One of the most common misunderstandings regarding cosmology is that people think of the universe as being extremely large and empty, with intermittent pockets of matter in the form of galaxies. Not true at all, and actually the exact opposite is closer to the truth.
From what we’ve been able to tell, the universe is actually *packed* with matter in the form of galaxies, dust clouds, and dark matter (the quantity of dark matter being a relatively recent discovery). So it was quite a suprise when NASA’s Wilkinson Microwave Anisotropy Probe (WMAP) satellite was running it’s study on the cosmic microwave background, and came up with a region nearly a BILLION light years across that was emitting almost no microwave heat – which means that simply nothing’s there.
I’m not sure yet what to make of this, but I’m sure there will be several thesis papers written on this topic in the coming year. Here’s the story from Dailytech.