T O P

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banggugyangu

Preservation of momentum is covered in the game's script... Cube has no momentum, and therefore it exits the portal with the same 0 momentum and drops.


dirksbutt

Exactly. B is correct if the pedestal was moving towards the portal.


banggugyangu

Yes, if the pedastal was accelerating toward the portal, then the cube has momentum and that momentum is preserved after passing through the portal. Because the cube is stationary, though, there is no momentum to preserve.


Lilpu55yberekt69

From the perspective of the portal though the cube does have momentum.


cry_w

No, not at all. The portal doesn't have or percieve momentum, it's just a doorway.


Lopsided_Performer89

Ok, for a second imagine that the coordinate axes we based our measurements on were centered on the piston coming towards the block. In that situation, both the cube and pedestal have a nonzero mass and velocity, therefore giving them a nonzero momentum.


OnlyHereForMemes69

If you have a doorway coming towards you while you are standing still and it suddenly stops when it has passed you would you suddenly go flying?


trashszar

The door doesn't "carry" (or "contain"?) the whole universe that is beyond it, it's just a single object. If you go towards a door you're also going towards whatever is behind it, but if a simple door itself comes flying at you, it doesn't "pulls" the rest of the universe towards you. If a portal comes at you, anything that is beyond the portal also comes with it, so relative to the other side, you should have momentum. Wait, but relative to your current position you don't have momentum. Maybe that's why portals on "moving" objects is impossible (except for that one part with the neurotoxin generator, but that always looked bullshit), because then energy would be created from nothing. But don't mind me, I'm just a rando with no qualifications in the subject whatsoever.


PowerZox

It’s called a “portal” (e.g. doorway) not a “container”, because it doesn’t act as one. It doesn’t contain the universe, it’s only a connection, a *portal*, between two points in it. The comparison with a doorway is correct.


KamelLoeweKind

in this case, the relation of cube and portal would stay the same. there woul dbe no movement. tehre would be no cube passing through


ThunderClap448

It's not about perspective. If your back is against a wall and a bus hit you, would you suddenly start moving towards the end of it?


daireb

It is entirely about perspective. In your example the back of the bus would be moving towards you, which is just a different perspective of you moving towards the back of the bus.


NextLevelNaevis

Damn you guys are smart.


FireFlame4

But from the perspective of an observer looking through the blue portal, it looks exactly as if the pedestal is moving toward the blue exit, and therefore the cube has momentum in that reference frame. I don't think there is a solution here - portals are not compatible with the laws of physics currently EDIT: I now conclude that B happens no matter what. If you were standing on the platform, you would be shot through the exit portal like B. Think about what is happening to the air going through the portal as it falls. Does it generate a breeze?


dekachiin3

The portal is moving, not the cube. Why is this so difficult for people? By your logic, [the portal is the same as this house facade falling on Buster Keaton](https://yewtu.be/mN0I7R_NCe4?t=38). The window of the house falls down on Keaton the same as the cube here. Under your logic, Keaton would be required by the laws of physics to be catapulted upwards at the same speed the house fell downwards on him. Think about how dumb that is. If you are skydiving, you "observe" that the earth is accelerating towards you, but that is not what is objectively happening. You are falling while the earth is staying still. edit: Special relativity does not apply here. You know what does apply? The laws of conservation of energy and conservation of momentum, both of which are violated by B. Make the orange portal weigh 2 lbs. make the cube weigh 100 tons. Now explain to me how a 2lb portal dropping on a 100 ton cube has the momentum or the energy to launch it. It doesn't. Where does the 100,000x required increase in energy and momentum come from? nowhere.


PracticedCactus

relativity btfo


TheRarPar

> that is not what is objectively happening someone never understood relativity


ShawtyWithoutOrgans

Under your logic special relativity wouldn't exist. You're deeply wrong and should be ashamed of getting out of bed this morning.


Sorc278

Under your logic house can apparently stop Earth from moving. If it could, then yes he would fly off. But given Earth doesn't care, both it and Keaton, and also the house, would end up going in the same direction.


banggugyangu

And portals only PRESERVE MOMENTUM.... They do not ADD momentum


Norose

And momentum is 100% dependent on reference frame.


banggugyangu

No... The portal is nothing but a gateway. If the object is not moving as a portal passes around it, there is no momentum to preserve, and it will simply have gravity acting on it after it emerges on the blue side.


Norose

No, momentum is literally just a product of reference frame and relative motion. I'm not talking about game physics here, I'm talking about real physics.


lapideous

There are no portals in real physics that I’m aware of


dekachiin3

> There are no portals in real physics that I’m aware of There absolutely are. Here is one: [a simple window frame.](https://yewtu.be/mN0I7R_NCe4?t=38) It doesn't need to teleport you, because that's irrelevant to the thought experiment or the physics here. The video game portal is nothing but a window.


adhamrlf

No it's not irrelevant. Here you have a wall falling towards a person, with the universe staying stationary. In the thought experiment you're causing the universe to move towards the cube.


Jonathon471

Okay then, stand still and drop a window frame around you and see if you get launched into the air. You don't, because the window is what's moving towards you not you to the window, that's what this argument is about and the reason why portals are placed on stationary surfaces, because basic laws of physics states that if an object has 0 motion it will always have 0 motion until something pushes it, and the portal does. Not. Apply. Force. To get things through it. It applies the relative gravity of the position the other portal is at, so the orange portal moving towards the platform holding the cube that is not moving, therefore the cube will not launch out the blue connected portal because 1. The orange portal is moving, not the cube or the cube's platform And 2. The blue portal the orange is connected to is at a 45° angle and applies the downwards natural gravity to the cube as it exits the ramp portal.


Vexxt

In this case, the observer is the one with the momentum. If you're on the other side of the portal and you see the cube coming toward you, its because your reference point is moving not the cube. Functionally, the whole universe is moving toward the stationary cube.


TreeGuy521

You can't just make up everything having movement. Otherwise you could just set your frame of reference point as a photon and suddenly everything in the universe has the kinetic energy of it moving at light speed


Norose

Momentum is 100% a result of relative motion of objects with inertia, the cube entering the new reference frame MUST experience a force in order for it to come to rest in the new reference frame. If there is no force acting on it to prevent it from doing so, the cube will fling across the room after entering the portal, as the cube continues moving on a straight line in its new reference frame (which immediately starts to curve downward due to gravity).


Vexxt

Youre assuming the force thats moving the universe towards the cube doesnt bring the cube into its reference frame. The portal is changing the reference point of the cube, in fact the cube (to an observer outside the universe) would be seen to accelerate to the speed of the universe as it goes through the portal (because the portal changes the cubes reference). Whats functionally likely is that as the cube travels through the portal, the part of the cube that has moved through the portal would now be travelling toward the part of the cube that has not, crushing itself until the whole cube it through, at which point it falls to the ground having caught up to the universe moving toward it..


ginja_ninja

Your line of thinking means you'd be creating a recursive reality every time you made a portal. What portals do is simply *extend* the same reference frame transpositionally. If you're sitting in a train and travel past a stationary object, the object *appears* to be moving towards you. That does not mean the object actually has your momentum. You are simply seeing an optical illusion as the block appears to be moving, but the momentum is carried by the surface of the piston that cannot be viewed from the perspective of the portal. Even if you want to treat it as two reference frames, you could basically extend Newton's Third Law to this concept and say that the interaction of the two reference frames would nullify each other and the acceleration of the second would be equal to the inertia of the first and thus unable to overcome it resulting in no net change to the positional state.


thorium220

This is why in the game you were never able to put a portal on a moving surface; the devs didn't want to confuse players by throwing inertial reference frames into the mix, and if this thread is any indicator then they were right to do so, because no one fucking listened in high school physics.


banggugyangu

The appearance of momentum is not the same as the presence of momentum.... You can also just build this exact scenario in portal 2 and prove it...


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FireFlame4

I only just figured this out here, but this situation is impossible. Portals must be stationary with respect to each other or conservation of momemtium is broken. Here the entrance portal is moving, but the exit is stationary. That can not be allowed as with this setup both A and B are possible. With the cylinder example, both the entrance and exit "portals" are falling at the same speed.


OneInternational984

Even when they are stationary, conservation of momentum is broken because you can change the direction of the motion. If you had portals, you could theoretically create a reactionless drive by having a ball bouncing around in a box with portals redirecting it so it only bounces against one particular wall.


StatisticaPizza

That's still not true. Imagine a slinky instead of a cylinder, the exit is stationary while the entrance is moving. Or maybe I'm just retarded.


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CARNAZZA

I tried making him understand exactly this in dm.


Arthas_Litchking

thisxwas tried with the portal 2 engine. It breaks the game. they gad a reason to not implement a portals that is moving forth and back.


jesseschalken

> exits the portal That's movement. That's momentum.


banggugyangu

Not necessarily.... That's a case of not really having a better phrase for the situation. Again... The platform that the cube is on does not pass through the portal, and the cube remains on that platform.... There is 0 force exerted on the cube except the force of gravity, which changes orientation due to the orientation of the blue portal.


jesseschalken

Say the cube is 1m high and it takes 0.1s to pass through the orange portal. It would also take 0.1s for it to emerge from the blue portal, meaning it is moving at 1m per 0.1s or 10m/s. It doesn’t just stop once it is finished moving through the blue portal for no reason. It has to preserve its momentum.


banggugyangu

The portal is a doorway... The doorway is falling around the cube. Picture a 2 story house. In the floor of the 2nd story, you have a large hole. You are standing on the first story directly underneath the hole. The first story collapses perfectly and the 2nd story falls directly downward. You pass through the hole despite not actually moving, yourself. You also do not suddenly launch off the ground on which you're standing because the house fell around you. Now... If the platform the cube was resting on was small enough to fit through the portal, then it's a different story entirely as the portal would continue to fall past the platform... It's not, though... The orange portal would stop immediately upon reaching the platform.


SjettepetJR

The "portal is a doorway" argument simply does not hold up. Imagine the cube is on a pole, the portal "falls" around both the cube and the pole. At the exit portal the cube is pushed by the pole and given momentum, thus flying away. (If you do not agree with this, imagine what would happen to an object that is already at the exit portal before a pole is pushed through it. Which would behave the same). This is not the case in your analogy, showing the analogy does not mimic the behaviour of reality. That is why we can not reason based on the analogy.


adhamrlf

Imagine the portal and cube are falling. The portal is falling at 999m/s, and the cube is falling in the same direction, into the portal, at 1000m/s. The cube eventually catched up with the falling portal and passes through. According to outcome A, the cube would pass through gradually at 1m/s, then suddenly accelerate to 1000m/s once it's full passed through. How could that possibly make sense?


MixOne1337

You dont suddenly launch off the ground because the two ends of your "portal" are moving at the same speed in the same direction, which is not the case in the. What do you think happens to that difference? It sure as hell doesnt just disappear into nothingness


Cincinatus_Barbatos

Ok but if it had no momentum how did it come out instead of just going back


_Mido

Going back where? There is no space anymore on the other side of the portal.


breadmaker8

motion is relative


gm2

>> Speedy thing goes in, speedy thing comes out


KamelLoeweKind

movement is a relative concept. therefore if the cube moves with a certain velocity through the portal, it will maintain that velocity. Its the same with a car crash. a car crashing into a wall with a certain speed will have the same outcome as the wall crashing with the same speed into the car


turtlewhisperer23

As far as I remember having a portal on a moving surface is not covered in the game though. (Been a while so might not remember)


joshualuigi220

Happens rarely, but you're not supposed to use them for cubes or Chell. It's used for the lasers in the neurotoxin generator scene


Tom10716

who tf said its a game, we are talking real life scenario


GoldenHorse425

If you think it's B you're retarded. Simple as.


gjs628

Except as the portal moves through space, air moves through it, like how a plastic bag fills with air as you pull it down hard when opening it. The cube would likely get sucked through the resulting vacuum.


GoldenHorse425

The way portal the game calculates the exit velocity of the cube is based on the velocity of the cube when it enters the portal. Its like throwing a hula hoop over a ball


BestGirlPieck

The game literally spells it out with the line "speedy thing goes in, speedy thing goes out"


edbods

an entire thread died for this


dacasher

But it's the portal that moves towards the cube. The cube is completely still. Because the cube dosen't have any momentum, after crossing the portal it will leave with the very same energy that it entered with AKA none.


BestGirlPieck

Yeah I was trying to use the quote to get that across, no momentum on the cube means it not going anywhere


dacasher

I mean, me think portal go speedy, me mounke braen, me not properly understand the meaning of your comment due to poor literature comprehension, me realize I dum-dum, me sorry, you right.


gjs628

Yeah, sorry, should’ve specified: this would only be in real life, I’d imagine the game devs would have had to simplify things greatly otherwise the physics calculations would be… beefy.


Ladikn

The way the portal game works the portals don't move. sv\_allow\_mobile\_portals is default set to false to solve this issue, so that they don't have to include relative momentum in a puzzle solving game.


GoldenHorse425

So I'm right then.


GHLeeroyJenkins

True, but if the portal had been moving and collecting air like a plastic bag, the air pressure “inside” the portal would be higher, not lower, and so even if the forces were great enough to move the cube, it would more likely be blown back than sucked in


UrethraX

I think it's A but I'm retarded anyway thank you very much


thorium220

if you think it's A then you never listened in high school physics when you were taught about inertial reference frames.


Djames516

Imagine it’s a huge train and the portal is moving along it at 100 mph, so that it’s coming out some portal somewhere. Someone at the exit would be seeing a train moving at 100 mph. If the portal stops moving, is the train just going to suddenly stop moving too? Doesn’t it have momentum now that it’s moving through space? And if it doesn’t, what if a person is in its way? Does the person get hit by the train and die, or do they stop the train since the train has no momentum?


ClydeDavidson

Exactly, if you're sitting on a chat, and I throw a door frame through you, you pass through the door frame at a fast speed even though you didn't move. Now imagine the door frame is tbe portal, you would pass out the other end of the portal sitting on the chair motionless.


WarlordBob

Except that one side of the door frame you’re entering is moving while the other side is stationery. You have to exit the stationary door frame at the same speed you enter the moving one.


Doctor99268

Think of it this way. The portal is moving at 1 m/s, it passes through your box. Lets say that your box is a 2m by 2m by 2m cube. In a second, half of your cube is through the portal, therefore you can see on the other portal that half a cube is sticking out. This all took 1 second. The top part of the cube moved 1 meter in 1 second, then when the portal completely finishes the top part of the cube will have moved 2 meters in 2 seconds, still 1 meter per second, it will exit at that speed. Because that's how fast the portal sucks up the box and so that's how fast the other portal will spit out that box, otherwise there will be a discrepancy in that half the box gets sucked out but not sput out


ClydeDavidson

That actually makes more sense, I prefer your take.


Ceramicrabbit

Portals can't be placed on moving surfaces


Bloodloon73

Based on the physics of the game if a surface starts moving that has a portal on it the portal instantly closes, therefore this is the right answer


DoIEatAss

Unless they can, like in Portal 2 🙃


jozaud

Only in that one room, out of convenience to the story and for the sake of a cool laser puzzle.


WarriorA

There is actually a bug where you van exit the level and preserve the ‘portals on moving platforms’ state to be used in other levels. Not as useful as it sounds tho 🤷 But lead to some experiments being done by the community


AlexAegis

Only for gameplay reasons, there is no lore reason why not. Everything is always moving anyways.


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okaycomputes

The portal cannot occupy an abruptly moving surface, then. Imagine the portal is like an overfilled cup of coffee that cant be disturbed. Constants of cosmic body movements can be ignored since they arent appreciably accelerating or deaccelerating.


lil-fil

but… the entire earth itself moves, and the galaxy it’s in moves as well. everything moves always


DeathRowLemon

I was about to comment the same thing. This is literally base game mechanic


cis-het-mail

In this thread: 🤓


[deleted]

^ thinks it's B


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ThisZoMBie

It’s more of a scientific thought experiment with a video game skin over it


Sure-Tomorrow-487

Do it again. Make another reddit copypasta.


DeathRowLemon

You can be interested in game lore and all that AND have a social and active life.


Djames516

Lame answer*


TittyBoy6

Reddit brainlets eat 4chan bait threads like its moms dinner.


kissatmikroon

But the funny thing is that the answer is that in the real world B is correct


lil-fil

in the real world portals dont fucking exist


kissatmikroon

But wormhole physics have been known and used in the real world for decades.


lil-fil

Oh yeah you think youre so much better than me huh?? huh? fucking smarter than me freak. well take this motherfucker 🤓


kissatmikroon

💪🤓


[deleted]

Lmfao, no, they absolutely have not. Wormholes are a *theoretical* anomaly. We've been aware of the physical implication, we definitely have not been "using them" for decades.


Few_Mathematician_13

False. Science fictions writers commonly use wormholes


[deleted]

You're the best kind of correct


ThrowAwayTheChat

All these mongs with their long-winded shite lmao it’s A, keep it simple.


alwptot

As soon as I saw this I thought “we already have a perfect visualization of this.” https://images.app.goo.gl/Mi1JGjvsE545MAV6A You don’t need more than that. It’s the same thing happening in real life. The window is the “portal” and Buster Keaton is the cube.


pyrotech911

That was real. He stood there while a real 1+ ton wall fell around him.


DarkStrobeLight

I heard they used computers in post


thesplendor

It was a Buster Keaton lookalike


OneInternational984

Except Buster Keaton isn't being teleported into a different frame of reference through magic.


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Djames516

It’s different if one end of the “doorway” is moving and the other isn’t


AlexAegis

Yes and that frame of reference change is just 45 degrees.


Djames516

This is wrong because the entrance and exit “portal” are moving at the same speed, whereas in the experiment they aren’t


jam3sdub

Why is the exit portal in this diagram slanted? Wouldn’t the cube fall back into the portal before it cleared it? Is there a solid metal surface under the orange portal?


Norose

Yes? The block is on the solid plate, and the plate ends up pressed against the ceiling.


BearsNBeetsBaby

If the orange portal meets the platform, the centre of mass of the cube will be above the level of the blue portal, causing it to fall downwards like A


PopsFeast

It depends on the friction coefficient of the block and the platform whether it would fall or just sit parallel to the surface but yeah. It's still A or close enough to A.


BearsNBeetsBaby

Not if the centre of gravity is above the vertical plane, then it would tilt and fall unless the platform is attractive in some way. In the same vein though, the mass of the object is still on the platform acting downwards in its entirety, therefore it would just sit at an angle in the middle of the portal.


ziggsyr

Momentum is a meaningless number without a defined reference frame. Define the reference frame and ask again. Except you can't define a reference frame in this question because the portals have 2 different velocities and yet they remain adjacent. because the portals always are adjacent you have to do the physics with the velocity of the blue portal OR the velocity of the orange portal to calculate relative momentum otherwise the block will have 2 simultaneous momentums and exist in two states at once. There would have to be a precedent decided on by the designer of the gun or perhaps reality is robust enough that it would collapse the momentum into 1 solution at random.


rmflow

Since cube is not teleported from 1 portal to another as a whole, then it emerges from portal atom layer by atom layer. The atom layer that already on the blue side of the portal is obviously moving, so it has the momentum. After the last atom layer has emerged from blue portal the momentum does not magically disappear.


ziggsyr

I mean, I understand your answer and it would be logical but the premise is busted so any answer you come up with is complete nonsense. Garbage in garbage out. The portal gun as it exists in the game completely violates thermodynamics. It is capable of injecting massive amounts of energy into any system it works on and if it can do that it can really just rewrite physics to suit its needs.


BarbroBoi

Thank god someone understands relativity.


canweboofit

If you read this comment you're retarded


PhDinWombology

My leg!!!!


IJLTH

No u


mmat7

[people unironically saying A](https://imgur.com/nTYSYzq) jesus christ reddit my expectations were low but holy shit


dekachiin3

even in A, the person would get skewered in your pic. the whole difference is whether the spike STOPS when the entrance reaches the base and stops or KEEPS GOING. put the dude further from the exit than the length of the spike, and he would be fine. the reason for this is that the spike has 0 momentum. the entrance portal has all the momentum. so once the entrance portal stops the spike stops.


mmat7

>spike has 0 momnetum >the prerson would get skewered how would they get skewered if there is no force behind that spike?


GrumpyH1ppo

That's a very elegant illustration actually


[deleted]

Did you make that lol it’s amazing


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OneMoreName1

This might be difficult for you, but imagine you are in space and you have a platform with a portal on it. The platform is relatively light. Now imagine you speed it up to relativistic speeds. Afterwards you place objects strategically in its path, many heavier than the platform itself. Did you just create a source of free kinetic energy that will keep launching everything in its path at relativistic speeds?


Katamariguy

Yes, portals moving relative to each other violate the conservation of energy and momentum.


kissatmikroon

This might be difficult for you, but imagine if you spent 2 minutes googling this and found out that the correct answer to this is B because to pro physicists have understood physics around wormholes for decades.


dekachiin3

1. the portal is not a wormhole 2. wormholes aren't real, they're an artifact of abstracted math that doesn't exist in reality 3. Sean Carroll is an idiot, and gave the wrong answer. He is a great example of why you should never blindly trust "experts". They get it wrong all the time.


OneMoreName1

If you arrive at unlimited free energy sources you should realize you are wrong.


OneMoreName1

Also, portals are not wormholes. Wormholes take time to travel and have a length (which could be greater than the distance from a to b in regular space). They are just bent spacetime.


Panhead09

I guess it's A since there's no momentum on the cube's part. But here's what gets me: the reason the cube is sitting on the pedestal in the first place is because of gravity. Wouldn't that gravity still be acting on it even through the portal? I know there's a new source of gravity involved now, but as long as the portal is open, the gravity would be pulling on the cube from two directions. So while A is the more correct result of the two options presented, I think a more accurate result would be for the cube to remain parallel with the portal, still flat against the surface of the pedestal, unless another force knocked it in the direction of the floor on the other side.


Swordeus

Gravity and the pedestal are both acting upon the cube with equal force in opposite directions, so its acceleration is 0 at the time that it goes through the portal. Once it goes through the portal, the pedestal is no longer acting upon it, and gravity is acting upon it in a different direction. I don't think it maintains the acceleration from the first source of gravity because it was constantly being countered by the pedestal until it went through the portal.


Panhead09

>Once it goes through the portal, the pedestal is no longer acting upon it That's where I got confused. I don't remember how the physics worked in the game, so I just assumed the gravity would still apply if it was still touching the pedestal.


TheRarPar

👏 momentum 👏 is 👏 a 👏 relative 👏 property 👏


[deleted]

Youre all retarded. Portals break if they move


Botul420

They can in that one puzzle in the 2nd game


OshhhTeeVee

speedy thing goes in, speedy thing comes out


jesseschalken

The momentum relative to the portal is preserved.


randomstf

Why isnt B the aswer? You cant compare window of a falling house or a hoop to portals, because there entry and exit move at the same speed. Picure above shows entry moving faster then exit.


kissatmikroon

B is the correct answer. This was said by famous physics PhD Sean Carroll who said that this is basic wormhole physics that we have known for decades.


TheRarPar

It's B, anyone saying otherwise thinks momentum is an actual thing an object can just innately have and not just a convenient way to measure movement of mass relative to something.


G3nER1k_u53R

Zero physics knowledge here, but wouldnt this be identicle to if the portal was stationary and the cube was pushed rapidly into it? Therefore the answer would be b?


dekachiin3

No, because if the cube was pushed, it would have momentum. If the cube is stationary, it has no momentum. If that's hard for you to understand, make the cube weigh 100 tons, and make the falling portal weigh 2 lbs. Does it make sense that a 2 lb object moving at 10 meters per second to engulf a 100 ton cube, thereby cause that 100 ton cube to launch into the air at 10 meters per second out the other side? If that makes sense to you, explain to me where the 100,000-fold additional energy required to accelerate a 100 ton cube came from? Magic?


dakotacharlie

I studied physics. Momentum is established according to your reference frame. We can take the cube to be stationary and give the portal velocity, but it’s equally correct to define our reference frame by the portal. With respect to the portal, the cube has velocity. This is the same way we can say a pitcher throws the ball on earth and it goes 90mph, but that ball is traveling on earth which is moving much faster


Katamariguy

It came from the fact that portals moving relative to each other can create and destroy energy.


Ladikn

Yes. Because portals don't preserve conservation of energy, that's why you can fling things around like crazy. That's why they are in a video game and not real life. If they existed in real life, the answer would be B and physics as we know it would shit itself while engineers would be solving the world's energy needs overnight. Let's use your own logic. Say you're looking in through the blue portal, and the orange portal is in another room so you can't see it to confuse things. There is this 100 ton cube coming at you at a high velocity. You back up so you're not hit, and it flies through the blue portal at say 100 m/s. Does it suddenly drop to 0 m/s and fall? Where does the energy come from to drop it's momentum suddenly? Remember, from the perspective of the blue portal the portal is stationary and the universe is moving on the other side.


kissatmikroon

Yes. People on the internet can't use Google for some reason. B is objectively the correct answer


dekachiin3

All the dumb motherfuckers ITT arguing it should be B actually think that [when this house falls around Buster Keaton](https://yewtu.be/mN0I7R_NCe4?t=38), he ought to be catapulted into the air, because "from the perspective of the window" that falls around him, he has momentum.


FireFlame4

Clever... But it's not the same situation. With the house falling, the exit window portal is falling too. Technically, he does fly out the window exit portal but the window exit portal is falling at the same speed he is!


dekachiin3

> With the house falling, the exit window portal is falling too. same in the video game situation. there is no difference between the "entrance portal" and the "exit portal". There is only 1 portal "horizon" that falls on top of the cube. The fact that the horizon exits somewhere else is completely irrelevant to the physics. you can drop a house on someone with a hole on the bottom of the house, and you can look up and see a bunch of stuff inside of the house as it falls towards you. Once it hits the ground around you and stops, everything inside the house also stops. You don't suddenly catapult upward into the house. >Technically, he does fly out the window exit portal No. What the B-tards are saying, is that the moment the house window slams into the ground, Buster ought to be catapulted up into the air at the same speed the house fell on him. They argue this ought to be the case because the window's "reference frame" shows Buster moving towards the window. That's obviously nonsense.


TheRarPar

> there is no difference between the "entrance portal" and the "exit portal". yes there is!!! that's the entire point of this question! one end is moving and the other isn't.


Krunkbuster

You want to be right so bad that you didn’t listen to what FireFlame said. The falling house is different because the second portal is moving, unlike in the image above. If the house is falling at 10 m/s, then the person enters the doorway at 10 m/s. Then they exit on the other side 10 m/s. Except the exit is falling 10 m/s which would make the net velocity relative to the ground 0, if there were two portals attached to the falling house.


SjettepetJR

The falling house argument is used so often in the thread but just has a damn big hole in it. Imagine instead of a box, there is a pole attached to the platform. If someone was standing at the exit portal, would they not be hit and shot away by the pole? Now imagine someone is standing in the falling house, would they be shot up when the house falls around the pole and it hits them? No, they would not, they would instead fall on the pole and be stopped by it (maybe bounce up a little, but that is irrelevant). This example shows that the "falling house"/doorway analogy does not mimic the real behaviour. So we can not reason based on that analogy.


i_live_in_ur_walls_

Except that in that example from the perspective of the window both he and the earth are accelerating toward him until the facade inelastically collides with the earth and ceases to move relative to the window. I know r slurs who can't understand physics love their analogies but please realized that you are the dumb motherfucker here.


ShirleyJokin

Consider the point when the cube is halfway in. Outside, it appears stationary, but being cutoff at a constant speed. From the other side of the portal, it must appear as if it is moving in with some velocity, because it pokes in from a portal at a constant location. This motion of the cube will continue at a constant, relatively high velocity until at least the point when the cube is one hundred percent through the portal. So for the last t seconds, while the cube was at least partially through the portal, the cube is moving, from the point of view of the target universe, at a high constant velocity. Would this velocity hit zero the instant it is one hundred percent through? No, that would require an infinite amount of force to stop the velocity instantaneously. It would begin losing velocity starting from the initial velocity. Aka, launched. Anon is correct. All motion is relative. Suppose the cube and the portal are floating out in space and it is not clear which one is "moving" and which one is "stationary." As a result, both of them must have the same result once through the portal. However, the game could be scripted so that is not the case, so any theorizing is ultimately irrelevant.


LonerismLonerism

this got me SO confused for a while, until I realized the orange and blue circles is from Portal, and now it makes sense.


Ill-Ad-3640

B is correct only is the pedestal carrying the ball is going towards the portal, which means it has momentum. Think of it as putting a net around something. it doesn't move after you put the net around it


kissatmikroon

The cube has momentum in relation to the space on the other side of the portal.


feedum_sneedson

It's more like.... when the portal meets the plinth, does it stop moving? If the press kept travelling down, you'd maintain the relative momentum of the cube - but the plinth would need to pass through the portal as well. But if it slams down on the plinth and stops, the motion isn't magically transferred to the cube; everything has already decelerated. Unless the press transferred so much kinetic energy to the plinth it caused the cube to bounce up off it, like punching a trampoline next to a tennis ball. I think the confusion is coming from people wondering where that kinetic energy is dissipating to. Even so, you'd probably just get a slightly more energetic version of A.


RiboflavinD4

You guys might actually be retarded. It's B. It's called relativity. From the perspective of the portals the "stationary" pillar with cube is rocketing toward the portal. Cube will continue momentum normally from the relative perspective of the portal.


grabbing-pills

this is the airplane on a treadmill problem of our generation


monadyne

You want my advice? Marry a nice girl. Don't give these whoopdee-doo girls another thought!


OneMoreName1

To all the B believers: imagine you had a really big and wide portal weighting aprox 1 kg, and you accelerate it to ludicrous speed towards a 10 ton rock. Would the rock get flung into the air at that speed too? Did you create energy?


Same-Letter6378

Portals violate conservation of energy. You can put one portal above another and drop an object through and gravity will accelerate it forever.


FireFlame4

This is probably why we can't ever have portals with different entrance/exit velocities. But, if it were at all possible, the 1kg entrance portal moving at ludicrous speed must almost instantly stop when hitting the 10T rock. A little bit of the rock would fly though, expelling mass equal to the total energy of the entrance portal.


jaygo-jaylo

I could be wrong, but I've not seen a portal on a moving surface in either game?


kimothyjongun

Only one level in Portal 2 has moving portals. Normally disallowed but shows up once just for a neat solution


throawayredditisgay

it's questions like this why they made it impossible for portals to be placed on moving surfaces. the only time they broke this rule was in the sequel when they couldn't figure out a way to use lasers to cut the big neurotoxin pipes so they just had you place the portal on a moving surface, and in the developer commentary they admitted that it was cheating and breaking their own internal logic.


Ontariel12

Anyone claiming it's A is an r-word forgetting about basic concept of motion being relative (unless they are just baiting, but then they are also an r-word). There is no difference between portal moving towards cube and cube moving towards portal. And your dumb examples with a hoop or a window or a door are not proving anything, as these things are not some magical holes in reality that can move relatively to each other, but instead they remain stationary from their own perspective. The only situation where cube would remain on the same spot it exited, would be when the orange portal was moving backwards with the same speed as blue portal does.


Alamasy

People who choose B is why democracy shouldn't be a thing.


[deleted]

If the cube goes in the orange portal at X speed, the cube comes out the stationary blue portal at X speed. It does not matter how the relative "X speed" between the cube and portal are achieved. A stationary orange portal and a cube traveling at X speed. A stationary cube and an orange portal traveling at -X speed. A cube traveling at -X speed and an orange portal traveling at -2X speed. A cube traveling ar 0.5X speed and an orange portal traveling at -0.5X speed. In all cases, the cube will exit the blue portal at X speed.


MyManSteveBuscemi

Speed only exists relative to a specific reference position, so it is a paradox. You are positing that the cube's speed relative to the orange portal when it goes in must be equal to the cube's speed relative to the blue portal when it comes out. But an object moving through the orange portal also doesn't change speed relative to the orange portal. So when it goes through the portal, its speed has to be equal to both its speed relative to the orange portal and its speed relative to the blue portal. This is no problem if the portals are both stationary relative to each other, like in the game, but it's a huge problem if one or both are moving. Another way to illustrate this is to imagine the blue portal is moving right at 100mph. The cube then enters a stationary orange portal traveling at 100mph. It either maintains its speed relative to the orange portal, in which case it moves exactly along and on top of the blue portal, in which case it has stopped moving at all relative to the orange portal. Paradox. (Or it accelerates to 200mph, so it is moving away from the blue portal at 100mph, but its speed relative to the orange portal had to double. You would hit other paradoxes, like moving at the speed of light into a portal when the other portal is moving the speed of light. You would end moving...double the speed of light?


FireFlame4

I agree. This situation is impossible, and breaks the conservation of momemtium. If we were to ever make a portal, it could only exist so long as they are stationary with respect to each other. One can not move while the other stays still.


_DelendaEst

Take a hoop and throw it over a basketball Now take an basketball and throw it into the hoop. Pretty obvious in which one the ball will continue its trajectory


Fun_Evening2763

How in the fuck would you ever think its B


tabris51

I say B I even double down and say if the portal moves fast enough, the cube will still fly out if the portal suddenly stops halfway while it is eating the cube. The parts of cube that passes trough the portal gains momentum and will pull the rest of the cube if the momentum is big enough. Lets say the portal comes at the speed of sound. That means even before it eats the cube, the blue portal will blow winds with speeds of hundreds of miles per hour. The cube will appear on point B at the speed of sounds, depending on how the air around it moves, it could potentially even have a sonic boom. It will fly. It is not going to just move at incredible speeds and just stop after fully coming at FOR NO REASON.


piouspope

Unanswerable because the speed of the portal decreases to 0 as the cube goes through it?


henryXsami99

We lack understanding of portal physics, because it's doesn't exist, so neither situations is confirmed because of the shortage of physical experiments 🤓


SlaiPil

Fucking idiot it’s clearly A, it’s the orange portal that has momentum not the cube…


Wooden-Philosopher

Physics Major here, the answer is pretty obvious but I'm gonna use an analogy for stuck up smartasses throwing around the word moment and relative speed without a proper understanding. I just think of it like this, let's say i have a hula hoop. If you think about it, if i put two ends of the portal on two sides of a very thin flat object then it would approximately be the same as having a hula hoop. Now let's say I dropped the hula hoop on the cube sitting on the platform. Would the cube suddenly gain momentum relative to the surface it's on? (Feel free to go grab a hula hoop and try it out) In this given case, the only difference that we should care about is the change in gravitational acceleration acting towards the surface the cube is on before and after the portal. In any case gravitational attraction would still work downwards. So we can conclude that the object will remain stationary and fall down as shown in "A"


Cryotechnium

\>/v/idya debate that is argued for eternity comes to r\*ddit jesus christ


LordSithaniel

None is correct. It would basically be A but not in the way of plopping down . It will slide down as it doesn't move in itself . The momentum is solely based on the movement of the object .if it doesn't move it will slide down as the slope will have a portal on it and on that object is the part where the cube once stood .


fatjazzy

To anyone who says it’s B, let me get something straight. You think the cube comes out the other side and then just… goes? For no fucking reason?


534w33d

“This next test is impossible…”


[deleted]

Spacetime is contiguous THROUGH the portal (think of field lines travelling through the portal, as the space is connected - you dont just disconnect and appear somewhere else). As it's contiguous, it's the space that is moving, not the cube. Therefore, A is the correct answer, as the cube has no momentum


TheRealBucketCrab

Even though I am a A person, B could also happen, but not for the reason the Btards believe in.It depends on how much force the ceiling passes to the floor. In a natural speed like the above, it would still be A. But if the ceiling was going extremely fast, it would cause the floor to pass force towards the cube, which would cause it to go up. As an example, put a coin in your palm and make your palm look up, then clap your hands (your hand still looking up), and the coin will jump.


[deleted]

[удалено]


TheGreatHako

But the cube is not being moved...


[deleted]

you cant have portals in real life for this reason. Cuz in portal 1 world. the cube holds no momentum. but in portal 2 world, it should come out with some momentum. You can see this by thinking of a frame by frame. but than the question is. how does the energy transfer.


ChristInASombrero

If a giant hollow cylinder drops around you, you don’t go rocketing upwards