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Translators: 时光, 东达, JJ Proofreader: 毫秒 Reviewer: 毫秒 Too sour!   Before we begin, imagine a game: someone gives you a lemon. Cut it open, then eat it without changing your expression.   Could you do it? If not, that is exactly the point. (If you could, pretend you could not!) The question we want to explore is why a lemon’s sourness has the power to twist your face into such a dramatic grimace. Sourness makes me pucker. | Credit: Shutterstock   Scientists are not entirely sure, but they think the answer involves three things: hydrogen ions, vitamin C, and our ancestors’ experience of feasting on tropical fruit in the trees.   The taste we call “sour” is directly connected to acidity. In chemical terms, sourness is your taste buds saying, “There are a lot of hydrogen ions dancing around ...

Author: A Millisecond of Eternity   Thousands of years ago, our ancestors erected milestones, drew detailed maps, and learned to find their position by observing the night sky so that they would not lose their way. Things are much easier now. A smartphone can meet our everyday navigation needs, and as long as you have a GPS receiver, you can find out where you are almost anywhere that receives a satellite signal. No more worrying about getting lost.   In the following sections, I will offer a simple introduction to the way GPS positioning works. The Global Positioning System is vast, expensive, and complex, but its fundamental concepts and principles are quite simple and intuitive.   The Global Positioning System, abbreviated GPS, provides accurate positioning, velocity measurements, and ...

Author: A Millisecond of Eternity A frame from the miniseries *Chernobyl* showing helicopters dropping sand and boron onto the reactor core | Credit: HBO   I recently came across HBO’s highly rated miniseries Chernobyl by chance. Curious to learn more, I sought it out and watched it. The series is almost textbook-quality in every aspect of its production, from its plotting and cinematography to its sound design. Even though viewers already know how the disaster ended, the oppressive, tragic atmosphere remains deeply affecting. It recreates the historical setting of the 1986 Chernobyl nuclear disaster to a remarkable degree, and I strongly recommend it to interested readers.   Returning to the subject: most readers will know something about the 1986 Chernobyl disaster, the worst nuclear ...

Author: 张贤 John Watson   When people hear that a child who falls should not be helped up, many think of the American psychologist John Watson. His method of making babies “immune to crying” was once widely popular. Its central rule was simple: do not pick a child up while the child is crying; pick the child up only after the crying stops. As the delay grew longer, the child would supposedly stop fussing and become a self-reliant, independent “perfect child.”   The theory still has many adherents, but from the standpoint of modern psychology, it rests entirely on a misunderstanding of human nature.   Research indicates that when an infant’s cries are repeatedly ignored, the infant’s brain releases high concentrations of cortisol, a stress hormone. Prolonged psychological stress of this k ...

Author: 一毫秒的永恒 Near-Earth asteroid Apophis (yellow orbit) will pass Earth in 2029, coming closer than some artificial satellites (blue dots). The purple line marks the orbit of the International Space Station. | Credit: NASA/JPL-Caltech   On April 13, 2029, a speck of light in the sky will grow brighter and move faster. At one point it will cross more than the apparent width of the full Moon in a minute and shine about as brightly as the stars of the Big Dipper. It will be neither a satellite nor an airplane, but the roughly 340-meter near-Earth asteroid (99942) Apophis. The asteroid will skim past Earth about 31,000 kilometers above the surface, closer than some artificial satellites; geosynchronous satellites orbit roughly 36,000 kilometers above the equator. That may sound frightenin ...

Author: 一毫秒的永恒 A few decades ago, astronomers could only dream of glimpsing the Moon's other side. This is a NASA visualization. | Credit: NASA's Scientific Visualization Studio   Look up at the bright Moon and it seems as familiar as ever, no different from the Moon of the past. Indeed, the Moon you admire is the same one our ancestors admired. After sunset, people around the world can see the same familiar shadows and shapes. It is easy to understand why ancient poets used the Moon to express longing for home and family.   From ancient times until the modern era, people on Earth could see only the Moon’s “near side.” Humanity did not see the “far side” until 1959, when the Soviet Luna 3 spacecraft flew around the Moon and returned photographs. In 1959, the Soviet Luna 3 probe took th ...

Author: 一毫秒的永恒   In the early hours of April 24, 019, a magnitude 6.3 earthquake struck Medog County in Nyingchi, Tibet. Tremors were widely felt in the surrounding area, but fortunately the region within 50 kilometers of the epicenter was extremely sparsely populated, and no casualties were reported.   Earth has earthquakes, but do other worlds in the Solar System “quake” too? Of course they do. Consider Earth’s satellite, the Moon. In 1969, American scientists first set foot on the Moon aboard Apollo spacecraft and installed 5 seismometers there. These continuously transmitted records of moonquakes to Earth, beginning humanity’s observation and study of lunar seismic activity. In 2019, signs of quakes were also found on our neighbor Mars. Marsquake signal detected by SEIS   The Seismi ...

Author: 一毫秒的永恒 A Poetic Name In this artist's concept, a supermassive black hole is surrounded by a rotating disk of matter. The faintly purple sphere of light above the black hole represents a feature of the corona containing high-energy particles capable of producing X-rays. Credit: NASA/JPL-CalTech   On April 10, 019, the first image of M87*, a black hole 55 million light-years from Earth, was released. It also received a name far more interesting than those of most black holes. This one may be the first lucky beneficiary in black-hole history: its new name was “Pōwehi,” a word in the Indigenous Hawaiian language meaning “embellished dark source of unending creation.” The name came from Larry Kimura, a professor and Hawaiian-language expert at the University of Hawaiʻi at Hilo. Pro ...

Salvation Author: 观复·钧天   Salvation is an activity in which people, dissatisfied with their material or spiritual condition, pursue a higher material or spiritual state. It begins with an awareness of the need to save oneself. During that process, the external power of “salvation by others” can either advance or obstruct it. The result is deliverance, and the highest state of deliverance is awakening: recognizing that things have always been as they are, that free will is as it is, that the natural environment is as it is, and that the course of history is as it is.   Viewed from within finite time and space, salvation is indispensable and runs through the whole of human existence. Humanity confronts the infinite with the finite: finite time and space face infinite time and space; finite ...

A still from a video simulation showing what a black hole's shadow might look like. The video was produced by Peter Galison and Chyld King for a short film about the Event Horizon Telescope project. The first image of a black hole will be unveiled at a press conference at 9:00 a.m. EDT on April 10, 2019 (9:00 p.m. Beijing time). Image: © EHT Outreach/YouTube   Some time ago, the EHT announced that it would hold a press conference on April 10, 2019. The following is part of the EHT’s statement:   On April 10, 2019, the Event Horizon Telescope (EHT) collaboration will hold simultaneous press conferences in several regions around the world to present its latest research results, together with numerous events organized by researchers and affiliated institutions. The press conferences will ta ...