Dark Matter and the Dinosaurs

Dark Matter and the Dinosaurs: Harvard Physicist Lisa Randall on Our Place in the Universe

If there is a connecting theme in my intellectual pursuits, it is the goal of finding connections between ideas that open up a new window of perception and expose some hidden truth. Harvard physicist Lisa Randall has written a stunningly beautiful example of the creativity that comes from the study of the intersection of great ideas, in Dark Matter and the Dinosaurs: The Astounding Interconnectedness of the Universe.

Did Dark Matter Cause the Extinction of the Dinosaurs?

Sixty-six million years ago, an object the size of a small city crashed into what is now the Yucatan Peninsula in Mexico.  The cataclysmic event, known as the K-Pg Extinction, killed off the dinosaurs and 75% of the remaining life on Earth. Randall’s book presents a hypothesis that seems simple, but quickly reveals massive complexity: that “dark matter might ultimately (and indirectly) have been responsible for the extinction of the dinosaur.”

To test this theory, Randall weaves an explanatory narrative that is approachable enough for readers unfamiliar with cosmology and particle physics, but thorough enough to satisfy the more curious.  Dark matter makes up 85% of the matter in our universe, but we cannot see or touch it.  It interacts with gravity, but not with light or visible matter. The theory that Randall and her colleagues have advanced is that the K-Pg impact was caused by a comet passing through a disk of dark matter on the horizon of our galaxy. When the cosmic wrecking ball touched the dark matter, it was deflected toward Earth and its dinosaur inhabitants.  It left a changed world, the death of the dinosaurs, and new evolutionary opportunities for mammals and their descendants.

The book succeeds on a fundamental level for its historical explanation of the theories of dark matter and the extinction event. But Randall excels in using this scientific explanation as a point of departure for bigger themes about the limits of our perception and our place in the Universe.

We See Very Little of the Universe

Our powers of observation are weak and contain massive blind spots.  As Randall reminds us, “the Universe contains a great deal that we have never seen – and likely never will.” The dark matter that Randall studies composes up to 85% of the matter in our Universe, and yet no one has ever seen it, or felt it, or heard it.  Physicists know that it is there because of its gravitational pull, but otherwise have been unable to conduct experiments on it.

At first mention to the uninitiated, this idea might seem contrary to the natural order. Why would there be matter that we cannot see or touch?  Randall points out that this is nothing more than a bias on our part in favor of overestimating our capacities:

People ask how it can possibly be that most matter – about five times the amount of ordinary matter – cannot be detected with conventional telescopes.  Personally, I would expect quite the opposite…. Why should we have perfect senses that can directly perceive everything?  The big lesson of physics over the centuries is how much is hidden from our view.

We rely on our senses every day.  Without confronting evidence to the contrary, we fall into the easy trap of believing that we can perceive and understand all around us.  But our blind spots are huge, and making sense of our relationship to the Universe requires us to confront this point and embrace uncertainty.

Telescopic image revealing the gravitational pull of dark matter.
Telescopic image revealing the gravitational pull of dark matter

Finding Freedom in the Cosmic Order

The greatest lesson I found in Randall’s book is the realization that we are central to nothing in the Universe of any cosmic significance, and that there is unparalleled freedom in embracing our insignificance.

Between 1500 and 1950, humanity fought against, and then accepted, three great intellectual revolutions.  First, Copernicus taught us that we are not the center of the Universe.  Centuries later, Darwin taught us that we are not the center of life on Earth. Shortly thereafter, Freud taught us that we are not even at the center of our own minds. Randall proposes that modern physics should cause us to undergo a “Fourth Revolution,” in which we realize that our fundamental physical makeup is not aligned with the majority of the Universe:

Not only is the Earth not physically the center of the Universe, but our physical makeup is not central to its energy budget – or even to most of its matter.

Theists sometimes advance an argument for intelligent design that supposes that the fact that the Universe is “something,” rather than “nothing,” is of some cosmic significance tending toward the existence of God.  At the very least, they argue, it is evidence that the Universe is not a random occurrence.  According to Randall, the idea that “something” is special doesn’t hold true under mathematical scrutiny.

One question I frequently hear is why there is something rather than nothing…. I just think something is more likely.  After all, nothing is very special.  If you have a number line, “zero” is just one infinitesimal point among the infinity of possible numbers you can choose.  “Nothing” is so special that without an underlying reason, you wouldn’t expect it to characterize the state of the Universe.

At first glance, one might consider these notions of insignificance to be depressing or saddening.  I don’t. One of the unavoidable conclusions of any consideration of the K-Pg event is that death and destruction lead to new life.  The K-Pg comet destroyed the dinosaurs and three-quarters of the Earth’s life, and yet without that extinction, it is likely that birds, mammals, and humans would never have had the evolutionary opportunity to exert their influence on the world.  As Randall puts it, “extinctions destroy life, but they also reset the conditions for life’s evolution.”

It’s worth remembering that the K-Pg extinction was not the first time the Earth had experienced an extinction event.  In fact, it was the Fifth Great Extinction.  Four times before, the Earth and its cosmic environment turned hostile to its global set of inhabitants, destroying and paving the way for new evolutionary paths.  We are the beneficiaries of the K-Pg extinction.  And if Randall’s theory is true, our entire race’s birth, development, and eventual extinction are the product of the seemingly random interaction of a comet and a disk of imperceivable dark matter on the edge of our galaxy. That random collision, some 65 million years ago, is responsible for the Mona Lisa, Hamlet, the Magna Carta, Taco Bell, and the Macarena.  All is Stardust, after all.

These things, of course, have a finite life.

In another four billion years or so, the Sun will turn into a red giant, and a few billion years after that, it will burn out completely.  According to current models, no forms of Earth-bound life – simple or complex – will survive in that distant future.

So what do we make of this?  The conclusion I keep returning to is that the bad day at the office doesn’t matter.  A disappointing outcome on a business deal doesn’t matter.  The things that cause  stress and anxiety and jealousy, that make me compare myself and my accomplishments to those of other people, that make me feel like I have failed in some way – they don’t matter.  They are of such infinitesimal consequence that they are not worth mental energy or focus.  The time we have is short and beautiful, and we should fill it with all of the love and charity and teaching and learning that we can.

I don’t know if Lisa Randall considered this type of impact when she wrote her book.  I have to believe that she considered its possibility.  In relying on lessons from cosmology, particle physics, biology, environmental science, geology, and contemporary culture, she has created a multidisciplinary masterpiece that gives a markedly unique perspective on our place in the cosmos.  Highly recommended.


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