“Astronomy is out of kindergarten, but only in about the third grade”: a tribute to Vera Rubin

vera-rubin

 

10 January 2017 – Vera Rubin, who transformed modern physics and astronomy with her observations showing that galaxies and stars are immersed in the gravitational grip of vast clouds of dark matter, died this past Christmas Day at the age of 88. She had a lifelong love of the stars, championed women in science and was blunt about the limits of humankind’s vaunted knowledge of nature. She was often quoted “We know very little about the universe. I personally don’t believe it’s uniform and the same everywhere. That’s like saying the earth is flat.”

She was refreshing.  Her work was required reading in my recently completed physics symposium. And as the science writer Dennis Overbye noted in his blog:

Her work helped usher in a Copernican-scale change in cosmic consciousness, namely the realization that what astronomers always saw and thought was the universe is just the visible tip of a lumbering iceberg of mystery.

He is speaking about her discovery of “dark matter”, her most celebrated contribution, that invisible stuff that makes up most of the mass in the universe. In the 1930s Fritz Zwicky, an idiosyncratic Swiss astrophysicist, had suggested that the brightly shining stars represented only a part of the cosmic whole. There must also be “dark matter”, unseen but revealed indirectly by the effects of its gravity. That conjecture languished on the margins until Rubin, working with her colleague Kent Ford, examined the puzzle of galactic rotation. Spiral galaxies such as Andromeda, she proved, were spinning so fast that their outer stars should be flying away into the never-never. They weren’t. So either Einstein was wrong about gravity, or gravitational pull from vast amounts of something invisible — dark matter — was holding the stars together.

Rubin and Ford expected the speeds to conform to Newtonian gravitational theory, whereby an object farther from its central mass orbits slower than those closer in. To their surprise, the scientists found that stars far from the center traveled as fast as those near the center. They found that something other than the visible mass was responsible for the stars’ motions. Each spiral galaxy is embedded in a “halo” of dark matter – material that does not emit light and extends beyond the optical galaxy. They found it contains 5 to 10 times as much mass as the luminous galaxy. As a result of Rubin’s groundbreaking work, it has become apparent that more than 90% of the universe is composed of this invisible material.

The discovery reshaped cosmology, though initially her colleagues embraced it unenthusiastically. Astronomers had thought they were studying the whole universe, not just a small luminous fraction of it. New theories developed on what the matter might be – but its fugitive particles escaped all direct detection. Dark matter, which hasn’t been directly observed, led scientists to say “we know what dark matter isn’t rather than what it is”.

And her findings highlighted how much we don’t know. Astronomers thought they were studying the universe, she once said, “and now we learn that we are just studying the 5% or 10% that is luminous.”

The castigation of the Nobel committee has already begun. Why hadn’t Rubin won the prize? (Only the living are eligible; she can’t win now.) Scientists on Twitter howled at the Nobel committee for ignoring her. In fact, no woman has won a Nobel prize in physics for 53 years. And only two women, total, have received Nobel prizes in physics: Maria Goeppert-Mayer (for her work on atomic nuclear structure) and Marie Curie. Last October, after an article on Rubin in the Washington Post, #NobelForVeraRubin started trending on Twitter.

Lisa Randall, professor of physics at Harvard University, is among many who thought Rubin sufficiently deserving and in her obituary she wrote: “Dr Rubin’s insight was revolutionary . The elephant in the room is gender.”

Prizes, after all, are awarded unfairly. This is true of science prizes as literary ones. A small group of people are invited to submit names. To nominate, you must be at least one of the following: a winner of a Nobel Prize in physics; a member of the Nobel committee; a member of the Swedish Academy; a tenured professor at a selected university; or a scientist invited by the committee to submit names. These people are busy and important, and attending to their own careers is enough of a burden. What’s more, to reach their sufficiently “notable” position, they’ve been in the field a while, accumulating allies and enemies. There are grudges to settle and favorites to be rewarded. No prize jury in any field is likely to reward solely on merit.

And even Rubin acknowledged the exceptional hurdles she faced and reportedly chastised conference organizers if they failed to invite female contributors. She advised even the Pope to put more women on his committees. In its review of her work The Economist noted:

– in her youth, when she arrived for a four-day stint at the Palomar Observatory, home of the world’s largest telescope, there were no women’s lavatories. No female astronomer had ever worked there before. How could they “when it would mean walking home late at night?”

– when in 1947 she requested a graduate-school catalog from Princeton, the dean told her not to bother: “women were not accepted for physics and astronomy”.

– George Gamow (later her doctoral adviser) said she could not attend his lecture at the Johns Hopkins Applied Physics Lab “because wives were not allowed”

– her master’s thesis was, her Cornell supervisor said, worthy of being presented to the American Astronomical Society. But she was about to give birth, so, he suggested, he would present it – but in his name. She refused. Her parents drove up from Washington, DC and took their 22-year-old daughter, nursing her newborn, on a grueling snowy trip from upstate New York to Philadelphia.

She noted that although all of these gender rows (and many, many more) were unpleasant, defeat was worse: “Protest every all-male meeting, every all-male department, every all-male platform”.

Though Rubin doubtless would have enjoyed the Nobel prize money, she ultimately came away with something more substantial. Elizabeth Lopatto who writes about science for The Verge noted the many subfields her work spawned. True, these are less likely to be written about by journalists than the yearly Nobel pick, but Lopatto noted they tend to leave a more enduring legacy. Every scientist knows their intellectual lineage; Rubin, as the matriarch of dark matter, will doubtless be remembered by those who matter most: the people who owe their careers to her discovery.

Aristotle has suggested that the recognition and appreciation of those in your field is far more valuable than fame itself; interviewed two decades ago, Rubin seemed to agree:

“Fame is fleeting. My numbers mean more to me than my name. If astronomers are still using my data years from now, that’s my greatest compliment.”

And so it shall be.

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