Science presents the great unsolved scientific mysteries of our time

Special issue marks the journal's 125th anniversary

What is the universe made of? What is the biological basis of consciousness? Can the world continue to sustain a growing population and growing consumption? In celebration of its 125th anniversary, Science has taken stock of some of the most important, yet-unanswered scientific questions and delved into 25 of them for a closer look at just what we do and don't yet know about our universe.
Questions like these show us how far science has come in explaining the natural world, and they also fuel the discoveries of the future, writes author and journalist Tom Siegfried in an introduction to the special 1 July issue of Science, published by AAAS, the nonprofit science society.