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Credit: Jean Lachat
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Interview of Wendy Freedman by David Zierler on December 21, 2020,
Niels Bohr Library & Archives, American Institute of Physics,
College Park, MD USA,
For multiple citations, "AIP" is the preferred abbreviation for the location.
Interview with Wendy Freedman, John & Marion Sullivan University Professor and senior member of the Kavli Institute for Cosmological Physics at the University of Chicago. She recounts her childhood in Canada, her early interests in science, and her decision to attend the University of Toronto, where she developed an interest in astronomy. She cites the Canada France Hawaii Telescope as the reason she stayed at Toronto for graduate school to work under the direction of Barry Madore. Freedman describes her postdoctoral appointment at Carnegie Observatories to work on the Cepheid distance scale, and she explains her decision to accept a position on the permanent staff at Carnegie. She narrates the origins of the Hubble Space Telescope Key Project, and she explains the resistance among theorists regarding the existence of the Hubble constant. Freedman discusses the importance of CCDs to measure the Hubble constant, and she marvels at Hubble’s long and productive life. She explains the inspiration for starting the Giant Magellan Telescope as an international collaboration, and she explains the opportunities that led to her becoming director of Carnegie. Freedman surveys the cooperative nature between the GMT and LSST projects and she projects optimism that GMT will propel fundamental advances in black hole research and for the search for exoplanets and possible for life beyond earth. She explains her decision to join the faculty at Chicago and she expresses pleasure at being able to work with students as a professor. At the end of the interview, Freedman reflects on the increasing complexity and expense of large-scale astronomy research and why it is important that the astronomy community relates its work and discoveries to the broader public.
Okay. This is David Zierler, oral historian for the American Institute of Physics. It is December 21st, 2020. I’m so happy to be here with Professor Wendy L. Freedman. Wendy, it’s great to see you. Thank you for joining me today.
Thank you, David. It’s great to see you to put a face to the name!
Alright, so to get started would you please tell me your titles and institutional affiliations and you’ll see that I pluralized both because I know you have multiple.
I am the John & Marion Sullivan University Professor at the University of Chicago. I am also a senior member of the Kavli Institute for Cosmological Physics at the University of Chicago. And I was formerly at the Carnegie Observatories in Pasadena for thirty years. And for the last eleven, I was director of the Observatories. That probably covers it.
When did you step down as director of the Observatories
I stepped down September 1st, 2014. That was actually thirty years to the day that I began as a Carnegie Fellow in September 1984.
Have you remained connected with the Observatory since, in the last six years?
I’m certainly in contact with people there, but I have no formal affiliation with the Observatories. I’m now with The University of Chicago.
And the chair at Chicago, who is or was John and Marion Sullivan?
They were donors to the university. I don’t know them personally. The position that I hold is a University professorship. When I was hired there were, I believe, eight of us at the time. So, it is an unusual position. Even though as my son likes to joke, everybody at a university is a university professor (laughter).
Did the Sullivan’s have any particular connection with astronomy or astrophysics as far as you know?
Not to my knowledge. No.
Well, Wendy, let’s take it all the way back to the beginning. Let’s start first with your parents. Tell me a little bit about them and where they’re from.
Okay. Well, I grew up in Canada. My parents both were from Canada. My father grew up in Toronto and my mother grew up in Hamilton, forty miles away. I was lucky in my childhood. My parents and my siblings and I had a wonderful family existence together. My mother is very artistic. A very talented writer and artist and musician. She was a pianist when she met my father. A concert pianist. She gave that up when the children came along. And then later in her life she took up writing. She always has had an artistic bent. And now, in her eighties, she’s taken up oil painting. And I inherited none of that (laughter).
She’s incredibly talented in many different ways. My father always had a curiosity about science. He was a medical doctor, a psychiatrist. And I’m sure that from him I inherited my curiosity, and he certainly fostered my interest in science. I have one brother and one sister. I was the oldest of the three of us. And I think to this day my sister remains my best friend. So, way back to the beginning. Our house was filled with music, I think because of my mother initially. But also, my father loved music. We all played instruments. And we all played them together. Not in a particularly serious way, we just had fun together. And then we all liked the outdoors. We did a lot of things outdoors together. We played sports. Football, hockey. We would go fishing. My father insisted that we all had to hook our own worms (laughter).
You’re going to do it and you’re going to do it for real (laughter).
And we would eat the fish. My mother would fry up what we caught. Later we all developed a passion for ice skating and pond hockey. So, with my father into his eighties, we all played ice hockey together. I was lucky growing up. I had a very happy childhood, I guess I would say.
Wendy, how many generations back does your family go in Canada?
One grandmother was born in Hamilton. Her parents came from Russia, originally. And then my other three grandparents all came from Europe and settled in Canada. And so, that was part of the closeness of our family. We were very close to my grandparents. And I was fortunate to have all four grandparents into adulthood. They all lived long lives. Two of them into their nineties, one past a hundred. So, I got to know them as an adult, which was also really nice. We all celebrated holidays together and ate a lot of good meals (laughter). My maternal grandfather became a dentist, an endodontist. He was actually the first endodontist in Canada, apparently. My paternal grandfather was a tailor. He had come from Russia. Interesting story. His father was a salesman and once, traveling between villages, he encountered a Cossack who slashed him with a long sword. He died from the infected wound. And my great grandmother had to raise my grandfather and his brother supporting herself by baking bread for a prison. Eventually she was able to bring them to Canada. We lost all of my maternal grandmother’s family. They lived in Poland. They were taken to concentration camps. So, we lost that part of the family. And then my maternal grandfather was from Romania. I guess I’m quite a mixture of European ancestry. And a second generation Canadian.
Wendy, growing up, how Jewishly connected was your family?
Religiously connected, I would say not at all. I had no formal Jewish education. But as a family, we celebrated all the holidays. It was part of what we did together as a family. We celebrated holidays together with my grandparents and enjoyed lighting Hanukkah candles and that kind of thing. But I did not grow up with religious training. It wasn’t a religious family.
What kind of medicine did your father practice?
Psychiatry. As he described it, it was his way, because he was very interested in science, to keep learning. But in those days, becoming a scientist wasn’t a practical thing. After growing up in the Depression, it was not something that he was encouraged to do. But I think he later encouraged me to pursue science because he hadn’t had that opportunity to do that. I think he really enjoyed what he did. And certainly, he was very well thought of in his profession.
And speaking of opportunity. For your mother being an accomplished concert pianist, did you understand that when she gave up that career to raise a family, how much of that decision making was simply a product of the times? In other words, had she come of age later on, would she have been able to square that circle and maintain her career while having a family?
I think it was certainly one hundred percent a product of the times. Later in life she went back to the piano. She was enormously talented. And I think at a different time she would have pursued a career. But she and my father had an incredible relationship. So, I don’t think it’s something that she regrets. I’m sure at some level she wonders what could have been. But I think she’s had a very happy life pursuing her talents. I think in the sixties, when I was a teenager and embarking on—and my sister also— on our careers, that’s when the women’s movement really started to take hold. In the seventies though, I think there were regrets. Suddenly there were opportunities there for young women. And in her day when she was in university, there just weren’t those opportunities.
Wendy, when did you start to get interested in science yourself?
Certainly, as a young child. Again, being fostered by my father. At various times he got me a microscope of my own, and a chemistry set. And I would spend hours down in our basement pricking my finger looking at blood cells and insects and just making slide sections of worms and anything I could get my hands on. I loved that. And all sorts of smelly chemicals and various things. And so, I did have a very early interest in science. I know I was interested in astronomy very early on. But it wasn’t something that I thought of as a career as a child. I wasn’t one of these people who ground my own mirror and knew at age seven that I wanted to be an astronomer. It came much later. I didn’t know there was such a thing as an astronomer. Even though I’d go to the library and read. I read every book on the shelf about astronomy as a kid. So, I was really interested in it. But I didn’t know anybody who was a scientist. I certainly didn’t know how to become a scientist. It was just something I was interested in.
In terms of cultivating your interest, certainly not within your own family, but I’m curious as a girl, societally, were you ever made to feel that science was not something appropriate for you?
Oh yes. One example, I remember that there was no requirement to take math in high school. And my sister wanted to drop math, but my father would not allow it. “You will take it.” And I remember that I thought it was strange that a lot of the girls opted not to take math. And then, the first time I took physics, which was as we called it grade ten in Canada, the physics teacher was not encouraging to the girls. I think he had the expectation that we wouldn’t need it. So, when he would start to get into a subject and get into the technical aspects of an issue, he actually would make the statement, “The girls in the class don’t have to listen to this.” So, yes, that was not encouragement.
Certainly, my grandparents thought I was nuts when they began to realize that I was serious and turned to science. It was just not something that a girl would do. And they were certain that it would destroy my life (laughter). And no one would ever want to marry me, etc. So, you get all sorts of messages that are not exactly supportive. And I didn’t, as I said, have any examples of people who were scientists. I didn’t know how you would become a scientist. So, it really wasn’t until later as I went along and then learned what the steps were that it began to occur to me that I could be a scientist. But I was very fortunate in grade twelve to have a physics teacher who had a master’s degree from Oxford and he was just a phenomenal teacher. High school for me was for the most part pretty boring. And to some extent it was that I wasn’t being challenged until I had twelfth grade physics. It was the first time that I was really forced to think and to reason things through and to try and solve something that was really challenging. And that clearly had a huge impact and really helped to propel my scientific journey forward. But I didn’t see it at the time. At the time, during high school I loved everything, really.
I loved history, I loved math, I loved science. I didn’t take philosophy, but my parents had a library where there was pretty much everything. History books, philosophy, all my father’s medical books. Literature. We were all really avid readers in my family and so, that was a large part of my education. The school stuff was kind of secondary and not very interesting until I found physics. And I loved biology and by the end of high school, I finally figured out that I wanted to do science. And part of the reason was that in ninth grade English, we had a poetry section and the teacher was very religious and so her interpretation of poems was in that context. Then in grade eleven, we did a lot of the same poetry with a different teacher and she was a hippie, flower child teacher (laughter). And everything was about love and the sixties and seventies and your grade depended on interpreting these poems in the way the teacher thought. And what I really loved about math was two plus two was four no matter who your teacher was. And that really appealed to me (laughter).
So, when I went off to university, I had the expectation that I would study science. I thought I would major in biophysics because I liked both biology and physics. But through Mr. Bowers, my twelfth-grade physics teacher, I had done a project on astronomy. So, the interest in astronomy was there. It just never occurred to me that it would be something that I would do as a profession.
Wendy, did you go to public school throughout your childhood?
Yes, throughout my childhood. I went to public elementary and high school. I was really fortunate in having a group of peers from elementary school right through high school that I was very close to. They were smart kids. Often I learned more from peers than from the teachers. Some of us even went on to university together.
And was University of Toronto an easy choice both because it’s such a top ranked school and it’s nearby. Was that basically the consideration for you?
Yes, it’s very different, I think, than the U.S. Certainly at that time. We went to grade thirteen in those days in Canada. And if you had an eighty percent or more average, you were automatically accepted- you would get into the University of Toronto. And my grandfather had studied at the University of Toronto. My father had gone to the University of Toronto. It was the best university in the country. My friends who were going on to university were going to University of Toronto. It just never occurred to me to apply somewhere else. It just didn’t (laughter).
It makes a lot of sense why you would start in biophysics to sort of split the difference between your dual interests in biology and physics. How then did you get an interest and develop an expertise in astronomy?
So, as I said, I had this interest at an early age. Then, in the twelfth grade, my physics teacher lent me a telescope which was the first time I’d ever had a telescope to use. And I wrote a report on the origin of the solar system. I don’t quite recall how I came upon that topic. But I loved it. It was one of the best things that I did in high school. It got me reading. And then, because I was interested in astronomy, I took freshman astronomy. I had a really good professor in my introductory course. Bill Clarke. He was just a phenomenal lecturer. He's the Clarke of Clarke Publishing—
—a member of the Clarke family. But his interest was astronomy. I believe he was part-time. But he was a phenomenal professor. When we were accepted to the University of Toronto, there was a day for high school students to go visit. And there was a lecture by a person on the faculty by the name of Tom Bolton. He was involved at the time in observations of the Cygnus X-1 system that turned out to be a black hole. He gave a talk on black holes. And I was just so excited. Because high school overall had been so boring, I felt like I get to go to university and it was kind of mind blowing for me. And university was like that for me. It was very exciting after high school. I really enjoyed it.
And so, I took astronomy. And then I took a biology class which turned out to be huge. And it was full of pre-med students. And it was taught in the Convocation Hall, which held, I don’t know, a thousand or two-thousand people. It was giant! And then the lab, we did with a headset. And we would go around to a lab bench with a headset. And the TA that I had was bored to tears. He just didn’t seem to like what he was doing (laughter). And on the other hand, I had a TA in astronomy, Steve Shore, who loved what he was doing and was excited about what he was doing. He’s the person that I learned about graduate school from- he was in graduate school. And I’m serious, I didn’t know what graduate school really was at that point. But he encouraged me to start thinking about it and said, “You’ve got some aptitude here. You should really be thinking about graduate school.” And that was the first time it ever was presented to me that, oh, Maybe there’s a step after university. I didn’t know where I was going to go other than that I was being encouraged to study what I was interested in. So, then I switched my major to astronomy and astrophysics, after that.
And Wendy, I’m curious, it’s a very institution-specific answer. So, at Toronto, administratively and intellectually, what was the divide between astronomy and astrophysics?
Well my degree is technically in astronomy and astrophysics. So, I think there really wasn’t much of a distinction. Astronomy is the application of physics to the broader universe. But historically a lot of people at Toronto had studied stellar astrophysics or stellar astronomy. And it didn’t have that much extragalactic focus. There was the astronomer Sidney van den Bergh who had done extragalactic work and Barry Madore, who became my advisor, and was a student of Sidney van den Bergh’s. And then Ray Carlberg, who was a postdoc at the time I was at graduate school, was working on N-body simulations. So, there were a few people there. And by the time I was a senior, my interests had really turned to extragalactic astronomy and the beginning of an interest in cosmology. The physics classes were very good. And my astronomy and astrophysics degree essentially was one lab short of a physics degree. I think I got a good education. I know I got a good education. And further, I really enjoyed it. It was, as I said, a huge contrast to high school.
And when you started to think about graduate school, did you get any advice about possibly moving beyond Toronto and seeing the broader world out there?
Well, it’s interesting. I think Toronto—it may be different now—tried to hold on to its best students. I did try and do something a little more at that point. And because I was interested in star formation and I had done these projects, I applied to Yale for graduate school. And got accepted. Which amazed me because, again, thinking beyond University of Toronto at that point was just not something that I was contemplating. And what convinced me to stay was the Canada France Hawaii Telescope, the CFHT. It was just about to be commissioned. It was a 3.6-meter telescope. It had incredible resolution. Mauna Kea is a 14,000 foot peak. The seeing was phenomenal and Canada had a partnership in this exciting, new telescope and Yale did not. And so, for me it was, okay, here’s this incredible opportunity. I did agonize over it though. The draw to Yale was strong. But, in answer to your question. Toronto really fought to keep me. And in fact, it was embarrassing for me, though it makes sense for institutions to try and hold on to, and encourage people, that they want. But that for me was new, to have two institutions and people from both institutions saying, “You don’t want to go there!” and “No! You don’t want to get there” (laughter).
And did you know if you stayed at Toronto that Barry would end up being your advisor? Was that part of the plan from the beginning?
No. I think again, in retrospect, it was because he was doing extragalactic work. And that’s where my interest resided. But, no. It wasn’t at that point. It was the opportunity to observe at CFHT.
Another question in terms of your undergraduate outlook. By the time you were ready for graduate school, how well formed were you in terms of pursuing theory or experimentation?
In my mind I wasn’t. I liked them both. I really enjoyed theory, but I think somehow when I began using telescopes and designing projects, it was a clear path again. I did a project with Ray Carlberg in graduate school. At the time he was working with someone by the name of Jerry Sellwood who had an N-body code. A rather sophisticated N-body code. And I kept asking Ray, “Well, what happens if you put gas into this?” It was N-body, just gravity. And he kept saying, “Oh, gas is just a tiny, little component. It’s not going to have much of an effect.” But my feeling was, okay, but it started off mainly as gas. And gas is dissipative. And what happens when you put a dissipative component into an N-body code? So, we started to play around with that and it did have an effect on the spiral arms of these spiral galaxies. The spiral arms were exerting a torque. And the gas was dissipative. It was cooling and the stars were acting only via gravity. So, it was a really interesting project and I really enjoyed it.
But, once I started my dissertation my interest in star formation and the coming on line of the CFHT became more pressing. The CFHT has a really wide field of view. It’s about a degree field of view. And as I said, it’s superb seeing half an arc second seeing that was unheard of in other observatories at the time (laughter). And a large aperture. It was an opportunity to study star formation in other galaxies. And I was interested to know whether the initial mass function was universal. The initial mass function is the distribution of mass for stars that form in a given volume at a given time within a galaxy. There had been all sorts of claims that the initial mass function changes from galaxy to galaxy and from environment to environment. With CFHT we could study galaxies that are nearby where we can resolve individual stars and measure directly what is happening. But as we go to distant galaxies, we don’t have the resolution to do that and we get only an integrated measurement. And so, with CFHT, it was possible to measure thousands and thousands of stars within an individual galaxy because of this wide field, galaxies in the local group like Andromeda and M33 and many others. When I started at CFHT, the only instrument they had available at the time was a photographic camera with glass plates as the detector. It had an amazing one-degree field of view.
And so, I started a study of nearby galaxies. And then to measure the photographic plates, I used an automated plate measuring machine that had been developed by Ed Kibblewhite, who later ended up at University of Chicago. But he was at Cambridge, England at the time. So, I spent a couple of summers as a graduate student using this automated plate measuring machine to measure thousands of stars. Before, people had measured maybe twenty stars or thirty stars per galaxy, and in some cases claim differences in the IMF that weren’t statistically meaningful. But then CCDs came online right toward the end of my thesis. Earlier, calibration of photographic plates was always an issue. This was one of the issues that Hubble and Sandage had in their Cepheid photometry, and this became clear as a result of getting CCD photometry of the Cepheids. So rather than just point anywhere in the field of these nearby galaxies, to calibrate the plates I got CCD phototometry of Cepheids in these same galaxies in which I was studying star formation. I was then able to measure, for the first time, the period luminosity relation, which we now call the Leavitt Law, as a function of inverse wavelength.
Now, photographic plates were sensitive to blue wavelengths. And it wasn’t possible to accurately correct for the presence of dust in these galaxies. It is sort of amazing when we think about it now. Gérard de Vaucouleurs was worried about reddening, but the photographic data weren’t good enough to make accurate corrections. And Allan Sandage did not correct for reddening at all. And so, using CCD detectors, which were sensitive to both blue and red wavelengths, what I found was that if you plotted the distance modulus from the B band all the way out to the I band, that is, B, V, R, I., the distance modulus to the galaxy was different in all of those bands. But not in an arbitrary way. When plotting as a function of inverse wavelength, the distance modulus decreased as you went into the near infrared. And if you fit what we know as the interstellar extinction law, you could correct for the amount of dust. And so, it very rapidly became clear that one, there was a problem with the photographic photometry because photographic plates are nonlinear and the calibration of them was really tough. And unlike the new detectors, it was not possible to obtain multiwavelength data. But with CCDs, for the first time, you could correct for the reddening. So, when I started, there was a fierce debate over the value of the Hubble constant, about whether it was fifty or one hundred. So, it was unknown to a factor of two. And most of the difference turned out to be for the nearby galaxies, a result of both the calibration of the photographic plates and reddening.
With CCDs being linear detectors, you had the ability to make much more accurate measurements. And with the wavelength coverage you could correct for the dust. That really started my interest in cosmology and being able to measure the Hubble constant accurately. And with the launch of the Space Telescope, which was supposed to have happened I guess in ’86, at that time imminent. There was a meeting in Aspen, I think in 1985. And Riccardo Giacconi, who was then the director of the Space Telescope Science Institute, that summer put out an announcement encouraging people to think about big projects that Hubble could do. He was worried that when you had a time allocation committee that the TAC would just divide all the telescope time into tiny little pieces. And so, he asked what were the big projects that Hubble could do that couldn’t be done any other way? So, at that meeting, the nucleus of the Key Project was formed, and we began to plan to undertake a big project. So, the pieces began to come together.
And just to get a sense of Barry’s style as a mentor, and also, how independent minded you were as a graduate student. Looking back, how closely connected was your thesis research with what Barry was doing? In other words, did he more or less hand you a problem relevant to his work? Or was he more hands off and you developed what you ultimately wanted to develop?
So, my initial interest as I said earlier, had been in star formation. And so, we had a series of conversations about star formation. I became interested in extragalactic astronomy in my junior year, when I started to take extragalactic astronomy. We had many discussions about using CFHT to do a project on star formation. He gave me a lot of freedom in my thesis to take it to areas that I was interested in. I did simulations of various effects, for example, crowding, on measurements of distances and a comparison of the upper end of the luminosity function in a sample of nearby galaxies, and then eventually Cepheid measurements. We have very different styles that I think are very complementary, which worked well for us in our collaboration. I think there’s no point really in collaborating with people who have all of your strengths and all your weaknesses (laughter). So, it’s been a very fruitful collaboration and my interest was toward the cosmology end. He was maybe more interested in the Cepheid end, and the Cepheids themselves. But they’re all important. I mean, understanding the Cepheids and applying them to cosmology. And we just have different ways of approaching problems. But it works really well. Always has.
And there’s always a duality with graduate research. On the one hand, you’re hyper-focused on your narrow slice of the thing you’re working on, but you also have to be cognizant of the larger, scholarly world and how you’re contributing to it. So, on that note, how did you see either at the time or retrospectively, how did you see your graduate research being responsive to those larger questions in the field?
I read a lot. I spent a lot of time reading when I was a graduate student (laughter). I had an interest in N-body simulations, understanding galaxies and how they were formed, and in terms of the Cepheid distance scale, my interest was in cosmology and the importance of being able to make measurements that were as accurate as you could make them. And I don’t know whether it was a conscious realization but certainly what was true was that not a lot of attention was paid to systematic errors, when there was a factor of 2 uncertainty. It was hard to get at what the systematic errors were. And that really struck me as important. You had to get a handle on the systematics. You had to understand what the uncertainties were in your measurement. And if you suspected that there was something, and having uncovered that dust was a big factor and that you could correct for it, then what started to bother me was okay, well, what about the metallicity of Cepheids? The abundance of chemical elements in their atmospheres? Could that also be affecting them? And so, that was something that using CFHT, the idea of making a measurement within the Andromeda galaxy where you knew that the Cepheids were all at the same distance, but that there was a measured abundance gradient in the HII region in that galaxy. So, could you answer the question if you got BVRI CCD photometry in different radial fields, corrected for dust, was there then an effect that could be attributed to metallicity?
And so that started that line of inquiry which we then followed up in the Key Project with M101. And to this day people are still arguing about what is the effect of metallicity. It’s a tough problem and neither theorists nor observers are able to answer the question unambiguously: some studies say the effect has one sign and other people say it has the other. And it really hasn’t converged. It’s one of the things that still worries me about Cepheids. But, in the factor 2 era, you couldn’t even ask questions like that. You had to get to the point where the data were accurate enough that we could measure smaller effects. And then examine the residuals, and ask, can we correlate those residuals with something that’s physically meaningful? And that intrigues me with stellar distance indicators like the Cepheids or these red giants that we can talk about it in a little while. With a stellar indicator, you can hope to ask questions that have to do with the underlying physics of the objects that you’re measuring. And tease out systematic effects. And it didn’t interest me to make many, many observations and statistically beat down the errors, but then still be left with systematic effects. But the idea that you could actually make measurements with some accuracy and say something about cosmology, that’s what really interested me. And still does (laughter).
And on that note, having contributions to cosmology, of course, in the early 1980s, you were really there at the creation of the field, in a sense.
A lot of what was happening at that time was pretty exciting. So, there was no HST at the beginning of the ‘80s and that, of course, got delayed with Challenger and then the spherical aberration. But ideas of inflation just had surfaced in the early ‘80s and the problem that there didn’t appear to be enough matter, that Omega matter was too low relative to the critical density equal to one that most theorists thought was the case. That is, the standard cosmology of the day was Einstein-de Sitter with Omega matter equal to one.
When we got our first results from Hubble, which were based on M100 and the Virgo cluster, it was just a single galaxy and a single cluster. And it had, I think we quoted, an uncertainty of twenty percent. But it was an important measurement in a sense that we hadn’t ever been able to measure anything about Cepheids that directly at that large a distance before. And it was one of the most distant galaxies in our sample. So, we knew as a result that we could do the project that we had set out to do. And we got a value of eighty with that twenty percent uncertainty. But, with an Einstein-de Sitter universe, that implied an age for the universe of eight billion years. Which was way lower than the ages of globular clusters that had been measured in the Milky Way. At that time, they were in the range of fourteen to eighteen- as large as eighteen billion years. And so, that was a huge problem. And even in the end when we published our final paper in 2001 and we got a value of seventy-two, that was still nine giga-years with an Einstein-de Sitter universe.
So, it wasn’t until the measurement of high-redshift supernovae, and an indication that there was dark energy, that it the age problem was solved. So, there was a period where there was a lot of consternation. What’s going on here? It wasn’t just the age problem. It had to do with large-scale structure and the fact that N-body simulations didn’t match the observations with Einstein-de Sitter, and that astronomers had not been able to find enough matter to allow for an Omega matter = one universe. And so, the discovery of dark energy really helped to solve a lot of problems simultaneously. But there was a lot of skepticism about high values of the Hubble constant in the early days. And particularly, Allan Sandage who was my colleague, had a lot of skepticism. But a high value of the Hubble constant of about seventy has now been confirmed in many ways over the past two decades.
Wendy, I’ll test your memory. Who was on your thesis committee besides Barry?
Hmm. Ernie Seaquist, I recall, was on the committee. He was a radio astronomer. I think Tom Bolton, but I can’t be positive. And I’m pretty sure Peter Martin. He worked on the interstellar medium. Yeah. And possibly John Lester who worked on stellar astrophysics. I remember him asking questions. But I’m wondering, I also took courses from some of them. So, I may be remembering them giving me exams in other classes, but I’m pretty sure that’s who was on. And I believe my external examiner was Paul Hodge.
And after you defended, what were some of the most compelling opportunities available to you? Were you thinking about faculty positions? Postdocs? What was available to you after you defended?
After my thesis, I applied for postdocs. I think I applied for six. I applied to the Carnegie Observatories that was my first choice (laughter). It’s where I wanted to be and I think probably most people who wanted to do observational astronomy, as a postdoc you had access to the two hundred inch at Palomar and telescopes in Chile. So, for what I wanted to do, there were very few places around where I could undertake the observations that I wanted. You had all this independence as a Carnegie Fellow and access to telescopes, which most places did not provide. So, that was my first choice, hands down. And I did get other offers. But I knew I wanted to go to Carnegie.
And what was the funding source at Carnegie? Was it a direct appointment? They funded you?
Yes, Carnegie Fellowships were completely funded. I don’t remember when they were started… I think in the 1960s. They weren’t open to women for a long time. If you applied in the early seventies, you got a letter from the director saying, “Thank you very much, but we don’t offer Carnegie Fellowships to women.” It was that explicit.
So, yeah. It was at that time, I think, still a two-year fellowship. And then very shortly after it became a three year fellowship. And yes, it was a dream job for me, it was certainly my first choice (laughter).
And did you think that this is ultimately where you would spend a career? Was that sort of baked into your initial interests?
No. Again, I think as things have happened during my career, I’ve found my footing at each stage. But I don’t think I was really thinking beyond that. Staying at Carnegie would have been my dream. But I don’t think I dared hope it. Very few positions came up at Carnegie. You know, people didn’t tend to leave. And so, I was very fortunate when I did get on the job market that that position did come open at Carnegie.
Given how explicit Carnegie was in terms of excluding women, really only a decade before, did you find the environment to be inclusive at that point? Had enough progress been made where these issues were not directly affecting your work?
I think from a personal point of view, I really got along with the scientific staff there. I didn’t feel that I was being excluded. I mean, even Allan Sandage at the beginning was super welcoming and friendly. There were occasionally comments that people would make in an offhand way, you know, I think especially today if you were to say them, they weren’t exactly- you could take them in a way that would be a real putdown. But I don’t think they were intended that way. I didn’t take them that way.
I got hired in ’87, so yeah, you know, eighty-five years at the institution, they did not have a woman on the scientific staff, the permanent scientific staff. Henrietta Swope had been there, but she wasn’t appointed to the scientific staff. And Vera Rubin had been appointed at Department of Terrestrial Magnetism in Washington, D.C., which was a sister Carnegie department. But never at the Observatories. And so, you asked, did I think I would be? It never occurred to me that I would be appointed to the permanent staff, let alone become its director. Because of course in a hundred years the institution hadn’t had a woman director either! (laughter) So, no I wasn’t thinking those I mean. No.
What was your initial project when you got to Pasadena?
I was trying to answer some of the questions about how to improve the Cepheid distance scale. For example, was there an effect of abundance on the Cepheid period luminosity relation? And I also had a project to study the velocity dispersion as a function of radius in galaxies. A project that I did with Leonard Searle and Ian Thompson. We never finished and partly that was because the Key Project started to happen, and things got busy. I had a couple of children too (laughter). And so, the Key Project really began to absorb most of my scientific cycles. But then, the Key Project was delayed, as I was saying earlier. And I don’t know how we would’ve done the project in the 1980s. We were actually really fortunate that it was delayed because first, Moore’s Law helped us in terms of computer speed and also disc space available. When I arrived at Santa Barbara Street, which is what we call the Observatories, in 1984, I think I had 5,000 kilobytes or some ridiculously small amount of disc space. And I had been at Cambridge where I’d had access to megabytes, I think. Or at least, many, many more kilobytes. And so, just dealing with large datasets at that time was really a challenge.
It was in the intervening time that we learned how to do the project and were able to get to the issue of how you correct for reddening. Barry and I were doing simulations to try and understand how you could measure the periods of Cepheids using Space Telescope using a small number of data points. When Hubble and Sandage did their observations, they literally had hundreds of nights of Palomar or Mount Wilson time. From the ground you had to worry about cloudy nights and bad weather and scheduling, in addition to scheduling other people who wanted to use a telescope besides those doing Cepheids. And so, we knew that time on HST was going to be at a premium, so how could we do this as efficiently as possible? So, we did a lot of simulations and showed that you could essentially use a power-law spacing that would allow you to measure the periods accurately for the range of periods we were interested in. And so all that happened in the interim between Challenger and the eventual launch, because ST was supposed to be launched, I think, in the next launch after that accident. And then in 1990 when it was launched, the spherical aberration was discovered. So, it wasn’t until end of 1993, the refurbishment mission, where Hubble was able to do what it was planned that it would do. And so, that gave us a nice chunk of time to really figure out how to do the project well. But when I went as a Carnegie Fellow to try and redo the local extragalactic distance scale, I didn’t know at the time that there was going to be this Hubble Key Project and that it was going to turn into the mammoth program that it did.
Did your work change substantively when you formally joined the scientific staff?
Um. No, I wouldn’t say so. I think it was a continuation. I mean, the Carnegie Institution is an unusual place. What Andrew Carnegie set out to do was to hire “the best and brightest men,” and then give them resources. And he thought good science would come of that. And that was certainly true. In the 20th century, the Observatories led essentially all of the big telescope projects. The solar telescope at Mount Wilson and then the sixty-inch, then the one hundred-inch at Mount Wilson, and then George Ellery Hale was also the one behind the two hundred-inch at Palomar. And so, the nice thing about joining the permanent scientific staff was the small number of duties. No teaching. We didn’t have to worry about applying for grants. We were funded by the institution. We could get grants and I did get grants, but it was for our own science. We didn’t have to support ourselves with salary. And we didn’t have a lot of committee duties the way you do at universities. We had the Carnegie Fellows. But there wasn’t a large administrative overhead. And so, it was a great place to do science.
And you were on the faculty, but were there any opportunities to teach or to interact with students in this role?
At the time, Jeremy Mould was at Caltech. When he would go away observing I would occasionally teach a class for him. I was interested in teaching at Caltech but they didn’t have a lot of courses that they could just give to people from the outside to teach. I did co-supervise some students while I was there, but in general, no I didn’t teach. And I didn’t have many students.
So, despite the geographic proximity, there were really no formalized partnerships between Carnegie and Caltech?
Well, when I arrived in 1984 it was a few years after the divorce between Caltech and Carnegie. And that had been a very bitter divorce.
And I didn’t share that history. So, I had good relations with a lot of faculty at Caltech. I worked with them on a joint colloquium committee. We still shared the sixty-inch telescope for a while. I worked a lot with Tony Readhead on various ways to improve the interactions between the two places. We both thought it was unfortunate that here we were in the same place and yet relations were so bad. There were many people there who wanted to have good relations. But, the older scientific staff at Carnegie had received a letter in their mailboxes. For decades they had been cross appointed to the Caltech faculty. And then one morning they were fired. So, it wasn’t an amicable divorce. There were a lot of hard feelings when I first arrived.
But because you didn’t experience any of that yourself moving forward, did you look for those opportunities? The next generation?
I really did try a lot, both as a scientific staff member, and also later when I became director. And it had been my hope that we could collaborate on the Large Telescope and we had discussions to that effect. But it didn’t happen, for various reasons. But I think it would have been good for both institutions. I think we could have built a telescope by now. On the other hand, if we both succeed, I should say when we both succeed at GMT and TMT, there will be two telescopes: one in the north and one in the south. And I think in terms of the science, everyone will benefit from that.
Wendy, what were the circumstances of you joining the Hubble Space Telescope Key Project?
So, going back again to this meeting in Aspen. I think it was 1985 in the summer. So, the nucleus of the team really formed then. And Marc Aaronson, who was at the University of Arizona, at that time was the principle investigator of the project. And in some funny sense, I became his deputy. I think in one of the proposals that went in I was even formally the deputy. I’m pretty sure that was the case. And so, he and I had very, very, long, extended conversations about scheduling and how we were going to do this project and what objects we were going to observe and who was going to be on the team.
And so, there was this circumstance that Barry and I were working on how to correct for reddening, how to measure Cepheid distances really accurately, how to test for metallicity, how to schedule the telescope and all things connected to Cepheids. And then and Marc was killed in an accident at Kitt Peak in 1987, which was horrible. Barry and I had become good friends with Maryann and Marc and he was killed just a week before our daughter was born. It was just an awful time. Then as things evolved, the spherical aberration was discovered. And things kept getting delayed, getting delayed, getting delayed. But when we did put our application in, I guess in 1990, even with the spherical aberration, we were observing M81, which was our closest target, and one of the fields in M101. And so, Jeremy Mould and Rob Kennicutt and I were co-PIs on those proposals. And we sort of loosely divided our responsibilities. But we had weekly telecons and we kept a very close contact throughout the Key Project. I was PI for the science because my expertise was in Cepheids, but we were all involved in all of the different aspects of the project. Rob led the budget effort and Jeremy oversaw management kinds of things. We were a triumvirate as some people on the team would refer to us (laughter).
And Wendy, in terms of establishing the overall research agenda, was the be-all and end-all the Hubble constant? Or were there other issues to consider as well?
Well, the name of our proposal was the extragalactic distance scale, but the focus of the work was to determine the Hubble constant. For that you first and foremost needed to measure the extragalactic distance scale. And the goal was to put this factor of two uncertainty behind us. The thrust of the project was okay, we’ll measure these Cepheid distances, but we had many different ways of measuring distances to check the Cepheids. And then we had five different secondary methods. And the way the program was designed was to get the statistical uncertainties for each of those methods to a five percent level. To allow us then to get an overall estimate of the systematics by comparing the different methods. And to do that in a robust way and measure a Hubble constant to ten percent. And we did in the end measure a value to ten percent, which has stood the test of time. Yes, there were various people in the group more interested in the distance scale itself rather than the Hubble constant, but that certainly was the overriding context. A factor of two uncertainty in the distance scale which translated to a factor of two uncertainty in the Hubble constant. It was just a crazy, huge uncertainty.
What were some of the most important, both technical and theoretical, challenges that you encountered as the project was getting underway?
Okay. So, technical, we were trying to measure the luminosities of Cepheids against the background light of the galaxy that the Cepheids were located in. These stars were blending and being crowded by other stars. And so, an important member of our group was Peter Stetson who had written a program (called DAOPHOT) to do photometry in crowded fields. Extract the magnitudes and simultaneously fit many different stellar point spread functions to allow you to measure an accurate Cepheid luminosity. We had twelve observations in the visual and four observations in the I-band, this was the spacing that Barry and I had come up with, and Stetson’s program allowed us to analyze those data all at the same time. And as I said earlier, we wouldn’t have been able to do that in the 1980s. We didn’t have the computer memory or the disk space to have all those data available at the same time. So, that was a technical challenge that we had to come up with a solution to. Theoretical, did you mean in the sense of our first results in the context of no dark energy? We were getting high values of the Hubble constant, which led many skeptics to disparage the work. I mean, I had two directors at the observatory tell me, “You’re probably going about it the right way, but Allan Sandage is clearly right.” Because we “knew” what the ages of globular clusters were. “And so you must be wrong. There’s not a cosmological constant. That’s not science.” And so, the theoretical climate at the time was not to be open to the presence of the cosmological constant. Cause it had been—
—you know, over history, people had introduced it before. And it had always gone away.
Right. My question is based on that, basically. That theoretically, there was an uphill battle just in terms of where this was all leading. If there was the prevailing assumption out there that this is nonexistent.
Right. There was very strong feeling that there was no cosmological constant. That it was absurd. And that a high value of the Hubble constant just was not an option. And so, we were finishing the Key Project, our last paper was published in 2001. And the measurements of distant supernovae were published in 1998, 1999. So those things were happening simultaneously. But during the mid-nineties, when we were getting our first results, people were insisting that there was no cosmological constant. You guys must be wrong. But, our group, and certainly I, felt that we were going to go where the data took us. Sandage though, was convinced by the ages of the globular clusters and just could not imagine that the Hubble constant could be high.
So, Wendy, let me ask a broad question at this point. Given how central the cosmological constant is to our understanding of the universe currently, what did it feel like to be sort of central to the research that caused this revolution in our understanding of how the universe works? It must have been exhilarating.
It was exhilarating. It was very exciting. But I didn’t really have time to be thinking about it- it was a very busy time (laughter).
Yeah, yeah (laughter). And busy because you were writing? Because you were presenting? Because you were analyzing the data? All of the above?
All of the above. And you know, we had young children. At that time, life was work and kids. You know? I don’t think I read a novel for I don’t know how long. And a movie, I didn’t- it was just very busy. You know, I look back at it as one of the happiest times of my life. I loved it. It was exciting, interesting, difficult, challenging, messy. It was fun. But incredibly busy. Yeah.
What were some of the feedback mechanisms, given that you were operating against these strong theoretical assumptions? What were some of the most useful feedback mechanisms in the data that were demonstrating to you that the prevailing wisdom of the time was just wrong?
Well, the data from Hubble, once the telescope was refurbished, they were just beautiful. I mean, it was, there’s nothing like the feeling of working with really accurate data (laughter).
Take our first results with the Virgo cluster. In fact, there were people on our team who had earlier done some simulations based on Cepheids in our Galaxy and said, “You’re never going to be able to do Virgo. It’s just not going to be possible.” And so, I just remember one afternoon, we’d gotten the first data from Hubble and for several years we had been getting Cepheids in M33, M31, all the nearby galaxies. And here was M100, you know, fifteen Megaparsecs or so away, and the data points in the light curve were like beads on a string. I mean it was beautiful. The phased Cepheid light curves had all the points lined up with almost no scatter. And it was just unambiguous that in the most distant galaxy we were observing, we could get beautiful data. That we would be able to carry out the project. And so, the fact that we could now correct for reddening, that we had linear detectors, that we’d gotten above the atmosphere, that crowding effects were minimal- we couldn’t have done this from the ground and the results were what they were. We did the best that we could with the data that we had available, and I didn’t see any other way to interpret them. Just, that’s what we got. So, just because someone tells you, or shouts at you in some cases, the case may be that the answer is something else. How do you argue with something that is just staring you in the face? That’s what the data are telling you.
And Wendy, as part of the triumvirate as you call it, right? In any successful collaboration, it’s so important to understand what each person brought to the table, both in terms of personality, research sensibilities, areas of academic experience. So, in that level, what were the things that you added? And what were the things that the others did?
I have enormous respect for Jeremy and for Rob. And you’re correct. They each brought individual talents. Jeremy used to talk about cracking the whip (laughter). He said it’s not my personality to crack a whip and you know, he was being facetious. But at some level, they were older than I was and had more experience and I don’t know if they had real experience in managing big projects because the Key Project really was the first big astronomy project. When we started, it was still an era where you’d publish a paper with one or two people, and that was kind of the norm. But we had a team of thirty over the course of the Key Project, many of whom contributed enormously to the effort.
I think also that Rob and I probably shared a really healthy dose of skepticism. I really need to see a lot of testing and proof. And so, both of us really pushed for that and it’s good to have people who are on the same page that way who are thinking of things that you both think are really critical to the endeavor. But we kept up, as I said, we were in contact weekly over the course of almost a decade. We had a lot to do with each other and I think it worked well. So, what did I bring? I brought a tremendous willingness to work very hard (laughter). A lot of expertise in Cepheids and measuring distances. And I think an openness. You know, they certainly shared that too. We were really pushing every sort of angle to make sure we had tested things as well as we could and it was hard because the data were becoming public. There are always differences of opinion on how fast you should publish and whether you should wait until the paper is refereed. But we would get on the same page. And so, I think that worked well. You’re asking about Rob and Jeremy, as co-PIs, but I should add that Barry also made an enormous contribution to the Cepheid science. I simply don’t believe that the Key Project would have been nearly as successful without his major involvement.
And because measuring the Hubble constant is a dynamic enterprise, in other words, this is not a one and done in the mid-1980s. Problem solved, right? Did you know at the time that measuring the Hubble constant would be a career long endeavor for you?
No (laughter). No, and I think too, in 2001 I was convinced I’d never work on the Hubble constant again. At that point I don’t think anybody saw any point in it. We’d measured it to ten percent. There had been the uncertainty to a factor of two for so long. It was just not obvious we could get to that level of ten percent, as we did. But with measurements of the fluctuations in the microwave background temperature and the ability to estimate the Hubble constant given a Standard Model of cosmology, this sharpened the question again. And it presented another opportunity to really test cosmology. So, it became really interesting to me again and the fact that we could now measure things with even better accuracy than was possible at the time of the Key Project and maybe learn about new physics beyond our current standard cosmology that now has dark energy and dark matter, or perhaps more about systematics, both of which have been part of the history of measuring the Hubble constant.
And to what do you ascribe the greater precision in measuring the Hubble constant? Is it better instrumentation? Is it just more minds on the data? Is it better theory? What are the things that allow for these phenomenal advances in precision?
It’s almost always been new technology. CCDs early on, the ability to get multiwavelength data and correct for reddening. And with Hubble, when we started, we didn’t have an infrared detector. There was the Wide Field Planetary Camera that cut off at the I band. Now we can get infrared data. In the intervening time we’ve gotten some data from Spitzer in the mid-infrared. So, we can really test both the corrections for reddening and for metallicity. During the Key Project we had different techniques, secondary methods, for measuring distances beyond the Cepheids. But what really emerged were the Type Ia supernovae that had a really small dispersion and were very bright, so they could be measured very far away. When we started the Key Project there were no galaxies that were close enough to have both measurable Cepheids and Type Ia supernovae. But in the time since the Key Project there have been more Type Ia supernovae that have gone off. And now the samples are larger. Nature is providing us with more objects. But in addition, the instrumentation continues to improve.
And just to give a sense of how fundamental this work is, I can’t help but smile thinking back when you said all of the things that were understood as a result of knowing that this was dark energy that you were dealing with because that’s not to say that the mystery of dark energy was solved at that point. It’s just you understood what the mystery was.
Yes. And still today, we don’t understand what the dark energy is and I would say I’m still open-minded on that question. We don’t know what we will learn in the next twenty to thirty years. I hope I am still around when we do understand it. And whether we will have a different view. There’s something we don’t understand, and it sure looks like dark energy. But we’re going to need to understand the underlying physics of whatever this is. And I think at this point we just don’t know. There’s no good theoretical explanation.
Wendy, there’s always the consideration when you’re involved in such fundamental research where to expend your energies in terms of publicizing your findings. What journals to publish in, what conferences to present at, what interviews to give in popular media, right? So, in that way, in those concentric circles, from the most specific to the broadest. What did you find were the most efficacious channels for publicizing your research generally?
So, most of our results we publish in The Astrophysical Journal and that tends to be the journal that I’ve published most in. And I think for obvious reasons the research that we were doing belongs in The Astrophysical Journal. We did publish the results on the distance of the Virgo Cluster in Nature. And I think that was important for those results because they were our first results from the refurbished Hubble Space Telescope. The diameter of the primary mirror was chosen to allow the discovery of Cepheids and the Virgo Cluster. In the 1970s, HST was being downsized for budgetary reasons, but the primary goal of the telescope was to solve the Hubble constant debate. I’ve talked to some of the engineers involved with Hubble, many of whom have told me that this was what went into that decision and so with HST, here was the first opportunity to get out almost into the Hubble flow and measure a Cepheid distance directly. And so that did get a lot of attention. When Riccardo Giacconi earlier had asked for people to think about large projects for HST, the Key Project on the extragalactic distance scale was one of three that was chosen (the others being observations of a Deep Field and also quasars).
But the Key Project got the bulk of the telescope time in terms of large projects at the beginning. And so, I think the fact that there was a controversy over the age and the fact that eventually as the project was finishing up, the evidence for dark energy became available. As you said, it was a time when things were converging and an interesting time. And then in terms of conferences, you know, there were a lot of invitations to conferences because people were interested in the results. And there was press because people were interested in the results. And so, that was different. You come into a scientific field and you are concentrating on your own research and you’re not even aware that anybody else would be interested in what you’re doing (laughter). But, yeah, it was interesting. And most people that you talk to are genuinely interested.
Right. Right. And given how beautiful the data was, people can still be stubborn, and they can hold onto their theoretical assumptions. Was the data so beautiful that essentially once you started presenting to this, all of those oppositions about the cosmological constant faded away?
I think it was likely again, the juxtaposition of our results and the observations of the more distant supernovae, and the sense that there was a dark energy component that people had been very resistant to thinking about until that time. So, there were those data and then there were elaborate N-body simulations that were showing that in Einstein-de Sitter universe you just didn’t end up with largescale structure that looked anything like that universe that we had. And so, I think as I was alluding to earlier, there were many pieces of this that came together and fit and so the time I think was ripe for people to have a sea change in thinking.
And just to fast forward to today. Did you ever imagine that the Hubble would have such a phenomenal lifespan? And it would continue giving such beautiful data and images?
No, I don’t think any of us expected that (laughter). You know, we’re at thirty years and still counting. It’s been amazing.
And so, just the way that you would ask a centenarian, what’s your secret, right? What are the secrets of the Hubble that allowed for this amazing lifespan that’s ongoing?
Well, tremendous engineers – I often think about this – don’t get a lot of the credit. It’s scientists that come in after they’ve spent years building this marvelous instrument. And we get to come in and do the science and that’s what people now are thinking about. But it was a tremendously engineered facility. Sad what happened with the primary mirror and the lack of testing. Those things happen. I think we all learned from that in our current generation of telescopes and some luck, too, right? It didn’t get hit by anything. Also, the ability to send up new instruments. The fact that the shuttle program was there and as new instrumentation, new capability came along, the telescope got not just fixed or repaired but actually became more powerful with time. And now there is this tremendous opportunity to have access to the Hubble archive that has led to an enormous amount of science. So, a huge part of the community has become engaged in Hubble science. But if another gyro goes, it won’t last forever. Well, we’ve been pretty lucky.
And do you expect any day like, it’ll be all over? Or do you really think at this point it’ll just keep going you know, on and on and on?
It can’t. But yes, at some level you just think because it has that it will keep going on and on and on. And I think many of us thought that it would be nice to have overlap between JWST and Hubble. JWST, which is a next generation space telescope planned first in the 1990s, has been delayed. We didn’t imagine that it would be this far out that we would be talking about that. But I think we all have a hope that there will still be some overlap between the two telescopes.
Wendy, was the process of setting up the Giant Magellan Telescope, was that sort of gradual for you intellectually? Was it a lightbulb moment? How did you come to initiate this project?
I became the director at Carnegie in 2003. It was right after the Key Project had finished. We were just starting a project on type 1a supernovae, our Carnegie Supernova Project. I had been asked to consider being the Carnegie director a couple times before that, right when I was in the thick of the Key Project. And in my mind, it was no way. Again, you asked at the beginning, did I see doing these things? I never thought I would be a director. I had no interest in doing it. I wanted to do research. I did not see that day ever coming. When asked if I would be interested, it was always “No, I’m not interested.” So, they put me on the search committee and I was involved in a couple of searches for the directors before that and then the next time I was told, “You can’t be on the search committee,” by the president of our institution, Maxine Singer. She asked me to think seriously about whether I would consider becoming the director. And so, I did think seriously about it, and it was at a time-
You must have been concerned that administrative duties would pull you away from the science.
Right. Yes. And so, I guess part of what had happened, I had started to become involved in some national committees like the Committee on Astronomy and Astrophysics, the CAA. And I was a member of the AURA Board. And the Astronomy and Astrophysics Advisory Committee. And I discovered that around that time, actually I did enjoy chairing. I’d always thought, I don’t want to chair committees. It takes too much time (laughter). But I discovered that there was an aspect to that that I enjoyed. And leading things. It was different. And the Key Project, of course, was part of that too. And so, by the time the job was offered to me and we were having discussions about large telescopes at that time and I’d thought about it seriously for the first time, then the job was offered to me, and I realized okay, maybe I should try this. Maybe I could enjoy this. Because by that time, I had given some thought to what I would do as director and I had a number of ideas. One of which was to become involved in a Large Telescope Project. Because that’s what Carnegie had done. It was Carnegie’s history. Carnegie had been behind the construction of every major telescope during the twentieth century in Pasadena. The Thirty Meter Telescope was called CELT at that time, the California Extremely Large Telescope. I had been on the visiting committee at Caltech for physics, math, and astronomy for a number of years at that point. They were looking for funding for a design study, and they were partnering at that time with the University of California, the way they had for Keck. And so, I was aware that more money was needed for the design study. We had just finished Magellan at Carnegie. When I start talking about this I become “we” and I’m Carnegie again (laughter).
I was at Carnegie for 30 years so I can’t help lapsing back into “we.” Before I became director, I visited the president of Carnegie and told her that there was this need for funding for the next generation of large telescopes. And, I remember being very concerned while I was on the plane that she would just throw me out of the office because here we had just finished Magellan in 2000. In 2002, the two telescopes were commissioned, and I was going to ask for money for the next generation. And I thought you know, it’d be perfectly reasonable for her to say, “Why don’t you use these telescopes for a decade before you come asking for more.” But I think the fact that we [Carnegie] had been involved in the major telescopes of the twentieth century made it unappealing to both of us to sit out the next generation. So, she offered to contribute a million dollars to CELT. And then we had a faculty meeting at Carnegie and to my delight all the staff were behind this despite the divorce from Caltech. Bitterness aside, we didn’t see how any of this was going to happen without becoming partners with Caltech.
And this was before I became director. There was a meeting where apparently this idea of Carnegie contributing to Caltech fell apart. I talked to the people who were involved in the meeting and in fact, different people had different views of how the meeting had gone and what had transpired. For one thing, the Caltech people told me that they didn’t believe that Carnegie actually had the money. Whatever. It fell apart. So, when I became director in 2003, CELT was going ahead. The message that Caltech had seemed to deliver, (what was heard by those at Carnegie, although the people at Caltech said this isn’t what transpired), was that Caltech didn’t want us as a partner.
Also, the central players in the Magellan Consortium who had built the 6.5-meter telescopes at Las Campanas had been thinking about the next step for a large telescope. Roger Angel came up with a concept at that time. It was actually two 20-meter telescopes, a “20/20”, with a second telescope being on a moving rail so that it would operate as an interferometer. And so, we began to have serious discussions about Carnegie and the Magellan Consortium coming up with a twenty-meter class telescope. Carnegie owns the Las Campanas site and Carnegie owns the Magellan Telescopes and operates them on behalf of the consortium. And it was clear that for a larger telescope, Carnegie wouldn’t have anything near a fifty percent share and that it would have to be a more distributed collaboration. And so, we started off a meeting in the spring saying, okay, I was chair of the council, that was what the agreement for Magellan said, the Carnegie director was chair of the Magellan Council. And so, the start of the meeting was, “Well, Wendy can’t be chair of the GMT”—it wasn’t GMT at that point, it was the twenty-meter telescope- “because she’s chair of the Magellan Council.” But somehow, I was asked to leave the room and then I got voted in as chair of GMT, the twenty-meter telescope (laughter). And that was a position I held for twelve years. So, again, it was not where- I did not set out to do that. Circumstances presented themselves and Carnegie had led these big telescope efforts and I will say without Carnegie the telescope would never have been launched. Ever. Ever.
Yeah. And why a land-based telescope? Was it ever up for a debate that your next big project, were you ever faced with the choice of: do I want to do space-based or land-based? Or this was just obviously what was coming next?
I think the difficulty is that space is so much more expensive than ground. And, you couldn’t put a 25-meter like the GMT in space. The next generation space telescope after Hubble is the James Webb, and it’s a 6.5-meter telescope. And that’s the size of our Magellan Telescopes. And so, in terms of resolution and what you can do with a 25-meter class telescope from the ground, it is very complementary to what you get in space. Ground versus space offer different strengths and different challenges. And I think too, the expertise at the Observatories and in our partnership resided in ground-based astronomy. So, we were not the group to do a space telescope, nor did we have access to the kind of funding that would be required to do that.
And how much discussion was there about the site? The proposed site for the telescope? I mean was Chile immediately the be-all and end-all or were there other sites that were considered as well?
We considered other sites. There was an enormous amount of discussion. It seemed to me important to have it. But inevitably we would pick Las Campanas because it’s a phenomenal site and Carnegie owned it. It was available. We weren’t having to renegotiate with the Chilean government or Mauna Kea or La Palma. We were also doing site testing at the time using the same equipment that other telescope projects were using. And so, we could make an apples-to-apples comparison of the seeing, of the precipitable water vapor level, and city lights, the light pollution.
And hands down, except for the mid-infrared, it turned out to be the best site in the world. Which surprised me because I had done a lot of work at Mauna Kea and I had the expectation that Mauna Kea had better seeing. The best I’d ever seen at the time. But, in terms of photometric nights, Mauna Kea has a lot of cirrus. And Las Campanas, 300 out of 365 nights a year are clear at Las Campanas. And the seeing is phenomenal and it doesn’t have a lot of light pollution. There has been so much astronomy in Chile, and I think it’s been good. It’s been a mutually beneficial thing both for astronomy and for the country itself. And a lot of the Chilean government people we’d met with many times, were very supportive of having the telescope there. So, it seemed crazy to me to be thinking about any other sites. But we had to go through the exercise and in the end, begrudgingly on the part of some, we picked Las Campanas. It’s a natural.
Are there considerations of a southern hemisphere versus a northern hemisphere site to think about?
Yes, and I think good ones. The Galactic Center goes overhead in the southern hemisphere. The Large Magellanic Clouds, Small Magellanic Clouds. And these aren’t cosmic reasons. You wouldn’t make a decision just based on that. But it is good to have access to both hemispheres so when transient objects occur, sometimes in the north, sometimes in the south, it’s nice to be able to have instrumentation available to follow those up in both hemispheres. And I think having different types of instrumentation just increases your ability to do good science.
So, I often would argue that having one telescope in the north and one in the south was an advantage, particularly when we were having discussions with NSF. Early on there were discussions about having a down select which I thought was not the right way to go because we weren’t dealing with NASA that competes projects and then funds them. Most of the money, in fact, almost all of the money to date has come from either private individuals or private institutions or foreign governments without the NSF. So, I argued many times that we would like two telescopes. And we had lots of discussions early on about how maybe the TMT for example could also come to Las Campanas because it might be a way of saving some money and having different and more kinds of instrumentation. We had a lot of discussions about potential ways we could collaborate, but those never came to fruition.
And from its inception, Wendy, was the idea that GMT would be an international collaboration? It wouldn’t just be the Americans in Chile?
No. Again, that all happened organically. And as I said, the initial nucleus was the Magellan partners. And then two of them dropped out because their administrations just didn’t want to think about big projects. We were left with Carnegie, Harvard Smithsonian, and the University of Arizona. And I guess, I’m trying to remember the timing, I think Australia was first. But anyways, Australia and South Korea happened around the same time. Australia had had the fire at Mount Stromlo at that time, and I had just reached out to Penny Sackett who was director offering my sympathy for what had happened and we began corresponding and she of course had to be thinking about what was Australia’s next step after the fire. She was also talking to people at TMT, but as she became familiar with GMT, we both agreed that GMT and Australian science would be a good match.
Eventually, they had internal discussions and decided to join the GMT project. In the case of South Korea, they had been working with Mexico to try and build an eight-meter telescope. And the Korean government had twice turned them down for funding to do that. There was a group who visited Las Campanas, when I happened to be observing. And I had discussions with them about the possibility of joining GMT. Then the president of the Korea Astronomy and Space Institution came to visit Pasadena, and eventually they joined the project. And then Texas. I chaired a visiting committee for Texas A&M University, and discussions evolved from there. Then the University of Texas Austin and the University of Chicago.
So it was actually personal relationships in all those cases. It was very much, here’s this project. We’re working on it. It’s an exciting project. Would you like to join us? It was organic. And then São Paulo, Brazil. Again, I had met people there and they were interested in the European Extremely Large Telescope. But there was a group from São Paulo who felt that that was extending beyond the means of the country. Yeah, so it was a lot of just meeting with the astronomers and then presidents or the heads of the institutions of various places. You have to have buy in from the top and the bottom. It doesn’t happen without one or the other. So, again, not a role that I anticipated playing. You know, it was an unusual collaboration because, first the Mount Wilson 100-inch was all Carnegie. And Carnegie could afford that. And the Magellan 6.5-meters, the institution couldn’t afford by itself, so we got partners. And then GMT we couldn’t afford even with U.S. partners, so it became international. We hadn’t done anything like that before and so, it was step-by-step learning as we went.
Wendy, I want to ask sort of a broad sociological question about support of big science in the United States and internationally. So, of course, particle physicists bemoan the fact that the SSC was never built. And where does the field go from there? I want to ask you in the world of astrophysics and astronomy, is the GMT your SSC? In other words, do you feel like societally, your field is being supported in every way that it needs to be and that you are not coming up against funding dead ends the way that say, high energy particle physics is?
Well I hope it’s not like the SSC in the sense that we don’t succeed in the end. That would be a huge tragedy in my view. I think we’re trying to do things now at a scale that is like what the SSC tried to do. These are hard things to do. And I think one of the things that I was concerned about when I was chair of the board was that we had all done projects that were single telescopes. And we’ve been very successful at it. So, people could argue, what was better, the technology of small mirrors for Keck or large mirrors for Magellan? And people did argue about those things. But the fact is both of them worked. And so did the Gemini national eight-meter telescope, with different technology, again.
And so, moving ahead with GMT, the worry for me was okay, we could do this at a scale of a single telescope, but now we’ve got seven mirrors and no one had done that before. And I got the feeling sometimes when people talked about it, it was okay, well, you just build seven mirrors and then they all work together. And that scared me. You have to phase these seven mirrors and this thing can’t flop around over the sky. This is a bigger engineering undertaking than we’ve done before and do we have the expertise to make it happen? And those things took a while to solve. But they are solved now. And so, I guess I also approached it from the point of view that came from watching Magellan being built. I wasn’t in the director’s seat when Magellan was being built. But I did see how long it took to cast the first mirror. And so, we were partnering with The University of Arizona that makes these phenomenal mirrors. Nobody can compete with them in terms of the surface quality of these mirrors. They’re incredible.
But the GMT mirrors were off axis. Six of the mirrors. And that had never been done before. This is where I had struggles with the early project manager who thought we needed the money for the design and my feeling was well, if we didn’t show we could make a mirror, we’re never going to have a telescope. And that turned out to be a challenge because the next open position in the queue at the mirror lab belonged to Mexico. This was the Korea-Mexico telescope that hadn’t yet been built. And they didn’t have the money to go ahead. And the LSST, which is now the Rubin Observatory wasn’t ready to do their mirror. And my feeling was if we didn’t do a mirror and we had to wait to get behind LSST, and I’d seen how long the first Magellan mirror had taken, that our chances for success would be minimal.
So, I argued really strongly and Steve Shectman, who was the project scientist, also agreed we should do a mirror and figure out how to do that. But we didn’t have the money to do it (laughter). The Air Force had paid Mexico a million dollars to go ahead in the mirror queue the last time around. So, Mexico said, you can have the next place in the queue, but you’ll have to pay us a million dollars. And I think at that point our total budget was about two million dollars. When I started the budget was half a million from Carnegie for a seed conceptual design study. And so, a few of us went out to Mexico and we talked to the people there and I explained, “I don’t have the money! If I had a million dollars, I’d love to give it to you. But I don’t have it.” And they were just going to put their mirror in a box and store it but what we did have were the plans for the Magellan Telescopes which we offered instead. Anyway, we got the place in the mirror queue and it took seven years to finish the first mirror. It was very hard to converge in the end to do this off-axis mirror. But I don’t think we would have a telescope if we hadn’t started early. The LSST or the Rubin Observatory, they didn’t finish their mirror ‘til, I think, 2015 or something like that. And if it took another seven years after that, so.
And in what ways, Wendy, with LSST were these competitive relationships and cooperative relationships?
I think by and large cooperative. They considered Las Campanas as a site at one time. They were looking at several different sites. I was a little concerned that if we had both telescopes doing construction at the same time using the roads and all the facilities, that could be an issue. But no. I think the projects are separate enough and they’re complementary. And I’m really pleased that Rubin is in the southern hemisphere because I think we’ll have enormous overlap when the two telescopes are operational.
And just to bring the narrative up to the present, where is GMT now in terms of its overall process?
The design for the telescope’s been completed. We’ve got five mirrors cast. And all the glass for all seven mirrors has been purchased. I think it was 2012 we leveled the mountain and more recently, the hard-rock excavation has been done. And a contract has been signed for the mount of the telescope. So that work is now going ahead. And right now, both TMT and GMT have a joint proposal in to the Decadal Survey. The instruction to both projects from the NSF was that they are no longer competing against each other. We should know the results of that in a few months. Both projects, if they’re highly ranked, will get funded by the NSF and so, I think that will finally allow both telescopes to go full speed ahead with construction.
And just to give a shout out perhaps to the engineers, if you can give a sense to the broader public who might be saying it seems pretty- like it takes a long time to create these mirrors. Why can’t this happen more quickly? Can you give a sense of just how involved the process of creating these mirrors are and why that’s so important?
Yeah. So, these aren’t things that we can go and buy off the shelf (laughter). This mirror facility has a rotating oven, the brilliant part of this is again, Roger Angel’s concept. So, mirrors like Palomar, the 200-inch mirror, were ground to give the parabolic shape to bring the light to a focus. But, for the size of the GMT, if you had had to grind your mirror, it would’ve taken something like twenty or thirty years. It’s a ridiculous amount of time. And so, Roger’s idea was that you’d start with a spinning oven. You would put in glass. The glass would become molten. And then because of centrifugal force, as the mirror is spinning, glass is melting, you would end up with the original parabolic shape that you wanted. The process involves making a mold, a honeycomb mold. If you had a solid piece of glass, it would take a long time for the temperature of the glass to reach thermal equilibrium. And what we learned in the 1980s, is that temperature differences in the dome or in the enclosure, had a huge effect on the seeing.
And so, you wanted something to be able to come into thermal equilibrium really quickly. And so, the oven has a mold made of silicate material. You get the molten glass in there, and then when the mirror is removed from the oven after it’s cooled for seven months really slowly because if you do it too quickly you’ll get cracks and bubbles, then the mirror only weighs about twenty percent of what it would have if it were solid. And then you can force air through the back of the telescope and reach thermal equilibrium really quickly. But the challenge with the GMT mirrors is that they’re off axis. So, the six mirrors are acting together to become this parabola and that had never been achieved before. And it turned out at the beginning that the outer rim just wouldn’t converge. And the specifications called for getting the root mean square fluctuations at the surface of this mirror to be twenty nanometers. Tiny, tiny. Less than, I’m trying to remember the exact number now. I used to compare it to the width of a human hair. Anyways, it’s tiny (laughter).
We had meetings of the GMT board. We thought maybe the project was going to fail if we couldn’t get the outer part of the mirror to converge. In the end, part of the problem was the pitch, the stuff that you use to grind the mirror. The other thing that Roger Angel had developed was a computer-controlled lap to do the polishing. But when it was coming back on this almost potato-chip shaped form, this asymmetric mirror, the pitch was, on this small scale, slightly changing its size. Newton used something really similar to polish his mirror, so this is not new technology. But where the failure was happening was that this thing was bending the lap and anyway, yeah it’s seven years later (laughter). This all converged and we got the first mirror. But it took a long time.
Wendy, this is such an exciting time to be talking to you because the project is so strongly underway and 2029 is really, you know, at this point it’s not that far away. It’s such an interesting time to ask this question historically. What are the things that you know you want to be looking for, that you couldn’t before, that GMT will allow you to see? And in terms of theory or even your imagination, what are you open to in terms of finding that you didn’t even think you’d be able to see or know of its existence in the first place?
I think one of the exciting areas for GMT is going to be the study of exoplanets and GMT will be, I hope, the first of these extremely large telescopes. Its first light instrument is going to be a spectrograph with really high resolution. And so that will allow detection of masses of planets comparable to the Earth, if they exist nearby. And it will allow us to study the atmospheres of these planets and look for signatures of things like water and carbon dioxide and ozone and methane and signatures that could be indicative of life elsewhere and I think that if we discover life elsewhere, it has to rank as one of the most important discoveries of humankind. We’ve only known about the existence of other planets now for a quarter of a century. And it’s been possible to measure masses of the more massive planets in those other exoplanetary systems. But we’re just getting to the point where technology’s going to allow us to do the Earth mass planets and study them in detail.
Wendy, I just want to interject on that point there. When you’re talking about possibly finding other life in the universe, what is it that GMT will be able to see that will suggest? Are you talking about like the Goldilocks Zone? Other Earth-like planets? Or are you talking about specifically being able to detect evidence of life itself?
Well, we don’t know what’s out there, right? Maybe there’s lots of microbial life elsewhere and I think the best evidence to date suggests that to have an oxygen rich atmosphere you have to have some sort of biological mechanism to keep replenishing oxygen or it will oxidize. You won’t have an oxygen-rich atmosphere if you don’t have photosynthesis or some biological basis. So, the radial velocity precision that this GCLEF instrument that GMT will have has a resolution of ten centimeters per second, which is phenomenal.
And so, what GMT will allow is what you need to detect an Earth going around our sun. Now people are at sort of tens of centimeters per second, maybe fifty or so. For the first time GMT will have enough sensitivity, these things are faint. The contrast between a central star and the Earth is something like a factor of 1010. And so, it’s really hard to do direct imaging, for example, of an Earth-mass planet. But you also have to have enough sensitivity. You’ve got to have a big enough light bucket to get enough photons to measure these kinds of radial velocities. So, GMT will be able to do that. And then there’s the question of what can you measure in the atmospheres? And part of that depends on what the distribution of nearby planets turns out to be. Is there life nearby that is detectable? What kind of life will it be? These are intriguing scientific questions now.
How long have people wondered, are there other planets? And of course, given the way we understood how the solar system formed, I think most people in the field assumed that there would be exoplanets eventually discovered. But the actual discovery happened only twenty-five years ago. Is there life elsewhere? The fact that life has arisen on Earth in so many different places and in so many different environments from subthermal vents on the ocean floor to if you drill down deep in the Arctic permafrost you find these things that breathe hydrogen and eat sulfur, and other exotic life deep on the ocean floor. It is amazing that you have life existing with no sunlight, and really high pressures. So, life is ubiquitous. And also, radio telescopes detect the presence of amino acids in space. So, the idea that there’s not life somewhere else seems really unlikely. What kind of life? How easy will it be to detect? Those are all open questions.
I’d like to juxtapose, Wendy, the maturity of the field of exoplanets versus the maturity of the field of star formation. Specifically, if we understand that our sun is a not particularly special star, right? Wouldn’t it then follow, not observationally, but theoretically, that exoplanets and even Earth-like planets would also be not particularly unique or special?
Yeah. I think that’s a fair statement. They’re unlikely to be special and I think the more exoplanetary systems that are discovered, the more that becomes clear. And I think early on, many of the planets that were discovered were really high mass. But that again, was available technology. They were just easier to find and now we’re pushing down to the point where technology is going to allow us to find more Earth mass types of planets and planetary systems. Anyway, I think it’s a huge realm that remains to be explored. And again, there will be a synthesis between space and ground-based telescopes that will contribute to answering these questions. It’s going to be an exciting decade. It really is (laughter).
Wendy, it’s a big night sky out there. How do you know where to point the GMT?
I think that coming back to your earlier question, you know some of the most interesting discoveries that have happened over time are the unexpected ones and I do secretly hope that there will be something that we’re not even thinking about now, that we don’t even know what question to ask. That something new will come of it. And as I said earlier, in astronomy it’s largely been the development of new technology that opens up a new window and wavelength or resolution or sensitivity and suddenly you discover something that you had no capability of discovering before. So, that may be the most interesting thing to come out of GMT. And we’re not asking the question yet.
What are some of the big, unresolved questions both with black holes and supernovae that GMT might be useful for?
I think with black holes you’ll be able to carry out a census really over the observable universe, which is going to be important with the next generation of telescopes. And I think with supernovae, there’re still questions I think that we need to address concerning potential, so going back to cosmology, of understanding the underlying physics of these objects. The microwave background observations set the bar really high for what can be inferred about the Hubble constant. Those groups understand very well the systematics of their instrument and if they make the simple assumption, but it is only an assumption, that the Standard Model that has dark matter and dark energy is correct, then you can essentially infer at the present day what the expansion rate is. And when they do that, they get a value of 67.4 +/- 0.5. So, it’s better than one percent. And we’re not there in terms of making these measurements locally with Cepheids and supernovae.
And so, this question of whether there’s additional physics beyond the Standard Model relies us on being able to make these measurements locally with really high precision. And not just precision, but again, accuracy. And so, when we use objects like supernovae, we use them in an empirical way because theoretically we don’t have the predictive power to actually go from first principles to do that. But at this point we’re learning that there appears to be dependence on the mass of the galaxy, how bright your supernovae is depends on whether you’re in an elliptical galaxy or spiral. The luminosity of your galaxy. We don’t understand the reason for that. It’s certainly nothing to do with the galaxy. It’s some sort of local physics that might have to do with the progenitor abundance or, we don’t know. But we want to sharpen those questions. And I think the same is true of the Cepheids. We were talking about a factor of 2 uncertainty in the Cepheids early on before the Key Project. Cepheids are going through a period of evolution where they actually cross the so-called instability strip in the HR diagram several times during their evolution and we don’t know what point in the crossing they’re at. But the luminosity depends what point they’re at. And maybe it’s related even to the metallicity.
These are just issues that we couldn’t address before. But if we’re going to try and aim for an accuracy of one percent, at that level then we’d better understand these things. Because they are going to raise their ugly heads at the one percent level. And they’re lost in the noise when you’re at the few percent level. So, I think there will be things that GMT will contribute to these kinds of questions too. And so, will JWST. And we’re going to learn a lot about those things and possibly about cosmology, which would be pretty exciting because again, the Hubble constant has a huge- it’s the most important of the cosmological parameters in terms of its effect on cosmology. So, if you can measure it really accurately, it helps you pin down the other parts of the cosmological model. And if there is something missing, an accurate value of the Hubble constant is what is going to point you there.
Wendy, going back to the Standard Model and really big aspirations in terms of moving the field forward and this is beyond GMT. This is a question about astronomy in general, right. In what ways might astronomers contribute to figuring out a way to integrate gravity into the Standard Model?
Well, I think the discovery of dark energy, even dark matter too, these discoveries came out of astronomy, right? They weren’t predicted theoretically. No one said, okay, this is what you need. And so, I think in that sense it will contribute a lot. Here’s this mysterious substance that we don’t understand, and yet it’s seventy percent of the overall mass and energy composition of the universe. That’s a pretty important constituent and yet, right now there’s no understanding of that. So how do you unify the fundamental forces and will there be a theory that will naturally bring quantum mechanics and general relativity into a unified theory? The people doing superstring theory view the cosmological constant as an enormous headache. It doesn’t arise naturally (laughter).
And yet, we’re learning something about the universe. These results are coming from astronomical measurements. I think it’s still an open question as to what we are seeing. I think the best evidence at this point is suggesting that we’re seeing something like Einstein’s cosmological constant where the ratio of the pressure to the energy density is -1. The w parameter. But we still don’t know if it evolves with redshift. And that’s something we’ll learn with new missions like WFIRST, which is now the Roman Space Telescope. And LSST is going to be finding many, many, many supernovae. And JWST and the big telescopes are going to give us better constraints there. So, I think we will either nail it down and say, okay, it’s pretty close to the cosmological constant. Or we’ll learn that maybe it does evolve even though the best evidence right now is not suggesting that that happens. So, I think that’s the kind of thing we will contribute.
The dark matter issue, that’s a tough one. I mean, decades now have gone into searching for this stuff. And the hope really was that WIMPs would end up being the dark matter. And that you could discover these in these experiments on the ground and also with accelerators like CERN or find evidence from the Fermi gamma ray telescope. That you would find some evidence for dark matter. What it is. But you’re really getting to the limit of the neutrino floor with WIMPs. And that’s looking like a dead-end right now after decades of exploration. So now there are a lot of creative ideas of other kinds of detectors and a lot of young people coming into the field. And it’s a phenomenally important and exciting area. But there is still a huge parameter space that remains open for exploring what the dark matter could be, ranging from some new elementary particle to primordial black holes. And maybe it’s not detectable! Maybe it doesn’t interact in a way that we’re actually going to detect it in a laboratory and so, it’s what keeps the field interesting, right? We keep looking for evidence and maybe we will learn something astrophysically again about its distribution, where it’s located on a scale that we don’t yet understand. But yeah, lots of open questions.
Wendy, perhaps it’s as much a philosophical as it is a scientific question, but when you say, when you’re willing to play around with the idea that dark matter is not detectable, do you mean detectable, ever? Not that there are some technical limitations that we don’t currently have? Or do you mean simply that there’s a force in the universe that is outside the boundary of scientific understanding or inquiry?
I mean, we know of its existence because it interacts via gravity, right? So, we detect that it’s there because of the effect that it has on the luminous matter that we can see. But maybe it interacts so weakly or not at all with baryonic matter, and if it doesn’t interact except by gravity, maybe there is no way for us to detect it. It’s a possibility.
So, the philosophical question there comes then. At what point does that brush up against the possibility of the universe having metaphysical aspects to it?
So, I guess the way I would frame that is I am not uncomfortable with the idea that there are things that just are beyond our ability to measure them. And that’s what science is about: Measurement. And I think it’s too early to give up on the idea that there will be a theory that will explain things naturally. The idea that there’s a theory of everything or whatever you would want to call it. A natural explanation for things like dark energy, a theory that that could emerge and also explain inflation in a natural way other than just suggesting that something like an inflaton was present. I think it’s too early to give up on the idea. I don’t particularly like the idea of an anthropomorphic view that because right now we don’t understand things that that must mean that there’s a multiverse and things we don’t understand. Which could be the case. But I don’t think we should give up on trying to understand. But it could take another century before we do understand. And fields of science go dry for a while because there’s no way of actually addressing the questions that are there. And that doesn’t bother me, it’s just where we’re at now. And that’s okay.
Wendy, back on planet Earth (laughter). What were some of your considerations in terms of stepping down from the directorship at Carnegie and joining the faculty at Chicago?
Around the point when I was at the ten year mark of my directorship, I guess I had thought in my own mind, about a decade would be the reasonable amount of time to get something done, and then someone else would do it. And actually, earlier than that, going back to our earlier discussion, I was so afraid that I would hate it that I told myself okay, if you really do hate it, if you’re really miserable, do it for two years and then get out. You don’t have to make yourself miserable. And at the one year mark I realized, hey, I’m actually really enjoying this. And if I’m going to step down after two years I’d better tell people so they can have a search and replace me. So, I realized at that point I was enjoying it and I wanted to continue doing it.
I did continue doing science as director. We had this Carnegie supernova project and we got these results from Spitzer for the Cepheids in the mid-infrared. But I was waking up with GMT, going to sleep with GMT. It was a big, by the time I stepped down it had begun approaching a billion dollar project. And when we started putting together a budget in 2004 or so, in not inflated dollars – so it’s not a fair comparison – but it was a $600 million dollar project. And I think my role in GMT, as we sort of touched on, was I brought the partnership together, found new partners, launched it in terms of starting mirrors early on. And also, how we did things. I was, again the model of Magellan, strongly in favor of having a central project office, getting people, the various partners, to give money directly to the project office. You start a negotiation, everyone wants the money for themselves, right? We want to build this instrument. We want you to buy this from us. What’s in it for us? And I didn’t see how you’d bring a project in on budget if you let everybody decide what they wanted. You have to build the telescope, carry out construction on the mountain, make the mirrors, and surely that has to be the project manager and the board’s decision of what to do. Not an individual partners. So, all that had to come together and we were working on a legal agreement to make these legally binding commitments. And my feeling at that time was, okay, when we go into construction, this could be someone else’s project. And I was sort of done.
I’d done it for a decade. I didn’t see myself doing it for the next decade. And I felt that I was still young enough and had enough energy to have another chapter of really being a scientist again. And that’s who I am. And that’s what I love to do. That’s what fires me up. But I did love being director. And the Carnegie director was -- it’s different from being a department chair or something in a university, I had a budget that could allow science. I could help seed different things at the observatory. I could start theory programs because I thought it was a good thing to do. It was fun. And I enjoyed the people.
And you probably also discovered skills in the political as well in organizational psychology realms that you never knew you had before in this position.
Yes. That’s a good way of characterizing it. I did. You know, there are parts of me that when you’re a research scientist, you don’t tap into. And I think I just enjoyed the people. For me, I enjoyed it a lot. But as we got into construction and more lawyers had to be involved and it just- that’s not how I wanted to spend the next decade of my life (laughter).
Yeah. And Wendy, how much of it was simply wanting to be part of a traditional academic environment and enjoying the trappings of, the life of a professor? Teaching seven hours, having graduate students, that kind of a thing?
Yeah, well the offer came out of the blue. I was not expecting it and I wasn’t looking for it and at the beginning I was being polite. They said, “Come visit.” So, I went, and I visited because I had no intention of ever leaving Carnegie. I love Carnegie. I still love Carnegie.
So, your thinking was you would step down from the directorship and join the staff once again?
But a lot sort of happened in the few months where I was talking to Chicago and thinking about how this would go. And you know, what would I do? And I think, so you’re right. The idea of having students of my own. So, through the Key Project I had students that I co-advised. I had students at Caltech that I co-advised. And I’d never taught before other than as a teaching assistant when I was a graduate student or the occasional class I would fill in at Caltech. And also, I think what Chicago was offering was the opportunity that Carnegie had offered me which was come just be a scientist again.
And I didn’t see that being easy when I had been director at Carnegie for eleven years and we were still in the throes of the telescope project. There’s no way I would realistically be able to distance myself from that. And the institution was changing its president. The president was a biologist. He made it really clear that he was going to lean on me to do GMT, and I thought uh, this is not going to work well. And then I had a little bit of a health scare and I was waiting for my doctor to get on the phone and I thought uh-oh, this is like a fork in the road. If this goes well, and I knew in that moment, okay, I’m going to Chicago. I’m going to have a new chapter. And it was scary and exhilarating, you know? And I didn’t know. Would I like it? I liked GMT, the Carnegie directorship. Was this a bad move for me?
And what were the family considerations? Were your kids out of the house at that point?
They were out of the house. My family knew before I did. I mean, they were telling me, “Take the position at Chicago. Are you crazy?” Cause they’d watched me in the last couple years of the directorship and it was taking a bit of a toll on me. And everybody, my kids, my husband, my parents, they were all, “Why wouldn’t you go to Chicago?” (laughter).
It was kind of funny. And so, I did and here I am (laughter).
Wendy, in what ways did this opportunity provide for you to take on new research? I mean, set aside the administrative burdens of the directorship itself, right? If you had just gone back to the staff at Carnegie, coming to Chicago, what new opportunities might you have had to pursue? New research endeavors, new science, that you might not have had had you gone back to the staff at Carnegie?
I think for me what’s been really exciting is the opportunity to work with really, really bright students. I’ve always been a co-advisor, it’s been somebody else who was the formal advisor. Even though I might’ve been the scientific advisor and I really enjoy the teaching. I don’t have a big load though, to the point where it really would interfere with doing the research that I want to do. So, it’s new and interesting. And it’s fresh. And I have new colleagues who are doing different things. And I have more time for the nuts and bolts. I also decided, maybe slightly crazy, that when I went to Chicago I was going to teach myself Python (laughter). And that’s just been fun. So, it’s like being a graduate or a postdoc again. But you’re not a postdoc. You don’t have to worry about your career. It’s a postdoc later in life and after being a director for so long, it feels kind of rejuvenating. It’s just a different way of being again. I don’t know, I feel younger (laughter).
Did you take on graduate students right away?
I think I waited a year. I was still involved with GMT when I left. I stayed as chair of the board for another year. And that’s because I wanted to have the legal matters straightened out. I felt if I walked away and we didn’t have a legally binding commitment, it would leave the project in total disarray. And I didn’t want to do that. And so, I waited. Then it was signed, and I felt, okay, the timing now is right for me. And then I think I took on my first graduate student that fall.
Have you had opportunity to interact with undergraduates and teach undergraduate classes?
Yes. And so, in fact, I’m in the midst now of writing some papers with some undergraduates that has been a real treat for me. They’re so smart! They’re so fun! Yeah. And I do. I have taught several undergraduate courses. And this quarter I’ve been teaching jointly with Neil Shubin, who’s an evolutionary biologist, paleontologist. And we teach a course called Origins to undergraduates.
So, we start with the Big Bang and go all the way through to galaxy formation and star formation. And he picks up on formation of the Earth and all the way to consciousness. A course I would’ve loved to have taken.
Yeah. Me too. Where can I sign up? That sounds great!
So, it’s fun. It’s been you know, again, a real change.
And between the undergraduates and particularly your graduate students and even postdocs, what are the kinds of things that they’re looking for in their careers? In terms of them being at the vanguard for the next generation in astronomy and astrophysics?
I think it varies student by student and I think it’s one of the things that I like, too. Everybody is different and everybody has their own interests. And I have students who clearly want an academic position and really enjoy cosmology. I have other postdocs now who are working with me to come back also to this question of the initial mass function that I was interested in early in my career. And we’ve been doing modeling and have a lot of Magellan observations that are kind of fun. And some of them I think want positions that don’t have to do with academia and academic career, ultimately. So, you know, there’s no one size fits all. I try and meet students where they’re at and where they want to go.
And just to bring the narrative right into the present. What are some of the things that you’re involved in now on a day to day?
Well, so day to day, right now, in the last month day to day, the proposals for the James Webb Space Telescope were due. With some students and postdocs and Barry, we put in some proposals for that which gets you really fired up about what JWST is capable of doing. The Gaia, the European parallax satellite, came out with their third data release a couple weeks ago. So, we’ve been pouring over those data with students.
It’s been a really busy month. And we’re learning a lot. And we should have something I think really interesting to say soon about the Hubble constant. And with a much firmer zero point that’s based on not just Cepheids or tip of the red-giant branch, which is what I’ve been involved in since I went to Chicago. And RR Lyrae stars and carbon stars, so we’re using several different distance methods again. It’s this strong feeling that I have that you don’t get the answer with one particular method. That the only way you can get a robust overall measurement of the systematics is to use different methods. And then you see what the systematics are and the different ones. So, that’s been really fun. I taught remotely by Zoom during the pandemic. That was an interesting new challenge. But it went better than I thought it would. I’m just now being joined by the dog we adopted during the pandemic and then learned a few weeks later that she was pregnant (laughter).
So, we have a litter of seven puppies (laughter).
Mazel tov! (laughter).
Thank you, and our son provided pictures for the shelter where we got her and they put them all up and within a day they’ve been claimed. So, they will leave us January 5th. (laughter). But it’s actually, it’s been a really nice kind of diversion from the pandemic.
Any plans to go back to Chicago? Or you’re going to wait until the world is vaccinated and it’s safe to travel again?
I’ve been traveling very little. So, the pandemic has turned out to be a really productive time. And I walk every day for exercise. But the not travelling I think has just allowed us to finish a lot of things that would’ve taken longer to finish. And I think, I have no desire to get on an airplane right now and risk getting Covid. Yeah. I’ll wait for the vaccine.
Sure. Wendy, for the last part—
But we have a grandchild arriving at the end of April.
And nothing’s going to keep me away from that.
Okay, there you go. Well. Wonderful. Wendy, for the last part of our talk, I’d like to ask a few broadly retrospective questions about your career and then looking forward to wrap things up. First, I’d like to ask, I certainly don’t want to burden you with every award and recognition that you’ve received over your career. But I am curious, among all of them, looking back, are there any that stand out that are most personally meaningful for you? Or stand head and shoulders above in terms of the validation by your peers that you’ve received?
The Gruber Cosmology Prize is meaningful to me. I think the Hubble constant has been such a longstanding problem and I think recognition that we had really made a difference in that problem was meaningful. The Heineman award of the AAS and American Physical Society, that was meaningful to me. And then election to the National Academy of Sciences. That was extremely meaningful.
One theme in your career on the sociological side has been there’s been no grand plan, right? You’ve never sort of plotted out what comes next. So, I want to ask on the scientific side, what are some of the constants? What are the same questions, no matter what new position you find yourself in, no matter what new collaboration you’re a part of, what are the same fundamental questions that have always been with you throughout your career?
I guess it’s designing an experiment or an observation, usually a series. I don’t see my work as this is what I’m going to do and it’s going to answer things. I guess I have seen it as a larger patchwork that takes a lot of effort to get to the ultimate thing that I’m trying to address. And it’s important to me to look under the rug. To really tease out and answer a certain kind of question. But if it was easy, it would’ve been done. And so, there are real challenges that you have to think about.
And so, I think in terms of what you’re asking, I really do try and map out in that sense, okay, what will it take to get there? What do we have to do in terms of calibration? What do we have to do in terms of understanding this particular effect? How can we test this result? I’m very big on testing and on doing things independently in different ways. And part of it is checking for natural human error. But the other is these astrophysical objects we’re using are limited, right? You would think that making measurements of things that are that far away … these aren’t easy measurements. We’re using objects that are complicated. They’re not necessarily going to give you a result without uncertainty. So, I think, and this comes from having been at Carnegie too. We had the opportunity to really take on long term projects. I’m not interested in a fast result or doing things maybe first or the fastest. I’m more interested in okay, how can we really learn something and what will we need to do it? And maybe it’ll take many years. It usually does take many years. So, maybe that answers your question.
Yeah. Absolutely. And in terms of astronomy being so much geared towards basic science, you know? It’s not necessarily about solving human problems here on Earth. Have you found over the course of your career that making the case for society to support the kind of research that you do, has it gotten easier? Has it gotten harder? What’s the long-term prognosis do you think for supporting the science that you do and that needs to be done?
I think it’s gotten harder. But I think it always was hard. You were just reminding me so, around the time of the Key Project, a reporter asked me, “So, how do I explain what you’re doing to Joe Six Pack?” And I think it is hard to explain what we do to Joe Six Pack, because it’s maybe a terrible name, but I have relatives, my own relatives who really thought I was nuts (laughter). And they don’t have any interest in what I do and in their lives, there’s no room to think about the universe.
And when some people think about it, it scares them. I’ve had people come up to me after talks and say, “How do you think about these things? Doesn’t it scare you?” And I really do see science as a phenomenal human enterprise. I mean it’s a journey we’ve been on for millennia. Asking questions, trying to learn about nature and the scientific process of experimenting, coming up with ideas, testing those ideas. Maybe some of them are wrong. Not maybe, sometimes some of them are wrong. And sometimes it’s the data, sometimes it’s a theory. But it’s a self-correcting process. We just keep asking questions and we might not have a final answer at a given time. We’ll learn that later. And it doesn’t matter who learns it, right? It doesn’t matter if you’re a senior faculty member or a graduate student. There’s no hierarchy in that way. The evidence will win out. Which is not to say that it’s always going to be right, because they’re going to be wrong things that we measure. But I don’t know of any other enterprise like that. The scientific enterprise. And I think it’s a phenomenal human achievement. It’s part of the answer to the Joe Six Pack. If we’re taking a car journey and we put shades up on the windows and we’re not interested in where we’re going, life is a lot less interesting.
And then, in addition, as part of that journey look at the things that have benefited humankind as we’ve learned these things. Science has been of enormous benefit. But it’s not that that’s what we set out to do. So that understanding that not all science is aimed at solving all our problems, disease or other problems. But it could be a spinoff. Nobody doing nuclear magnetic resonance ever envisioned how we would be depending on these things for our lives. And Einstein sitting and thinking about gravity and gravitational waves and general relativity and the fact a hundred years later all of our handheld devices would have GPS, you know, this is not what motivates scientists. But the spinoffs we’re not thinking about, those things can have enormous consequences. And I don’t think people appreciate that in a general sense.
And so, I do worry as people start thinking about science as a political issue. That scares me and concerns me because I don’t think it is a political issue. And if people don’t learn about science and the scientific process, then I can see how they can come to that. I think as scientists we do have a responsibility to try and help the public understand what it is that we do. Which is why, with the interest in the Key Project results and public speaking that I’ve done, I do enjoy talking to the public. And I do feel that it is something that as scientists, we should try and do. Because I find it fascinating and I feel enormously lucky to have had the career that I’ve had. And sharing that with people who don’t do science, I think, and having them understand you know, why is this exciting, is an important thing to do. Just staying up in your ivory tower, I don’t think is the right place to be all the time.
Wendy, on that note of excitement, for my last question, looking ahead. What are the things that you’re most excited about? That you’re most optimistic about in terms of being a part of fundamental discovery for the remainder of your career?
So, it’s funny that you’re asking me this question now because occasionally I will ask myself over the years, okay, what do I want to do next? And I’m at that point right now because I think we’re learning something really interesting about the Hubble constant and I think the Gaia results are going to be fun and the project we have now with the tip of the red-giant branch offers a completely different way of measuring the Hubble constant independent of Cepheids. But I do want to have another- I still think I’m young enough and enthusiastic enough that I do want to have another chapter. I’ve been getting my feet wet a little bit with this project with the IMF. But I’m playing around with some ideas, probably not ready to talk about them yet. About where do I want to head that would be completely different and the opportunity to be able to do that really excites me.
That’s awesome. Well, we’ll have to stay tuned for that (laughter). Wendy, I want to thank you for spending this time with me. It’s been fantastic learning all about your career and I really appreciate this. So, thank you so much.
Well, thank you. It’s been a pleasure talking to you.