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The Hardest Thing About Science II: Nouns & Verbs

by Shane L. Larson

Friends and family who travel around with me know I have a fatal weakness for one of the most ephemeral manifestations of the human brain: museums. Museums ostensibly exist for the singular purpose of capturing and showing what we as a species have learned, what we have discovered, and what still gives us wonder about the vast and mysterious world around us.

A “Little Free Library,” one of the modern forms of libraries, found in neighborhoods around the world.

In many ways, they are like their sister institutions, an equally ephemeral result of our unique brains: libraries. Libraries ostensibly exist for the singular purpose of storing the knowledge our species has accumulated, dispersed freely and at will to anyone who walks through the doors. I have a fatal weakness for libraries as well.

What do I mean by fatal weakness? I mean if I walk into one of these spaces, I’m consumed by it. In a museum, I linger and dwell at every exhibit, I read the detailed descriptions, I go back to previous exhibits to see how it is all connected. In a library, I walk down the aisles brushing my fingers lightly over the spines of books, drinking in the titles, sometimes pulling one off the shelf to thumb through the pages.

Every now and then, I ponder why we first decided to create these museums and libraries. Often when people think about museums and attempt to describe them, they describe the things there: artifacts, rocks, shards of lost civilizations, exquisite pieces of art, stuffed creatures that once roamed the wilds. 

Consider what you might see if you visit the Adler Planetarium in Chicago. There you can see a star show on the planetarium dome, touch a fragment of the dwarf planet Ceres with your own bare hand, see a life-size model of the Opportunity rover on Mars, and stand next to the Gemini 12 capsule that carried Jim Lovell and Buzz Aldrin around the Earth for almost four days in 1966. 

The Gemini 12 capsule, on display at the Adler Planetarium in Chicago.

But these are all things, and while the things are a focal point that draws you into the museum, they are not why you are there. You stare, and linger, and imagine something quite different and ephemeral. What is that? 

Dr. Michelle Larson, the President of the Adler, describes this dichotomy  as “nouns” and “verbs.” The nouns are what attract our attention, but what we are looking for and hoping to find are verbs. 

Standing in front of Gemini 12, a thin pane of plexiglass keeping you barely a half meter away, you reach out your hand. What are you doing? Hoping to verify the construction of aluminum? Check that the paint is peeling? No, much more. 

Closeups of the Gemini 12 capsule, showing the cramped space of the crew cabin (left), and the scorched heatshield (right).

The almost involuntary movement of your hand is because your brain is imagining what it was like to hurtle through the vacuum of space at nearly 28,000 kilometers per hour (more than 17,000 miles per hour), protected by the thinnest veneer of metal and insulation — was it terrifying or exhilarating or both? You look at the tiny window, and try to imagine seeing the color and light that was seen as the capsule plummeted down to Earth on the way home. The blast pattern of char on the back of Gemini 12, where the heat shield protected Lovell and Aldrin from the 2700 degree Celsius inferno, makes you wonder: if someone touched the window would it feel warm? Staring at the tiny confined space where the astronauts lived for almost four days you wonder: did it smell in there?

The Gemini 12 capsule, the noun, is just a vehicle to stimulate your thinking about the experiences, the verbs

This spills over into hobbies. Consider birdwatching. For some of us, birds are sortable at best into “robins,” “ducks,” and “little brown birds.” But for people who identify as birders, there is a certain unconstrained joy that people find in seeing the widest possible variety of our feathered friends as they can. They meticulously stare at birds through binoculars in the backyard, slog down park trails to remote copses of trees, and diligently put food and water in the backyard, all to be afforded a chance to see a blue-winged teal, or an eastern meadowlark, or a tufted tit-mouse.

A collection of birds from the winter in Illinois. A bluejay (top left), a tufted titmouse (lower left), and a cardinal (right). [Photos: M. Larson]

The birds are nouns, but birders aren’t collecting birds. They are collecting the experience of seeing birds, the verbs of birding. Birding is a verb! The joy is seeing the delicate splash of color of feathers iridescent in the sun, of projecting your own joy on a bluejay who looks thrilled to have a peanut in its mouth, or hearing a mother cardinal squawking at her fledglings encouraging them to take wing for the first time.

Looking at the Moon through a telescope or binoculars always fires the imagination. [Photo: S. Larson]

Amateur astronomers are the same way. We stand out in the backyard, hunkered down in our winter jackets against the cold, peering intently into the eyepiece of a telescope, straining to see photons that have spent two million years sailing the void from the Andromeda galaxy to Earth. The telescopes, the photons themselves, are just nouns. They are cool things unto themselves. But the astronomer is experiencing the light, drowning themselves in the existential awe of imagining the enormous gulf that photon has crossed to ultimately fall into their eye. Perhaps the light originated right next door, on the Moon, or perhaps it started its journey long, long ago far across the Cosmos in a star in a galaxy so far away humans haven’t named it. That light journeyed for longer than humans have been on Earth, and ended its voyage rattling through a few telescope mirrors and terminating on the retina of an eyeball. Imagine the journey that light took. 

All of the practice of science can be thought of in this way: it’s nouns and verbs. The nouns are the things you get taught, that you can look up on Wikipedia, that you hear about on the news. Science is the process of acquiring knowledge. Knowledge is a noun. Science is a verb.

Consider a journey in your mind into the deepest levels of your body, to the nuclear heart of your cells where the secrets of life are hidden away. Today we know that in the nucleus of every one of your cells, we can find DNA — a long ladder of matched molecules (denoted A, C, G, and T). The order of those molecules along the billion-rung DNA ladder spell out the unique information needed to create and define every single living thing on Earth. But there was a time when we didn’t know that at all. The first people to know about the the delicate double helix of this master molecule were Rosalind Franklin and her graduate student Raymond Gosling, who in 1952 took the very first picture of the molecule by bombarding it with x-rays. Today that picture is known as “Photo 51,” and its role in the discovery of DNA’s structure is storied and fraught with all too human conflicts.

Photo 51, originally captured by Raymond Gosling and Rosalind Franklin in 1952. [Image: Wikimedia Commons]

Stare at that photo for a moment, the way scientists in the 1950’s did. Look carefully at the twist and weave, and see the rungs connecting the sides of the ladder. DNA is incomprehensibly smaller than your eye can see, but the picture captures its delicate form and spells out the previously unknown truth of how you and I and every lifeform on Earth are one with each other, siblings on the deepest levels.

Now lift your head up, and soar out to the enormously larger scale of the solar system. Voyager is NASA’s longest lived space mission, currently 45 years old and still pinging Earth with its lonely beacon as it sails beyond the Sun, farther from home than any object ever made by humans. But in early 1979 when it flew past Jupiter, it was young and in the prime of its life. It carried a suite of instruments to sense and record everything it could as it passed by the largest planet in the Sun’s family. Among the most precious things Voyager did was take pictures, and send them home to Earth like any good interstellar tourist might. Before Voyager even arrived at Jupiter, we knew about the “Great Red Spot.” It is a massive hurricane-like malestrom, twice the size of the planet Earth. It has been known to exists for the entire 400-years that humans have had telescopes and first pointed them at Jupiter; we have no idea how old it really is. 

Voyager I view of the Great Red Spot as it approached Jupiter in 1979. [Image: NASA/JPL]

But just look at the Great Red Spot, the way Voyager did. Observe it, study it. It is exquisite in form, in shape, in complexity, in color. It almost doesn’t look real. If you saw that picture hanging on my wall, you might think it was a painting, a creative outburst of some exquisite artist here on Earth. But it is indeed a painting, a massive and beautiful canvas of chaotic color made by Nature itself.

It is easy to get swept up in the nouns of science: knowing the exact genetic code for slime molds, the chemical structures of ant pheromones, the age of the oldest crocodile fossils, the distance to the farthest quasar, the diameter of the Great Red Spot, the number of teeth a great white shark has, or the temperature at the heart of the Kilauea Volcano. These are great things science has taught us. But they are not science in and of themselves. 

Science is the art of inventing ways to do the hard work of discovering. It may sound simple to figure out how many teeth a great white shark has, but it probably isn’t. It seems obvious perhaps that it is “hot” in the center of Kilauea, but I assure you no human has or could survive there. The how of getting all these bits of information, the experience of discovering, and expansion of our thinking about the world around us — that is science.

This is one of the hardest things about practicing science in the modern world: hanging on to the verbs, remembering the verbs, and giving them voice.

Science is a verb.


This post is the second in a short series pondering what kinds of things make science difficult. The posts so far in this series are:

1: The Hardest Thing About Science – Language

2: The Hardest Thing About Science – Nouns & Verbs (this post)

The Hardest Thing About Science I: Language

by Shane L. Larson

One of the “features” of the modern world is memes percolating through our social media feeds, online browsing, and texts from friends. Sometimes these memes are humorous images, sometimes they are captures of tweets and posts, sometimes they are interesting facts. Let’s spend a few moments considering these last ones.


Examples of common memes that relay information or observations about science [Images via your favorite local internet browser].

Memes that relay “interesting facts” are often tidbits of history, trivia, or scientific knowledge that are surprising or provocative. Many of these memes are absolutely correct, yet surprising, and they get rebroadcast over and over again.


Why are such memes surprising and appealing? Sometimes they remind us of how little we know, or how it used to be when we were in school, or how silly complex questions can sound. They play with our deeply rooted notions of humor, playing word or pun games that juxtapose everyday language against the language of science. Chemistry memes are particularly good at this, where designations for the chemical elements — the 92 naturally occurring substances that the Universe creates everything from — are used to create words or funny turns of phrase. Like this meme about the element mercury, represented by its chemical symbol “Hg” (which comes from the Latin word for mercury, hydrargyrum — literally “liquid silver”).


Sometimes the reason is the propositions of science are used as beacons of stability in a world rife with randomness and illogic. Particularly in today’s world, where ideological arguments boiled down to soundbites are casually tossed around without much thought, people long for the ideals of impassioned debate moderated by reason and data. This is of course the standard that science aspires to, so memes promoting such ideals are popular.

But the memes of considerable interest are the ones that give you pause, and provide a delectable moment of cognitive dissonance. They challenge your thinking and world-view about something that seems ordinary, but apparently is not. 

Consider this very common repeated science factoid about the color magenta.


If you are like most people, you may read this and go, “What? WTF does this mean? Of course magenta exists! Look at this shade of lipstick right here!

But to understand what is going on here, we have to dissect every little bit of the meme. First, of course “magenta” exists, because that square of color is clearly there, and recognizable in the array of colors people might call “magenta.” But the second part is the piece to consider carefully: it is a color your brain is using to interpolate between red and violet. This is where the science part of this factoid is. It has been presented to drive you into cognitive dissonance, but no effort has been made to really help you understand what it means in the concrete world of science… this is the failure of such memes.

It does, however, illustrate one of the hardest things about science: the imprecision of language. Human language, which we depend on every single day and use as a malleable all-purpose tool, cannot easily convey with precision and accuracy what science has to say about most phenomena in the world. Color is a classic example. What does a scientist mean if they make a pithy statement like “magenta does not exist”? They mean something very precise, but the language of our common vernacular means something quite different.


Consider the color in this image. What color do you name this? Show it around to family and friends and ask them what color they call it. You will get a wide range of answers: green, yellow-green, fluorescent green, fluorescent yellow, fire-engine green, safety-vest yellow. Well, what color is it? We all recognize this color, but there is no universal name for it, though using any of these names mentioned, and a few examples, would quickly firm up the color under discussion in conversation.

But that isn’t precise enough or good enough for science. Scientists need to know exactly what color is under discussion — perhaps they are trying to create an LED light to create that color, or making a sensor that responds only to that particular color when it is scanned. In this case, this color is very close to the dominant color of light shed by our parent star, the Sun — the reason we use this color for attention and safety is your eye has evolved over millions of years to be sensitive to this color.


The “blackbody spectrum” of the Sun. The hill-shaped curve shows how much light the Sun emits in each color, and it peaks in the “safety-vest yellow” range of colors (at a wavelength of 500 nanometers). [Image: S. Larson]

So what do scientists do, when language isn’t up to the task? We layer on a bit of mathematics. In the case of color, physicists use a number called wavelength (often denoted by a lower case Greek letter lambda: λ). In the classic rainbow spectrum of light, cast by raindrops or sun-catcher prisms, or bevels on your windows, every single color has a unique number that scientists use to identify it.


The approximate colors and associated wavelengths of light that are visible to the human eye (the “visible spectrum”). [Image: S. Larson]

In the communication of scientific ideas, this ability to clearly and unambiguously quantify something is critical. Consider the following two conversations about color:

Conversation 1:

    Father: I put your red jacket in the closet.
    Daughter: I don’t have a red jacket.
    Father: Yes you do, you wear it every day.
    Daughter: Pop! That is burgundy.
    Father: <blank stare>

Conversation 2:

    Astronomer 1: It was too red to show in the image.
    Astronomer 2: The camera should have picked it up. 
    Astronomer 1: The wavelength was around 720 nanometers.
    Astronomer 2: Oh, you mean really red.

As astronomers, we still depend on language just like everyone else, but we have a mechanism to fall back on more precise statements and specifications needed to understand the world around us. In the case of color, that is wavelength.

But what about the magenta? What does it mean that it “doesn’t exist”? It means that for a scientist, there is no quantifiable number — no wavelength — that identifies where in the spectrum of light the color you and I call “magenta” can be found. It cannot be found in the spectrum! Yet it clearly exists when you and I stare at this little colored square. It is, in fact, a mixture of pure colors from the spectrum — the violet and the red mentioned in the original meme.

In the rainbow spectrum, where each color has its own unique numeric label, if you take a bit the violet color, and mix it with a bit of the red color, and throw that light at your eye, your brain says “whoa! look at that magenta!” 

In many ways, the meme is being dishonest to get a shock out of you. The amount of violet and red to be mixed can be quantified to make different shades of magenta — otherwise printers and lipstick makers would have a much rougher time making things this color! There is an exact, quantifiable way to specify every shade of magenta you put on the table. 

Nature can make magenta, but Nature doesn’t make magenta as a fundamental building block.


Salt crystals are not fundamental objects; salt itself is a combination of fundamental elements, sodium and chlorine. [Image: Wikimedia Commons]

It’s no different than elemental chemistry. “Salt” does not exist on the periodic table, but salt clearly exists in the same way magenta exists. In the fundamental, quantifiable world of the chemical elements (the building blocks of which everything on Earth is made), there are two uniquely identified substances: one is called sodium (Na) and one is called chlorine (Cl), and when I bond them together, I get something that is not elemental, but a mixture that we call NaCl — sodium chloride, or “salt.”

Saying something “doesn’t exist” has a multitude of interpretational meanings, but it means something very specific and very precise.  In the context we’ve been discussing here it doesn’t mean you can’t find something you and I would call “magenta” in the Cosmos — it means none of the fundamental building blocks of color, the rainbow of light, are called “magenta.”

This is one of the hardest things about science. Language is evocative and emotional and nuanced and, ultimately, imprecise. And since we are social creatures who in large part think in terms of language and act in response to language, it makes it hard — very hard! — for our brains to engage in the discovery of the world around us with the rational, quantifiable approach of science.

Moreover, it is hard to express personal enthusiasm and joy for the wisdom and knowledge that science has brought our species, when science itself is ideally more grounded — that dichotomy make the communication of science using this ratty tool we call “language” all the more difficult.

But we still try. With a few funny graphics and memes, a few stories and quips, and a few written words like these ones here…


This post is the first in a short series pondering what kinds of things make science difficult. The posts in this series are:

1: The Hardest Thing About Science – Language (this post)

2: The Hardest Thing About Science – Nouns & Verbs

Everything’s Gonna Be Alright

by Shane L. Larson

The inimitable Mary Fahl has a remarkable song that I listen to all the time, especially on days when it seems impossible that the world has not totally fallen apart. It is a sonorous and passionate piece called “Everything’s Gonna Be Alright.” It opens:

Blind Willie Johnson in a capsule singing ‘bout the soul of man
Encoded traces of the human race and what we understand
A human choir out in the distance trav’ling by a satellite
Symphonic strains of our existence burned into a single byte
Mary Fahl performing “Everything’s Gonna Be Alright.”

For the uninitiated, Mary’s song may seem strange or obtuse — lyrical renderings of language that may have philosophical meaning if contemplated long enough, or may inspire deep visceral emotions if interpreted in certain ways, or simply seem to be pleasant nonsense in the way only songs and poetry can be.

But in reality, Mary’s song is a tribute, heartfelt and full of wonder, for one of our species’ most audacious and hopeful acts: the creation of a message that will far outlive our civilization, promising whoever hears it that we are sometimes better than we often are. The message was created, physically engraved in precious metals, and cast out into the wild voids of the Cosmos, never to be seen again.

That message is known as the Voyager Golden Record. Two copies of the record were minted from disks of copper plated in gold, shrouded beneath protective covers of aluminum, and mounted on the side of each of the two Voyager spacecraft. 

The Voyager Golden Record; the panel on the left shows the cover (inscribed with information to decode the record), and the panel on the right shows the record itself. [Images: NASA/JPL]

Launched 16 days apart in the autumn of 1977, the Voyager spacecraft were ostensibly part of humanity’s first reconnaissance of the solar system, sent to explore the giant worlds of the outer solar system — Jupiter, Saturn, Uranus, and Neptune. They swung by each world, dutifully snapping pictures and radioing their precious scientific data back to the distant rock from which they hailed. As they passed by each world, gravity latched on to them, propelling them ever faster and farther, on to their next destination.

Voyager flight paths through the solar system [Image: NASA/JPL]

Voyager 1 passed Saturn in November of 1980, and the Ringed Planet flung it up and out of the plane of the solar system, toward the constellation of Ophiuchus. In August of 1989, after a twelve year journey, Voyager 2 passed by Neptune, letting the icy giant’s gravity swing it down and out of the solar system, propelling it in the direction of the constellation Sagittarius. After fleeting and tantalizing glimpses of our cosmic neighborhood, the Voyagers have started the long, slow sail to the stars. Today they are the most distant physical artifacts of the human race, both of them more than 20 billion kilometers away, the Sun and Earth mere flecks of distant light.

Powered by small nuclear generators, the Voyagers’ energy is nearly spent. They will dutifully continue to transmit faint bleeps of information back to Earth, but within a decade or so they will fall silent and grow cold, hurtling ever onward toward the stars. Time, space dust, and cosmic radiation will take their toll on these artifacts of Earth, but the Golden Records were designed to stall such inevitable decay for as long as possible. Made of metals that are unreactive and change slowly over time, and encased behind protective aluminum covers, they should resist the long slow death, surviving for a billion years or more..

But what possibly could we have put on the Golden Records to warrant such care and concern about their survival? Mary Fahl told us up front:

Encoded traces of the human race and what we understand

Within the limitations of a physical object that could survive a billion year journey into deep space, we captured what we could about our species, the planet on which we live, the lifeforms we share the Earth with, and the meager understanding of the Cosmos we have gained. Together with greetings in many languages of the planet, and a selection of music from around the world, we engraved the information on 12-inch disks of gold covered copper, and sent them to the stars. It was a gesture of hope and optimism that, in some imagined future, an intelligent species somewhere across the empty sea of space might stumble across Voyager and be able to know something about who we were, faint echoes of a lonely planet and species that once dreamed of sailing to the stars.

Blind Willie Johnson [Image: Wikimedia Commons]

The key elements of the Voyager record are the protective cover, an included stylus (phonograph needle) to play the record, 115 images, a collection of the “sounds of Earth,” spoken greetings in 55 languages, and 90 minutes of music in 27 tracks. Blind Willie Johnson is the second to last track, singing  Dark Was The Night, Cold Was The Ground, a blues Gospel song, with no words but Johnson murmuring and humming along with his soulful guitar picking.

By today’s standards, the amount of data on the record is miniscule — a handful of images that are 512 x 384 resolution, and only 90 minutes of music. But that’s all there is, a small snapshot of life on Earth at the end of the 20th Century. It is likely one of the only artifacts of humanity that will survive our species; for some distant intelligence that might someday find Voyager, it is the only thing they will ever know of us.

The assumption we are making is that whomever might find Voyager will make an attempt to decode the Record. It’s an all together human assumption — if you found a bottle washed up on the seashore, a message carefully preserved inside, would you open the bottle to read it? Of course you would! In our optimism, we trust the receivers of our message will do the same.

On the surface, it seems to be an audacious thought, that a message encoded on a facsimile of a phonograph record could be received and decoded by an extraterrestrial who knows absolutely nothing about us, our technology, our species, our cultures, or our languages. But the message was designed with precisely that concern in mind. Astronomers call the idea of receiving such a message “communication without preamble,” and believe understanding it is predicated on a single fact: that the receiving civilization is technologically skilled.

The Voyager record cover provides protection, but also has information about how numbers are expressed (the “barbell” in the lower right is a hydrogen atom, whose properties should be known), instructions for how to play the record (the image of the stylus on the circle in the upper left), instructions for how to get data off the record (the information on the upper right, showing the data and the first image), and a map of where Voyager came from (the starburst on the lower left). [Image: NASA/JPL]

One of the great truths of the Universe, and perhaps the greatest mystery, is that everything is governed by an immutable set of rules that we call The Laws of Nature. The idea, the logical chain of reasoning, is that if you are capable of travelling into space to discover Voyager, it means you have a deep understanding of those self-same laws, enough so that you can harness them to travel the void of space yourselves. So we encoded the Voyager message using the common foundations of astronomy, physics, and mathematics that apply in every corner of the Cosmos, and trust that an understanding of those foundations will provide enough of a clue to decode Voyager’s precious cargo of sounds, music, and images. 

If you think deeply about this, you might argue that an alien species that recovers Voyager may not have eyes to see as we do, so images may not carry the same meaning. They may not have ears to hear as we do, so music may not be perceivable in the same way. But consider: there are many phenomena in Nature that our senses cannot perceive, yet our intellect and technology make us perfectly capable of detecting and understanding. If an extraterrestrial species is technologically capable, we think they will similarly be able to apply their intellect to understand the story Voyager has to tell.

How do you decide what to include in a message you are sending to the stars? What do you put in a time-capsule to represent our planet and ourselves to an audience we will never know? What do you send to a world and a biology and a history and an intellect completely alien to our own? What do you want beings a million years from now to know about us?

We could be cynical, we could be optimistic, we could be realistic, we could be practical. What should we be?

It is often pointed out that we could have included images and messages about our great failings. The wars we fight, the violence we inflict on one another, our great failings in justice and equity for all the citizens and life of the planet. We could have included images of atomic mushroom clouds, of dead school-children, of wasted and decimated landscapes destroyed by our short-sighted obsessions. But we didn’t do that. We took a very neutral stance, perhaps a sanitized vision of our world. We included pictures of our planet from space, of a tropical island, of a mother and child, of a farmer in Guatelmala, and 111 others. A cynical person might suggest we were being overly deceptive, and not showing the truly ruthless and sad character of our species. Perhaps, but I think not.

Just a few of the images included on the Voyager Golden Record. See a more complete list at NASA’s Golden Record Site. [Images: NASA/JPL]

No, flipping through the image library of the Voyager Golden Record one also gets the sense that this is not just who we are, but what we hope we are — a species that is living through the challenges of our own adolescence, a species that is for the moment surviving, and a species that aspires and believes that many thousands of years hence, our descendants will still be here, wiser and better off than we. We tried to choose a series of images that say we learned enough to build Voyager, and while we’re aware of the dangers we currently face, we are also aware that we are part of a much larger Cosmos.  Our meager collection of images and music is a realization of what we have learned, manifested in the optimistic act of constructing an impossibly limited message containing a few precious tidbits of life on Earth, from a species called “humans.”

And we tossed the message into the Cosmic Void, knowing not where the tides of space might take it.

There is absolutely no consequence if Voyager is never found, nor if the message is never decoded. There is a certain solace we gain from the mere notion that it might be found and might be decoded. Perhaps that solace is rooted in a deep fear — the fear that we are alone in the Cosmos, and everything that we are and think and do will someday perish, extinguished utterly from the Universe.

But I much rather like to think that the solace is rooted in optimism. We believe that it is worth shouting into the Void, shouting that we were here and this is who we were. We believe that, perhaps, there will be beings as intelligent and curious and emotional as we, and that they too might find joy in the discovery of Voyager. We imagine they might feel inexorably compelled to decode the carefully constructed message, and discover that they also are not alone in all the expanse of the Cosmos. We imagine that they too might be struggling through their own adolescence, hoping to not destroy themselves. We imagine that if they receive this small, meager message from Earth, the knowledge that they are not alone might help them somehow. We imagine that such a message might help us.

It is remarkable to think that the act of creating the Voyager Record is an act of optimism, and precisely what Mary Fahl’s lyrical exploration suggests to me. It suggests that despite all the challenges our species faces, despite all the clear failures that we foist upon ourselves, that some part of us still knows the remarkable things we can achieve, and we imagine the good that could result.

In days of gloom, in days of sadness, no matter what we do here on Earth, Voyager sails ever onward, its Golden Record cradled carefully on board, a message for a billion years from now. Perhaps, as Mary noted, “everything’s gonna be alright.”

Pandemic 03: Survivability Traits

by Shane L. Larson

Over the millions of years that natural selection produced modern humans, countless traits were selected becasue they were somehow advantageous to our suvival. Ultimately, some 40,000 generations ago, modern humans began walking the lands of Earth; experiments that Nature had made as it grew our branch of the Tree of Life were terminated without a second thought. Today, there are no archaic humans left — gone are those that came before us, erased but for a few fragments and bones that rise from the tomb of the Earth.

A skull of homo rhodesiensis, an ancient ancestor of humans. The Universe has long experimented with what makes humans good survivors; today there are no homo rhodesiensis left. [Wikimedia Commons]

One might ponder what it is about humans that made us the fittest in our long line of ancestors? The Latin name for our species gives a clue to what we think the advantage is: homo sapiens means “wise man.” More often than not, our intelligence, our brains, are regarded as the prominent trait that made our survival most likely. The ability to make tools, to solve problems, and to plan for possible futures are all powers of the brain that suggest its development was a good survival trait.

But for those of us who think about life in the Cosmos, we eventually ask whether or not human intelligence is a survival trait or not? Look at the utter disregard our species has for the finite resources on our planet, or the fact that we are willfully ignoring the accelerating climate crisis, or any of a hundred other existential global threats we are ignoring. It makes one question whether our intelligence is being used for survival at all.

Interestingly, the brain is just like every other physiological trait we have — it was built by Nature through a long chain of experiments in survival. The earliest parts of the human brain to develop, the paleomammalian cortex (or limbic system), is the core of human emotion and response to external stimuli, particularly danger or threats. It evolved over time, like all of your biological systems, to protect you and give you a better chance at survival. One of its safety responses is to control your psychological response to threats. Sometimes that response is designed to protect you from very tangible direct harm; at other times it is designed to protect you from very tangible threats, but ones which may harm you by overwhelming your reactions until you are completely debilitated.

We see both of these deeply ingrained threat responses playing out right now in the ongoing crises that have ensnared the world.

Death has always preoccupied humans, in biological imperatives, deep psychology, and art. This 17th Century painting from Philippe de Champaigne is often associated with the Stoic philosophies surrounding Memento Mori: “remember that you will die.” [Wikimedia Commons]

Consider how we humans perceive and deal with death. A single death can transform your worldview — the death of a close friend or a loved one has profound impact on your mental state, precisely because of the deep personal relationship you shared. Death acutely focuses your attention on the fact the memories you carry with you will be the last ones you have with that person. It also acutely focuses your attention on your own mortality.

But you don’t have to be personally related to a person, or even know them, to feel grief at the loss of life. You feel the same pain, as if it were a friend or a loved one, precisely because you understand the deep personal loss from the death of a single person. Your brain has been wired from your personal experiences to understand how single people change one another’s lives. You extrapolate those experiences to people you don’t know when you hear of their death. The result is you are devastated, tortured by grief when they die. The deaths of famous people are a curious mix of the two, since you often ascribe deep personal evolution to your exposure to music, writing, sports, and film.

As a result, the loss of David Bowie knocks you down, because you remember driving in your car with friends listening to “Scary Monsters” over and over again, and those powerful memories are inextricably melded with your knowledge of Bowie. Chadwick Boseman’s death sent you into a paroxysm of tears, not just because you admired him in 42, but because your own family has been ravaged by cancer. Your rage at the murder of Breonna Taylor was stoked by the fact that she was murdered in her own home, a place of perceived safety and sanctuary.

Tragically, our brains behave in the exact opposite way when the scale of the tragedy expands beyond numbers easily related to your own personal experiences. Word of a family dying in a car crash or an apartment fire invokes a terrible sense of tragedy. News of an airliner going down may fuel your fear of flying, but large groups of people being overwhelmed by disaster becomes, for the most part, abstract to your brain. The reason is your brain is defending itself in a rather peculiar way. You absolutely can imagine the tragedy of the deaths of thousands of people — but multiplying the agony of grief for a single person a thousand-fold would destroy your psychological balance, and your brain knows that. It clings to the abstractness of large, anonymous numbers, and lets your thoughts gloss over the fine-scale human details of the tragedy. This effect is called psychological numbing.

Map of confirmed COVID-19 infections per capita (total divided by local population) as of 17 Sept 2020. The global scale of this crisis is beyond normal, everyday human experience. [Wikimedia Commons]

Which brings us to the current crisis. Without fail, the coronavirus Pandemic is a global crisis, not to be shirked and ignored. It kills people — 948,000 worldwide, and 202,000 in the United States (as of today, 17 September 2020). For virtually everyone who contracts the disease, there are long term consequences that we are only now beginning to understand — cardiovascular damage, fatigue, deterioration of your joints, and damage to your nervous system. The dire effects are why scientists and public health experts are so adamant about controlling the spread of the disease.

But unless you or a family member or a close friend have had (or died) from COVID-19, your brain protects itself. The psychological numbing associated with the scale of the pandemic takes over, and underpins all your thinking, regulating your personal behaviour as well as guiding your response to widespread social safety measures designed to cap the disease. Numbing can dull your sense of danger, leading to you not being as safe as you can be. An unfortunate lack of perceived danger might convince you that everyone who is responding with great caution are being silly, and it could lead you to rebel against social safety measures like a teenager against curfew. Your brain is protecting itself by convincing you it isn’t as serious as it is, but it is lying to you. You can control such responses, but only through diligent practice and self-reflection, and fearless trust in what the scientific data is really saying, not what we want it to say.

And so, our conversation returns to where it began. The brain of homo sapiens, with its capacity for abstract thinking and predictive speculation is the product of millions of years of evolution. Each stage in the long chain of natural selection helped our ancestors survive a ruthless and dangerous world, leading to us today.

So are our brains a trait that makes us fit for survival? The Universe developed our brains because along the way it seemed to be protective. But psychological numbing exposes us to threats that can decimate our species, like coronavirus to be sure, but other existential threats are on the horizon: pressures of population on limited natural resources, human wasting of natural environments, and the catastrophic collapse of the climate at the hands of humans. 

One could easily conclude that on the scale of our civilization, psychological numbing is not a survival trait, and the great experiment known as “humanity” will terminate, and fade into oblivion. It has happened before, with megalodons, sabre-tooth tigers, and trilobytes. That termination has happened to humans too — gone are our ancestors, Australopithecus, homo erectus, and the Neanderthals. But it has happened to our civilizations before too — gone are the ancient cultures of the Indus Valley civilization and Mesopotamia, and only fragments of the ancient Anasazi remain in the American Southwest, all erased by droughts that destroyed their supportive, agricultural systems. Humans are not immune to being erased by the Universe.

The Tree of Life is vast and tangled, but many more species have died than have lived, unable to survive the challenges the Universe throws at them. [Image: Pixbay]

But on the other hand the Universe has stirred another ability into the experiment — our capacity for reason, the ability to look at the Universe, figure out and predict what is happening and why, and doing something to protect ourselves. In some fashion, we have learned to utilize that trait and act in complete contraction to other biological imperatives our brain would like us to respond to. The Universe is testing out the idea that software updates, designed to circumvent hardware weaknesses and previous programming, might be a good survival trait.

Whether or not our reason adds to our survivability in the long term remains to be seen. We have yet to come to the end of this crisis, and do not yet know if our civilization can collectively shore up our defenses, or if we will continue to capitulate our future on the basis of wishful thinking. 

Either way, the Universe does not care. The Universe is callous, ruthless, unflinching. It is no mere tyrant, it simply has no reservations about terminating experiments that cannot survive in the face of adversity. Perhaps homo sapiens will sink into extinction; perhaps there will be some new strain of humans, homo postero, that will not be so fact resistant, and can survive more adversity than we.

As a brilliant fictional scientist once observed, “Life finds a way.” The Universe will find a strain of humans fit for survival, even if we are not.


This is the third in a series of posts about scientific reasoning, instigated by the Pandemic of 2020. The first post and links to the rest of the posts in this series are:

Pandemic 02: Numeracy and Data

by Shane L. Larson

Let’s talk about “numeracy” — to be clear, I define this to be the ability to use and understand numbers and data. It is similar to “literacy” but related to quantifiable things, things that can be measured, and things that obey well defined and incontrovertible rules. Specifically, I want to talk about your numeracy.

I have spoken with many thousands of you at public lectures, and many more thousands of you have sat through my introductory physics and astronomy classes. I certainly hope there are many more thousands of you reading this. At this moment, my former students have a certain advantage over all of you — they know better than to utter the words “I’m not good at math,” lest I get out an actual soapbox (I’m quite short), stand up on it, and wax on and on about how that simple phrase, “I’m not good at math” is a lie you have been taught to repeat. You might call such a soapbox speech a “rant,” or so my teenage daughter tells me (she also knows to never utter the words “I’m not good at math”).

Many people like to opine that they are “bad at math” because they struggled at one point in the past, or because someone told them they were, or because it is cool to say you are “bad at math.” In fact, most of you aren’t bad at math at all — you just aren’t practiced at recognizing that fact.

I can already hear your objections. I know you will insist that you are bad at math based on a poor past experience in a calculus class, or the fact that you struggled with solving cubic equations, or because you don’t have a foggy clue what tensors are. Fair enough. But I don’t remember any of the soliloquies Shakespeare wrote in Hamlet; I can’t diagram a sentence, nor do I precisely remember the definition of a transitive verb, and I suspect the only reason I know about conjunctions is from singing Schoolhouse Rock songs. But I would not deem myself “bad at English” or “illiterate” as a result (my former English teachers might disagree; sorry Billie Wright!).

But this is precisely my point about math. You are not “innumerate” and “bad at math” — there are sophisticated and complex advanced topics you may have been taught at one point in your life and perhaps didn’t fully grasp and may not remember today. They were taught to you in order to develop the neural and cognitive framework of your brain, just like you were taught about diagramming sentences and iambic pentameter. Today, decades after you were last in a classroom, you may not remember all the details but you still have that cognitive framework. You are perfectly capable of using it. You are “numerate” and I know you are because I see you be numerate every day.

You very seldom fail to order the correct amount of pizza. Calculating incorrectly in either direction can be disastrous; you are numerate enough to do this.

For example, suppose your book club is going to meet next Saturday and you need to order pizza. What do you do? You count up how many people are coming, you estimate how many pieces of pizza each person will eat (based on prior observations), you add a few extra pieces in that your partner and kids will take, and based on the number of slices in a pizza, you place an order. You pretty much get it right every time. Seldom have you ordered 78 pizzas for 7 people because you are “bad at math.”

What if you are trekking across the country on your National Parks road trip. Your dependable late 90’s economy car gets maybe 28 miles per gallon, you’ve got 3/4 of a tank and are heading out onto the long stretch of I-90 between Sioux Falls and Rapid City and quickly calculate when to stop for gas so you don’t run out. You pretty much get it right every time and have seldom been stranded out in the middle of South Dakota.

You regularly and successfully calculate how much gas you need to make long trips. You are numerate enough that you have seldom, if ever, run out of gas in the middle of South Dakota.

You are perfectly capable of assimilating data (data are things like previously knowing how many pizzas are eaten or how far you drive on a tank of gas) and using current conditions (things like how many people are coming to your club meeting, or how much gas is left in your tank) to make a numerical calculation (how many pizzas to get or how much gas to buy). You are fine at math. More to the point, you are numerate. You don’t think about it, of course, because the risk associated with over-ordering pizza is low; you seldom have to make a 400 mile run in your car without hope of seeing another gas station soon. It doesn’t change my point that you are, in fact, numerate.

The value of being numerate cannot be overstated in the face of the crisis the world faces today. Understanding what COVID-19 numbers are telling you, and perhaps more importantly what they imply about your personal risk, is critical to safely weathering the Pandemic so you can emerge on the other side. In the sea of numbers we hear each day, how do we absorb those numbers and use them?

Numbers have a certain implacable relentlessness to them, a modicum of unassailable truth that is regularly at odds with the distinctly human need to rationalize.  That being said, a number’s implication for how it impacts your life requires context, otherwise it’s just a number devoid of how it relates to the world. We can use your numeracy to illustrate how context is important, and then apply it to understanding the current crisis.

Let’s begin with a learning experiment — a simple example that illustrates how information combines together to inform you about the world. Imagine I have a carpeted living room with a nice square grid pattern in the carpet, 20 squares by 20 squares (400 squares total). For some extravagant reason beyond the scope of this blog post, imagine I have dropped some nickels on the carpet; a lot of nickels. You are enjoying your lunch, and trying to decide if it is worth interrupting your delicious sandwich to go pick up all the nickels before someone else does. So you send me in to check the situation out.

An experiment in dropping nickels on a carpet. Each square of carpet is the same size, and the same number of nickels were dropped each time. What is shown is what landed and stayed in each square.

CASE A: I come back with two nickels. Do you go pick up nickels or not? Without any context you really can’t decide. Unhappy with me, you send me back into the room and I come back with five more nickels! Now you have a total of seven nickels, or 35 cents! Do you go pick up the nickels or not? This is all about context of the data — what do the nickels I brought back to you represent? Did I bring you all the nickels, or just a fraction of the nickels? How many more nickels might there be? 

CASE B: This time when I come back, I bring you 7 nickels, but I tell you they were all the nickels in one square of carpet.  This is context. Context allows you to start figuring things out, because you are numerate. In particular, if every square has 7 nickels on it, and the room is 20 by 20 squares (400 total squares), then the room would have 400 x 7 = 2800 nickels, or $140! This is good context, but we could still do better.

CASE C: In the last example, you made an assumption. Assumptions are neither good nor bad — assumptions are limited. The important thing about assumptions is that when you make them, you try to be clear about what the assumption is, so if your understanding of the situation improves (you get more data), you know how to update what you think is going on. Above, you assumed every square had 7 nickels. Is that true? You send me back into to find out.  I come back and tell you I looked at three more squares, and they had 23, 18, and 20 nickels in them respectively. This is greatly improved context, because you have many pieces of data. There are simple and complex ways of looking at data, even when you have only a few bits of information. One of the easiest is the average.  What is the average number of nickels on a square?  Based on our observed data:

   Average = (7 + 18 + 20 + 23)/4 = 17 nickels per square (on average)

So now you can estimate that in the room there would be 400 x 17 = 6800 nickels, or $340 dollars! It is definitely looking like you should be collecting those nickels.

A simulation dropping 8000 nickels on a carpet that is 20 x 20 squares wide. Note the highlighted random square — this one has 7 nickels, the first square we talked about in our discussion. [Image: S. Larson]

This image above shows the data this example was drawn from — a 20 x 20 carpet grid, with 8000 nickels ($400) dropped on it.  The first experiment where I brought you only 7 nickels told you something, but by collecting more data you developed a clearer picture of what was going on in the living room.

Now let’s use this example to help us understand something about the Pandemic.

As the coronavirus Pandemic has surged in the United States, considerable noise has arisen around testing and what the number of tests and results mean. Fortunately, you can use your numeracy to understand what the data is telling you. Two common testing numbers are reported for most states: 

  • The number of tests administered
  • The number of new daily cases (number of positive tests)

In and of themselves, these numbers have no context, except that most of us have some rudimentary knowledge of our state to provide context — the critical knowledge here is the population. Population provides a simple way to understand how widespread the disease is: 500 cases in a county with 20,000 residents has different implications than 500 cases in a state with 1 million residents.

One of the most common points of discussion in COVID-19 testing is whether or not the number of cases is rising just because we are testing more. At the heart of this talking point is the more fundamental question, the question we really want to know the answer to: how do we know if the coronavirus is spreading and growing in our state or not?

Testing is just like our nickel example above, and you can use the nickel example to help guide you in your thinking. 

NICKELS: Each square has some random number of nickels in it. If I look at one square, I get some sense of how many nickels there might be. If I randomly look at many different squares, I get a better, more reliable picture of how many nickels there are in the entire area of the carpet. If I get 7, then 23, then 18, then 20 nickels, there are on average (7 + 18 + 20 + 23)/4 = 17 nickels per square.

COVID-19: Take a fixed number of people, say 100. If I test those 100 people, I get some sense of how many COVID-19 infections there might be. If I randomly pick many different groups of people, I get a better, more reliable picture of how many COVID-19 infections there might be. If I get 7, then 23, then 18, then 20 infections, there are on average (7 + 18 + 20 + 23)/4 = 17 infections per 100 people.

Reporting the number of infections together with the number of tests given is called  the positivity (or, more correctly, the positivity rate), and is a way of giving context to the data. Another way to give context is to report the total number of cases divided by the population (typically reported per 100,000 people, rather than the full population; this is more similar in size to a typical community and helps personal visualization about how widespread COVID-19 might be in a small city. Cases per 100,000 also is easier to talk about without making arithmetic errors!). Most state health departments and most major COVID-19 tracking sites that report daily data report both of these important numbers, giving you a better way to understand the risk.

So how do you tell if things are improving, holding steady, or getting worse? You watch how a number like the positivity changes over time. The number of known cases does increase with time. The number of known cases does increase with the amount of testing deployed. But the positivity rate accounts for that fact by always thinking about the data in fixed, similar sized chunks. In our examples above, deploying more tests means more groups of 100 tests to include in the average. Just like counting more squares on the carpet gives a better idea of the number of nickels, increasing the number of tests improves how well we know the positivity rate, which more accurately captures how COVID-19 is spreading in our communities. So the rule of thumb is:

  • If the positivity rate is increasing, then for any random group of people you pick, more of them are sick with COVID-19
  • If the positivity rate is holding steady, then for any random group of people you pick, the disease is not increasing rapidly
  • If the positivity rate is decreasing, then for any random group of people you pick, the disease is slowly being eradicated

You could also replace “positivity rate” in these rules of thumb with “cases per 100,000” if that is an easier number for you to relate to. The story the data is telling you will be the same either way.

Now keeping all of this in your head can be hard, even for those of us who “do numbers” every day. Use your mental examples, like the nickels on the carpet, to keep you grounded. Tactile, hands on examples that you could actually recreate on your living room floor are often easier for your brain to work with, since they are easily visualized or even created, making it easier to stick in your mind.

We will come back to using simple mental models to keep our reasoning grounded in some more of our upcoming discussions. Until then, be safe, be well.


This is the second in a series of posts about scientific reasoning, instigated by the Global Pandemic of 2020. The first post and links to the rest of the posts in this series are:

Pandemic 01: Learning in a Time of Crisis

by Shane L. Larson

For many of us, we have not been under the tutelage or mentoring of someone in in a learning environment for a long time. Classrooms were a regular part of our lives years if not decades in our past. Once we left classrooms behind us we did not quit learning, we just changed what we learned, and we totally changed the balance of what we learned. 

Nowadays, you learn on the fly and on your own. Maybe you were tutored in your current job skills during your first week at your company. You’ve probably done a lot of learning by trial and error (especially on home projects, like building decks, learning to garden, or sponge painting a wall so it looks good). Maybe you learned through a lot of hard knocks, starting your own business and figuring out how manage employees, price products effectively, and manage supply chains. And perhaps you still learn by surfing the web when your curiosity gets the better of you and you want to know what the life-cycle of catfish are, or how they built the Grand Buddha at Leshan, or who invented waffles anyhow? You never stopped learning, you just stopped going to school.

But there is a simple fact here: you are plenty smart, and plenty capable of taking unfamiliar information, assimilating it, and working with it. Your everyday learning life says that very clearly, and it works great for most things, especially if they are low risk, meaning they don’t threaten life and limb. Small errors can be corrected, methods and skills can be practiced without terrible consequence. But what do you do when things get really complicated?

The global pandemic caused by the coronavirus outbreak has flooded all of our lives with new information. Daily infusions of numerical data, graphs, predictions, extrapolations, models, parameters, error bars, data quality factors, trendlines. If you don’t think about data and numbers and scientific implications every day, it’s all a bit overwhelming and has a tendency to exacerbate uncertainty that abounds with a crisis that is fast moving and constantly shifting as dew data and findings come to light.

My fellow scientists and I encounter this kind of data, and in particular this kind of data onslaught, every single day. We’ve spent our entire careers reading graphs, looking at numerical data, building predictions from that data, and assessing implications and possibilities.

But if you aren’t a scientist, how do you dip your hand into the COVID-19 firehose and gather enough information to help you feel informed, enough information to perhaps quell some of the anxiety you may feel, and most importantly make an assessment of risk to help yourself plan accordingly?

Some of you are lucky enough to know a scientist or medical professional, and you may have reached out to them to ask a question or two, dipping your toe back into that learning environment you left behind in classrooms long ago. For those who know me and have had the courage to ask, I have fielded many such inquiries, answering questions about how to understand data and the implications of data and predictions to the best of my ability.

The answers to those questions aren’t always clear, because for many aspects of this crisis we are simply still ignorant. For many other aspects of this crisis, we understand in crystal clear terms what is going on, but uncertainty hinges on the fact that what is to come is largely dependent on what we do now. Understanding that our knowledge about COVID-19 and the coronavirus is evolving is just as important a lesson as being able to read a graph or understand a trendline. Understanding there are incontrovertible uncertainties, and what it means for personal risk, is essential. Understanding that there are actionable things we can do to minimize risk is absolutely critical. All of these lessons are there, in the firehose of data.

So for the next few posts, I’m going to spend some time doing what I do — trying not just to answer some of the questions I’ve been asked, but also trying to remind you of the skills someone once taught you long ago in a science class. Back then, you might have asked why you need to know all this science stuff. THIS. This is why. Because sometimes life in the modern world requires you to think a bit like I think and look at graphs and data.

These posts will feel a bit like your old science class did, and some of you remember that you didn’t enjoy that class. I get that. But at this stage in my career, I have taught introductory science to thousands of students, and I’ve talked to thousands of you on the public talk circuit. In all of those  experiences, I have discovered a secret:

You can understand this, better than that little voice in the back of your head gives you credit for when it says “I hated science!

I know, because I’ve talked to you. So let’s talk about the Global Pandemic, and the COVID-19 crisis for a few posts. Your life, and the life of your friends and family depends on it.

— — — — — — — — — — — — — — — —

This is the first in a series of posts about scientific reasoning, instigated by the Global Pandemic of 2020. The links to the rest of the posts in this series are:

The Work to Be Done

Note to my Readers: The last time I posted, we were discussing Antarctica; I have more to say about that, and it is not disconnected from issues surrounding human activity on this planet, but current events have overtaken us, and that discussion will pause for a time, allowing us to focus on the convulsions our society is facing in light of global responses to the coronavirus pandemic, and now the long-overdue rebellion against the injustices visited upon people of color around world. It is of the latter that we will speak today. – s


As the current upheaval embraces our society, sparked by centuries of racial injustices in our country, I have heard scientific colleagues express quietly they are uncomfortable. Their quiet mumblings take the usual form of “I just want to be able to do my work.”

There is undeniable resistance to participating in the calls for racial justice, to demanding that we begin to tear down the structural support of all the systems that enable and prop up racial injustice. Such resistance is born from an indelible recognition that we, white people and mostly males, have benefited from and enjoy the protections of those systems. In science in particular, indignation in the face of worldwide protests and disruption of “normal life” is born of an intense understanding that no matter what we do or have done to combat the ills of our society, no matter how aware we claim to be, each of us is a paragon of privilege, embedded in a system that has favored us, unaccountably in contradiction of our stated ideal of “merit alone.”

I hear repeatedly, “but this is politics; I want to work on science, not participate in politics.” This is NOT politics; the label “politics” is a shield we hide behind to avoid conflict. This is precisely our work as scholars, and in particular as scientists. The fundamental purpose of teaching and practicing science is three-fold:

  1. To objectively solve problems using data and evidence based reasoning;
  2. To build human knowledge;
  3. To use that knowledge to improve and enrich our lives

All scholarship, but science in particular, thrives from having many minds together. Science advances through a diversity of voices and minds, a diversity of experiences and worldviews, a diversity of thought and approach. In spite of our proclaimed ideals of dispassionate logic and evidence based thinking, we as a profession have eschewed and avoided that diversity, and are less than we imagine ourselves to be as a result. Like the rest of society, we have marginalized our fellow humans who have aspired to participate in the most unique and valuable of human endeavours, the seeking of knowledge which serves no other purpose but to improve and enrich our lives.

We are well accustomed to data and careful scholarly research, and claim to have an unswerving respect for facts no matter what cherished beliefs they challenge. The data tell a sad and malevolent story of our failure to engage and support people of color in the scholarly enterprise. We have an undeniable bias against people of color. Witness: Despite making up nearly 13.5% of the US population, Black Americans only make up 6% of the professoriate; Latinx and brown Americans make up 18.3% of the US population, but only %5 of the professoriate (Pew Research link). Our chosen metric of success, particularly in the sciences, is citations of published work, a supposed mark of scholarly awareness of your contributions. Scholars of color are severely and uniformly undercited (Journal of Communication, 68, 254 [2018]). Studies of racial representation at scientific conferences is nascent, but conference talks and panels are still dominated by white males (Nature 573, 184 [2019]).

These findings are all based on research and data; their implications are uncomfortable to contemplate but clear in their message: there is tremendous work to be done. The protests around us are, in part, about exactly this work — the structural inequities built into our system that prevent people of color from engaging in the same work as you and I. The protests around us are, in part, precisely about the fact that we have ignored this for decades, or at best, ineffectually addressed this for decades.

My white colleagues may be reading this right now and saying, “but I’m already doing my part.” It is time to do more. Whatever you’ve done before was good, but the work is not over. The work is never over, and you know that, otherwise you would not recognize that you’ve attempted to improve racial justice in our society.

There are many many suggestions for what you can do as a white citizen to help break down the structural inequities in the country; I will not repeat them here (nor could I possibly link to all of them — I’m personally starting with suggestions from Perri Irmer, President and CEO of the DuSable Museum of African American History in Chicago). But as scholars and members of the university community, there is plenty you can do beyond your own personal education — just look at the data I linked to above, then take it to heart.

Work to improve the representation of people of color in university faculty; ensure that your citation practices do not exclude scholars of color; and do not allow your professional societies or colleagues to host conferences with exclusive speaker line-ups or panels of white males.

This is the beginning of the work to be done. Within your departments do not let unjust language be used without penalty; do not let people of color be silenced in departmental debates and conversations; do not let their work and contributions go unnoticed or be claimed by someone else; promote them as you would promote yourself or students who work with you.

It’s time to speak up and use the positions the system has put you in. You may be uncomfortable, but this is the work to be done, and you are the only one who can do it. It’s no different than what you tell your students: you aren’t being graded for how hard you work, you’re getting graded for what you accomplish. There is no extra credit, just the work you have to do.

Black Holes 5: Inklings & Obsessions

by Shane L. Larson

There are many exotic phenomena in astrophysics — some pervade the public consciousness, and others do not. Most folks have heard of the “Big Bang” and probably about “dark matter.” Fewer people have heard of the “Cosmic Microwave Background” or “neutron stars.” Perhaps even fewer have heard of “cosmic strings” or “radio jets.” But of all the strange and wonderful things astronomers and physicists have contemplated, the most universally known and recognized are probably “black holes.” Just about everyone has heard of black holes, and just about everyone has some cool science factoid they know about black holes and keep in their pocket — they pull the factoid out anytime the subject of black holes come up because the factoids typically MELT YOUR BRAIN.

On the left, an optical image from the Digitized Sky Survey shows Cygnus X-1, outlined in a red box. Cygnus X-1 is located near large active regions of star formation in the Milky Way, as seen in this image that spans some 700 light years across. An artist’s illustration on the right depicts what astronomers think is happening within the Cygnus X-1 system. Cygnus X-1 is a so-called stellar-mass black hole, a class of black holes that comes from the collapse of a massive star. New studies with data from Chandra and several other telescopes have determined the black hole’s spin, mass, and distance with unprecedented accuracy.

I find black hole factoids to be a curious mix of some things that are true, some things that are speculative but possibly true, and some things are are outright fiction. Where do all of the exotic facts about black holes come from, how do we all learn them, and why are some right and some wrong? Wondering about this led me to contemplate when I first heard about black holes.

Black holes have long been a passion of mine — my mom will tell you I was always kind of obsessed with them. But when did I first hear about and learn about them? I certainly can’t answer that question definitively, but I do know some things about my early exposure, so I can try to understand what strange and awesome ideas first attracted my attention.

The earliest encounter of which I am certain is during the 1979/1980 timeframe. This was the time that many people saw Disney’s epic space opera The Black Hole, replete with adorable robots, killer robots, really awful bad dialog, and archetypical mad scientists. It has often been derided for its scientific inaccuracies (most notably by Neil deGrasse Tyson [link]). I definitely saw The Black Hole. Multiple times. And I still watch it sometimes. Neil’s right, there is a lot of inaccurate science about black holes in The Black Hole, but there is a lot that I think was okay too (more on that later). There are definitely modern movies that get the science more uniformly correct (Interstellar), but I don’t mind The Black Hole — certainly not as much as Neil. The point here is this is a known anchor point in my love affair with black holes.

So what could a movie like The Black Hole teach me about real black holes? If you ask almost anyone, they know the correct fundamental thing: a black hole is an object whose gravity is so strong, not even light can escape — even The Black Hole got that right. Since nothing can travel faster than light, nothing can escape. If you fall into a black hole, your fate is sealed. It is this idea of being trapped forever, without recourse or hope of rescue, that lies at the heart of our fascination with black holes. They are strange; indubitably. But to be inescapable suggests a kind of absolute and infinite supremacy. 

Me in elementary school. I’m not sure what I’m doing, but I’m pretty sure I’m not getting into trouble! [Image: Pat Larson]

In 1979/1980 I was in fifth grade, and I was gobbling this stuff up left and right. I was a well known fixture in both my school library (Hygiene Elementary School, in Colorado), and in the Longmont Public Library, where my mom had gotten special dispensation for me to have an “adult” library card so I could prowl through all the science books in the grown-up section. My parents also exposed me to a steady diet of books at home, and while they were all nominally “family books,” some of them made it to the bookcase by my bed and never went through anyone else’s hands. In 1980 one such book was Roy Gallant’s lavishly illustrated Our Universe, published by the National Geographic Society.  I was certainly enraptured with outer space by then, steadily fed by the ongoing exploits of Viking and Voyager as they played out on the pages of National Geographic. But this book — this book. Blew. My. Mind.

It is a book filled with great pictures from an exquisite generation of space probes, and from the best telescopes the world knew in the pre-Hubble era. But the art and scientific illustrations are what sucked me in. Paintings of the surface of Venus. Speculations of what weird alien lifeforms evolution could have created. Stupendous cutaways of planetary interiors and atmospheres. All of it was linked together with Gallant’s trademark lucid storytelling.  This ode to the Universe captured my mind and imagination and never let go. That first copy my parents gave me was read cover-to-cover, and carried for miles and years everywhere I went, pulled out of my backpack in moments of wonder and curious indulgence.

Examples of the art and technical imagery in Roy Gallant’s “Our Universe.”

Near the end of the book, Gallant talks about black holes in just 4 short paragraphs, but accompanies the text with a lavish, full-page artist’s idealization of a black hole in space, tugging on a nearby star, bending the shape of spacetime, and absorbing a beam of light that was inexorably caught in its pull.

He asks in the caption of the picture, “Can you imagine a star so massive that its gravitation eventually crushes it out of existence, leaving only a black hole in the sky?” This is classic Gallant, imploring the reader to immerse themselves in the mystery, throw caution to the wind, and employ their imagination — take what little knowledge you have and simply speculate. That is where good ideas come from, and it is the basis for all science.

The artist’s representation of a black hole in “Our Universe.” [Image: Helmut K. Wimmer]

In many ways, the reason you and I are having this little blog conversation is precisely because astronomers know that black holes exist in Nature and are the central players in many astrophysical phenomena. But reading Gallant’s text it is clear that when he wrote Our Universe, the existence of black holes was still a subject of much debate among scientists. Today there are many ways that we have measured the properties of black holes and confirmed their existence, not the least of which are the many that have been detected via gravitational waves. But still, pictures of black holes remain elusive. The best we have so far is the Event Horizon Telescope picture, a silhouette of a black hole against the backdrop of stuff around it.

The picture in Gallant’s book is an attempt to show a black hole as a three dimensional object in real space, but how do you do that?  It was a noble attempt, and it is certainly not what a black hole looks like, but it served its purpose — it got my attention, it fueled my imagination, and it made me ask questions then go see if the answers were known. To this day I keep copies of Our Universe nearby — one in my office and one in my study at home. It is never far from my mind nor my fingertips, and I often pull it down and lose myself in the epic stories it tells.

The other thing I know happened to me in the fall of 1980 was my first exposure to Carl Sagan’s Cosmos. Starting in late September, every Sunday night, I sat rapt on my parents’ living room floor in front of the television, whisked away to worlds and places in the Cosmos I had only previously imagined, transported by the magic of film, the lilting and elegant soundtrack of classical music, and Sagan’s poetic and sonorous narrative. One of the most widely known episodes is Episode 9, “The Lives of the Stars” which famously begins with Sagan declaring, “If you wish to make an apple pie from scratch, you must first invent the Universe.”

Sagan uses his famous declaration about pies to introduce the concept of the chemical elements — the atoms from which all the beautiful and complex structures of Nature are built. Beyond the simplest elements — hydrogen and helium — very little was created when the Cosmos was born. Almost everything on the periodic table is created by stars during their lifetime, and a great deal of it (the heaviest elements) during the catastrophic death throes we call supernovae and gamma ray bursts. In telling us about the death of stars, Sagan uttered the magic words I had heard before — black hole. In his trademark penchant for poetic description, he called it “a star in which light itself has been imprisoned.”

Sagan’s Cosmos was the first place I was introduced to the ideas of black holes in the context of general relativity, beginning with masses curving space and affecting the motion of other masses, and also a discussion of the principles of black holes as tunnels [Images from Ep 9: “The Lives of the Stars”]

He had led us to the existence of the super-strong gravity of black holes through an imagined tea party with Alice and her friends in Wonderland, but then he hung on it all the modern picture of curved spacetime. It was, as far as I know, my first exposure to Einstein’s brilliant realization, and it has ever since dominated my destiny. Today, I have a doctorate in theoretical physics, earned for studying the magical mysteries of that self-same curved spacetime.

Me and J. Craig Wheeler. He’s one of the reasons you’re reading this blog right now!

For many of us, our interest in black holes might be piqued by these kinds of exposures, and then we go back to our lives as dental hygienists or soybean farmers or city managers. But this was all still swirling in my mind when I entered college, and in the true traditions of higher education, my exposures took those latent passions and exploded them into what would become my life. I was an undergrad at Oregon State University and at that time there was a stupendous class on campus called “Rocks & Stars,” run by the indomitable Julius Dasch. This was one of the most popular classes on campus, and had a regular stream of guest speakers who visited and talked to us about cool stuff.  I have strong memories of one visit from J. Craig Wheeler, a supernova expert from the University of Texas at Austin.

Supernovae are one of the pathways for making black holes in the Universe, and Wheeler gave us a spectacular talk that culminated with him reading to us from a science fiction book he wrote, called “The Krone Experiment.” I won’t give it away (go read it!) but what I remember from the talk was Wheeler talking us through what would happen if you were standing on a sidewalk and a micro-black hole came booming up out of the ground next to you. What would you see and experience? It’s the sort of question that just captures your brain and won’t let go. To be honest, it was the perfect question to ask a young scientist in the throes of deciding to commit their career to studying these enigmatic objects.

I think every one of these stories illustrates a key fact in my mind: it didn’t matter what I heard about black holes in my youth, only that I did hear about black holes. Exposure did what it should: it filled my head with all kinds of possibilities, all of them totally brain-melting, and made me pay attention and ask questions later.

This last point is the most important point here: we want people to ask questions. Either because they are confused, or because they are idly curious, or because they want to learn more. To that end, having mind bending movies like The Black Hole is stupendously important, and I don’t care if they get the science perfectly right! I have colleagues who often grouse about bad science in movies, complaining vociferously that the producers should have taken a basic science class, or gotten a good science advisor. They proclaim, “Is it really that hard to get the science right? The right science is just as cool!” 

But people aren’t watching The Black Hole to learn science (I certainly wasn’t) — they are being entertained, itching a part of their brain that wants to be asked “is that even possible or real?” And that serves its purpose, because eventually every one of them ends up in an audience somewhere at a public lecture and raises their hand and asks someone like me “is what happened in the movie real?”  THAT is where we get the science right. The movie’s job was to put a question in someone’s mind, to make them care enough to know what the right answer might be, and then in some other part of their lives have some discussions about science, what is known, what is not known, and what the other mysteries of the Cosmos might be.


This post is the last in a series about black holes.

Black Holes 01: Imaging the Shadow of Darkness

Black Holes 02: What are black holes made of?

Black Holes 03: Making black holes from ordinary stuff

Black Holes 04: Singularities, Tunnels, and Other Spacetime Weirdness

Black Holes 05: Inklings & Obsessions (this post)

Black Holes 4: Singularities, Tunnels, and Other Spacetime Weirdness

by Shane L. Larson

I think one of the great things about the modern world is the propensity of information. Information is free and easy to come by, and it possible to learn about anything you want. More-or-less, the total knowledge of our civilization has been written down in books and documents, and disbursed to libraries, websites, and other mediums of communication. It is not always easy to discern what is authentic and what is not, as is clearly the case when one looks at the wild, apocalyptic wastelands of modern social media. But none-the-less, it is easy to indulge your desire to simply learn. We consume books and podcasts and documentaries, sacrificing time we could spend on woodworking or yardwork or binging TV shows in favor of trying to recapture how we felt in 2nd and 3rd grade, before school became about exams and homework and was just about how awesome all the far flung corners of the world and Nature could be. 

I think deep down all of us are lifelong learners; I’ve met many of you at public lectures or here at the blog. Some of you are quiet, and sit in the back with contemplative furrows on your brow; others of you are more exuberant and can barely contain your questions. Either way, you all show up, because you remember how cool it was when you were first learning. But I’ve noticed something interesting in my years talking to all of you: as a rough rule of thumb, I can usually triple the attendance of any talk if it is about sharks, volcanoes, dinosaurs, or black holes. Vast numbers of you succumb to your curious inner child if I talk about the right things. 

People’s minds, young or old, can be captured if we talk about science in ways that stimulate their interest and imaginations. [Image: Bill Watterson]

What is it about these topics that inspires deep interest in people? I think, at the heart, they are very real examples of the Universe’s ability to put you in mortal danger with implacable indifference. Never mind that it is unlikely you will encounter any of these dangers in your life. Pondering being faced with a highly improbably danger in the Universe allows us to ask ourselves, “what would I do?” in much the same way we watch super-hero films and imagine ourselves in the fray. 

Black holes are notable in this list because not only do they have the mystique of danger about them, but they are suffused with a long list of exotic, mind-bending phenomena that add to their mysterious nature.  

Let’s talk about some of the exotic things you have hard about black holes, and I often get asked about.

“Is everything is going to get sucked into black holes?” 

This is probably the most common question I get about black holes! The simple answer is “no” — black holes are not little Hoovers running around the Cosmos sucking stuff up. I’ve thought a lot about where this idea comes from, and I think it is a mis-extrapolation of the inescapability of a black hole. When you are far from a black hole, its gravity is exactly the same as the gravity produced by ordinary objects of the same mass. If you are orbiting far away from a billion-solar mass black hole, the gravity you feel is exactly the same as if you are orbiting around a dwarf galaxy that has a billion sun-like stars in it!  If we could magically replace the Sun with a one solar mass black hole, the Earth would continue along in its orbit as if nothing had happened because the gravitational influence is exactly the same! 

Far from the black hole, you cannot tell if you are orbiting a black hole or a star of the same mass — their gravity is identical unless you get close. [Image: S. Larson]

If you are silly (or unfortunate) and fall into a black hole, you are never going to get out. The gravity of a black hole is so strong that it can trap anything inside it; that is true. But it is not infinitely strong and able to influence everything outside it. 

“What does it mean to get spaghettified?” 

When you get close to a black hole, the gravity can become more intense than anywhere else in the Cosmos. Imagine you are jumping in feet first. The gravity is strongest close to the black hole, so your feet are pulled on more strongly than your head, which is farther away. The result of this dichotomy of gravitational strength is the black hole tries to pull you apart, much as you stretch a rubber band by pulling on opposite ends. Physicists call this difference in force a tidal force, and the process of pulling you apart is called tidal disruption. Stephen Hawking, in his famous book “A Brief History of Time” called this effect “spaghettification.”  

Some ways of falling into a black hole will feel less painful than others. [Image: S. Larson]

Somewhat paradoxically, the spaghettification effect is strongest near the event horizon of small black holes, and weaker near the event horizon of larger black holes. The spaghettification effect is also stronger when your head is farther away from your feet (so tall people will suffer more than us short people). The two rules of thumb for surviving spaghettification when you are jumping into black holes are this: 

  1. Jump into the biggest black hole you can find; million solar mass black holes are much more fun to jump into than solar mass black holes.
  2. Belly flopping into black holes is safer than jumping in feet first.

“Do black holes really bend time?” 

The movie Interstellar has revived broad interest in black holes and inspired wide-ranging conversations about what black holes are really like. One of the most common conversations we have is about time, which usually begins with “what was the deal with the guy who got old when he didn’t visit the black hole?” This plot device could just be accepted at face value, like we do with so much science fiction, but in this case it is rooted in the physics of the real world. General relativity predicts that the closer you are to a source of gravity, the slower your clock ticks compared to someone very far from the source of gravity. Here I use the word “clock” in the physics sense: anything that keeps regular time, whether it is a digital watch, a wind-up pocket-watch from your grandparents’ day, an hour-glass, or the steady beat of your heart.  

Consider two people, one close to the black hole and one farther from the black hole. Every clock ticks slower when you are close to the black hole — this could mean an actual clock that tells time, but it can also mean a regular biological clock, like your heartbeat. [Image: S. Larson]

The bending of time is definitely one of those counter-intuitive predictions of general relativity, but if space and time are one entity (“spacetime”), then bending space very strongly must necessarily also bend time. It doesn’t take much to bend time by a measurable amount — the bending of time is the central physical effect behind the Global Positioning System, which you use everyday on your phone to navigate to the nearest ice cream shop (or coffee shop — whatever). The difference between the bending of time around the Earth and the bending of time around black holes is the strong gravity near the black hole makes the effect much more pronounced. 

“Are black holes are infinitely dense? What does that mean?” 

Anything labeled infinity is, generally, an anathema to scientists. “Infinity” is a perfectly good concept in mathematics, but with respect to the natural world, it seems that the Cosmos is only filled by things that are finite and measurable. That is not to say there aren’t enormous, gigantic, mind-bogglingly huuuuuuge numbers, but they are all tiny compared to “infinity.” In the natural sciences, we have often encountered “infinity” in the mathematical ways we describe Nature, but we’ve found most of them were simply artifacts of our early poor understanding of how the world works, particularly on the microscopic scales of fundamental particles. Gravity is the last frontier in this regard, and there are many persistent “infinities” we encounter, and they often manifest themselves in the study of black holes. 

An example of your common experience with density. This cube of tungsten and this clown nose are about the same size, but the tungsten is significantly heavier. Why? because more stuff is packed into roughly the same amount of space. [Image: S. Larson]

To think carefully about this, let us be precise about what we mean. “Density” is a common concept in physics and chemistry. It is how much stuff (mass) is squeezed into a given amount of space (volume). Dense objects feel heavy in your hand, while less dense objects feel lighter.  As a matter of practical everyday experience, you most often encounter the notion of density when thinking about things floating or sinking in water (objects more dense than water, like rocks, sink; objects less dense than water, like styrofoam, float). 

So let us define the “density of a black hole” the way we define the density of any other object in the Universe: the mass of the black hole, divided by the volume of the black hole. Those of you who are practicing gravitational physicists will recognize that we should be careful when computing the “volume”, but for practical purposes here let us use the ordinary formula for the volume of a sphere where the radius of the sphere is the radius of the event horizon of the black hole. This is practical and intuitive, and will illustrate our point effectively.  

The first picture of the black hole at the heart of M87, formed by light being bent around the inner most regions of space outside the event horizon. This black hole has a diameter larger than the diameter of our solar system! [Image: Event Horizon Telescope Collaboration]

Imagine two black holes: one that is the mass of the Sun, and one that is one billion times the mass of the Sun (a bit smaller than the black hole in M87 that was the subject of the Event Horizon Telescope picture). The solar mass black hole only has a radius of about 3 kilometers, and a density of about 18 quadrillion times more the density of water (1.8 x 1019 kg/m3, for those calculating themselves). By comparison, a 1 billion solar mass black hole has a radius just under 3 billion kilometers (about the radius of Uranus’ orbit); it would have density of only 2% the density of water (numerical value: 18 kg/m3; slightly less than the density of styrofoam). If you could somehow drop it in a gigantic cosmic bathtub, its density suggests it should float. 

If black holes were solid objects and could interact with the world like ordinary “things,” a calculation of their density suggests some are less dense than water and could float in a cosmic wading pool. [Image: S. Larson]

It can’t float, of course — the event horizon is not a hard surface that water can act on and thus provide buoyancy in a ginormous cosmic pond. Water would flow right through the event horizon and disappear, so all the water in the cosmic pond would essentially flow into the black hole like some kind of drain.  But that’s not the point in the floating analogy. As a general rule, we think we understand the physics of things that have densities less than the density of water, so the idea that the density of a black hole is the same as materials that do float is a strange and discomfiting result. And it should be! Just remember your discomfiture is related to the odd nature of black holes — density defined in the classical way really doesn’t apply to black holes the way we’ve done it here, because as we’ve noted before, they are mostly empty space! This odd result has little to do with their overall size, and more with what lies at their heart… the singularity. 

“The Singularity” 

The real mystery of black holes lies at their heart, in the center of the space defined by the boundary of the event horizon. All the gravity of the black hole is concentrated there. All the matter that collapses to form the black hole is still being drawn together even after it falls through the area we call the event horizon. Gravity keeps pulling it inward, inexorably inward, squeezing it smaller and smaller with a force so great no known force in Nature can stop it. Everything that fell inward to create the black hole gets squeezed down smaller and smaller, becoming more and more dense. Eventually it gets squeezed into a space that is vanishingly small, or so general relativity predicts. This point of zero size with everything squeezed into it is infinitely dense, and is called the singularity. The laws of physics as we understand them break down before you ever really reach the singularity, at a distance away from it called the Planck length, about 10-35 meters (0.00000000000000000000000000000000001 meters). This is the length where we expect the physics is governed by quantum gravity, a description of gravity, space, and time on the tiniest scales. We have searched for such a mathematical description of Nature for many years, but so far have been unsuccessful. 

How do physicists think about the singularity? It is an infinity, and infinities are anathemas to physicists. More often than not we are trying to understand what is happening far away from the singularity when thinking about the Cosmos. This is, more or less, what astronomers do because they are observing the Cosmos outside the event horizon, which is far from the singularity. Easy peasy — you don’t even have to waste one brain cell on the singularity if you don’t want to! Sometimes physicists pretend they are okay with the singularity being infinitely dense, and use the classical laws of physics (general relativity in particular) to understand the influence of the singularity around it. Gravitational physicists often do this, in particular because they are trying to understand how the world behaves under the influence of strong gravity. All the tales and imaginings you have heard about the inside of black holes are figured out by scientists thinking about the singularity this way. The last prominent group that thinks about the singularity are the quantum gravity squad. There are many ideas about what a complete description of quantum gravity will look like — all of them are clever, and elegant, and exotic. But we don’t yet have a way of experimentally testing any of them. Someday we will be able to test them. The day we understand quantum gravity, it will tell us something about the true nature of the singularity. 

“Are Black Holes Spacetime Tunnels?”

The last and most famous example of spacetime weirdness and black holes is the astonishing idea that for some kinds of black holes, if you jump in, they may in fact be tunnels. For the movie nerds out there, this is the central plot device in many science fiction stories. For perfectly spherical black holes, there are no tunnels — if you jump in a black hole, the singularity lies in your future; you will be crushed ruthlessly and mercilessly.  But for black holes that happen to have electric charge on them (expected to be few) or are spinning (most black holes found in Nature are expected to be spinning) there are trajectories inside the event horizon that do not end at the singularity. They end… somewhere.   

Scientists struggle to visualize black holes just as much as ordinary people, so we have developed a special map called a Penrose diagram. As you go up the diagram from bottom to top, time increases from the past to the future. As you go left or right on the map, you change where you are in space. Here the white areas are the ordinary Universe, and the yellow areas are inside a black hole. The one on the left is a Schwarzschild black hole that has no tunnel; if you are inside, the singularity lies to your future and there is no ordinary Universe you can get to. The one on the right is a charged black hole, which might have a tunnel. If you are inside, you can avoid the singularities on the left and right, and possibly emerge at the top of the diagram. [Image: S. Larson]

In these kinds of black holes, if you avoid the singularity you come out of something that looks mathematically similar to a horizon. The difference is you come out of this horizon, emerging from the inside to the outside. Such things are variously called “wormholes” or more commonly “white holes.” They are, in essence, the other end of the black hole, like it is some kind of giant culvert or tunnel that connects one place to another. 

Tunnels to where? you quite astutely ask. The truth is we don’t know, but there are several possibilities. One possibility is the tunnel emerges somewhere else in our observable Universe. As an astronomer this is a very intriguing possibility, because it suggests there may be something that could be observed with telescopes. Sadly, to date, we have not seen anything exotic and unexplained that might be a white hole.  

Another possibility is that it may emerge somewhere in our Universe, but outside the observable part of the Universe. This idea is a bit harder to wrap your brain around, because it hinges on understanding that the Universe can be larger than what we can observe and could, in principle, go on forever. The “Observable Universe” are just those parts of the Universe that are close enough for us to observe in a telescope because light has had time to reach us in the time since the Universe was born. An easy way to think about this is to think about your home state where you live. Most of us can walk only a few miles per hour — let’s say 3 miles per hour. That means in one day, you could only walk 3 miles per hour x 24 hours = 72 miles. If you started walking right now, by this time tomorrow you could be anywhere in the state within 72 miles. Does that mean the rest of the state isn’t there? Of course not — it just means the parts of the state you could get to at the fastest pace you could walk (the “Observable State”) is only 72 miles away in any direction. 

If I start at Northwestern University and walk for 24 hours at 3 miles per hour (average walking speed of a human) I can reach anywhere inside the red circle. I can get no farther, but that doesn’t mean there aren’t more places outside the circle! The Universe is the same, only the time is not 1 day, but the age of the Universe, and the speed is not walking speed, but the speed of light. Inside the circle is what we call the Observable Universe, but it is not the Entire Universe. [Image: S. Larson, Map by Google]

A third exotic possibility is that the white hole may emerge not in our Universe, but in some other Universe. A Universe that is not our own, but is somehow parallel to our own. It is an interesting possibility to ponder and imagine because it opens up all kinds of possibilities. Are the laws of physics the same there, or is the other Universe some weird place that doesn’t have stars and planets and galaxies? Do all of our black holes emerge as white holes in the other Universe? Where do black holes from the other Universe go? Do they emerge in our Universe, or do all white holes in all the other Universes emerge in only one of the other Universes? Some things we can imagine within the realm of science and do calculations and simulations about, but others are mere speculation that we have yet to ponder and consider seriously. It makes your head spin, but these are the things that great speculative science fiction about black holes are made of.  

The last possibility is that tunnels through black holes simply do not exist at all, that Nature somehow closes them off, or we have not fully understood the mysteries of black hole insides completely yet. There is much we still have to learn.

Which of course is the point. Black holes, on any given day, seem completely unfathomable, especially in the context of the weird implications about what they do to the world around them. But is precisely that mystery that draws our attention time and again. Partly because we like that feeling of being completely baffled by Nature, but also because some deep part of us knows that these inscrutable mysteries hide deep and precious secrets, secrets that lie at the core of how Nature and the Cosmos work. 


This post is the fourth in a series about black holes.

Black Holes 01: Imaging the Shadow of Darkness

Black Holes 02: What are black holes made of?

Black Holes 03: Making black holes from ordinary stuff

Black Holes 04: Singularities, Tunnels, and Other Spacetime Weirdness (this post)

Black Holes 3: Making black holes from ordinary stuff

by Shane L. Larson

If you are exploring the Cosmos, and either by design or accident, find yourself plunging toward a black hole, on a beeline that takes you directly across the horizon, you don’t encounter anything along the way; all you feel is the inexorable pull of gravity pulling you farther and farther down. When you reach the event horizon, the nominal “surface” of the black hole, what do you encounter? 


The event horizon is simply the invisible line in space where gravity has become so strong that even if you were travelling at the speed of light, you could not escape; the event horizon is a boundary that once crossed, Nature says you are never coming back out — the inside of the black hole and only the inside of the black hole is in your future. That’s a big statement, but you cross this point in space without even an alarm to let you know you are trapped. It’s as easy as walking across a line drawn in the sand at the beach.

A black hole with the MASS of the Sun is not even close to the SIZE of the Sun! Here the approximate size of a solar mass black hole is shown near the city of Evanston, IL — only about 6 kilometers (4 miles) across. What is it made of? Nothing tangible — it is empty space, filled with nothing except gravity itself! [Map: Google; Image: S. Larson]

Through the horizon and as you fall inward you still encounter absolutely nothing. This has previously led us to ask, “What is the black hole made of?” Based on what you experience, we had concluded “a black hole is made of pure gravity.” But gravity, as we learned early on in our thinking about the world, is a consequence of mass (or energy if you take the modern understanding of mass and energy being related). That normally would imply that the black hole was made of mass of some sort, but as our gedanken experiments have paradoxically shown us, there is no mass to be encountered when travelling toward and into black holes! 

A thoughtful cosmic explorer (or astronomer) would take that bit of confusing information and ask a very pointed question: “how do you make a black hole, then?” The motivation for such a question is built out of our common experience. If you want to make something, whether it is a gallon of dandelion wine, a guitar, or a cinnamon roll, you take other things and transform them into the new thing.  So what are the other things that can be transformed into a black hole? And how do you change them from being ordinary things into pure gravity? Those are very good questions, and to be honest with you here at the beginning, we don’t know all the answers. We only know part of the story, the penultimate explanation for how it happens. Some of the story is still unknown, and lies beyond the boundaries of what we currently understand about the Cosmos. That is part of what astronomers and physicists investigate and attempt to understand every day.

Astronomers have seen many phenomena in the Universe that are explained by black holes. The question is where do they come from? [Image: Wikimedia Commons]

How do we start? Where ever you are, look around you and pick up the nearest thing you can see. Maybe it’s a rock, a bagel, a book, a Lego brick, your cat — whatever. Here I’ve picked up a fountain pen. Why does the fountain pen, or any other object, have form? What is it that makes it a solid tangible object? If you try to squeeze the fountain pen, it may deform slightly, but generally resists any effort to squeeze it out of shape. Why? Because as you press the fountain pen, the building blocks of which it is made, the molecules and atoms, fight to hold their shape. They press against their neighboring atoms, and when the pressure from your fingers tries to force them closer together, they press back against you in tandem, resisting your attempt to move them.

If you press hard enough, you can sometimes squeeze them together or change how they sit next to each other. Sometimes you are stronger than a material and break the object. Some objects are hard to compress, but they can certainly be deformed if you apply a force to them in specific ways. It’s hard to flatten a paperclip into something like a piece of foil, but it is not too difficult to bend it back and forth into a new shape. Ultimately what you can do physically to any object depends on how the building blocks of its structure respond to forces applied from the outside.

(L) Very solid objects, no matter how hard I squeeze them, retain their shape. The atoms that they are made of resist external forces. (R) Some objects can be deformed, bent, or broken, like these paperclips — their atoms resist some external forces, and yield to others. [Images: S. Larson]

Now consider a slightly different example. Go to your kitchen and find a party balloon in your junk drawer. Blow it up and tie it off so it is maybe 20 centimeters across. Take a couple of sheets of aluminum foil, and wrap the balloon up. What happens when you try to squeeze the foiled balloon? It deforms a little bit under the force of your hands, but when you let go the pressure from inside the balloon pushes it back into its round shape.

A balloon wrapped in foil as a heuristic model of a star. The balloon presses outward against the pressure from your hands that is trying to collapse the foil.

This simple balloon and foil model is completely analogous to a star. The foil is playing the role of the outer layers of the star that we see when looking through our telescopes (the “atmosphere” or the upper layers of the star). Your hands pressing down are like gravity, trying to pull everything that makes up the star into the center. Opposing the inward press of your hands, the balloon represents something inside the star pressing outward against the pull of gravity. We know the outward press is the energy released by nuclear fusion deep in the core of the star. This balanced state, where the inward pull of gravity is precisely counterbalanced by the outward push from the energy created by fusion, maintains the round and stable size and shape of the star. Astronomers call this state hydrostatic equilibrium.

When the balloon is popped, nothing prevents your hands from collapsing the foil. This is similar to fusion ending in the core of a star — nothing presses outward, and gravity collapses the star.

Now, gently hold the foiled balloon in the palm of your hand and have a friend pop the balloon with a needle. The support from the balloon vanishes, leaving you holding an unsupported shell of the foil. You are gravity, so squeeze the foil down. It should be easy — there is nothing to fight back against you. You can, and should, squeeze the foil down into a small, aluminum ball. Ball it up, and squeeze it into the smallest ball you can. Once you’ve squeezed it as hard as you can, stand on it trying to squeeze it smaller. If a member of your family is stronger than you, ask them to squeeze it even smaller.

How small did you make it? Can you make it any smaller? The answer is “probably not.” Why? Because all of the aluminum atoms in the foil are resisting being pressed together, far stronger than you can press them together with your hands or feet. This is not dissimilar to the fountain pen we discussed above — all the atoms that make up the aluminum are pressing out, resisting being pushed any closer together than they already are.

The exact same thing happens in Nature. Gravity takes collections of stuff — stars, planets, anything round — and tries to pull it together as strongly as it can. Eventually everything gets crowded together, and through a variety of interactions resists the inward pull of gravity. For stars in the middle of their lives, they exist in hydrostatic equilibrium, with the inward tug of gravity balanced against the outward push from the fusion in the core.

Squeeze the foil as hard as your possibly can. Eventually your strength will be matched, and the ball will get no smaller.

When a star reaches the end of its life, the fusion in the core shuts down. That moment is like you popping your balloon — the star suddenly finds itself without much outward pressure at all, and the inward pull of gravity takes over — the star collapses. The collapse is the beginning of a supernova explosion. 

For our interests here we are not interested in what gets blown out, but what happens in the innermost core. There, the titanic pressures of the collapse and explosion break apart the atoms, and breaks apart the nuclei of the atoms. You may recall from school that atoms themselves are made of smaller bits — the smallest bits are called electrons which orbit around a nucleus made up of bits called neutrons and protons. Like you standing on a wine glass, the inward force of gravity during the collapse crushes every atom, breaking every one apart into these shards called electrons, protons, and neutrons.

In the soup of protons and electrons and neutrons that results, the protons and electrons are forced together and turn into a neutron plus a small particle called a neutrino. This conversion process is called “neutronization” (really — sounds like something from a superhero movie, right?) — the conversion of most of the matter of the core into neutrons. 

A neutron star (diameter 20 km) scaled to the Chicago skyline. [Image: LIGO-Virgo/Nick Gertonson/Daniel Schwen/Northwestern]

This core that remains is called a neutron star when it settles down, and its gravity is extreme beyond belief.  It has about 1.5 times the amount of stuff in as the Sun, but squeezed down into something about 20 kilometers across — the size of a city.  At the surface, the gravity is 200 BILLION time stronger than the gravity you are experiencing right now on Earth. What are the consequences of such extreme gravity? Imagine you could take a walk on a neutron star (and you could certainly NOT walk, but go with me here) and you had the unimaginable misfortune of encountering a cliff only ONE MILLIMETER high. What would happen if you fell off? On a neutron star, falling off a one millimeter high cliff means when you reach the bottom you will be travelling about 227,000 kilometers per hour (141,000 miles per hour)!

The gravity of a neutron star is extreme, but a neutron star, like its parent star, maintains its shape as a round, spherical object — it is in hydrostatic equilibrium! Gravity is trying to press down, but something just as strong is pressing back. In this case, it is the neutrons that make up the star. Neutrons do not like to be near each other and push back when they are squeezed into small spaces — this is called “neutron degeneracy pressure” (for the quantum mechanics aficionados among you, this is a consequence of the “Pauli exclusion principle”). The reason gravity could not collapse the neutron star is because the neutron degeneracy pressure is enough to stop it.

But there is a funny truth about gravity. All four of the fundamental forces of Nature have a range of distances over which they act, and their strength varies over those distances. They also each affect only certain kinds of objects in the Cosmos. Gravity, however, is completely indiscriminate — it acts on and affects everything that has mass and energy, which as it turns out is everything in the Cosmos!

The consequence of that simple fact is if you make a big pile of anything, gravity always tries to pull it closer together, and will succeed in pulling it together until it is opposed by a stronger force (for example the hydrostatic equilibrium, and the neutron degeneracy pressure examples we noted above).

We only know the masses of a few neutron stars, most between the mass of the Sun, and two times the mass of the Sun. Can heavier ones exist in Nature, or do they all turn into black holes? Explore the stellar graveyard on your own with this interactive tool at CIERA. [Image: Frank Elavsky/Northwestern University]

Most of the neutron stars we have observed in the Cosmos up to now have masses between about 1.4 times the mass of our Sun, up to around 2 times the mass of our Sun. Why aren’t their bigger ones? We certainly see huge stars, up to 30 or 40 times the mass of the Sun — when they explode, they definitely have larger cores that should leave behind bigger remnants, bigger stellar skeletons. So can a neutron star bigger than the ones we’ve found in the Cosmos exist? You can imagine taking one of the known neutron stars, and slowly piling more and more mass onto it. Each jelly-bean or rock or bit of starstuff you drop on the neutron star increases its mass, which increases its gravity, which makes gravity pull inward more strongly. Eventually, gravity will get so strong that the neutrons cannot resist any more — gravity overwhelms the degeneracy pressure, and presses the neutrons closer together. 

Concentrating all the mass of neutrons together makes gravity even stronger, which pulls all the mass of the neutron star even closer in a never-ending cycle of just making gravity stronger. At this point, there is no known force in the Universe that is stronger than gravity. Nothing can oppose gravity’s inexorable inward pull, and everything that was a neutron star gets smaller, and smaller, and smaller, until the gravity is so strong that not even light can escape. We have a name for that.

A black hole.

So at last, we arrive at the answer to our question: we make black holes by squeezing matter together. Black holes are not stuff but they are made of stuff in the beginning. 

Where is all that stuff now? It is concentrated somewhere behind the event horizon, where we cannot see. Mathematically, the laws of gravity suggest it is concentrated into an infinitely dense point called a singularity. It is… … … something. Something that completely defies our understanding of the Laws of Nature, and is the subject of much consternation and study on the part of modern physics and astronomy researchers.

Now we are curious creatures, and it is completely natural to ask “what is inside the black hole?” or “what is inside the event horizon?” The answer quite pointedly is you can NEVER know unless you jump in yourself! The emphasis really is on the word UNLESS — nothing prevents you from jumping in and looking around; the only prohibition is on your ability to come back out to visit your friends who watched you jump in. The prohibition that the speed of light is the ultimate speed limit in the Cosmos, coupled with having to travel faster than the speed of light to get out of the event horizon, means you will never hear about anything that happens on the “inside” of a black hole second hand!

But we can use our mathematical understanding of gravity to predict what you would experience if you jumped in, and the predictions are weird and disconcerting. We’ll talk about some of that gravitational weirdness next time. 


This post is the third in a series about black holes.

Black Holes 01: Imaging the Shadow of Darkness

Black Holes 02: What are black holes made of?

Black Holes 03: Making black holes from ordinary stuff (this post)