Probably a useful thread necro here, what with portal 2 out recently.
I think the only way to avoid breaking physics is to stop treating the portal like a wormhole and guess at the properties of the technology as created within a coherent realm of physics.
I think the in-game portals are not so much wormholes as some sort of a nonmatter thing
. Relevantly, an in-game portal bolt will stop at the interface of a portal rather than travel through it, proving that it has a surface of some sort. I'd guess that a portal-on-a-board being pushed through another portal would just collapse the pair of portals, for similar reasons. Also, we should observe that portals, whatever they actually are, are mounted on matter objects
, not into the fabric of spacetime. I don't really know how a literal wormhole would interact with a moving planet, but I'd guess there's a reasonable chance it might try to slide up or down the distorted spacetime of the gravity well, or perhaps decide to "sit still" in some IRF other than the surface of our rotating, orbiting planet in our rotating, moving galaxy. (Does anyone with an actual physics degree know whether the "fabric of spacetime" is stationary with respect to the matter inhabiting it? I'm curious). Anyway, I think Portal portals can't be wormholes.
I would probably try to explain away the conservation of energy violation by assuming that the portals require energy to maintain a portal, and that moving things around within a gravity well charges the potential energy difference to the generator. Therefore, if I place a 1kg beach ball in an infinite 1 m/s terminal velocity fall between two portals separated by 1m, the generator has to kick in 1J every 1s to bring the ball up to the higher level of potential energy. If this isn't supplied, the portal collapses cutting the ball in half wherever it ran out of energy. One could not therefore derive energy from an infinite waterfall and a water wheel, since the infinite waterfall is being "paid for" externally. This also lets us avoid peculiar gravitational and electric field topography around portals; electric and gravitational fields go across the width of a portal like it isn't there, and objects changing potential energy are handled by the generator.
The game is sort of ambiguous about whether portals exert force on the walls behind them, but they almost have to. Considering that air molecules are presumably constantly transiting an portal, a wall with a portal on it either needs to be pushing inwards every time a molecule enters and exits, or else the floor behind the portal is experiencing zero atmospheric pressure
from the back surface of the portal. This would rip oval-shaped holes through drywall, or anything else not built like a space shuttle (though it might explain why they felt the need to dig the enrichment center into the bedrock). The atmospheric pressure argument would also mean that any unsecured object with a portal would tend to move around with a force equal to atmospheric pressure times the surface area of a portal. Even if the portal excludes air molecules somehow, one could just as easily propel a car/spacecraft by sticking both orange and blue portals on the inside surface of the rear window, and repeatedly throwing/catching a ball through the portals.
The same goes for the portals-on-pistons pancaking question in the original discussion from '08. If there is no force transferred to the wall/piston, then you can effectively compact any object to an arbitrarily high pressure and temperature for no energy cost (or perhaps two atmosphere-portalsurface-pistonlengths, per the pressure thing above). By making the portal push back against the piston with the pressure of a pancaked experimentee (as compressed skin enters and exits the portal in an equilibrium), we avoid this problem. This similarly keeps us from cheating the delta-volume strokes of internal combustion engines.
As far as relativity, causality, and time travel are concerned, the game obviously does not inform us whether there is a light speed time lag between entering one portal and exiting another. The closest we get to that situation in the game is when...
...making that uninformative. It seems somehow not in the spirit of the game to stick your arm into a portal that connects to the surface of another planet, and wait for a round trip communication delay when you try to wiggle your fingers. But I imagine the physics would work just fine with a delay.