate, at least for its time, was the pendulum clock. According to Lexico, a pendulum is “a weight hung from a fixed point so that it can swing freely backward and forward." It was discovered by physicists that regardless of how heavy the weight was or how wide it swung, it would swing for the same amount of time as long as its length remained constant. With the correct length, a pendulum’s period (the time it takes to swing back and forth) could equal a specific amount of time (i.e. 1 second). The period of the pendulum regulates the gears inside the clock, which in turn, control the hands of the clock. Many pendulum clocks still exist today, mainly for stylistic purposes. If you have ever seen a pocket watch (or any watch for that matter), you may be wondering; how does the pendulum fit inside the watch? It doesn’t. Instead of a pendulum, watches contain something called a balance wheel, which has the same functionality as a pendulum.

The main issue with pendulum clocks is that they can differ based on elevation level. Gravity might be considered the same value around the world, but in reality, its value changes depending on how close you are to the center of the Earth. The farther you are from the center of the Earth, the weaker Earth’s force of gravity becomes. Gravity is an important part of the pendulum's period equation. If the gravity changes, the period of the pendulum changes as well, which means that pendulum clocks at different elevations have different periods. In other words, they keep track of time at different rates.

Enter the quartz clock. The structure of the quartz clock allows for smaller-sized clocks and higher accuracy. How does quartz, a common mineral of silicon and oxygen, keep time? Well, quartz is a piezoelectric mineral, which means that it produces an electric voltage when pressure is put on it. Quartz clocks actually use the reverse process: if given an electric voltage, a quartz crystal will vibrate exactly 32,768 times in a second. A quartz clock contains a circuit that counts the number of vibrations and creates its own electric pulse every 32,768 vibrations, which is equivalent to one second. The quartz system can be implemented into the gears of a mechanical clock or used to display time on a digital clock. Despite still being widely used today, quartz clocks can be slightly inaccurate due to temperature and pressure changes.

Fun Fact: Quartz can be found in all colors but blue!

The most accurate type of clock to date is the atomic clock. These clocks are so accurate that they measure time better than Earth’s movement! As mentioned before, it is not radioactive like an atomic bomb. Atomic clocks get their name from how they use atoms to keep track of time. They still have a spring and a vacillating weight, but they use “the natural vibration frequencies of an atomic system,” according to Merriam-Webster. There are a variety of atoms an atomic clock can use to keep time including hydrogen (H) and rubidium (Rb); atomic clocks employ different methods on different atoms. For instance, cesium atomic clocks isolate cesium (Cs) atoms at a certain energy level while rubidium atomic clocks observe the changes in rubidium gas. Cesium atomic clocks are considered the most popular, but in recent years, more accurate atomic clocks have been created using other atoms such as ytterbium (Yb) ions (ions are a charged atom) and aluminum (Al) ions.

Atomic clocks aren’t known for their commercial use, but in reality, many people use them. How? If you own a smartphone or a computer in which you don’t manually input the time, you use an atomic clock. To be more specific, you use the super-precise atomic clocks located elsewhere. If you live in the United States, you most likely use the set of atomic clocks that reside in the United States Naval Observatory. Your phone or computer syncs to that specific set of atomic clocks so that all phones and computers display the same time across the country. Besides providing us information about the position of the planets for space exploration, these clocks enable the use of Global Positioning System (GPS) navigation and Internet synchronization.

Clocks are definitely something we take for granted. Throughout the day, clocks only receive cursory glances from us even though we would be lost without them. Sometimes, it’s good to take a step back and be appreciative of the things we take for granted. I hope you learned something new today! Keep a lookout for the next post!