The Silence of the Universe: A Reaction
"O God, do not remain silent"
I recently read a beautifully resonant essay by physics professor Chet Raymo on the silence of the universe. In it he recounts an experiment from high school with a ringing electric bell in a glass jar. They slowly pumped the air out of the jar, and though the clapper kept smacking against the vibrating bell the sound was dampened, then snuffed out. Silent. Sound requires particles to travel: air molecules colliding with air molecules to pound on our eardrums and communicate the songs and cries of the world. But in empty space – well, it’s empty. Raymo writes “The trackless trillions of miles between the stars are a vacuum more perfect than any vacuum that has yet been created on Earth… The silent vacuum of the bell jar was a million times inferior to the vacuum of space. In the almost perfect vacuum of interstellar space stars detonate, meteors blast craters on moons, and planets split at the seams with no more sound than the pulsing clapper of the bell in the evacuated jar.”
According to the American National Standards Institute, sound is defined as “oscillation in pressure, stress, particle displacement, particle velocity, etc., propagated in a medium…” Lots of complicated words, but we can parse some of them. Oscillation: a back and forth swinging, as moods. Pressure: a pushing force, as deadlines. Stress: a twisting tension, as shoulders. I think of it like this: an event happens, like my vocal chords vibrating, which pushes on the air, causing particles to move together, bump into each other, which in turn causes other particles to bump into each other: a great pressure wave moving from lightning source to thundering crash on your pounding ears.
As creatures acquainted with pressure, familiar with stress, versed in our daily baths of vibrating, waving air, we don’t need a definition to understand the significance of sound. We come to expect it, rely on it. No silent movies now: an event of significance should be accompanied with sound. Raymo tells another story about witnessing a teen on a skateboard crash into a small child. Though he could see the event – the mom’s mouth open, the forceful impact, the expressions of pain and terror – he was too far away on that day to hear any of it, the sound “absorbed by the gray wool of the November day. The child’s body simply lifted up into the air, and, in slow motion, as if in a dream, floated above the promenade, bounced twice like a rubber ball, and lay still. … It was as if watching the tragedy… framed in the cold glass of a telescope, utterly silent.”
It’s eerie to witness a scream that you cannot hear. And, Raymo points out, it’s eerie too that these events happen – mothers scream, we scream – and yet the universe continues on its merry way, indifferent, apparently, to the little pressure waves of our existence. This silence of the universe is incredible, deafening to Raymo. “I turned up the volume of my indignation all the way up and I heard nothing,” he writes. And he goes further: “The physical silence of the universe is matched by its moral silence. A child flies through the air toward injury and the galaxies continue to whirl on well oiled axes. But why should I expect anything else?”
I hear him. His pen cries from the page a cry of all our animal hearts. A cry against senseless destruction, senseless pain, senseless plummeting of planets on their paths, of stars and people alike to their senseless cold end. In the words of the Psalmist, millennia ago: “My God, my God, why have you forsaken me? … I cry out by day, but you do not answer, by night, but I find no rest.” And now, our best observation based models of the universe end in a cold, silent nothingness, much colder and more senseless than my someday buried body under frozen winter ground. An end where even black holes are thought to evaporate, capitulating to the oppressive nothingness of the night.
Raymo, later, drifting in a canoe, asks what it is he wants to hear out of all that silence. “A scrawny cry, perhaps,” he writes, quoting Wallace Stevens,”’A scrawny cry from outside… a chorister whose c preceded the choir… still far away.’ Is that too much to hope for? I don’t ask for the full ringing of the bell… A scrawny cry will do… from far off there among the galaxies.” His desire is nothing new. The Hebrew psalmists also cried “O God, do not remain silent; be not quiet, O God, be not still.” And me too. I’d like a thunderclap from on high, a bell, a burning bush. But that’s not my lot, nor most of us, as far as I can tell.
Yet, when listening for a scrawny cry, I acknowledge my difficulty hearing. I remember a time, under pressure and stress, laying in bed, wondering about my future, you might say praying – I’m not sure. I remember hearing a clear – could you call it a voice? a whisper? Words tumbling into my brain as if from outside, offering peace, guidance I didn’t yet understand, some hard to believe illumination, knowledge of a landing place within the next year. It was weird. And might just be my psychotic brain, a mishappen neuron firing, disturbed, perhaps, by the silence. Then again, the words proved true, I think, but then again again, memory is a reconstruction. So I wrestle: do I accept that voice? or reject it – face its implausibility in the fact of that intractable, indifferent, inaudible universe?
The other day I was at a meal in west Humboldt Park, Chicago, a beautiful but suffering neighborhood where everyone knows a kid who’s been killed, where men sleep in tents and without them, silent stupors both natural and under the oppressive vacuum of narcotic drugs. I found myself talking with an older woman who’d lived in this part of Chicago for more time than I’d been alive. “I used to be angry,” she told me. “I used to be bad.” But then she recounted – a feeling? – “the Lord told me to star making cakes for my enemies. I didn’t understand.” Neither do I. He told you? How? I wanted to ask. But I stayed silent. She continued: “Then I was sitting in my room one night and this light came all around me and it was nothing I’d ever experienced before or again and when I left my room people – strangers – wanted to hug me. They’d come up and ask if they could hug me. I’d been touched. Apparently it happens, you sort of glow afterwards, though it doesn’t last long.” What do I make of this witness, this bell still clanging in my head? Is it craziness, or Truth?
I guess, on reflection, I find myself at some difference with Raymo. For one thing, if there’s something I learned from my thesis work on galaxies it’s that they, at least on cosmic scales, are far from “well oiled.” So many galaxies struggle for so long to make stars that my thesis advisor hypothesized – how much in jest? – that they are “too shy to shine.” Galaxies smash into each other at surprisingly frequent rates, destabilizing orbits and sending stars hurtling to that vacuous dark of night. Galaxies bleed gas, dust, and stars, their guts oft expelled by supernova explosions, or jets from their supermassive black hole hearts. It’s a chaotic and complicated place. Which is, I suppose, a solace, in a sense, for my chaotic and complicated soul.
But more, sometimes I wonder if space is actually as quiet as it seems. Though it’s true that there are fewer particles per cubic meter in the densest parts of interstellar space than the emptiest vacuums humans have ever created on earth, space is so vast that if you could weigh all those isolated, punctiform particles in the Milky Way you’d find they make up almost as much material as exists in all its stars. In fact, in the known universe, more particles exists floating between the stars than in the stars themselves.
What’s more, these particles aren’t static. They are moved by great galactic pressure waves – great galactic sound waves – which traverse these hidden vacuums, whisper one meter to the next. Giant waves much larger than our solar system, nothing that could ever fit in our ears. Yet we know they are there by careful analysis of radio waves emitted by the free floating particles and collected in our telescopes from a great distance away. Indeed, our models depend on them. As it turns out, from these low rumbles of interstellar matter form the life giving suns that energize our planet and decorate our nights.
Let me attempt to explain. In grad school I spent a lot of the time with an equation for something called the Toomre Q parameter. It’s an equation that tells us something about when stars form in galaxies. Essentially, in order to make a star, the particles floating between the stars need to be disturbed, to experience some pressure such that they are compressed, just like the air by my vocal chords. In space this little compression can be enough for the particles to gravitationally attract, and be pulled together into a star. The Toomre Q parameter approximates these compressions – the instabilities in the stuff between the stars. Said again, it estimates when that stuff might oscillate enough – hear me: beat enough, resound enough – for the interstellar particles to get attracted together to form a star. Interstellar matter is like a great drum head, an oscillating membrane on whose beat the great song of star formation depends.
The equation looks like this:
Kinda pretty, don’t you think? We had a joking “rule” in grad school that every time you mentioned an equation at a talk you lost half your audience. Probably true here too, but I want you to see something cool. Here’s what the letters mean:
Q – if this gets small enough, stars are likely to form!
𝜋, G, Σ, 𝜅 – you don’t care for this discussion. You might recognize 𝜋 (pi): 3.141526…, and correctly guess G for gravity! Σ, 𝜅 – fun greek letters to make the equation look fancy and tell us about density (Σ), how things are moving (𝜅), and the contorted wrinkles of our foreheads trying to parse all this.
cs – THE SPEED OF SOUND IN SPACE. This variable quantifies the great singing pressure waves of our Milky Way, and not just us, but all 200 billion known pulsing galaxies out there to the edge of what our telescopes can see.
What I’m driving at is that the sound waves hiding in the great vacuum of space hold the keys to what makes a galaxy shine. Does this mean anything? I don’t know. But I find it comforting, in a way, for those times I feel empty inside: more vacuous, more hollow than a cubic meter of outer space.
Indeed, I’m compelled by the complicated messy beauty of all this. The order and disorder, the patterns and variety, the swirling awesomeness of space out there sometimes feels a din so loud I sometimes need to duck my head and cover my ears. “The heavens declare the Glory of God,” the psalmist also wrote. “Day by day they pour forth speech.” So much speech, I guess, that this ill-informed shepherd of 3000 years ago noted that though he, like us all, lives in the dark shadow of death, his cup overflows. What did he hear that might create such splashing? Could it be that in fact the universe, far from its apparent silence, might be ringing a resounding gong, if only we had ears to hear it?