Introduction: "What IS the portal paradox?"
The internet is perfect for arguing and it is hard to swing a stick without causing someone to explain to you about how you swing it in the "wrong" way and how, because of this, you are betraying your inferior intelligence (etc., etc., etc.). What's even more frustrating is when the person doing the explaining makes an obvious, glaring, mistake that is lost in their condescension. This makes you want to go in and fix it. This is a dangerous impulse and should be avoided at all costs. XKCD had the right of it in the comic "Duty Calls". It is precisely this combined with the internet laws "Muphry's Law" (a post correcting someone's spelling/grammar will inevitably contain a spelling/grammar error itself) and "Poe's Law" (unless some obvious indicator of sarcasm, or parody, is used there is nothing one can post/say that is too absurd that someone won't take it completely seriously) that leads to the maelstrom of content emanating from poorly worded physics problems on reddit/twitterX/etc..
The classic example is the "airplane on a treadmill" problem, but paradoxes like the "envelopes of cash" exist as well (which is also linked in the first blog post I linked at the start of this sentence). However, as much as these problems are landmines of discussion and disorder, they are interesting, which is at least partly why they become so infamous in the first place. And, personally, I have had a keen interest in the physics of "the portal paradox" for a while now. I think are really cool and worth explaining. Plus, I'm sick of people being wrong on the internet and if I don't write this down they might continue to be more wrong and that is unacceptable (note: that last clause was sarcastic. I don't expect this article to actually "correct" anyone, but it would be cool if someone learns something from it.).
Anyway. The portal paradox is, like all these problems, pretty straightforward. You have a cube, or a ball, or some inanimate object, on a pedestal and a plunger that will crush it directly above. There is a portal on the crushing face of the plunger and the "out" portal is off to one side, pointing upward at a 45 degree angle. The Plunger shoots down, fast, enveloping the cube. Does the cube whoosh out of the exit portal (Option B) or does it just "plop" out with no momentum (Option A)?
There are some reasonable answers to both but I think to examine which it might be and why we need to really break the problem down and address some of the issues with the setup.
The Series
In this series of five articles I will examine the portal paradox, and try to answer the question of A vs B.