Dark Matter and the Dinosaurs: Harvard Physicist Lisa Randall on the Astounding Interconnectedness of the Universe
A thrilling cosmological detective story of how the universe evolved and what made our very existence possible.
By Maria Popova
Every successful technology of thought, be it science or philosophy, is a time machine — it peers into the past in order to disassemble the building blocks of how we got to the present, then reassembles them into a sensemaking mechanism for where the future might take us. That’s what Harvard particle physicist and cosmologist Lisa Randall accomplishes in Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe (public library), which I recently reviewed for The New York Times — an intellectually thrilling exploration of how the universe evolved, what made our very existence possible, and how dark matter illuminates our planet’s relationship to its cosmic environment across past, present, and future.
Randall starts with a fascinating speculative theory, linking dark matter to the extinction of the dinosaurs — an event that took place in the outermost reaches of the Solar System sixty-six million years ago catalyzed an earthly catastrophe without which we wouldn’t have come to exist. What makes her theory so striking is that it contrasts the most invisible aspects of the universe with the most dramatic events of our world while linking the two in a causal dance, reminding us just how limited our perception of reality really is — we are, after all, sensorial creatures blinded by our inability to detect the myriad complex and fascinating processes that play out behind the doors of perception.
The Universe contains a great deal that we have never seen — and likely never will.
Randall weaves together a number of different disciplines — cosmology, particle physics, evolutionary biology, environmental science, geology, and even social science — to tell a larger story of the universe, our galaxy, and the Solar System. In one of several perceptive social analogies, she likens dark matter — which comprises 85% of matter in the universe, interacts with gravity, but, unlike the ordinary matter we can see and touch, doesn’t interact with light — to the invisible but instrumental factions of human society:
Even though it is unseen and unfelt, dark matter played a pivotal role in forming the Universe’s structure. Dark matter can be compared to the under-appreciated rank and file of society. Even when invisible to the elite decision makers, the many workers who built pyramids or highways or assembled electronics were crucial to the development of their civilizations. Like other unnoticed populations in our midst, dark matter was essential to our world.
But the theory itself, original and interesting as it may be, is merely a clever excuse to do two more important things: tell an expansive and exhilarating story of how the universe as we know it came to exist, and invite us to transcend the limits of our temporal imagination and our delusions of omnipotence. How humbling to consider that a tiny twitch caused by an invisible force in the far reaches of the cosmos millions of years ago hurled at our unremarkable piece of rock a meteoroid three times the width of Manhattan, which produced the most massive and destructive earthquake of all time, decimating three quarters of all living creatures on Earth. Had the dinosaurs not died, large mammals may never have come to dominate the planet and humanity wouldn’t be here to contemplate the complexities of the cosmos. And yet in a few billion years, the Sun will retire into the red giant phase of its stellar lifetime and eventually burn out, extinguishing our biosphere and Blake and Bach and every human notion of truth and beauty. Stardust to stardust.
One of the book’s central threads is the essential capacity for uncertainty that science requires of its practitioners. The same impulse that gave rise to religion — to do away with doubt and rest into certainty — is also present in science, for it is a profoundly human impulse and science is a profoundly human endeavor. Throughout the history of scientific breakthroughs that Randall chronicles, new theories are consistently met with opposition by scientists who have grown attached to older models. But therein lies the premier forte of the scientific method as a tool for advancing humanity’s conquest of truth — in the face of sufficient evidence, even staunch supporters of older models begin to doubt them and eventually accept the newer ones.
Randall captures this succinctly, perhaps with an eye to the rest of contemporary culture where opinions are formed with little consideration and opposition is dismissed on principle — in a sentiment that calls to mind Carl Sagan’s Baloney Detection Kit, she writes:
Only when existing scientific ideas fail where more daring ones succeed do new ideas get firmly established.
For this reason controversy can be a good thing for science when considering a (literally) outlandish theory. Although those who simply avoid examining the evidence won’t facilitate scientific progress, strong adherents to the reigning viewpoint who raise reasonable objections elevate the standards for introducing a new idea into the scientific pantheon. Forcing those with new hypotheses — especially radical ones — to confront their opponents prevents crazy or simply wrong ideas from taking hold. Resistance encourages the proposers to up their game to show why the objections aren’t valid and to find as much support as possible for their ideas.
Dark matter itself is a supreme example of this ethos. Although scientists have confirmed its existence, they don’t actually know what it is and believe that it’s made of a new elementary particle that doesn’t obey the forces that drive ordinary matter interactions. But the very search for dark matter is predicated on the leap of faith that despite being invisible, it has interactions, however weak, that human tools made of ordinary matter will eventually detect. Randall — who has previously written beautifully about the crucial difference in how science and religion explain the world — notes that this assumption is “based partially on wishful thinking.” But in that partiality lies the supremacy of science over truth-seeking ideologies built solely on wishfulness. Where humans hope and fear, experiments prove and rule out.
One of the most scintillating parts of the book illustrates this aspect of science in action. Randall tells the story of the unlikely and slow-burning revolution that led to our present understanding of how the dinosaurs perished — a riveting global detective story thirty years in the making, beginning in 1973, when a geochemist proposed that a meteoroid impact caused the extinction of the dinosaurs, only to be dismissed by the scientific community.
The notion remained radical until a geologist named Walter Alvarez — whose dramatically titled book T-Rex and the Crater of Doom inspired Randall’s speculative work — embarked upon an investigative adventure that began in the hills of Italy and ended in one of the greatest breakthroughs in planetary science. The story is also a supreme testament to both the power of interdisciplinary collaboration and the humanity central to science — Alvarez worked with his father, the Nobel-winning physicist Luis Alvarez, to solve the mystery.
The duo detected an unusually high concentration of iridium — a rare metal put to such mundane uses as fountain pen nibs — in the clay deposit separating two differently colored limestone layers. Because Earth is intrinsically low in iridium, they suspected that an extraterrestrial impactor was responsible for this perplexing quantity. After a team of nuclear chemists confirmed the anomaly, Walter and Luis Alvarez proposed that a giant meteoroid had hit the Earth and unleashed a downpour of rare metals, including iridium.
But rather than the end of the story, this was merely the beginning, sparking a worldwide scientific scavenger hunt for the actual site of the impact. Since craters are typically twenty times the size of the impactor and Alvarez estimated that the meteoroid was about ten kilometers in diameter, scientists set out to find a crater nearly 125 miles wide. Despite the enormity of the target, the odds of finding it were slim — if the meteoroid had hit the ocean, which covers three quarters of Earth’s surface, the crater would be both unreachable and smoothed over by sixty-six million years of tides; had it hit the land, erosion, sedimentation, and tectonic shifts may have still covered its traces completely. And yet, in a remarkable example of what Randall calls the “human ingenuity and stubbornness” driving the scientific endeavor, scientists did uncover it, aided by an eclectic global cast of oil industry workers, international geologists, three crucial beads of glass, and one inquisitive reporter who connected all the dots.
In 1991, NASA announced the discovery of the crater in the Yucatan plane of the Gulf of Mexico. But it wasn’t until March of 2010 — exactly thirty years after Walter Alvarez had first put forth his theory — that a collective of forty-one elite international scientists reviewed all the evidence that the meteoroid killed the dinosaurs and deemed it conclusive.
The story, which Randall tells with palpable reverence and exhilaration, brings home one of her central points — science, at its best, methodically applies the known tools at our disposal to reach into the unknown with systematic audacity. She writes:
The beauty of the scientific method is that it allows us to think about crazy-seeming concepts, but with an eye to identifying the small, logical consequences with which to test them.
There is a necessary observation to be made about the book that might seem banal to point out, but as artist Louise Bourgeois once resolved in her diary, “never depart from the truth even though it seems banal at first”: Randall is one of a handful of scientists at the leading edge of physics born with two X chromosomes, and perhaps one of a dozen women in the entire history of science to have reached this caliber of influence. It’s rather heartening and perhaps uncoincidental that, throughout her riveting tour of the scientific discoveries that laid the foundation of our present understanding of the universe, she takes care to name the many women who overcame imposing odds in male-dominated fields to make major breakthroughs — trailblazing astronomer Vera Rubin, who confirmed the existence of dark matter; nuclear chemist Helen Michel, who confirmed the high level of iridium that became the first clue that a meteoroid wiped out the dinosaurs; astronomer Wendy Freedman, who first measure the Hubble constant; geologist Joanne Bourgeois, who pinpointed the area where the deadly meteoroid struck; Julia Heisler, a Princeton undergraduate who quantified the degree of uncertainty that still makes predictions of periodicity reliable.
Randall touches on her own experience as a female scientist only once, only obliquely, but rather tellingly: She mentions that people sometimes mistake her job title for “cosmetologist” — and even this remark is made not gratuitously but solely in the service of advancing knowledge as she traces the etymology of the word “cosmos” to the Greek kosmos, meaning “good order” or “orderly arrangement,” noting that both the universe and the standards of human beauty are undergirded by the art-science of order.
Dark Matter and the Dinosaurs is a wonderfully stimulating read in its entirety. Although Randall points out that there are “no shortcuts to scientific knowledge,” she covers an impressive amount of material and connects a vast constellation of dots with captivating clarity — a formidable feat of bridging our solipsistic and short-sighted human vantage point with the expansive 13.8-billion-year history of the universe.