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Is This What the Big Bang Sounded Like?

William Cocke
for National Geographic News
Updated March 22, 2005
 
As University of Virginia astronomy professor Mark Whittle tells it, the big bang 13.7 billion years ago spawned a big noise along with billions of stars and galaxies. Whittle has come up with a soundtrack to the birth of the cosmos—and it doesn't sound anything like a bang. (Listen to Whittle's conception of what the universe's first million years sounded like, compressed into five seconds.)

The noise was more of a "descending scream, building into a deep, rasping roar, and ending in a deafening hiss," he said. To approximate the sound of creation, the astronomer used recent advances in cosmic mapping, sophisticated computer programs, and some basic musical concepts.



Whittle, whose primary area of research relates to galaxy formation, presented his cosmic riff at a recent meeting of the American Astronomical Society in Denver. He explained that sound existed in the first 380,000 years of the universe. At the time, a rapidly expanding, hot, glowing fog produced a thin cosmic atmosphere conducive to sound waves.

"[T]he universe is expanding, so it was smaller in the past, and all the matter we now see in stars and galaxies was spread out uniformly to make a hot thin gas," he wrote in a paper accompanying the presentation. "It is within this atmosphere that sound waves could form, grow, and move."

"Cosmic Genome" Project

In 1963 researchers Arno Penzias and Robert Wilson of Bell Labs discovered a faint microwave glow across the sky. This cosmic microwave background radiation, they said, represents the ancient afterglow of the big bang.

Since microwaves lie outside the range of human vision, scientists need special telescopes to analyze them. In 2001 NASA launched one of the most sophisticated microwave-imaging instruments yet, the Wilkinson Microwave Anisotropy Probe (WMAP).

In 2003 the satellite and its science team produced the most detailed microwave map of space to date. The map detailed minute variances in the brightness of this background radiation, which Whittle likens in scale to "a bacterium on a bowling ball." The fluctuations revealed the peaks and troughs of sound waves moving through the hot gas of the young universe.

"We are actually seeing the sound waves," Whittle said. "There are little ones on top of bigger ones, all adding to give the appearance of random patchiness."

The WMAP team used computer programs to find the proportion of wave sizes generating the sound spectrum, just as a prism converts light wavelengths to color. From this, Whittle could turn the relative number and strength of waves of different sizes into the relative loudness of high and low pitch notes.

This sound spectrum spans about ten octaves. The top five octaves correspond to acoustic waves—the primordial sound of the universe, just 380,000 years into its existence.

Whittle says the age of this young universe is analogous to a human life just 12 hours after conception, and he compares the sound waves to cosmic DNA.

Whittle believes his soundtrack can shed light on how matter was distributed in the early formation of the universe. "In a sense, studies of these ancient sound waves are a kind of cosmic genome project," Whittle said. He notes that just as DNA determines human development, sound waves determine the growth of stars and galaxies in the developing universe.

From a Scream to a Whisper

Whittle will tell you that his project breaks no new scientific ground.

But Ted Bunn, assistant professor of physics at the University of Richmond in Virginia, says Whittle's central insight is that the ripples that were around in the early universe were sound waves.

Specialists were aware of this fact, but very few researchers outside the field have known this, Bunn said.

"The physics of the first 500,000 years or so [of the universe] has been generally thought of as being very abstract and very difficult to understand … it's a very engaging way to think about the subject," he said.

Ironically, the big bang was initially silent. Only as time passed did sound begin to grow. Whittle's work suggests the cosmic concert slowly grew in volume until it reached about 110 decibels—about the level of a typical rock concert. The sound waves were so huge (about 20,000 light years in length) and so low (about 50 octaves below hearing range) that the astronomer had to adjust them to the range of human hearing.

His soundtrack, which sounds like a jet engine decelerating into television static, condenses millions of years of cosmic noise into a span of about five seconds.

Whittle has also managed to tease out the fundamental (a physics term that describes a component of lowest frequency of a periodic wave) and harmonics of the big bang. "Though it's not quite the heavenly choir, it's got notes in it. It's a kind of chord," he said.

The universe provided a unique, if somewhat imperfect, concert hall for what may have been creation's opening chord, Whittle said. (For music buffs: "There are a range of intervals," he said. "But the primary one evolves from a major to a minor third—a classic modulation.")

For some time cosmologists have used sound as a diagnostic tool. "By listening to the universe, you can figure out its structure," Whittle said. "For example, by measuring the basic pitch, you measure the density of the universe."

The true value of Whittle's work may be that it connects one more human sense—hearing—to the wonders of the cosmos. "It lends a whole new way for a human being to internalize and relate to, emotionally and intellectually, these very distant but very important times," he said.

The creation of the universe "is the beginning of everything, from which we all come," he said. "This is no small potatoes … this is the big picture. It's been on humans' minds for thousands of years."

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