A tethered pocket universe will usually have one or more permanent openings through which one could fly, drive, or perhaps even walk right through. Original artist unknown.

Pocket Universe Accessor
Tech level: 19
Pocket Universe Gateway
Tech Level: 23
Pocket Universe
Tech Level: 25
Pocket Universe Generator
Tech Level: 26

A pocket universe is a portion of our own space/time that has been deliberately truncated off from the rest of the universe, to exist independently either at a tangent to, or completely outside of, our own continuum. They are sometimes also called pocket dimensions or baby universes.

Pocket universes have become a very common motif in soft science fiction, super hero stories, and even fantasy worlds. However, they do occasionally show up in more serious science fiction, especially in stories that deal with more esoteric quantum theories. Examples of artificial Pocket Universes have been seen in the novels Eon and Eternity by Greg Bear, in the Traveller RPG, in various Superman Comics, in the Ben 10 cartoons, and in Dr. Who, where one apparently makes up the interior of the TARDIS.

Some fictional cosmologies assume pocket dimensions were naturally formed during the Big Bang, as a result of extreme fracturing of space/time at the moment of creation. Some also believe that they may be a consequences of certain ongoing natural processes, especially involving multiple universes and brane theory and the like. However, this article addresses only pocket universes that are created artificially.

Manufactured pocket universes are at the extreme far horizon of possible future technology, one that seems nigh-magical to us today. Though their creation seems unlikely according to our current understanding of physics, if they do prove possible, they would be one of the most powerful expressions of technology imaginable--each would be an artificial, if limited, cosmos unto itself.

Because pocket universes are a very ‘soft’ science fiction technology, this article is almost pure speculation, based on musing by theorists and ideas explored in science fiction.

Creating pocket universes would require an intimate understanding of dimensions other than the four (three of space and one of time) that we’re familiar with. It has been theorized, as in Einstein’s General Theory of Relativity, that these familiar dimensions are curved into a higher dimensional plane, often called hyperspace, like a two dimensional piece of paper would be curved into our own three dimensional world. As the dots on that paper could not easily perceive the curving of their two-dimensional universe, we too are often blissfully unaware of this hyperspace giving greater over-all form to our more familiar 3 + 1 dimensional space. But we have seen some evidence for this warping of space both directly and indirectly, in the form of the effects of massive objects on planetary orbits and gravitational lensing effects observed on stars in deep space.

A two dimensional metaphor for the nature of pocket dimensions may be to envision the universe as perfectly flat plane of pliable material with no width, such as rubber or plastic film. This very stretchy material, with the proper techniques and application of force, can be bent and bumped and warped in all kinds of ways. You can even force a very deep curving hole that breaks through it entirely—what we may call a black hole or a singularity.

But what you can also do is stretch this material and push on it until it forms a distinct bubble separate from the rest of the plane of pliable material. You can constrict the tether of material connecting the bubble to the plane until only a narrow ribbon remains, or you may truncate the bubble off and have it resting on the surface of the plane. You can also have the bubble float free entirely.

Keep in mind these are metaphors for a very basic understanding only. Remember, we’re talking about our 3+1 space warped into one or more higher physical dimensions, something that’s not necessarily easy for our poor analog meat brains to envision.

So how exactly would one go about creating such a pocket universe? The extreme warping of space may be accomplished through the use of highly advanced and powerful artificial gravity technology, and perhaps combined with the creation and fine control of singularities and wormholes. Extremely sophisticated manipulation of the universe’s quantum scale may also be necessary. All this points to an absurdly high technological level, at the very horizon of what we in the 21st century may be capable of comprehending.

How to create a pocket universe.


Pocket universes in science fiction seem to come in three general types: tethered, tangent, and severed.

A tethered pocket universe is one that still has an easy physical connection to its parent cosmos, through what is for all intents and purposes an unusually stable and robust wormhole connection. Entering the miniature cosmos might be just as simple as walking right into it. Though a ‘tether’ is used as an example in the 2D/3D metaphor, in a 3D/4D reality this connection could look like any kind of three-dimensional volume, perhaps like an actual doorway or opening if built into another artifact, or maybe a visual discontinuity of some kind floating directly in mid-air or space.

These ‘tethers’ usually come in two varieties—open and directional. An open access can be entered and exited from any direction on either side of the portal. In this way, they act very similar to conventional wormhole mouths. A conditional access can only be entered and exited from one or maybe several directions only. The portal would invisible and undetectable except from the designated directions it can be accessed. In fact, one could walk or drive a vehicle right through the position where the entrance is supposed to be and never know what was there if approached from the wrong direction. From the proper direction, however, the entrance of the pocket universe is clearly visible.

Tethered pocket universes may have more than one tether point, and where this portal connects in both the pocket universe and in the main universe may be made movable. The Way, from Greg Bear’s novel Eon, is an example of a tethered pocket universe. Dr. Who’s TARDIS may be another, if one considers the interior of the Doctor’s ship to be a pocket universe that ‘travels’ through time and space by merely shifting its tether point (the timeship’s entryway, aka the blue police box.)

A tangent pocket universe closely coexists side by side with its parent universe, but is physically truncated off from it. The two cosmi may still be attached through different layers of subspace and/or they may still share the same basic levels of quantum foam, but unaided travel from one to the other is not possible.

These pocket realities require specialized devices called accessors (see below) to enter and exit them. However, as the relationship between parent and offspring universe is static, tangent pocket universes can be reliably entered and exited any number of times, though usually from one or more predetermined set of coordinates in both the main cosmos and the pocket dimension. Usually (though not always) the act of travelling from a parent universe to one of its offspring, even a tangent one, is depicted as being easier to achieve than travelling from one full dimension to another. Though physical travel from pocket universe to the main one and vice versa may be difficult, signals and other types of information exchange may be easier to obtain, depending on the nature of the subspace/quantum separation between the two. The Phantom Zone from Superman lore could be considered a tangent pocket universe, as could Grandfather’s pocket universe from the Traveller RPG.

A severed pocket universe is the same as a tangent one, except that it is no longer attached to its originating cosmos in anyway. Neither travel nor the exchange of signals and information can be readily obtained from it. It is at this point truly a universe unto itself, though it may still have other restrictions of a pocket universe. It may hold its ‘position’ to the main universe, meaning access to it can be reliable, or it may be drifting or such through inter-universal quantum fluctuations and probabilities, meaning access to it may fluctuate between easy and all but impossible. Travel to a severed pocket universe is often depicted as much harder to achieve than to a tangent one, and may require something as resource-intensive as creating a interdimensional wormhole.


Pocket universes in science fiction are usually limited in some ways that the mainstream parent universe is not. The most common type of limiting factor is overall volume. While the real universe may measure billions of light years across, pocket dimensions are usually much smaller, running from a few microns across to many thousands of kilometers. Some may even be large enough to contain entire worlds or solar systems, but these aren’t typical. Some very advanced pocket universes may have one or two physical parameters that can be considered the same scale as our universe. For example, the Way from Greg Bear’s Eon is seemingly infinite, but only in one direction.

Its unknown if the expansion of space/time in our universe carries over into pocket universes. In stories it is implied that the pocket universe remains at a static volume once created, but this might only be in the short-term as humans measure time. Over millennia and eons, the pocket universe may keep expanding like the normal universe does, but perhaps at a different pace.

Another common feature of pocket universes is their extreme hyperspatial curvature. The parent universe may be open or saddle-shaped in its overall structure, but there is often little doubt that a pocket universe is definitively a closed cosmos that curves back on itself. For example, if a resident traveled straight in a single direction, the curvature of space in the small universe would eventually bring the traveler back to the very same spot he started from.

People in the pocket dimension may not notice this effect in casual everyday circumstances, but further investigation can reveal the truth. For example, in the old Land of the Lost tv series from the 1970s, the characters one day looked through a telescope and saw their own distant backs, confirming they were in a pocket universe. In Grandfather’s pocket universe from the Traveller RPG setting, the background space in the truncated solar system is slowly turning from black to gray and in the far future will one day be a bright white, as the light from the pocket dimension’s star has nowhere to go and endlessly cycles through the curved space/time of the pocket dimension.

A pocket universe may also experience the passage of time differently once separated out from its parent cosmos. The flow of time within may be greatly accelerated or greatly slowed down compared to the mainstream universe.

Physical laws may also be altered by the engineers in order to fit a particular need its builders may have. Alternately, something may go wrong in the creation process, and the physical laws within may be skewed in some random way. This may prove very hazardous to potential travelers to the pocket universe, as even minute alterations to the constants and laws of our own world can cause our bodies or our technology to spontaneously stop working.

The creators of the pocket universe may fiddle with physical laws in order to create items or technology that may not be possible within their normal cosmos. For example, in the novel Anathem by Neal Stephenson, the orders of the avout used specially-designed particle accelerators to create microscopic, short-lived pocket universes of slightly skewed physical laws in order to create New Matter, a material with many unusual properties. In the Traveller RPG setting, the Ancients used specially-designed pocket universes with collapsed dimensions to create their robust teleportation devices.

Pocket universes may also be created with inherent, large-scale instabilities that will cause them to collapse after a set amount of time. This may be a deliberate feature put in by its creators, or it may be the result of an imperfect formation. When a pocket universe collapses, it may just evaporate away, fading away into the quantum foam bit by bit like a ghost, or it may spontaneously collapse into a singularity. An example of a collapsing pocket universe can be found in the Star Trek: The Next Generation episode "Remember Me," where an experiment in warp bubble manipulation creates an inherently unstable pocket universe that traps Dr. Crusher.

Tech Level: 19

If a civilization is advanced enough to cross interdimensional barriers, it can also find ways to access tangent pocket universes that may already exist. The ability to create such miniature universes is still reserved for higher tech levels, however. Detecting the existence of, and determining the hyperspatial coordinates of, a tangent pocket universe may also require separate interdimensional sensor technology.

An accessor would be similar in operational principle to an Interdimensional FTL drive, in that they would use some unknown advanced form of gravity and quantum manipulation to warp the very fabric of space and time to reach parallel dimensions. As the parent universe and its offspring may still be connected via subspace or a shared quantum ‘foam," travel to and from the pocket universe may be easier and require less energy than a true interdimensional hop. Hence, an accessor may be easier to manufacture and operate, and may require less technical sophistication.

Because pocket universes are "smaller" than naturally occurring universes, they may not be accessible except under certain circumstances, or only from certain predetermined coordinates in real space. For example, in the Traveller RPG universe, Grandfather’s pocket universe is only accessible from certain points around the Regina star system.

An accessor would move a predetermined mass (such as a starship or a group of intrepid explorers) into or back out of the pocket universe when activated. Usually there is no formal movement involved; when activated, the user(s) will see the old universe fade away and the new one fade into existence around them. Other types of technology can sometimes serve as an accessor. For example, both the warp drives and transporters of Star Trek fame can be considered accessors as they have been shown being used to occasionally move ships and people between connected universes.

Accessors can be used to travel to severed pocket universes as well, but only by ‘hopping’ from adjacent dimensional space to adjacent dimensional space. This may require only a few hops, or many hundreds in an indirect manner. Note that the severed pocket universe may not even be along the ‘chain’ of related realities that the accessor can enter, or may drift away in the mean time.

Tech Level: 23

Creating an open, two-way doorway in and out of either tangent or severed pocket universes would require wormhole technology, which becomes available at Tech Level 23. These would also be the only way to directly access a severed pocket universe without a number of intermittent dimensional hops that would be required using an accessor or interdimensional drive. As with an accessor, determining the existence and hyperspatial coordinates of such pocket universes will usually require separate interdimensional sensor technology.

It would for the most part look and act very much like a ‘standard’ wormhole; the entry way at both ends would be spherical, and would visually ‘reflect’ the environment on the other side of the opening. However, each end would exist in a separate universe.

But also like conventional wormholes, they would require tremendous amounts of energy and/or negative matter to both set up and to maintain. They would also be inherently unstable, and could collapse if too large a mass is moved through them or the wormhole mouth is impacted with sufficient energy.

The wormhole openings into and out of tethered pocket universes are considered far more stable and robust than these gateways, but would have the same vulnerabilities, only to a lesser degrees.

Tech Level: 25

Both warp drives and wormholes, technologies discussed in the FTL section, involve the extreme warping of space/time through gravity and quantum manipulation, and the creation of pocket universes may be a natural outgrowth of those technologies (assuming they’re possible at all, of course.) Like with wormholes, a complete mastery of gravity manipulation, quantum engineering, and the custom creation of singularities may be required. However, warp bubbles and wormholes are usually assumed to require constant monitoring and upkeep in order to keep them working. A pocket universe by contrast is usually stable and independent, requiring no further intervention after its creation.

Pocket universes may occupy only the volume of a few atoms, or they may be many billions of miles across, or even larger. The nature of a pocket universe (including its type, volume, density, physical laws, flow of time, etc.) are set at the moment of its creation and generally can’t be altered afterward.

What exactly pocket universe-creating devices would look like would be anybody’s guess. At this Tech Level machinery is all but indistinguishable from magic from our 21st Century perspective, so it could take on any number of forms. But even so, creation of a pocket universe even at Tech Level 25 would not be an easy feat, so the machine or machines would probably still look impressive or distinctive in some way.

Purposes of a pocket universe may include:

--To conduct experiments investigating the creation, formation, structure, and ultimate fate of our own universe, in miniature.

--For storage and preservation of valuable items and locales, up to and including entire cities, planets, solar systems, and perhaps even entire civilizations. The pocket universe in question may also have a time differential from its parent universe, allowing time to pass much more slowly, helping to preserve said treasures for the long term.

--To isolate dangerous super-science experiments from the rest of the universe. Grandfather’s pocket universe in the Traveller setting was created partially for this purpose

--To isolate undesirable elements from an environment while still keeping access to them nearby, so to speak. For example, in the comic book series DC One Million, all major cities on Earth were contained in their own individual pocket universes, allowing the planet to return to a completely natural state.

--If the time differential allows a much faster flow of time within the pocket dimension, experiments requiring months or years or even centuries could be carried out within hours or even minutes instead.

--To facilitate faster than light travel by setting up pocket dimensions to act as interdimensional ‘bypasses’ between points light years across. Would work very similarly to the Interdimensional Drive, but in this case the dimensions traveled into would be artificially created.

--For easy transportation of a possibly unlimited number of goods. They can be tethered pocket universes with their entry wormhole tied to a literal suitcase or storage trunk or other such object, or they may just need an accessor set to the right hyperspatial coordinates. The number of objects they could store would depend on their internal volume and configuration; it could be small and knapsack sized, or it may contain a whole planet of use as storage space.

--To act as energy sinks for a teleportation system. The Ancients in the Traveller RPG setting used planets and solar systems tucked away in pocket dimensions for this. They were used to "soak up" the energy created by an object teleporting thousands or millions of miles in one jump, where velocity differentials between the origin and destination points that could be measured in tens of thousands of miles per hour or more.

--To act as a potentially unlimited energy storage device. Upon its creation, the pocket universe is saturated through with radiation and heat energy. When the pocket universe is accessed, this energy readily pours through into the mainstream universe and can be used for various purposes. The amount of energy available depends on its volume and the energy density contained within.

--To act as a bomb enhancer. Imagine an atomic bomb detonated in a small pocket universe only three feet wide. The energy would have nowhere to go and the entire force of the bomb would be held in suspension and concentrated, even more potent than the bomb would have been on its own. When released with an accessor or wormhole, the explosion would be more devastating that using the bomb just by itself. (However, there would be an upper limit to how highly concentrated you could make the explosion—too much energy concentrated in one spot would create a kugelblitz, or a black hole created solely by energy. The newly formed kugelblitz would likely destabilize and collapse the small pocket universe itself. However, the energy densities for this to occur are literally astronomical.)

--To imprison criminals and entities considered too dangerous to otherwise incarcerate. The Phantom Zone from the Superman comics and the Null Void from the Ben 10 TV series were both used in this capacity.

--To act as a safety buffer to explore interdimensional spaces. The pocket universe in this case is used as an intermediary space to buffer its parent universe should something go wrong with such exploration.

--To create a shelter against a cosmic disaster. A tangent or severed pocket universe can protect a planet or solar system from almost anything occurring in its originating universe, up to and including the death of the parent cosmos.

--As a monument to the building civilizations’ existence, just to prove that it could build something as amazing and awe-inspiring as its own customized universe.

Tech Level: 26

Up to this point, creation of a pocket universe was a singular, monumental event for the building civilization. One Tech Level later, however, the technology may improve to the point that machines can manufacture pocket universes in quick succession, perhaps only taking a few minutes apiece. The devices may also be small enough to carry around in one’s hands, with most of its operational machinery located, appropriately enough, in a tethered pocket universe. They would also be able to function easily as accessors and could create interdimensional wormholes in order to enter its creations.

More than likely these generators would only be able to create pocket dimensions up to a certain size, but could otherwise customize the new miniature cosmos according to whatever the user’s needs may be.

A visit to a pocket dimension may not always be a pleasant experience. Tha Phantom Zone, with its skewed physical laws, was used to house and punish dangerous criminals. Image copyrght Time-Warner/DC Comics.

Further Information

In Print

Eon and Eternity by Greg Bear

Anathem by Neal Stephenson

The Classic Traveller supplement "The Secret of the Ancients"

Superman comics, et al

In the Media

Star Trek, et al

Doctor Who, et al

Ben 10, et al

On the Web





Article added 1/20/10