Sound is a basic condition of our surroundings that we have come to understand, use, and create. We breathe, we hear, we speak. We live, we sense, we think. As far as we know, we are the only place in the universe where this happens.
We developed our sense of hearing because we live in an ocean of air. Air, a life sustaining mixture of gases, is breathed in and out by everything that lives within it. On earth, air makes up a remarkably thin skin of atmosphere that provides a medium through which sound travels as undulating waves of pressure. The roar of the wind, the crack of lightning, the dripping of rain, the cackle of birds, and the cacophony of voices all uniquely disturb the air. Life long ago developed sense organs to detect sound for defense and to aid in survival. Before life evolved out of the sea, sense organs for sound developed under water, as sounds transmit there as well.
Our ability to think is fed by the senses we use for survival. Surrounded by sound and light, our ears and eyes, like those of other creatures, allow us to gauge our surroundings beyond our immediate touch. Also like other creatures, we have developed ways to communicate with sound.
The chanting of the sacred syllable OM, as a chord that aspires to contain one’s full vocal range, is a set of audible frequencies we create with our vocal cords, but its meanings are a metaphor for our existence in a universe that we now know is fundamentally wave-like in nature. If we take the utterance of OM as a chorus of sound, we can consider how this set of waves in air is metaphorically parallel to our current understanding of the underlying nature of the universe.
The vibration of our vocal cords is like that of a violin string or the surface of a drum. We make high or low pitch sounds by changing the length of the vibrating mechanism, or by adjusting its tension. The instrument, once disturbed, vibrates back and forth at a particular rate, which we hear through the air and recognize in our brain as high or low pitch. This vibration back and forth actually resembles the apparent motion of an object in a circular orbit viewed from the side. And if we plot this periodic motion along the axis of time, we see a sinusoidal wave. Vibrational wave action is not unique to the sound we hear. We measure it not only in strings and drums but also in water waves and light.
While looking closely at the rainbow of colors made by a glass prism, Sir Isaac Newton noted that the white light of the sun was bent (or “refracted”) through the glass by different amounts depending on the color. Red is less bent than blue, thus the colors of the rainbow are dispersed across the full spectral range, a “chorus” of light. Unlike sound as pressure waves, however, we discovered that the sun and the stars we see transmit their light not through a medium, like a gas, but instead by a disturbance of electric and magnetic fields. These fields fill space such that even the vacuum of space has electromagnetic properties. The fields surround a source that, when in motion, displaces the field. Fields in periodic motion cause a periodic disturbance that then radiates through space as waves. This propagation means that space itself can carry energy and information. Just as sound is the undulating pressure in the medium of air, light is the undulating electromagnetic field in the non-medium of empty space.
Wave actions in air, water, or fields in space all share the ability to pass through one another and in the process either amplify or reduce each other as they do so. Waves from two stationary sources create a predictable pattern of interference that can either be heard or seen in the cases of sound and light. Through the early twentieth century it was established that even matter itself behaves like a wave, culminating in a 1961 experiment showing that electrons passing through two slits in a wall amazingly behave just as sound and light, creating an interference pattern. This wave-particle duality on atomic scales is challenging to fathom yet plainly measurable, and it forms the basis of the universe we know. Electrons bound in atoms occupy discreet and wave-like spatial domains that define electrodynamic architectures of form. These atoms are the building blocks of molecules, they are the bases of replicating patterns of DNA, and they comprise the materials that surround us.
Light and atoms interact by exchanging energy, and we exploit this to study the depths of space. While light travels very fast, space is still very big. The light from our sun takes just over eight minutes to reach us on earth. This means we actually see it eight minutes in the past. The light of stars in distant galaxies can take millions or billions of years to traverse the vast tracts of emptiness between us. Our telescopes are like time machines, looking deeper into the past as we extend our gaze farther away. When we look far enough, we ultimately reach back 13.8 billion years, nearly to the beginning of the universe and the Big Bang itself. It has been obvious for almost a century that the universe is expanding, as nearly every galaxy we observe is quickly moving away from us. Running the clock backward, this implies that in the past the universe must have been smaller, and consequently hotter, very dense,and opaque. We remain immersed in that glow leftover from the universe’s birth, which shines faintly today as a phenomenon we call the Cosmic Background Radiation. In it we see minute temperature fluctuations within the early universe, when matter and light strongly interacted as they fell toward and bounced away from the slight density enhancements that eventually matured into the tremendous galaxy clusters we see today. The acoustic power of these oscillations captures the first chorus of the universe, literally the harmonic sounds of the seeds of the largest structures around us.
As recently as late 2016 we gained the ability to detect some of the feeblest imaginable sound waves, whispers of the collision and joining of enormous black holes. A black hole is so massive and compact that, according to Einstein’s theory of general relativity, it severely warps the spacetime around it, generating an inescapable gravitational field. A black hole in orbit will produce ripples in spacetime just as an accelerating charge emits electromagnetic radiation. These gravitational waves carry energy away from black hole pairs orbiting each other, causing them to fall toward each other in an ever tightening death spiral and culminating in their ultimate coalescence into one large black hole with a tell-tale, and very final, chirp. After decades of carefully calming and quieting our instruments to detect gravitational waves, we have found as many as three such systems in just months, remarkable proof of the existence of the first members of our newest chorus.
Our knowledge of cosmic totality on the largest of scales is in sync with our knowledge of the exchange between matter and energy on the smallest of scales, and both can be analyzed through our knowledge of waves. The vibrational disturbance of forces in periodic waves is something we use to map the outer reaches of our knowledge. As such, the chanting of OM, although limited to sound waves in air, can be viewed as a metaphor for our current understanding of the foundations of our existence.
About the Contributors
Carter Emmart is the director of astrovisualization for production and education at the Rose Center for Earth and Space at the American Museum of Natural History (AMNH). He was one of the original team members at AMNH of the NASA funded Digital Galaxy Project that helped redefine how a planetarium theater can present science to the public. He directs space show production and oversees software development for interactive use of the 3D universe atlas known as the Digital Universe.
Tim Paglione is a physicist whose main field is the microwave spectroscopy of interstellar molecular clouds. He studies primarily the very largest clouds in galaxies, which form the most massive stars. These stars live furiously, greatly affecting their surroundings with their winds and radiation, then die dramatically in giant explosions that enrich the interstellar medium in heavy elements.
