Brian Greene, a professor of physics and mathematics at Columbia University, has created an online science education platform. He tries to "build a bridge" with things you know about, and then "bring you across that bridge to the strange place of modern physics."

    Recently I had a chance to ask Greene about wormholes (a hole which some scientists think might exist, connecting parts of space and time that are not usually connected), time travel and other mysteries of the universe. I asked him a million-dollar question: What if I went through a wormhole and prevented my parents from meeting? "Most of us believe that the universe makes sense," Greene said. Although there are several interesting theories about time travel, he added, the laws of physics would probably prevent something so illogical from taking place. The good news is that the time paradox（悖论） is open for future physicists to solve.

    When asked how physics could become more exciting for kids, Greene said that books by Stephen Weinberg, Leonard Susskind, and other physicists, "make it a great time for people who want to learn about big ideas but aren't yet ready, perhaps, to learn math."

    When I pointed out that some students still might find physics boring, Greene said that the key is to teach them about things that are strange. "The basic stuff is important," Greene said. "But I think it's really important to also describe the more modern ideas, things like black holes and the Big Bang. If kids have those ideas in mind, then at least some of them will be excited to learn all the details．"

    Greene has followed Albert Einstein's lead in trying to solve the mysteries of the universe. Now he wants kids to do the same. As Greene said, physics is "not just a matter of solving problems in an exam." It's about experimenting, showing an interest in strange phenomena（现象）-- and having fun!

    Then the servant knocked in a very guarded manner; the door was opened on the chain; and a voice asked from within, “Is that you, Poole?”

    “It's all right,”said Poole,” Open the door.”

    The hall, when they entered it, was brightly lighted up/The whole of the servants, men and women, stood crowded together like a flock of sheep .At the sight of Mr. Utterson, the housemaid broke into crying hysterically but softly; and the cook, crying out” Bless God! It's Mr. Utterson,” ran forward as if to take him in her arms.” What, what? Are you all here?” said the lawyer impatiently.” Very irregular, very unseemly; your master would be far from pleased.”

    “They're all afraid,” said Poole.

    Blank silence followed, no one protesting; only the maid lifted her voice and now wept loudly.

    Blank silence followed, no one protesting; only the maid lifted her voice and now wept loudly.

    “I told your tongue!” Poole said to her, with a violent accent that proved his own anxiety; and indeed, when the girl had so suddenly raised the note of her mourning, they had all started and turned towards the inner door with faces of dreadful expectation.” And now,” continued the servant, addressing the knife-boy,” reach me a candle, and we'll get this through hands at once.” And then he begged Mr. Utterson to follow him, and led the way to the back garden.

    “Now, sir,” said he, “you come as gently as you can. I want you to hear, and I don't want you to be heard. And see here, sir, if by any chance he was to ask you in, don't go.”

    Mr. Utterson's nerves gave a jerk that nearly threw him from his balance; but he recollected his courage and followed the servant to the foot of the stair. Here Poole signed to him to stand on one side and listen; while he himself, setting down the candle and making a great and obvious call on his determination, went up the steps and knocked with a somewhat uncertain hand on the red baize of the cabinet door.

    “Mr. Utterson, sir, asking to see you,”he called; and even as he did so,once more violently signed to the lawyer to give ear.

    A voice answered from within:” Tell him I cannot see anyone,” it said complainingly.

    “Thank you,sir,” said Poole, with a note of something like triumph（胜利）in his voice; and taking up his candle, he led Mr. Utterson back across the yard and into the great kitchen.

    “Sir,” he said, looking Mr. Utterson in the eyes, “Was that my master's voice?”

    “It seems much changed,” replied the lawyer, very pale, but giving look for look.

    “Changed? Well, yes, I think so,”said the servant, “Have I been twenty years in this man's house, to be deceived about his voice? No, sir; master's killed; he was killed eight days ago, when we heard him cry out upon the name of God; and who's in there instead of him, and why it stays there, is a thing that cries to Heaven, Mr. Utterson!”

    “This is a very strange tale, Poole; this is rather a wild tale, my man,” said Mr. Utterson, biting his finger,” Suppose it were as you suppose, supposing Dr. Jekyll to have been--well, murdered what could cause the murderer to stay ? That won't hold water; it is not reasonable.”

    “Well, Mr. Utterson, you are a hard man to satisfy, but I'll do it yet,” said Poole. “All this last week（you must know）him, or it, whatever it is that lives in that cabinet, has been crying night and day for some sort of medicine . It was sometimes his way--the master's, that is --to write his orders on a sheet of paper and throw it on the stair. We've had nothing else his week back; nothing but papers, and a closed door, and the very meals left there to be taken in secretly when nobody was looking .Well, sir, every day, and twice and there times in the same day, there have been orders and complaints, and I have been sent flying to all the wholesale chemists in town. Every time I brought the stuff back, there would be another paper telling me to return it, because it was not pure. This drug is wanted bitter bad, sir, whatever, for.”

    Sometimes just when we need the power of miracles to change our beliefs, they materialize in the places we'd least expect. They can come to us as a great change in our physical reality or as a simple coincidence in our lives. Sometimes they're big and can't be missed. Other times they're so subtle that if we aren't aware, we may miss them altogether. They can come from the lips of a stranger we suddenly and mysteriously meet at just the right instant. If we listen carefully, we'll always hear the right words, at the right time, to dazzle (目眩) us into a realization of something that we may have failed to notice only moments before.

    On a cold January afternoon in 1989, I was hiking up the trail that leads to the top of Egypt's Mt. Horeb. I'd spent the day at St. Catherine's Monastery and wanted to get to the peak by sunset to see the valley below. As I was winding up the narrow path, I'd occasionally see other hikers who were coming down from a day on the mountain. While they would generally pass with simply a nod or a greeting in another language, there was one man that day who did neither.

    I saw him coming from the last switchback on the trail that led to the backside of the mountain. As he got closer, I could see that he was dressed differently from the other hikers I'd seen. Rather than the high-tech fabrics and styles that had been the norm, this man was wearing traditional Egyptian clothing. He wore a tattered, rust-colored galabia and obviously old and thick-soled sandals that were covered in dust. What made his appearance so odd, though, was that the man didn't even appear to be Egyptian! He was a small-framed Asian man, had very little hair, and was wearing round, wire-rimmed glasses.

    As we neared one another, I was the first to speak, "Hello," I said, stopping on the trail for a moment to catch my breath. Not a sound came from the man as he walked closer. I thought that maybe he hadn't heard me or the wind had carried my voice away from him in another direction. Suddenly he stopped directly in front of me on the high side of the trail, looked up from the ground, and spoke a single sentence to me in English, "Sometimes you don't know what you have lost until you've lost it." As I took in what I had just heard, he simply stepped around me and continued his going down the trail.

    That moment in my life was a small miracle. The reason is less about what the man said and more about the timing and the context. The year was 1989, and the Cold War was drawing to a close. what the man on the trail couldn't have known is that it was during my Egyptian pilgrimage (朝圣), and specifically during my hike to the top of Moses's mountain, that I'd set the time aside to make decisions that would affect my career in the defense industry, my friends, my family, and, ultimately, my life.

    I had to ask myself what the chances were of an Asian man dressed in an Egyptian galabia coming down from the top of this historic mountain just when I was walking up, stopping before me, and offering his wisdom, seemingly from out of nowhere. My answer to my own question was easy: the odds were slim to none! In a meet that lasted less than two minutes on a mountain halfway around the world from my home, a total stranger had brought clarity and the hint of a warning, regarding the huge changes that I would make within a matter of days. In my way of thinking, that's a miracle.

    I suspect that we all experience small miracles in our lives every day. Sometimes we have the wisdom and the courage to recognize them for what they are In the moments when we don't, that's okay as well. It seems that our miracles have a way of coming back to us again and again. And each time they do, they become a little less subtle, until we can't possibly miss the message that they bring to our lives!

The key is that they're everywhere and occur every day for different reasons, in response to the different needs that we may have in the moment. Our job may be less about questioning the extraordinary things that happen in our daily lives and more about accepting the gifts they bring.

    FOR ALL the technological wonders of modern medicine, from gene-editing to fetal(胎儿的) surgery, health care—with its fax machines and clipboards(资料夹)—is often stubbornly old-fashioned. This outdated era is slowly drawing to a close as, slowly, the industry catches up with the artificial-intelligence (AI) revolution. And it should have happened earlier, argues Eric Topol, a heart doctor keen on digital medicine.

    Dr Topol's vision of medicine's future is optimistic. He thinks AI will be particularly useful for repetitive tasks where errors arise easily, such as selecting images, examining heart traces for abnormal symptoms or recording doctors' words into patient records. In short, AI is set to save time, lives and money.

    Much of this is imaginary—but AI is already defeating people in a variety of narrow jobs for which it has been trained. Eventually it may be able to diagnose and treat a wider range of diseases. Even then, Dr Topol thinks, humans would watch over the rules, rather than being replaced by them.

    The author's fear is that AI will be used to deepen the assembly-line(流水线) culture of modern medicine. If it awards a "gift of time" on doctors, he argues that this additional benefit should be used to extend the time of consultations, rather than simply speeding through them more efficiently.

    The Hippocratic Oath holds that there is an art to medicine as well as a science, and that "warmth, sympathy and understanding may be more important than the surgeon's knife or the chemist's drug". That is not just a cliché: the patients of sympathetic physicians have been shown to do better. As Dr Topol says, it is hard to imagine that a robot could really replace a human doctor. Yet as demand for health care goes beyond the supply of human carers, the future may involve consultations on smartphones and measurements monitored by chat robots. The considerately warmed stethoscope(听诊器), placed gently on a patient's back, may become history.

    Plastics remain one of the most - used materials for making many things. Things made of plastics can be very strong and last a long time. Plastics are also much lighter than metal and can easily be formed into different shapes. Plastics can take hundreds of years to break down on their own. And very few kinds are highly recyclable.

    A team of researchers working at the US Department of Energy says it has created a kind of plastic that could lead to products that are 100 percent recyclable. It recently reported the discovery in a study in the journal Nature Chemistry.

    The researchers say the new material is a plastic polymer (聚合体)called polydiketoenamine, or PDK. The team reports the material can be broken down in parts at the molecular (分子的)level. It can then be built up again to form plastics of different shapes, textures and colors. The researchers say this process can be repeated over and over again—without the plastic material losing any performance or quality.

    "Most plastics were never made to be recycled," lead researcher Peter Christensen said in a statement. " But we have discovered a new way to assemble plastics that takes recycling into consideration from a molecular perspective. "

    Many plastics have different chemicals added to them to make them more useful and powerful. The problem is that these chemicals attach to the monomers (单体), which remain in plastics even after the material gets processed at a recycling plant. The research team reported that, with the newly discovered PDK material, the monomers could be recovered and separated from any chemical additives.

    Next, the researchers plan to develop PDK plastics "with a wide range of thermal and mechanical properties. These plastics could be used for many kinds of cloth, as well as things such as 3D printed materials and foams. In addition, the team is trying to include plant - based materials in the process.

The Big Ben is located in the tower at the eastern end of the Houses of Parliament, Westminster, Greater London. It was designed by Edmund Beckett and Baron Grimthorpe.

The Big Ben is very famous throughout the world, but nobody really knows why it is called Big Ben. There are two hearsays about this. Some people say that it was named after Benjamin Caunt, a boxer, who was called Big Ben. More people believe it was called after Welshman, Sir Benjamin Hall. He was the commissioner(特派员)of the work at the time of its installation in 1859. A story was told that during a debate in the Commons on what to call the bell, Sir Benjamin was about to give his ideas when a MP who sat behind the front bench shouted, "Let's call it Big Ben!" Then this name came into being.

The bell hasn't gone through a smooth road since the beginning of its design. Because there was great disagreement about the design of the clock. It took fifteen years to build. In 1857, the bell was completed and tested on the ground, but a four-foot crack appeared and the bell had to be cast again. Finally, the clock started ticking on 31 May, 1859, and struck its first chime(报时)on 11, July. Then in September, the bell cracked again. It was silent for four years but was eventually turned a quarter of a revolution(旋转). In this way, the crack was not under the striking hammer. Craftsmen made a square above the crack to stop it growing longer and it can still be seen today.

The Big Ben is famous not only for its 13-ton weight, but also for its accuracy(准确性) which is a result of its precise mechanism(机械装置). Even one extra penny's weight on the balance will cause a gain of two fifths of a second in twenty-four hours. Although there have been several problems, the bell is still striking today. Its chimes can be heard all over the world on the B. B. C.