A sling ring opens magical portals of varying sizes between two locations. A sorcerer imagines the destination, concentrates, holds the hand wearing the ring upright and with the other gesticulates in a circle, and the portal opens with a burst of yellow sparks around the edges of the portal.

How might this function as technology

It can’t.

Teleportation, even given cutting-edge concepts of quantum entanglement, is limited to bits of information. All the writing on this topic that I can find online says that physical portals require too much energy. So we have to write the totality of this device off as a narrative conceit.

We can imagine the input working, though, as a reading-from-the-brain interface that matches a sorcerer’s mental image of a location to a physical location in the world. As if you were able to upload an image and have a search engine identify its location. That said, reading-from-the-brain has edge cases to consider.

• What if the envisioned place is only imaginary?
• What if the sorcerer only has the vaguest memory of it? Or just a name?
• What if the picture is clear but the place no longer exists? (Like, say, Sokovia.)

Perhaps of course the portal just never opens, but how does the sorcerer know that’s the cause of the malfunction? Perhaps a glowing 404 would help the more modern sorcerers understand.

@scifiinterfaces has you covered, Steven.

The gestural component

The circular gesture is the mechanism for initiating the portal, an active meditation that likely makes concentrating on the location easier. If we had to compliment one thing, it’s that the gesture is well mapped to the shape of the portal, and having a gesture-concentration requirement ensures that portals aren’t just popping up at whim around Kamar-taj anytime someone wearing a ring remembers a place.

OK. That done, we’re at the end of the compliments. Because otherwise, it’s just dumb.

No, really. Dumb.

The physical design of the Sling Ring is dumb. Like Dumb and Dumber dumb. There are plenty of examples of objects or interfaces in movies that only exist because a writer was lazy, but the SlingRing™ deserves a special award category unto itself.

• First off they aren’t rings, they are more like a set of brass knuckles as designed by a 10 year old who’s never seen a brass knuckle.
• It restricts the movement of two fingers on the user’s hand which seem to be critical to casting all other spells in the film.
• It makes any kind of physical combat with that hand significantly more difficult which, curiously, is something sorcerers seem to do a lot of. Punching someone while wearing a sling ring would likely break a finger or three.
• It’s interesting to note that the sentience that makes other relics special may also be their security. However, any sorcerer can apparently pick up any sling ring and use it. Have you ever been bowling? The first 5 minutes of any trip to a bowling alley is trying to find the right sized ball. So unless there’s someone making bespoke sling rings for new magicians, there’s going to be a lot of poorly sized sling rings out there. This might explain why Strange’s ring is loose enough that it can easily fall off or be pulled off, which is inconvenient at best when fighting another sorcerer.

Redesigning this device as a single ring, or a glove or a wristband, or a necklace, or a tiara or a codpiece…frankly just about anything would be better than this tragically flawed artifact and would likely solve all of the above problems.

Hang on, let me remove my not-sling-not-ring first.

And what the heck does sling even mean in this context?