2009, THE INTERNATIONAL YEAR OF ASTRONOMY, MARKS 400 YEARS since Galileo introduced the telescope. UVic astronomer Chris Pritchet is part of the effort to commemorate the anniversary. He’s also a member of the recently completed Supernova Legacy Survey team. They used the Canada-France-Hawaii Telescope (above) to detect faint, distant supernovae. Their results could help explain our expanding universe.
How do supernovae, or exploded stars, change our view of the universe? About 80 years ago Hubble, and others, thought that if the universe was expanding it should be slowing down because of gravity. But in 1999, two groups of (supernovae) researchers showed that the universe wasn’t slowing down—it’s actually expanding faster and faster.
How did they prove it? Special classes of supernovae all have pretty well the same luminosity at maximum light. So if you look at a supernova and you can see where it is in the universe, based on how fast it’s moving away you can also measure its apparent brightness. It’s a chain of reasoning, but you can say how big the universe was at that cosmic epoch.
And so they’re like cosmic markers. Exactly. It’s basically a way of seeing how fast the universe was expanding in the past compared to today.
How can that expansion be explained? It means that the universe is filled with some remarkable property, dark energy (not to be confused with dark matter), which pushes out. Somehow the universe is creating dark energy. It goes against all the conservation laws that we know. The total energy content of the universe should be fixed. It’s not. It’s growing, basically as time cubed. So it’s a remarkable discovery.
So is it leading to more questions than answers? This is telling us something about physics that we don’t know about. It’s probably an indication of the most remarkable new physics in the past 70 or 80 years. If there is dark energy, then where does it come from, why should it be there, and why does it have the precise value that it does?
How does this all connect with your work? Ours is the largest sample of distant supernovae. We have the most precise measurement of the nature of dark energy. What we found is that dark energy is very much like something called vacuum energy, a certain type of dark energy that Einstein postulated in the early years of general relativity theory, then rejected. It looks like the universe is filled with this stuff.
So what’s next? I think the next thing people have to do is measure how the properties of dark energy vary with time, if at all. Dark energy, if it’s vacuum energy as Einstein postulated, then its properties should be invariant with time. If we see variation in the properties, then that would indicate that dark energy is something else.
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