# How do 3-D wormholes work/shift space compared to 2-D portals?

#### greswd

Wormholes, or Einstein-Rosen bridges, are often hypothesized to be spherical in shape. The hole parts, that is.

The 2007 videogame Portal gives a different take on hyperdimensional shortcuts.

In the game, "portals" are these oval-shaped, planar holes in the fabric of spacetime, and they serve well as hyperdimensional shortcuts, reducing the intervening distance between two distant points to zero.

The planar portals are intuitive, we can clearly see how they shift space, how they work just like doors.

Spherical wormholes, by contrast, are pretty unintuitive and complex when it comes to visualizing just how they shift space.

If the distance between two wormholes could be reduced to nothing, just like with the portals, what would it look like if a solid cube (companion) was thrown into one of the spherical holes?

And not "look like" in terms of light rays, but in terms of the actual physical events.

I figure that the cube reaches the spherical center of one hole and emerges from the spherical center of the other, but I can't imagine how the space is physically shifted in the intervening journey.

The film Interstellar, while cool, didn't demonstrate what happens clearly.

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#### Tghu Verd

but I can't imagine how the space is physically shifted in the intervening journey
I'm prepending this with "It's all hypothetical"...

If there is no space in the interior of the wormhole, then there is nothing to imagine. Nothing special happens to your cube per se, because there is no 'space' to shift. The wormhole interface, irrspective of the spherical exterior shape, is a 2D object. Portions of your cube exist in both locations, it's no different - conceptually - to if you put it down on a table. At the atomic level, there is no boundary for the atoms to interact with, they are just here or they are there, depending on how far through the wormhole you've pushed it.

If there is some interior manifestation to the wormhole, like a tube, it has to take time to traverse (otherwise it's 2D), so your cube would disappear and then eventually reappear if smaller than the interior distance, or merely disappear and then take some time to reappear, if it is longer than the interior distance. Note that if there is 'space' in the interior it has to be compatible with our space time, otherwise your cube would be destroyed or deconstituted in some fashion.

There is a simulation by Corvin Zahn that doesn't actually show an object interacting with a spherical wormhole, but if you watch it closely you can get an idea of what would happen to one, , and also includes the underlying physics at https://www.spacetimetravel.org/wurmlochflug/wurmlochflug.html.

#### greswd

If there is no space in the interior of the wormhole, then there is nothing to imagine. Nothing special happens to your cube per se, because there is no 'space' to shift. The wormhole interface, irrspective of the spherical exterior shape, is a 2D object. Portions of your cube exist in both locations, it's no different - conceptually - to if you put it down on a table. At the atomic level, there is no boundary for the atoms to interact with, they are just here or they are there, depending on how far through the wormhole you've pushed it.
But portals are planar. The two portals, being two planar surfaces, fit together perfectly, being in complete contact.

In the case of spherical wormholes, its one convex surface with another convex surface.

A convex surface and a concave surface might fit, but two convex surfaces, that's tricky.

#### Tghu Verd

Since it's all theoretical, there is no reason to think wormhole surfaces can't render in our 3D space convex - or concave - while being connected with zero length internally. It's not easy to picture, though, that's for sure!

#### greswd

Since it's all theoretical, there is no reason to think wormhole surfaces can't render in our 3D space convex - or concave - while being connected with zero length internally. It's not easy to picture, though, that's for sure!
Oh, zero internal length is not an issue. The issue is, as mentioned, the convex to convex interface.

#### Tghu Verd

Yeah, I get that. I've even tried to draw what it could look like, and I can't get past there having to be space in the 'interior' to create the convex shape. But I've never been known for my imagination

#### greswd

Yeah, I get that. I've even tried to draw what it could look like, and I can't get past there having to be space in the 'interior' to create the convex shape. But I've never been known for my imagination
Lol

though actually, interior space isn't much of an issue.

the issue is that a convex entrance should have a concave exit, how can it the exit be convex as well?

And a planar entrance should have a planar exit, and the game Portal shows that perfectly.

#### Tghu Verd

Well, Portal is a game, so they can do what they like, of course.

Still, 'exit' and 'entry' are arbitrary terms, which I've used myself on the basis that the wormhole is 'opened' from one end - the obvious entry. But it could be that a wormhole instantiates from the inside out, so there is no actual entry and exit. And it could be that interior "pressure" (as a concept, if it has no interior dimension that term is a probably not right) blows each end 'out' into our 3D spacetime, forming a convex shape at each end.

#### greswd

Well, Portal is a game, so they can do what they like, of course.

Still, 'exit' and 'entry' are arbitrary terms, which I've used myself on the basis that the wormhole is 'opened' from one end - the obvious entry. But it could be that a wormhole instantiates from the inside out, so there is no actual entry and exit. And it could be that interior "pressure" (as a concept, if it has no interior dimension that term is a probably not right) blows each end 'out' into our 3D spacetime, forming a convex shape at each end.
Either side can be the entry, and either side the exit, but there still has to be an entry and an exit.

Portal has created something that makes physical sense, spatially, so I'm wondering how it is with wormhole models.

#### Tghu Verd

There is this treatment for a simple wormhole geometry - https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.084044 - which seems to say the ends in our universe are spherical. There is an illustration in a Phys.org article referencing the work that shows concave ends, but it's not clear to me whether that's just artist interpretation or a consequence of the treatment.

#### greswd

There is this treatment for a simple wormhole geometry - https://journals.aps.org/prd/abstract/10.1103/PhysRevD.97.084044 - which seems to say the ends in our universe are spherical. There is an illustration in a Phys.org article referencing the work that shows concave ends, but it's not clear to me whether that's just artist interpretation or a consequence of the treatment.
sorry, where's the illustration?

#### Tghu Verd

Now you're testing me. Sorry, I can't immediately find the page, but recall it looked like a black hole render. If I can trawl it out of the browser history I'll post it in.

"How do 3-D wormholes work/shift space compared to 2-D portals?"

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