The good news is that Katherine Freese’s cosmic cocktail recipe, with its 3oz dark matter and ½oz hydrogen and helium, is a perfect match for the six parts gin to one part vermouth of the traditional martini. All the other things we know about – radiation, neutrinos, heavy elements and black holes – add up to less than an olive’s worth. The bad news is that the remaining 7oz we have to contend with is the ice of the cosmological constant or dark energy, which will gradually dilute the cocktail by accelerating the expansion of the universe while it maintains a constant density.
Freese describes the puzzle of dark matter in the universe as the “longest outstanding unsolved problem in all of modern physics”. (A proper theory of superconductivity may yet give dark matter a run for its money, but that is another story.) What she means is that nearly all the relevant scientific community agrees that there is gravitating material that neither emits nor absorbs light or any other form of radiation. But we cannot agree on what it is or is most likely to be despite nearly 40 years of proposing and ruling out candidates.
By the time you read this review, several groups may have converged to claim firm detection of some WIMP or dark matter candidate
The story has two key aspects. First is the gradual accumulation of astronomical evidence – on scales from individual galaxies on up to clusters and the whole observable universe – for non-luminous matter outweighing the luminous by 5 or 6 to 1. Is there dark matter in this room? Yes, undoubtedly. But we live in an unusual part of the cosmos that is heavily dominated by ordinary, luminous matter, made of atoms, molecules and all (called baryons); and we could not live elsewhere.t
The second aspect of the story is the flowering of many different schemes for describing the forces that bind ordinary matter (called electromagnetism, the nuclear force and the weak interaction) and how these forces might be brought into closer communication with the force that you know best, gravity. None of the schemes has been wholly successful, but many of them imply the existence of non-baryonic, possible dark matter particles, with names such as WIMPs (weakly interacting massive particles), axions and Z-balls.
Katie (to her friends, and I count myself on the ragged edge of this enormous group) is by training a theoretical particle physicist. Thus she has been involved in suggesting several of these schemes and their particles, designing experiments to look for them, and comparing output data with what you expect from the various classes. Three sorts of experiments are possible if you want to look for the hypothetical particles:
- Make some dark matter particles out of something else in a giant laboratory accelerator, like the Large Hadron Collider at Cern that was caught making some Higgs particles a year or two ago
- Catch a few of them as they pass through your lab
- See high-energy photons (X-rays or gamma rays) coming from some place in space where dark matter particles are decaying or crashing into each other and annihilating.
Most astronomers would call the second and third of these observations rather than experiments, but the author and her close collaborators are physicists.
Versions of all three searches are currently in progress, and, at any given moment in the past decade or so, one or two experiments have seemed to be recording marginal evidence for one sort of dark matter or another, while some other experiment gives conflicting upper limits for the same sort. Thus, it is possible that between the writing of The Cosmic Cocktail and your reading this review, several groups may have converged to claim firm detection of some particular WIMP or dark matter candidate. But I wouldn’t bet the rent money on it.
This book blends two rather different flavours, and I am not sure which is the gin and which the vermouth. First is the enormous excitement of working on a front-line problem in science, which is obviously not unique to physics. The other is the great fun Katie has had, and continues to have, being a female physicist. I, 14 years her senior, have similarly enjoyed myself, and we are not by any means unique. A contemporary female astronomer described her arrival at her undergraduate institution in Scotland as: “Look at all the lovely men!” Indeed, there are large numbers of lovely, intelligent, exciting men (and women) in the physical sciences. We three have each had some subset as husbands, sweethearts, close friends, mentors and surrogate fathers, uncles and siblings.
Sadly, today’s young female scientists do not seem to be having the same experiences, or at least not feeling the same way about the process. I’m not sure why. Perhaps it is because there are more of them – at least eight others appear in The Cosmic Cocktail, most somewhat younger than the author. Perhaps science now attracts different sorts of women from those of 30 or 40 years ago. Or perhaps all of life is now more real, earnest and difficult.
Several passages in The Cosmic Cocktail report liquid martinis or, more often, good wine and food as an intrinsic part of conference-going, the awarding of prizes and general schmoozing with one’s scientific colleagues. I hope for the sake of my younger fellow female scientists that ever-tighter budgets and the need to pay the rent will not bring to an end this aspect of being part of the physics community. I hasten, however, to assure you that the winos mentioned in the section on supersymmetry are particles associated with the W boson, not the experimenters, and they are pronounced “weenos”.
Justice to our scientific ancestors requires a few words about words. The phrases “dark matter” and “dark stars” appeared in print as far back as 1922, in papers by Jacobus Kapteyn and James Jeans, who looked for them in the disc of our own Milky Way. The disc does indeed contain gas and very faint stars that they could not detect. Modern “dark stars” are made of dark matter particles, with accreted hydrogen and helium, and modern dark matter means the non-baryonic kind. Neither has been seen, but the names are old.
As an aside, this volume repeats a few common misconceptions, for instance the multiplication of epicycles on top of epicycles in Ptolemaic cosmology up to the time of Copernicus; Einstein having rejected the cosmological constant as “his worst blunder”; and a universal belief in the early 20th century that the Milky Way was all the universe. The claim that the Andromeda Galaxy weighs about a billion times as much as the Sun merely needs multiplication by 100 or so. And just as Fritz Zwicky did not coin the phrase “dark matter”, he did not discover the first supernova, although he did spearhead the first deliberate search for them.
A number of other front-line particle physicists, cosmologists and so forth have also written up their versions of the dark matter story. Some include dark energy, which is an even less satisfactory tale, because there do not seem to be any very strong candidates. But none of the other accounts I’ve read is more fun than The Cosmic Cocktail.
Inveterate traveller, lover of “sports, sports and more sports” and grad-student habitué of New York City’s legendary nightclub Studio 54, Katherine Freese is George E. Uhlenbeck professor of physics at the University of Michigan, although she is “about to move to Stockholm (on leave from Michigan) to become director of Nordita, the famous theoretical physics institute of the Nordic countries. I’m excited!”
Born in Freiburg, Germany to two academics, Freese moved with her family to the US at nine months old. “I was raised bilingual, with my parents and grandmother speaking German to my brother and me, and we answered in English. I really like having the bicultural perspective. Sometimes I hear the voice of my grandmother watching ‘those Americans’ when they do strange things, like eat horrible white bread (she called it wobble bread). Isn’t that the definition of American…this multiculturalism? I learned to observe and study people and their behaviour, without being judgmental, and that is a good thing.”
“Yes,” says Freese in response to the inevitable question, “I was a studious child. I taught myself to read very young. When I was 10, I read Dante’s Divine Comedy for fun. I really liked Hell but got bored somewhere in the middle of Purgatory. I also loved Macbeth at that age but thought Romeo and Juliet was really stupid; I haven’t changed my mind about any of this.”
Her parents encouraged her interest in the life of the mind. “Both were biologists. My dad, originally a physicist, obtained his PhD at the University of Göttingen from Werner Heisenberg, then switched to biology (with Max Delbruck) while a postdoc at Caltech. That’s where my parents met, since my mother was a biology postdoc there. My parents played seminal roles in the foundations of molecular biology; my dad founded the department of molecular biology at the University of Wisconsin.
“I grew up in DC because they both held positions at the National Institutes of Health. Both of them encouraged my going into science. I think my dad’s secret wish was that I would someday get a Nobel Prize. I am extremely grateful for their encouragement. The notion of a woman scientist was not foreign to me, given the job my mother had. I dedicated The Cosmic Cocktail to them, as well as to my PhD advisor David Schramm.”
Asked about her undergraduate days at Princeton University, Freese says: “I am an extrovert and always sought out people to hang out with. I had a lot of friends who were math and physics majors and we spent hours together everyday at dinner in the eating hall. My boyfriend was a Near Eastern history major, but by the end he could talk the physics talk too. We played a lot of tennis. He graduated before me and I went and visited him in Afghanistan. That was an experience - it felt like I’d gone backwards in time about 500 years.”
At university, she continues, “I had expected that we would get together to discuss deep thoughts about the world, but instead it felt more like a trade school: the point was to shove as much knowledge about a given field into our heads as quickly as possible so we get onto making progress. In fact there is a lot to be said for what we did learn. It was the best way to move forward to the point of being able to do important things, be creative, etc. However, it was too intense. I had to take two years off to recover afterwards, and that is too much. I think we were just an anomalous year; we had so much work piled up on us during junior year that the entire class had to take incompletes in our lab course and finish over the summer. After that the curriculum was revamped. There was no time to be dreamy, that’s for sure.”
Freese currently lives in Ann Arbor, “about two miles from my office. I live alone (well I rent out the downstairs to a friend of my son’s). I also rent a studio in NY. I travel A LOT.”
Alas, Ann Arbor is resolutely “a college town. Everybody is either until the age of 23 or married. Not a great town socially for someone like me, who likes to have fun at bars and nightclubs, but not with people younger than my son. On the other hand, what I love about Michigan is the summer. There is no better place for outdoor activities: swimming, kayaking, sunsets on the Great Lakes, etc.”
Asked about her non-work pastimes, and whether she is irritatingly accomplished at any of them or merely an enthusiastic amateur, Freese says she is keen on “Sports, sports, and more sports. I exercise seven days a week and if I skip a day, I can’t sleep (they say that exercise is more addictive than heroin). I swim, ski, play tennis, bike, used to run (but after a skiing accident my knee won’t let me), and do weights at the gym.
“The most important sport in my life has been swimming. I started swimming competitively when I was 8, and have pretty much always been on some team. Now I participate in Masters swimming during the summer and swim in the winter at a university pool together with a group consisting of undergrads, graduate students, academic faculty and local people, ranging in age from 17 to 65. The great thing about swimming is that age matters very little.
“As a kid we played neighbourhood sports in my front yard - basketball, dodge ball, and my favourite, baseball. I got used to playing with boys as the only girl in the group. I suspect that part of the reason I’ve felt comfortable working in a primarily male field is that I got used to playing with the boys from age five on up.
“The only sport I was ‘irritatingly accomplished’ at,” Freese observes, “was water polo. I started playing as an assistant professor at MIT. Women’s water polo was not an NCAA sport, which meant that I could play on the undergraduate team, and I did. The combination of swimming and baseball from my childhood made the sport easy for me. When I moved to Michigan, I kept playing. One day the coach put me ‘in the hole’, the central offensive position, and it was pretty obvious that this was the position that I was born to play. I think I scored 11 points in that one game (and for water polo, that’s huge). I was 35 and 36 years old when I went to the collegiate national championships (with the 18-year-olds); the second time we placed sixth. It’s a sport you can’t do casually, because you need the whole pool. I missed it terribly for about a decade after I ‘retired’ from the sport.”
There are, of course, many questions - and quite big ones - that scholars in Freese’s discipline hope to answer. Asked to name those that she hopes and wishes will be answered in her lifetime, she says there are two.
“First: what is the Universe made of? I think the dark matter part will be answered in my lifetime, while I think the dark energy part is still pretty far off. The dark matter problem has been around for 80 years and I do think we are going to solve it!
“I also want dark stars to be discovered. This was an idea that my collaborators and I had in 2007. The first stars to form in the Universe could have been powered by dark matter annihilation rather than by fusion, and they could have grown to become a million times as massive as the Sun and a billion times as bright. The James Webb Space Telescope, the sequel to the Hubble Space Telescope, will have the capability to discover these. That would be so exciting!”
In the meantime, what if a good fairy were to offer Freese the gift of any skill or talent she does not now possess?
“I would sleep well every night and I would need only four hours of sleep. My whole life I have required a minimum of eight hours a night to think clearly, to do my job, yet half the time I struggle to get it. One of the hardest things for me as a student was the fear that I would sleep poorly the night before an exam. It did happen a few times and the grades tanked. One stereo playing down the hall in the dorms could cost me, big time. It would be great if I could be like most other successful people I know and get away with a whole lot less sleep.”
Such a gift would, of course, leave more time for parties. “I am moving in September to Stockholm [to take up her post at Nordita], and I just found out last week that I have been awarded a $15 million [£8.75 million] grant from the Swedish government. One of the first things I’m going to do is to have a conference with some of the luminaries in astrophysics and particle physics, and to host it in the City Hall where the Nobel Prizes are awarded. The events hosted there are amazing, as I discovered when I was awarded an honorary doctorate in 2012 from Stockholm University. There was a dinner for 850 people with singing waiters in a historic room decorated from floor-to-ceiling with gold mosaics.”
And as for legendary parties of the past, was Studio 54 as great as they say? “Hell yes,” Freese retorts. “It was like a sandbox for grown-ups. I nearly flunked out of grad school because I went so often, and it was totally worth it. It was the best nightclub in the world in my lifetime. I still love dancing.”
The Cosmic Cocktail: Three Parts Dark Matter
By Katherine Freese
Princeton University Press, 264pp, £19.95
ISBN 9780691153353 and 9781400850075 (e-book)
Published 25 June 2014