Well to be honest, huge is not the first word that springs into mind when you say one millimeter (that’s 0.0393700787 inches for you metrically challenged), but when it comes to atoms it’s a behemoth. The usual diameter of an atom is of the order of one Angstrom, which is 0.00000000001 meters, so we’re talking about an atom approximately seven orders of magnitudes bigger!

One of the first theories put forth to explain the behavior of atoms, was the so-called Bohr model, named after one of the greatest physicists ever to live, the Danish Niels Bohr. The basic premise of the model was that electrons orbit around a core of protons and neutrons, much like the moon orbits the earth. He used classical physics to calculate several properties of atoms based on this model, but it was ultimately wrong and the correct theory of atoms was found with quantum mechanics (which he had a big hand in founding). You can check out this explanation of it (also linked in the press-release), it looks kind of childish with the cartoons and everything, but it actually does a pretty good job of explaining it in a simple way.

The story does not end there though! As it often happens, once you scale things up from the very tiny, to the somewhat large, things stop exhibiting the weird effects of quantum mechanics, and start behaving more like classical systems we know and love from our every day life. This holds true for atoms as well, so atoms that are at a sufficiently large scale actually DO behave like the Bohr model predicts!

The scientists over at Rice University managed to make one of these very large Bohr atoms and observe it’s circular path around the nucleus. Like i said before, the size of the atom was close to one millimeter, a far cry from the one angstrom they usually are. The large size was achieved using lasers to excite the atom and electric fields to manipulate it into the configuration they wanted.

You can check out their press-release here, it’s quite short actually and to the point, and also discusses in a little more detail how they actually managed to make the potassium atoms so large, so i recommend reading it.