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1. Where did you first learn about warm dense matter? Was it by doing experiments, or in a classroom? (Vardhan - California)
On my “Featured Scientist” page I mentioned plasma, which is a state of matter like a gas. In a plasma, the atoms—very small pieces that make up everything—are pulled apart into smaller parts called electrons and nuclei. Warm dense matter is another state of matter scientists have discovered that is kind of like a solid and kind of like a plasma. It’s dense like a solid, but very hot, so some of the atoms have lost their electrons like in a plasma. On earth we can only make warm dense matter for tiny fractions of a second, but scientists think warm dense matter is commonly found in the extreme environments of space, like the centers of giant planets like Jupiter.
I first learned about warm dense matter when I was working as an undergraduate research assistant! (An undergraduate research assistant is a college student who works in a research laboratory, often at the college or university where they go to school. This is usually one of the first steps on the road towards becoming a scientist!) It turns out that warm dense matter is very difficult for scientists to study using computer models. This is because warm dense matter is kind of like a solid and kind of like a plasma, but not enough like either one for computer models of solids or plasmas to give us very good answers. So, experimental physicists in my field have to make a lot of measurements of warm dense matter and give data to theoretical physicists so they can design better computer models.
During one of the first experiments I helped to perform, scientists were shooting one target with a high-power laser to make a beam of protons, then pointing the proton beam at a second target. Some of these protons would slow down in the second target, which actually made it hot enough to explode! But, if we studied the second target very soon after it got hot, it hadn’t had time to explode, meaning that it was at a high temperature but still very dense. So, we had made warm dense matter on Earth! The measurements we made of this warm dense matter will hopefully help theoretical physicists better understand how to study it with computer models in the future.
This cutaway view of Jupiter from SLAC National Accelerator Laboratory shows an artist's impression of the warm dense matter at its core. The pressure at the center of Jupiter is likely many millions of times greater than the pressure we feel on the surface of the Earth!