Scientists have created a pair of clocks so precise they could keep close-to-perfect time for billions of years.
They are the most sophisticated* clocks ever made and could be used to learn more about space-time*. At the moment, they take up a whole laboratory*, but if they could be made smaller, they could even measure what is happening inside the Earth.
They are a type of clock called an atomic clock made with huge lasers* and an element — which is a pure substance found in nature — called ytterbium.
The scientists published the results of their clock-making experiments in a science journal called Nature last week.
Physicist* William McGrew from the US government research laboratory National Institute of Standards and Technology (NIST) was part of the study.
He explained to online magazine Smithsonian how accurate these clocks are.
“If our two ytterbium clocks had been started at the beginning of the universe, at this point in time they would disagree with each other by less than one second,” said Dr McGrew.
Atomic clocks have been used since the 1960s to measure time.
Until these ytterbium clocks, most atomic clocks were made using another element, called cesium.
Right now, the definition of time — or of one second — is based on what happens in a cesium atomic clock.
There are many atomic clocks in use, including on satellites orbiting Earth. These clocks are what make GPS* navigation apps such as Google Maps work. They can tell us our location or the distance we have to travel accurate to about a centimetre.
Atomic clocks don’t look like a clock as we know them — it’s not like a wristwatch or a clock on the wall with cogs* and dials and hands. They use atoms, which are the smallest piece of all matter, plus lasers. A chair, your body, a tree, the air and planets are all made up of atoms.
Atoms are so tiny we can’t see them without a special type of strong microscope. An atom has a middle part, called a nucleus, and other tiny bits, called electrons, that buzz around the nucleus. The way the electrons buzz around depends on how much energy is in the atom at that time.
An atomic clock is made by adding energy to an atom and measuring what happens.
ATOMIC TIME SCALE
Modern digital clocks are set to the time of the International Atomic Time Scale, which is the combined measurement of more than 400 atomic clocks.
Until the 1960s, before atomic clocks, time was measured by charting the movement of planets, stars, comets and galaxies around the universe, but all these things speed up or slow down over time, so that isn’t a very precise* way to tell the time.
VIDEO: Timelapse of the Milky Way moving across the sky from New Zealand
More than 30,000 years ago, humans measured time (years, months, days) by the moon, the sun and the stars they could see in the sky and the shadows from the sun they could see move across the ground.
People drew charts to show others how the movement of planets and stars related to time. They were a type of calendar. The earliest-known star chart is carved on a mammoth tusk 32,000 years old found in 1979 in a cave in Germany.
The earliest Egyptian star map is 3500 years old. The earliest known Chinese calendar is about 4000 years old, although ancient Chinese records suggest that astronomers* had created a yearly calendar of 366 days by about 3000BC, which is 5000 years ago.
As instruments such as telescopes were invented and became more sophisticated, astronomy charts to help with telling time became more detailed and more accurate.
INVENTIONS FOR SHOWING TIME PASSING
Sundials were a way to measure the movement of the sun across the sky. A sundial can be as simple as a stick stuck upright in the ground and a clock drawn on the ground below the stick, marked with the hours of the day. As the sun moves across the sky, the shadow from the stick moves around the clock, casting a shadow on the hour markings so the reader knows what time it is.
Ancient Egyptian sundials were called merkhets and were very accurate. They used a weight on a string (so the string was perfectly vertical*) instead of a stick stuck in the ground.
Sandglasses measure a set period by the time taken for sand to move from a top container, through a small opening into a bottom container. A sandglass, sometimes called an hourglass, can measure any period of time, depending on how much sand there is and how fast or slow it moves.
Water clocks use the same idea as a sandglass, except water moves from one container to another. Measurements on the container show the reader how much time has passed.
Mechanical clocks replaced water clocks from about the year 1300. By the mid-1300s, many cities around Europe had big mechanical clocks in a tower in their town square.
There is a mechanical clock in Prague, in the Czech Republic, which was made in 1410, though lots of parts of it have been replaced over the centuries.
- sophisticated: very complex
- space-time: a maths model scientists use that use the three dimension of space and the dimension of time to explain what happens in the universe
- laboratory: a place where scientists experiment
- lasers: tool to make a special beam of high-energy light
- physicists: scientists who study matter and energy
- GPS: short for Global Position System
- cogs: mechanical wheels in a machine
- precise: exact
- astronomers: scientists who study the universe and planets, stars, galaxies, comets
- vertical: straight up and down
LISTEN TO THIS STORY
- How many of the new type of clock did they make?
- How big are these clocks at the moment?
- Is your body made up of atoms, the smallest pieces of matter?
- How was time measured before the 1960s?
- What’s another name for a merkhet?
1. Clocks over time
Choose 4 of the different ways to measure time described in this article. Placing them in order from the oldest to the most modern method, write down the name of each one then draw a picture and one sentence summary of that method.
Discuss with a partner why you think it is important for us to have such a precise measure of time. Write down the reasons you think of together.
Time: Allow 30 minutes
Curriculum links: English, Science, History
With a partner see if you can you identify all the doing words/verbs in this text. Highlight them in yellow and then make a list of them all down your page. Now see if you and your partner can come up with a synonym for the chosen verb. Make sure it still makes sense in the context it was taken from.
Try to replace some of the original verbs with your synonyms and discuss if any are better and why.
HAVE YOUR SAY: If you could invent a new, better version of something, what would you want it to be?
No one-word answers. Use full sentences to explain your thinking.