Story posted October 04, 2011
The 2011 Nobel Prize in Physics, awarded to three U.S.-born scientists, made the day for astrophysicist Thomas Baumgarte, who chairs Bowdoin's Physics and Astronomy Department.
"I spent part of my lecture this morning explaining it to students," said Baumgarte, who researches black holes. "The impact of their discoveries is huge; it's hard to overstate that."
Physicists Saul Perlmutter, Brian Schmidt and Adam Riess overturned the longstanding assumption that the expansion of the universe was slowing down. Instead, the trio and their research groups discovered evidence of an accelerated expansion, driven by a mysterious force known as dark energy.
Baumgarte explains the import of their discoveries and takes us from the Big Bang to the Big Rip.
Q: What is the crux of this Nobel-winning discovery?
TB: We have known for a long time -- since Hubble's famous discovery about 100 years ago -- that the universe is expanding. But what we had not known until the late 1990's is the exact rate of the expansion and how this expansion changes with time. It is very intuitive to assume that the rate of expansion decreases with time. Imagine that you throw a marshmallow in the air. On the way up it slows down because of the gravitational pull of the Earth, right? By the same token, you would think that the gravitational attraction between galaxies leads to a slowing down of the expansion of the universe.
But what this research group discovered, to everybody's surprise, is that the universe's expansion is not slowing down. It's speeding up! It was kind of shocking when their results came out a little over 10 years ago -- the result is just as counterintuitive as suggesting that a marshmallow would continue to accelerate upwards after you throw it in the air.
Q: How does this change how we think about the universe?
TB: The bottom line is, we now know that we understand only about five percent of the matter that makes up the universe. Ninety-five percent is unknown; it is dark matter and dark energy. Dark matter is stuff that is somewhat mysterious in the sense that we can't see it. It could be a new elementary particle, for instance. People are building detectors to try to see it.
The biggest part, 70 percent, is made up of stuff called dark energy that is completely mysterious, really weird stuff. We don't have the slightest clue what it is but it is what makes the universe expand at an accelerating rate.
Q: So does this mean the Big Bang theory is being thrown out the window?
Peter Nugent '90 is an astrophysicist and senior scientist at Lawrence Berkeley National Laboratory, where Nobel-winner Saul Perlmutter conducts his research. Nugent recently spotted the closest Type-1a supernova in the last 25 years.
TB: No; the Big Bang refers to the big explosion in which the universe was born. The discovery of dark energy affects the end of the universe. Before this discovery, astronomers speculated about a Big Crunch, when the universe would collapse into itself again, a kind of mirroring of the Big Bang. With these new results, however, we know that that will not happen. The universe will continue to expand, at an increasingly fast rate. Galaxies will move away from each other and eventually will disappear from the visible sky. It is being called the Big Rip, suggesting that the universe will be torn to pieces. Of course, this is nothing immediate to worry about; you should keep paying your credit card bill.
Q: Do these findings have any effect on your research?
TB: Not immediately, because the effect of this expansion and the dark energy is important only on scales much larger than galaxies or even galaxy clusters. I work on black holes, which are much smaller than galaxies.
The big deal is that we just realized how little of the universe we understand. It means that it's a new puzzle that needs to be solved. It's a huge challenge for physics. These are subjects that are dear to my heart so I'm happy to see them in the spotlight.
Read Baumgarte's engaging 2009 Convocation talk about this subject, "A Curious Universe."
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