In order to pull off this trick, researchers Timo Virtanen and Erkki Thuneberg of the University of Oulu had to create a special type of fluid know as a Fermi Liquid. In order to explain more, let me quote from the article on Wired Magazine.
"When chilled down into a Fermi liquid, particles no longer interact strongly with one another as they do at higher temperatures. Instead there appear quasiparticles, which are the combination of a particle itself along with how it affects the environment around it. Like the original particle, each quasiparticle carries spin, charge and momentum."
"The researchers calculated that the quasiparticles ricochet around in the liquid like bullets, increasing the force on the pendulum. They do not, as ordinary particles would, interact with each other strongly enough to create resistance to the pendulum moving through them. “That’s why the behavior is different,” says Thuneberg."
So, at these super cold temperatures, the particles in the fluid literally change how they interact with one another and with outside objects. Instead of interactions with particles slowing down the down the pendulum as it passes through the liquid, the quasiparticles are imparting their energy into the pendulum through collisions. The energy from these collisions is speeding up the pendulum.
I am amazed that it is even possible to do this at all. It is counterintuitive and marvelous results like this that keep me coming back to science for more and more. This research has some practical implications and will likely be used to better understand many systems, but it may not be something that is going to change how we live or will likely ever lead to a something you see at the store. It is the kind of research that is driven by curiosity. These are the breakthroughs that capture the imagination. This beautifully depicts how science, while being rigid and tough, is simultaneously filled with some of most exciting stories there are to tell.
Image is by Loadmaster (David R. Tribble). Used via Creative Commons and Wikimedia Commons (http://commons.wikimedia.org/wiki/File:Clock-JungHans-6932.jpg)