The following passages are excerpted from a review of Richard Panek’s The 4 Percent Universe: Dark Matter, Dark Energy, and the Race to Discover the Rest of Reality, published by Houghton Mifflin Harcourt on January 10. Panek will appear at Berkeley Lab in person on Friday, January 28, to discuss his book. In relating the discovery of dark matter and dark energy, the author shows how physicists and astronomers at Berkeley Lab and the University of California at Berkeley not only contributed to the study of dark matter but pioneered the techniques that revealed dark energy. They remain at the forefront of dark energy research. The full review, along with others, may be found here.
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For 20 years or so after the first Star Wars movie came out, most people who mentioned “dark” and “universe” in the same breath were talking about Darth Vader and the Dark Side. Doubtless some of the movie’s fans were also astronomy fans who’d heard about the evidence for real dark matter — not what it is (nobody yet knows what it is) but what it does, flattening galaxies, speeding up their rotation, and invisibly sculpting the structure of the visible night sky. Yet the import of that particular dark stuff had not yet excited a wider public.
Things started to change in 1998, when two teams of supernova collectors — the Supernova Cosmology Project led by Saul Perlmutter, based at Lawrence Berkeley National Laboratory in California (Berkeley Lab), and the competing High-z Supernova Search Team, led by Brian Schmidt of the Mount Stromlo and Siding Springs Observatories in Australia — announced they’d found strong evidence for a universe whose expansion wasn’t slowing under the mutual gravitational attraction of matter, visible or dark, but instead was accelerating, propelled by something unknown. It couldn’t be matter so presumably it was energy. Dark energy.
Within weeks, interest in the dark universe had accelerated beyond fans of astronomy and science fiction. Word swiftly got around: what we see, to the farthest reaches of the night, is a small fraction of the stuff that fills the universe. What we know is only four percent of what is.
Or, as Richard Panek puts it in the prologue of his extraordinary new book, “It’s 1610 all over again.” That was the year Galileo Galilei (physicist and master publicist) astounded Europe with his Starry Messenger, detailing the telescopic observations that proved Nicholas Copernicus’s description of a sun-centered universe was more than just a mathematical convenience.
Panek set out to be a fiction writer, but he was bitten by the science-writing bug early on. He has produced quiet masterpieces, including Seeing and Believing: How the Telescope Opened Our Eyes and Minds to the Heavens (Viking, 1998). He knows a paradigm shift when he sees one, and in 2006 he began investigating how dark matter and dark energy had been dragged into the light.
Dark matter is the quiet backstory of his narrative. Part of Panek’s gift is sketching distinctive personal qualities in a few words, as he does for the dark-matter pioneers. Vera Rubin “didn’t like the controversy … didn’t like everyone challenging her on every number.” Jim Peebles was “all angles … elbows and knees … a man of conflicting sensibilities.” Panek lets the reader see how these utterly unquantifiable variables of character have shaped our rational understanding of the universe we live in.
The scientific exchanges over whether the shapes of galaxies and clusters of galaxies demand that there be some extra invisible matter in the universe were generally civil; over the decades there were arguments about dark matter, some even “virulent” and “rancorous” by Panek’s account, but never a cut-throat competition, with one group of researchers trying to beat a competing group to the right answer by any means at hand.
When it comes to the story of dark energy, virulent and rancorous are mild adjectives. From its beginnings there was head-butting opposition to the very existence of the Supernova Cosmology Project (SCP). The SCP was part of the program of the Center for Particle Astrophysics, jointly established by Berkeley Lab, a Department of Energy national laboratory, and the University of California at Berkeley. Although the center was supported by the National Science Foundation, its name gave away its genesis. Astronomers don’t do particle astrophysics. Physicists do.
Nevertheless the center’s founders thought it would be politic to include some people in the star-gazing business on its advisory board. One of those was Harvard’s doyen of supernovae, Robert Kirshner, who opposed the Supernova Cosmology Project virtually from the moment he heard about it.
The physicists who started the SCP claimed they were going to weigh the universe, measure its shape, and learn its fate. “They used this giddy language in proposals to solicit funding,” Panek writes. “They all told themselves that they were the ones who were finally going to solve some of the most profound mysteries of cosmology – of civilization itself.”
To do this they proposed to measure how fast the universe was expanding, or rather how quickly that expansion was slowing down. Expansion started with the big bang, and everyone assumed it was now slowing because of matter’s mutual gravitational attraction. But would it finally stop and reverse, leading to a big crunch? Would it coast to a standstill? Or would the universe expand forever?
To answer these questions the SCP intended to use distant supernovae of a particular type, Type Ia, as standard candles – objects whose distance could be calculated with confidence because they were bright enough to be seen across billions of light years and were also, or so the physicists believed, very similar in their brightness. Brightness was one measurement. Redshift was another.
How much the wavelength of light from these standard candles stretched before it reached Earth, shifting the identifying frequencies of cosmic objects toward the red end of the spectrum, indicated how much space itself had expanded and stretched since the light left the supernovae. So by comparing the brightness of Type Ia’s to their redshifts, the SCP would be able to compare the present expansion of the universe to its expansion in the past.
In Robert Kirshner’s opinion, the SCP didn’t know what it was doing. At first, “Kirshner emphasized that the Berkeley search team hadn’t yet found a supernova, needed to be careful about photometry [measuring brightness], couldn’t account for dust [which reddened the light] — and didn’t know whether Type Ia supernovae were standard candles,” Panek writes. When, after much tribulation, the SCP did find a distant supernova in 1992, “Kirshner complained that they still needed to be careful about photometry, still couldn’t account for dust — and still didn’t know whether Type Ia supernovae were standard candles.” Invited by the editors of Astrophysical Journal Letters to review the SCP’s paper describing their first supernova, Kirshner delayed their paper on the grounds that “They hadn’t yet learned anything about cosmology.”
With an initial small sample the SCP did indeed make bad guesses about the universe’s weight and shape. But in 1994 they started collecting Type Ia supernovae by the fistful, having developed and applied methods that should have been obvious — particularly to doubting astronomers. A Type Ia supernova goes off in a typical galaxy perhaps once in a century. By photographing thousands of distant galaxies and then photographing the same batch some weeks later, a few supernovae are statistically certain to have gone off somewhere in that vast collection of stars. Sorting them out wasn’t easy, but with the right detectors and computer programs it was inevitable; Type Ia supernovae could be had on demand.
The size of SCP’s dataset began to multiply. Once the SCP and several other supernova hunters had shown that distant Type Ia’s could be used to do cosmology, and once the SCP proved they could be found on demand, competition to measure and weigh the universe quickly got organized….
[In 1994 Brian Schmidt and Nicholas Suntzeff formed a team of astronomers that called itself the High-z Supernova Search Team (z stands for redshift)….]
… Early in the fall of 1997, in data from 42 supernovae, SCP team member Gerson Goldhaber found evidence that only a small part of the universe is matter. High‑z team member Adam Riess soon reached the same conclusion. Early in 1998 both teams announced their findings that expansion isn’t slowing at all; it’s accelerating, because some three-quarters of the cosmos is made up of a “cosmological constant” or other form of what soon came to be called dark energy.
All agreed the universe is accelerating — and they agreed that knowing why will require more data and new research methods. So the competition continues to this day, with opponents still grouped roughly as in the beginning, fielding different proposals for funding the space satellites and ground-based surveys that will be needed to assess the nature of dark energy. Unless it’s an illusion, a flaw in Einstein’s theory of gravity — and maybe even if it is — dark energy is the most profound cosmological discovery since, well, 1610. It’s the stuff of Nobel Prizes.
Talk about competition. To their credit many, if not all, of the scientists on both sides have tried hard to rise above the snide blogs and dueling press releases that marred the decade of rivalry following the 1998 announcements. (It’s time to confess that this reviewer wrote many of those press releases on behalf of the SCP.)
Panek quotes Brian Schmidt speaking at a press conference the day before the bestowal of the prestigious Gruber Prize in Cosmology at Cambridge University in 2007, a prize shared between the leaders of the competing teams and also equally among the team members. “Our teams, certainly in the U.S., were known for sort of squabbling a bit,” said Schmidt. “The accelerating universe was the first thing that our teams ever agreed on.”
Panek writes, “The award ceremony at Cambridge wasn’t only about posterity…. It was about history … posterity in motion.” He tells how Perlmutter and Schmidt, in the lecture that followed the ceremony, narrated “the history of modern cosmology, sometimes finishing each other’s sentences,” a modern history that began in 1965 with the discovery of the cosmic microwave background and brought with it a new way to do cosmology, opening new vistas on the possible. It was a time when “Perlmutter and Schmidt were themselves as young as the universe.”
The most profound discoveries since Galileo deserve a chronicler whose passion for accuracy, love for the human story, and grace with words is the equal of the tale he tells. In Richard Panek, the scientific saga of dark matter, dark energy, and the other four-percent of the universe — all that’s left to us to see with our own eyes — has found a spell-binding bard.