This 'world' is so named in honor of Murray Leinster, SF writer, who had an intriguing idea or three.
There are four worlds, one might call them Alpha, Beta, Delta, and Gamma. Each world is practically identical on planet Earth, although in deep space very different forms of aliens have arisen that raise the bias levels in variable fashion.
In each world, the bias for one of the four biases is several levels higher than in the other worlds. Thus in Alpha, the Tech bias is 13@2. In the other worlds, its 10@1. Likewise with Psi in Beta which is 4@10, and 1@5 in other worlds. In Delta, magic is 4@1, and in other worlds its 1@3. In Gamma, Body is 15@10, and in other worlds it 10@2.
Also, these worlds have innumerable small gates that open and close on irregular schedules. Some gates float as they are influenced by gravity (these tend to be larger gates with more mass to them).
These gates are invisible and practically non-detectible except with specialized equipment.
Thus, you could walk down the street, get in a cab, be driven through a gate, and arrive at a bank where the cashier lives in another reality than the one you came from, and the one he works in. The next time you go to that bank, you could walk there, and thus enter another gate, and arrive in the first cashier's home reality, but the cashier that waits on you (and looks identical to the first one) is actually living in his house in a fourth reality.
Each universe is very similar. In part this is because the constant immigration, and emigration tends to average things out.
Dopplegangers resist meeting each other because at a certain subconscious level people are aware of what's going on, and so they use their innate pschyic potential to block dop's from approaching themselves, or they make themselves sick to avoid the dop.
Also, culturally, the people in these Lines tend to be rather absent-minded and not aware of their surroundings. This is a choice not made consciously, and reinforced by their culture because again this allows them to avoid facing the truth.
Those who tend to be 'aware' of surrounding structures more than most often end up being stay-at-homes. And indeed, there is a much larger percentage of stay at homes than some civilizations.
Also, those groups that are at the cutting edge tend to find themselves in a friendly world, and to stay put once they find it. Thus much psi work is 'garbage', but there are Centers for the Study of the Mind in the high psi universe. And so on....
I might need to make it harder to get started in magic and psi in these worlds.
Let's revise a bit.
Level two and three of magic and psi is powerblocked except for clairsentience. The top indig skill in magic and psi is 5@2. The deity in charge is neutral, and generally unfavorable to showing himself except to deeply serious seekers. Also psi static from the gates is a -10 sit mod penalty which is equivalent to the magic penalty from the deity named The One.
This makes it hard for a psi or mage to jump from Level One to Level Four.
Most people do not believe in the cutting edges of psi or magic or science. Few people have seen butterflies as they can only breed in one of these four worlds.
The effect is that many times searchers go out to study some effect, and find it to be nonsense...in the world they are in. Others study longer and find that the effect is strangely inconstant. Sometimes it works, sometimes it doesn't.
Thus these worlds very slowly advances in tech/magic/psi.
This slow advance is aided by the general skepticism of the public. In the Prime Universe, technogeeks and technophiliacs serve a door-opening function. A new technology is created, and the technophiles gou out to buy it at extremely high prices. This funds the research debt incurred, and allows the inventor to build more at a cheaper rate, and thus get the rest of us who don't think spending 5,000 dollars on a giant flat screen tv is a good idea, but might consider it at $850 dollars or at $500 dollars.
This door-opening function does not happen in this set of four universes. It is extraordinarily hard for a new insight into reality to spread as most such insights are regarded as the puffery of charlatans.
Without tech advances, many problems are excaberated. When England ran out of wood for its fires, it shifted to coal. The same thing happened here, but it took far longer, and caused much more hardship.
History is littered with more collapses of civilizations and technological dead ends and resource loss than our history is. They do not rise as high, and they fall quicker.
There are less totalitarian governances on the good side. With the alternate worlds so tangled, its hard to run a crisply efficient totalitarianism. There was a Nazi Germany and Communist Russia, but both were evils more on the scale of the Spanish Inquisition than the mountainous horrors they were in the Prime Universe.