There is a popular mis-conception about radiometers.
They do not run in a vacuum.
Here's the wrong explaination:
The black side "absorbs" em energy particles (mostly visible light) and the light side reflects them. The reason it moves is the difference in energy imparted between elastic and in-elastic collisions.
This seems intuitively obvious, but if you watch a radiometer (or read the little pamphlet that comes with it) you will see that according to the above explanation IT'S SPINNING THE WRONG DIRECTION. The black face is on the trailing side of each "paddle".
The right explaination:
The AIR immediately adjacent to the dark side is heated. This local volume of AIR expands and becomes more active. The higher energy collisions push on the black side more than the lower energy collisions on the white side. This makes it spin with the white faces leading and the black faces trailing.
There's a notable shortage of AIR in a vacuum (sorry, sarcasm doesn't play well in text).
Now that being said, it may still require a partial vacuum. I know these things sure look like a light bulb.
Anybody know if they pop when they break?
I wonder if filling the container with 1 atm of helium would accomplish the same thing as a partial vacuum? Hydrogen might even work better, and it would be easier to destroy the evidence if the whole thing turns out to be a waste of time.
-Dan M