Solving The Portal Problem 

Option B, because as I see it, the orange portal isn't a force acting on the cube, it's pushing the rest of the universe.

My analogy for how portals would work in those situations is a bit like the door analogy, where you have a door and a room behind the door that move together. If you move through a stationary door at a certain velocity, you end up moving in the room the door leads to at that velocity. If you're stationary and the door and room are moving towards you, if you pass through the door you (ignoring friction) end up moving through the room at the speed it's moving towards you at. If your frame of reference in the situation is stationary outside the room while you watch the room envelop a stationary cube, the cube remains stationary from your point of view. If your frame of reference is inside the room and moving with it, the cube appears to move towards the door and keep moving after it passes through. I believe this works, and TL;DR velocity that the cube has relative to someone moving with the first portal doesn't need to be the same as the velocity of the cube relative to someone moving with the second portal. TL;DR squared, B is viable.

The problem I have with option D, is that when we look at the moving portals in-game (gas production), we can see that there is no additional space created between the two portals like with the spring analogy. Because if we apply the spring analogy to those moving portals, one end of the spring would move up or down and the other stays stationary, which would mean the laser and other light could no longer travel through the portals in a straight line.

I have thought about another option, because only problem in option B is that cube has to gain some momentum, to be shoot in a space. And i thought, what if moving portal, so the cube enters it creates a counter force to the portal, making it harder to move, and that force creates shooting momentum for that cube. So the cube gets momentum from portal momentum, stealing his movement force.

14:30 I'm amazed anyone has trouble with the idea of the the cube having 2 different velocities when the whole idea of portals is that the cube can be in two places at once. So if discontinuous positions are allowed, then you logically have to allow for discontinuous velocity (and acceleration, and jerk, and so on...) along with it because velocity = position over time, as every highschooler should know. So like, if we accept the premise of portals existing, the answer has to be option B. It's literally just kinematics. You don't even need to know anything about physics or conservation of energy or forces.

Portals (at least in half-life universe) can move relative to each other since Moon moves relative to Earth. And if even if moving portal stops half-way the half that passed will already have momentum and will pull the other half with it

The portal to the Moon tells us a lot about how the portals work. The portals are instantaneous holes. There is no delay for the speed of light. Passing through the portal disregards all reference frames than the portal’s: even though the Moon Portal is orbiting the Earth and is moving much faster than the Earth Portal, you exit the Moon Portal at the exact same speed relative to the portal as you entered the Earth Portal with. Which all points to option B. The orange portal falls, say at 10 m/s. That means the cube enters it at 10 m/s. That means it exits at 10 m/s. If the blue portal were also falling at 10 m/s, then the portal velocities cancel and the cube would emerge stationary, like when the Mythbusters fired a cannon at 50 mph from a truck the other way at 50 mph and produced a stationary cannonball. But the blue portal isn’t moving. It doesn’t cancel out the 10 m/s the cube exits with, so the cube goes flying. Yes I know the cube was stationary before the portal fell on it. But that doesn’t matter. In Portal, the only reference frame that matters during interactions with a portal is the portal’s.

At least from a game perspective, where you want things to look intuitively, option B would work best. From portal A, you would see the background from portal B rush towards you, and then you would be flying out of B. From portal B, you see player A rushing towards you and then fly out of B. In both cases it looks realistic and would be a pleasing game mechanic. Considering portals are magic, you can really fit them to your needs.

The easiest argument for option B, I think, is to consider what happens at the stationary portal. Imagine the moving portal is traveling a single discrete unit every arbitrarily long step, which is just a fancy way of saying the timeframe doesn't really matter. As the moving portal passes one step over the cube, the topmost face of the cube is now one unit away from the boundary of the stationary portal. Take one more step, and the cube is now two units extruded from the portal. This continues until the moving portal fully passes over the cube. From the stationary portal's frame of reference the top face of the cube, and thus the cube as a whole, just moved away from it by one unit every step. This is the definition of velocity. You can't impart velocity and thus momentum on an object without force being applied, of course, but if we reframe the hypothetical it's easy to see where the force could be coming from: the piston. It would be consistent (if still unrealistic) to frame our math such that the force necessary for the piston to move the orange portal over the cube from the cube's frame of reference is the same amount of force necessary to move the cube at the same speed from the blue portal's frame of reference. Of course, that still doesn't explain that one scene from Portal 2.

My head-canon of moving portals and conservation of momentum is this; For a stationary cube to go through a moving portal, a force, equal to the change in momentum, must affect either the cube or the portal (or the force split equally between the portal and the cube ("equal and opposite force concept"), but my brain is too fried at the moment to figure out which one makes more sense.

Physics has no problem with conservation laws being broken so long as their associated symmetries are broken, which they are even for "static" portals as we see in the games. Neither energy nor momentum - linear or angular - are conserved. The momentum one you can easily see by the fact that portals can change direction of motion, while the energy one is seen, for example, when you fall through portals - that being said, option A does break stuff harder. You could try to save conservation of momentum if portals feel a force as stuff goes through - which we don't notice in the games because they're attached to walls and/or because they're fairly massive themselves (which also means you can't gently balance a portal over your head). I guess you could also say portals have some energy which can be consumed or fed into as stuff is transported, and then stop working when out of energy - but then the energy initially stored in portals would have to be so large as to be impossible to test in-game. If you keep all stuff conserved this way, then you could say the portal is essentially pushing the block through to the other side - it is also pushed back but not enough to stop it. (and holy shit that telegraph video is bad)

The best idea that I have is that when the cube goes through the orange portal, it doesn't flop out of the blue one, but rather ends up sliding down the ramp, given that now the gap created by the blue portal is filled by the connecting platform that held the cube. Alternatively, depending on the thickness of either the portal rim or the moving or stationary platform, the cube could get caught on some edge and be held onto the ramp

As GlaDOS said "speedy thing go in, speedy thing go out" which parallel fact is also stationary object go in , stationary object comes out. It has no inertia of its own so i conclude option A.

1) We know energy need not be conserved as a change in position changes your GPE, as Portal players well know. 2) Imagine standing under the portal and looking up. You're already travelling quickly relative to the things on the other side of the portal before the portal hits you, so you would continue to move quickly afterwards by flying out the other side. I think the key property of a portal is that as you pass through it, nothing changes (other than the direction of gravity i guess? Maybe for a "realistic" portal, the Earth would be pulled quickly towards it by the influence of the Earth's gravity on the other side, or maybe not I don't know enough general relativity to apply it to different topologies)

this was really well made

Speed is relative, so to the orange portal, the cube is rushing up towards it. There will be momentum upon transversing space, its just not the cube that exerts the energy until the potential energy it has stored is released. Such in this case would essentially be like something pushing the cube through, then the potential energy the cube already had is released on the sloped surface, like pushing a cube through a door that leads immediately down stairs.

The answer is Z the portal closes because you cant have moving portals (except for in neurotoxin sabotage where for some reason you can) so the cube glitches out because it gets crushed by the panel

that was a really cool and well edited intro!

Ok I'm gonna make an insane argument. Light moves slower for objects having speed, and if it's the case: while portal moves down, covering the cube, the TOP half will show up LATER than LOWER, since at lower end portal is stationary. That means that depeding on the orange portal speed, cube either pops in "instantly" sitting on blue portal, or emerges from it's halfway point like 4th dimension rotation.

I recommend starting with the explanation from right after the intro and then doing a title card with a shortened intro (~15 seconds or shorter) for better retention 👌

"The math breaks when the two halves of a portal move in relation to each other." That reminds me about how the reason portals can not be placed on moving platforms (with the exception of that one scripted moment in the neurotoxin place) is because it was too hard for valve to program

Love the intro

I'm first year physics My thoughts: Portals as understood in real life can only theoretically exist if you bend space and time. When you bend space and time, you end up with gravity, therefore all Portals would have a very strong gravitational force. Though very similar to a black hole a portal would most likely be hollow, to allow for the transportation of objects in both directions. You wouldn't get stuck in the middle for the same reason, if you were to make a hole through the earth you would fall straight through to the other side, because of momentum from being pulled by the gravitational force. Depending on how far teleportation will determine the strength of the portal's gravity. Through a wall would be minimal, much like walking through a door. Across a mile would not only be gravitationally noticable, but axially as well, sence every mile you travel on earth, the earth bends at about 8inches. Creating a portal through the entire earth would most likely yealed a similar result as falling through the earth, but that's only entering the portal, as the earth would also be sucked through both ends creating a chaos reaction, and the apocalypse. Ooh also according to laws of time, it would take you the same amount of time to teleport through the earth as it would to fall through it. You are welcome 🤗

4:30 The moving portal transfers its momentum to the cube

9 views. Huh. I think this video has the lowest views to quality ratio i've seen. You explained stuff quite well though, despite what you said.

I personally think if no outside force affected the cube after it exited it would just stay on the ramp on that angle. My basis for the reason why is that if the portal is basically just a tube/hole in space that connect one area to another then it should not be applying force to what is inside it. For a basic example for something you could do yourself: step 1. get a small object then try to make a tube either with your hands or by using some objects. Step 2. Move this tube over the object. Step 3. The object shouldn’t have suddenly had the force of the tube but going in the opposite direction. If the tube is taller the object chosen then it would stay inside the tube but since the length between portals in game is basically nothing then it should be sitting on the floor of where the portal of where the cube entered from colliding with and sticking out of the exit portal. I do not know what the big physics involved in this needing to the complicated stuff but I know that if nothing applies force to an object it don’t change momentum.

Another animation you could make to disprove A is to have the same platform with the cube, but make the portal bigger, and have it consume the platform entirely. On the exit portal, you would clearly see the platform being pushed outside of the portal. That's assuming the singularity thing isn't true lol

Definitely B. The room with the piston is #1 and the destination room is #2. From the point of view of the cube Room 2 is approaching at high velocity. Momentum will then carry the cube forward at a normal arc. The paradox, of course, is that Room 1 & 2 are the same room. In portal 1 portals could not be moved, the connection would break. The complication was added in Portal 2. To preserve relativity the updated version makes more sense.

just gonna throw this in for the algorithm. great video btw

I believe it is option B that is correct. Think about it in reverse: If you jumped into the stationary end of a portal that had a moving exit, then your momentum would be the same both going in and coming out, and your velocity would have the velocity of the moving end of the portal added to it, resulting in you going faster than you would if both ends of the portal were stationary. And since the portals are traversible in both directions, this logically means that jumping into the moving end of the portal would have the same outcome: the moving end's velocity gets added to your own. Thus, due to how they operate on "Speedy thing goes in, speedy thing comes out" logic, option B is the correct answer. [EDIT]: "Portals cannot exist if they do not move in tandem" Tell that to the time we use them to slice up the Neurotoxin Generator so that it implodes.

Your Schroedinger equation is missing the rest mass term, so the wavelets are travelling in the wrong direction relative to the envelope of the wave packet. Of course, if you put in the rest mass term then you have a horribly stiff differential equation prima facie. This can be dealt with by integrating the rest mass term alone before applying the usual predictor/corrector method. The rest mass term can be integrated at once without the need for recursion.

Hey I'd recommend shortening your intro. Someone who hasn't seen your channel before and is unsure if they are interested in your content might not wait 30 seconds to find out

If we assume the portal itself doesn't lose energy when transferring the cube does that mean the piston pushing the portal feels a resistance proportional to the energy it takes to accelerate the mass going through the portal to the speed of the portal?

Before I watch the video, my thoughts: If - Both portao stationary, they don't affect momentum. - Both portals move at the same speed, they also don't affect momentum (think of doctor strange moving you to another place by moving both portals through you) Therefore You gain momentum equal to the difference of the portal's momentum relative to each other. This also means that valve already made that in Portal 2 when you shoot a portal at the moon niw that I think about it...

What would happen if you went through one portal and the other side was completely flipped horizontally? Would you walk out and perceive the world flipped? And would the world perceive you flipped?

I'd say kinda A depending on which way gravity is facing compared to portal 1, because portal one will kinda be like a magnet (if portal 1 is facing down towards gravity dropping onto the cube) and once more mass is out of portal 2 than portal 1 until both portals are fully next to each other creating basically a wall kinda just making the cube plop out. I could explain this way better with a proper diagram lol

i'd say it's a bit of a and b. while others say the cube has no forces acting on it, there actually is. gravity and air pressure. gravity is pulling the cube one direction and once it passes through the portal both air pressure, air current and gravity change. gravity pulls the cube a different way, and while the box isn't moving, the air is still getting displaced by it, which in turn will give it resistance. all that and the box should find itself being flung out equal to or less than the speed the portal it was entering was going. heck, what about the air the blue portal would be having. if one is moving, wouldn't the air being pushed through it, make a vacuum like pull? wouldn't that also make the portal go through with a little momentum?

Surely the blue portal would move as well, as the blue and yellow portal have to remain stationary to each other So what would happen is the blue portal would either sink into the ground (if the piston was strong enough to break the ground), or the piston just wouldn't be able to push the yellow portal. Assuming the blue portal has successfully buried into the ground and had empty space in front of it (e.g. there was a chamber below), the cube would enter the yellow portal and exit the blue portal in whichever manner it normally would if it was pushed into the yellow portal with the same velocity instead. So if a cube normally maintains its momentum when passing through a portal, it will be shot out (where the kinetic energy of the cube comes directly from the work done by the piston). If instead a cube doesn't normally maintain its momentum when passing through a portal, then it would just plop out of the blue portal like expected. Since, in the game, objects maintain their momentum through portals (e.g. the player doing a portal jump), then the expected result would be that the cube gets shot out of the blue portal at a velocity based on the angle of the blue portal to the blue portal's direction of velocity (as the blue portal would be moving, due to what I initially mentioned). So if the blue portal was facing directly up as its moving directly down, the cube would exit at twice the blue portals velocity. If the blue portal was facing down, it would exit at half the blue portals velocity. This, of course, is a contradiction though, as the blue portal would be able to instantaneously overtake the cube. So, the cube wouldn't enter the yellow portal in the first place if the blue portal was facing down or horizontal or anywhere between those. The cube can only enter the yellow portal if the blue portal is facing up or just above horizontal or anywhere in between those. Judging from the drawing, the blue portal is the second case, so the cube would exit the blue portal at some speed in between the blue portal's velocity and twice the blue portal's velocity. I might be entirely wrong though, so feel free to correct anything I have stated.

There are so many problems with the portals that I beleive that we will never be able to create / use them. For example: If one portal is on the surface of the planet and the other is in space, would the earths gravity pull the objects that are in the space into the portal ? And the other way around: Would the air preassure simply push all the atmosphere through the portal into the outerspace, leaving the earth without its atmosphere ? The only explanation for this would be: Some air should pass through the portal and, until the pressure and the gravity would equalize, resulting in the exit of the portal having it's own bubble of atmoshere around itself. I beleive that could work in case of two 3D portals that use higher dimentions to connect themselves, but so far we do not have any proof of there exising any additional spatial dimentions.

Option A is just ignoring the conservation of momentum because it goes from there being x momentum on the portal and 0 momentum (relative to the environment) and then has 0 momentum on the portal and 0 on the cube. I'd like to say conservation of momentum shouldn't be broken in these scenarios so the cube should have x momentum so that both the start and end have the same momentum. Edit: After seeing you say about option D, I would say that portals are 1d, there is no "inside" of a portal because the whole point is that the inside of the orange portal is what's on the other side of the blue one?

I always looked at it like option A, the cube does get momentum, it moves out the exit portal with the same velocity the entry portal moves over the cube.

I'm glad I was recommended this video. Here at 135 views.

It has to leave the portal at the same rate it enters, ergo if it enters quickly it has to leave quickly, simple as that, doesn't matter why it enters quickly, ots relative,

You could make the math work I think, but in my mind the side effect would be the relative mass of the portals would be linked to the mass of the entire universe, since that's what you're effectively bending around in the higher 4d space, So very very very hard to move portals, potentially, depending on how those 4d forces translate

Dude's got a random 20k IDR stick to the wall as background lol

Can I talk about the paper analogy for portals for a second? Because nobody talks about how anything going through one end would be flipped over because the paper is folded. Or in 3d it would be like the persons right hand became their left and left hand became their right while to their perspective the entire world would be flipped where normally a right turn around a corner would be a left to them. This isn't even to mention how the chemical structure of their bodies being chiral in nature means that when they come out the other side, normal food becomes toxic to them as their bodies aren't able to process molecules with an opposite turn. This could potentially even be a worse problem if for example sub atomic properties turn out to be flipped as well. Things like the polarity of light or spin of an electron might be massive issues to contend with. Or they might just be innocuous. Not exactly sure what the spin of an electron determines or if it's considered chiral at all and if so does it have a significant impact on chemistry. In conclusion: be extremely careful how you fold your space in your portal demonstrations.

I do have to question though, what if both a or b could be right? We assume that the manifold is perfectly flat, what if the manifold is bulbous on one side? You may argue that there is no difference between one side or the other, but I think it’s fairly reasonable to say that if the cube doesn’t go through the portal, the cube does not get accelerated. Also, if you have portals at different angles, “down” (gravity) will be quantifiable different between one side and the other, thus implying that there are separate sides.

"Portals cannot exist if they do not move in tandem" Is this based on the argument that time dilation causes wormholes to become time machines, and therefore they're not allowed to move relative to eachother? Otherwise, my search-fu is failing me (but I did find an interesting article about how one particular geometry of wormhole inevitably becomes a time machine over time)

you jump, the entire world falls down from below you, then rushes back up to hit you, why doesnt everything start flying up when the world suddenly stops? the portal lifts up, the world falls, then the world rushes up to hit the portal, would the cube fly upwards through the portal? or will it have no momentum relative to the world like everything else?

I think with the way theyre presented in the portal universe, there is some sort of singularity within the portal and nothing should ever pass through it because its just breaking the laws of physics entirely. Really, there should be some amount of space in between the portals that is not outside of either portal, ie a wormhole. If we think about it as a wormhole, things like the slinky analogy start to make more sense, though I think even in that analogy it should move through rather than get stuck. If its a wormhole and there is some amount of space between the portals, then as a portal moves over a particle, its moving the space between as well. It could be growing the space, like a slinky though maybe there are ways for the distance to be constant and very small, but im not entirely sure it matters. Either way, some amount of spacetime, and all the associated quantum fields, including the Higgs field which gives inertia, are moving around the particle. Since the inertia giving field is moving around the particle and it wasnt before, the inertia of the particle should resist that, but its stopped by the normal force of the platform, so it moves through the portal. It should then take some amount of time to navigate the space in between (no doubt rotating to the new orientation), before exiting with the same speed it entered at. At the very least, the box should start moving through the portal with the same entry speed as the descending portal. Either it will get stuck as there is an impossible singularity between the portals, or it will travel through with the same exit speed. This is of course ignoring the fact that any wormhole would surely generate gravity like that of the singularity at the center of a black hole, right? So really it should just BE a black hole.

The portal problem was also solved pretty well by this guy btw: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-ao1qVi5Qp3Y.html His equation for how it works is pretty simple

Now here's another question: What if you have one of the portals really close to a black hole? If portals are affected by gravitational time dilation (which, why wouldn't they be?), then after some time one portal should be in the future while the other should be in the past. Would it be possible to use these portals as a time machine, or would going through the portal in the future to the one in the past transport you to an alternate universe

It is clearly option B. If the object traveling through the portal changes in energy then that energy is provided by the portal gun. If the object changes in momentum, then that momentum is transferred to something else, presumably all other matter which exists.

The actual answer to the paradox is that the portal breaks when the platform starts moving, causing the box to be crushed between two mundane plates. Portals can't be on moving surfaces and shut up about Neurotoxin Sabotage.

put a can on a table cut a hole in a wooden plane slam the hole over the can the can doesn't shoot out the top of the hole, does it? it just stays still while the plane moves same thing

7:20 notice how to orange portal stops moving exactly at the same time the pillar stops moving. maybe the pillar is sort of "on top" of the orange portal in some way?

What happens if you drop the portal half way onto the pillar? Does it get pulled through into space?

Portals are just holes IMO, after all, to know what would happen, just cut a hole in a wall, smash the wall onto a cube, the cube wont come out the other side magically because nothing is touching the cube, a hole is empty space. Nothing can truly touch at a molecular level, so some part of the cube wouldn't be inside the blue portal, but, let's say we're on gravity 0, you smash a portal agaisnt a free-floating stationary cube, the cube would come out the other side, but would have no extra momentum, there's no way that for a empty space to transfer something.

option z it stops and nothing goes through

“You can’t give it momentum without it having a force” hmm what an interesting concept. What if, let’s say, there was something that could give it momentum without applying a force. Purely hypothetically. Let’s say it bends spacetime or some bs like that so that its lack of movement becomes movement. Maybe it changes the angle of the spacetime axes such that the temporal velocity of the cube becomes slightly transferred into spatial velocity. What if. What if we called it something like, I dunno, GRAVITY

i'm not smart in physics, but wouldn't the cube get teleported through the orange portal, and fall through the blue portal immediately because the portals don't add momentum, but gravity would technically pull the cube down, right? feel free to disprove this.

this again?

What you said around 17 minutes in is EXACTLY the reason why I think the way you do. You know the classic reference frame explanation about an outside observer looking at a train where a kid dropped a ball? The observers within the train can't tell that the ball is maintaining any momentum because it doesn't launch forwards at the speed of the train from their point of view, to them it just looks like it falls down and that's that. But from an outsider's perspective, the ball just kept flying in the same direction the train was going. It maintained its momentum. The same thing applies for portals, only that, since we're suddenly changing directions, the effect is the other way around, and now the inside observer is the one that can tell that they are conserving momentum, while the outside observer would simply see someone breaking the laws of physics. It is so disheartening to see so many people pat themselves on the back and act like they are geniuses and dismiss thought experiments such as the one made in this video, when they themselves are trying to justify an option that simply goes against the most basic of physics that one should have probably gotten a hold of at highschool at the very least... feels like reference frames are too hard for some people to understand. Also, the thing about the cube having 2 velocities could also be understood in different ways depending on how we're thinking about the cube. 1) the cube is 1 single rigid body -> Then, we could think of the 2 "different" velocities as 2 measurements of the cube's velocity made with different reference frames: one on the orange portal side, and the other on the blue portal side. 2) the cube is composed of 2 sections of mass of a rigid body affected by different forces / 2 rigid bodies that are connected, each of them being on either side of the portal -> Then, the 2 velocities could be thought of the same way, but on top of that, we would also have to account for different forces acting on the body of the cube, for example, how does gravity affect the cube when it passes through the portal? If we imagine the 2 portals being close together, for most people it might be harder to realise that this poses a problem, but, the vector of the force that gravity acts upon the cube is different from each other from the point of view of the other side of the portal. 3) the cube is composed of particles -> same as options 1 and 2, only that now it becomes extremely apparent that there is a gradient of forces going on here, which would mean that even if the option where the cube plops out the other side were to be correct, the cube would start moving to the side and accelerating upwards from the point of view of the platform side, because on the side where it comes out, it's already starting to be affected by gravity and hitting the edge of the portal as it falls to the ground... which would then prove that the option where it flies out is the one that makes most sense, as the portal DOES allow the cube to conserve its momentum, it's just harder for an outside observer to realise this. In short... reference frames and relative velocities are very important... and that's why option B is the more correct one out of the 2... or better said, the least wrong one... if we account for any other options tho, both are clearly wrong, but with the level of physics and intuition given in the game, it is safe to say that option B would be the most likely in the universe of the videogame Portal. As for your final take, I am not too sure, we don't really know what could happen, but I guess that having played the game for so long has made me biased to feel like a derivative of option B would be the most correct. The idea of the cube not coming ever out on the other side of the portal feels correct as well, but something inside of me wishes that it would actually come out just like in option B lol. And all of this is not even accounting for relativity, which, by adding a small pinch of it, it all adds up nicely and quite elegantly too. In any case, the people supporting option A think of themselves to be more scientifically correct than those that support option B, or any of the other also probably valid options (again, as you said, we're working with something that breaks the laws of physics so yeah...), all the while also supporting for ideas that go against the laws of physics, all so that they can justify option A... conservation of momentum? broken. Reference frames? broken, apparently they think that there's some kind of "global" or "universal" frame (as if we were in a videogame lmao). Relativity? Also broken. As you said, this is a problem of science communicators. They dumb down things to the point where they actually start causing misconceptions.

portal cant move like dead grandparents so answer c

Ok you can easily prove b is correct you just gotta make it more clear to people put the image of the upside of blue portal transparent on orenge and move em smooth with the camera attached to the block I actually gonna do it just give me a sec

Sorry to break it to ya, the paradox has already been solved, by James Lambert.

8:11 I actually laughed

Bro I've already watched this video but it's 9 days old WHAT THE FUCK

Remember me when ur famous

If you think of a similar scenario, where the input portal is stationary, and the output portal is for example on the wall of a moving train. A: If you instantly gain the momentum at the output portal, then you can step through onto the train. B: If your momentum is conserved, then you will get sliced up and splat against the back of the train. Since it's nearly impossible for the in and out portals to have identical linear and angular velocity relative to some universal reference frame, then in case B portals are basically guaranteed to kill you. So I pick A. This is the same as case A in the original scenario, since the stationary cube gains the momentum of the output portal, which is also stationary.

I wonder if the people who made this problem ever played the game

Regarding option A: The cube doesn't have any starting momentum. The cube enters the portal, comes out the other side positioned on a slant with respect to its original starting position, meaning its effected by gravity and falls/slides onto the floor. Its literally that simple.

I feel like youre arguments are all valid but are expressed realy badly and you pretty much have to assume the viewer already understands all of them before you explain them.

Spoiler question: So if that's the case and you don't come out if one portal is moving relative to the other does that mean you will when they both move in tandom? Like the slinky? Or are you trapped in it forever? 🫣 (Obviously it's not real so I'm asking opinion rather than for a real answer lol)