image and video credit: David Walker, Micscape; image source

Studying Brownian Motion

Click on the photo above to see a video of Brownian motion--the random jiggling of small particles due to molecular bombardment--in this case, the particles are fat globules in diluted milk.  You can also see this higher-res video.

To find out how a physicist stopped Brownian motion in its tracks, check out Hold Still, from the American Physical Society's Physical Review Focus.  

(This feature was updated on July 18, 2013.)

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Brownian Motion Simulation

For a java simulation of a small particle battered by molecules, visit Brownian Motion, from the American Institute of Physics exhibit Einstein: the Great Works.

[This feature was revised on 4/16/08.]

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image credit: Jason McNeill; image source; larger image

Fluorescent Nanoparticles

The bright spots in these images are nanoparticles, consisting of about 20 polymer molecules, which fluoresce--give off light of a different frequency--when illuminated with laser light.  The image on the right shows these nanoparticles implanted in macrophages (part of the vertebrate immune system), where their fluorescence will be used to track their movements in the cell.

For the track of a single molecule, see this micrograph by Christoph Naumann.

Einstein on Brownian Motion

Einstein's 1905 explanation of Brownian motion settled the issue of the existence of atoms and molecules, as described in David Cassiday's essay.  

(This feature was updated on October 15, 2011.)