In this series of posts, we sit down with a few of the plenary speakers of the 240th AAS meeting to learn more about them and their research. You can see a full schedule of their talks here, and read our other interviews here!
There is no doubt that modern astronomical surveys have completely revolutionized cosmology. For example, the Sloan Digital Sky Survey (SDSS) was the first to detect baryon acoustic oscillations using measurements of over one million galaxies. Professor David Weinberg, one of the early designers of SDSS, has almost that number of research interests. Weinberg was not only key in designing the main spectroscopic galaxy sample of SDSS; his research has changed our understanding of the chemical evolution of the Milky Way, galaxy formation, and the content and properties of dark energy and dark matter.
Weinberg is the Distinguished University Professor and Chair of the Department of Astronomy at The Ohio State University. He is the 2021 co-winner of the Dannie Heineman Prize for Astrophysics, for his essential contributions to facilitating, guiding, and participating in transformative science resulting from modern large-scale astronomical surveys at optical wavelengths, in particular SDSS. The title of his lecture at #AAS240 is “Asteroids to Reionization: The Broad Reach of Survey Astronomy.”
A Beginning Rooted in Popular Science Books
Weinberg first became interested in physics around age 12 through reading popular science books. One book that had a particularly significant influence on him was “One Two Three… Infinity,” by George Gamow. This book inspired him to continue reading other popular physics books and to take physics courses in high school. Weinberg notes that reading popular science books early on helped establish a strong foundation for his physics career. “I think the fact that I had read a lot of popular science books and history of science books was important for me because those first physics courses were kind of interesting… but they were a lot of work and a lot of solving equations about inclined planes. So it was really important that the popular science reading left me with some vision of where [physics] could lead to.” After high school, Weinberg would go on to receive his B.S. in Physics from Yale University and his Ph.D. in Astrophysics from Princeton University.
Following the Data
I asked Weinberg how he became interested in such a wide array of diverse research topics. He responded that he has always just followed the path laid out by observers and instrumentalists. “Specifically for theorists, in [choosing problems] and deciding what you are going to do in the next five years, looking to where the observations are improving is a good guide. Because it usually means that the current models that usually exist are not yet adequate. And in 20 years, [you should think about where] new instrumentation is going to allow big changes in the observational data five to ten years down the line– that’s a good opportunity to get in on a new project before other theorists realize that project is going to be important. So it’s super valuable to have instrumentalists who you can talk to and can learn from.”
More recently, Weinberg has been focusing on understanding the chemical evolution of the Milky Way using measurements from the Sloan APOGEE Survey, a high-resolution spectroscopic survey of 100,000 Milky Way red giant stars. His goal is to better understand the formation history of the Milky Way, and then connect that to the formation history of other galaxies. Last month, his paper on the star formation history of the Milky Way’s galactic disk was covered by astrobites! In summary, Weinberg and his collaborators used the ages and metallicities of Milky Way stars to try to infer its star formation history. As stars die, the heavier metal by-products of their explosions and pulsations are released into the interstellar medium where new stars are then born in more metal-rich conditions than older ones. This leads to a well-understood trend where younger stars are metal-rich and older stars are metal-poor. The authors used this relation to determine that most of the Milky Way disk stars we observe today were created during and after a massive star formation event 13 Gyrs ago.
Focusing on the Bigger Picture
Weinberg is also busy on the cosmology side, where he is investigating the S8 tension, a discrepancy between the level of clustering of dark matter measured from galaxy surveys versus from the Cosmic Microwave Background. This tension is not worrisome but exciting for Weinberg, who emphasized that one of the greatest (pleasant!) surprises of his career has been the incredible speed at which progress has been made in cosmology. Weinberg remembers, “When I was a graduate student, Lambda seemed like a possibility, but certainly a pretty extreme one. When I gave talks as a graduate student and postdoc in the late 80s and early 90s, I would start out with my list of what I considered the five main questions in cosmic structure formation. (1) Did cosmic structure form by gravitational instabilities? (2) If so, what were the initial conditions? (3) What is dark matter? (4) What is w? (5) What is the relation between galaxies and dark matter? And what’s particularly encouraging to me, having been in the field for 30 years now, is that to a large extent, most of those questions have been answered.”
Advice to Early Career Astronomers: Focus on your Writing!
Weinberg’s advice to aspiring scientists is to improve your writing skills early on. “My best advice to undergraduate physicists is to work on becoming the best writer that you can, because your product– the thing that lasts, is papers, and the quality of the papers has an effect on how impactful they are.. And being good at it makes a huge difference.” Weinberg remembers “the single most impactful class in college that he took in terms of its impact on him” was not a physics course, but a writing course, where they had to write one thing every day. And becoming good at writing early on really helped him succeed to this day. “Between papers, recommendation letters, and mostly emails, I probably write 1000 pages a year if I added it all up. So the ability to write something that is decent quickly has been super important.”
To hear more about survey astronomy, tune into David Weinberg’s Plenary Lecture at 4:40PM PT on Monday, June 13 at #AAS240!
Edited by: Katya Gozman
Featured Image Credit: AAS