Undergrad Intra-Universe Wormhole Metrics

[Onyx]

TL;DR

Are there any metrics for intra-universe wormholes?

Are there any metrics for intra-universe wormholes?

 

[Drakkith]

"Intra" means "within", as in within our own universe, which would be redundant since wormholes are already theorized as connecting two places with our universe. Did you mean 'inter-universe' wormholes? As in between two different universes?

 

[Onyx]

"Intra" means "within", as in within our own universe, which would be redundant since wormholes are already theorized as connecting two places with our universe. Did you mean 'inter-universe' wormholes? As in between two different universes?

The most famous wormhole solution, the Ellis wormhole, describes two separate sheets with opposite signs of the radial coordinate. Hence, this is a wormhole that connects two different universes. This article implies that intra-universe metrics are more rare, and says that the Aichelburg-Schein timehole is an example. So actually I already knew that there is such a metric, but my question is what would be the simplest metric to describe one (intra)?

 

[PeterDonis]

The most famous wormhole solution, the Ellis wormhole, describes two separate sheets with opposite signs of the radial coordinate.

Yes.

Hence, this is a wormhole that connects two different universes.

No, not necessarily. Both sheets could be part of the same universe, just in different places.

 

[PeterDonis]

This article implies that intra-universe metrics are more rare

That article is somebody's personal blog. It's not a reliable source.

 

[vanhees71]

Hm, this somebody seems not even to be willing to reveal his name, or didn't I simply not find it on the above linked website?

 

[berkeman]

Hm, this somebody seems not even to be willing to reveal his name, or didn't I simply not find it on the above linked website?

Do you mean the blog website posted by the OP:

This article implies that intra-universe metrics

If so, the person's name is in the website URL and also under "Contact" there. But as Peter said, it's not a valid reference.

 

[Onyx]

I just emailed a physicist and he said that any intra-universe wormhole can be made into intra with a change in structure, but I'm not quite sure what that means.

 

[Ibix]

I just emailed a physicist and he said that any intra-universe wormhole can be made into intra with a change in structure, but I'm not quite sure what that means.

What Peter said in #4, guessing from your paraphrase of what was said.

 

[berkeman]

he said that any intra-universe wormhole can be made into intra

Sounds like a little Physicist humor to me...

 

[Onyx]

Sounds like a little Physicist humor to me...

Another thought: perhaps a true intra-universe wormhole metric would be one where there is an option for two points to be causally connected via the "long way" or the "short way". In the Ellis wormhole there is only the path through the wormhole.

 

[PeterDonis]

In the Ellis wormhole there is only the path through the wormhole.

Not necessarily. See my post #4.

 

[Onyx]

Not necessarily. See my post #4.

But how would a traveller get from $l$ to $-l$ without passing through the throat?

 

[PeterDonis]

But how would a traveller get from $l$ to $-l$ without passing through the throat?

By traveling through the rest of the universe from one exterior sheet to the other.

In an idealized Ellis wormhole, where the mathematical description is taken to be exact all the way out to infinity, the two exterior sheets are not connected, each extends to infinity separately--but in an idealized Ellis wormhole, there is nothing else in the universe anyway, in either exterior sheet, so the question of whether it's an "inter-universe" or "intra-universe" wormhole is meaningless; it's a wormhole and it's the only thing that exists.

Obviously such an idealized solution is pointless to discuss when you're asking questions like the one in this thread--just as with other idealized solutions like a Schwarzschild black hole, which describes a black hole alone in a universe where nothing else exists, it's pointless to ask many questions that people want to ask about black holes. To make your question meaningful, we have to consider the Ellis wormhole as an approximation, where the "infinity" at large distances in any exterior region is not actually infinity, but just where the solution merges into the rest of the universe. And if we treat the Ellis wormhole that way, then the solution itself cannot tell us whether its two exterior regions are part of the same universe or different ones. Either is possible.

 

[Onyx]

I did end up finding a paper that describes a so-called intra-universe wormhole. It involves a Majumdar-Papapetrau solution with two spherical volumes replaced with the corresponding portions of a Reissner-Nordstrom solution centered at $r=0$. Thus, a non-simply connected spacetime is created.