Robert L. Curbeam, Jr. moves silently through space as he repairs a camera on the International Space Station.

NASA/Getty Images 

Before we begin to talk aboutspace, we should probably define it. For the purposes of this discussion, we'll consider space to be the region of the universe outside of the Earth's atmosphere.

You've probably heard that space is a vacuum. A true vacuum refers to the complete absence of matter. But how can space be a vacuum? Space contains stars, planets,asteroids, moons and comets, just to name a few cosmic bodies. Isn't that a lot of matter? How can space contain all these massive bodies and still be a vacuum?

It's because space is big. Between these large objects are millions of miles of emptiness. This empty space -- sometimes called interstellar space -- is practically devoid of all matter, so it's effectively a vacuum.

Sound waves can travel only through matter. Since there's almost no matter in interstellar space, sound can't travel through it. The distance between particles is so great that they would never collide with each other. Even if you could get a front seat for the explosion of the Death Star, you wouldn't hear anything at all.

Technically, you could argue that there are ways a human could hear in space. Let's address a few scenarios:

• Radio waves can travel through space. So, if you're wearing a space suit that contains a radio unit and one of your buddies sends you a radio message that there's pizza in the space station, you'd be able to hear it. That's because radio waves aren't mechanical -- they're electromagnetic. Electromagnetic waves can transmit energy through a vacuum. Once your radio receives the signal, it can convert the signal into sound, which will travel through the air in your space suit without a problem.
• Let's say that you're drifting through space while wearing a space suit and you accidentally bump your helmet into the Hubble Space Telescope. The collision would make a sound that you could hear, even though you're in space. That's because the sound waves would have a physical medium to move through: Your helmet and the air inside your space suit. You'd still be surrounded by a vacuum, so an independent observer wouldn't be able to hear anything, no matter how many times you rammed your head against asatellite.
• Imagine that you're an astronaut on a space shuttle mission. You've decided to step out into space but forgot to put on your space suit. You press your face against the space shuttle. You wouldn't have any air in your ears, so you couldn't hear in the traditional sense. However, you might be able to make out a few sounds through bone conduction before the perils of space caused you to expire. In bone conduction, sound waves travel through the bones of the jaw and skull to the inner ear, bypassing the eardrum. There's no need for air, so you could hear your fellow astronauts partying inside the shuttle for about 15 seconds. After that, you'd likely be unconscious and well on your way to asphyxiation.

So despite the wisdom of Hollywood filmmakers, it's impossible to hear noises in space. We suggest the next time you watch a science fiction film, you plug up your ears whenever anything happens within the vacuum of space. It'll make the film seem more realistic and probably work as a great conversational topic with your friends once the movie's over.

• Bone conduction. Encyclopedia Britannica. Retrieved February 26, 2008, from Encyclopedia Britannica Online. http://www.britannica.com/eb/article-9080583
• Mad Sci Network. http://www.madsci.org/
• spaceflight. Encyclopedia Britannica. Retrieved February 26, 2008, from Encyclopedia Britannica Online. http://www.britannica.com/eb/article-9384200
• Sound. Encyclopedia Britannica. Retrieved February 25, 2008, from Encyclopedia Britannica Online. http://www.britannica.com/eb/article-9109557
• The Physics Classroom Tutorial. Glenbrook South Physics. http://www.glenbrook.k12.il.us/gbssci/phys/Class/BBoard.html
• Weir, Laila. "High-Tech Hearing Bypasses Ears." Wired. September 16, 2004. http://www.wired.com/science/discoveries/news/2004/09/64963

(Source: How stuff works?)