The setting is the surface of the moon. A boxy school bus of a spaceship glides into the field of view and slips past crater walls, the rising Earth in the far distance. The transport ship moves silently, without engine rumbles, as it ought to in the vacuum of space. What we hear instead, in this moment in Kubrick’s “2001: A Space Odyssey,” is the sound of voices, a chorus intoning György Ligeti’s setting of “Lux Aeterna” (eternal light), one of the central movements of the requiem, the mass for the dead.
Voices enter and become mesmerizingly lost in a wash of singing that feels completely free of melody. It’s like a slowly building wall of sound, from which an occasional sung note emerges as if at random. Even without the lunar landscape of the film, this music chills one to the bones. Kubrick could not have found a better soundtrack to express the cold emptiness of space.
And as it happens, the aptness of this metaphor is not just artistic, but also scientific. Fellow sky walkers, indulge me today as we walk through one of the greatest scientific discoveries of the modern era, the cosmic microwave background, and why it finds so apt a metaphor in Ligeti’s music.
It’s not just noise
Our story begins in 1964 with physicists and astronomers Arno Penzias and Robert Wilson. While at Bell Labs, Penzias and Wilson were working on a sensitive microwave antenna intended for measuring radio waves bounced off of weather balloons (see Figure 1). The problem was that no matter what they did, they could not eliminate a faint microwave noise in the antenna’s signal. They supercooled the antenna receiver with liquid helium; they canceled out any possible effects from human activity; they chased pigeons out of the antenna and cleaned up their droppings. They were left with the antenna continuing to report microwave energy equivalent to a few degrees above absolute zero.
Figure 1: The horn antenna at Bell Labs. (Courtesy photo, NASA)
What then could account for this unexplainable signal? And why did it appear to come from everywhere and anywhere? Wherever Penzias and Wilson pointed their antenna, they found the same noise.
Word of their puzzling discovery spread through Bell Labs and beyond, and next thing you know, the two were visited by Princeton physicist Robert Dicke. As it happens, Dicke was one of several theoretical physicists who had predicted the existence of background microwave radiation as a consequence of the Big Bang.
Birth of the universe
We are all aware that in current accepted scientific thinking, the observable universe began in an unimaginably enormous expansion, the so-called Big Bang. The mathematical intricacies of this model are daunting (think Sheldon Cooper and friends from the eponymous “The Big Bang Theory”), but the overall storyline is accessible in lay terms to the likes of us, fellow sky walkers.
At the moment of the Big Bang, all the matter and all the energy of the universe were packed into a point unimaginably small, dense, and hot: the singularity. The lay image of what happened next is that all this matter exploded outward into the inviting but otherwise empty realm of space. The accepted scientific model tells a more complex story, however. Space wasn’t already there to accept all this matter. Instead, space itself was packed into that same unimaginably dense singularity. So as the observable universe burst into existence, so did the space that it came to fill. In other words, space grew to accept the matter and energy that would come to make up the universe. Think of this as resolving the paradox of what did the universe expand into, if what it was going to expand into didn’t exist yet.
With a name that always reminds me of bicycle pumps, this process is known to physicists as cosmological inflation. By this model, key to what came next is that the entire universe spent its very initial moments in a space more condensed than a single proton (we’re talking trillionths of trillionths of a second here). At that scale, the entire substance of the universe was subject to the laws of quantum mechanics, the rules of the road for particles and the rest of what is infinitesimally small.
It’s all noise
And here’s the crux of the matter. Quantum mechanical effects are not deterministic in the same way that 1 + 1 = 2. Instead, what happens at the infinitesimal scale is best explained as a calculus of probabilities, where outcomes are subject to a degree of uncertainty—a degree of randomness, or noise. How this affected the birth of the universe is that while it spent its initial moments in an unimaginably small space, the randomness of quantum mechanics led to all the stuff making up the universe clumping nonuniformly.
Several hundred thousand years later, all that nonuniformly clumped stuff had expanded and cooled enough that protons and electrons could combine into hydrogen atoms; until that time the universe had been just a free-floating nonatomic cloud of particles (a plasma). Also liberated from the plasma were photons, the particles that carry light.
The clumps of hydrogen eventually would become the building materials of galaxies; what started out as only the slightest of quantum fluctuations in the plasma became amplified through the action of gravity as barely clumped hydrogen drew in more hydrogen, the clumps ultimately growing into protostars and protogalaxies. It’s because of that original random quantum clumping that we now actually have galaxies, solar systems—and us.
As to what is left of the primordial light, it’s the cosmic microwave background. It may go against the grain to think of microwaves as light—the first is what we cook with, and the latter is what we see. In fact, both visible light and microwaves are just different frequencies on the electromagnetic spectrum that also comprises radio waves, X-rays, and so forth.
Since Penzias and Wilson’s 1964 discovery of the cosmic microwave background (which won them the Nobel Prize), astronomers have been at work drawing its map. Figure 2 shows the map as recently established by NASA’s WMAP space probe. The variations in color correspond to diminutive variations in the temperature of the microwave background. The fact that they are clumped visually into islands is exactly what physicists would expect, given the quantum clumping of the early universe. It’s a truly vertiginous thought: What was once clumping at the subatomic level is now clumping on the cosmic scale—quite some origin story.
Lux aeterna
Figure 2: The cosmic microwave background, as mapped by the WMAP space probe. (Source: NASA/WMAP science team)
I used the words “primordial light” to describe the cosmic microwave background, and indeed it is the universe’s oldest electromagnetic energy, its oldest light. In fact, at age 13.82 billion years, this is the closest we can come to eternal light, to lux aeterna, bringing us full circle to Kubrick’s film and Ligeti’s music.
“Lux aeterna luceat eis” goes the text of the requiem: “Eternal light, shine upon them.” To my ear, Ligeti’s setting of this text is the musical equivalent of the WMAP spacecraft’s map of the cosmic microwave background. Ligeti offers us a wash of undifferentiated sound from which occasional islands of notes emerge, fragments of melody clumped together like the clumps in the map.
What is really jaw-dropping, however, is how the music is made. Each of the 16 vocal parts sings essentially the same notes, just as in a round like “Row, Row, Row, Your Boat.” But Ligeti breaks the rules. Instead of the voices starting at predictable time intervals and singing at the same tempo, their starts and tempos are perturbed in small ways: Some voices fit five notes in the time that others fit four, for example. It’s fully notated music, so it’s not actually random, but to the ear these perturbations may as well have been randomized in the same way as quantum mechanics randomly perturbed the early universe. The effect we perceive is clumping: Be it galaxies or music, we experience it the same way.
Fellow sky walkers, if you’ve indulged me this far, indulge me a little further and look up this music on the internet. It is readily available on iTunes or as free YouTube videos. And then, with one of these last warm nights of the summer, take a blanket out to your yard or your favorite sky-walking spot, and just lie back and look up. You will not see the primordial light, as it is just the faintest of microwaves and invisible to the eye, but you will be bathed in it anyhow. Lux aeterna is also the light of the living for these last and so very alive days of the summer.
Marc Vilain walks the night sky from the roadways and fields of Harvard.
