A Dark Science

Written by: Chami Amarasinghe

Edited by: Kate Giffin and Austin Shannon

For a hundred years now, evidence for invisible matter has been piling up (1). Eighty-five percent of the mass in our cosmic neighborhood is transparent (2). We are completely awash in this invisible substance, dark matter. It far outweighs the stars, planets, asteroids, gas, dust, and us (3). The evidence lies plainly in the night sky. Stars and galaxies are accelerated by the gravity of dark matter (4, 5). Light emitted from distant objects bends in its presence (6). But, despite its ubiquity, nearly nothing is known about the fundamental particles that make up dark matter (7). How heavy are they? Why are they so prevalent? If they are everywhere and interact with the atoms of our world, could we detect them as Earth travels through space? Dark matter particles have long been searched for in experiments but none have been found (8). The devices built to detect them are the most sensitive ears we have opened to the skies, and they continue to grow in size and complexity as scientists continue their search (9). Discovering the nature of dark matter would upturn our understanding of the universe, but history warns of dead ends. It is not predetermined that dark matter particles will be discovered (10).

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All of space is filled with a specter, pervasive but discreet, and as old as the universe. We know this because it left imprints in the ancient light created by the first atoms (11). Having left its mark, this substance flowed under gravity into patterns, assembling congregations of mass (12). It ushered the newly formed atoms along and spun them into galaxies, soon to spark life with the birth of the first stars.

Dark matter. The enigmatic essence, once a sculptor of the cosmos, now binds together the structures in our cosmic habitat: stars, galaxies, and clusters of galaxies, opposing the expansion of space (13). Dark matter swirls with the Milky Way round and around, its heft evident in regions bereft of stars. It is everywhere, and yet we are unable to detect the particles it is composed of. We have observed and admired its handiwork, and yet we do not know its nature.

Pooling streams of time bring you, traveler, to the year 3023 C.E.

Generations of theoreticians and experimentalists have transformed dark matter research into an august tradition. Much more is known about how this invisible shroud wreaths around every galaxy in the universe and about how it molded the largest cosmic structures. The age’s wealth of astronomical data has convinced every skeptic of its existence, and there is no doubt that it is everywhere, around you and distant galaxies alike. Yet still, as it was a millennium ago, you are not privy to its nature, and the mystery runs ever deeper.

These are the ending stages of the lunar gold rush. Having stripped the moon of its minerals, the last of the prospectors are moving on to the outer planets, leaving behind a drilled and hollowed rock. Concordant with a long history of Earthly, underground laboratories that started as mines (14), the desecrated moon has perfect conditions for a dark matter detector, which has finally been built (15). A giant ocean floats in the center of the moon, unbothered by gravity. Capillaries of sensors penetrate this liquid core, recording the faint sparks and crackles it makes each time a particle passes through. Such tell-tale signatures are rare. The rock shell entombing the detector stops nearly everything, creating a quiet environment to listen for dark matter particles (16).

You submerge into the current of space-time and flow into the moon’s artificial core. The sensor bays latch on to your presence as you settle in, suspended in a drop, to listen. All is quiet at first as you learn to hear with your new ears. Then, softly, a quiet roar rises into focus, from the direction of the sun. Neutrino particles, nature’s swiftest messengers (17), come pouring from our star, through the lunar rock and make the detector hum in static, reminding you of light rain in the forests of old. You occupy the sound, reassured in its seeming constancy. Below the hum, the liquid core quivers with tremors from deep space, sounding like whale song that has been forgotten to time. These tremors are from ancient stars exploding; their quakes are conveyed in all directions by neutrinos. Energetic bolts from the supernovae hit the detector and spritz the soundscape with cracks, faint and sharp.

The sound of the thunderstorm is the music of the universe. You hear it from inside the most titanic instrument operated in these rivers of time. Yet despite its sheer size and ingenuity of design, the detector at the core of the moon has not recorded a single crackle, fizz, or buzz from the passage of dark matter.

You retreat to the dying Earth and hold your fists to the night sky like skinny antennas. Thousands of dark matter particles are flowing through them each second, and you are completely, blindly, attuned. As you raise your gaze beyond your clenched fists, you notice that Polaris, the once steadfast north star, is no longer occupying its familiar location (18). The gradual shift of the Earth’s equinoxes has dethroned the beacon that once guided civilizations. With this realization fear surges through your trembling fists: a fear that science itself may be imperiled by the mechanics of the universe.

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While it is true that in the history of physics, new generations bring paradigm shifts — like the revolutions of relativity and quantum mechanics — it is uncertain if this trend will continue. Predicting major shifts in thinking is a futile endeavor because much of scientific progress is made through incremental advances.

Disciplines of discovery are steeped in murky scientific waters where incremental progress is difficult to contextualize. This difficulty is best expressed through the doctrine of falsifiability, which guides us to use frameworks that can be easily disproved by empirical observation (19).

In the case of dark matter, your instruments will only ever have two logical responses to the question, “Are we able to detect it?”:

i) An uproarious “YES”, or,
ii) “Not yet,” which invites the question to be asked the next decade, and if negative again, the next century, and many times more again.

We may be trapped in this loop, but a kind of progress can be made, slowly. We will keep discovering not what dark matter is, but what it cannot be. The decades and centuries of null results will have firmly established that dark matter does not belong to any particle type detectable by past experiments.

Will the questions being posed to nature have morphed into something more satisfactorily falsifiable? If so, how will the future scientists have come to accept their lot? They will have been solemnly bested by the universe; the pursuit of knowledge for the sake of knowledge wrested from them. The interaction of dark matter with ordinary matter is not required by any law to be substantial enough for human observation. It may be arbitrarily reclusive. Currently, our capacity to deal with such facts is limited because the scientific endeavor is still in its adolescence. Like the obstinate hydra, human curiosity will continue to raise its numerous probing heads. But some day, one head may decide to slump down and refuse to rise. After all, it is difficult to think of dark matter ever being materialistically valuable to a creature. Maybe, when the weight of a history of null results disincentivizes progress, curiosity will morph into another tendency of our descendants: our drive to mythologize (20).

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Drying rivulets of time bring you to the end of the universe. The end of everything, the age of great cosmic rips (21).

Deep in the far future, the star systems of Aldebaran, Fafnir, Rukbah, Zhu Shi, Thaharu, Jyestha, and Wasat flash by you in a loop. You come to rest on Thaharu, formless, not needing to ossify your body into space. Just as well. The council of atomic elders whom you came to witness are disembodied. They have dispersed onto these seven asterisms and built shrines on hollow-cored derelict planets, following darkness, their inky god, Karuwal. The shrine planet of Thaharu is smothered in a dense smog through which its coral structures protrude, ornate even in ruin, a beacon in an expanding waste. You flow into its center and hear the elders pray and weep.

^{Karuwal…Thou dost dwell deep!
In stars and galaxies vast.
We ask your solace, Cosmic Weave,
For this our final cleave.}

Vines have sprung loose from the temple at the planet’s core. The empty Thaharu shrine, once a prime pilgrimage site, reverberates with the elders’ sobs. The elders are weeping for Karuwal. They weep longingly for the misguided beliefs and futile science of their Milkdromedan ancestors. They lament the time when Karuwal was a source of puzzlement, and later, religious fervor. Time has run out. The great Disconnect is upon Thaharu, separating it from the other stars and isolating it in the tattered universe. The elders weep for their god that was splintered by the expansion of space, a god they will now never understand.

You gush, wakeless, into the home system before it too is Disconnected (22). The Earth has vanished in some ancient war, and the once-vibrant sun has long been extinguished. In the abandoned detector at the center of the moon, the rain has stopped. Distant stars, the survivors, are methodically silenced one at a time, as they expand away too fast for their messengers to reach the moon. And then, there reigned silence and darkness, more profound than it ever was. The unknown finally replaced by the unknowable.

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Today, the spirit of the search burns bright as we delve wide and deep into the dark matter mystery. The quest to understand it remains compelling and we learn more with each year. Our detectors await, dormant and deep underground on Earth. They convey to us the sounds of stars echoing throughout the universe. Although it gives pause to know that we may never hear the dark wind no matter how keenly we listen, the unknown captivates us, and the journey itself remains an adventure.

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