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)