Its A

and from the reference frame of the cube the portal is moving towards it

in relativity you could just as easily say the sun revolves around the earth, the math would just be way more complex if we account for everything else

in reality this thought experiment is nonsensical

portal does not respect relativism

it's A

"this thought experiment is nonsensical"

said no actually intelligent person ever.

what is imparting velocity in b.

yes
Imagine observing through the stationary portal. You see the cube approaching at the speed that the moving portal approaches the cube.

The piston that moves the portal

>said no actually intelligent person
this thought experiment is literally not possible in any capacity, it doesn't make sense. even wasting time considering it is a sign of low iq

That's why it's a thought experiment and not an experiment. Did einstein go at the speed of light on his bike?

"even wasting time considering it is a sign of low iq"

this is a fantastically low iq thing to say about literally any thought experiment. the objective is to make absurd pointless speculation.

Depends on the made up laws of physics we are using in this fictional scenario. There is no answer that isnt nonsensical if you assume actual physical laws apply

There is no difference between the image in OP and a similar image with the platform the cube is on rushing towards the above ceiling instead. Relative to blue's reference frame, orange is moving at a high speed, and relative to the orange portal the cube is moving. Therefore, relative to the blue portal the cube is moving.

>Portal on a moving surface.

GTFO

Probably. He was a cool guy and doesn't afraid of anyspeed.

Depends on the gravity outside of the system.

Relative to the orange frame, the blue portal and cube are moving at the same speed. So the orange portal wouldn't see any motion through the blue. If the cube were to shoot through at that point, momentum wouldn't be conserved.

From the cube/blue frame (they're the same) it's still a.

So in all cases, it has to be a to maintain conservation.

...

Momentum is not conserved in Portal. It's A.

What isn't a moving surface?

>An empty door frame is shot at you and stops just as it passes you. Do you stand still, or start flying forward for some mysterious reason.

Clearly A.

Only correct answer reporting in.

Portals can't be attached to moving surfaces and should a surface with a portal on begin to move, the portal will dissipate. End of discussion.

All portals are moving in some reference frame. Therefore your premise must be wrong.

You retards are assuming portal universe works like our universe and respects relativism. The existence of portals themselves negates relativity. In glados words "a speedy thing comes in a speedy thing comes out" so it's A.

A surface with a portal that then accelerates, will lose the portal.

So simply shoot a portal onto an already moving platform and you have the same problem.

the part of the cube that haves gone though is moving relatively to everything around it and thus has momentum and is not going to suddenly stop for no reason

the force from the smashing plate would be transfered to the plate under the cube. some of that force would go into the cube sendibg it upwards.
result somewhere between A and B.

OP is dumb.
Also I don't want to sound like a shill but paint 3D is pretty good.

It's B
t. Stargate

If B were true, where would the kinetic energy of the cube come from?

The time during which the cube is on both sides of the portal.

Explain faggot

Just as reasonable as saying it doesn’t reject it; what’s your point? The true idiots are the ones trying to use relativity to explain away the already nonsensical concept of a portal

During this time the cube is moving relative to the blue portal and the orange portal simultaneously. If you ascribe to the separate momentum hypothesis the cube gains momentum by pushing down on it's pedestal. If you ascribe to the single momentum hypothesis the cube only needs to be moving relative to the exit portal to continue doing so after the plates hit.

>portals aren't real so you are an idiot for explaining how they could work in their fictional universe on this thai illustration board.
ok

>reference frame of entrance
>cube doesn't move, room is dropped on top of it

>reference frame of the exit
>cube moves towards exit and exits with speed

>cube gaining an instantaneous velocity when it goes through the portal violates everything anyway

>object is 99.999...% through the portal
>the gravity imposed on said majority of the object does not exist

>object is 99.999...% through the portal
>The object does not continue moving at speed and instead stops and slides down the surface.

who cares, portals aren't real?

>moving

It had no velocity to start with. The gravity causes it to topple and fall down like fig A.

Portals preserve momentum *relative to the portal surface*, not *relative to the earth*. This implies that answer B is correct.

>it had no velocticy to start with
Weird, why is it moving at 99.99% then?

They do not preserve momentum relative to the portal surface because there is no point we can say is THE portal surface.

Put a blue portal at right angles to an orange portal. Which is the surface for which you consider momentum is conserved?

>Which is the surface for which you consider momentum is conserved?
Both, the portal essentially mates the two surfaces regardless of their angle meaning there is a continuous reference frame.
You don't measure the portals separately relative to their positions in space you essentially create two separate spaces on either side of a single portal.

>They do not preserve momentum relative to the portal surface because there is no point we can say is THE portal surface.
It behaves as though there is. That's the whole point. It bends space such that there IS a single portal surface.

>Put a blue portal at right angles to an orange portal. Which is the surface for which you consider momentum is conserved?
The magic "surface" whose front is the blue portal and whose back is the orange portal. Thus, when something moves such 1 m/s towards (and normal to) the blue portal, it will end up moving with 1 m/s away from (and normal to) to orange portal, after crossing the portal.

There is a "surface" with a front and a back making up the two portal endpoints, magically stitched together in a space-bending way. It is relative to this pseudo-surface that momentum is preserved, when something crosses the portal. I can assure you that this is mathematically well-defined, despite my usage of words like "magical".

Your interpretation is at odds with the game. If "the" surface of the portal is a coherent reference frame through some kind of distortion and stitching of space then we should be able to conclude that a moving portal towards a stationary object is equivalent to a stationary portal approached by a moving object (which you can picture by choosing some side of the portal or another). Thus if the motion of the portal could impart a momentum on an object then trying to move into a stationary portal would be equivalent to trying to impart momentum on the surface to which the portal is attached. Therefore from the perspective of the player, trying to walk through a portal on a wall would be like moving the wall.

Which is to say, if a moving portal can move an object, then a moving object can move a portal.

But, this is not what happens. Moving through a portal does not result in transfer of momentum (or, given our horrible space, transfer of speed, to be more technical).

Therefore B is incorrect, A is correct.

ITT: Retards arguing over the physics of a literal physical impossibility.
The only ones who can solve this problem are Valve if they decide to make a Portal 3 featuring this scenario - and the particular solution is completely up to their creative decision.

>Moving through a portal does not result in transfer of momentum
Have you never actually played the game or are you just a moron? The conservation of movement through the portals is the entire basis of of the flinging mechanics used throughout the game.

If a portal can move an object, then an object can move a portal. But this is not what happens. An object going through a portal maintains its motion, it doesn't attempt to transfer that motion to the portal.

A

Interesting. So if I understand your line of thought correctly, if I were to put a piece of drywall on wheels (vertically), and then put a portal on it, and run into the other end of the portal, I would accelerate the moving wall backwards when exiting it? Equal and opposite to my own momentum forwards, with my momentum that I had before making the jump distributed among both?

I think I could agree with that. I don't there is anything in the game to contradict this hypothesis; portals in the game are always attached to solid heavy objects that aren't going anywhere, like walls.

>So if I understand your line of thought correctly, if I were to put a piece of drywall on wheels (vertically), and then put a portal on it, and run into the other end of the portal, I would accelerate the moving wall backwards when exiting it?
If B were the correct interpretation, then yes, this is a consequence. Which would mean attempting to go through a portal attached to a brick wall would be like running into a brick wall. So B cannot be the correct picture.

>Which would mean attempting to go through a portal attached to a brick wall would be like running into a brick wall.
Why is that? I don't think I follow that part.

If the motion of the portal transfers that motion to the object it passes over, then this is equivalent to the perspective that a moving object transfers that motion to the portal. Well, the portal is "attached" to a massive wall, so trying to move the portal is trying to move the wall.

This is the diagram in the OP: the portal is moving because the thing the portal is attached to is moving, and thus the portal is a way to transfer the motion of the plate to the motion of the box in picture B. We cannot test this since the game does not allow us to put portals on moving surfaces. But the equivalent scenario is a moving box approaching and attempting to pass through a stationary portal. If B is the correct picture, this should mean that the portal transfers the motion of the box to the motion of the wall. As you might have some experience with walls you know that this is not, in fact, how the game behaves. Thus B cannot be the correct interpretation of Portal mechanics even in hypothetical scenarios already blocked by the developers.

It's A. The cube never gained any velocity. If the platform were moving B would be true

read the thread dipshit, the cube does have velocity from the moving portals reference.

it's b, even if the individual atoms would be motionless as they passed through the blue portal would be emitting a continuous stream of cube matter at the rate that it moves through the portal, pushing the translocated part of the cube forwards. If the portal would stop halfway through the rest of untranslocated cube would be visibly yanked upwards through the portal due to the other part being set into motion. Anyone who believes that it'll just plop out motionlessly is doing too much simplification, because that scenario makes no actual sense.

>the velocity of the cube is zero
It's been a while but I think the portal does give it a push as it passes through. It's >0.

Irrelevant game play has shown us that portals do not say in place on moving platforms therefore the question is flawed

For any kind of sane physics to hold, the relative velocity of two objects should be independent of the path the displacement between them is measured along. Not only does OP's scenario fail that test, it doesn't even ensure that objects have zero velocity relative to themselves.

This is a computer science question

So is it both moving and not moving at the same time? If the portal stops halfway over the block, does the stationary half just start moving, and go the rest of the way through the portal?

This is the exact same thing
you should all know now

...

>posting picture for the reference frame of the hand (read portal) and completely ignoring the reference frame set on the cube

Path independence only matters if momentum is conserved, which it clearly can't.

Portals absolutely *could* respect relativism, it just means that the portal itself would be expending the energy that is imparted.

Thus, if you had an otherwise stable portal with a limited power supply supporting it, sending too much mass through would eventually collapse said portal (as the energy of it decreased).

Makes sense to my mind at least.

...

>it goes through the portal violates everything anyway

Who said it's instantaneous? Moving a portal would cause a pressure differential on the non-moving exit portal either way. Basically, the moving portal would feel like it's launching a bunch of shit into the non-moving portal. it would feel windy as fuck, and the extra pressure would cause the moving portal to be that much harder to move.

If we assume that the portal itself has power, couldn't the equal and opposite reaction affect the portal itself, which is, due to energy consumption and/or warping of space, increasint the effective mass?

Or... sorry if that didn't make much sense. Maybe the portal can only be on stiff objects because the portal itself is stiff, with respect to space, and absorbs the forces that would normally send it backwards.

Why can't someone test this on portal?
I'm sure its going to be A.

It has to be B. Imagine when the block is halfway through the portal. The portion of the block is going to have to move just as quickly as the orange portal to get out of the way of the second half of the block. That momentum isn't going to just disappear.

Because game physics =/= real physics

Brainlets btfo

Leave it to Veeky Forums to have an 80 reply thread arguing about the physics of Portal in 2018

The hypothetical answer to your hypothetical question is C

oh sweetie

people have glitched/hacked the game to allow portals on moving surfaces. In one case the portal acted like a wall and the box didn't pass through. In another it was unstable, the box went crazy and shot off in some random direction.

Assuming the rocket is moving with constant velocity, A.

why not B?
where does the momentum go if its a?
THE VELOCITY CANT GO FORM X to X-Y
it cant be A it has to atleast be something between A and B the cube has to fly in a parabolic arc

>THE VELOCITY CAN'T GO FORM
haha you sperg
Also portals don't follow relativistic physics, so it's A

The object stays whole the entire time. There is no cut through the object during transfer. There is no momentum to go anywhere. The cube is not moving, and it continues to not move in another spot until gravity plops it down the ramp.

so the cube exits the portal at the speed of 1 cube length/time it takes the moving platform to travel 1 cube length
yes or no?

you should be able to tell this right away

The part of the cube that has already gone through the portal has to move to make room for the rest of the cube.

yes and no
when you look at the picture you see that the platform which the cube is standing on never loses contact and thus stays its reference frame
so you have to imagine its like the cube is glued to the surface of the platform and only when it has completely moved through the portals it becomes unstuck and then forces like gravity can start influencing its state

so we as the observer percieve the cube as moving at some speed but the cube itself never expieriences any force acting on it

Let's just say that when 80% of the cube is through the portal on the slope, we stop the platform above it. Logically, the cube will then be pulled out by gravity as its centre of gravity (or mass idk which one) right?
People who say B don't take into account this fact, the forces the cube is feeling will change according to how far it is outside of the sloped portal. It's literally common sense.

Yes, and the part that has still not gone through is being pulled down by gravity which is proportional to the volume of cube on both sides.

at 50% it begins to roll through on it's own, unaided by the continued approach of the orange portal.

The speed of the orange portal is irrelevant because since no force is directly acting on the cube other than gravity.

Idfk but ill throw a

>50/50 Chance or a more fucked up ratio and then we will be so much bugged.

Screencap other thread.

It'd be B. Velocity is relative. If the cube is traveling relative to the rest of the room when being pushed by the orange thing and the orange thing suddenly stops while the cube is on the other side of it, the cube's velocity will be changed.