#version 1
version 1
The spheres are in reality equipped with hypodermic needles that releases a strong drug filled with nano-bots that plugs into your nervous system, after their first usage you get connected to the Collective, a network of humans, creatures and other aliens connected with each other with the solely purpose to expand the network by using the computational power of the network and the drones creatures plugged into the Collective.
The network force you to a wild catch of monsters to train them, this rather time-consuming but mind effort-less task is designed to keep your brain at low usage in order to use the remaining computing power for the Collective, you will not notice you are part of such a network.
#version 2
version 2
Each ball is crafted inside a huge particle accelerator (that's why they are costly) and actually opens to a curved space where time flows really slow (and that's why weight would not matter, it is just reduced by the time flow). Consider it a white hole, or a naked singularity. Rumors about accidents are known (vanishing buildings, especially with outdated balls).