Given the inky blackness of space, I suppose it shouldn't have been surprising that we can't detect the parts of the cosmos that do not glow like the stars or radiate other types of energy. Cosmologists, observing galaxies rotating at speeds too fast to be possible given those observable components, have hypothesized unseen particles called dark matter.
What is it doing, and what is its composition? In “Mystery of the Hidden Cosmos,” Bogdan A. Dobrescu and Don Lincoln delve into the complexity of this unseen universe. Dark matter could contain a world of particles. Dark atoms and molecules could perhaps clump together into galactic disks that overlap with the ordinary matter disks and spiral arms of galaxies such as Andromeda. Experiments are under way with the aim of detecting such complex dark matter. “The real message,” Dobrescu and Lincoln write, “is that we have a mystery before us and that we do not know what the answer will be.”
The smiling people in the photograph are members of Scientific American's international family: the magazine is translated into 14 languages; its sister publication, the bimonthly Scientific American Mind, is translated into seven. Every year we try to gather to discuss how better to serve our readers and the global enterprise that is science. Interestingly, the first Scientific American translated edition was started when the magazine was already 45 years old—in 1890!—La América Científica é Industrial. That edition was eventually folded, and it was some decades before we firmly established a series of translations that we see today. Now it's hard to imagine it otherwise.