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Vacuuming Out the Cobwebs

September 16, 1999

There's a scene in Star Trek where some crewmembers get shot out into space when they lose a wall in their cabin on the Enterprise. Someone comments that they were sucked out into space. Commander Data, ever the pedant, says ``Actually, they were blown out, not sucked out.''

Data was right, though the sucking part is a common misconception-- so common that even news reporters sometimes get it wrong. On the ABC News website is an article about a flashlight used by Buzz Aldrin during a spacewalk. The flashlight is up for auction, and the article says:

             You now have a chance to buy [the]

             It'll probably cost a couple of grand, though.
             And it's not even in pristine condition. (Offering
             persuasive testimony that glass really is a very
             slow-flowing liquid, not a solid, the flashlight's
             thick lens was blistered and warped by the
             powerful sucking force of the vacuum of
First off, you can't really say glass is a liquid. It's another common misconception, and to be honest the arguments are long and dreary so I won't recount them here. If you want to know more, try the Sci.Physics FAQ entry about glass.

So anyway, what's the difference between getting sucked out and blown out? It's the cause of the force. Space is a vacuum, and any air in a container under pressure will want to expand. The work done to expand the air comes from the pressure of the air itself, and not from the vacuum. If you say ``the vacuum sucked'' then you imply it's the vacuum doing the work. If you say ``the air blew'' you imply the air did the work, which is technically correct.

As a last thought, I'll be honest and admit I don't understand why the lens is blistered at all. NASA knew the flashlight would be used in a vacuum, so I assume it was built to let the air inside leak out slowly, not catastrophically enough to damage the flashlight! Maybe the flashlight was damaged in some other way. I invite anyone with further information to send it along!

My thanks to Bad Reader Dan Gerhards for sending this to me.

©2008 Phil Plait. All Rights Reserved.

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