In the dark

Although cosmologists know a great deal about how our universe expanded and evolved over most of its history, they know relatively little about the first seconds that followed the Big Bang -- and next to nothing about the first trillionth of a second. When it comes to how our universe may have evolved, or to the events that may have taken place during these earliest moments, we have essentially no direct observations on which to rely. This era is hidden from view, buried beneath impenetrable layers of energy, distance, and time. Our understanding of this period of cosmic history is, in many respects, little more than an informed guess based on inference and extrapolation. Look far enough back in time, and almost everything we know about our universe could have been different. Matter and energy existed in different forms than they do today, and they may have experienced forces that have not yet been discovered. Key events and transitions may have taken place that science has yet to illuminate. Matter likely interacted in ways that it no longer does, and space and time may have behaved differently than they do in the world we know. With this in mind, many cosmologists have begun to consider the possibility that our failure to detect the particles that make up dark matter might be telling us not only about the nature of dark matter itself, but also about the era in which it was created. Buy studying dark matter, scientists are learning about the first moments of the Big Bang.