We have these "magical" items everywhere in fiction; from the classic rabbit coming out of a hat illusion, to the TARDIS from Doctor Who, to Newest Magical Beast Newt Scamander Briefcase. These items all share same characteristic: a container with interior spaces that are much larger than they appear to be externally.

My question: Are there any possibilities of how this could be done based on science theorems and/or hypothesis?

To narrow things down I will set some rules:

  1. A teleportation answer is not acceptable. The answer must take some form of a container, not Portal's hula-hoop like gate.

  2. All item inside aren't just compressed, at least if we get inside we wouldn't feel that our body had been shrunk down.

  3. Main question is about Volume differentiation. However you can try to answer the weight differentiation of the interior vs exterior, but its not necessary.

Bonus: If there exist possibilities, would there be some limit to the difference of the exterior volume vs the interior volume?

Can we put a portion of our universe with some galaxies inside a peanut size container?

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    $\begingroup$ Look at how to fit monsters in your pocket $\endgroup$
    – Kys
    Dec 1, 2016 at 19:29
  • $\begingroup$ @Kys I've seen it, that's why I add rules of no teleportation portal, and compression of matters. But if this question are still considered the same and by forum rules considered answered, please do tell me. I will close it. $\endgroup$ Dec 1, 2016 at 19:48
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    $\begingroup$ In the end, it's all Timey Wimey Wibbely Wobbely stuff.It's all about phyiscs, physics, physics... $\endgroup$ Dec 1, 2016 at 20:55
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    $\begingroup$ It's explained in one of the older Dr. Who TV shows. Something along the lines of "Do you know how something very far away can be very big, but you can fit it between your fingers from a distance? Well it's like that, just on the inside." $\endgroup$
    – Raydot
    Dec 1, 2016 at 23:57
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    $\begingroup$ two words: Pocket Dimension. Or, if you remember classic Looney Tunes, the "Portable Hole." $\endgroup$ Dec 3, 2016 at 3:28

5 Answers 5


I have done some thinking about making an “abcess” or “bleb” of folded spacetime on the far side of a throat that’s smaller than the room it contains.

I’ll illustrate using flatland. Draw a small circle. Inside that circle, push the flat sheet perpendicular to the plane, making a deep dent; continue stretching as if to make a wormhole. Then inflate the dead-end like blowing up a balloon.

The flatlanders outside the circle are not affected. Upon reaching the circle they find a tunnel to a room that’s “bigger on the inside”.

When I came up with this, I had been thinking that the throat could be shrunk to microscopic size and a submarine can be inside, providing miniaturization. Access to the outside world is through this throat, so I was speculating on how it would appear.

The “mass” is essentially screened, appearing (on the outside) as a constant mass of the wormhole stabilizing structure, or an apparent mass that being what would cause the same curvature of spacetime seen near the wormhole mouth.

That is, consider a normal wormhole, where you assume that the mouths can be moved independantly. If it’s the same for a wormhole leading to a pocket universe or a rented warehouse in this universe, moving the mouth does not make you drag around everything you have stored too.

So, I have a mechanism whose only purpose is to support the wormhole mouth and hold the door. It might look like a prehung door for sale at the hardware store, or might need more support equipment so it's like a small phone booth. You can move that around and it’s just the mass of the door and the mouth. But if you go through the door the warehouse at the far end holds a huge amount of mass.

Now just having a wormhole to a warehouse elsewhere is too mundane. Lead to a pocket universe, but keep the ability to move the two mouths independently and not pulling on the pocket universe space.

  • $\begingroup$ I remember a fictional gadget Doraemon's Gulliver's tunnel? The object that go through gate A to gate B is scaled down, while object that go through gate B to gate A is scaled up, and the scaling factor is the same for any object. Is the throat you mention work in a same way? $\endgroup$ Dec 2, 2016 at 2:49
  • $\begingroup$ @HarizRizki no. I elaborated by post. The Gulliver Tunnel doesn’t seem to explain anything though. $\endgroup$
    – JDługosz
    Dec 2, 2016 at 5:11
  • $\begingroup$ Oh I see now. I seem to anchored to 'miniaturization' before. $\endgroup$ Dec 2, 2016 at 5:20
  • $\begingroup$ Your method also made it easier to imagine to create the space without the creator needed to be a higher dimensional being. I get it. $\endgroup$ Dec 2, 2016 at 5:24
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    $\begingroup$ In a normal wormhole, you assume that the mouths can be moved independantly. If it's the same for a wormhole leading to a pocket universe or a rented warehouse in this universe, moving the mouth does not make you drag around everything you have stored too. $\endgroup$
    – JDługosz
    Dec 2, 2016 at 6:03

In such matters, it's always helpful to scale things down to the familiar. So, imagine for a moment that you are a 2-dimensional being. You can move freely left or right, back or forward, but you have no conception at all of up or down. Then suppose that your house exists on a sheet of paper.

I, a three-dimensional being, can take that piece of paper and fold it several times. Each time its size halves, while at the same time having exactly the same surface area inside the folds.

By the time I've folded it several times, I can place it easily inside a small square in your 2-dimensional world. As long as I line up the entrances carefully, you can pass through a gap in the square and walk back and forth across the surface of the sheet of paper. Because it's folded through a dimension you have no access to, your perception is that the paper is bigger on the inside.

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    $\begingroup$ +1, this answer is very interesting! I just don't know if it solves the problem about the weight difference. Scamander's briefcase is not heavy but holds many heavy beasts. In your line of thought, the folded piece of paper would have the same weight of the unfolded paper, which is not the case. $\endgroup$
    – Zanon
    Dec 2, 2016 at 1:04
  • $\begingroup$ I got some thinking that if you do it like this you will 'sacrifice' the upper dimension at least in that particular space. I mean If we are 2 dimensional being that can observe a 3 dimensional space (but we can't access them freely) then we can't observe them anymore in a folded paper space, since the 3rd dimension there had been filled with a stack of folded 2 dimensional space). If we apply this same rule on 3 dimensional space then I think the 4th dimension (if we agree the 4th is time) in the container would also cease to exist, because we try to multiply the container volume. $\endgroup$ Dec 2, 2016 at 2:58
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    $\begingroup$ Time isn't "the" fourth dimension, it's a different type of dimension. Space dimensions and time dimensions work differently. If you folded three dimensional space through a time dimension, then you'd be able to travel in time by walking from one side of a room to the other. Instead, "Bigger on the inside" objects fold or offset space through a hidden fourth spatial dimension. $\endgroup$
    – Werrf
    Dec 2, 2016 at 4:05
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    $\begingroup$ @Zanon the weight is in the 3 dimensional space, not in the two-dimensional. For a 2D creature, the folded paper does not weight more. A pan-dimensional object needs to be weighted in its top-most dimensional space. $\endgroup$ Dec 2, 2016 at 13:30
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    $\begingroup$ @Werrf I actually do travel in time when walking from one side of a room to the other ;) $\endgroup$ Dec 2, 2016 at 16:58

D&D's Bag of holding (and other spells & effects) describe the use of pocket dimensions to achieve this. Also see: Rope Trick. The bag does not compress or use a portal; the inside of the bag is an actual extradimensional and finite space with rigid boundaries. For the Bag of holding, these boundaries have some connection to the physical outside of the bag: If the bag is pierced, within or without, the bridge to the dimension disappears and you lose all your stuff forever.


You can construct Einstein metrics which have the property of "Bigger on the Inside". For example

$$ ds^2 = -c^2 dt^2 + a(r)^2 \left( dr^2+r^2 d\theta^2+r^2 sin^2 \theta \, d\phi^2 \right)$$

with $a(r) =1 $ for $r > R$ and $a \gg 1$ for, $r < R$. If you calculate the volume inside a sphere of radius $R$ you will find a much greater volume than normal but a standard surface area.

You can calculate the Einstein tensor of this geometry to find the matter configuration needed to create this geometry (I believe it would violate certain energy conditions.)

  • $\begingroup$ Welcome to WorldBuilding jman! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Aug 23, 2017 at 20:50

Some theories about Space time I have heard imply that it can expand not only indefinitely (Big rip theory, which is that the universe never stops expanding), to being able to expand in such vast quantities that the spacetime between 2 objects, and hence the distance between them, can increase so that if both objects emmited light that went at C for eternity toward eachother, they would never meet (One of the theories about the Big Bang was that it became light years in diameter in at most a few seconds). It is common that Space time is not limited to things such as the speed of light, and even today we observe Redshift of galaxies that implies that light being sent from us now will never reach them because of the amount of space being created between us and them.

So what does all of this have to do with Hammerspace and the like? Its simple, Because space can theoretically expand like this, then the idea that we can selectively make it expand in a contained area is also not far fetched. There is no Teleportation or anything, Its just the physical space inside of a container has been forcefully expanded, and is contained in the container.

Of course, We are no where near technologically advanced enough to determine if this is actually possible, and what would actually happen to surrounding space time and the container if we tried, but so long as this is not a Hard Science universe, Hand wavium away.

  • $\begingroup$ I like how you based it in expandable universe theory. But I notice you need some 'ambiguity' to make it happen. Like dot A and dot B in a transparent bag C must be further apart when you see them with your face in the bag. While it not that apart when you see them from the outside. I imagine this kind of space is like a rearview mirror, nice. $\endgroup$ Dec 2, 2016 at 2:41

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