In many sci-fi tropes, a warp gate or artificial traversable wormhole almost always resemble a funnel however in reality its working principle is a wormhole. I would like to know how does it appears to look like a funnel when it is functioning like accepting visitors?
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1$\begingroup$ Since link-only answers are frowned upon, I'll just drop this in a comment. I've always found this video to be the single best way to wrap one's head around the geometry of a wormhole: youtube.com/watch?v=8tX7KQSKMtQ $\endgroup$– QamiDec 4, 2021 at 13:53
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$\begingroup$ Oh, and original video in higher resolution here: tempolimit-lichtgeschwindigkeit.de/filme/wurmlochflug_lang/… $\endgroup$– QamiDec 4, 2021 at 13:56
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3 Answers
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The simplest solution would be that it looks the same from whichever direction the 'gate' is approached. Wormhole entrances (and exits) are spherical 'points' in space but regardless of the angle of approach any observer looking into the event horizon sees the 'tunnel' effect. The effect is a product of space/time distortion within the wormhole on photons entering and emerging from it. (Looking back after you exit would reveal the same view.)
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Simple space time deformation, caused by the mass of the wormhole. Nothing dissimilar from what a massive object like a neutron star looks like.
When the warp gate is active, its influence is no longer contained and extends also to its surroundings, giving it the peculiar funnel appearance.
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Wormholes conceptually could have all sorts of different topologies. Not all of these are realistic in terms of general relativity, but science fiction often doesn't bother with the details.
The 'funnel' or 'tunnel' type of wormhole is a case of a flattened 'cross-over' gate. It's easiest to think about the 2D analogue - Flatland people living in a 2D plane come across a 'gateway' region linking them to another universe, another plane lying parallel to their home universe. There are many ways of configuring the surface joining them.
The figure on the right shows the 'round' version - corresponding to a spherical wormhole in 3D. The obvious problem with it is that the surface is strongly curved so a Flatland being approaching it will be stretched and squashed uncomfortably as they try to approach the gate. Unless the gate is much bigger than the beings trying to pass through, they will be ripped apart.
The figure on the left shows the tube 'crossing over', turning inside out, apparently passing through itself. (We need an extra dimension to allow them to pass one another). Now the gate is a straight line in Flatland (corresponding to a disc in 3D), and when you walk into the West-facing side in universe 1 you walk out of the East-facing side in universe 2, and vice versa. Now the route through the gate is fairly flat rather than being curved, with most of the distortion being concentrated at the edges of the hole, and the distorting forces for travellers are much more tolerable.
Sci-fi wormholes usually have the flattened geometry of the cross-over gate. In 3D universes, they appear as a circular ring around a circular disc-shaped opening in each universe.
