How does time work?

Home References Science & Astronomy Time is all around us, a constant that keeps the world and universe ticking. (Image credit: Shutterstock) From the beginning of the universe to the present day, time is one of the few things we regard as regular and unchanging. Time works by measuring periods between the past, present and…

an abstract view of a wormhole with a clock overlaid
Time is one day of us, a constant that retains the enviornment and universe ticking. (Image credit: Shutterstock)

From the beginning of the universe to the present day, time is with out doubt one of many few issues we regard to boot-liked and unchanging. Time works by measuring periods between the previous, present and future. 

However that is a straightforward, albeit imprecise resolution to an incredibly complicated topic. 

Time is one day of us and is the premise of how we file lifestyles on Earth. Civilizations upward thrust and tumble, stars are born and extinguished, and our way of tracking how those moments say to the present stays unchanged. However time is not as constant nor as straightforward because it could perchance most likely perhaps perhaps unbiased seem.  

How It Works

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In the 17th century, physicist Isaac Newton saw time as an arrow fired from a bow, touring in a appropriate away, straight line and never deviating from its course. To Newton, one 2nd on Earth modified into the identical measurement of time as that identical 2nd on Mars, Jupiter or in deep arrangement. He believed that absolute motion is potentially not detected, which supposed that nothing within the universe had a constant velocity, even gentle. By applying this theory, he modified into in a position to amass that if the velocity of sunshine could perchance perhaps perhaps fluctuate, then time must be constant. Time must tick from one 2nd to the next, with out a disagreement between the scale of any two seconds. That is something that it be straightforward to advise is correct. Each day has roughly 24 hours; you fabricate not dangle eventually with 26 and one with 23. 

On the different hand, in 1905, Albert Einstein asserted that the velocity of sunshine would not fluctuate, however is a constant, touring at 186,282 miles per 2nd (299,792 kilometers per 2nd). He postulated that time modified into extra like a river, ebbing and flowing searching on the consequences of gravity and arrangement-time. Time would velocity up and dreary down around cosmological our bodies with completely different plenty and velocities, and subsequently one 2nd on Earth modified into not the identical measurement of time in all areas within the universe. 

Connected tale: What’s arrangement-time?

Decades later, Einstein’s theory modified into confirmed to be correct. In October 1971, physicists J.C. Hafele and Richard Keating tested Einstein’s theory by flying four cesium atomic clocks on planes world vast, going eastwards and then westwards. 

Of their paper printed in 1972 within the journal Science, Hafele and Keating reported that the airborne clocks were about 59 nanoseconds slower than a ground-essentially based entirely mostly atomic clock when touring east, and 273 nanoseconds faster than the ground-essentially based entirely mostly version when touring west. Their outcomes supported Einstein’s theory that time fluctuates for the length of the universe. 

How prolonged is a 2nd?

There are two predominant suggestions of measuring time: dynamic and atomic time. The broken-down relies on the motion of celestial our bodies, including Earth, to retain monitor of time, whether it be the rotation time of a miles-off spinning basic particular person equivalent to a pulsar, the motion of a basic particular person across our evening sky or the rotation of Earth. On the different hand, a spinning basic particular person however, these suggestions are seemingly to be not gradually entirely unbiased. 

The extinct definition of a 2nd modified into in accordance with the rotation of Earth. Because it takes the sun eventually to upward thrust within the east, place of dwelling within the west and upward thrust again, a day modified into nearly arbitrarily divided into 24 hours, an hour into 60 minutes and a minute into 60 seconds. On the different hand, Earth would not rotate uniformly. Its rotation decreases at a fee of about 30 seconds each and each 10,000 years attributable to components equivalent to tidal friction. Scientists dangle devised suggestions to tale for the changing velocity of Earth’s rotation, introducing bounce seconds, however for potentially the most unbiased time that you just must mosey even smaller.

Atomic time relies on the vitality transition within an atom of a definite component, repeatedly cesium. By defining a 2nd the use of the form of those transitions, time could perchance perhaps perhaps unbiased furthermore be measured with an accuracy of shedding a minute piece of a 2nd in 1,000,000 years. The definition of a 2nd is now outlined as 9,192,631,770 transitions within a cesium atom, Scientific American reported.

Atomic clocks: The most unbiased monitor of time

Atomic clocks provide potentially the most unbiased monitor of time on Earth. The total GPS blueprint in orbit around Earth makes use of atomic clocks to accurately monitor positions and relay info to the planet, whereas total scientific facilities are place of dwelling as a lot as calculate potentially the most unbiased measure of time — steadily by measuring transitions within a cesium atom. 

Connected tale: NASA very most attention-grabbing activated its deep arrangement atomic clock

While most atomic clocks rely on magnetic fields, well-liked clocks are the use of lasers to monitor and detect vitality transitions within cesium atoms and preserve a extra positive measure of time. Despite the proven fact that cesium clocks are for the time being historical to retain time world vast, strontium clocks promise twice to boot-known accuracy, whereas an experimental plot in accordance with charged mercury atoms could perchance perhaps perhaps decrease discrepancies even additional to less than one 2nd misplaced or gained in 400 million years.

Time: The fourth dimension of the universe

Scientists as soon as thought that arrangement and time were separate, and that the universe modified into merely an assortment of cosmic our bodies arranged in three dimensions. Einstein, on the opposite hand, presented the thought that of time because the fourth dimension, which supposed that arrangement and time were inextricably linked. His well-liked theory of relativity suggests that arrangement-time expands and contracts searching on the momentum and mass of nearby topic. 

Many years after its proposal, Einstein’s theory of well-liked relativity modified into confirmed attributable to NASA’s Gravity Probe B, which demonstrated that arrangement and time were certainly linked. Four gyroscopes were pointed within the route of a miles-off basic particular person, and if gravity didn’t dangle an fabricate on arrangement and time, they’d dwell locked within the identical place of dwelling. On the different hand, scientists clearly noticed a “frame-dragging” fabricate attributable to the gravity of Earth, which supposed the gyroscopes were pulled very pretty out of place of dwelling. This means that the fabric of arrangement could perchance perhaps perhaps unbiased furthermore be altered, and if arrangement and time are linked, then time could perchance perhaps perhaps unbiased furthermore be stretched and shriveled by gravity.

Connected: NASA gravity probe confirms two Einstein theories

Why time moves excellent ahead

Despite the proven fact that Newton and Einstein came up with conflicting theories to effect how time works, both students agreed that time moves excellent ahead. To this point, there could be not a bodily evidence that anything else within the universe can dodge time and switch backwards nor jump ahead. And scientists are seemingly to be not entirely positive why time moves excellent ahead, however they’ve theories. 

One theory relies on the 2nd regulation of thermodynamics. This regulation states that every little thing within the universe tends to switch from low to high entropy, or from uniformity to dysfunction, beginning with simplicity at the Gigantic Bang and spicy to the nearly random association of galaxies and their inhabitants within the present day. That is acknowledged because the “arrow of time,” or most steadily “time’s arrow,” seemingly coined by British astronomer Arthur Eddington in 1928, analytic thinker Huw Stamp said at Séminaire Poincaré in 2006.

Eddington urged that time modified into not symmetrical: “If as we apply the arrow we uncover extra and additional of the random component within the remark of the enviornment, then the arrow is pointing in direction of the future; if the random component decreases, the arrow functions in direction of the previous,” he wrote in “The Nature of the Physical World” in 1928. To illustrate, within the occasion you were to seem for a basic particular person in nearly uniformity, however later saw it explode as a supernova and become a scattered nebula, you’ll know that time had moved ahead from equality to chaos.

One other theory suggests that the passage of time is attributable to our increasing universe. As the universe expands, it pulls time with it on tale of arrangement and time are linked as one. However this means that if the universe were to prevail in a theoretical limit of expansion and begin as a lot as contract, then time would reverse — a shrimp paradox. Would possibly perchance well time truly switch backwards, with every little thing coming relief to an period of simplicity and ending with a “Gigantic Crunch”? It be not going we are going to be around to search out out, however we can postulate on what we advise could perchance perhaps perhaps happen.

Scientists could perchance perhaps perhaps unbiased not dangle the total answers, however over the previous century they’ve made impressive development in thought how time works. From historical time-telling sundials to well-liked atomic clocks, we can now monitor the passing of a 2nd extra closely than ever earlier than. Time stays a elaborate topic, however attributable to scientific visionaries, we’re getting nearer to unlocking the secrets of this not-so-constant universal constant.

Extra sources and discovering out

To be taught extra regarding the thought that of time dilation, which we didn’t dive into well-known here, test out this explainer from the College of Mississippi. There are a total bunch movies on YouTube that could perchance perhaps perhaps unbiased will enable you to visualize the thought that of time and the way in which it truly works. Here’s a immense one from the National Institutes of Requirements and Know-how. Be taught extra about how time continues to stump even the excellent physicists within the enviornment in “The Listing of Time” by Carlo Rivelli (Riverhead Books, 2018). 


  • Ramsey, Norman F. “History of Atomic Clocks.” Journal of research of the National Bureau of Requirements (1977) vol. 88,5 (1983): 301-320. doi: 10.6028/jres.088.015
  • Eddington, A. S. (1933). The increasing universe. Nature, 132(3332), 406-407. 
  • Stamp, Huw. “Time’s Arrow and Eddington’s Disclose,” Séminaire Poincaré XV Le Temps (2010) 115 – 140.

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Jonathan O'Callaghan

Jonathan O’Callaghan is a contract arrangement and science journalist essentially based entirely mostly within the UK, on a well-liked foundation writing and reporting for a form of publications world vast. He specialises in conserving industrial spaceflight, arrangement exploration, and astrophysics, however furthermore studies across a tall need of science, from CRISPR to climate change.