In the vast majority of science fiction and fantasy that uses portals, the portals are a kind of two dimensional object or a long tunnel. Often, if a portal is a free standing door, those on the 'wrong side' of the portal can't even see it.

I study 3-manifold theory in mathematics, which is the study of possible shapes of universes. In math, two-dimensional planes don't make good portals. What we do instead is basically take spherical portals, one in each world, where going through one sphere takes you out in the corresponding points of the other sphere.

This would look very different from most portals in fiction. Essentially, as you approach a portal world A, you would see what looks like a large spherical mirror, except instead of reflecting your world, you would see another world, world B. As you approach the sphere, you experience no sudden transition and can't even tell when you cross the line, but world B appears larger and larger as world A appears smaller.

Once you leave the portal in world B, you would turn around and see behind you what looks like another spherical mirror I which world A is reflected. There is no tunnel, and no sharp transition.

Are there any instances in fiction where such a portal is used? I seem to remember something like this in the very end of The Chronicles of Narnia, where they go to the Garden of Eden and find another world inside of it, but I'm not sure.

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    Sliders the TV show had portals that acted this way, but they got the visual representation wrong. Not that it would make much sense to see it as you describe it (or even to experience it for real, I suppose). I'm not aware of any that describe it thus where the portal is macroscopic.
    – John O
    Commented Jul 5, 2013 at 6:35
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    This is an interesting view. To me, the major issue with portals is that, if they let people through, they should let any or most matter and energy through. If the two sides are dissimilar, it should create an unbalance resulting in strong physical phenomena, the most obvious and simple being a violent wind, but probably also much more energetic events which would probably be beyond any kind of airlock to control.
    – babou
    Commented Jul 5, 2013 at 7:55
  • If I would sell portals, I owuld make then like doors, i.e. the true representation would be hidden from the user, and a single point of entry presented as a door. Much easier to work with it. The sphere thing sounds more like a prototype, without the second projection-step ;)
    – flq
    Commented Jul 5, 2013 at 9:44
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    Spherical doesn't make sense, by the way - if an object was transferred through to the other side as it entered the portal, and exited out the other surface, parts of it would either be in two places at once or it would end up distorted when it came out, because it was entering and exiting a convex shape. One of the two ends would have to be concave to avoid the distortion. I'm guessing that's why fictional portals are generally either flat or (if they have distortions like Stargate and Farscape) have a "tunnel" that you go through.
    – Izkata
    Commented Jul 5, 2013 at 13:24
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    I think they distort the local geometry to avoid this problem Commented Jul 5, 2013 at 13:51

7 Answers 7


The game called EVE Online contains wormholes which are linking distant solar systems together. They are represented in the game as a 3 dimensional sphere which resembles a mirror. Here is a video recorded by player showing off wormholes from close up:

On a presentation made at the EVE Online fanfest 2008, where wormholes were first shown to the public, CCP's lead game designer CCP T0rfi stated that the visual design of wormholes is based on this idea:

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    This third video is exactly what I had in mind! Commented Jul 5, 2013 at 12:45

For non-mathematicians the way to understand the shape of a wormhole is to start in two dimensions where we can represent space by a flat sheet. A wormhole is where two parallel sheets are joined together. This diagram (attempts!) to show how the wormhole joins the two sheets:


Start with the two sheets representing the two different regions of spacetime, then punch out a circular hole in both. Now bring the two sheets together and glue them along the edges of the holes. The bottom diagram is supposed to represent the two sheets brought together and glued along the edges of the circle.

When you've done this, you can start on the upper (blue) sheet, travel towards the wormhole and when you reach it you'll go though it and find yourself moving away from the wormhole on the lower (red) sheet. Incidentally, if you start in the blue sheet and look towards the wormhole you'll see light from the red sheet that has travelled towards the wormhole, through it onto the blue sheet, then away from the wormhole towards your eye. That's why Brian says the wormhole will look a bit like a mirror.

Anyhow, the point is that to a Flatlander living on either sheet the wormhole looks like a circle. If you now replace the 2-D sheets by 3-D spaces you join them in a similar way but this time by cutting out a sphere in each and joining them along the surface of the sphere. That's why the wormhole will look like a sphere. Sadly my drawing skills aren't up to drawing the 3-D diagram.

Actually the wormhole can be any 3-D shape. See Negative Energy and Wormholes on the Physics Stack Exchange for how to make a wormhole in the shape of a cube. You could make the wormhole an arbitrarily thin disk, subject only to your generating system being able to generate enough curvature at the edge of the disk. This would resemble the conventional circular portal.

All very well, but what Brian actually asked was if any authors had treated wormholes properly in their books, and the answer is that yes, of course, many have done so. For example in Axiomatic by Greg Egan and Cosm by Gregory Benford and doubtless lots of others. Gregory Benford actually references Matt Visser, who wrote a non-non-nerds guide to wormholes back in 1989.


In Jeffery Lords' "Blade" series, book 19: "Looters of Tharn" (June 1976), an alternate-Earth civilization invaded another alternate-Earth by use of a transdimensional portal. Said portal was spherical in design, acting like a bubble in space. The Konis shtafari/Peace Lords'(as they called themselves) first initiated a short-term dimensional doorway into the Tharn world to put people and machinery across, who constructed their own dimensional doorway machine to go back. When two machines, one on each alternate-Earth, were synchronized, a large freestanding sphere was made in mid-air so that large transport aircraft could be used to shuttle people and machinery back and forth. The "aliens" were repelled by the barbaric Tharns by destroying their dimensional door machinery on their side of the portal.

In "Reboot", the Canadian CGI-animated action-adventure computer animated television series that originally aired from 1994 to 2001, computers have "programs as people" living inside them, similar to the Tron movies. When an Internet connection is made from the computer (someone's home computer) to the "Supercomputer" (CERN?), a spherical, two-way portal is made. Throughout the TV series, these portals are three-dimensional free-floating spheres, never 2-dimensional screens. Good for the visualization of a three-dimensional portal.

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    +1 just because someone else on the planet remembers the 'Blade' books... and wish I could give another for mentioning 'Reboot!' :)
    – K-H-W
    Commented Nov 8, 2014 at 23:34

The 2014 movie "Interstellar" uses spherical mirror-like wormholes appearing very much as described above. One character even expressly explains why the portal would be spherical rather than a 2D surface.


The "collapsar jump" in Joe Haldeman's Forever War acts as a spherical portal:

Twelve years before, when I was ten years old, they had discovered the collapsar jump. Just fling an object at a collapsar with sufficient speed, and out it pops in some other part of the galaxy. It didn’t take long to figure out the formula that predicted where it would come out: it travels along the same ‘line’ (actually an Einsteinian geodesic) it would have followed if the collapsar hadn’t been in the way – until it reaches another collapsar field, whereupon it reappears, repelled with the same speed at which it approached the original collapsar. Travel time between the two collapsars … exactly zero.


Brian Lumley's Necroscope books utilize spherical portals.

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    Please expand a bit on this, for instance describe the portals as they exist in the book and explain how it matches what Brian is looking for.
    – Kevin
    Commented Jul 5, 2013 at 20:56

Expanding on a previous answer that was given, asked for expansion then left.

The Necroscope series of books utilises spherical portals as a gateway between our world and the homeworld of a vampiric alien species called Wamphyri. The portals are two ends of a "Grey Hole" which are connected to form a wormhole. There are 2 of these wormholes, and travel is only one way, if you attempt to pass back through one you have entered it pushes you back. These were formed by 1) a white dwarf that crashed to the Wamphyri home world "starside" and 2) a failed Russian Nuclear Fusion experiment. As these are virtually small suns there is no world B visible through the portal on world A just light from the spheres. Travel through them is almost instantaneous and if you entered via the "bottom" of the sphere on world A you exit from the bottom on world B.

So other than the mirror like rendition of world B by the portal on world A this matches a lot of what you mention.

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