Portals to Parallel Earths
In this setting events diverge when massive breakthroughs in physics are made. The breakthroughs effectively prove the many worlds interpretation, but more drastically they allow portals to be opened to parallel universes. Other advances are made because of this knowledge but none remotely as significant as the portals that can be made. Events in this setting diverged very recently so other than the things caused by the portals and breakthroughs in a certain area of physics, things are pretty much the exact same as our world.
Where the portals go: New portals connect to the equivalent positions in the parallel universe. New portals connect to worlds exactly the same as our own, however the instant the tunnel between them is opened symmetry breaks and random quantum events cause them to start diverging.
It is of note that the parallel universe you just reached through a new portal, will have equivalent portals in their universe that lead to parallel versions every universe that your portal leads to. This means in addition to the portals that exist in a given universe every universe connected to also has portals connecting to parallel universes themselves. Thus the number of connected universes is actually infinite.
Once a portal has been made to a another universe, the worlds are permanently linked. Future portals can be opened to that specific universe if you have the energy readouts from any machine that has opened a portal there before. If you can't obtain energy readouts from a machine you can obtain them by using specialized equipment on any area that the portal was near because of subatomic portals that occasionally still open leaking barely detectable energy, this detection equipment costs around a hundred thousand USD.
Portals connect to the exact position in the other world. Portals can be moved but both sides of the portal are physically connected and can't be moved apart. Opening a portal between two preexisting worlds is impossible if there isn't a portal machine at the same location in both worlds. The portals can be made as small as 2 meters in diameter starting out at about 130 thousand USD, the price of a portal goes up almost linearly with the diameter of the portal, not with the surface area. The technology used will obviously remain unspecified, but it involves the use of small particle accelerators, as thus the machine and created portal tend to be circular.
Note: While portals may cost upwards of 130 thousand USD the power requirements to open a portal and keep it open aren't very high, as thus you can pay to open a portal and pay a flat fee for however long you want to keep it open. Given the cost of opening a portal for a few minutes anyone can afford to do it.
In this setting the oldest portals were opened by researchers a few years ago, as thus no worlds have had longer than that to diverge. The older worlds usually have diverged somewhat since opening. There are thousands of portals, just from the early scientific testing of this technology, and most of their energy signatures are easily available online, which means nearly anyone can travel to them. It is of note that some people may find due to the events diverging over a few years, that their double in a world is actually quite different, due to the effect of a random event in the time since they diverged.
Economics: Given most of the worlds are so similar and the fact portals open to the same position in both worlds, it is obvious that most economic trade is pointless, because the worlds aren't sufficiently different. However, the one main commercial use for this technology (other than selling machines and portals) is taking advantage of having duplicate selves to perform larger amounts of mental work. For instance, scientists in different worlds may coordinate to run different calculations on supercomputers and then share their results allowing them to perform that calculation much faster. Entertainment may also become more competitive, worlds may decide to create different media, so that they can make material different than that of another world, afterward the different media will be shared between worlds.
For tasks where the final result is information (which can have different worlds do different parts of the same calculation, or work on different things, then share the information) the production of that sort of information will become dirt cheap and there will be a far larger amount of this information. One example of an area where improvement should be expected to increase is animation. With thousands of cheap portals, a company can choose to do animation that would otherwise be slow with many, many portals each connected world can choose to only do a tiny amount of the total work and at the end they share their work with each other and each profit off the end result. The improvement made in animation is analogous to the improvements made in any mental task.
Portals can never be made such that you can generate energy or decrease total entropy: The portals connect to the same point in both worlds so you can't use them to decrease travel time. The portals are supposed to be made using potential future technology and as such, aren't magic and are constrained by realism. Of course once we learn more about physics it seems unlikely we will find out we live in a world where this technology is remotely possible, but it still can't be completely ruled out.
The Actual Question:
With all of that in mind, what would be the large scale global economic effects of this technology? On the personal level the biggest effect will likely be using the portals to meet your doubles, but on the larger levels the main use of this is to perform utterly massive amounts of mental work and calculations quickly. What would be the effects of this technology be on the global level, how would this affect economies and governments?
How would the fact that calculations and mental work could be done in massive amounts, in incredibly short times affect the economy. I think it's a given that many jobs will be cut. After all why have thousands of people do a job if literally one person can do it by collaborating with their doubles, provided they know how to do the entirety of the task.