Gravitational effects of portals at different heights
Summary: I am looking for a portal transportation mechanism that is consistent with the laws of thermodynamics.
Portals (or wormholes or gateways, something that connects two different locations in space-time), are usually portrayed with interesting side-effects:
When one of the portals is placed directly above the other, you get a perpetual motion machine - things that fall into the lower portal instantly appear from the higher portal, accelerate, then fall into the lower portal again.
When one portal is placed at the bottom of an ocean, water comes gushing out at high pressure from the other one.
when one portal is placed in space, air is sucked out from the other location
by logical extension, portals at different heights and atmospheric pressures would generate a constant and strong gust of air trough the portals, although that one is usually not portrayed much.
These effects are usually either actively exploited (Valves Portal game), or prevented by some special security mechanism (Stargates in the tv show disassemble and later reassemble matter)
However I am looking for a 'realistic' portal mechanism that does not have those sort of effects. The standard portals strike me as unrealistic for the following reasons:
For one thing, such a portal clearly violates conservation of energy, or it would need some sort of special mechanism and power reserve to account for the difference in potential energy between the two portal locations. Any custom mechanism that converts the energy difference into something else risks violating the second law of thermodynamics.
For another, should a portal not transport electromagnetic and gravitational forces just as well as matter and light? Electromagnetic and nuclear forces at least have to work through the portals. Since these forces hold matter together, a solid object would fall apart when it is transported through the portal.
I would therefore expect that when a electrically positive charge is placed next to one portal, the other portal would attract negatively charged particles.
Likewise, if a planet is placed next to one portal, the other portal should attract matter. Therefore the air from the planet would not escape into space through the portal, since all air that passes trough is strongly attracted back towards the portal.
I have however some trouble envisioning all logical consequences of such a portal mechanism.
If two portals are placed a different heights, someone approaching the higher portal should perceive a gravitational pull towards the portal, right?
Would someone approaching the lower portal also perceive a 'push' away from the portal, essentially some sort of anti-gravity force? After all, when passing through the portal they would gain potential energy, which cannot be gained for free.
If one portal is placed in the ocean, would a bubble of air form around that portal, or a bubble of water around the other portal?
I realize that these sort of questions could be answered kind of arbitrarily, given that no such portal system exists right now. I am looking for the most consistent and natural mechanism, in line with the laws of thermodynamics; in particular the law of conservation of energy.
Is there a way to get such a consistent gate mechanism, without hand-waving all difficulties away as 'magic'?
I am mainly interested not in the physical mechanism that would make such portals possible, but in the observable consequences such portals would have, assuming they are possible.
(As far as i understand, the current best physical concept for wormholes, a traversable Einstein"“Rosen bridge, involves a large mass within the wormhole itself, as well as surrounding negative-density stabilization structures. So the wormhole itself would have a couple weird gravitational effects. For now, I would like to ignore these additional effects and thread them as negligible)
This post was sourced from https://worldbuilding.stackexchange.com/q/3474. It is licensed under CC BY-SA 3.0.
1 answer
This is a really cool question, and I think I can (partially) answer it. Here goes.
If two portals are placed a different heights, someone approaching the higher portal should perceive a gravitational pull towards the portal, right?
I'll assume that you're talking about an object in between the two portals. In this situation, it would be as if the point in space where the upper portal lies were actually where the lower portal is - closer to the planet. The lower portal, on the other hand, would essentially be farther from the planet. But would anything happen because of this? Well, the portal is supposedly a "hole" in space. It's a two-dimensional opening. That means that there is no way for a three-dimensional object to only be at that point. The three dimensional object would have to be partly outside the portal, and so would feel the same pull of the planet as it would feel if the portal wasn't there. In the case of the higher portal, there would still be a pull towards the planet. Whether or not the object would move towards the portal would depend on how far it is away from it - in other words, whether or not the portal's gravity balances out the normal gravity.
Would someone approaching the lower portal also perceive a 'push' away from the portal, essentially some sort of anti-gravity force? After all, when passing through the portal they would gain potential energy, which cannot be gained for free.
This depends. The "anti-gravity pull" would come from the upper portal. Again, it depends on the distance between the portals, and where the object is in between them.
If one portal is placed in the ocean, would a bubble of air form around that portal, or a bubble of water around the other portal?
Here's an experiment that can give you the answer. Take a 2-liter bottle of soda (already empty). Fill it with water, so that it is entirely full. Screw the cap on tight, so no air can get in. Now take a toothpick and make a small hole midway down the bottle. What happens? (I'll hide the answer if you want to do it for yourself)
The water will not flow out! Now put a second hole in it. Here, the water will flow out.
This represents what would happen if the ocean and atmosphere were not connected - which they are. Now do the experiment with the bottle open.
The water will flow out.
I highly doubt such a portal could exist. As you pointed out, it would violate conservation of energy (continued increase in kinetic energy), as well as special relativity (the object would move instantaneously - thus faster than the speed of light). If you're really pressed, you have to invoke magic. There's no realistic way for this to work.
Note: I know about the theorized Einstein-Rosen bridges, but they're highly speculative and have some key problems. See the Wikipedia page.
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