“How do you think we solve the dark matter problem?”
There was an awkward pause. I was in my seventh and final year of graduate school, my 11th year of formal physics education, and no one had ever asked my opinion about a major problem in my field of expertise, cosmology, which studies the origins and evolution of the universe and its contents. I was completely unprepared to respond to such a question, much less to the person who had asked it.
I had introduced myself to Dr. Vera Rubin, the woman who first conceived of the technique that found evidence for dark matter, because, for one, she was Vera Rubin, and two, I thought that because her son had hosted me at his Passover Seder some years before, I had an in. But I hadn’t really thought through what else I was going to say, and it hadn’t occurred to me that she might be interested in my opinions about science.
I don’t recall at all what I said in response, but I do remember Rubin asked me if I would sit with her at the lunch banquet that was next on the schedule at the 2009 Women in Astronomy conference. She corralled another older white woman, and as we sat down, she turned to me and the other young women astronomers at the table to ask, like a total fangirl, “Do you know who this is? It’s Nancy Roman! The mother of the Hubble Space Telescope.”
The next day, when we were on our way to the White House for a meeting with the chair of President Obama’s newly formed White House Council on Women and Girls, I was asking Rubin about her ongoing research (she told me that at age 80, she was still going to the office frequently), when I realized she was carrying a purse, a no-no for White House visits. When I explained the situation, she said, “Oh! When I came here for an award, they let me keep my purse!”
She very easily could have said, “When I came here to receive my National Medal of Science from President Clinton…” But as I was learning quickly, Rubin was more interested in science and encouraging young scientists than in advertising her significant achievements.
I wouldn’t have objected to her having a kind of pride in her 1993 Medal of Science, given that I had always assumed it was a stepping stone to something greater: the Nobel Prize in Physics. Finding the first physical evidence for dark matter was just that big of a deal. Although Fritz Zwicky first proposed that something called a “dark matter” might exist, Vera Rubin was the astronomer with the vision to do an experiment that would find it. Along with astronomer Kent Ford, who was an expert instrument builder, Rubin used a new technology to study the movements of stars in galaxies. They discovered a mismatch between what physics told them they should see and what they actually saw in what would be called the “galaxy rotation curve problem” and what is known today as the “dark matter problem.”
The issue was this: Well-understood physics allows us to calculate how quickly the Earth orbits around the sun based on how far the Earth is from the sun and how massive—“heavy”—the sun is. The same rules apply for stars in a galaxy, which are rotating, or orbiting, around the galaxy’s center. Rubin, who had been marginalized from studying mainstream problems in astronomy because of her gender, approached Ford about using a new instrument he had built to study the intensity of light in different wavelengths, an advanced spectrometer that could allow her to study the movements of stars in greater detail. (The physics of spectra is discussed in ”The Physics of Melanin” in Bitch’s Winter 2017 Chaos Issue.)
What Rubin and Ford found would change physics forever. The movements of the stars at the edge of the galaxies they studied didn’t match what physics predicted based on their mass, which could be estimated based on how much light they were emitting. In other words, there was a mismatch between the amount of matter they could count and how physics told us that matter should be moving. At the speeds the stars were going, the galaxies should have been flying apart, rather than being held together by gravity.
Something was missing from the calculation. Something that wasn’t luminous, something dark, was holding the galaxies together. And although it would take years and much more data to fully convince the global astro/physics communities, eventually this result came to be widely accepted as a fundamental feature of cosmology. It has affected research in physics on every scale. In 2016, we still have no idea what constitutes the dark matter except that it isn’t like everyday matter because it doesn’t radiate light like everything else does. Thousands of scientists work on experiments that hope to directly catch a dark matter particle. All of our computer simulations to study the formation of galaxies fudge a dark matter–like candidate to make the simulations match observational data from telescopes. It’s impossible to properly interpret most of our data about galaxies and the early universe without taking the presence of dark matter into account. Hundreds of new research papers are published every month with new theories about what the dark matter is and new data telling us what it’s not, as well as Dr. Rubin’s favorite interpretation of the data, that our theory of gravity needs to be modified, not our understanding of matter.
Thanks in large part to Dr. Vera Rubin, the woman who couldn’t get into an astronomy PhD program because she was a woman, we now believe that dark matter likely makes up about 80% of the matter in the universe, and finding out what it is continues to be one of the greatest unsolved mysteries in all of physics. If she had been arrogant about her discovery in a field known for arrogance, my younger self would have understood. But Rubin was hungry for answers, not adulation, and she knew her search meant asking for help from young Black women PhD students who had the audacity to introduce themselves.
Because of this, I remember Dr. Vera Rubin as the first physicist to treat me like I had a brain, like I too was a scientist with contributions to make to our field of study. Until she asked me what I thought, it had never occurred to me that I could have an opinion about dark matter that mattered. But I think it is in part thanks to her that I have since come to believe that I do, which is one reason I have become an expert on what I think should be your favorite dark matter candidate, the axion (whose origin story includes another esteemed woman, Dr. Helen Quinn).
Thus, I was devastated by the Boxing Day news that Vera Rubin had died. Not long after we met, she arranged for me to give a talk at her scientific home, the Carnegie Institution for Science, but Snowmaggedon 2 intervened that week, and we never met again. I long to listen to her talk about her life again. I also feel a deep bitterness that the Nobel committee refused to recognize her contribution. In the coming months, it will be argued that because we have not directly detected dark matter with a particle experiment, the prize was not yet deserved. But we still don’t know the cause of cosmic acceleration, which was recognized in an award to three men (of tens who worked on its discovery) in 2011.
Rubin never talked to me about the importance of promoting women in physics and astronomy, but she didn’t have to. I met her at a women in astronomy meeting, and she dared to treat me like a scientist. Even though she never got her due, she kept her eyes on the real prize: answering scientific questions that fascinated her and opening doors for people who wanted to join her in the quest. I will spend the rest of my life trying to live up to that example, and, I hope, solving this magnificent problem she uncovered for us. As Adrienne Rich wrote for Caroline Herschel, another woman astronomer who never seems to get her proper due:
I have been standing all my life in the
direct path of a battery of signals
the most accurately transmitted most
untranslatable language in the universe
What a joy it is to try and translate this universe. How great it will be when the opportunity to do so is broadly available to everyone, not just mostly white men.