Imagine Magazine - Johns Hopkins - September/October 2011 - (Page 6)

In My Own Words Exploring the Dark Side of the Universe RISA WECHSLER, PhD Cosmologist Assistant Professor of Physics, Stanford University and the SLAC National Accelerator Laboratory Member, Kavli Institute for Particle Astrophysics and Cosmology When dr. Risa Wechsler looks up at the night sky, she sees more than stars. She sees a universe full of sweeping changes wrought over billions of years, a sky full of data useful for answering big questions. Her love of these big questions led her to physics and cosmology, and she now spends her days studying galaxy evolution to reveal the nature of dark matter and dark energy. The scientist as a middle schooler In middle school I liked math, but other topics, too. I attended summer programs at the Center for Talented Youth, where I took classes in math, of course, but also in world geopolitical structures and archaeology. Although I had broad interests, I had a pretty clear idea from middle school on that I wanted to be a scientist. I just wasn’t sure what type of science I was interested in. clear picture of what the universe is made of, but we did know that the universe as we know it couldn’t be explained solely by gravity acting on the visible mass. We now know that most of the universe is made up of something we can’t see with our eyes at all. The Earth is made mostly of oxygen and silicon, and the atmosphere is made mostly of oxygen and nitrogen. But the universe is made up of something completely different. Normal matter—consisting of all the elements on the periodic table—makes up only about 5% of the universe. Everything else is different from what you learned about in your standard chemistry class and from what you interact with in your daily life. Most of the mass in the universe is dark matter, and it’s called “dark” because it doesn’t emit or absorb light. We know by looking at the movement of stars in our own galaxy and the way the universe has evolved that there has to be more mass than we can see. Dark matter is pervasive in the universe. There was some evidence of the existence of dark matter in the 1930s, but it wasn’t widely accepted until the 1980s. Even then, we really didn’t know how large a contribution it made to the total contents of the universe. It’s only in the last 10 years or so that we’ve gone from dark energy and dark matter being hypothesized to where we have measurements of these various constituents accurate to the few-percent level. Dark matter makes up approximately 25% of the universe, and dark energy, a mysterious form of energy that might explain why the universe is expanding, about 70%. Finding my niche When it came to choosing a college, I was looking for a place where I would be challenged, have great peers, and have opportunities to do research. At MIT, a lot of students get involved in research quite early, so that was a good fit. The intensity of life at MIT was also very good preparation for a career in research. I was always interested in fundamental questions and originally thought about going into particle physics. But the big questions in cosmology—What’s the universe made of? How did it evolve?—appealed to me. I shifted my focus to cosmology toward the end of college and continued to pursue that interest in graduate school. A perspective measured in billions I’m working on figuring out how the universe works, including learning exactly what dark matter and dark energy are and how they act. Because we can’t see them, I study the cosmological structures they act on: galaxies, clusters of galaxies, and the universe as a whole. After the Big Bang, matter was evenly distributed in the universe. Today, though, stars and planets are not evenly distributed, and even galaxies are clustered because gravity pulls them together. Measurements of cosmic microwave background radiation have given us a very clear picture of fluctuations in the density of the universe, starting from about 400,000 years after the Big Bang. That’s the time frame I study: the last 13.2 billion years. Numbering the darkness When I started graduate school, we didn’t have a 6 imagine Sept/Oct 2011

Table of Contents for the Digital Edition of Imagine Magazine - Johns Hopkins - September/October 2011

Imagine Magazine - Johns Hopkins - September/October 2011
Contents
Big Picture
In My Own Words
Physics Is…
Making the Team
Nuclear by Nature
Physics: The Next Generation
Telescopic Views
Exploring the Mysterious Lives of Stars
Around the Universe in Three Weeks
Selected Opportunities & Resources
Book Buddies
Meeting the (Economics) Challenge
Off the Shelf
Word Wise
Exploring Career Options
One Step Ahead
Planning Ahead for College
Students Review
Creative Minds Imagine
Mark Your Calendar
Knossos Games

Imagine Magazine - Johns Hopkins - September/October 2011