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Reading Katie Mack’s review of “The Elephant in the Universe” (Books, July 9), I was struck that some of our most brilliant minds are doggedly searching to find answers about an entity for which they cannot find proof but have observed its effects. It is also huge, representing most of the universe. Some find me rather naive in believing in something with similar characteristics: God.
Judith Gallagher-Braun
Yardley, Pa.
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Appeared in the July 13, 2022, print edition as 'Another Great Convergence.'
The original article:
BOOKSHELF
‘The Elephant in the Universe’
Review: Dark Matter Mystery
For decades, astronomers puzzled over the strange behavior of stars and galaxies. Something else had to be out there.
By Katie Mack
July 8, 2022 11:22 am ET
For nearly a century, astronomers have been finding hints that the stuff we are made of— atoms, molecules, everything constituting ordinary matter—is, cosmically speaking, insignificant. Then, with the use of more powerful telescopes in the 1970s, stars within individual galaxies were found to be moving at impossible speeds. Where the outermost stars should have been hurled off into intergalactic space by their motion—like children flung off a merry-go-round spun too fast—they continued their breakneck gyres, unperturbed. As the evidence mounted, some astronomers began to suspect that the stars we see in the night sky are mere window dressing—sparks of light embedded in massive but invisible clumps of the only truly important substance in the universe. In the writer Govert Schilling’s phrase, it “provided the scaffolding for the growth of cosmic structure.” Not knowing what to call an unseen substance that vastly outweighed everything else, they leaned into the mystery and dubbed it “dark matter.”
Decades of investigation have brought us nothing to contradict those astronomers’ suspicions of our essential unimportance, nor any answers as to what dark matter might be made of. We have found no real leads, but many dead ends. We’ve ruled out every species of tangible object ever observed in the heavens, along with every atom and subatomic particle ever measured in the world’s most precise and powerful experiments. It’s not dim stars; it’s not cold gas; it’s not, apparently, made of anything that constitutes the stuff of us. Nonetheless, study after study has found seemingly incontrovertible evidence that dark matter not only governs the motions of stars and galaxies, but is responsible for their very existence. Invisible matter—or something that acts exactly like it—has directed the evolution of the universe from the earliest moments of creation, when cold hydrogen began to gather in the deep gravitational wells created by its presence and ignited the first stars.
If we take seriously the notion that dark matter is real and abundant, dozens of seemingly disparate cosmic puzzle pieces suddenly fall into place: the stability of our own Milky Way, the formation of the “cosmic web” of galaxy clusters and giant voids, the pointillist patchwork of tiny blips in the fading background light of the big bang, the overall shape of spacetime itself. Alternative explanations have been proposed, but so far astronomers and physicists around the world have been forced to accept the scenario that best matches the data: that more than 80% of the matter in the universe is invisible to us. To make matters more perplexing, just a few decades ago we found reason to believe even dark matter’s cosmic dominance is dwarfed by a mysterious phenomenon that we, in our increasing desperation, call “dark energy.” One is almost tempted to despair of understanding the cosmos at all.
Scientists are obstinate creatures, however, especially when faced with unanswered questions. The dogged persistence of physicists and astronomers facing a seemingly insurmountable task is the underlying theme of Mr. Schilling’s latest work, “The Elephant in the Universe: Our Hundred-Year Search for Dark Matter.” Across 25 chapters, each devoted to a specific observation or experiment seeking clues to dark matter’s existence or composition, Mr. Schilling, who has previously written about the discovery of exoplanets and gravitational waves, presents an impressively comprehensive birds-eye view of a research topic that is both many decades established and yet still at the very cutting edge of astronomy and physics.
Along the course of this whirlwind tour, we catch glimpses of the lives and motivations of many of the key thinkers and builders who have defined the dark matter problem, as well as those who hope, sooner or later, to solve it. Mr. Schilling introduces us to some of the elder astronomers who did the first calculations to lay out the parameters of the problem, such as Jacobus Kapteyn, who first suggested the possibility of dark matter in 1922, and Nobel Laureate Jim Peebles, who drew a dark matter line between the tiny ripples in the primordial cosmic soup and the large-scale structure of the cosmos today. We meet rival experimentalists Elena Aprile and Richard Gaitskell, racing to build devices to capture an as yet-undescribed particle that might account for dark matter’s existence. And we’re introduced to a wide range of starry-eyed upstarts who have abandoned long-standing dark matter hypotheses to get creative about new models and approaches.
Overall, one gets the impression of walking down a long university hallway, stepping through a doorway to interrupt a researcher toiling away in the lab (scribbling equations, tapping out computer programs, aligning telescopes or building giant particle detectors), and then quietly shutting the door again and moving on to the next one. No one shouts “eureka!”; no final answers emerge; everyone is determined, confident and, ultimately, a bit confused. As a dark matter toiler myself, to whom much of that hallway is a well-worn track, I am not an outside (nor impartial) observer. From my perspective, the representation of the current state of affairs in dark matter research presented by “The Elephant in the Universe” is largely clear and informative, and it offers even a working scientist a useful overview of the history and politics of the field. Of course, as any insider would, I can quibble with some of the science as presented, and with the balance in the presentation of different scientific approaches. There are distractions, such as a long and strangely vehement attempt to downplay the contributions of the late dark matter pioneer Vera Rubin (the book goes so far as to claim that her prominence in the field is the result of “reverse gender inequality”).
I would have also liked to have seen more discussion of how a scientific consensus is reached —why exactly so many physicists are so convinced dark matter is real, despite the fact that a smoking-gun particle has yet to be detected. Taking only the astrophysical evidence for dark matter’s existence, which is both compelling and, unfortunately, all we have to go on, it’s quite possible that dark matter will remain undetectable. Yet even if all the experiments come up empty, it won’t make the existing data go away. (When you have sailed across an ocean on the wind, you don’t stop believing wind exists just because you never saw it.)
Putting aside these issues, if you’re after a non-technical overview of why dark matter is so important and what we’ve been doing all this time to try to understand it, “The Elephant in the Universe” will fit the bill. What it will not and cannot do is provide a thrilling, climactic story arc or even a moderately satisfying conclusion. Dark matter is a fascinating mystery to wrestle with, but it is also deeply frustrating in its uncertainty and the seeming lack of progress toward an answer. Perhaps this really is the most apt representation of how science is done. We continue down the long hallway, trying one thing and trying another. We follow new leads or invent new ways to track down the old ones, and along the way we learn a little bit more about our universe. Cosmic afterthoughts that we are, it may just be the best we can do.
—Katie Mack holds the Hawking Chair in Cosmology and Science Communication at the Perimeter Institute for Theoretical Physics in Waterloo, Canada. She is the author of “The End of Everything (Astrophysically Speaking).”
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