The Baby Universe's First Cry: A Million Years in 5 Seconds
By KENNETH CHANG
Published: June 8, 2004
DENVER, June 2— If the universe is created with a bang but no one is around to witness it, does it still make a sound?
Some 13.7 billion years later, Dr. Mark Whittle, a professor of astronomy at the University of Virginia, says yes.
Sound has played an important role in research on the Big Bang, the explosive birth of the universe. In 1963, trying to track a mysterious hiss generated by their microwave antenna, Arno Penzias and Robert Wilson of Bell Labs discovered the cosmic microwave background, a faint glow of photons left over from the Big Bang.
Satellites now show minuscule ripples in the cosmic microwaves. Dr. Whittle realized that the ripples -- slight variations in density of matter that would determine where stars and galaxies would form -- could be seen as sound waves bouncing through the infant 380,000-year-old universe.
''I have done what is the obvious thing, turning the information into real sounds,'' said Dr. Whittle, who presented his aural findings here at a meeting of the American Astronomical Society.
Sound waves propagate with just the slightest disturbances. The sound of a voice compresses air by one part in five million. The differences in pressure in the primordial gases were 1 part in 10,000, and that corresponds to a satisfyingly loud, but not lethal, 110 decibels -- rock concert volume.
Some massaging of the data was needed. The cosmic sound waves stretched 20,000 light-years, moved at half the speed of light, and were about 50 octaves below what people can hear. Dr. Whittle shifted the sounds to the human audible range, producing a chord like the sound of a jet engine. He used computer models to generate the cosmic chords from creation for the first million years and condensed them to five seconds.
The Big Bang actually erupted in complete silence. In the first instant, the mass of the universe was spread out completely evenly. No pressure differences, no sound.
But after that, the quiet vanished.
''For the first 400,000 years,'' Dr. Whittle said, ''it sounds like a descending scream falling into a dull roar.''
Over the first million years, Dr. Whittle said, the music of the cosmos also shifted from a pleasant major chord to a more somber minor one.
Listen to the Big Bang. The audio is at http://www.nytimes.com/science/.
Photo: Fluctuations in microwaves from outer space reflect sound waves of the early universe. (Photo by WMAP Science Team)