Portals

If A were to happen, with what velocity does the object come out of the portal? It just moves quickly then comes to a stop without being strapped down or anything? Where does the momentum of its motion upward and to the right go?

If B were to happen, where does the momentum come from? When the piston smashes the lower plate, does some of the piston's momentum transfer to the object? If so, how does this work in cases where the piston has very low mass and the object has very high mass? If the object's momentum came from the piston, how would such an object come out with more momentum than the piston had to start out with? Where does the extra momentum come from?

Math or gtfo.

Sorry to break your immersion but you shoot an event trigger

How do you know an object is moving, user?

Should momentum be conserved from both frames of reference, the one of the cube and the one of the portal?

If you believe it's A, I have to assume you are mentally handicapped.

Then explain why it is b.

/thread/

LOOK AT IT FROM THE ORANGE PORTAL'S PERSPECTIVE YOU WANG

THE CUBE IS *LITERALLY* IN MOTION

Okay, so where does the momentum come from?

I mean, a rule with portals is that they don't respect conservation of energy in such a way that if you send it back, the opposite effect occurs (i.e., gain potential energy going to a higher elevation and negate potential energy going to a lower elevation). If you were to push the object back through the portal, what would happen? Surely, the piston wouldn't start to lift back upward as you pushed the object against the floor on the other side. You would just be pushing the object against the floor.

It's A

Box has no relative inertia and the portal doesn't impart inertia to it

What force causes the cube to slow down once it's come out the orange side?

portal 2 is not canon

It's glued to the platform obviously

portals only have one side, the box is not moving

>portals only have one side
?

...

That's not oranges frame of reference. That's blues frame of reference.

From oranges frame of reference the cube is not moving

It was never moving, so it can't slow down. The portal is like a hula hoop

If it's not moving, how does the top of the cube change from being flush with the inclined plane to being above the inclined plane? Any point on the cube has to change positions from the orange portal in order to get above the orange portal.

It changes when it moves relative to the blue. But since it is not moving relative to orange, as soon as the entire cube is covered by the blue, its motion relative to the blue no longer matters

Here is a hint for those who dont know the answer:
If you changed the weight of the piston, but the velocity was kept constant, would the cube's velocity change coming out of portal B?
If you changed the velocity of the piston, what effect would it have on the cube as it passes through the portal?

Consider kinetic forces.
The movement is velocity based, not acceleration based until you consider the phonetic movements of a solid

These are objectively the dumbest responses in these threads.

B, because it's tested before.

gr8 b8 m8

What?

>Okay, so where does the momentum come from?
The portal is moving the entire universe, including the cube. Like bruh it's so simple how can this be more simple. If you were on the other side of the orange portal, the things that you would see looking THROUGH that portal would be moving toward you.

>Surely, the piston wouldn't start to lift back upward as you pushed the object against the floor on the other side.
Of course it would, brainlet. Pushing an object through one side of a portal makes it come out at the same speed. So there would be a force separating the cube from the surface of the blue portal.

Worst bait I've ever seen.

People tell me what happens in this scenario.

BTFO

>If you changed the weight of the piston, but the velocity was kept constant, would the cube's velocity change coming out of portal B?
No.

>If you changed the velocity of the piston, what effect would it have on the cube as it passes through the portal?
The cube would exit the orange portal at exactly the velocity of the platform.

>The portal is moving the entire universe, including the cube.
That just makes your position worse. Where does the kinetic energy of an ENTIRE UNIVERSE go when the portal stops?

>Where does the kinetic energy of an ENTIRE UNIVERSE go when the portal stops?

It disappears. Portals do not conserve energy, this is a very, very, very well know fact.

When you pass an object from a portal at a higher height to a lower height, where does the potential kinetic energy go? It disappears. The only reason you can make perpetual motion machines with portals is precisely because they do not conserve energy.

Imagine the piston stops midway on the cube.

If A is right, the cube will be sticking halfway out of the blue portal.

If B is right, the cube will shoot out of the portal, just as if the piston came fully down upon it.

In fact, if B is correct, if even a single atom of the cube touches the portal, the rest of the cube will be sucked through.

Seeing as we do not see this type of behavior in the Portal games, we must conclude A.

I see what you're saying and it makes sense. Minor point though, what you're referring to is called "gravitational potential energy". There's no such thing as "potential kinetic energy".

>this question AGAIN

If the piston stops half way through, it comes out at HALF SPEED.

Simple mathematical proof:

Let's say the speed of the piston is v, and the mass of the cube is m. Now let's calculate the momentum relative to the surface of the portal.

The portion on the blue half is moving at speed 0, with mass m/2.

The portion on the other side is moving at speed v, with mass m/2.

We know that portals conserve momentum. So we know that the final speed "x" multiplied by the total mass "m" must equal the total sum of momentum

x*m = 0*(m/2) + v*(m/2)

x*m= v*m*(1/2)

x = v*(1/2)

x = v/2

Half the speed, mathematically proven.

It's the same as if a sticky ball of mass m/2 moving at speed v runs into a stationary ball of the same size. They stick together, and continue on moving as one large object with mass m and speed v/2.

Wrong.

You can't just do the calculation when mass = m/2.

The cube is accumulating mass, and therefore momentum as it comes out the exit portal.

So the cube would come out at full speed even if a single atom went through the portal.

Wrong wrong wrong. The instance the cube begins to exit the second portal, it is already at maximum velocity! And unless some force acts to slow it down, it will continue at maximum velocity.

meaning is right

>Wrong
No you

>You can't just do the calculation when mass = m/2.
Yes I can

>The cube is accumulating mass
No it is not. If the portal has stopped, the cube is not accumulating mass.

I can also do the same calculation for the piston starting out fast, decelerating and coming to a slow stop as it passes the cube. This would involve calculus and I could do this for you if you want!

In fact doing the calculus would be fun, I'd be willing to do it if people want to see...

seeWhat is slowing the cube down to half speed? Nothing, therefore it will continue at maximum velocity.

>And unless some force acts to slow it down
The tension force from the other side of the cube.

If the cube was made of sand or something it would just rip apart in two. But since they are connected, the moving part of the cube has to pull the non-moving part, slowing it down.

>What is slowing the cube down to half speed?
Tension.

Under this interpretation, the cube would be accelerating out of the exit portal. Because the portion exerting a tension force is constantly decreasing. But this is not the case. The cube does not accelerate out of the exit portal, it exits with constant velocity.

CS majors pls stop trying to do physics

>Under this interpretation, the cube would be accelerating out of the exit portal.

Ok, what situation are you talking about?

Are you talking about the situation where the portal passes through the cube without stopping or....what?

>Because the portion exerting a tension force is constantly decreasing
If you are talking about after the piston stops, no. The portion is the same... Why would it change? It is always the upper half and exactly the upper half.

>CS majors pls stop trying to do physics
Your memes won't help you know.

Jesus you are dull....

Ok so you claim that if the piston stops halfway, the cube will exit with 1/2 velocity.

This means that when the pistol is at 1/4 down the cube, the cube will be exiting with 1/4 speed. At 3/8 way down the cube, it will be exiting with 3/8 total speed... and so on...

This means that observing the cube from the exit portal, one will see the cube accelerating out. Starting slow and gaining speed.

This however is not possible. The cube is always exiting with constant velocity. Precisely the downwards velocity fo the piston to be exact.

>This means that observing the cube from the exit portal, one will see the cube accelerating out.
>thinking wit portals iz hard xD

You would not see the cube accelerating out. If you were looking into the orange portal, you would see the cube approaching you at exactly the speed v, and it will continue at that speed.

Now if the piston where to stop, the bottom half of the cube would start accelerating at a rate that you can calculate by how fast the piston is stopping. If the piston stopped instantly (which is not possible) the BOTTOM half of the cube will accelerate an infinite amount for a zero length of time. Only because you are saying that the piston decelerates an infinite amount in 0 time.

When you actually bring the piston to a decelerated stop, this problem disappears. It involves calculus but I can do because I'm actually educated.

I think he wants to see the calculus. I'll derive the formula for you now, but only because you asked so nicely.

Real life portals when?

The box is at all times at rest on the surface. Portals can be thought of as doors between two points in space rather than contiguous rooms. If you throw a ball through a door it retains it's energy in the other room. Same with portals. HOWEVER, if you move a door over an object at rest, the object will remain at rest. The correct interpretation of OP's picture is that, in fact, space is moving relative to the box. the correct answer is a.

there is in fact a sequence from Portal that demonstrates this. After escaping, there is a puzzle that involves casting a portal on the roof and riding a pillar into it, which point the pillar stops. Although your velocity relative to the portal is non-zero, when the pillar comes to a stop on the other side, you don't fly off of it.

The inclined plane is in motion, dipshit.

>Portals can be thought of as doors between two points in space rather than contiguous rooms.

If you want to use the old "door" analogy thing, Please see this image for the correct interpretation.

It's not just like moving a door. It's moving a door, AND ALSO MOVING THE ENTIRE REALITY BEHIND THAT DOOR TOO. See image.

>inb4 what if the portal stops
I have an image for this, too.

newton's 1st law only applies to objects who's net force is zero. The box is affected by gravity, therefore the first law does not apply.

This is true. Portals can't exist.
Imagine if you were the cube. The situation from your perspective is the orange portal comes toward you at say 10 m/s. Now consider falling into a stationary orange portal at 10 m/s.

From your perspective as the cube, these two situations are identical, you can't tell the difference between them. So the same thing must happen in each(first postulate of special relativity). Since when you fall into the portal, you fly out of the other with the same speed. The same thing must happen when the portal is pushed towards you.

And if the portal is placed on an accelerating surface then that "ENTIRE REALITY" would feel an acceleration?

What about if you placed it one a rotating surfaced, would that entire reality get tilted on its head?

The answer is neither because if you account for shockwave feed back it will bounce a little due to its attatchment to the floor.
Assuming the portal will work on a flat surface while smoothing is not an issue it will not catch on the edges and then slide down the portal as per figure A

Try slamming your fist down on a table to see the coins jump and jangle.

You are quite literally retarded.
>>Non-trivial space time
>Can't apply standard conservation rules
That doesn't mean a god damn thing. Given any portal situation, we can calculate what is going to happen next. We have perfect predictive ability with portals, and this fact stays true.

It still operates within it's own rules. Sure you can build a perpetual motion machine, but given the exact height of the two portals, the amount of water your are using and properties of the turbine you can always predict exactly how much energy it will produce. The math doesn't explode or anything, every still works out.

And since we can predict the unique outcome of any situation, we should be able to find the unique outcome of this situation in the OP.

Great picture, it proves my point. If you stop the train, the box stops too. Same with this problem.

If you think about portals, energy is conserved relative to the entry environment THROUGH the portal, and then forces from the new environment immediately begin to act on the object. Standard kinematics can be applied with portals if each portal jump is aligned with the last and the forces of each environment are applied.

>inertial reference frames don't exist
Tell us more about how you never even took a high school physics class.

>And if the portal is placed on an accelerating surface then that "ENTIRE REALITY" would feel an acceleration?
Yep!

>What about if you placed it one a rotating surfaced, would that entire reality get tilted on its head?
Yep!

Of course you would never be able to tell unless things from one side of the portal interact with things on the other side of the portal, and the point where the portals meet.

>If you stop the train

You've activated my trap card.

If you suddenly stopped the orange portal with respect to the blue portal, using the door analogy your situation would look like this.

It's pretty clear forces don't propagate through portals. If you cast one portal on the ceiling and a second on the wall next to you, you don't fall through. Yet, the ceiling is immediately next to you.

Except you're a retard, and improperly modeled the problem.

the blue and orange portals cannot move relative to each other because they are the same point in space. So, when you stop the blue portal, you stop the motion of the orange portal, and the space that exists around it, relative to an observer from the blue side.

>the blue and orange portals cannot move relative to each other
Yes they can. The actual SURFACE is the same point in space, but as you can clearly see in the pic here: the piston is moving relative to the triangle. I do trust you have working eyes.

Yep, but unlike you I have more than a second grade critical thinking capacity and recognize the distance from blue to range through the portal is zero, and that the orange portal approaches the cube and then stops, and the cube, at no point, attains any kinetic until it's mass is exposed to the gravity of the orange side and it accelerates off the platform.

This problem can be solved very trivially by examining the forces acting on the cube. You have blue side's gravity, the normal force of the platform, and orange side's gravity. The box remains at equilibrium until it is acted on by a force.

As a final reminder for your /v/ sized brain, the space around the orange portal is in motion relative to the cube THROUGH the portal.

Let me see.. how would I put this...

At the time that the piston is passing over the cube, at that time what is the speed that the cube is exiting the exit portal?

You can say the speed it zero, or else the cube would either

1) never emerge from the portal

2) it was already on the other side of the portal resting there

So the speed cannot be zero.

The cube is exiting the portal at speed v. And unless it is acted on by some outside force, it will continue to move at speed v.

*You can't say the speed is zero

Portals are essentially holes in space. So it's just like having a platform with a hole. The hole being there won't impart any additional momentum. So A occurs.

...

>as soon as the last atom of the cube passed through the portal, the cube, which was once moving at a certain speed will immediate stop

An object in motion will stay in motion unless acted on by an outside force. What force would cause the cube to suddenly stop in mid air?

Assume no gravity, as this does not change the fundamental question.

See pic

Well these problems have a *fairly* simple solution, which would be to require force to push the portal based on what is moving through it.

Of course maintaining any significant speed would require a tremendous amount of force, as the change in velocity is almost instantaneous. And the box in my mind is getting sucked into the portal as you push and it accelerates. Interesting problem.

People who say there is no answer are willingly refusing to think abstractly.

If you take a pole and stick it along the first green arrow, it would behave like it is standing still.

If you take another pole and stick it where the second green arrow is (threw the portal) that pole will behave like the red box is moving. It all depends on where you are. If you know where you are, you can always say, for certain, what will happen next.

No contradictions.

Of course you could blast me the fuck out of you find a situation where this leads to a contradiction/ non-predictable situation.

>actually trying to argue conservation of energy
*cough* perpetual motion machines *cough*

As I'm thinking about it, I believe it could work fine, as long as portals have some thickness. This seems reasonable, there's already limitations on allowable surface.

In game, object was affected by gravity depending on which side of the portal the center of the mass of our object was.
Easily observable by making a portal on a wall and ceiling and sticking the box halfway through.

a) suppose the piston was stopped an inch before half of the box (regardless if it stopped instantaneously or gradually):
Scenario A) the box would remain stuck almost halfway through blue, dead center.
Scenario B) the box would be pulled from blue by the part of the box that passed orange.

b) suppose the piston was stopped an inch behind half of the box (regardless if it stopped instantaneously or gradually):
Scenario A) the box would slide down the blue and possibly fall out due to gravity.
Scenario B) same as b-B.

Now, suppose case B is correct and the piston moves and decelerates in such a way that:
1) for a brief duration t as box enters orange the pulling force on the blue side P is greater than gravity on orange side G;
2) after time t, P < G and eventually P reaches 0;
3) box's center of mass, taking all pulling forces into account, NEVER crosses portal threshold.
Such scenario is well-defined.

From the pov of blue, box would jump a bit out of the portal and then return to being stuck dead center.
From the pov of orange, box would jump a bit into the portal and then go back into original position (suppose perfectly even gravity).

But if the box is pulled (by itself, huh), then it's actually accelerating, and momentum is preserved.
Hence the thing that makes the box "fly out speedily" in case B is the momentum accumulated over the time by the box pulling on itself.

So the requirement for scenario B to make sense, is for the passing through orange to cause object to pull on itself.
And if that's the case then the speed at which box makes it out of the blue portal is not constant (assuming constant piston speed) but accelerating.

So still inconclusive, unless you assume that it preserves piston velocity then there's your contradiction.

I don't even know why the fuck you're talking about gravity, it has literally zero effect on the problem. Assume no gravity.

>Hence the thing that makes the box "fly out speedily" in case B is the momentum accumulated over the time by the box pulling on itself.
Totally wrong. In the vanilla problem, the box is not pulling on itself. In the vanilla problem, the box is already IN motion from the very beginning, and simply stays in motion.

>there's your contradiction.
How do you figure that? Please explain with zero gravity since gravity does not actually affect the problem.

The gravity is important because it's an observable game fact that distinguishes to which space does the object in question belong.
So, which instance of physic forces are applied to the object (we are dealing with two sets of those).

And, as observed, it belongs to the space whose gravity affects it. The transition point being the center of its mass.

The box is not in motion the way we normally define motion, it's in motion in one space (instance of observable universe), while not being in motion in another space.
Pov refers to which space we're referring to at that time.

And the only contradiction is if we both assume B is correct *and* box flies out with the piston's velocity.
Because if we assume B then the movement is accelerated, not constant.
Short proof: orange moves over part of box => part of box accelerates => part of box pulls box => box moves in the opposite direction as orange => more box passes orange in next instant of time.
Hence accelerated, not constant.

Get fucked: youtu.be/Ajf7hahKKXo?t=1m5s

>orange moves over part of box => part of box accelerates

Ok now I see the fault.

First: What is acceleration?

It means it goes from one velocity to another. A change in velocity. But there is no change in velocity here.

As the cube is exiting the portal, it exits at speed v. On that side of the portal, it was always at speed v, and thus the velocity has not changed.

In fact, on BOTH sides of the portal, if you look at the cube's speed relative to the surface of the portal, you will see that one one side it is moving as speed v, and on the other side it is also moving at speed v.
The speed never changes from 0 to v, the speed is always at v from the very beginning.

>b-b-but the exit portal is not moving relative to the cube!
That's only if you draw a path from the exit portal straight to the cube without the path passing through the portal. The cube does not take this path, however. If you draw the path through the portal (the actual way that the cube goes in the problem), you will see that on that path, the exit portal is indeed moving at speed v relative to the cube.

Your logic just uses the path that the cube doesn't take, and that is why you get the wrong answer. You feel like all paths should be equal, but this is neither necessary nor accurate. It's not necessary because cubes can only take one path.

it's a.
>inertia
clearly bait. what is the box's state before it enters the portal/literally just a hole? however fast the hole is moving doesn't affect the object it passes over, though in this case there's the change in the gravity.

>there is no change in velocity here
The way I see it, there is.

In one space the part of box that's going through orange is having its velocity set to v, up from zero. (thus in this space, it will pull the box)
In the other space the very same part has its velocity set to zero, down from v. (thus in this space, it will not pull the box)

Imagine someone removes blue (without loss of generality, placing another blue where it instantly disappears) while box is almost halfway through. Box gets crushed.
Imagine someone removes blue while box is over halfway through. Box gets pulled from blue by that part of it, that was already out of blue.

Magical laws of portals somehow nullify all forces of both spaces that would make the box go crazy and keep it together instead, so from both perspectives the transition is smooth as if the portal was not there (just a plain hole in single instance of universe).
The way I see it portals are interweaving two instances of same universe, and the only "weird" physics happen in-between. But! We know for a fact that portals do it in such a way that maintains seamlessness, even in case one portal disappears midway.

I'll think on it more, now I gotta go.

No dumbass you need a consistent set of rules to get make a prediction. Notice how everyone here is just using Newtonian physics to try and answer the question, conservation laws come from conserved Noether currents. In non-trivial space times these currents need not exist, the classic example is in GR where there is no global conservation of energy. To summarise:
>You're applying Newtonian physics to something that is manifestly non-Newtonian.
There is literally no way to answer this question.

What would happen here? My guess is that the stick would keep moving with the portal.

Cube doesnt move space does reeeeeeee

>literally not canon
>relevant
(((HMMMMMMMM)))

Kys you fucking mongoloid

Again, the cube was never moving with respect to the orange, so it shouldn't move at all.

The mistake you're making is that you're thinking about this as though the orange portal being dropped onto the pedestal is the same as the pedestal being rammed against the orange portal. If the speed-lines were underneath the bottom pedestal as opposed to the top one, then it'd be B.

It's a lot easier to visualize if you face the blue portal straight up instead of sideways.. If I drop an orange portal on top of a cube, is the cube just going to get some sort of "speed boost" and shoot upwards out the blue? Go drop a hula hoop around a box and see what happens. What experiences the change is the orange portal, not the box.

Your matter exits the blue portal at the same rate it enters the orange portal, so I imagine if you're rapidly being ejected through the blue portal than B would be the likely scenario.
Staring into the blue portal, it would appear that the cube is moving toward the orange and not the other way around.

-better yet, imagine a scenario where we have the blue portal facing upwards, and the orange portal only rushes halfway down the length of the box and then abruptly stops. toes the top half of the box fly up, while the bottom half stays put or something? Not really, no. You'd get a tiny hop at most, since the top half of the box will briefly be moving quickly on the lefthand side as it "grows" out the top of the blue portal. It wouldn't be enough to actually pull the bottom up though unless this were super fast. Though I guess theoretically if the orange platform were moving insanely fast and stopped immediately when it hit the stoppers, you could rip the box in half.

Here you go, best I can do.
It proves that B can't be the case, but it's still inconclusive whether A must be the case.

The key here is observing that portals are designed so that they relay matter between them as if they were holes to other places.
Obviously passing through a hole under normal circumstances doesn't make the box accelerate - it preserves its momentum.

For B to be true, the box would need to emerge out of blue with initial velocity being that of piston.
So at some point during transition, some force had to be given to the box, suppose (without loss of generality) that it happens midway.
Then the moment orange passes half of box, the box is "sucked up" into the piston and out the blue.

This is inconsistent with what either orange-reality observer AND blue-reality observer expects if portals were replaced by holes.
Orange expects box to stay put throughout the whole ordeal as no forces are exerted on it.
Blue expects his room to keep approaching the box at constant speed, and, after crossing the threshold, for the box to start falling (due to it now being subject to blue gravity).

Assuming option B however:
Orange sees box sucked up the piston at middle-box threshold, inconsistent with what they'd expect.
Blue sees his room approach the box, and then after threshold is crossed the box continues approaching him at the room's pace (how are these related?).

Any issues with this logic?

>Any issues with this logic?
more with the initial assumption , but I'm just playing devils advocate here

Between t 1 - 4 on the lefthand side, all of the parts of the box which are through the portal are moving with respect to the blue portal (by virtue of the fact that they're moving with respect to the orange portal). You're moving at some speed V through the portal. Look at but imagine the box is a hamburger. First, the top bun goes through. Then, from underneath, the burger comes up. If you're standing on flat ground and suddenly the floor beneath you raises (presumebaly at a high speed) what happens? You hop upwards. If you replace the burger with something gooey like a shmore, you might even pull the bottom up (although it would also be pulling you down, which I think evens everything out, hence why I think either the box breaks in half or stays still, depending on the properties of the box and how fast the portal was dropped down).

Yeah, the initial assumption is crap. It's essentially "portals break physics to maintain a certain goal, no matter what", and we use the thing they maintain as substance for proof.
It sucks, but it's what we're given (by virtue of game's explanation of how portals are supposed to operate).

I also get your point. What you are saying is just one of the ways portals could be breaking physics to do what they are supposed to do, my example is just another way.
Of course, at this point it's speculation, however it's not the B some people were suggesting here for sure.
It could be some weird variant of B, but the box most *certainly* doesn't preserve piston's velocity. That just observably doesn't make sense.

...

you are rarted

Do objects travel through the portal continuously or as a whole?
In other words, is the object physically on the orange side until the entirety of the object has finished passing through the portal?