Stephen Aitken - Listen Up!: Exploring the World of Natural Sound

An illustration depicting the evolution of the universe over 13.77 billion years, starting at the bottom with the Big Bang and moving up through time to the present day at the top.

MARK GARLICK/SCIENCE PHOTO LIBRARY/Getty Images

S cientists who study the origins of our world mostly agree that the universe started with an explosionthe Big Bang. That was 14 billion years ago. Most people have heard about it, but nobody has actually heard it. Until now!

In 2003 John Cramer, a physicist at the University of Washington, received an email from an 11-year-old student doing a school project on the Big Bang theory . He wanted to know what the Big Bang sounded like (who wouldnt?). The email got Dr. Cramer wondering too. He decided to analyze the cosmic microwave background , the leftover electromagnetic radiation from the Big Bang. Using this data, he calculated the frequency of the sound waves created during the formation of the universe. They were below the range of human hearing, so he made them billions and billions of times louder. What he discovered was surprising. The Big Bang wasnt a bang at all. When Cramer first played the sound through speakers, his two Shetland sheepdogs leaped up and started barking wildly at what sounded like an alien spaceship landing. After realizing there was no immediate danger, they (sheepishly) settled back down in the corner. The sound coming through the speakers was a deep, rumbling hum.

Sound Bite

Have you ever wondered what it sounds like on the moon? Outer space is a vacuum , with only a few scattered atoms floating around. Atoms need to touch each other for sound to be transmitted. Thats why on the moon you wont hear a thing.

A fighter jet breaks the sound barrier. Shock waves cause condensation of water vapor in the air, resulting in a halo-like effect around the plane.

Katerina_S/Shutterstock.com

Sound Science

Okay, lets get into a little sound science. All living things emit some form of energy. Sound is energy. It travels through dry air at over 767 miles per hour (1,234 kilometers per hour). So what happens if you go faster than the speed of sound? Well, fighter jets do it all the time. When a jet breaks the sound barrier, it creates a sonic boom , a shock wave of 200 decibels (dBs) that sounds like a clap of thunder. To give you an idea of how loud that is, your whisper to a friend in class is about 20 dBs. Your ears will start hurting at about 130 dBs. But even 85 dBs can damage sensitive ear parts. So be careful with those earphones!

All sounds have a frequency, determined by how many sound waves are created per second. When the time between waves is shortin other words, the waves come more oftenthe sound is high in frequency. When the waves are slow, or less frequent, they produce a low note or frequency. Humans hear sounds between 20 hertz (Hz)a hertz is one cycle or beat per secondand 20,000 hertz (20 kHz). Some animals, like tarsiers and dolphins, communicate at higher frequencies, so we dont hear all of their calls. Others, like giraffes and alligators, can communicate at frequencies lower than the human hearing range.

Sound Bite

Spiders have eight legsall the better to hear you with. Fishing spiders use their hairy legs to hear approaching bullfrogs and avoid being gobbled up in the flick of a tongue.

A female emerald jumping spider, about

0.3 to 0.5 inches (8 to 12 millimeters) in length. Very fine white hairs called trichobothria, found on the legs of some spiders (inset), help them hear. Top: Stephen Johnson; INSET: Jim McLean

The Evolution of Hearing

So what were the first animals to evolve the ability to hear? Biologists who study evolution believe that bony fishes were the first to hear, around 400 million years ago. The fish adapted a mechanism they used to keep themselves upright in water into a means of detecting sound wavesin other words, hearing.