Dear curious reader,
Your question reminds me of an experiment: You put a ringing alarm clock in a jar and use a hose to slowly suck out all the air. As the air escapes, the ringing gets quieter until there’s no sound at all.
The inside of the jar becomes what scientists call a vacuum. It’s empty. Just like space.
Despite any zooms and explosions you may have heard in movies about outer space, sound actually can’t travel through empty space. That’s why on the moon, where there is no air, astronauts have to use radios to talk with each other.
But here on Earth, all kinds of sounds are traveling through air, water, and other objects. The molecules that make up these objects help the sound travel.
That’s what I found out when I visited my friend Allison Coffin to learn more about how sound moves. Coffin is a brain scientist here at Washington State University. In her research, she investigates hearing and hearing loss.
She explained that when you hear a sound, somewhere around you an object was moving, or vibrating. If you’ve ever strummed a rubber band you’ve probably heard, and maybe even seen, this at work.
The molecules that make up water or air sort of bump into each other as they vibrate. They pass on their motion to neighboring molecules.
While sound doesn’t travel through empty space, there are other places off our planet where scientists have detected sound waves. For example, some scientists have used different machines to pick up sound waves from gas clouds beyond our atmosphere.
“In general, the sounds are probably so low a frequency, a mega bass, that our ears can’t hear it,” Coffin said. “In fact, I don’t know of any animal on Earth that could hear sounds so low.”
Meanwhile, in Earth’s atmosphere, animals can hear a range of sounds. Sound that travels through air moves about 1,114 feet in a second. Underwater, sound moves about four times faster.
Coffin explained how sounds beneath Earth’s water tend to have a low frequency. The sounds travel a lot farther and reach their destination faster than high frequency sounds.
“Think about songs of baleen whales, like humpbacks and blue whales,” she adds. “Higher frequency sounds don’t travel as far because they bounce off things and get reflected back (by) things like corals, rocks, and boats.”
The songs of baleen whales can travel so far that some scientists have found that whales can hear each other from nearly a thousand miles away. That’s farther than the distance from Seattle to Los Angeles.
The next time you hear a sound, think about all of the molecules that helped carry it to your ears. Think about how far it traveled and what it traveled through. And remember, it’s quiet out there between the planets and stars.
Got a science question? E-mail Dr. Wendy Sue Universe at Dr.Universe@wsu.edu. Ask Dr. Universe is a science-education project from Washington State University.