ONCE children asked why the sky is blue. Today Chinese children ask if time travel is possible and what are toxic food additives. A new set of science books has answers, reports Yao Minji.

German mathematician Georg Cantor (1845-1918), the inventor of set theory, famously said "asking the right question is harder than answering it."

Many Chinese people grew up reading "100,000 Whys," the most popular set of science books for children; more than 100 million books have been sold since 1961. At the time of the latest edition, published in 1999, the People's Daily called the popular set "a foundation of the country's shining castle of great scientists" and it was supposed to inspire a new generation of scientists.

The past decade has revolutions in many scientific fields, children have a lot more questions and now publishers want to answer them.

But general interest in science and reading has fallen off, so publishers face a big challenge in making the books appealing and in asking the right, intriguing questions.

A new edition, the sixth, is to be released late in 2012 or early in 2013, according to the Juvenile & Children's Publishing House in Shanghai.

For years the science books, aimed at students from fourth to ninth grade, were so popular and infuential that a very curious child was often given the nickname "100,000 Whys," like 31-year-old Lu Yufeng, a biochemistry researcher with a pharmaceutical company in Shanghai.

"I was the type of kid who asked a lot of questions in class," he says, and classmates teased him with the name. When he was in the eighth grade, he won "100,000 Whys" (1980), the fourth, 10-book edition, for getting the highest score in the final exam.

This summer he came across the books while he was cleaning and felt nostalgic. "The book was one of the initial forces that made science interesting to me when I was a boy and drew me into biochemisry," he tells Shanghai Daily.

Certainly, there were never 100,000 questions in any of the five editions, they usually answered 2,000-3,000 questions. The forthcoming edition will still answer the classics: Why is the sky blue? Why are clouds colored? Why don't the sun and moon fall down? How does a washing machine clean clothes? How did the universe begin? Does the universe have a limit?

The new edition will contain new questions asked in interesting ways, such as. "Why do scientists continue pursuing nuclear energy even after disastrous leak at Chernobyl and Fukushiima?"

Hong Xingfan, deputy chief editor of the publishing house, says questions were collected from several dozen schools and universities in Shanghai and they came up with more than 10,000 questions.

"The higher the students' grades are, the more boring their questions are," Hong observed, saying many students these days are too pressured and busy to be curious.

Editors say they were surprised about the shift in the type of questions and cited a great difference between questions asked today and those asked 10, 20 or 30 years ago.

Common questions today:

"Can I travel back in time?" "Why do I feel sad?" "Why do people put melamine into milk powder?"

They are still writing the answers.

These question show children have picked up a lot of scattered information from the Internet and television. The time-travel questions reflect the trend of extremely popular time-travel dramas, in which young people typically travel back into ancient Chinese history. They reflect a lot of misunderstanding, which editors hope to correct through fun, scientific explanations.

The melamine question indicate students are paying a lot of attention to the news and social media, generating questions like "Is 2012 really the end of the world?"

The famous series was first published in 1961, when the concept of popularizing science was almost unheard of. At that time, Chinese scientists and publishers agreed that science would become key to the nation's development and making science attractive to children in books was seen as a way to nurture the next generation of scientists.

The books answered questions about agriculture, animals, astronomy, biology, chemistry, engineering, geography and geology, mathematics and physics.

Questions were compiled from readers' letters and proposed by top Chinese scientists including Li Siguang (1889-1971), father of China's geomechanics; mathematician Hua Luogeng (1910-1985), famous for his works on additive prime number theory, and Mao Yisheng (1896-1989), structural engineering expert and pioneer of modern bridge engineering, among many others.

It was a tradition for the publisher to have noted scientists as consultants, who often suggested new fields of inquiry and reviewed answers.

The new addition will tap 100 top scientists from the Chinsese Academy of Engineering and Chinese Academy of Sciences.

When the fifth and latest edition was released on September 18, 1999, the line outside the Shanghai Book Town on Fuzhou Road extended more than 1,000 meters, looping several times around the large book store.

"That was the peak of '100,000 Whys' and the last prime time for science popularization books, when they had the largest market share in children's books," according to Hong, the deputy chief editor.

Market share and popularity of popular science books dropped rapidly after 2000, yielding to children's literature and comics such as the Harry Potter series and books by Chinese children's author Zheng Yuanjie (among all Chinese writers, he ranked No. 2 in income this year).

The rapid expansion of the Internet made it more convenient and faster to search for answers online, even though such answers, especially in science, can be wrong or not very accurate.

"Today's teenagers are used to searching answers and information through Baidu or Google, which poses a great challenge to the '100,000 Whys' series. It forces us to think about how to propose great and innovative questions with more accurate answers," says Yang Xiongli, a scientist from CAS and chief editor of the set's "Brain and Cognitive Science" book or installment.

A book about the brain and how it works is a new addition to the set, reflecting a huge number of children's questions about their feelings and state of mind, such as "Why do I get angry?" and "Why am I happy?"

Editors say many new questions reflect self-involved young people and they hope to answer them through cognitive science.

From the 1970s through the 1990s, there was great demand for scientists and engineers to help China modernize. A common saying at the time was "mathematics, physics and chemistry can help one travel around the world without fear."

Today, young people seem more intersted in business, finance and fields that generate high personal income.

The year 2000 was a low point for science publishing for children and young people.

"In the worse days, we had only four members in the science department. At its peak, '100,000 Whys' had a team of its own with more than a dozen editors," Hong says.

The publishing house had wanted to revise the books in 2008, but editors worried that children were experiencing information overload and were also overloaded by school work and pressured by high expectations.

"They are so pressured that they don't even have time or leisure to think about asking interesting questions. They are too busy to be curious," says Hong.

The new edition will have 4,500 questions in 18 book installments known as fascicules, as the first step. It hasn't been decided whether it will be available as e-books, but portions will appear online and a website will be set up for interaction and new questions. The publisher has a weibo (Chinese twitter) account for spreading science news and collecting questions.

Why? Why? Why?

Q: Are birds the dinosaurs that survived extinction?

A: When you see the huge and fierce tyrannosaurus, have you ever thought that it might taste just like chicken?

Tyrannosaurus mainly eat meat, can walk with two feet and run just like chickens run. This kind of dinosaurs may be closely related to birds. American scientists have discovered that its ankle bone is very similar to that of early birds. Canadian scientists have found the way they lay eggs also resemble that of birds. They lay eggs one by one rather than all once, like crocodiles. Dinosaur eggs are also more similar to bird eggs, with single-layered tough shells ...

Think about it, chicken and duck, used for our common dishes, may well be evolved dinosaurs, how do you feel about that?

Q: How is the armor of Iron Man made?

A: First, Iron Man's armor needs to be bullet-proof, which means highly dense materials. In the original comics, it is made of titanium covered with iron that has rearranged molecules similar to what we call a titanium alloy. It's very light and has steel-level density under normal temperature. It can stop small bullets, but not large bullets or canon balls.

Currently, the best used armor material is depleted uranium armor (DU armor).

Q: Is sugar the sweetest thing in the world?

A: First we discuss how we taste "sweetness." The human tongue contains a lot of taste buds, which are formed by special protein. Different taste buds can combine with different molecule and some do so with sugar, which generate neural signals to the brain. That is the taste of sweetness.

There is a standard of sweetness to meassure levels of sweetness. Cane sugar is the base, level 1, and the sweetness of other things can be discovered by comparing them with cane sugar. Usually, it takes a lot of people for the test. The test starts with pure water and sweetener is added gradually until half of the tested group can taste that the water is different.

We find that many sweeteners, natural or artificial, are much sweeter than cane sugar. For example, the serendipity berry from Africa contains a kind of protein called monellin with a sweetness level of 2,000 to 3,000.