[TheAntipodean]

This may be a dumb question but what does the shadow fall on for the scientists to take a picture of it? If is is landing on the 'lens' then wouldn't 'silhouette' be a more appropriate term?

As far as I understand all matter is made of atoms so at the atomic level there wouldn't really be matter (wall, ground etc.) for the shadow to be cast on.

Amazing nonetheless.

[bmuon]

It took a little googling. Here's a potential answer.

The paper the article is based on talks about "absorption imaging". Googling that I found another paper [1] in ArXiV which describes the method a little bit: "absorption imaging, where the attenuation of a laser beam passing through an atom cloud is measured, is the workhorse of ultracold atom experiments. The shadow cast by the atom cloud onto the CCD allows an estimation of the atomic column density."

And if I understood correctly, a CCD is a "charge-coupled device" [2], sort of a digital camera. And that's where the shadow falls.

[1] http://arxiv.org/pdf/1101.4206v2.pdf [2] http://en.wikipedia.org/wiki/Charge-coupled_device

[yakiv]

Actually, if you're curious, there's matter that isn't made of atoms, such as neutrinos.

[yk]

The article uses 'shadow' in the sense of: region of less light behind an object. But actually, at this small scales the wave nature of light becomes quite important, since for an object smaller than the wavelength the distortion of the light wave is damped exponentially on an scale of the wavelength. So I think the word shadow is as appropriate as silhouette, since both somehow imply light rays ( and are therefore a rather loose usage on the meaning of the words).