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What does a Bose-Einstein condensate look like?

    The simple answer is that it looks like a dense little lump in the bottom of the magnetic trap/bowl. This lump of condensate is like a drop of water condensing out of damp air when it is cooled. When it first forms, the condensate is still surrounded by the normal trapped gas atoms, so it looks a bit like a pit inside a cherry.

    Could I just look into the experiment and see it?

    In principle yes, but there are several reasons it is difficult. First, it is quite a small lump, so you would need a microscope. Second, you would have to illuminate it with the special deep red color to which the rubidium atom responds. (Click here to learn more about atoms and the colors to which they respond.) Third, you would have to look very quickly, because shining light on the condensate quickly heats it up so much that it goes back into being normal gas atoms. The way Wieman and Cornell first looked at it was to turn off the trap, and then, after a little while, take a snapshot picture of the cloud. When they looked at the darkness of the different parts of the cloud, they could see a very dark blob form in the center as they got the cloud colder. You can see this in the pictures of their actual data as they cool the atoms from 400 billionths of a degree above absolute zero down to 50 billionths.

Click to view larger image. Grey scale has been converted to color, with white indicating darkest densest part of the cloud.

    So the atoms on the edges of the picture are spreading out, but the Bose-Einstein condensate peak in the middle doesn't?

    You are right about the atoms on the side, and almost right about the condensate. It actually does spread out, but the way it spreads out shows some of the reasons it is quite a special little lump.

    I was beginning to wonder what the big deal is over just a little lump.

    This lump spreads out as slowly as any atoms possibly can that are not stuck together, as they are in any solid material. There is a basic law of physics requiring them to spread called "the Heisenberg uncertainty principle" that says you cannot simultaneously know the exact location and the exact speed of anything, including atoms. Since we can see about where they are located, then we can't know exactly how fast they are moving. If they were stationary, we would know they were moving with zero speed. So that's why they spread out. But to really understand the uncertainty principle is another story.

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