www.whyville.net Apr 19, 2009 Weekly Issue

Science Specialist

Absolute Zero?

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In the United States, most people are familiar with temperature measured in degrees Fahrenheit. However, being from Canada (eh), I am most familiar with the Celsius scale. On the Fahrenheit scale, water freezes at a temperature of 32 degrees Fahrenheit and boils at 212 degrees F. Absolute zero on this scale is not at 0 degrees F but at -459 degrees F. While the Celsius scale sets the freezing point of water at 0 degrees C and the boiling point at 100 degrees C. On the Celsius scale, absolute zero corresponds to a temperature of -273 degrees C.

In most science classes, students learn to use the Kelvin scale. This scale uses the same temperature steps as the Celsius scale, but is shifted downward. On this scale, water freezes at 273K and boils at 373K. Only on the Kelvin scale does absolute zero actually fall at 0K.

Temperature is a physical quantity which gives us an idea of how hot or cold an object is. The temperature of an object depends on how fast the atoms and molecules which make up the object can shake, or oscillate. As an object is cooled, the oscillations of its atoms and molecules slow down.

But what happens at absolute zero? Well, matter cannot reach absolute zero, because of the quantum nature of particles. This has to do with Heisenberg's uncertainty principle which states that we can never know exactly both a particle's speed and position. The more precisely we know its speed, the less precisely we know its position. If an atom could reach absolute (one never has), its temperature would be precisely zero, which implies an exact speed of zero. However, knowing the atom's speed exactly means we know nothing about its position.

At room temperature an atom is moving at approximately 500 meters per second or 1,100 miles per hour. If scientist slow it to a temperature of say 200 microKelvin (that would be 460 degrees F or 238 degrees C) then the atoms start to move about 20 centimeters per second or 0.45 miles per hour. At this speed, scientists can look at atoms in more detail, and can learn a lot about the internal structure of an atom. As atoms cool to near absolute zero, their waveforms spread out (remember we can think of an atom either as a particle or as a wave). When that happens, all of the atoms at that temperature form one big super atom, and this is called a Bose-Einstein condensate.

Is anything actually at Absolute Zero? The coldest place is space, and there it is 3 degrees above absolute zero.

Absolute Zero, Absolute Cold!


Author's Note: This was submitted to the blog by Heather, one of our corespondents.


Editor's Note: For more blogs from Dr. Rabiah, visit Science Chicago's website at: http://www.sciencechicagoblog.com


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