On earth, we're slowed down by the muck of the everyday world. Matter slows us down, rubbing against us and taking away our speed and power. Gravel, air, even slip-n-slides, exert some friction on us. This frictional force runs counter to our motion, and it can't be escaped anywhere on earth. Eventually, inevitably, it will slow us to a stop.
Ah, but in space all the rules are different. In a vacuum, with no matter to rub up against like a strangers on the bus, we could move forever. If we started in a spin, we'd never stop unless we had a collision with some kind of asteroid. It turns out, that even in the vacuum of space, we'd get dragged back. The vacuum isn't as entirely devoid of matter as most people make it out to be. It's only devoid of permanent matter. In a vacuum, tiny, temporary, particles pop in and out of existence all the time.
These particles, at first glance, shouldn't drag down a spinning object. Since they are popping up on all sides, hitting it from every direction, their cumulative effect should be zero. At least two physicists at the Spanish National Research Council say this isn't the case. If a particle hits a spinning object in the direction of its spin, a part of its momentum may be transfered to the object. If, however, a particle hits a spinning object counter to its direction, more of its momentum will be transferred to the spinning object. If particles moving counter to the object's motion hit with more force than particles moving with the object, the object will eventually stop moving. Not even in space is motion preservered.
Via New Scientist.