Karl Gebhardt on dark matter and the expansion of the universe

Karl Gebhardt: Right now we have one of the greatest mysteries of our times. And as scientists, we have a responsibility to understand what that is.

That’s astronomer Karl Gebhardt of the University of Texas at Austin. He’s talking about dark energy. More than 70 percent of all energy in our universe is thought to be dark energy. But – though theoretical models say it should exist – astronomers have yet to detect dark energy.

Karl Gebhardt: What HETDEX is going to do, it’s going to look at an early time in the universe that has not been explored yet in terms of how fast the universe is expanding.

Gebhardt hopes to measure dark energy, through a project called HETDEX, the Hobby Eberly Telescope Dark Energy Experiment. The idea is that dark energy causes the expansion of the universe to speed up. HETDEX will peer at galaxies and supernovae over 10 billion light-years away, looking at the pattern of how they’re distributed.

Karl Gebhardt: Our universe is expanding, so that pattern’s expanding. So all you do, you measure that pattern at different times, and that tells you how fast the universe has expanded.

Astronomers expect that expansion rate to increase, due to dark energy.

Karl Gebhardt: And so when we have in our HETDEX survey a large sample of galaxies, we just make a map and we find the pattern. And we measure how large that pattern is, how large it appears to us, we compare it to what we know, and we’re done. That tells us how much our universe has expanded.

Gebhardt expects completion of the dark energy telescope by 2010.

The latest theory is that ever since the Big Bang, 13.7 billion years ago, our universe has expanded. Scientists expected that the gravity from all the universe’s matter created back then would cause that primal expansion to slow down. But measurements of supernovae suggest that the expansion is actually speeding up, fueled in a sense by dark energy.

Our thanks to:
Karl Gebhardt
Professor of Astronomy
University of Texas at Austin

June 6, 2008

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