Have you ever wanted to travel back in time? What about traveling into the future? There's an easy way to do it. One way you can make a time travel journey is by writing a letter to your future self to be opened in the future. To your future self, the letter will be a visit from the past. 

    What can be gained by writing a letter to yourself? Depends on how good your letter is. You have the chance to say something to your future self. What would you want to say? You'll be able to talk to yourself 5,10,15 years down the road. There may be instructions for your future self, or you may have goals that you will want to reach.

    There are a lot of things you could include in your letter or letters to yourself. The more you include, the better the letter will be to you. Be creative with what you put in your letter. Include a picture of yourself or family to show the period from which the letter came.

    You can store your letter in many different ways. You can give your letter to a friend or family member to keep and mail to you. If you can get others to take part, have them write letters to themselves as well and ask someone to be the letter holder until it's time to send the letters. You can also use a service online to store your letter and e-mail it to you. Ready to write to yourself two and a half years down the road?

Paris

Passengers carried per day: 4.4m

Cost of ticket: 80p flat fare

Length: 131 miles    Lines: 14   Stations: 297

    In Paris there are pleasures for those who use the Metro(地铁) — many of them artistic. The graceful Art Nouveau dragon-fly entrances are just the most noticeable on a Metro system which celebrated its 100^th anniversary by spending 30 million francs (£2.9million) on making its stations works of art. On my way home I pass Bonne Nouvelle station in the heart of Paris's cinema district. There, during the cinema festival this summer, special lighting effects dot the platforms and films are projected onto the large advertising boards.

    More than anything the metro is efficient. “When I worked on line 4”, says a retired driver, “we had exactly 30 minutes and 15 seconds to complete the journey. If it took any longer, they cut our pay.” But there are problems. Many Metro stations have too many stairs, and changing lines at big interchanges(交换) can be tiresome.

Moscow

Passengers carried per day: 9m

Cost of ticket: 12p

Length: 164 miles    Lines: 11   Stations: 162

    The first underground passage for the Moscow Metropolitan started in 1932. Three years later the trains started running. They haven't stopped since— every 90 seconds or two minutes during rush hour, every five minutes the rest of the time, from 6 a.m. till 1 a. m. There may be a crowd of people but there is seldom a wait.

    The trains take you through spacious and spotless stations. For tourists it's a major sightseeing attraction: from Russian Art Deco to neo-classical, the Metro stations are not to be missed.

Tokyo

Passengers carried per day: 7m

Cost of ticket: 90p ~ £1.68

Length: 177 miles    Lines: 12   Stations: 209

    Trains do not just arrive on time in Tokyo. They stop right on the platform mark so that passengers can line up knowing exactly where the doors will open. Train driving is a respectful job for life, for which the applicants must pass a strict screening of health checks, interviews and written exams before they can put on the enviable uniform, cap and white gloves.

    However, overcrowding means it is far from perfect. At rush hours, some stations employ part-time platform staff to push in passengers. Carriages can be filled to 184% of capacity(容量). The main reason for such conditions is that the Tokyo subway station system has only 15 miles of track for every 1 million people, compared to 36 on the London Underground. New lines are under construction, but at a cost of £500,000 per meter of rail. Progress has been slow.

Mexico City

Passengers carried per day: 4.2m

Cost of ticket: 11p flat fare

Length: 99 miles    Lines: 11   Stations: 175

    Fast, relatively safe, and very cheap, Mexico City's underground is an ideal place of order and efficiency compared to the disorders above. The Mexican capital's underground system is the biggest in the continent and one of the most subsidized (获得补助的) networks in the world.

    The first trains leave the station at 5 a.m. and the last after midnight as the crowd move from the outskirts of the 20 million-strong megacity (大城市). Mexico City's Metro also attracts a sizeable group of passengers who are unwilling to spend hours in traffic jams. There is a master plan to build new lines and extend existing one, but financial constraints (约束) complicated by the fact that the system runs through different jurisdicitons (管辖权) mean progress is slow.

    Once upon a time, there was a beautiful bird, which was very curious about hell. When she was little, her mother always told her that if she didn't master the flying skills, she would go to hell. She was so curious about hell that she always asked others what hell looked like, but no one was sure, because none of them had ever been there. Some said hell was a place full of water, and others told her that hell was full of burning fire. However, the bird knew they were lying. She wanted to find out what hell was.

    When other birds were learning flying skills, she always hid herself and watched them. She thought in this way she could go to hell and see what hell looked like. However, she spent so little time learning flying skills that one day she was caught by a little boy. The little boy gave her to his grandpa in the countryside as a gift. The old man liked her very much. He made a delicate cage and put her in it. The bird was very worried because she thought she couldn't find out what hell was like staying in this small cage. However, she couldn't escape. Day after day, she just stayed in the cage, watching other birds flying. She lost her freedom and she became sadder and sadder. At last, she became ill. The old man finally opened the cage, but she was too weak to fly. Lying on the ground, she thought of the question that she ever asked all the time.

    “What does hell look like?”

    “Hell is a small well-decorated cage.” Before she closed her eyes forever, she finally answered that question herself.

    At 27, after serving in World War II, I dreamed of owning a piece of land. So I moved from central Illinois to Shelbina, Missouri, and bought 236 acres for $6,000. The land was situated on a dirt road and was half farmland and half trees, with an old house that had no running water or electricity. Obviously, it was not what you'd call a perfect farm. But it was mine.

    I was alone for the first time in my life, and I found it liberating. My days were filled from dawn until dusk with plowing and planting corn. Dinnertime came and went, and I barely remembered to eat.

    I wouldn't say I was a great success at farming in Missouri. However, when I went to the store to buy some tools, I met a nice woman named Claudette working behind the counter. I also ran into her at St. Mary's Catholic Church in Shelbina each week. I found out later that her manager kept asking her about “that tall boy from Illinois living out in the country in an old house with no water, no electricity and no housekeeper.”

    Claudette and her sister soon visited my farm and put up some curtains. To show my appreciation, I took Claudette out for a ride in my truck. We married in 1954 and have now been together for more than 62 years!

    I later sold the Missouri farm for a $3,500 profit and bought 40 acres in Illinois. For many reasons, buying the Missouri farm was a good idea. I will always cherish memories of owning the farm and meeting my beloved.

                                       Cell phones：Is there a cancer link?

    Could your cell phone give you cancer? Whether it could or not, some people are worrying about the possibility that phones, power lines and Wi-Fi could be responsible for a range of illnesses, from rashes to brain tumors.

    Some say there is evidence to support the growing anxieties. David Carpenter, a professor of environmental health sciences at the university at Albany, in New York, thinks there's a greater than 95 percent chance that power lines can cause childhood leukemia (白血病). Also there's a greater than 90 percent chance that cell phones can cause brain tumors. “It's apparent now that there's a real risk, ”said Carpenter.

    But others believe these concerns are not justified. Dr Martha Linet, head of radiation epidemiology (流行病学) at the US National Cancer Institute, has looked at the same research as Carpenter but has reached a different conclusion. “I don't support warning labels for cell phones, ”said Linet. “We don't have the evidence that there's much danger.”

    Studies so far suggest a weak connection between EMFs (电磁场) and illness—so weak that it might not exist at all. A multinational investigation of cell phones and brain cancer, in 13 countries outside the US, has been underway for several years. It's funded in part by the European Union, in part by a cell phone industry group. The final report should come out later this year, but data so far don't suggest a strong link between cell phone use and cancer risk.

    Alice Moore is a teenager entrepreneur (创业者), who in May 2015 set up her business AilieCandy. By the time she was 13, her company was worth millions of dollars with the invention of a super-sweet treat that could save kids' teeth, instead of destroying them.

    It all began when Moore visited a bank with her dad. On the outing, she was offered a candy bar. However, her dad reminded her that sugary treats were bad for her teeth. But Moore was sick of missing out on candies. So she desired to get round the warning, "Why can't I make a healthy candy that's good for my teeth so that my parents can't say no to it?" With that in mind, Moore asked her dad if she could start her own candy company. He recommended that she do some research and talk to dentists about what a healthier candy would contain.

    With her dad's permission, she spent the next two years researching online and conducting trials to get a recipe that was both tasty and tooth-friendly. She also approached dentists to learn more about teeth cleaning. Consequently, she succeeded in making a kind of candy only using natural sweeteners, which can reduce oral bacteria.

    Moore then used her savings to get her business of the ground. Afterwards, she and her father secured their first business meeting with a supermarket owner, who finally agreed to sell Moore's product-Cancandy.

    As CanCandy's success grows, so does Moore's credibility as a young entrepreneur. Moore is enthusiastic about the candy she created, and she's also positive about what the future might bring. She hopes that every kid can have a clean mouth and a broad smile.

    Meanwhile, with her parents' help, Moore is generally able to live a normal teenage life. Although she founded her company early on in life, she wasn't driven primarily by profit. Moore wants to use her unique talent to help others find their smiles. She donates 10% of AilicCandy's profits to Big Smiles. With her talent and determination, it appears that the sky could be the limit for Alice Moore.