Theory history: Submitted 2009-03-21, Likely 2009-06-08, Still alive 2011-03-27, Doubtful 2014-04-06, Debunked 2016-01-15
The submachine network (subnet) is made up exclusively of areas that were once populated and used by humans, but were somehow isolated from the rest of the world. -The lighthouse is buried. -The basement no longer has an exit. -My guess is that the lab is on a mountain peak... ETC.
This relates to the perception = reality theory (not my theory...). It goes something like this: The more often an object or area is seen or otherwise sensed by living beings, the more likely it is to actually exist. This means that unexplored places don't exist until they are explored (0% chance of existance). This isn't impossible, even in real life. Heavily populated areas have a 100% chance of existing.
So, what about places that definitely existed once, but are unlikely to exist now, because all the humans have left? These form the subnet. The submachine is alive, and it's the only thing perceiving the areas of the subnet. This means that these areas only just exist (something with a 10% chance of existing doesn't just exist 10% of the time, it 10% exists).
The submachine makes it possible to teleport between subnet areas (though it doesn't seem to like it when people do it.)
Mur never "entered" the subnet in the conventional sense. When he was buried in the lighthouse, the lighthouse became part of the subnet, because only the submachine and Mur were perceiving it - it became "less real".
Becuase there are so few humans in the subnet, it's existance is low, and weird things happen. (Like bells levitating blocks.) The subnet is unique, because any area that could be explored by humans but has low existance would disappear a while after the explorers left (0% existance) - when they came back, it would be a new place (though it might look the same.) Since the submachine is always perceiving the subnet, it remains at low existance instead of vanishing periodically.
Einstein and other animals have a lesser perception of the world than humans (makes sense - lower intelligence = lower perception.) If they enter underpopulated areas, those areas eventually become low-existance, and they can walk through walls and stuff.
The submachine doesn't like intruders, possibly because they make the subnet too real. There's not too many of them, so the levitating blocks and such still work, but the submachine can't do some things that it would have been able to do otherwise...
Clarifications: -Remembering somewhere or something is, in a sense, perceiving it. The submachine areas aren't just underpopulated, they're forgotten as well.