Alicornutopia

But, um, you can reach through a one-way portal and bring something back? Or reaching through requires the setup of a two-way portal?

You can reach through a one-way portal and bring something back; your hand/arm/reaching stick/whatever's attachment to itself overrules the can't-go-through-the-portal-from-the-wrong-side rule, and if you pick something up you can bring it back through too.

It's like a teleportation portal/screen, but it teleports in a 'atom by atom' way. There isn't a back route as there isn't anything to send the atoms back, and you can't detect it as there is nothing on the other end. Does that make more sense? I could go try to read all the posts on it and try to write a better way?

~It's maaaaagic~

Suppose you make a portal from a cave to a forest. The forest end is in midair, pointing north; that is, if you stand in the cave and throw something through the portal it appears in the forest traveling north, and if you put your arm through then your arm will appear in midair in the forest pointing north.

Suppose I stand in the forest, on the south side of the output-portal, and look north at the place where stuff appears. You stick your arm through, and it appears in midair, pointing away from me.

Can I see the internals of your arm with bone and stuff, in cross-section? Can I poke it?

Light from the forest isn't hitting the arm's internals, so it's just dark. It can be poked and this is liable to be harmful.

Why is light not hitting the arm’s internals? It should pass through the back end of the output end of the portal, which doen’t really exist (because the portal output doesn’t), and hit the object right in front of that (the internals of the arm). If Lambda can poke your arm in this case, she should be able to shine a flashlight on it.

The portal output is already weird about light since it's letting you see the output side from the input side, and I prefer not to have gore there.

That said, this might be something that Lurker can adjust when she casts. (She prefers not to have gore there, too, though less firmly than I do.)

What happens if the portal-spell-bearing object breaks while something (or someone) is partway through the portal?

There's - how was it Kappa put it? - kind of a mess.

(The whatever-it-is is cut neatly into two pieces, one on either side.)