How can it be bigger on the inside

Question

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?

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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.)

Answer 5

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.