By David Shiga
Imagine trying to figure out what’s happening in a film from just a few scattered frames near the end. Now, let’s make it even more challenging: The star of the movie is invisible as you watch the rest of the characters going about their business. That’s what astronomers are up against in their quest to understand the cosmos.
The structures of the universe evolve so slowly from the human point of view that they appear as still images. To make matters worse, astronomers in the 1970s began to realize that most of the material in the universe is unseen. They called it dark matter. Just as blowing leaves suggest the presence of wind, the motions of visible matter such as stars and galaxies betray the gravitational pull of dark matter.