This week the world’s largest general science journal, aptly named Science, takes a different and more humble tack, presenting a list of the 125 biggest quandaries that scientists have failed to fathom.

This catalogue of bewilderment, part of the journal’s 125th anniversary celebration, is the product of a months-long survey of more than 100 leading researchers in myriad disciplines, who were asked to focus on questions that have a chance of being answered in the next 25 years. Beyond offering a glimpse of the many nagging gaps remaining in the human knowledge base, it reveals the enormousness of scientists’ ambitions and the great versatility of the scientific method, which has proved so valuable as a way to make sense of the unknown.

“Reading through the questions gives a wonderful sense of all the incredibly intriguing things scientists are looking at these days,” said Colin Norman, Science’s news editor, who ushered the initial list of submissions through 17 versions to get it down to a mere 125.

Here is a sampling of the mysteries that scientists themselves most want to solve:

What is the universe made of?

The answer may seem obvious: matter and energy. But physicists who have been studying the details have some disturbing news. If you take every atom in the universe, and all the detectable energy in and around them, it adds up to less than 5 percent of what has to be out there, as determined by how the galaxies are behaving. Scientists have concluded that in addition to ordinary matter, there must also be “dark matter” — mysterious stuff that gets the universe up to about 30 percent full. That leaves 70 percent of the universe consisting of “dark energy,” a nice name for something that no one has a clue about.

A related question: Is ours the only universe? Many cosmologists suspect the answer is “no.” Ours may be just one of countless universes in a “multiverse” that is bubbling with big bangs. To settle that question, a related query will have to be answered in the affirmative: Is it even possible to know anything beyond our universe?

How much can the human life span be extended ?

Human life spans have stretched amazingly in the past few hundred years. In the 20th century alone, the average U.S. life span grew to 77 years from 49, an increase of more than 50 percent.

The longest any person is known to have lived is 122 years. That was Jeanne Calment, a Frenchwoman who died in 1997. No one knows why she lived that long (she smoked cigarettes until she was 97, when she quit for her health). Perhaps it was her wry sense of humor. Asked on her 100th birthday what kind of future she anticipated, she responded: “A very short one.”

In general, scientists reckon that longevity is the result of a unique combination of genetics and life habits, and they suspect that with attention to those things the average human life span can be increased substantially.

More here.