1: Put two portals on ceiling 2: Put a cube half way through 3: Gravity pulls on both sides equally therefore the cube doesn't fall 4: Profit

There's only one way to address this issue: _Portal 3._ _Which in itself will cause a paradox because Valve don't count to three._

my physics teacher (slightly suggested by me since we were both gamers and I was the one who provided him a copy of the game to play) used Portals related lessons several times to explain concept like inertia or the meaning of accumulated and static momentum He used this problem in one of his lessons, and was the funniest one imho, since the class was very interested in this problem and came up with a lot of solutions for both option A and B

Years ago, I was trying to program a small 2-D platformer game that had a mechanic where a user exiting one side of the screen would reappear on the opposite side (same with top to bottom). I tried adding an extra mechanic where the user could resize the game frame to solve puzzles and I ran into this same question. I realized that I had accidentally backed into creating a Portal style game in 2D with moving portals. In terms of physics, the proper answer is that the object leavers the exit portal with the speed and acceleration it had RELATIVE to the entrance portal. And that speed and acceleration is relative to the exit portal (not the environment). While it makes for an interesting thought experiment, it creates a lot of problems for a programmer. For example, if the user is shrinking the game frame, the portals are moving toward each other. An object entering a portal gets a speed boost from both the entrance AND the exit portals (because they are moving toward each other). If a user allows the player to go through the portal several times while shrinking the screen, the user will accelerate each time, until the player is going so fast that the frame rate of the program can't keep up. This creates weird problems with the collision engine (player is moving so fast they pass straight through solid objects) and the rendering engine (player is moving so fast that it creates an optical illusion where it looks like they are moving backward). After breaking my brain on this for a while, I realized why portals really aren't allowed to move - it creates physical possibilities that are impossible to replicate with a computer. I ended up abandoning the project because the physics was not something that could be simulated with a computer. I'm guessing that the developers of Portal had these same issues, which is why the portals can't be placed on moving surfaces.

"The portals never move" *Cough cough* neurotoxin generator *cough cough*

"Speedy thing goes in, speedy thing comes out."

if a portal in this game's rules, as I have understood, is in a surface and it starts moving, the portal disappear instantly

Consider what you would see looking into the exit portal. You would essentially see the ground pushing the cube out of it. When you think about it like that, it seems like it would have to be relative to the object and the entry portal.

Aperture Science wants to remind you, that you can't put Portals on moving walls. Thanks. Edit: "Could you guys stop commenting the same stuff on my two year old comment."

To quote GLaDOS from Test chamber 10, "Momentum, a function of mass and velocity, is conserved between portals. In layman's terms: speedy thing goes in, speedy thing comes out."

The portal, in my opinion, would behave as if the bottom platform was pushing it into the portal, since the platform moving towards the portal, and the portal moving towards the platform are essentially the same thing in this context.

Assuming that portals are only windows as seen in the games, the only force applied on the cube to move him is the gravity force at any speed of the orange portal

I think this paradox is the entire reason that Valve implemented a "no portal on moving platforms" policy except for one exception where it would be impossible to put an object through it

"speedy thing goes in, speedy thing comes out" but what if speedy thing was never speedy? [queue vsauce music] what if, instead, stationary thing goes in speedy hole: does it come out the other fast or slow?

i have watched this video a dozen times in the past 3 years and my answer changes every single time

I always thought of the portals as gates or doors. Normally stationary you walk through one side come out the other. If a door frame is throw thrown at you yourself won't gain any momentum from that. Also my problem with B is, you don't have any momentum to start with even if a portal is moving at you fast and slams down on top of you you should still be standing on the same ground so what force will pull you up.

My science teacher used portal as an example to explain this and he played it for us as well which is super surprising

I rule in favour of Option D. When the stationary object is consumed by the portal, the source engine crashes.

I think we could measure speed relative to the environment and still have B happen in a game if the teleportation takes both the object and portal's speed relative to each other into account. For instance, if cube and orange are both moving towards each other at a speed of 1, then cube exits blue at a speed of 2, but if both are moving in the same direction, then if orange is faster than cube, then cube would exit blue at the speed of orange - cube. The same thing would then apply to the speed of blue relative to cube. If blue is moving forward, then cube exits at its new velocity plus that of blue.

What stationary cube people are missing is that they're perceiving the cube as the fixed point in space here, when in reality you should view it as the opposite. Portals are effectively an infinitely expandable fixed point in space, where the entrance "percieves" space at a fixed point relative to it when it's moving (despite still being a fixed point in space), and the exit has the space from the entrance moving relative to it. This is an important distinction. To the exit portal, the floor in this case is launching the cube at the same speed the entrance portal is moving. If the second portal is moving away from the direction the floor is moving relative to it, it adds to the speed of the launch, as the floor will still be coming towards it at the same relative speed no matter what the portal is doing, but it is also moving relative to the object through it. The floor effectively gains the speed of the exit portal, causing a farther launch. This is also why if you put two portals on opposide sides of a wall and move them both past the object, its effectively no different than cutting a hole in said wall. The second the entrance portal stops is the second the cube launches. No different than a catapult. Obviously there would be some weird gravitational stuff involved as one part of the portal would be feeling gravity at a different point to the other initially, but in a space without gravity this is how it would work. If you have it stop half way down the cube, the launch would likely be half as powerful as well, as only half of the cube is moving relative to the exit portal, while the other half is stationary relative to the entrance portal.

I feel like Henry just tackled this century-old paradox because he just bought it from the Steam Summer Sale lmao

Everyone should play portal once in their life. Such a great game

another option is that if an entry portal moves then the exist portal has to move at the same speed. So the speed should be relative from the portal to the object itself, I think of portals like tubes or rings which are the same, the only difference is what is bigger the length or the diameter.

You remember that game, hole in the wall? The things passing through the holes didn't push the objects unless they clipped the side of it. The way this boils down in terms of portals is simple. 1. The portal is moving down, meaning it presses into the ground which moves the location but adds 0 velocity 2. The portal is moving sideways, and since it can't be an open shape the bottom of the portal, however small, pushes against the object. With a small enough gap between the edge of the portal and the ground, the object would be picked up slightly since it's easier to lift up then be pushed.

0:16 the technical term is "Speedy thing goes in, speedy thing comes out,"

Minutephysics: the portal para- Me: *Speedy Thing Goes In Speedy Thing Comes Out*

А вы преставьте порталы в качестве дверной рамки. По сути портал это и есть дверь. И вот представим: лежит объект на поле и на него падает дверная рамка, что произойдёт? Дверная рамка упадёт на объект, а объект продолжит стоять на месте как не в чём не бывало. Так почему если бросить на обьект портал, он должен вдруг из не откуда получить скорость? Портал это дверь ведущая из одной точки в другую, ваша дверь в комнате, ведёт из комнаты в коридор, а падающая рамка на объект ведёт объект в одно и тоже место. Но портал позволяет вам появится а другом месте с теми же характеристиками. Если бы портал имел какое-нибудь гравитационное поле, то да, я бы поверил что вылетить из портала будет возможно, так как он вас своей гравитацией вытолкнет, но без гравитации, там нечему вас выталкивать.

In my opinion, Scenario A seems the less plausible. Portals connect two points in space without creating any new space. Therefore, the time it takes for an object to enter one portal should be identical to the time it takes for the object to exit the other portal. So, if an orange portal moves slowly towards an object, than that object should also emerge slowly from the blue portal. Similarly, if the orange portal moves toward an object at like Mach 10, then that object should theoretically exit the blue portal at an equivalent velocity. The velocity of the object relative to the portal has to be preserved so that the time between entering and exiting the portal stays consistent. If it doesn't, then where would the object momentarily exist? Given that portals don't create new space, just connect existing spaces, the relative velocity at which an object enters a portal should dictate the velocity at which it exits. Since the object exits with a certain velocity and has mass, it would also possess momentum, thus it would result in Scenario B (or maybe C). The only way Scenario A could work is if the portals somehow momentarily changed the mass of objects as they passed through, but that just feels like making up rules. Thoughts? (note i am not an expert in physics or anything so my reasoning could be wrong.)

Minutephysics: It depends whether you think more like a programmer or more like a physicist. Me, dual majoring physics and computer science: *Visible confusion*

Portal right now costs 0,81€ on steam. This can't be a coincidence.

Actually there are moving portals in the game, you shoot one at the moon, the portal on it then moves quite dramatically with respect to the portal left on earth. And that also proves that velocity is seen relative to the entrance portal, not environment or a combined system. :D

Any one who argues for case A seems to forget a fundamental thing here. Even in the worst case scenario. The first part of the cube, the top, goes through the portal. And then the rest of the box pushes it through, giving it some velocity. The way by which you go from orange portal to blue is irrelevant Think of the situation at the destination, static portal. Thing comes out at speed. Just because it was standing still before the moving portal hits it doesn't change that It's moving on the exit side. And will hold that velocity

Moving portals should be in portal 3. But that will never happen because valve can't count to 3.

The portals aren't teleportation. It's just making a continuous space where there normally isn't one, it's no more teleportation than you walking into your kitchen.

Quite frankly, A makes no sense at all unless you only think of the (impossible) case in which the entire solid object instantaneously moves from one side of the portal to the other. I've always arrived at B by imagining what happens while the portal is in the process of moving over the object. While this is happening, the object is presumably emerging from the out-portal at the same rate that the in-portal is traveling downwards. If this is the case, then the particles composing the object ARE moving with momentum through the out-space, unquestionably. And there's no reason that they wouldn't retain that momentum as the object finishes emerging. Another way to think about it, in light of your example at 3 minutes, is that those slices DO appear on the other side, unmoving, but the next slice is right behind it and pushes it forward... which just produces the same effect as B. Or, if you assume that the slices don't retain their bonds and can't affect each other when on opposite sides of the portal, then they're just going to become a soup of particles trying to occupy the same space. (Though, since characters never have to consider the risk of being cut in half by going partway through a portal and then stepping back, I would assume that atomic bonds do hold.) There's no model in which an object can emerge from the portal both intact and without momentum. The option are B and disintegration. A much simpler example that indicates why it's B is this: Consider what would happen if the box were sitting on a tall pillar, narrow enough to pass through the portal. The portal passes over the box, and the box is now on the opposite side, but so is a portion of the pillar. As the in-portal continues to go lower, more of the pillar emerges from the portal as well, pushing the box diagonally up and to the right. And then, if you stop, the box is going to go flying in that direction. (this is essentially the same thing as what happens in the box-only case, just on an object scale rather than an atomic scale)

My interpretatios is like this: You are standing on the ground in universe A. Universe B is on the other side of the portal, facing up. The portal comes down on you at 5mph. You emerge from the floor of universe B at 5mph, driven by the floor in universe A. You don't pop up, because universe B hits the ground of universe A once you are fully emerged. Or if it kept going, a cylinder of ground would continue to rise up out of the portal. Like using a hole saw. Universe A and Universe B are in fact the same universe, but I think this is consistent with how the game works, and makes sense from a physics perspective. It's kind of like slamming a cup down on top of a spider to catch it. The spider enters the cup real fast, but doesn't continue heading up until it hits the base of the cup, because once the cup hits the ground, the speed of the cup quickly matches the speed of the spider.

"It's a paradox, there is no answer!" ~GLaDOS, 2011

Maybe this is why you can't have a portal on a moving object.

For some reason this made me think of the portals like slinky's. And I'm just imagining moving the portal onto a stationary object the sane as dropping one end of a slinky over a stationary object. Now I'm wondering what the environment inside of the portals is like. I'm sure none of this would match up with theories of wormholes, teleporters, or quantum tunneling larfe scale objects but my brain went there

Thank you for making this video it was very cool 😎

I always thought of them as a ring that was split. Teleportation is like putting a ring around something else, but this coming out of the ring is placed different in spaces. As if it was a tunnel with the length of 0.

Aperture Labs uses quantum tunneling if I remember correctly whereas Black Mesa was dabbling in wormholes

"how could a stationary object come out of a stationary portal?" That's the answer! The portal is not stationary. You treated the two ends as separate things, but they are the same points in spacetime. The thing is... The orange portal acts like a moving camera, and the blue one as the screen you see the footage. If B was correct, than you're creating a force from nowhere

In relativity, there is no absolute motion (as was mentioned) which means the notion that the portal is moving is exactly as valid as saying the cube is moving and the portal is stationary. Thus the behavior of a cube moving into the portal is EXACTLY the same as the portal moving towards the cube. Since we know the effect of a cube moving into a portal, we know the effect in a hypothetical 'real' world where the portal is 'in motion' would be identical. Consider a portal that is stationary and a cube passes into it... We know the effect. Now consider that the portal is sitting on the back of a truck that is in motion and cube is stationary.... Then consider that the truck is on a rotating planet.... and so on and so on. At no point will you ever discover a fixed point. Motion is relative. The only thing that matters is the motion within the frame of reference.

Quote by GlaDOS: "Momentum, a function of mass and velocity, is conserved between portals. In layman's terms, speedy thing goes in, speedy thing comes out."

According to GLaDOS in the first game: "Momentum, the function of mass and velocity, is conserved between portals. In laments terms: Speedy thing goes in, speedy thing goes out". Since the object enters the portal with zero momentum, we must assume it leaves the portal with the same momentum. Thus, the correct answer, according to GLaDOS, is option A

The reeality is I think A, but what we perceive is B because the estra bits that try to make it through the moving portal shove bits that already made it through out of the way. This results in no pancake cube.

197 is going WILD on this paradox

*Minutepsysics:* Let's talk about Portal Paradox which isn't actually a paradox... *Me:* That's a nice paradox.

Valve: Portals can't move Also valve: Let's use moving portals towards the end of the second games

The way it would work is option B. The portals canonically are trans-dimensional, so they open up holes to other dimensions, not the same dimension. It's just lucky there's an infinite number of imperceptibly near-identical dimensions. It's important to note that the way the game is programmed and the way the portals function canonically are not the same thing. In fact, it might've been even easier to code if they'd thought about the way option B explains the mechanics of trans-dimensional gateways. What the portals actually do is as follows: The entry portal changes your velocity relative to the exit portal. That is the simplest way to think of it. The way to imagine this in practice is to imagine a cube (say, a companion cube) is sitting perfectly balanced on top of a long, thin, metal pole. The entry portal flies down over the cube, and because the pole is thinner than the cube, the portal slides down some of the pole, too, before suddenly stopping. If you were observing the exit portal, you would see the metal pole spear out of it with the cube at its tip. The pole would appear to be thrusting the cube through the air until the pole stopped moving (at the same time the entry portal stopped), but because the cube isn't attached to the pole it would fly off, maintaining the velocity the entry portal gave it relative to the exit portal. The only reason the pole doesn't fly off, too, is because it's firmly attached to something that can't fit inside the entry portal (i.e.: the ground) And the velocity achieved by the entry portal isn't fast enough for the mass of the pole to tear/break itself when the portal stops. (Theoretically, if the portal moved fast enough and stopped fast enough (read: instantaneously), there is a speed at which an object would simply rip itself apart and fly away from the exit portal with its newly-imparted velocity.) If you think it's option A, your brain doesn't work right. And option C or any other option ignores how the portals canonically function. Option B is the only result that makes any sense. I think the more interesting question to all of this is: How could you utilize the imparted velocity to do fun and interesting things? For example, if the entry portal only moved partway down the cube and then suddenly stopped, how fast would it need to move and how much of the cube would it need to transport before the mass and velocity of the cube on the exit side were enough to lift the cube off of its platform on the entry side?

Option b makes the most sense to me at first blush, but the saddest thing about portals is that they /can't/ obey conservation of energy, so it's all kind of moot. This is exemplified by the what happens when you place a portal on a floor and a portal directly above it: anything that falls through the floor effectively has infinite potential energy.

Portals don't work on moving platform... Except for that one time in the neurotoxin generator room

2:17 and considering Valve themselves have referred to the portals as “quantum space holes” in some promos for Portal 2, this is _the way_ the portals work.

Nice video man!

C: it would shoot out of blue at a angle because the cube is traveling at x velocity downwards while the portal is moving at y velocity left . Let’s let x and y equal 3 and you have the cube moving 3 velocity downwards and 3 left, and since the portal would flip the velocities it would travel both directions at 3 velocity. (Up and right) Also we use pythagorean theorem to solve the velocity which would be 3^2 + 3^2= c^2 9+9=c^2 18=c^2 √ 18=x x=3√ 2, so the velocity of the cube was 3√ 2 N theoretically

absolutely no one: minutephysics: lets give this old paradox that the internet has argued about for a decade another step of complexity

But GLaDOS already answered that. "In layman's terms: Speedy thing comes in, speedy thing comes out."

Thanks for that final puzzle you left us with. I WANTED to sleep tonight but now…

If you imagine the portals as infinitely short tunnels, you can expand the concept to a general case for all wormhole-like pathways. When you slam a tube down around an object, the object doesn’t gain momentum through the tube; the motion of the object relative to the tube is entirely dependent on the tube. In this way it can be argued that case a (plopping out on the other side) is the resolution of the paradox. On the other hand, if you consider the portal as comparable to a hand coming down around a wet bar of soap, an argument can be made for case b (object goes flying). When you grab a bar of soap, you need to exert force upon the bar as you grip it. This force commonly and easily launches the soap out of your hands, in spite of not adding any apparent momentum to the soap. The energy gained by the soap is sourced from invisible interaction between the object and the passage it travels through (in this case, the hand). This argument, essentially, is that one cannot actually pass freely through a portal which is in motion. In order for the object to gain speed as it passes through the portal, the portal itself would need to be exerting some force on the object (otherwise the object would remain inert, according to the generalized case of a tunnel of arbitrary length). Either a moving portal “squeezes” objects passing through due to some unseen interaction between the membrane/field of the portal and said object, or the object does not gain momentum. Put into terms of energy, unless some unseen mechanism transfers energy from the moving portal to the object enveloped by the portal, it’s impossible for the portal to cause the object to accelerate. Yet another example would be jumping through a window on a moving vehicle, without touching the frame of the window, while the start and end point of the jump are both stationary from the perspective of the person jumping. The properties of the vehicle don’t matter - it could be a bullet train loaded to maximum capacity, or it could be a bike meandering through a neighborhood. From the perspective of the person jumping, all that changes is which side of the window they occupy. In order for the person to fly like a rocket out the other side of the window, the vehicle would need to transfer some kind of energy or momentum to them. Barring some kind of novel discovery about topology or vector addition, I feel like this one isn’t toooooo hard to suss out. But then again I dropped out of college lmao

I'm surprised you didn't mention gravity. The block sitting experiences torque as soon as it begins to pass through. It should exit the second portal with rotation.

In the games, the portals disappear if placed on a moving surface. Which can be explained by the logic that portals must remain at a constant distance and orientation from each other.

It depends on why the moving portal is moving, is it falling under its own weight or is a force being applied to it? Energy conservation says that for stationary portals the kinetic energy of the cube is maintained (speedy thing goes in, speedy thing goes out) so logically this still applies to a moving portal, the energy being used to move the portal over the stationary cube is added to the kinetic energy of the cube. If a very strong piston pushes the portal over the cube very quickly, then the cube will shoot out of the other end quickly, if the portal is falling with a weight of just a few grams over a cube that weighs much more, then only a very small force will be applied to the cube, and it will just barely plop out of the other end. In fact, if the end portal is angled upwards, then there may not be enough energy being added to the cube for it to fully emerge from the other end. There is no paradox as long as you understand the rules as explained in the game, the paradox only seems to appear if you fail to fully understand what is going on.

Portals are just sort of like portable space; the game calls them interdimensional doorways or something like that. The cube in this situation isn't moving, but rather, space is moving around the cube, if that makes any sense. It would obviously be option A. If the cube itself had velocity, i.e. it were thrown through the portal, obviously it would retain its speed relative to the environment since it's akin to just throwing an object through any old space, like a doorway.

Option D. : When a portal move its just disappear

All I wanted to do was play portal, not question the exsistance of universe. But I'm glad I did.

For option B, what happens if the portal stops moving halfway across the object? Does the object get pulled through since half of it now has a velocity but the other half doesn't? Would objects get ripped apart if the speed is too high?

Bro left us with more questions than the beginning

"In the game, the portals pretty much never move relative to the environment." Boom. Problem solved!

2:40 the ground gets closer to the portal The cube on the other end is affected by gravity I imagine it like a box going through a hoop If I drop the hoop onto the ground the cube is just in the middle and therefore on the other side of this hoop (other portal)

I believe option A makes the most sense as the cube has no force applied to it when it enters, which means it has no force on the exit, creating no velocity. It wouldn't pile on itself either as moving the orange portal closer past the cube would in turn change the position of where the rest of the cube is at the ends of the blue portal.

All these questions are easy to answer if you always consider the reference frame to be the portal closest to the cube (or part thereof). When you do this the calculation becomes deceptively simple; 1) calculate the forces acting on the portion of the cube still on the orange side of the portal (if any) 2) calculate the forces acting on the portion of the cube on the blue side of the portal (if any) 3) sum them to determine the total force acting upon the cube as a whole.

Physicists: Valve what will you do about moving portals? Valve: We'll make them disappear if they move. Physicists: Surprised Pikacu face.

I love that 12 years later were still talking about Portal

I never conceptualized Portals the way Stargates are (eventually) explained. Portals are physical "holes" connecting one space to another - no intelligence, no deconstruction and reconstruction on the other side. If one portal is pressed against a wall, it doesn't cause anything entering the portal to be destroyed on a subatomic level on the other side - it just means you bump into the wall at the portal's boundary. [Stargates intelligently deconstruct any person/object entering the event horizon on one side, and reconstruct them on the other side, employing complicated tricks to (mostly) give the object the same relative orientation/speed/physical condition as when they entered, erring on the side of safety when necessary - they were, after all designed to transport people. Nothing can be partially on both sides of a Stargate pair. The major exception (which may have been by design explicitly for defense, and discovered very early by SGC) is if a barrier is placed extremely close to the event horizon, the connection can still be made and the origin gate will accept "passengers", but the receiving gate, though operating, can't reconstruct them in the space available.]

The literal term for portal is a doorway or hole between two places, if you have a moving door, your speed relative to it will stay constant

In the game, GLaDOS explicitly points out "how the momentum is changed [when going through the portal], or more precisely how it is not" in a situation where portals are perpendicular to each other. I find that difficult to interpret in any way other than "B", that is, momentum is maintained, but frame of reference is shifted (and rotated) from one portal to the other

It plops because the object does not have momentum. It would work as a visual truck, where the object quickly appears, but does not have velocity. Then, gravity will still take effect, and it will slide down the metal platform thought the portal, and fall on the floor as if it were set there normally.

Portals act like a door between 2 different spatial locations, it was stated at some point... So imagine an open door falling around you. Case A : Nothing happens as you pass through and you can walk over it. Case B : You're very confused as you realize you've been catapulted through the air at the same speed the door was falling even though it didn't touch you at all so any transfer of energy should be impossible.

Answer to the bonus question: If the portals were like 3D printers, the cube would come out slanted.

‘Depends if you think like a programmer or a physicist’ But when you program video games you have to think like both 😭😭😭

Imo it's option A, unmoving object will still remain stationary at the exit. Reasoning : portal is not a phisical thing, it's hole in fabric of reality, it doesn't affect object in any mean other than make it reapear elsewhere, so the only difference portal's speed would inflict upon object is that it reapeared faster, it didn't moved, it just begin to be in a new place. Regarding example from 3:00, I find it hard to explain without image why I disagree with it, but I'll try my best : A stationary object would reapear layer by layer, as you shown, but they wouldn't be squished, they would emerge out, but right after they would do it completely, they would stop. Object wouldn't have kinetic energy or velocity, movement would illusin made by rest of universe shifting to make space for it. Imagine flying ball that has 0 velocity, it just is hanging in a place. If you would throw hoola-hop thrue it it wouldn't make ball faster. Honestly, this ridle is less about logic and phisicsand more about how you understand a portal, in my reasoning why I disagree with 3.00 i explained it in a way that makes stationary portal both being and being not in motion, in example from 4:00 there are several ways cube could go out, diognally beign one of them.

I think the solution to the last puzzle would be the cube come out diagonally. The way I thought about it is with replacing the cube with a pole. If you put a pole into a stationary portal that connects to another stationary portal and move the pole along the axis parallel to the portals it will move on both sides. Now imagine if you put the pole in at one far end of the moving portal, that end of the pole would emerge out of the far end of the stationary portal, and if you imagine that the pole is the correct length that its end would enter the portal in the time it takes for the portal to move its own length. that would result in the end of the pole entering the moving portal and exiting the stationary one at the opposite end of the portal than when in entered, giving both vertical and horizontal movement which means that a pole would exit diagonally, and everything should work the same way with a cube just over less length making it less noticeable

"THIS. SENTENCE. IS. FALSE! don't think about it don't think about it" That's the true Portal Paradox

Who feels like he wants to go and play portal again after watching this video

This smooshed my brain into another dimension.

Imagine a flat surface with 2 portals connecting one side to the other, this would basically simulate a flat surface with a big hole in it. If you agree that a cube "crushed" by this portal surface would remain unchanged, in the same way it would if "crushed" by a surface with a big hole on it, then you simply have to agree that the cube's velocity is relative to both portals and have to accept scenario B.

Don't look at it like a portal, but like a hole in a wall with the possibility of changed gravity in the other room.

Items are locally measured to the environment. As GLaDOS explains in the game, "Speedy thing goes in, speedy thing goes out"

The thing that makes me cross my arms and say "A" is: how does the cube change from still to moving without making contact with anything? For it to fly out the other side of the portal, something would need to give it energy. The moving platform doesn't touch it, the platform it's sitting on isn't moving, then would it be the portal? Since it perfectly conserves momentum, (aside from changing direction) it shouldn't add or subtract any energy, right? What clinches it for me is shifting my thinking about what the portal does. It's not actually moving the cube, it's shifting where the cube is. Yes, a fast-moving portal will cause a cube to appear out the other side quickly, but that doesn't mean the cube is moving quickly, just that the portal's plane of "being somewhere else" is passing over it quickly. It quickly changes from gravity pulling it in one direction to gravity pulling it in the other direction. Also, the moving platform's energy dissipates into the stationary platform.

I would assume that it would plop out, and not fly out, because imagine the portal as a ring/hoola hoop, it just has a distance between the entrance and exit, a box that has a hoola hoop slammed down around it DOES NOT send the box flying up, it stays there, without momentum, therefor, in should be the same scenario if there were portals to do it with.

Yes, but consider this: *PERPENDICULAR UNIVERSES*

Speedy thing goes in, speedy thing comes out.

I'm gonna comment this before watching the video so that any conclusions there don't influence my initial conclusion: Considering the portals are basically just the shortening of a gap between two places (like if a tunnel were squished into a door), I think of it like this: since the orange portal is moving quickly towards a solid surface, it means that the object on the surface (the cube) will pass through the portal quickly, but since the cube doesn't have any momentum itself, it just plops out the other end after the gravity changes. Imagine the cube is attached to the floor, and when the gravity changes from the orange portal pushing over it, it becomes detached from the floor and plops out. It's not actually attached to the floor of course but that's, I think, a good way of visualizing it since it achieves the same result

Speed is indeed relative. If two cars moving at 60 mph collide head-on, the resulting impact is as if a car moving at 120 mph hit a stationary car. That said, any object colliding with a portal inherits the speed of the object relative to the portal. This would include angle of attack speed, so to answer your question at the end, an object dropped into a portal moving side to side would come out the other portal at an angle and at a velocity greater than the acceleration of gravity would dictate, as the velocity of the portal would be added to the velocity of the accelerating object. Also, the whole speed is relative thing is why I firmly believe the speed of light is NOT the universal speed limit. Case in point, place two lasers facing each other. Turn them on. The light relative to us is capped at the speed of light (C), but the photons from the opposing beams approach each other at 2*C. Now, take those lasers, and point them in exact opposite directions. The photons are now still C compared to us, but they are moving away from each other at 2*C yet again. Now, imagine you accelerate the laser emitter to C relative to us, and then turn it on facing in the direction of travel. The photons relative to the emitter are moving at C, but relative to us, the photons are moving at 2*C. Finally, let's accelerate both laser emitters to C, but in opposite directions from us (point of origin). Both emitters are pointing towards the direction of their respective travel. Turn them both on. This is where it gets even more interesting. Now, relative to us, the emitters are moving at C, and their photons are moving at 2*C, and the emitters relative to each other are moving at 2*C, but the photons are now moving away from each other at 4*C. Best part is, I don't have a college degree, never took a physics class (wasn't required to graduate high school), and I drive for a living. Yet I have never heard anyone give me a convincing reason as to why the speed of light can't be broken. FTL happens all the time, countless times every day. I see it happen every day at work as cars approach me with headlights on. The photons emitted from my head lights relative to the photons emitted from their headlights are approaching each other SIGNIFICANTLY faster than C. Funny how time doesn't slow down just because two cars are passing each other. If it did, I'd be late to my pickups all the time. Maybe I'm just obsessed with light. "Light" was actually the first word I spoke as a baby. It's always fascinated me, as does speed and physics in general. One can learn a lot through independent study and just by observing the world around them.

There is another option. Both portals are spatially linked to each other and if one moves so must the other. That way if one moves causing an object to pass through it, the other moves as well with the object exiting it while maintaining it's stationary property.

Too many people use the word "paradox" when what they're talking about is a "conundrum" …

I believe you need to look at it from the state of the exiting portal. If the exiting portal is stationary then the object gains the momentum difference of the object and the entering portal. If the exiting portal is moving at a faster rate than the entering portal then the object will follow the exiting portals momentum minus the momentum the object enters the entering portal.

Have you seen the Mythbusters episode where they fire a ball out of a tube at 30mph while on a truck moving at 30mph? The ball appears to remain stationary. Now imagine a cube floating in the air, and two portals are back to back so, they act as if they're not there (as soon as it goes into one portal, it's coming out the other, like the portals aren't there). Now imagine swiping the two portals at the floating cube. The cube would appear to stay in place, which to me, would indicate it's coming out the second portal at the same relative speed it's entering the first portal at, like the ball exiting the tube at 30mph on a moving truck. This is option B, which is against my initial guess of option A.

Shoots out the portal at an angle, again it's relative speed so it's equivalent to it travelling at a angle towards the portal