Ragebait answers only
Everyone else is wrong. (Ragebait.)
Speed of approach = speed of separation.
If the box left the blue portal at a slower speed than it entered the yellow one, the top of the box would be moving slower than the bottom of the box, which would compact the box dramatically during the transition, but we can see that its size is unchanged and it is still square.
The top of the box is pushed rapidly out of the blue portal by the bottom of the box being thrust into the yellow portal. (The bottom of the box is pulled rapidly up into the air by the top of the box which is already moving quickly.)
It should be a.
Imagine if the cube was actually a long rod and the orange portal start with the column half way inside it. Then the orange portal moves, in this case it would be very odd for the rod to jump in this scenario like in case b, the thing you would expect would be for the rod to stay still (besides tipping sideways a bit) consistent with case a.
Stop stealing all my upvotes
You asked a question and they gave an answer. Why wouldn’t they get the upvotes?
I’ve just never had a comment on my post get more upvotes than the post itself.
Am angy
and upset I didn’t think of posting that image in the first place
Perfectly understood the assignment, 10/10, no notes.
There’d be no cube but yes
In the first moment of exit, it might look like this though
deleted by creator
You can’t place a portal on a moving surface in either game, so neither.
you can in one specific spot in portal 2!
Two, if you count… the big one at the end
it doesn’t look like it’s moving though. and considering how many things in portal 2 move when they look stationary or vice versa…
As far as the game engine is concerned, “stationary” is relative to the… other comparatively big thing: the former big thing is moving very quickly around the latter, even if it looks stationary because it has a lower angular velocity
pretty obvious tbh
So now we just need to build this test in there and we are set
So the cube is just smashed?
It’s a practical answer which is slightly upsetting because I wanted more discourse.
No, cubes cannot be destroyed by crushing. The portal disappears when the surface starts moving and then the cube stops the surface’s descent.
what about the portal on the moon?
Well, everything is moving or not moving, relatively
Someone should write a thesis on it (or whatever it’s called). Could call it something like The Relativity Theory.
It’s unstable and will dissipate on its own when the relative displacement between them will be too great.
Skill issue
You’d make a horrible scientist.
It said ragebait answers only ¯\_(ツ)_/¯
If it is a question of real life physics, then B would be correct
Damnit, you are correct, my bad.
Scientists know when to use existing knowledge.
This was answered decades ago
In that situation both portals (the inside and the outside window frame) have equal, but opposite velocities and therefore cancel out any momentum from the person.
When dealing with OP’s scenario, only one portal is moving.
wikipedia.org/wiki/Steamboat_Bill,_Jr.
Nearly a century ago. Fun fact, this movie inspired Steamboat Willie, the very first appearance of Micky Mouse.
The problem with this analogy is that both sides of the window are at the same point in space so there is no pressure differential. What if the blue portal was at the bottom of the Mariana’s Trench? What force displaces the water to place the cube on the other side?
It wouldn’t. Same as if the other side of the portal was a brick wall. It wouldn’t go through or would be smooshed by whatever force is driving the portal.
I guess the odd thing is, if the orange portal can be moved, the pressure from the brick wall would be directed at the attachment point of the orange portal, otherwise why wouldn’t the orange portal keep moving, since it is not “touching” anything?
If the blue portal was deep under water, the pressure would force the water out the orange portal.
According to a gravitationally accurate simulation a guy did for Youtube, the correct answer is_
… ah, ragebait answers only. Well, mission accomplished, probably >:3
For anyone who doesn’t know, Optozorax on YouTube has made a finite element analysis simulation of gravity ontop of his portal simulation so we can get an answer to the question. The answer is both. Both happen depending on how fast the portal is moving and the where the second portal is placed in the gravity well.
deleted by creator
I’m not sure if it’s the alt text or simply the post’s body, but it reads “Ragebait answers only”
Option B. Portals already break a couple of laws of physics and can reverse entropy, but I like to think you should look at the speed of an object relative to the portal.
Speedy thing go in, speedy thing come out. Clearly explained in game.
But In this case the cube has no speed, the platform does, so it wouldn’t just suddenly start moving.
It has speed relative to the portal though. Everything has some speed because we’re orbiting the sun, etc
The cube does have a non zero speed, it just depends what frame of reference you are measuring it by.
Frame of reference. If a person is hit by a train, from their perspective, they were standing still and the train was moving. But a person in the train can stand up and walk around without difficulty, they can stand on one foot and balance, they can jump up and down and not go flying away; so they are standing still from the trains perspective, it’s everyone and everything outside the train that’s moving.
What happens isn’t a transfer of momentum or energy or velocity; it’s a change in the frame of reference. That can’t happen in real life and breaks a lot of different laws of physics, so people are having trouble wrapping their brain around it.
The portals are a frame of reference. Both the IN and OUT portals have their own, separate frame of reference. The player’s reference doesn’t actually factor into it. When you go through a portal, you are switching from the IN frame of reference, to the OUT frame of reference. And in this situation, the IN frame of reference has you flying toward the portal at whatever speed it’s approaching you.
If anything, it’s rapid exit from the portal would cause an increase in pressure on the top of the cube, causing it to stay in place. The cube still isn’t moving regardless of the velocity relative to the moving platform.
At what point in time would the cube start moving away from the platform it’s sitting on, and what forces act on the cube?
Also shit changes frame of reference all the time irl, and portals a could be thought of as wormholes, which which could theoretically exist IRL.
Alright, since you didn’t like my last explanation for some reason, let me try again.
You know how when you stick your hand out of a moving car, you feel a massive rush of wind, even if it’s not windy out? Ok, so imagine sticking a portal out of a moving car, what do you think happens to the air? Does it come to a dead stop after it exits the portal? Why not? The air itself wasn’t moving, only the car with the portal was.
Solids in this case will work the same way. It doesn’t matter if a solid is moving toward the portal, or the portal is moving toward it, what matters is the relative velocity.
From the orange portals frame of reference, the cube, and everything else in the world, is rushing toward it. So the cube (as well as the entire world around it) has a velocity relative to the orange portal.
But only the cube goes through the portal, the rest of the world does not come with it. At that point, the frame of reference changes. You can think of it like this: The cube has an velocity of X with respect to reference frame Y; once it leaves the portal, it keeps that velocity X but the reference frame changes from Y to Z. The velocity doesn’t disappear.
What if the blue portal is at the bottom of the Marianas Trench?
Niether. Moving surfaces break portals instantaneously.
Portal 2 has moving surfaces, with the cop-out that it’s accelerating surfaces that cause the portal to break.
spoiler
No matter that you literally put a portal on a different planet…
Portal 2 (story mode) only has laterally moving surfaces, that inherently don’t cause things to enter the portal. The moon portal is stationary in the engine.
Portals don’t stay on moving platforms.
But if they did, it would be A as the cube itself has no momentum.
WHAT DID YOU NOT UNDERSTAND ABOUT RAGEBAIT. ANSWERS. ONLY.
… Uh
u mad?
So really I saved this comment and you’re all welcome.
It seemed to work.
Except that one time when you use portals to cut the neurotoxin pipes.
Yeah, but those are moving from side to side. To my recollection, you never see a portal in a wall that’s moving in a direction that’s perpendicular to the plane it’s in.
The speed of one thing is the same speed of the other if you change the reference point. So the cube has momentum but the moving platform does not. It’s more about having a velocity in respect to the portal it’s going in or coming out of or an average of both. Like when you jump into a portal, you come out faster on the other side. Now what if that out portal was traveling at the same rate? Would you be traveling just outside the portal or double speed (in relation to the ground and static objects in the same room)?
Ragebait answers only
I’m giving so many people Fs on this assignment because you failed to read all the instructions.
The correct answer is B due to the graphical conservation of speed lines.
I did it deliberately.
Lemmy reads more than most but people aren’t good at reading
I think any answer is a ragebait answer because nobody here understands physics
That’s definitely a ragebait answer
Judging by the most highly voted answers on physics.stackexchange, it’s also true.
Trick question. Fun answers are not ragebait. Serious answers (correct or incorrect) are ragebait. You get an F.
If the downward moving portal hits the platform and there is some elastic rebound, then the object will bounce outward slightly.
Rage bait answer: Portals can’t exist, it is from a child’s game.
Better rage bait answer: portals can’t move relative to each other. If they do, the one that is moving ‘pops’ and disappears from the surface. So this scenario is impossible inside the parameters of the game, so it’s not worth thinking about.
(The devs realized a lot of stuff could get horribly broken if portals could move, so they can’t move)
Except that they can move in that one level with gas and lazers )
Scripted exception
Honestly the worst decision they could have made while writing. I’m still kinda’ mad about it and I don’t know why.
I think they experimented and wanted them to be able to move in more places. But with engine limitations they only left it in one scripted place where there are no physics objects that can interact with it.
Even stationary portals break conservation of energy unless there’s some unseen location changing energy to compensate, but yes, it gets more complicated with relative movement. In lore though, it is established that portals can move with hugely different velocities relative to each other at least with enough distance when you
spoiler
shoot one portal to the moon :::.
B.
Momentum/velocity is not an intrinsic property of an object, it is a relative property between two objects in a frame of reference.
Behind the yellow portal is the part of the universe where the blue portal is. The yellow portal, and therefore the space where the blue portal is, has momentum relative to the cube.
Put yourself in the frame of reference of the cube. You see the yellow portal come toward you. Imagine there are objects on the other side of that portal. You see those objects rush toward you through the portal. Why would the objects just stop dead when you came through the portal? (If they did just stop, it would be as though you hit a wall, and you wouldn’t actually go through the portal at all.)
Agreed. Also consider the duration of the time that the portal is passing over the cube. It is moving at speed, the entire way through the portal and out the other side and then it just stops dead immediately once through? That would hardly be a conservation of momentum anyway from any frame of reference and does not make any intuitive sense.
This exactly. Consider an object that isn’t a point mass (like the cube) going through. As the first atoms go through: if they just stopped relative to the portal boundary, that would suggest the next layer of atoms need to exert force on the first layer to push through. But portals in the game Portal do not have any resistance to objects passing through them.
“speedy thing goes in, speedy thing comes out.”
So stationary thing goes in, stationary thing comes out.
Speedy or stationary relative to what?
To the portal if course. That’s why it comes out speedy at the other end.
But the game treats the portals as holes in reality. If a whole falls on you do you suddenly pop up out of the other side? No.
It would plop. It would only fly up if the platform the cube was on moved up towards the portal.
I think the game treating portals as fuzzy holes in reality is more just a limitation or oversight in the physics engine. It completely ignores relativity and makes the portals no longer logically consistent and pointless to argue about. Velocity and angle conservation relative to the portal is established elsewhere though, so running with that gives you the “fly up” result.
> stationary
> comesChoose one. There is no “plop”, all of the cube has to emerge on the blue portal’s plane
The object going into the portal has no momentum so it would be A.
No momentum in relation to what? Momentum doesn’t exist in isolation.
Momentum relatively to the source game engine grid.
“speedy thing go in, speedy thing come out.”
So A.
As I said, there is no “speed” in isolation. Speed is a relative property of an object and a reference frame (i.e. another object, like e.g. a planet)
In this particular case it is speed with respect to the fixed reference frame of the game.
To the space outside of the blue portal. Moving the orange portal doesn’t drag the whole surroundings, so assuming both places are on the same planet, the momentum of the box in relations to both places is the same
Moving the orange portal kinda does ‘drag the whole surroundings’. It moves an entire universe.
The cube is stationary relative to the universe of the platform it’s on, but it has momentum relative to the universe through the portal. The question is which universe is the cube in? What is the boundary of the portal surface?
As Optozorax taught us, gravity must act through the portal.
Well, it doesn’t in the only source of knowledge we have: the game Portal. I don’t know enough about gravitational forces to have a coherent theory on it, gravitational waves moving through space-time is a bit beyound my real understanding. But in the game if you put a portal on a ceiling, it doesn’t “suck” you until you’re throuth it, so there it isolates gravity somehow.
At this point, I consider Optozorax’ research the primary source of how portals work. If the games disagree, they’re wrong.
If you stick to the premise that the portals exist in a universe with GR, then we can pay much know that space-time is locally flat in and around at least the middle parts of the portal. We know this because things don’t get fucked up when they’re going through.
The object’s momentum is preserved. Movement of the entrance portal does nothing. Think of it like stepping though a door, except you’re Buster Keaton and the door hole is falling on you.
I brought this up on another comment that’s for some reason now deleted but, if the universe moves around you, would you not perceive it as movement?
There is no such thing as an absolute inertial frame of reference. If you are in free fall on earth, you would experience the same sensation as being in space. The only things that would tell you otherwise are the air resistance hitting you and what you can see.
So no, you would not be able to tell the universe is moving around you unless something else in the universe hit you.
The first part made sense, then you contradicted yourself at the end^^ If the universe moves around you, you could literally see things moving. It would be the same as you moving relative to everything else
Seeing things counts as something hitting you: photons.
True. But then thats not the exception
Think about it more fundamentally. Instead of a person with senses, think of an object experiencing forces. Thats what an inertial reference frame means.
Exactly. Seeing was just an example. The whole universe moving around an object would cause that object to experience forces.
But senses are just ways for an object to experience forces.
I know if I’m hanging upside down because my senses are telling me my body is being pulled down from my head. I’m feeling the gravitational force pulling me down.
An object moving in the universe is indistinguishable to the universe moving around an object. To any observer or to the object itself the forces experienced are the same
well, in my opinion it is a bit of a paradox. i think you are partially correct.
your door analogy may be right from the perspective of the platform on which the cube is. however, one flaw is that the whole space is moving, not just the door. as soon as the cube enters that door, it will be inside that space, and if you consider the cube part of it, moving that space “downward”, then due the cube being held by the platform, you could consider the cube moving “upward” in the space behind the orange portal. if you consider preserving momentum there, then as soon as the apparatus stops moving, the cube should not stop its momentum and move further up in the space.
or look at it like this: if you are behind the orange portal, meaning you are looking at the blue portal, you will see a cube moving towards you. then as soon as the platform hits the wall of the orange portal, the preserved momentum should make the cube “fly”.
the change of perspective leads to two different conclusions, therefore i think it is a paradox.
the problem sort of is that there are two “spacetimes” that are kind of being changed. one could interpret it as both of these effects “pulling” against each other since when the cube has partially passed the portal, one part of the cube is “in one of the spacetimes”, ant the other part in the other. ultimately though, the cube then would actually fly because in the limit (infinitesinally close to when the platform hits the portal wall) the cube is completely on the other side of the portal, so from the view of that spacetime, the cube does get pushed and should fly.
i don’t even remember if it is possible in the video game for walls with portals that move. a video game would probablt have some kind of “center of mass”, like a single vector of coordinates where describing the position of the object. there is no notion of “partially” being somewhere (except for collision boxes, but i don’t mean that). so also from that view the box would fly. however, in most video games (with or without portals), if a platform moves up and suddenly stops, the object won’t travel further in that direction anyway, especially not ulwards (even sideways usually not).
As for the portals moving in the game, portals are destroyed if the panel they’re on is moved except for one specific part, where you can put a portal on a panel moving laterally to get a laser to cut the tubes connecting to the neurotoxin tank. That part needed to be explicitly programmed to allow it, and it’s not possible without cheating to physically reach that portal.
Whats the difference between an object moving and everything else moving? For an observer on the sun every one of us has huge momentum which would be preserved when entering a portal. Momentum is always relative to some frame of reference. Momentum ‘toward’ the portal would be conserved and mirrored through the other portal.
The difference in this case is that the object has 0 momentum and the portal doesn’t impart its momentum to the cube because you can’t collide with the portal. There is no force acting on the object to make it move.
Of course it has momentum relative to the portal.
That is not how either relativity or momentum work. The cube is still inert and the portal’s movement would have no effect on it unless it has some acting force that pushes it when passing through. Even if the exit portal was moving, the cube would remain stationary unless it had nothing to rest upon and gravity pulled it down.
Correct. If a stationary door/portal has no affect on the cube’s velocity than that’s also true for a moving door/portal.
What if the portal on the moving platform had a wall right in front of it, so moving though the portal would cause the box to run into the wall. You’d have a scenario where the box wouldn’t be able to move through the portal, but you’d have energy being generated by the moving arm “pushing down” on the box. The only way that could work is if the moving portal is transferring energy to the box, and therefore require option B.
Although that being said, portals break the laws of physics, so there probably can’t be a “right” answer.
More like a hole in the wall with you standing perfectly still while the wall moves past you.
Except the wall has no mass or width.
It would move really fast through the portal then slide down from stand still. So yea B is correct.
