Does Self-Control Deplete Over the Course of the Day? Maybe Not, Says New Study

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For months now, I’ve been trying to cut out sugar from my diet. I’ve read about all the ways my sweet tooth will be the death of me, and I’ve resolved to give it up. And yet, even as I write this, my long-term goal to eat healthy is losing out to my eternal desire to eat M&Ms at my desk. Is it because it’s the end of the day, and I’ve been trying to make choices for eight hours already? Or is it something else?

A new study in PLOS One pushes back on the popular theory known as "ego depletion," which hypothesizes that self-control is a finite resource that depletes throughout the day, much like energy levels. Instead, researchers from the University of Toronto and the learning technology company Cerego found that people's self-control depletes when it comes to doing one task for a long period of time, but that self-control fatigue isn't a factor when you're switching tasks. In other words, it's hard to say no to the box of cookies all day long, but saying no to the box of cookies won't impede other acts of self-control, like your ability to focus on your homework instead of turning on the TV.

The study used data from Cerego, which publishes online study materials, examining the study behaviors of two groups of college students using the Cerego system as part of semester-long psychology courses. The researchers looked at data from two groups of users, one group of 8700 students and one of almost 8800, focusing on how long they worked during each session and how well they performed at the memory tests within the curriculum.

If self-control really is a finite resource, it should be depleted by the end of the day, after people presumably have spent many hours resisting their first impulses in one way or another. But the researchers found that this wasn't true. Overall, students didn't do any better if they used the program earlier in the morning. Instead, performances peaked around 2 p.m., and people logged in to use the software more and more as the day went on, suggesting that the motivation to learn doesn't fall off at night (though that may also be because that's when college students do their homework in general).

However, mental resources did seem to be drained by doing the same task for a long period of time. The researchers found that after a certain point, students' performance dropped off, peaking at about 28 minutes of work. They made about 5 percent more mistakes 50 minutes into the session compared to that peak.

When it comes to the idea that we exhaust our store of self-control, the authors write, "the notion that this fatigue is completely fluid, and that it emerges after minutes of self-control, is under considerable doubt."

The notion of ego depletion comes from a 1998 study in which researchers asked participants to hang out in a room full of fresh-baked cookies, telling them to eat only from a bowl of radishes, leaving the cookies untouched. Then, those volunteers worked on an impossible puzzle. Volunteers who had spent time avoiding the delicious pull of cookies gave up on the mind-boggling task an average of 11 minutes earlier than a group of volunteers who were brought into the same room and allowed to eat as many cookies as they wanted. (Lucky them.)

Since then, the idea has taken off, leading to hundreds of subsequent studies and even influencing the habits of people like Barack Obama, who told Vanity Fair in 2011 that he only wore blue or gray suits in order to cut down on the non-vital decisions he had to make throughout the day.

This current study isn't the first to challenge the theory’s veracity, though. In 2016, a 2000-person replication study by some of the same authors (with scientists in 23 different labs) pushed back on the theory of ego depletion, finding that short spurts of self-control didn't have any effect on subsequent tasks. This study just adds to the evidence against the well-established idea.

So it's looking more and more like ego depletion isn't a good excuse for my afternoon vending-machine habit. Perhaps the true secret to excellent self-control is this: Just be a raven.

15 Facts About Nicolaus Copernicus

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Polish astronomer and mathematician Nicolaus Copernicus fundamentally altered our understanding of science. Born on February 19, 1473, he popularized the heliocentric theory that all planets revolve around the Sun, ushering in the Copernican Revolution. But he was also a lifelong bachelor and member of the clergy who dabbled in medicine and economics. Dive in to these 15 facts about the father of modern astronomy.

1. He came from a family of merchants and clergy.

Some historians believe that Copernicus's name derives from Koperniki, a village in Poland named after tradesmen who mined and sold copper. The astronomer's father, also named Nicolaus Copernicus, was a successful copper merchant in Krakow. His mother, Barbara Watzenrode, came from a powerful family of merchants, and her brother, Lucas Watzenrode the Younger, was an influential Bishop. Two of Copernicus's three older siblings joined the Catholic Church, one as a canon and one as a nun.

2. He was a polyglot.

Growing up, Copernicus likely knew both Polish and German. When Copernicus's father died when he was around 10, Lucas Watzenrode funded his nephew's education and he started learning Latin. In 1491, Copernicus began studying astronomy, math, philosophy, and logic at Krakow University. Five years later, he headed to modern Italy's Bologna University to study law, where he likely picked up some Italian. During his studies, he also read Greek, meaning modern historians think he knew or understood five languages.

3. He wasn't the first person to suggest heliocentrism ...

 A page from the work of Copernicus showing the position of planets in relation to the Sun.
A page from the work of Copernicus showing the position of planets in relation to the Sun.
Hulton Archive, Getty Images

Copernicus is credited with introducing heliocentrism—the idea that the Earth orbits the sun, rather than the sun orbiting the Earth. But several ancient Greek and Islamic scholars from various cultures discussed similar ideas centuries earlier. For example, Aristarchus of Samos, a Greek astronomer who lived in the 200s BCE, theorized that Earth and other planets revolved around the Sun.

4. … but he didn't fully give credit to earlier scholars.

To be clear, Copernicus knew of the work of earlier mathematicians. In a draft of his 1543 manuscript, he even included passages acknowledging the heliocentric ideas of Aristarchus and other ancient Greek astronomers who had written previous versions of the theory. Before submitting the manuscript for publication, though, Copernicus removed this section; theories for the removal range from wanting to present the ideas as wholly his own to simply switching out a Latin quote for a "more erudite" Greek quote and incidentally removing Aristarchus. These extra pages weren't found for another 300-some years.

5. He made contributions to economics.

He's known for math and science, but Copernicus was also quite the economist. In 1517, he wrote a research paper outlining proposals for how the Polish monarch could simplify the country's multiple currencies, especially in regard to the debasement of some of those currencies. His ideas on supply and demand, inflation, and government price-fixing influenced later economic principles such as Gresham's Law (the observation that "bad money drives out good" if they exchange for the same price; for example, if a country has both a paper $1 bill and a $1 coin, the value of the metal in the coin is higher than the value of the cotton and linen in the bill, and thus the bill will be spent as currency more because of that) and the Quantity Theory of Money (the idea that the amount of money in circulation is proportional to how much goods cost).

6. He was a physician (but he didn't have a medical degree).

After studying law, Copernicus traveled to the University of Padua so he could become a medical advisor to his sick uncle, Bishop Watzenrode. Despite spending two years studying medical texts and learning anatomy, Copernicus left medical school without a doctoral degree. Nevertheless, he traveled with his uncle and treated him, as well as other members of the clergy who needed medical attention.

7. He was probably a lifelong bachelor …

An etching of Copernicus, circa 1530.
An etching of Copernicus, circa 1530.
Hulton Archive, Getty Images

As an official in the Catholic Church, Copernicus took a vow of celibacy. He never married and was most likely a virgin (more on that below), but children were not completely absent from his life: After his older sister Katharina died, he became the financial guardian of her five children, his nieces and nephews.

8. … But he may have had an affair with his housekeeper.

Copernicus took a vow of celibacy, but did he keep it? In the late 1530s, the astronomer was in his sixties when Anna Schilling, a woman in her late forties, began living with him. Schilling may have been related to Copernicus—some historians think he was her great uncle—and she worked as his housekeeper for two years. For unknown reasons, the bishop he worked under admonished Copernicus twice for having Schilling live with him, even telling the astronomer to fire her and writing to other church officials about the matter.

9. He attended four universities before earning a degree.

A Polish stamp of Nicolaus Copernicus.
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Copernicus spent over a decade studying at universities across Poland and Italy, but he usually left before he got his degree. Why skip the diplomas? Some historians argue that at the time, it was not unusual for students to leave a university without earning a degree. Moreover, Copernicus didn't need a degree to practice medicine or law, to work as a member of the Catholic Church, or even to take graduate or higher level courses. 

But right before returning to Poland he received a doctorate in canon law from the University of Ferrara. According to Copernicus scholar Edward Rosen this wasn't exactly for scholarly purposes, but that to "show that he had not frittered his time away on wine, women, and song, he had to bring home a diploma. That cost much less in Ferrara than in the other Italian universities where he studied."

10. He was cautious about publicizing his views.

During Copernicus's lifetime, nearly everyone believed in geocentrism—the view that the Earth lies at the center of the universe. Despite that, in the 1510s Copernicus wrote Commentariolus, or "the Little Commentary," a short text that discussed heliocentrism and was circulated amongst his friends. It was soon found circulating further afield, and it's said that Pope Clement VII heard a talk about the new theory and reacted favorably. Later, Cardinal Nicholas Schönberg wrote a letter of encouragement to Copernicus, but Copernicus still hesitated in publishing the full version. Some historians propose that Copernicus was worried about ridicule from the scientific community due to not being able to work out all of the issues heliocentrism created. Others propose that with the rise of the Reformation, the Catholic Church was increasingly cracking down on dissent and Copernicus feared persecution. Either way, he didn't make his complete work public until 1543.

11. He published his work on his deathbed.

An antique bookseller displays a rare first edition of Nicolaus Copernicus' revolutionary book on the planet system.
An antique bookseller displays a rare first edition of Nicolaus Copernicus' revolutionary book on the planet system, at the Tokyo International antique book fair on March 12, 2008. The book, published in 1543 and entitled in Latin "De Revolutionibus Orbium Coelestium, Libri VI," carries a diagram that shows the Earth and other planets revolving around the Sun, countering the then-prevailing geocentric theory.
YOSHIKAZU TSUNO, AFP/Getty Images

Copernicus finishing writing his book explaining heliocentrism, De Revolutionibus Orbium Coelestium (On the Revolutions of Celestial Orbs), in the 1530s. When he was on his deathbed in 1543, he finally decided to publish his controversial work. According to lore, the astronomer awoke from a coma to read pages from his just-printed book shortly before passing away.

12. Galileo was punished for agreeing with Copernicus.

Copernicus dedicated his book to the Pope, but the Catholic Church repudiated it decades after it was published, placing it on the Index of Prohibited Books—pending revision—in 1616. A few years later, the Church ended the ban after editing the text to present Copernicus's views as wholly hypothetical. In 1633, 90 years after Copernicus's death, the Church convicted astronomer Galileo Galilei of "strong suspicion of heresy" for espousing Copernicus's theory of heliocentrism. After a day in prison, Galileo spent the rest of his life under house arrest.

13. There's a chemical element named after him.

Take a look at the periodic table of elements, and you might notice one with the symbol Cn. Called Copernicium, this element with atomic number 112 was named to honor the astronomer in 2010. The element is highly radioactive, with the most stable isotope having a half life of around 30 seconds.

14. Archaeologists finally discovered his remains in 2008.

Frombork Cathedral
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Although Copernicus died in 1543 and was buried somewhere under the cathedral where he worked, archaeologists weren't sure of the exact location of his grave. They performed excavations in and around Frombork Cathedral, finally hitting pay dirt in 2005 by finding part of a skull and skeleton under the church's marble floor, near an altar. It took three years to complete forensic facial reconstruction and compare DNA from the astronomer's skeleton with hair from one of his books, but archeologists were able to confirm that they had found his skeleton. Members of the Polish clergy buried Copernicus for a second time at Frombork in 2010.

15. THERE ARE MONUMENTS TO HIM AROUND THE WORLD.

The Nicolaus Copernicus Monument in Warsaw, Poland.
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A prominent statue of the astronomer, simply called the Nicolaus Copernicus Monument, stands near the Polish Academy of Sciences in Warsaw, Poland. There are also replicas of this monument outside Chicago's Adler Planetarium and Montreal's Planétarium Rio Tinto Alcan. Besides monuments, Copernicus also has a museum and research laboratory—Warsaw's Copernicus Science Centre—dedicated to him.

11 Spectacular Facts About the Moon

Matt Cardy/Stringer, Getty Images
Matt Cardy/Stringer, Getty Images

The Moon is Earth’s closest satellite in our solar system, but in many ways, we hardly know our neighbor. Scientists aren’t entirely sure how it formed, and other facts, like its shape (more egg-like than spherical), and the consistency of its surface (dusty but firm), were confirmed only recently. With the 50th anniversary of the Apollo 11 Moon landing this year, and NASA preparing to return to the lunar surface for the first time in decades, it’s time to brush up on these facts about the Moon—from colorful names for full moons to the first landing on the dark side of the Moon.

1. The Moon may have formed when a giant object in the solar system hit Earth.

Scientists aren't in total agreement on how the Moon formed, but the most widely accepted theory is the giant impact hypothesis. According to this theory, an object the size of Mars called Theia collided with Earth 4.5 billion years ago when the solar system was still new and chaotic. The impact dislodged matter from Earth’s crust, and the debris attached to whatever was left of Theia through the force of gravity.

This scenario would explain why the Moon is made up of lighter elements found in Earth’s outer layer, but it still leaves some questions unanswered. If the giant impact hypothesis is correct, about 60 percent of the Moon should consist of the impact object. Instead, its composition is almost identical to that of Earth. There are alternative explanations: one posits that the Moon is a space object that got caught in Earth’s orbit, and another one suggests the Moon and Earth formed at the same time, but none is as popular as the giant impact theory.

2. The Moon is the perfect size for solar eclipses.

Moon covering sun during solar eclipse.
Masashi Hara/Getty Images

A lucky set of circumstances make total solar eclipses, as seen from Earth, possible. The Moon is just the right size and distance from our planet to appear as the same size as the Sun in the sky. When the Moon passes between the Sun and the Earth, it covers the Sun perfectly with an impressive corona illuminating its edges. If it were any smaller or farther from Earth, it would look like a blot on the Sun during a solar eclipse.

3. A full Moon has different nicknames in different seasons.

A full moon can have many colorful names, but they don’t always describe a special celestial phenomenon. Some are used to refer to a full moon that appears during a certain time of year. A harvest moon, which is the full moon closest to the autumn equinox, is the best-known example, but there are many others, including a wolf moon (first full moon of January), strawberry moon (June), and sturgeon moon (August).

4. It’s the largest moon in the solar system relative to its planet.

Our Moon isn’t the largest in the solar system (that distinction goes to Ganymede, one of Jupiter’s 79 moons), but it is the biggest in relation to the planet it orbits. With a diameter of 2159 miles and a surface area of 14.6 million square miles, the Moon is a little more than one-fourth the size of Earth. The dwarf planet Pluto has an even smaller moon-to-planet ratio. Pluto’s largest moon Charon is nearly the size of its host body, leading some astronomers to refer to the pair as a double-dwarf planet.

5. The Moon is shaped like a lemon.

The Moon may look perfectly round in the night sky, but it’s actually more of an oval shape. It came out wonky billions of years ago when super-hot tidal forces shaped its crust, heating up some areas hotter than others to form a lemon shape rather than a perfect sphere. Gravitational forces from Earth have helped to exaggerate the Moon’s oblong appearance over eons.

6. Scientists thought Moon dust would cause lunar landers to sink.

Lunar module over moon's surface.
NASA/Newsmakers

When preparing to send missions to the Moon, some scientists feared that a thick layer of dust on the body’s surface would cause complications. One of the strongest proponents of the dust theory was Thomas Gold, an astrophysicist at Cornell University. He insisted that the Moon was covered in seas of dust soft and thick enough to swallow a lunar lander. Though the Moon’s surface is dusty, the layer is too thin to cause problems, as the successful landings of the Soviet Luna 9 and the American Surveyor spacecrafts proved in 1966.

7. The Moon is international property.

Astronauts Buzz Aldrin and Neil Armstrong may have planted an American flag on the Moon in 1969, but it belongs to the world. Countries like the Soviet Union and the U.S. made sure of that at the height of the space race in 1967 when they signed the Outer Space Treaty, a document declaring that the Moon would be a “global commons” and any resources discovered there would be used for the good of the world overall. In keeping with the spirit of the agreement, NASA shared soil samples taken from the Moon with Soviet scientists upon the Apollo 11 mission's return.

8. Humans have left strange things on the Moon.

Since the first people landed on the Moon in 1969, its surface has been home to more than just dust. Earth artifacts left on the Moon by astronauts include two golf balls, an obscene Andy Warhol doodle, and a message from Queen Elizabeth II. Eugene Cernan, Apollo 17 commander and one of the last people to walk on the Moon, traced his daughter’s initials into the soil when he visited in 1972. Without any wind or weather on the Moon, the letters TDC could remain there forever.

9. The "dark side of the Moon" is the result of synchronous rotation.

Even though the Moon is constantly rotating, only one side of it is visible from Earth. This is because the Moon is locked in synchronous rotation. It takes the Moon just as long to complete one full rotation as it does for the body to orbit around the Earth once, so the same side always faces our planet. This isn’t a coincidence—the Earth’s gravitational forces have gradually pulled the tip of the slightly oblong Moon to point toward the planet, creating something called tidal lock.

In January 2019, the Chinese space agency landed the first lunar probe on the unexplored dark side of the Moon. The Chang'e 4 spacecraft sent the first photographs of a massive impact crater on the dark side to Earth, giving scientists their first glimpse of that unknown region.

10. One astronaut was allergic to the Moon.

Apollo 17 astronaut Harrison “Jack” Schmitt discovered the hard way that some people are allergic to Moon matter. Following a survey of a valley in the Sea of Serenity, he climbed back into the crew’s lunar module and tracked in a lot of Moon dust with him. The dust affected him as soon as he removed his spacesuit, triggering red eyes, sneezing fits, and other symptoms that lasted two hours.

11. Humans are going back to the Moon soon.

After completing several manned missions to the Moon, NASA ended the Apollo program in 1972 as budgets tightened and public interest waned. That means most people alive today have never witnessed a manned lunar landing, but now, following a hiatus nearing 50 years, NASA is finally preparing to return to the Moon. The next manned lunar expedition will be ready to launch “no later than the late 2020s,” according to the space agency. One of the goals will be placing a command module, called Gateway, in the Moon’s orbit that astronauts can reuse over multiple missions.

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