# Bridging Realities: a pendulum and its virtual self

Physicists link a real pendulum to a virtual one in world’s first mixed reality experiment.

People have been linking their identities with online pseudonyms since the beginning of the Internet. Games such as World of Warcraft and Second Life make these identities more tangible, allowing players to create digital avatars to represent themselves.

Avatars can take actions, construct and destroy virtual objects, trade with currency, and travel through virtual worlds in addition to exchanging ideas verbally. Interactions among avatars become more real as headsets allow players to hear other human voices in addition to seeing an animated representation of the person. We all know that the actions of real people control virtual realities, but a recent experiment has shown that a virtual world can affect objects in the material world.

A pendulum.

Vadas Gintautas and Alfred Hübler of the Center for Complex Systems Research at the University of Illinois have been linking the real world a virtual one using that classic physics device, the pendulum. In fact, they just published an article about it in Physical Review E.

While most players enhance or completely transform their appearance when they create an online avatar, Gintautas and Hübler tried to create a virtual pendulum that closely resembled their real one. They put the two pendulums into communication.

Diagram of the pendulum.

The details of this communication are a bit complex, so brace yourself for some vocab. The fixed point is the point from which a pendulum hangs. Don’t be fooled by the word “fixed” – this thing moves around. The angle of the pendulum’s swing is measured as it rotates around this point, and zero means it hangs straight down. Last but not least, the natural frequency of the pendulum is the rate at which it prefers to swing.

That said, the fixed point of the virtual pendulum moves depending on the angle of the real pendulum. Likewise, the angle of the virtual pendulum determines the location of the fixed point of the real pendulum. Moving the fixed point of a pendulum is a method of driving it.

When Gintautas and Hübler made the virtual pendulum, they programmed friction into the system. When the real and virtual pendulums don’t connect, it’s called dual reality. Friction drags them to a stop. When mixed reality occurs, the two pendulums drive one another. Moving as one, they defy the friction forces that would ordinarily halt their swinging. Mixed reality only occurs when the two pendulums have comparable natural frequencies.

It is possible for a real pendulum to become one with its virtual identity, but mixed reality cannot happen with real people and their avatars. While the players exert full control over their online identities, the avatars don’t significantly influence their players. This is probably fortunate for Warcraft players who would prefer not to die with their characters.

Even so, mixed reality may actually prove useful in the real world because it can occur only when the two systems are sufficiently similar. A system with unknown parameters may be synced up to a virtual system whose parameters are set by physicists. The unknown factors in the real system can be determined by changing the virtual system until they shift from dual reality to mixed reality. Then, the physicists will have good estimates for the values of the unknown parameters.

Second Life real estate that players can purchase with their virtual money.

Apart from human identities, World of Warcraft and Second Life intersect the material world economically. US dollars may be used to buy both Second Life linden dollars and Warcraft gold (although, you have to buy gold from other players through sites like Peons4Hire). In the case of the coupled economies, transfers go both ways.

Gintautas and Hübler are curious about the possibility of mixed realities emerging from these coupled economies. After all, if two synced pendulums could overcome friction forces, perhaps synced economies could escape recession.

Picture Credits
Pendulum: Josef Stuefer
Diagram: alpinekat, using the GIMP
Treehouse: Jacob Earl