Zero Gravity: The Lighter Side of Science

Water in Zero Gravity

By Sabine Hossenfelder

Photos by NASA/Glenn Research Center Boiling on Earth, boiling in space–small bubbles merge into one large bubble.

In my apartment the heating is in the ceiling. This is not a joke. I’ve wondered where the guy grew up who had this ingenious idea. Had he never heard that hot air rises? But NASA has provided me with a hint regarding this question.

This morning, I was staring at the tea water, waiting for it to boil. Did it ever occur to you that the rising heated water is necessary to get the temperature homogeneously distributed? But what if the hotter water with smaller density does not rise because there’s no gravity? Well, it stays where it is.

Here’s how boiling looks in zero gravity: The heated water stays close to the heater. Regions further away from the heater stay cooler, so the actual heated part boils earlier. Once it begins to boil, the vapor bubbles don’t rise, but join each other due to surface tension. Eventually, one large bubble forms that clings to the heater. Cool, eh? I mean, hot. It looks like this.

(NASA has the full video available at http://science.nasa.gov/headlines/images/boiling/bubble0g.mpg. You can also watch a water balloon burst in outer space here: http://www.space-video.info/misc/balloon.html).

Now I’m convinced the guy who constructed my heating came somewhere from outer space. That’s just how things are up there, why bother. All I have to do is sleep on the ceiling.

Sabine Hossenfelder is a theoretical physicist at the Perimeter Institute. She writes the Backreaction blog (http://backreaction.blogspot.com) with her husband, Stefen Scherer. A full article on boiling water in zero gravity can be found at http://science.nasa.gov/headlines/y2001/ast07sep_2.htm.