Did you know that everyone on Earth is technically living in the past? This might sound like a sci-fi plot, but it’s actually a quirk of human biology. Our brains take about 80 milliseconds to process events, meaning we perceive everything slightly after it happens. This delay contributes to some physicists’ belief that the concept of “now” is merely an illusion.
Time perception varies significantly across different cultures. In the Western world, we often think of time as a straight line moving from left to right. However, this isn’t universal. For instance, people who read right-to-left languages like Arabic and Hebrew often perceive time flowing in that direction. The Aymara people of the Andes see the future as behind them and the past as ahead, reflecting the unknown nature of the future. Similarly, some Indigenous Australian cultures visualize time as moving from east to west, influenced by their directional language.
Time can feel different depending on what you’re doing. When you’re engrossed in an activity, time seems to fly by, but it drags when you’re bored. This happens because your brain focuses less on time when you’re engaged. Dopamine, a neurotransmitter associated with pleasure, might also play a role. Higher dopamine levels can slow down your internal clock, making time feel like it’s passing quickly.
Time can be defined in various ways. Astronomical time is based on Earth’s rotation, with a second being one-sixtieth of a minute. Atomic time, however, is more precise, measuring time through the oscillations of a cesium-133 atom. This method is the most accurate way to track time.
Albert Einstein revolutionized our understanding of time with his theory of relativity. He showed that time is relative, meaning it can change depending on speed and gravity. For example, the faster you move, the slower time passes for you. This is why astronauts age slightly slower in space. Gravity also affects time; the closer you are to a massive object, the slower time moves.
Gravity has also influenced the length of our days. Over a billion years ago, a day was about 18 hours long. The moon’s gravitational pull has gradually slowed Earth’s rotation, leading to longer days. Interestingly, while the Earth’s orbit around the sun hasn’t changed, the number of days in a year has. During the dinosaur era, days were shorter, resulting in more days per year.
There are two ways to measure a day on Earth. A solar day, based on the sun’s position, is 24 hours. A sidereal day, based on fixed stars, is about four minutes shorter. This discrepancy sometimes requires a leap second to keep atomic and astronomical time aligned. Leap seconds can cause issues for technology, as they are added irregularly.
The Roman calendar was notoriously inaccurate, prompting Julius Caesar to reform it in 46 BCE. He introduced leap years to account for Earth’s orbit not being exactly 365 days. However, the calendar was still slightly off, leading to the creation of the Gregorian calendar in 1582. This calendar refined leap year rules to better align with Earth’s orbit.
Time zones were standardized thanks to the railroad industry. Before the 19th century, local times varied widely, complicating train schedules. In 1883, North American railroads adopted a system similar to today’s time zones. The concept was further developed at the 1884 International Meridian Conference, establishing the prime meridian in Greenwich, England.
Daylight saving time (DST) was first proposed by an entomologist in 1895 to extend daylight hours for insect hunting. Germany implemented it during World War I to conserve coal, and the U.S. followed in 1918. DST has been linked to health issues like increased heart attacks and car accidents, but it also reduces koala collisions.
Humans have tracked time for millennia. The oldest known lunar calendar, dating back to 8000 BCE, was found in Scotland. In 1090, Su Song in China built a water-powered clock tower that tracked celestial movements. The Maya used multiple calendars, including the Long Count calendar, which ended in 2012, sparking apocalypse theories.
The most accurate clock is at the National Institute of Standards and Technology in Colorado, measuring time with an aluminum ion. Meanwhile, the default setting of 10:10 on clocks is chosen for aesthetic reasons, as it creates a symmetrical look.
Einstein’s theories suggest time travel could be possible by moving faster than light or using wormholes. However, these remain theoretical due to technological limitations. Cosmic strings, theoretical energy streams, might also allow time travel by bending space-time.
Stay tuned for our next episode, where we’ll explore fascinating stories about historical figures’ body parts. If you have any interesting tales, share them in the comments!
Conduct a simple experiment to explore how time perception varies with activity. Choose two activities: one engaging (like playing a video game) and one monotonous (like watching a clock). Record how long you think each activity lasted without checking the time. Compare your perceived time with the actual time to understand how engagement affects your perception of time.
Create a visual map that illustrates how different cultures perceive time. Research and include at least five cultures with unique time perceptions, such as the Aymara or Indigenous Australian cultures. Present your findings in a class discussion, highlighting how cultural perspectives influence our understanding of time.
Use an online simulator to explore Einstein’s theory of relativity and time dilation. Experiment with different speeds and gravitational fields to see how they affect time. Write a reflection on how this experience changes your understanding of time as a relative concept.
Research the history of calendars from the Roman to the Gregorian calendar. Create a timeline that highlights key changes and reasons for these adaptations. Present your timeline to the class, explaining how these changes reflect humanity’s evolving understanding of time.
Participate in a debate on the pros and cons of daylight saving time (DST). Research its historical context, benefits, and drawbacks. Formulate arguments for or against DST and engage in a class debate to explore its impact on modern society.
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Every person on Earth is living in the past. This may sound like the plot of a sci-fi time travel thriller, but it’s actually a fact of human biology and the complexities of time. Our brains don’t perceive events until about 80 milliseconds after they’ve happened. This fine line between the present and the past is part of the reason why some physicists argue that there’s no such thing as “now” and that the present moment is no more than an illusion.
Hi, I’m Erin McCarthy, editor-in-chief of Mental Floss, and welcome to the List Show from my living room. The potential impossibility of living in the present is just one intriguing fact about time that I’m going to share with you today.
Throughout history, different cultures around the world have experienced time in various ways. In the Western world, we tend to think of time as linear, flowing from left to right, but this isn’t the case for everyone. Language affects how people conceptualize time, particularly the spatial metaphors they use to describe and map it. Those who read languages that flow from right to left, such as Arabic and Hebrew, generally view time as flowing in the same direction. The Aymara, who live in the Andes mountains in South America, consider the future to be behind them while the past is ahead. In their view, the future is unknown and thus behind you, where you can’t see it.
Some Indigenous Australian cultures, which rely heavily on directional terms like north, south, east, and west in their languages, visualize the passage of time as moving from east to west. If they’re facing north, for example, the past would be to their right (east), while the future would be to their left (west).
Individual people can experience time differently, too. You’ve probably noticed how time seems to speed up when you’re racing against a deadline or having fun, and how it tends to drag when you’re bored. This is because when you’re focused on something, like a big work project or a party, your brain pays less attention to how time passes. But when you’re bored or your brain is less stimulated, you become more aware of the passing of time, making it feel slower. One study proposed that dopamine, the neurotransmitter and hormone that helps us feel happy, may be an additional factor. It showed that increased dopamine production, which happens when you’re enjoying something, may slow down your body’s internal clock, making time feel like it’s flying by.
Science has a number of different ways of defining time. To discuss just a couple, there’s astronomical time, which is measured in relation to how long it takes Earth to rotate on its axis. In astronomical time, a second is one-sixtieth of a minute. Then there’s atomic time, which dictates the numbers you’ll see on a clock. According to atomic time, one second equals approximately nine billion, one hundred ninety-two million, six hundred thirty-one thousand oscillations of a cesium-133 atom. Measuring the vibration of an atom is the most accurate way to track time.
We can thank Albert Einstein for a lot of our current understanding of the physics of time. Rather than viewing time as a set order, he proved that it’s actually relative. For example, according to Einstein’s theory of special relativity, there’s an inverse relationship between your speed and the speed of time: the faster you move, the slower time moves. This is why someone traveling through space will age slower than people still on Earth. Astronaut Scott Kelly was born several minutes after his twin brother Mark, but after Scott spent 340 days living on the International Space Station, he returned to Earth about 5 milliseconds younger than his brother. Had Scott been traveling at a speed close to the speed of light, that age difference would have become much more pronounced.
Einstein’s theory also states that gravity can warp time. If you’ve seen the movie “Interstellar,” this concept may seem familiar. The closer you are to a massive body, such as a giant black hole, the slower time would pass for you. Gravity’s effect on time isn’t limited to intergalactic travel; here on Earth, gravity can vary for a number of reasons, including your altitude. Since you’re changing your distance from the center of the Earth, if you put synchronized atomic clocks at various altitudes, eventually these clocks would fall out of sync. A clock at the top of Mount Everest and one at sea level would diverge by about a day and a half over the entire 4.5 billion-year history of the planet.
Gravity is also the reason why our days are getting longer. Over a billion years ago, a day on Earth lasted around 18 hours. Our days are longer now because the moon’s gravity is causing Earth’s spin to slow down. In Earth’s earlier days, the moon was closer, which caused Earth to spin much faster than it currently does. Longer days also mean shorter years, in a way. The time it takes the Earth to orbit the sun hasn’t changed, but the number of days within a year has. Back when the dinosaurs roamed 70 million years ago, days were only around 23.5 hours long, and the year consisted of 372 of those slightly shorter days.
There are two ways to think of the length of a day on Earth. You probably learned that one day on Earth is 24 hours, but it actually takes the planet 23 hours, 56 minutes, and 4.0916 seconds to rotate on its axis. This is the difference between a solar day and a sidereal day. A solar day is 24 hours, whereas a sidereal day is roughly four minutes shorter. We measure solar time based on the sun’s position in the sky, while the sidereal day is measured based on the location of fixed stars.
Because astronomical time and atomic time don’t always align, we occasionally get a leap second. Earth’s spin speed can be unpredictable; atmospheric winds, northern hemisphere winters with heavy snow, and other significant weather systems can affect how fast the planet rotates. To keep the difference between astronomical time and atomic time to less than 0.9 seconds, the International Earth Rotation Reference System Service will occasionally announce the need for a leap second. Most people won’t notice a leap second, but they can be a significant issue for tech companies because leap seconds are added irregularly, making it challenging for developers to incorporate them into their codes. This has caused websites like LinkedIn and Reddit to crash in the past. A bug caused by a leap second in 2012 led to chaos on Qantas servers, resulting in over 400 flight delays.
The length of a year on Earth can also be complicated. The original Roman calendar was quite messy, so much so that in 46 BCE, Julius Caesar mandated a 445-day long year to help bring the calendar back in sync with the seasons. At the same time, Caesar asked the astronomer Sosigenes to help reform the calendar. Most years were set at 365 days, but to account for the fact that Earth’s revolution around the sun doesn’t take exactly 365 days, leap years were implemented every four years. The month of February was given an extra day to make up for what is essentially a rounding error in the calendar. However, Sosigenes made a miscalculation, so the calendar continued to be slightly off. He thought a year lasted 365.25 days, but it’s actually around 365 days, 5 hours, 48 minutes, and 45 seconds, equivalent to about 365.242 days. This tiny error had significant consequences; by 1577, the Julian calendar was off by 10 days, meaning key Christian holidays were being celebrated on incorrect dates. Pope Gregory XIII took issue with this and established a commission to get the calendar back on track. In 1582, the Gregorian calendar was created. Rather than having an extra day every four years without exception, years that are divisible by 100, like 1700 or 1900, skip the leap year unless the year is also divisible by 400, like the year 2000, in which case the leap year is reinstated. Even this system isn’t perfect, though; it has an error of one day every 3,236 years.
We can thank the railroad industry for standardizing our time zones. Up until the 19th century, towns and villages synchronized their clocks to the local solar noon, creating thousands of local times that varied and made scheduling transportation a major headache. Train schedules in different cities had to list dozens of arrival and departure times for each train to account for all the many time zones. On November 18, 1883, railroad companies in the United States and Canada began using a system very similar to the standardized time zones we still use today. In the UK, railroad companies began using a standard London-based time in 1840 after an engineer named Sanford Fleming missed a train in 1876. He set out to change the way time worked, originally proposing a concept he called “cosmic time,” in which the world would run off an imaginary clock located at the planet’s center. Essentially, a line from the center of the planet to the sun. He then suggested splitting the world into 24 time zones, labeled with letters of the alphabet, with each zone spanning 15 degrees of longitude. His original plan to create a standard cosmic time was rejected, but it laid the groundwork for a similar standardization called universal time. Nations present at the 1884 International Meridian Conference established the groundwork for dividing the world into 24 time zones, with the prime meridian (longitude 0 degrees) running through Greenwich, England.
Even with the advent of standardized time, people still struggle to keep their clocks in sync. One London family used this to their advantage and made a living by selling people the time. An astronomer named John Belleville would set his pocket watch to the time at the Royal Observatory in Greenwich. He would then travel around the city and visit his network of subscribers who paid to set their own clocks by Belleville’s pocket watch. After Belleville died in 1856, his wife and later their daughter Ruth carried on the tradition. Ruth continued to sell the time until World War I, when improved technology made her role less important and the war made traveling around London too dangerous.
Time zones can still be complicated. Big countries like Canada and the United States have multiple time zones, while China, another large country, has only one. China adopted Beijing Standard Time to foster unity, but the effect can feel a bit uncanny, as two cities in the country can be at roughly the same latitude but experience sunrise hours apart according to their clocks. In some parts of China, for example, the sun doesn’t rise until nearly 10 AM.
Speaking of confusing time changes, here are a few facts about daylight saving time. Though many people believe the biannual time change was adopted to keep farmers happy, that’s a myth. The first person to seriously advocate for daylight saving time was an entomologist who wanted more sunlit hours to look for insects after work in the summer. He proposed his idea to a scientific society in New Zealand in 1895. Daylight saving time wasn’t officially implemented until 1916 when Germany became the first country to adopt it in an effort to conserve coal during World War I. The United States didn’t follow suit until 1918. Daylight saving time ended on a national level after the war, but individual states and municipalities kept it going until World War II, when the entire nation went on what was effectively a year-round daylight saving time. After World War II, the entire nation was again picking and choosing daylight saving time. It’s been reported that in Iowa back in 1964, there were 23 different combinations of dates that communities turned on and off daylight saving time. In 1966, the government officially mandated a standardized daylight saving time for the entire United States, though individual states can opt out. Up until 2007, daylight saving time ended in October. It’s been reported that the candy industry lobbied to wait until after Halloween to change the clocks back an hour.
Daylight saving time does more than make people lose an hour of sleep; it can have some concerning health effects. Studies have linked daylight saving time with an uptick in heart attacks, car crashes, and mining injuries. The extra hour of daylight is beneficial for koalas, though; researchers found that koala car collisions decreased by up to 11% during daylight saving time.
We can’t talk about time without mentioning a few clock facts. People have been tracking time for thousands of years. In 2013, archaeologists found what is thought to be the world’s oldest lunar calendar while excavating a field in Scotland. The calendar, which consists of a series of 12 pits that mimic the moon’s phases, dates back to around 8000 BCE. Sundials read differently depending on the hemisphere you’re in. In the northern hemisphere, the sun casts a shadow that moves from north to east to south to west. In the southern hemisphere, the shadow moves in the opposite direction. Our concept of clockwise is based on the way sundials in the northern hemisphere tell time.
In 1090, an innovative clock was built in China. A man named Su Song created a water-powered clock tower that measured time and tracked the movements of the planets and stars in the night sky. Su Song built a giant water wheel within the clock tower; buckets attached to the wheel would fill with water and then tip once full, causing the wheel to rotate and demarcate time. The Maya had multiple calendars to measure time, but the most familiar to apocalyptic theorists is the Long Count calendar. These calendars measured around 5,125 years, beginning around August 3114 BCE. The Long Count calendar cycle came to an end around December 21, 2012, sparking a craze of conspiracy theories about the apocalypse.
You’ll find the most accurate clock at the National Institute of Standards and Technology in Boulder, Colorado. The clock keeps time by measuring the vibration of a single aluminum ion and should remain accurate for 33 billion years. The clock sitting on your bedside table isn’t quite as precise. If you’ve bought a new clock or watch recently, you may have noticed the default setting was 10:10, give or take a few minutes. There are various theories behind this particular choice of time, but it all comes down to aesthetics. Setting the time to around 10:10 allows the hands of an analog clock to be displayed in a neat, symmetrical way that doesn’t obscure any logos in the center of the clock’s face. Clocks were once set to 8:20 and occasionally still are, but the hand’s downward angles can make it look like the timepieces are frowning.
Traveling back in time is possible, theoretically at least. According to Einstein’s theory, you could travel back in time by moving faster than the speed of light, as long as you could somehow have infinite mass. Since that probably won’t work, you could create wormholes between two points in space-time. This would also be challenging, as humanity still hasn’t invented the technology to build a wormhole. Alternatively, you could try bending space-time by plucking some cosmic strings. Two of these theoretical strings, which are thin streams of pure energy moving in opposite directions at nearly the speed of light, could theoretically warp space-time enough to create a closed time-like curve, also known as a time machine.
Our next episode is all about the infamous body parts of historical figures. If you know of a strange, funny, or otherwise interesting story behind a historical body part, leave it in the comments for a chance to be featured in that episode. Thanks for watching!
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Time – A continuous, measurable quantity in which events occur in a sequence from the past through the present to the future, often considered as a fourth dimension in physics. – In physics, time is a fundamental concept that allows us to understand the sequence and duration of events in the universe.
Perception – The process by which sensory information is interpreted and understood, often influencing how scientific phenomena are observed and analyzed. – The perception of time can vary significantly between different cultures and historical periods, affecting how societies develop their scientific understanding.
Gravity – A natural phenomenon by which all things with mass or energy are brought toward one another, including planets, stars, and galaxies. – Isaac Newton’s law of universal gravitation was a pivotal moment in the history of physics, providing a mathematical explanation for the force that governs planetary motion.
Einstein – Referring to Albert Einstein, a theoretical physicist whose theory of relativity revolutionized the understanding of space, time, and gravity. – Einstein’s theory of general relativity introduced a new way of understanding gravity, describing it as the curvature of spacetime caused by mass.
Culture – The shared beliefs, practices, and values of a group of people, which can influence the development and acceptance of scientific theories and discoveries. – The scientific culture of the early 20th century was profoundly shaped by Einstein’s revolutionary ideas, which challenged traditional notions of physics.
Calendar – A system for organizing and dividing time into days, months, and years, often based on astronomical observations. – The Gregorian calendar, widely used today, was developed to correct inaccuracies in the Julian calendar by aligning more closely with the Earth’s orbit around the Sun.
Measurement – The process of obtaining the magnitude of a quantity relative to a defined standard, crucial for scientific experimentation and validation. – Accurate measurement of time and distance is essential in physics experiments to ensure reliable and reproducible results.
Evolution – The gradual development and change of systems over time, often used to describe biological processes but applicable to scientific theories and technologies. – The evolution of astronomical instruments has significantly enhanced our ability to observe distant celestial objects and phenomena.
Astronomy – The scientific study of celestial objects, space, and the universe as a whole, often involving the observation and analysis of stars, planets, and galaxies. – Astronomy has a rich history, with ancient civilizations using the stars to develop calendars and navigate the seas.
Travel – The movement from one place to another, which in a historical context, often refers to the exploration and discovery of new territories and ideas. – The concept of time travel, although speculative, has been a topic of interest in physics, particularly in the context of Einstein’s theories.
