Shedding Light on Dark Matter

摘要

The "stuff" that makes up the universe is mostly invisible. Matter that we can see or detect, such as the substances that make up the planets, stars, and interstellar dust, comprises only 4 percent of the total. The rest of the mass in the universe, most scientists believe, consists of dark matter—matter of unknown composition that does not emit or reflect electromagnetic radiation and is therefore difficult to observe directly. Determining the nature of this "missing mass" is one of the most important problems in modern cosmology and particle physics. Several kinds of particles have been proposed as dark-matter candidates, and many experiments and searches are under way to detect them. One candidate is some kind of a weakly interacting massive particle (WIMP). Because WIMPs do not interact with electromagnetism or interact strongly with matter, they are nearly impossible to detect directly.