OK, here comes some GCSE level stuff so get ready.

When you're in a portal, going through a portal, or you are in the scope of a portal - lets say that you have not entered it or exited it yet, but the portal is above and below you - what happens to the gravitational potential energy? Would you be in a vacuum? If so, why should you be falling through the one in the floor and not just staying still if there is no top and there is no bottom.

i guess you would have infinite gravitation potential energy, but gravity still acts downwards because of the large mass in that direction, when entering the portal the gpe still changes to kinetic energy as normal, and you just magically regain some gpe every time you fall through. essentially its just a very long fall. Your physics only acts as if you exist in one location, any physical properties of the other side of a portal has no affect on you whatsoever.

No you wouldn't be in a vacuum because a vacuum is an area with no mass and theres still air etc.

That's my take on it, Im sure other people will either agree of alter my idea.

Firstly, I don't get where a vacuum came from.

The way about this is to consider how forces act through portals. It appears that no force acts through a portal (put a portal on a wall then one on the roof and an object next to the one on the wall will not be dragged through by gravity), instead they just teleport objects and keep the object movement the same on either side.

This would mean that if you are in the air, you would have the same GPE with or without a portal below you. All this GPE gets converted to KE. You go through the portal, keeping all your KE and gaining more GPE. Incidentally this would be impossible due to it being perpetual motion (where does the energy come from?).

Also, as a matter of interest, if forces did act through portals, you would end up with one of the two following situations in a recurring portal;

The gravity would be infinitely large - All the individual gravities get added together, meaning you end up with a huge gravitational force, which means you would accelerate insanely fast.

The gravity would be zero - If the portal cancels out the effect of objects below it for objects above it, the distance to the Earth would be infinite (no end to the portals, after all), which would mean you could hover. This one is slightly flawed in the fact that the mass around the portal would still effect you, so is more for funny than workable.

Thanks you have enlightened me.

This will now become the boring "did you know" at work today

LOL, what inspired you to ask, btw?

Just a puzzling thought that I couldn't work out.