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December 8, 2000
7:23 PM   Subscribe

Now for something a lot different, and for geeks only: Bose-Einstein Condensation. More inside
posted by Steven Den Beste (3 comments total)

 
BECs result from some of the weirder aspects of quantum mechanics. Ultimately it all starts with the Heisenberg principle, which says that the error in the measurement of the position of a particle multiplied by the error in measurement of its momentum must always exceed a certain value.

Now this is not a statement about our incompetence in building measurement equipment. At the quantum level, all our intuition about things having exact positions and exact speeds are wrong. The Heisenberg Principle is a fundamental statement about how matter really operates, but it usually only manifests at the level of particles as small as electrons. (And a damned good thing, too, because chemistry wouldn't work without it and we'd all be dead.)

So: momentum is the product of speed, direction and mass of a particle. Temperature is also speed of a particle. If you lower the temperature of a particle, its speed drops, and that means that its momentum also drops. Lower the temperature enough (like damned near absolute zero) and since the speed is nearly zero, you have a very, very good measurement of the momentum of the particle (because the momentum is damned near zero since it is constrained by the speed/temperature).

At which point the Heisenberg principle kicks in; the product has to still exceed that constant, and if your knowledge of the momentum is very precise, then the position of the particle must get very diffuse. Which actually happens; they begin to cover really quite large volumes, orders of magnitude larger than normal.

In a BEC, a large number of particles all of the same kind (so far, Hydrogen or Sodium or Rubidium) are all caught in an atomic trap and then cooled down extremely close to absolute zero, thus making their momentums very precise (that is, very near zero) and as a result they suddenly grow immensely in size, and overlap. Indeed, they lose their identity as individual atoms and the whole cloud takes on new behaviors. The resulting mass is the BEC, and it has all sorts of strange characteristics. "Weird" doesn't begin to describe them.

The theory behind this has been known for 70 years, but the first one was formed only in 1995. Since then, work on them has exploded all over the world.

There's a marvelous article about them in this month's Scientific American, but they didn't put the article online. However, they gave the link above in the bibliography for that article.

[As should be apparent, this has nothing to do with breast implants.]
posted by Steven Den Beste at 7:39 PM on December 8, 2000


Very good explanation of this weird stuff, Steven.

Here's a link about that interesting fellow Bose.
posted by lagado at 3:24 AM on December 9, 2000


Steve and Lagado, I thank you, and my spinning brain thanks you. These excellent links led me to many other excellent links. Bose, Heisenberg, String Theory, Quantum blah, blah, blah....

And now it's 4 a.m. and my eyes hurt and I'm sitting here a little dazed in my freshly rocked world. Note to self....figure out universe in the morning. Must sleep now.

Things were much simpler when the answer was 42.
posted by Optamystic at 3:57 AM on December 9, 2000


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