The world is broken down into 5 continents: North America, South America, Eurasia, Africa, and Austrailiartica. These landmasses exist in separate dimensions called realms, and are separated from each other. Along with these continents are smaller landmasses that exist alongside them in dimensions called demi-realms. These worlds can be as small as an island (Monaco), or as large as a state (Texas). Each of these large and small realms contain a massive warp gate that can be used to travel between worlds. One demi-realm that is of great significance is called the Nexus.

The Nexus is important because it links all realms to each other. Every warp gate in each dimension leads to the Nexus, and one must travel there in order to connect with any other world. For this reason, all manner of trade, travel, and commerce between realms must be conducted through this realm. This system of warp gates are controlled by a supranational organization that is responsible for the maintenance and regulation of these gates. This is meant to prevent any individual world from monopolizing their specific gate at the expense of other worlds, allowing unrestricted passage between realms.

As the Nexus is the center of the warp gate system and the only way to get to other worlds, all manner of traffic will coalesce around it. While in our world, there exists many ways to travel from one place to another, in this world, 7 - 8 billion people exist together in this universe, all needing to make the journey to the Nexus to get to anywhere else. This is likely to lead to congestion in this one specific area, slowing down traffic and backlogging movement exponentially. The organization needs to design a system to regulate warpgate travel to make it as efficient and quick as possible. How can they accomplish this goal and what steps should they take to facilitate this process?

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    $\begingroup$ It depends on a lot of things that you have not specified. How big are the gates? How much power is needed to operate them? How big is the network beyond Earth? How much traffic is using the Nexus? $\endgroup$
    – Slarty
    Commented Sep 22, 2020 at 12:47
  • $\begingroup$ Are gates always open? If not, then how many gates are open simultaneously at the Nexus? How big is the Nexus - can we put warehouses there? Can we roll freight trains through the gateway and switch them at the Nexus? Approximately how many gateways are in a realm like Africa? $\endgroup$
    – user535733
    Commented Sep 22, 2020 at 15:57
  • $\begingroup$ "Intranational" means within the same nation. London to Dover is intranational. Is that what you mean? $\endgroup$ Commented Sep 22, 2020 at 16:04
  • $\begingroup$ "This system of warp gates are controlled by a supranational organization that is responsible for the maintenance and regulation of these gates. This is meant to prevent any individual world from monopolizing their specific gate" you will actually end up with the nexus demi-world actually ruling all of them. $\endgroup$
    – Ángel
    Commented Sep 23, 2020 at 0:06

5 Answers 5


The Nexus is a Giant Train Switchyard:

Given the nature of portals as commonly portrayed, I'm assuming they are relatively small, and that it takes energy to keep them open. The real chokepoint is right at the portal, and beyond that, the limits are no different than open spaces.

While raw speed may be helpful for your system, what you really need is a giant rail system carrying people (but more critically goods) through your gate system.

Your portals have rail lines leading up to them and a constant stream of trains coming and going. As each well-organized train goes through the gate, the cars are decoupled and recombined to assemble trains destined for the final destination. Those trains then proceed through the gate going into the other realm.

Outside the nexus, trains can either stay trains, or they can have train stations connected to ports or airports, but these things are less critical. The real critical step is with trains loaded with stuff going through portals.

Because of the restricted nature of rails, many complex schemes and arrangements have been created to handle train traffic, even traffic going in multiple directions on the same tracks. The basic protocols of trains are well worked out, and the speed and volume of materials you can get through a portal are optimized. Peter Hamilton had just such a train system via wormholes in hisCommonwealth Saga.

I like Ash's answer here, but it relies on very fast trains which may be tricky to run safely. A modified version of it could certainly work, but any reasonably fast set of trains would work just as well. I'm also not sure the connections between worlds are continuous, and if they ever shut off, it would break the vacuum of the system and the whole thing would come to a screeching halt.

train yard


I think you are seeing a false problem when looking only at the three dimensional aspect.

Think of two rooms connected by a corridor. This is the 3D equivalent of your realms connected by the portal. However, since they belong to different dimensions, there will be at least a fourth dimension along which the realms are located.

This means that in a coordinate system you can have the same $(x,y,z)$ coordinate for the location of the entry point but a completely different $(u)$ for the additional dimension, so that what you see as single entry point is actually only the three dimensional projection of a four dimensional gate.

In the same way you can locate multiple gates just by moving along $(u)$ and keeping $(x,y,z)$ constant, reducing the load on each channel.


What you need is the actual infrastructure of seaports, airports and whatever the equivalent is for land between countries. Some customs, security and logistics personnel in place and you're good to go.

Each gate nation will have staff on both sides. You can issue visas to people from other gates, and have agreements with other nations so that as long as people and goods follow some standards, you impose less red tape and taxes on them (as long as no one pulls a Gatexit).


You're basically taking global travel and forcing them through 5 bottlenecks. That's going to make it tricky. You can't fly planes too often through the same airspace, wake turbulence will rip them out of the sky. Trains and ships are your best bet, however you'll need to run dozens of these in parallel to avoid bottlenecks, making your portals very large.

There is one way to port all global trade through 5 portals, each 10m wide. Elon Musk will be happy.

The Vactrain (aka Hyperloop, aka VacMagLev, etc.)

enter image description here

Basically a large cylinder about 5m in diameter, kept in vacuum, using magnets to accelerate the train at 1000's of km per hour in friction-free vacuum.

You can have a network of these snaking out into the major cities, into the portals, into the nexus, and then back out into the respective districts.

I don't know how big your nexus is, but you can design it like a roundabout - One large circle (50km across? Smaller is fine - just will lower your speed limit) with vacuum tube trains travelling at 1000's of km an hour, connecting into and out of the portals. (This assumes the single access point is per dimension - if this is wrong and it's single access point in total - see below):
enter image description here

Switching / merge can be computer controlled to maximise speed. To join a carriage into the ring, you just need to prepare a gap large enough to receive it by strategically slowing down and speeding up other cars.

If your nexus "dimensional breach points" must all be close together, there is another design for the central ring that can work. If you can only have one breach, and it needs to be as small as possible, you can make the iris design meet at a single, shared, dimensional breach about 25m high x 10m in diameter (5 stacks, of 2-wide 5m cylinders).

enter image description here

If the dimensially common area must be one single region, I'd make it red region in this superimposed photo of all dimensions:
enter image description here

Which looks like this in the dimension of the ring (The ring need not be in the nexus - it can theoretically go anywhere). Perhaps the dimension with the biggest space near the breach?:
enter image description here

The cars are wider than a 737 so passenger carriages can theoretically do 2 stories, 6 seats across with a central isle (in economy class) (baggage underfloor or up top). Space isn't at a premium like air travel so it need not get that sardine-like.

These passenger tubes stop in central terminals, and can transfer onto local trains / busses / ferries / etc.

An existing 8ft shipping container can be carried through these tubes too, so you can have rapid transport of dry goods, refrigerated stock, etc. This can hook into existing logistics chains - these can be loaded onto trucks, barges, etc without double handling.

You're probably looking at a speed of at least 1000km / hr. Possibly more. The maximum throughput is limited really by power and switch speeds. Assuming you have really good power and really fast switches, 34 shipping containers, or 5280 passengers can pass through any point in a tube per second.

Shanghai port currently does 21 million 40ft containers per year. One of these tubes fully powered running 24/7 can carry to 1.07 billion of them per year.

Atlanta airport currently does 110 million passengers per year. One of these tubes fully powered running 24/7 can carry 1.6 billion passengers per year.

If the track is really straight, you can increase the power and increase the radius of the central circle, and those throughput numbers can go up, basically linearly on the lower of the rate of change in power / turn radius. One design proposed on that wikipedia link could get up to 31,500km/hr - (I haven't calculated the G forces on that in the turns but suspect that's a bit much. Oh and it was meant for space launches.)

This will handle current (2019) travel and trade demands to those regions, through a single 5 * 10m portal into the nexus per region. However you're probably going to want have a 10m * 10m portal, to at least allow room to grow to add a 3rd and 4th track vertically.


These continents sound as though they exist in a highly advanced, dimensionally-complex world, so how necessary is it to have a supranational organization attempting to centrally plan its functionality? The nexus could, instead, be described as a complex adaptive system utilizing basic tenets of complexity theory for traffic mitigation. This study might address similar problems: Time-dependent vehicle routing problem with path flexibility by Yixiao Huanga, Lei Zhaoa, Tom Van Woenselb, Jean-Philippe Grossa:

"The corresponding routing problem is a time-dependent vehicle routing problem with path flexibility (TDVRP–PF). We formulate the TDVRP–PF models under deterministic and stochastic traffic conditions. We derive important insights, relationships, and solution structures. Based on a representative testbed of instances (inspired on the road network of Beijing), significant savings are obtained in terms of cost and fuel consumption, by explicitly considering path flexibility. Having both path flexibility and time-dependent travel time seems to be a good representation of a wide range of stochasticity and dynamics in the travel time, and path flexibility serves as a natural recourse under stochastic conditions. Exploiting this observation, we employ a Route-Path approximation method generating near-optimal solutions for the TDVRP–PF under stochastic traffic conditions."


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