For decades, some cosmological studies indicated that the universe is younger than the oldest stars, an obvious impossibility. Wendy Freedman at the Carnegie Observatories in Pasadena, California, recently used the Hubble Space Telescope to determine how quickly the universe is expanding, then ran the picture backward to figure out when it all began. Her international team estimates the cosmos is 12 billion years old--almost exactly the age of the most ancient stars.
Does this end the age debate? Before, people were arguing whether it was 10 billion or 20 billion years old. Now we're talking about differences of a billion or two.
Why is it such a hard problem? To get the age, you need to know how fast the universe is expanding, so you need velocities and distances. Measuring velocities turned out to be easy, but measuring distances turned out to be much harder than anyone anticipated. There's dust between stars, which blocks light. If you don't correct for that, you get the distances wrong.
Why does it matter how long the universe has been expanding? The fact that we can measure an expansion rate at all tells us the universe had a beginning. There was a time when galaxies were close together, and before that there was the Big Bang. It touches on the question of where we came from.
What is the biggest unsolved problem in astronomy? We don't know how galaxies came to be. We have no idea about a time between roughly 300,000 and 1 billion years after the Big Bang, when the universe was very hazy. There were no stars yet, no galaxies yet. We have very little light available from that time. It's a "dark ages."
How will we ever learn about the dark ages of the universe? By looking at infrared radiation, astronomers can access a lot of this region. A new generation of telescopes planned for the next decade will go above the atmosphere, which blocks infrared radiation, and tell when the first stars and galaxies appeared.
What is your personal motivation for doing this kind of work? Part of the joy of being human is you ask questions and you discover--it's natural human curiosity.