十大科学问题 科学发现 英语原版.doc

WHY IS THE SKY BLUEI see skies of blue and clouds of white, Louis Armstrong crooned in his 1968 song What a Wonderful World. And he probably did, given that his song is an ode to optimism. European researchers have discovered that light from the blue part of the spectrum influences the emotions in a positive way, making us more responsive to emotional stimuli and more adaptable to emotional challenges source: Opfocus.But we digress. The reason the sky appears blue is because of an effect called scattering. Sunlight has to pass through the Earths atmosphere, which is filled with gases and particles that act like the bumpers on a pinball machine, bouncing sunlight all over the place. But if youve ever held a prism in your hands, you know that sunlight actually is made up of a bunch of different colors, all of which have different wavelengths. Blue light has a relatively short wavelength, so it gets through the filter more easily than colors with longer wavelengths, and as a result are scattered more widely as they pass through the atmosphere. Thats why the sky looks blue during the parts of the day when the Sun appears to be high in the sky (though its actually the spot on the planet where you are standing that is moving, relative to the Sun).HOW OLD IS THE EARTHAt sunrise and sunset, though, the suns rays have to travel a longer distance to reach your position. That cancels out blue lights wavelength advantage and allows us to see the other colors better, which is why sunsets often appear red, orange or yellow sources: NASA, ScienceDaily.The Earths age is something that people have been arguing about, at times bitterly, for a long, long time. Back in 1654, a scholar named John Lightfoot, whose calculations were based upon the Book of Genesis in the Bible, proclaimed that the Earth had been created at precisely 9 a.m. Mesopotamian time, on Oct. 26, 4004 B.C. In the late 1700s, a scientist named the Comte de Buffon heated up a small replica of the planet that he had created and measured the rate at which it cooled, and based upon that data, estimated that the Earth was about 75,000 years old. In the 19th century, the physicist Lord Kelvin used different equations to set the Earths age at 20 to 40 million years source: Badash.But all that was trumped in the late 1800s and early 1900s by the discovery of radioactivity, which was soon followed by calculation of the rates at which various radioactive substances decay source: Badash. Earth scientists have used that knowledge to determine the age of the Earths rocks, as well as samples from meteorites and rocks brought back from the Moon by astronauts. For example, theyve looked at the state of decay of lead isotopes from rocks, and then compared that to a scale based on calculations of how lead isotopes would change over time. From that, theyve been able to determine that the Earth formed approximately 4.54 billion years ago with an uncertainty of less than 1 percent source: U.S. Geological Survey .HOW DOES NATURAL SELETION WORKSLike the age of the Earth, the theory of evolution - first developed by biologist Charles Darwin in the mid-1800s - is another subject that people tend to get worked up about. If youve ever seen the classic movie Inherit the Wind, you probably already know about the infamous Scopes Monkey Trial of 1925. Famous attorney Clarence Darrow argued unsuccessfully upon behalf of a high school biology teacher named John Scopes, who was accused of violating a Tennessee statute that banned anyone from teaching that humans were descended from a lower order of animals, and decreed that the Biblical story of creation was the only acceptable explanation source: Linder. In recent years, its been anti-evolutionists whove fought in court and in legislatures for require that children learn creation science in school, in addition to evolutionary theory source: Raffaele.And if theres an idea that particularly bugs anti-evolutionists, its Darwins central concept, which is callednatural selection. Its really not a difficult idea to understand. In nature, mutations - that is, a permanent change in the genetic blueprint of organisms, which can cause them to develop different characteristics from their ancestors - occur randomly. But evolution, the longer-term process by which animals and plants change over multiple generations, is not up to chance. Instead, changes in organisms tend to become more common over time if the change helps the organism to better survive and reproduce.For example, imagine that some beetles are green, but then, a mutation causes some beetles to be brown, instead. The brown beetles blend into their surroundings better than the green beetles, so not as many of them are eaten by birds. Instead, more of them will survive and reproduce, and may pass along the genetic change that will make their offspring brown. Over time, the beetle population will gradually shift to being brown in color. That, of course, is the simple version. In practice, natural selection is based upon averages, not specific individuals, and its not quite as smooth and orderly of a process source: UC Berkeley.WILL THE SUN EVER STOP SHININGThis question reminds us of another pop song, Skeeter Daviss 1962 single The End of the World, in which the singer wonders why the sun keeps on shining after her boyfriend apparently has dumped her. The conceit of the lyrics is that the reality around us - whether its the shining sun or the birds singing in the trees - is more durable than our fragile little feelings. In truth, though, our lovelorn lass had the misfortune to be born too soon - by about 5.5 billion years, give or take a few. Thats the point at which the sun, which like any other star is a gigantic fusion reactor, will run out of the hydrogen in its core that it burns as fuel to create sunshine and will start burning the hydrogen in its surrounding layers.Thatll be the start of the suns death spiral, in which its core will shrink and its outer layers will expand massively, turning it into a red giant. In a final burst, the sun will roast the solar system with a blast of heat that will temporarily turn even the usually frigid vicinity of Pluto and the Kuiper Belt (out past Neptune) into a celestial sauna. Its likely that the inner planets, including Earth, will be either sucked into the dying giant, or else turned into cinders source: Overbye.On the plus side, unless humans manage to colonize the solar systems of other stars, nobody is going to be around to experience this final inferno. The sun, which is about halfway through its expected lifespan, is already gradually heating up, and a billion years from now, its expected to be about 10 percent brighter than it is now. That increase in solar radiation will be enough to boil away our planets oceans, leaving us without the water that our species depends upon for survival source: Overbye.HOW DO MAGNETS WORKBleeping magnets: How do they work? Thats the question that rappers Insane Clown Posse posed in their single Miracles a few years back, which led those snarkmeisters at Saturday Night Live to ridicule them unmercifully. And that was unfortunate, because its a perfectly reasonable thing to ponder. A magnet is any object or material that has a magnetic field - that is, a bunch of electrons flowing all around it in the same direction. Now, electrons - like rappers from Detroit who wear clown masks, curse a lot, and drink Faygo Cola - like to hook up in pairs, and iron has a lot of unpaired electrons that are all eager to get in on the action. So, objects that are solid iron or have a lot of iron in them - nails, for example - are going to be pulled towards a sufficiently powerful magnet. The substances and objects attracted to magnets are called ferromagnetic substances source: University of Illinois.Humans have known about the phenomenon of magnetism for a long, long time. There are naturally occurring magnets, such as lodestone, but medieval travelers figured out how to rub steel compass needles against those stones so that they picked up electrons and became magnetized, which means that they developed their own magnetic fields. Those magnets werent particularly durable, but in the 20th century, researchers developed new materials and charging devices that enabled them to make more powerful permanent magnets source: Stupak. You can actually create a type of magnet, called an electromagnet, from a piece of iron by wrapping an electrical wire around it and then connecting the ends to the poles of one of those big batteries with the clips on top source: University of Illinois.WHAT CAUSES A RAINBOWTheres something about this atmospheric phenomenon that has inspired awe in people since ancient times. In the Book of Genesis, God put a rainbow in the sky after the Great Flood and told Noah it was a sign of a token of the covenant between me and Earth source: Biblos. The ancient Greeks went further, and decided that the rainbow actually was a goddess, whom they named Iris. But they made her an ominous figure - the bearer of the Olympian gods tidings about war and retribution source: Lee and Fraser, pg viii. And over the centuries, great scientific minds ranging from Aristotle to Rene Descartes sought to figure out what process created rainbows striking array of colors source: Broughton and Carriero.Since then, though, scientists have nailed it pretty well. Basically, rainbows are caused by the droplets of water that remain suspended in the atmosphere after a rainstorm. The droplets have a different density than the surrounding air, so as sunlight hits them, the droplets act as tiny prisms, bending the light to break it up into its component wavelengths, and then reflecting them back at us. That in turns creates the arc with bands of colors of the visible spectrum that we see. Because the droplets have to reflect the light at us, in order to see a rainbow, we have to be standing with our backs to the sun. We also need to be looking up from the ground at an angle of approximately 40 degrees, which is the rainbows angle of deviation - i.e., the angle at which it bends sunlight. Interestingly, if youre in an airplane and you see a rainbow from above, it actually may look like a disk, rather than an arc source: Physics Classroom.WHAT IS THE THEORY OF RELATIVITYWhen someone refers to the theory of relativity, what they really mean are two theories, special relativityand general relativity, which were devised by theoretical physicist Albert Einstein in the early 1900s source:. But no matter what you call Einsteins body of work, its undoubtedly baffling to most non-scientists. Einstein thought of a clever way to explain it: When a man sits with a pretty girl for an hour, it seems like a minute. But let him sit on a hot stove for a minute and its longer than any hour. Thats relativity. source: Mirsky.And that actually sums it up pretty well, though the details are a bit more complex. Before Einstein, everybody pretty much believed that space and time were fixed qualities, which didnt ever change, because thats the way they look to us from our vantage point on Earth. But Einstein used mathematics to show that absolute view of things was an illusion. Instead, he explained, space and time both can undergo alterations - space can contract, expand or curve, and the rate at which time passes can shift, as well, if an object is subjected to a strong gravitational field or is moving very quickly.Moreover, how space and time appear can depend upon the vantage point of a person observing them. Imagine, for example, that you are looking at an old-fashioned ticking alarm clock with hands to tell the time. Now, imagine putting that clock in orbit around the Earth, so that it is moving really fast, compared to your position on the surface. If you could still see the clock hands, they would look smaller to you than they would on Earth, and the ticks of the clock would be slower source: Cornell University .The clock moves more slowly because of a phenomenon called time dilation. Space and time are actually a single thing, called space-time, which can be distorted by powerful forces such as gravity and acceleration. So if an object is moving very fast, or has really powerful gravity acting upon it, time for that object will slow down, compared to an object that is not being subjected to the same forces. Its possible, by using mathematical calculations, to predict just how much time will slow down for a fast-moving object.That probably sounds pretty weird. But we know that it actually is true. The Global Positioning System (GPS), whose satellites depend upon precise measurement of time to provide map positions on Earth, is proof. The satellites are whizzing around the planet at about 8,700 miles (14,000 kilometers) per hour, and if engineers didnt adjust their clocks to compensate for relativity, within a day, Google maps on our smart phones would be giving us positions that were 6 miles (9.86 kilometers) off source: OSU Astronomy.WHY IS THE BUBBLES ROUNDWell, actually, bubbles are not always perfectly round all the time, as you probably have noticed if youve ever used one of those toy thingies to blow soap bubbles. But bubbles want to be spherical, and if you blow one thats more cigar-shaped initially, it struggles to reshape itself. Thats because bubbles basically are thin layers of liquid whose molecules stick together because they are attracted to one another, a phenomenon called cohesion source: USGS. This creates what we think of as surface tension - that is, a barrier that resists objects trying to move through it source: USGS. Inside the layer, air molecules that are trapped cant get out, even though theyre pushing against the water. But thats not the only force acting on that layer. On the outside, more air is pushing inward at them. The most efficient way for the liquid layer to resist those forces is to assume the most compact shape, which happens to be a sphere, in terms of ratio of volume to surface area source: Popular Science.Interestingly, scientists have figured out ways to make bubbles that arent round, so they can study the geometry of the surfaces. Theyre able to create bubbles that are cubical and even rectangular, by suspending a thin layer of liquid on a wire frame that that is molded into the desired shape source:NEWTON.WHY ARE THE CLOUDS MADE FORHopefully, this wont disappoint Joni Mitchell fans too much, but clouds are not actually bows of angel hair and ice cream castles in the air. A cloud is a visible mass of water droplets, or ice crystals, or a mixture of both that is suspended above the Earths surface. Clouds are formed when moist, warm air rises. As it ascends higher and reaches a space thats cooler, the moist warm air cools down, too, and the water vapor condenses back into tiny water droplets and/or ice crystals, depending upon how cold they get. Those droplets and crystals stay massed together because of the principle of cohesion, which weve previously discussed. The result is a cloud source: Britannica . Some clouds are thicker than others because they happen to have a higher density of water droplets.Clouds are a key part of our planets hydrologic cycle, in which water continually moves between the surface and the atmosphere, and changes in state from liquid to vapor to liquid, and sometimes to solid as well. If it werent for that cycle, there probably wouldnt be any life on our planet source: NASA.In 1803, a meteorologist named Luke Howard came up with four main cloud classifications, whose names were based on Latin words. Cumulus, which is the Latin word for pile, describes those heaped, lumpy clouds that we often see in the sky. Cirrus, which means hair, is the term for high-level clouds that look wispy, like locks of hair. Flat-looking, featureless clouds that form sheets are called stratus, which is the Latin word for layer. Finally, there are nimbus clouds (the name actually is Latin for precipitating cloud) are low, grey rain clouds source: NASA. And sometimes they combine like the very tall grey lumpy clouds you see before thunderstorms called a cumulonimbus!WHY DOES WATER EVAPORATE AT ROOM TEMPERATUREWe humans like to think of reality as a nice, stable place, where various stuff stays in the same place unless we want it to go somewhere else. But dream on. In reality, if you look at water at the molecular level, it acts like a bunch of puppies crowding into a dog bed, with molecules bumping each other and jostling for position. When a lot of water vapor is in the air, molecules will get bumped up against a surface and stick to it, w