hey /sci/, I know this contains a video game reference but /v/

>>8911770
A is correct, there is no momentum transfer to the cube.

>>8911783
that's correct but people keep arguing that "relativity" makes b correct

>>8911787
how would that even work?

>>8911787
Reference frames only factor into it if the orange portal is moving at a high speed so the cube is held against it, then it suddenly stops

>>8911787
>>8911783
Neither is correct, as analysis of the momentum of the problem depends on the reference frame, and therefor the problem is ill-posed.

This is precisely why portals are not allowed to move in the game, and break when the surface that they are on does move.

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>>8911796
something like this

>>8911770
There's some non-trivial spacetime going off. So you can't apply standard conservation rules to it, which leads to it being unanswerable.

>>8911770
Portals dont work on moving surfaces.
They collapse therefore that scenario is irrelevant.

Think about it this way. As far as the cube is concerned, it hasn't moved, gravity's just suddenly moved off to the side.

>>8911829
But portals are not fixed in space, related be to another observer, they are moving, with whatever planet they are on. Put a portal on a fixed surface extending outward toward the edge of our atmosphere. Now imagine space ship, relattively static in space around it. When the globe rotates, and the portal captures the space ship, you are still faced with OP's conundrum

>>8911816
You just changed it to now a a force is acting on the cube.
Good job at accomplishing nothing.

>>8911783
/thread

>>8911787
Those people are retarded.

>>8911798
No.

>>8911851
From the orange portal's perspective, the cube is pushed through it at quite a high speed. Scenario B assumes it maintains this speed.

Though I suppose the actual answer to the problem is "portals don't real"

The most confusing thing about the picture is that when portals are around, there's no such thing as a global inertial reference frame. This makes arguments that rely on conservation of momentum really easy to get tripped up by.

Let's say you want to argue (A) based on conservation of momentum. To make that kind of argument you first choose inertial coordinates on spacetime and then argue that the momentum of the block before and after it passes through the portal in those coordinates is equal. I think the intuitive thing is to use the coordinates "as shown in the picture"; these coordinates are discontinuous at the portal, where as you pass through the plane of the portal there is a sudden rotation, translation, and velocity shift in your coordinates.

Alternatively, someone else might come along and choose coordinates that go smoothly through the portal, but are discontinuous somewhere between the left and right sides of the picture. Choose coordinates on the left side of the picture such that the orange portal is not moving with respect to us, and on the right side choose coordinates "as shown" (such that the blue portal is also not moving). There's no reason to believe these coordinates are any "fundamentally" worse than the ones that are discontinuous at the portal, but everyone agrees that in these coordinates the block does something like (B) (since on the left side we're seeing it fly into the orange portal).
How does one distinguish between these two cases? The fundamental difference between these coordinate systems is that in the latter case, the block does not pass through the region of space-time where our inertial coordinates are discontinuous, so classical conservation of momentum should hold. In the former case, there's no reason to expect that conservation of momentum should hold, since we haven't made a choice of coordinate system encompassing everything interesting about the system that looks anything like classical Newtonian physics.

TLDR: (B)

>>8911862
From orange frame of reference, the cube is not moving. The orange portal has the same reference frame of the cube. So it's still a

>>8911841
No you aren't, it's still the same problem, you just have a static ship instead of a static block and a moving portal on a planet instead of a moving piston. there's still no momentum transfer.

Portals are just different perspectives in space.
Like opening your front door and seeing your backyard.

Perspectives cannot transfer energy.
Therefor A

>>8911887
I'm responding to
>portals don't work on movingly surfaces

Say I set up a normal door frame on a track, and then stood in front of a wall at the other end of the track. If the door starts accelerating down the track towards me, am I suddenly shot forward when the frame passes over me? No, of course not. Same thing with portals, so A.

>A moves at 40mph to envelope B and is ejected at C which is moving at 40mph for a net change of 0
This is a door

>A moves at 40mph to envelope B and is ejected at C which is moving at 0mph for a net change of 40
This is a non existent portal anons are sperging about.

The numbers must be equal not counting gravity and wind resistance.

Its B. Only trolls and retards would say otherwise.

>>8911770
A is correct.

If B were correct that entire game would need to be redone.

However, neither A nor B can even work in that game since portals can't move like that.>>8911770

>>8911770
B is obviously correct.

If the piston slams down on the cube at 10 meters per second, then 10 meters of cube enter the portal per second. That means 10 meters of cube had better come OUT as well, otherwise the cube would get squished by passing through the portal, which the picture makes clear definitely does not happen. And if 10 meters of cube come out of the portal per second, that means the cube has a velocity of 10 meters per second relative to the exit portal -- that's what velocity is.

>>8911770
Nobody has been able to justify why "A" because it's not "A". Go ahead, try to prove it, you will fail.

>>8911811
>>8911829
And no, the answer is not "There is no answer lol".

In the game, objects come out of the portal the same speed that they went in. I can prove the answer is (B).

Let's look at an atom on the top face of the cube. Also for simplicity, let's say that the cube is 1 cubic meter and the portal is travelling at 1m/s. We are not even going to look at the blue side of the portal, we will focus on what is happening on the orange.

Now the atom on top of the cube hits the blue portal at t = 0. Now let's calculate that atom's distance from the orange exit portal.

Well, after 0.5 seconds we know that the blue portal has half-way consumed the cube (0.5m). So where is the other 0.5 meters of the cube? Sticking out of the orange portal. So what is the atom's distance from the orange portal? Easy, it's 0.5m.

After 0.5s, we have gone from a distance of 0m to 0.5m. Brilliant, this means that the atom is travelling at 1m/s on the other side of the portal! And it will keep at that speed unless acted on by an outside force, that is how atoms behave. So that atom will keep traveling at 1m/s UNLESS some of the other atoms of the cube are holding it back via electrical forces.

So how do we know that the top atom won't get held back by any of the other atoms? Easy. We just proved that the top atom on the cube travels at 1m/s when it exits the portal. This also holds true for every other atom in the cube. So in total, all atoms of the cube are traveling at 1m/s away from the orange portal. Therefore the whole cube is travelling at that speed, therefore the answer is b. Otherwise the entire cube would have to slam to an abrupt halt just after the last atom exits the portal, and this violates inertia.

Just think of it intuitively: If you throw a ball in a portal at 3 m/s it will come out at 3 m/s.

>>8911840
Think about it this way. As far as the orange portal is concerned, a cube has just emerged at X speed and shows no signs of stopping.

>>8911770
A is correct. Relative to the portals, cube is moving fast, so it quickly appears. But relative to ground/earth the cube is not moving, so it falls to the ground after quickly appearing. The portals add zero momentum. Otherwise there would be some kind of inertia that had to be of overcome when the portal moves over the cube as the piston instantly accelerates the cube. This would generate a ton of heat, etc. But these affects are never touched upon by the game or anyone that ever discusses this question because it is assumed these affects are not relevant, because everyone knows A is correct

>>8911829
in one location in Portal 2 you have to place a portal on a moving surface

>>8912008
Nice long wrong answer, faggot.

>In the game...
portals don't move.

>>8912008
Think about it this way. The piston instantaneously halts after 75% of the cube passes through the portal. Are you going to have the 25% of the cube still under the piston magically jump off the platform suddenly?

>>8911937
you're not displaced in space like you would be when going through the portal
also, both the exit and the entrance are moving in the same frame of reference relative to you and at the same velocity

>>8912137
if its going fast enough, yes

>>8911770
It's obviously B.
Anyone saying otherwise is a turbo brainlet.

>>8911770
obviously A is correct. The cube has no initial velocity and the portal passing around it does not impart it any velocity as it moves around the cube. The stationary cube remains stationary (before it slides off the second platform).

>>8912137
The top 75% has quite a bit of momentum at this point and will pull the remaining 25% through.

It's unanswerable because such a fucking device doesn't exist you /v/edditors

>>8912008
>In the game, objects come out of the portal the same speed that they went in.
Wrong, objects come out of the portal with the same MOMENTUM that they went in relative to the exit portal.

>>8912223
the portal is not a force acting on the cube

>>8912229
and the same mass, so that means it's the same speed you faggot imbecile

>>8912229
and assuming that what went in has the same mass as what came out it will have the same velocity. unless the "portal" transforms some of the kinetic energy into angular momentum but I have never played the stupid game this question is about so whatever.

>>8912233
>>8912237

The answer is still A, because even if the moving portal sees the object with a speed V, it also sees the stationary exit portal with a speed V, and thus the velocity of the object relative to the exit portal is 0.

>>8912008
if portals didn't move you'd be right
after that, speed is relative depending on which one you're looking at, so your idea on what happens is ridiculous

imagine the portal stopped halfway
according to you the box will still be thrown out and lifted for some reason

your shitty idea of mechanics of a fucking videogame is inconsistent, so
>there's no answer lol

>>8912240
>The answer is still A
obviously

but we are assuming a coordinate transformation accomplished by the portal upon the cube without respect to the displacement of the matter in the location of the cubes materialization. You must presuppose annihilation of the matter in the location of the cubes materialization (impossible) or the whole thing is impossible.

>>8912137
This is the first argument I have seen in many discussions on this topic that actually changed my mind and caused me to update my thoughts. Good job, anon. Credits are deserved.

I maintain that answer A is obviously wrong, but I am now in doubt about answer B as well. The physics of portal-with-movable-portals is one for which it is not clear whether it can mathematically exist as an extension of Newtonian physics. While it was obvious to me that A would not be a consistent extension of Newtonian physics, I thought that B could be; but now I am more inclined to say that neither A nor B works as a consistent extension of real-world physics. Meaning that either (1) the behavior would be something unlike either A or B; or (2) a physics of moving-portals can be an extension of Newtonian physics, but the high-level behavior of objects therein is NOT an extension of the high-level behavior of objects in Newtonian physics; or (3) the extended physics is contradictory in its entirety.

The discussion managed to change my mind. Well done, anon, and thank you.

>>8912275
>I said "there's no answer lol" was wrong but now I realize it was right
video game mechanics are usually shitty and inconsistent.

>>8912283
No, that's oversimplifying things.

Most people saying "there is no answer" are deferring to the fact that (1) the game doesn't let you know this so the question is moot, or (2) the fact that this isn't real OR supported by the game means we can't get more experimental evidence, or (3) portals aren't real so the question is silly. I don't support any of these; exploring the nontrivial consequences of a hypothetical extension of physics is entirely legitimate.

There have been some people claiming the scenario is inconsistent (that is to say, incompatible with any consistent physics); but they are not in this thread, and I have never seen anyone offer an *explanation* of that, just a flat claim to dismiss the argument. (And no, a reference to the impossibility in the game does not count, for it is the inconsistency of an extended hypothetical physics that we are discussing, not a property of the game.) This is the first time ever I have seen an argument causing me to take seriously the possibility (I'm not entirely convinced yet) that no such extended physics might be possible.

>>8911880
then how did the fucking cube exit the portal faggot
jesus christ so many faggots in here acting like they know shit when this scenario is intentionally ambiguous
before entering blue, the cube's particles have no momentum wrt the frame of reference of the room
upon entering blue, the particles exiting orange are imparted momentum since they're FUCKING MOVING wrt the room
wrt the frame of reference of the blue (and orange) portals the cube is moving

kill yourself portals aren't even fucking real and this is just one reason why

>>8912306
so your idea is everyone was wrong because nobody bothered to explain it to you?
honestly I call people in threads like this idiots and tell them to fuck off with the unanswerable videogame "physics" bullshit pretty often
you shouldn't assume so much about what people who don't say the same as you know. they might know more.

>>8912324
>then how did the fucking cube exit the portal faggot
Displaced by the cube's own weight normal to the surface of the inclined plane the orange portal.

>>8912117
>t. IQ of 80 with no imagination or abstract reasoning faculties

>>8912231
that doesn't change the fact that the particles that have moved through to the other side have been imparted momentum in some fashion
whether or not the portal itself imparted the momentum doesn't change the fact

>>8912306
most people saying that "there is no answer" weren't deferring to any of your retarded arguments
it's really easy to see why the scenario is self-contradictory and your inability to see this while maintaining superiority is hilarious

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What would happen now?

>>8912328
so objects which move wrt an inertial frame don't have momentum?
thanks for the enlightening idea, i'll be sure to collect my Nobel this year

>>8912351
l-lewd.

>>8911888
>>8911937
Jesus Christ I'm amazed at how retarded this board can be sometimes.

>>8912108
>>8912212
>exits through portal B with (obviously) non-zero velocity with respect to the room, and thus the Earth
>remains stationary
this is really activating my almonds

>>8912224
>we can only talk about things that physically exist in reality guys
>the entirety of mathematics is bullshit guys please believe me those things don't even exist in reality all mathematicians are liars
Stop breathing my oxygen.

>>8911937
No, you continue to move with the same velocity, relative to the doorframe, unless some force acts upon the doorframe or you. It's B.

>>8912374
This is literally physics and not math. Discussing retatded vydia shit has no purpose other than pure cringe, because the only thing we know it's that it makes something teleport magically into some place. It's you retatded faggots that are always analysing comic book shit and just being a neckbeard autistic manchildren faggot.

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what now, /sci/ ?

>>8912467
i'm at a pure loss

>>8911816
I see the scenario this same way, if the portals can move relative to each other then you have to consider everything behind the portal to be like a second universe moving along with it, otherwise if you put portals on entities moving at very different speeds (like the moon, as a totally random example wink wink), by maintaining your velocity relative to the entrance portal you would go flying and splat against a wall whenever you passed through them

moreover, I think if the portals can change the direction of your movement based on their relative angle they should also change your speed based on relative speed

>>8912402
>"This is literally physics and not math"
>theoretical physics isn't a thing
Stop posting any time.

>>8912513
>Theoretical physics is math

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>>8912467
where's my grant money

>>8912551
shouldn't the surface behind the portal actually collide between itself when the two portals also collide ?

>>8912229
This is wrong too.

Momentum magnitude is conserved, not direction.

>>8912563
the tricky part of this scenario is keeping in mind that there is nothing behind the portals, everything behind the orange is what's in front of the blue and visa versa

>>8912563
No, the tricky part is even getting as far as supposing the portals move, which they don't. The moving portal question has no basis in either virtual or physically reality.

>>8912008
Portals dont work on moving surfaces.
You can write 2 more walls of text that doesn't make it right.

>>8912580
i made that picture because it's the only "lore" friendly paradox you can actually make.

portal can move but not forward or backward, only up/down/left/right. the game also handles portals that move forward and backward but they're never shown.

ie: ur wrong & stupid, stupid.

>>8912569
what about the orange portal ? it's not shown in the picture but it should definetely come out of the blue portal

>>8911770
So, uh, forgive me for asking supid questions. My intro physics classes were quite a while ago now.

I feel like a lot of people here are focusing on Newton's First Law and while I think that's interesting I also know that the interactions here are a bit too complex for me to say what's going on with that in this particular instance.

However, I'm just thinking about Newton's Third Law.

So based on Newton's Third Law we know that if the cube is sitting on the platform it starts on that it must be pushing down on the platform with a force equal to the relative force of gravity and the platform is pushing the cube up with the same force, right?

But then when the portal passes over the cube there force gravity exert's on the cube changes direction instantaneously and becuase of that the cube's center of gravity relative to the platform shifts to it's corner instead of it's center.

So would that cause the cube to sort of try to rotate then? Because the force it's exerting on the platform goes from being evenly distributed across it's surface to being weighted to one side of it's surface on a gradient. Like, would the change cause the forces to suddenly become unequal and thus cause the top edge of the cube to be pushed forward and cause it to rotate?

>>8912008
>And object in motion tends to stay in motion and an object at rest tends to stay at rest.

>~Isaac Newton

>>8912592
the orange portal never enters the blue portal, it doesn't do anything

>>8912580
portals aren't exist, aspie

First of all, assuming a break through were made and we could create portals, would portals be flat as depicted in this game or would they be 4th dimensional or maybe 3rd?

>>8912622
Isn't the point of them that they're two-dimensional interconnected holes?

>>8912632
But if they're connected, would they really be two-dimensional? If you can directly travel through them, would that define them as 3rd dimensional or 4th dimensional?

Can you actually travel through things with a second dimensional nature?

>>8912622
>>8912632
>>8912652

if they really are 2D, wouldn't the edge be able to cut through anything ?

>>8912664
Can 2D objects interact with 3rd or 4th dimensional objects? Or can they only be displayed?

>>8912664
Define "cut"

>>8912336
It does, the energy has to come from somewhere

The cube has inertia that must be overcome to accelerate the cube. There must be a reactionary force due that that inertia. All the usual physical mechanics must still be present and balanced. All the portal does is bend space-time between two regions. For all the cube is concerned it has not moved, space just bent around it, but the cube never accelerated. Momentum is concerned.

The only way B would be right is if blue portal was on the equator and orange was at a different latitude, then the cube would maintain it's higher momentum from the angular velocity it had on the equator with respect to the new space. And even then, it wouldn't be the portal giving the cube momentum, but the orange portal falling away/behind the cube

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>>8911862
>>8912224
>>8912324
>>8911974
>>8912620
HEY GUYS! DID YOU HEAR THESE ANON'S?!

THEY SAID PORTAL'S AREN'T REAL!

>>8912594
Technically, gravity would get really wonky when you get close to the portals, because now the Earth is nearly equally close to the cube above as it is below.

>>8912737
I thought about that but in the end I gave up and decided that gravity just wouldn't pass through a portal or shit will get fucked really quickly.

>>8912725
The cube wasn't accelerated, though, from the perspective of the orange portal it was always moving.

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>>8911770

>>8911770
in order for a paradox not to be created the exit portal has to be moving at the same velocity as the entrance portal. the moving exit portal then deposits the stationary cube in the different location.

>>8911770
A. The cube is not moving through the portal, the portal is moving around the cube.

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>>8911770
I wish someone would just make a gif of someone putting a cube on a raised platform through a hula hoop already.

>>8911770
It's not real, so really, whatever you would like to happen is fine

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>>8911825
Probably best answer in this thread, only one which got no (you)s

Contributing with my take on this, more precisely why is this not tractable with classical mechanics.

btw the "portals violate energy conservation laws anyway" is not a good argument. This is only because of the way gravity is dealt with in the game, you could have a gravity potential that works with portals. And gravity is not even necessary here.

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>>8912828
Right, so in the orange reference frame, the plinth isn't moving. In the blue reference frame, the plinth is moving upward and then stops. So that means that every part of the system that goes through the portal is given motion as soon as it goes through that portal.

If the cube remains static after passing through the portal, it'll just plop down. However, if you consider the smasher continuing to push downward so the portal consumes the plinth, the plinth will clearly be moving upward in the blue reference frame until the smasher stops. That essentially makes the plinth into a pinball plunger. Guess that makes it B.

>>8912117
The earth moves
>inb4 they don't move relative to each other
In the ending of the second game you put a portal on the moon.

>>8911770
Wow. That is some ancient bait. I'm impressed that somebody animated it.

>>8913689
Point out 1 ACTUAL EXAMPLE of something that is inconstant with portals.

Yes everyone knows portals aren't real. But the rules are very well established, and you can extend these rules to moving portals with zero inconsistency. This extension of rules can only happen in one logical way, we have shown what that way is. Getting the answer requires thinking with portals, something the game tries to teach you to do.

I'm sitting here and you still haven't pointed out a single inconsistency. (Inconsistent with PORTALS, we already know portals can make perpetual work machines.) But within the logic of moving portals there is nothing inconsistent with B.

Its A, simply because otherwise you could make a perpetual motion machine for infinite energy

>>8914523
This is just a hypothetical situation, so what is wrong with hypothetically having infinite energy?

If you can accept the existence of portals, surly you can accept having infinite energy. This is just a math problem. The rules may contradict our reality, but in a world with portals there are still rules, just different rules.

We can predict what will happen in any situation with portals, because we know the rules.

Also, you don't even need moving portals to have perpetual motion machines. Just place one portal on the ceiling, one portal on the ground, drop some water down the portal and you've got an infinite energy waterfall. It is infinite energy, but the important thing this that this all behaves in a predictable way.

It is self-consistent.

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For people saying that from the Orange exit portal's point of view the cube is not moving: This is wrong. Imagine yourself on the other side of the orange portal looking in. What do you see? You see a cube, the platform, the ground, everything moving toward you at exactly the speed of V (speed of the blue portal).

From your perspective, the cube is travelling at V. See image. And the cube will tend to stay in motion all throughout passing through the portal.

>>8912108
>But relative to ground/earth the cube is not moving
Wrong

>>8914583
Yes, but it stops moving once the piston goes all the way down on the platform.

>>8914799
What happens when the platform it's sitting on has a velocity then doesn't have a velocity? It's a pinball plunger, like >>8913724 said.

>>8914583
What you see in the portal doesnt matter. Only what the portal is fixed to. The orange portal itself isn't moving with respect to the cube. Since the orange portal is in the same frame of the cube, seeing the cube moving toward you through the portal implies the orange portal can also be seen moving towards you. Therefore, there is no net motion of the cube no matter how you look at it.

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>>8914807
So if the piston stopped in the middle of the cube, this would happen?

>>8914820
no, the cube is a solid object. if the part that's moving has enough momentum, it's going to pull the rest of the cube through the portal.

>>8914828
The cube is not a solid object. Replay the game. Objects going through the portal are destroyed and redrawn coming out the other end. There isn't even symmetry of the redrawn object.

the entrance and exit of the portal must be linked such that they move through 3 dimensional space with the same velocity at all times. If portals were to be "real" they would have to possess that limitation or else they create paradoxes that break the laws of physics.

the OP question statement is flawed because the pictured situation can not take place.

>>8911770
The way how I always imagined it was like moving a hula hoop over/around something, so when the hula hoop moves over it, the object doesn't move, from the perspective of the object, it never moved, so gravity would just change direction and you'd get option A.

If you imagine the hula hoop's sides as being each separate portals, then the idea still is the same, and the object still doesn't move.

I feel like this is one of those "troll science" things from ages ago

>>8911770
Dunno why this thread is still going...

Glados does repeatedly say and demonstrate that momentum of the object is not changed by portals, and that they effectively act as holes.

If there was no piston behind the blue portal and it was just a hole, rather than a portal, if it was just a hole being laid down upon the cube, the cube would not gain momentum, at least until you tilted the table it was resting on.

We also know if you attempt this in game, the piston just gets stuck. (Even if you have to cheat a bit to allow the test.)
https://www.youtube.com/watch?v=S85nudR6D-Y

Further, assuming the cube can fit through the orange portal, it should have already fallen through the portal, gaining only the momentum from that fall.

The blue portal is a hole, so it shouldn't impart additional momentum.

The B answer assumes that the cube picks up the Blue portals reference frame.

...and we know if you stick yourself between the two portals, things just get weird:
https://www.youtube.com/watch?v=0TZd95BCKMY

>>8914820
Things glancing off the side of portals do not get damaged in game - though it seems they should, as that's effectively an infinitely thin edge.

>>8912477
>moreover, I think if the portals can change the direction of your movement based on their relative angle they should also change your speed based on relative speed
In the game, they change vector but not velocity.

"In the game" being the key phrase here - we're trying to apply physics to magic.

>>8914820
Only if the cube was made of mush or something...

The cube moves out at half speed, and I can calculate it for you:

This is simple momentum. As soon as you stop the piston, the bottom half of the cube's speed relative to the orange portal suddenly becomes zero. (think if you were looking through the orange portal and you would see everything on the other side suddenly stop moving relative to you)

But the top half of the cube that has already passed through the portal is moving at speed 1 m/s.

(Let's say the cube is 10 kg)

So the momentum of the top half is 5kg * 1m/s = 5 kg m/s

And the momentum of the bottom, non-moving cube: 5kg * 0m/s = 0

Momentum is conserved, and the total momentum is 5 kg m/s.

It's the same as if you threw a sticky ball at another stationary sticky ball floating in space. The two balls will stick together and move at half the original speed.

So when the top part pulls the bottom half, it is transferring it's momentum to the bottom half. The total weight is 10 kg, we know the total momentum is 5, so now let's solve for the velocity:

10 * V = 5

V = 5/10

V = 0.5 m/s.

It is half of the original speed of 1 m/s.

>>8912137
I can do the same calculation for stopping at any rate (not just suddenly), and any point along the cube, with any given density of the cube.

>>8912275
Don't fall for it. I'm glad you are thinking, but keep thinking and read what I wrote above.

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Speed is relative.

Another thing why scenario A would not work:
While the object is moving through the portal, the part coming out of orange portal would have a velocity and a mass but no momentum or kinetic energy.

>>8912553
It could still follow the conservation of energy if the object with the orange portal on it "feels" a force upwards when its pushing the cube into the portal. But yes, obviously Portals would allow to break that law.

>>8914820
>>8914861
if portals would work like this, a human could not survive going through the portal because parts of the body such as the beating heart are not moving at constant speed.

>>8911811
Have you actually played the game? Theres multiple times when you can have portals move with a surface even in the 1st game.

>>8911770
TEH POVEROV BIG SUKA

Option B doesnt rly make sense since that would mean the entire cube gets accelerated as it enters the portal. If you would stop mid way through the cube would get sucked up into the portal under that model.

>>8915436
>cube would get sucked up into the portal
so?
also it gets pulled up, not sucked

>>8915355
They are moving at a constant speed of 0 because no matter how you look at it, it's a

File: correct answer to the portal problem.gif (67KB, 500x364px) Image search: [Google]

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Scenario A is correct in the OP gif

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B is the correct and pic related is why.
Portal act on their surfaces. Blue copies, yellow prints. Since blue is moving it copies faster than yellow prints so compression is created and that propels the box outward. Think what happens if the piston is moving near the speed of light - All atoms are copied and printed onto the yellow portal's surface near instantly and the box is compressed to a near 2D shape. The internal pressure will cause the box to bounce to an incredible speed.

>you can't compress atoms like this because atoms will push other atoms.
Bravo anon that's called a 'force' and it causes motion!

>but where does the kinetic energy of the box come from?
It comes from you pushing the piston retard. The piston isn't going to slide effortlessly, you have to apply pressure otherwise the piston will jam and stop copying the box (portals will refuse to copy). If you don't believe me consider if yellow portal was facing a metal wall. By this argument I can drop the piston onto the box effortlessly and the yellow portal will readily print the whole box inside the crammed space. This will of course create an immense pressure which will in turn create heat at the wall which I can use to boil water, turn the turbines and power a city. i.e perpetual motion.

But really it boggles my mind people would even think it's A only by considering newton's first law. You can clearly see the box moving while the blue portal is copying it and the yellow is printing it. The box should keep moving. What, do portals act as "pliers" until they completely copy an object?

>>8915298
>that image
I had an idea you may need to "feed" the portals energy to account for the violation.

for example to teleport 1kg 1m heigher it'll cost you exactly 1J of energy that you need to feed to the portals.

you can also make an infinite waterfall like in that pic put it'll be harder and harder to maintain it as the water accelerates.
if you ever stop giving portals enough energy they cease existing and the water will splash onto the ground.

>>8915572
There is no copy and printing. The space adjacent to the Orange portal is also adjacent to the blue portal. Think of the two portals as a tunnel of length 0.

When one of the portals moves, it is actually changing the entrance/exit point of the tunnel. It is the bent space connecting the portals that is moving.

In this scenario it is not the cube that is getting pushing through the portal, but the portal that is getting pulled past the cube. The portals, so long as the cube passes through without touching, do NOT interact with the cube at all, therefore no energy is exchanged and no change in momentum, positive or negative, will result from the cube traversing the tunnel.

>>8914510
>Point out 1 ACTUAL EXAMPLE of something that is inconstant with portals.

This question.

>>8914510
was it too hard to open the image i carefully drew to explain that? let me rephrase it then :

if portals "act like holes" like >>8914953
says the game mentions, then this scenario is not well determined by the rules of physics.

of course you can say they just ensure the momentum of an object going in, measured in the frame of the portal it is going in, is the same as when going out of the other portal in its new frame. Then it would be B.

tl;dr : either you say they just warp space and then the physics don't apply properly, either you make up sufficient rules and state them in the op with your question.

At lot of this comes down to the argument of what the Portal actually is. Is it a collection of particles with its own properties, ei can it have momentum?

I think not, myself. I like to think of it as a sort of a tube between two points in space that moves things through with whatever energy they started with.

>>8911937

But you have to exit the orange portal. And you will be exiting the orange portal at the same rate at which you are entering the blue one. So as you emerge from the portal you are moving in respect to it. The observation of movement means you have a velocity and will continue moving until acted on by other forces so B.

There is no answer to this question. But it's certainly an interesting thought experiment.

>>8916002
But the cube isn't moving, the portals are. The blue portal and the orange portal are one in the same, they occupy the same space.

It is not the cube that moves through the portal, but the portal the moves around the cube.

Otherwise, there would have to be some interaction between the portal and the cube, as that would be the only way for the cube to gain momentum. Where does the energy for this interaction come from? And what mechanism exists to allow it to happen? Which of the fundamental forces is doing the work? Because in game, the portals do not do any work

>>8912005

Wouldn't the cube experience a vacuum effect?

What I mean is that the first half of the cube would be moving around 10 m/s which would apply a force pulling the second half of the cube into the portal, and as it passed through it would still be imbued with the 10 m/s as it changed frame of reference.

So Wouldn't the cube interact with itself? The first 1/10th of the cube suddenly accelerates to 10 m/s exerting a force on the rest of the cube causing it to accelerate in the direction of the portal. Which will cause the next bit of mass from the cube to enter at a velocity greater than 10 m/s. Which in turn exerts a greater force on the remaining mass of cube and so on.

So technically shouldn't the velocity of the cube be greater than 10 m/s as it leaves the portal?

>>8916011

The point is that if we observe the cube leaving the portal at the rate in which it is entering the other portal it is by definition observed to have a velocity.

Another anon in this thread put it this way: if the cube enters the one portal at 1 meter per second we will see it exiting the other at 1 meter per second.

It has to exit the portal at the rate in which it enters the other so motion has to take place and it has to take place over a period of time i.e. the block has a velocity.

Neither solution can satisfy our known laws of physics. As either way we are violating something.

Maybe the portal has to slow down as mass enters it? Perhaps we could get around the law of conservation that way, but I'm not sure. It's simply a tricky problem with no clear answer.

>>8916047
Sure, but it isn't the cube that is moving. It has the same inertia and momentum as before the piston started moving. Even if the perceived velocity of the cube is 1m/s, the perceived momentum unchanged. As soon as the piston stops moving, the perceived motion is gone.

Portal dare I say it /our game/

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Good news everyone. I figured out what that thing you just incinerated did. It was a Morality Core they installed after I flooded the enrichment center with a deadly neurotoxin to make me stop flooding the enrichment center with a deadly neurotoxin. Incidentally you should all get comfortable im going to warm up the Neurotoxin Emitters.
You've been wrong about every single thing you've ever done, including this thing. You're not smart. You're not a scientist. You're not a doctor. You're not even a full-time employee. Where did your life go so wrong?

>>8911770
B is correct. If there is no spacetime friction occurring inside the portals, the box will remain unchanged in speed. Imagine the press was inverted and you'll be able to picture why B is correct.

>>8916071
so if the blue portal continued moving past the cube, would the cube shoot out of the orange portal? what if it started reversing, would the cube be sucked back in?

>>8911770
A. The moving pillar plays no part in the interaction of the portal and cube. Space-time on either side of the portal would not change. The pillar only facilitates their interaction.

>>8916176
Samefag here. whatever speed that the pillar was moving the portal to the cube, it would do the exact same thing. Slower or faster.

>>8911770
'A', and this is a troll.

>>8916171
No, and there wouldn't be any sucking. The moving portals folded space in order to move while sustaining the portals. This folding space is where all the affects would be, not in anything that passes through the portal.

However, the portal would be gaining gravitational potential energy, but not because it is getting raised, but because the bending of space is pulling the rest of the universe further below the cube. When the piston reverses, the space would begin to unfold, and then the portal would again pass through the portal (assuming it is glued to the platform and didn't fall off because of the change in gravity on the orange side of the portals). But it wouldn't be "sucked" though, it would be that the portal rise up past the cube due to the unfolding space. So long as the portal didn't physically touch the cube, there would be no fundamental physical force acting on the cube to change it's momentum.

>this many brainlets stating the answer is A

If the cube 'doesn't have momentum' when it exits the portal, it would have to exit as an infinitely thin plane. The portal very clearly imparts momentum to the cube.

>Well if the piston stops 75% of the way down the cube, it will get pulled out of the portal.

yep, that is correct.

>>8916213
I just saw this post explains it in a lot more detail. This is correct.
>>8915572

>>8912008
You're a mongoloid. You don't even understand what speed is considering you think there is a unique number for speed that each object has regardless of reference frame

>>8912392
The doorframe is an inertial reference frame, dipshit. Your portal that moves and then stops isn't. Relative to the inertial frame that is travelling with the portal then continues to travel at the same speed, in answer A the cube has the nonzero velocity you are saying has to be there.

>>8911770
B is right. The cube has to exit the orange portal at the same rate it enters the blue one.

>>8916176
>>8916181
Imagine standing in front of the orange portal looking into it. As the piston drops you see the cube rapidly approach you. Does the cube magically lose all momentum or does it continue through and hit you in the face?

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>>8915298
this is what would happen within a minute.

>>8916488
Then just put a funnel up top that feed to the wheel. Stop nitpicking diagrams like an autist.

There are actually moving Portals in the Level with the neurotoxins in Portal 2

>>8915608
>>8915298
There's no point in trying to make portals consistent with conservation of energy, there could be thousands of methods for generating infinite energy with them.

>>8916680
someone should use a hax in that level and launch a cube through the portal while it's moving.
if it comes out of the other portal at the same angle then at least according to the source engine A is correct, but if the angle is tilted then B is.

>>8916743
>give it up, Einstein, your theory of relativity doesn't work! just look at all these paradoxes it causes.

This is a great relativity question! It's best looked at in terms of reference frames.

First identify the frames. There's the bottom half of the press which holds the box, and the top half of the press which contains the input portal, which is then equivalent to the platforms frame since it contains the output portal.

From the top half of the press/portal's frame of reference, the box is moving quite quickly, and the scenario looks like the bottom half of the press is pushing the box upward very quickly and then suddenly stopping. In this case, scenario B is correct.

From the bottom half of the press' frame of reference however, the box is at rest and only the top half of the press/portal is applying any force, which would result in scenario A.

In any other physics problem we would choose the resulting scenario based on which inertial frame WE were in to see what would result RELATIVE TO US... which at first seems to be that of the bottom half of the press, since it is at rest relative to us. But we are clearly ALSO in the reference frame of the top half of the press, since the output portal on the platform isn't moving relative to us and it is connected to the input portal/top half of the press.

So we have a paradox because we are simultaneously at rest relative to two inertial reference frames that are moving at nonzero velocities relative to one another.

Sadly, this means that neither is correct because the above situation is unphysical - we can't use any intuition we have to solve the problem.
The only other resolution would be to come up with an argument for why the top half of the press and the platform are not in the same reference frame despite being connected by a portal.

>>8916295
>you think there is a unique number for speed that each object has regardless of reference frame
What? When did I ever say that? What part of the proof requires anything like that?

I am not calculating the "inherent speed". I am calculating the speed RELATIVE to the orange portal. And I am doing this by using speeds RELATIVE to the surface of the portal, not "inherent speeds".

Again, there is no part of the proof that requires object have a "unique speed number", because if the whole system was moving left at 2m/s it would still be the exact same. And you would use calculations from the speed that the cube is going relative to the portal, you wouldn't need to bother with the 2m/s because the question you are trying to answer is "how fast is the cube finally moving RELATIVE to the orange portal?"

>>8916763
well I wouldn't want to discourage you from continuing your work on inventing portals, of course

>>8916775
>we can't use any intuition we have to solve the problem
>i can't into thinking with portals

If you make logical deductions, starting from what we know about portals, you see that there is only one specific answer, and it's B.

The only frame of reference we care about is the surface of the portal.

At every single point before the portal touches the cube, the cube is moving at V speed relative to the surface of the portal.

At every single point while the cube is going through the portal, the cube is moving at V speed relative to the surface of the portal.

So after the cube has passed through the portal, of course the cube is still moving at V relative to the surface of the portal. Since objects tend to stay in motion, and motion is relative to some frame of reference.

In order to prove B wrong there must be some force acting on the cube to change it's inertial tendency.

>>8916800
You can absolutely use intuition. Yours is just shit.

The frame of reference of the orange is the same as the cube. What you see looking through the orange is blues frame of reference. You could also place the orange portal closer to the blue so that you see the orange portal moving towards the blue at the same speed as the cube. Since the speed of the cube and the speed of the orange portal are the same relative to the blue portal, the cube doesn't fly out of the orange. Since the orange portal surface is just looking at the blue frame, you wouldn't expect it to fly out just from looking at the orange. Therfore, it's a.

>>8916800
> In order to prove B wrong there must be some force acting on the cube to change it's inertial tendency.

As soon as any part of the cube has passed through the portal, gravity is constantly acting against the upward movement of the cube. I don't claim that this disproves B, but it at the very least lessons its motion after moving through the portal.

>>8916818
No, the frame of the orange is the same as the BLUE'S.

That's what this debate is about. And that's the paradox. We at rest relative to 2 moving frames.

they both violate conservation of momentum in case there's no energy transmitted to the cube inside the portal (forces), assuming portals conserve the momentum relative to them. so portals have to give the cube kinetic energy making the only reasonable answer B.
you should also check it doesn't violate any physical laws in both reference frames (assuming you can define such thing as a portal reference frame, which doesn't have a well defined position)

A. The portals are simply the entrance and exit to a door frame expanded through space-time. If you throw a door frame on someone they wont come flying out the other side. Neither will the cube when pushed through the portal. The empty space in the "door frame" has no kinetic energy to transfer.

>>8916818
>The frame of reference of the orange is the same as the cube.

Think man, if a cube is moving relative to some object A, and object A is not moving relative to object B, then the cube must also be moving relative to B.

The cube is moving relative to the blue portal. The inside of blue portal is not moving relative to the orange portal, because these portals connect two places instantaneously making them the same place. So the cube must be moving relative to orange.

Watch this gif,
>>8914583

>>8916850
the portals are supposed to conserve momentum, it can't be A. it has to be B or impossible

>>8916863
The momentum of the object traveling through it. Not the momentum of the frame

>>8916870
I don't understand what you mean. Momentum has to be conserved relative to the portal. Relative to the "lab" not really as in the game it happens all the time when the cube changes direction for example

>>8916882
Youre think in physics we already have. The portal itself would pretty much require a unification theory and working knowledge of physics in multiple dimensions. There is literally no momentum to conserve. The portal itself is only the rings. The ends of the portal basically occupy the same space time. Think monsters inc. doors

>>8916891
>you're thinking in physics we already have
so are you in your original post talking about having no KE to transfer or whatever
>the portal would require another theory
I agree with you but momentum conservation is a fact of the universe and any new physics won't and can't change that

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>>8916850
>>8916850
This is an important problem, and you bring up a good point.

Here is the door analogy as I see it:

You aren't just throwing a door, you are throwing a door and the entire reality behind that door too.

It would be like having a cube floating above a train track in space. A train is headed right for the cube, and there is an open door on one side of the train.

The train moves along the track, the door goes around the cube. See image. Now, the cube is still standing still as far as it's concerned. But from the perspective of someone on the train, the cube appears to be rocketing toward the back of the train.

i don't see what's so hard to understand. the cube is moving relative to the blue portal, it should be moving in relation to the orange portal as well

>>8916901
I forgot to say that momentum conservation is the basic assumption of all this (that comes from the portal properties in the game)

>>8916904
Too hard for A babies to conceptualize.

>>8916904
typical brainlets, it's pretty much the only postulate of the portals in the game

>>8911770

If it's a matter transporter it's scenario a.

If it's a wormhole it's scenario b.

If it's a matter transporter that can give momentum to the object during assembly then it's scenario b.

If it's a wormhole that consumes the kinetic energy of the object as its energy source then it's scenario a.

>>8916824
>>8916855
Take the cube out of the picture, the blue portal is definitely moving with respect to the orange.


Instead of them being portals, mark them as respectively colored x's. Surely you agree the piston is moving relative to the floor.

What goes on inside of the portals is irrelevant.

>>8916903
this is why the entrance and exit of the portal have to have the same velocity.

portal entrances and exits can not move relative to one another or else they create paradoxes that break the laws of physics.

if anyone ever did try to set up star gates they would have to make them stationary relative to one another.

File: what now.png (5KB, 343x328px) Image search: [Google]

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what now?
will the cube permanently disappear?

>>8917496
>cube touches itself
>pistons jam
>cube keeps accelerating faster and faster downwards while bottom and top touch

Imagine there's a basketball on the ground. You drop a hula hoop on it and it goes through. Does the basketball magically fly through the air?

>>8917546
>both portals move at same speed in that case
>but in OP only one portal is moivng

>>8915762
>The space adjacent to the Orange portal is also adjacent to the blue portal
Are you implying that's the same space?
Because then if I hover my hand above Orange portal my hand should also appear beneath the blue portal and that clearly doesn't happen.

>>8917551
The point is the cube doesn't 'emerge' at some speed.

>>8917496
the cube becomes crushed by itself.

The piston is not crushing it, the cube is being crushed against itself. (in a way, an infinite stack of itself)

The cube is occupying less and less space but with the same matter, so it compresses.

>what happens if the two portals touch each other, and there is no distance between the two pistons at all?

I'd like to imagine it'd be like one of those hydraulic presses and the cube is smushed out from the sides of the rim.

>what happens if the two portals touch each other and then go through one another??

The pistons would crush each other. Assuming the portals just keep moving.

>>8912568
Go back to high school
Speed is a vectorial magnitude, so is momentum

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>>8917559
You're right the cube slowly changes position but its speed is zero.
>wait... woah speed IS the change in position!

>>8917554
I'm glad someone made a gif explaining why someone would think it's A but the gray area is moving respective to the cube so what you've actually described is pic related.

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>>8917626

>>8914510
Portals break causality by allowing things to teleport instantly, which is faster than c. Anyways it is b. Consider if instead of the blue portal moving towards the cube, the cube moved towards the blue portal. From the reference frame of the cube these two situations are exactly the same. Since the cube is in motion in one situation, it should be in motion in the other situation since the cube won't be able to tell the difference.

>>8917659
Yes, I'm sure there is a way to travel time (in a certain predictable way) with portals. I'm sure of it.

>>8917626
>>8917632
Yeah, I suppose it's the same scenario as your picture. I was trying to reconcile the point that several others brought up about how the portals moving relative to one another doesn't make sense.
You did a similar thing in your picture, ie both portals are moving. I'm just not quite sure what to make of the whole situation.

Guys is this in a vacuum? Because if not what about air. Wouldn't the blue portal go down fast like in the gif and create a suction outwards through the orange portal that will pull the cube towards it?

>>8917554
Nice diagram, but it's still misleading. The cube is ejected from the orange portal at the same rate it enters the blue one. That diagram works when you show the orange portal moving with the blue one, but if the orange is stationary then the cube still has to exit it a a quick rate. Think about the momentum of the cube or the blue portal relative to one another. That velocity can't just disappear.

Portals cannot move, you clearly forgot how to think w/ portals

>>8912137
What's the difference between a cube being fired at a portal at e.g. 10m/s and a portal moving 10 m/s towards a cube. The speed the cube is traveling relative to the portal is the same in both cases.
Are you saying the cube will have 0 speed when exiting the portal for both cases?

>>8917626
>>8917632
I'm going to make a gif explaining why it's B

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>>8918448
You bring up an interesting point.
If you stand close to an Orange portal you would feel a breeze from the Blue portal collecting air. By the same principle if the Blue "collects" a cube it should come out to hit you in the face just like air so it's B.

>>8911770
the energy of the blue moving wouldn't be projectet on love cube, i's a hole, the cube will fall down

>>8911770
what would happen if you press two portals together with something between
>A:Would it create a black hole
>B:Would they create a reverse energy at the pistons
>C:Would the delete the mass between
>D:Would the mass between get transferred in another universe after crashed
>E:Something else (Describe)

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okay, but what happens in THIS scenario?

>>8919009
>>A:Would it create a black hole
No
>B:Would they create a reverse energy at the pistons
Yes, you would have to apply force on the pistons.
>C:Would the delete the mass between
See:
>>8917575

File: Same thing.gif (249KB, 507x347px) Image search: [Google]

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OKAY PEOPLE.

If this gif does not convince every single one of you that the answer is (B) then there is no hope for you.

And if you say there is "no answer", you're retarded it's simpler than you make it.

Here is how to look at this gif: this is in space, no gravity, in a vacuum, just for simplicity, ok? There are two scenes:

In scene 1, both of the outsides of the portals are moving at the same speed. This is like a hula hoop.

Scene 2 is just scene 1 but the orange portal is standing still. Imagine it like a split screen of scene 1, with one camera following the orange portal. I made the cube a long prism so that you can see that the object is changing position as it exits the orange portal, and will continue to change position unless acted on by a force.

>what happens if the piston stops halfway?
Then the object moves from the orange portal at half speed. I can make a gif of this, too.

>what would happen according to laws of physics if we made something that does not obey laws of physics

>>8919150
More like
>if we made different laws of physics, under those laws what would happen in this situation?

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What if it were possible to put portals on curved surfaces?

>>8919192
so objects will get bigger, and it produces infinite air?

>>8919144
You ignored the whole problem though.

What you should draw is the orange portal moving up with the cube at the same speed because that's what's actually happening. It makes no sense for only the cube to move relative to the blue portal when in reality, the cube, the platform and the whole floor are moving to the blue portal. Since the orange portal is fixed to the floor, it is also moving at the exact same speed as the cube relative to the blue, so the distance between the cube and the orange never changes. Hence it's a

>>8919208
But the distance has to change, the cube moves out of the orange portal.

>>8919102
how can they create a reverse energy, if the portals have no own mass, no own energy, no back surface and no thickness

>>8919192
>What you should draw is the orange portal moving up with the cube at the same speed

Draw the orange portal moving up..? At what point in the animation does the orange portal start moving up? Did you stop typing in the middle of you post because you realized you were wrong?

>>8919219
meant for:
>>8919208

how can the portals have a color anyway

>>8919013
underrated

>>8911787
fucking kek. All these retards trying to explain things with reference frames as if they know physics. Any real person who knows physics knows that the reference frame of portal B is a non-inertial reference frame as it accelerates to a stop.

tl;dr answer is A, too many brainlets like
>>8916775
>>8911878
>>8912008
etc
don't understand highschool physics.

>>8919257
You don't understand high school physics.

What is Momentum? It is speed. What is speed?

Speed is a change in position over a change in time.

Now look at the change in time when the cube exists the orange portal. At that point, is the cube's position changing? Yes.

Is there a change in position over a change in time? Yes.

Is there speed? Yes. Is there momentum? Yes.

Wouldn't a moving portal create a dimensional bending and create endless subdimensions

>>8911770
I'd like to say it's actually both A and B

there's no physical law stating that multiple forces can't act on an object
And most of you are making a very obvious mistake

the problem is the gif is too simplified:
A makes it seem like it teleports instead of transfers, which is incorrect
B makes no definite clarification as to how fast the piston is actually moving, leaving it to whoever is observing the gif to make a biased assumption about it's speed

Those who picked A removed the energy behind the piston's movement out of the equation and let the environment be the main affector

Those who picked B made the assumption that the position and force behind the portals are the only forces present and removed everything else from the equation

so it's actually:
A is correct if the local forces are stronger than the forces behind the portals
B is correct if the forces behind the portal is greater than the local forces

it only "appears" to be either A or B

I didn't even go to college and even I could figure out the problem

>>8919267
Except where you know, the cube isnt moving so your premise is flawed. Unless you mean from the reference frame of the portals which in that case it is, but a fictitious force stops decelerates the cube to a stop, resulting in scenatio A being correct. I've already explained this, but clearly you lack reading comprehension.

The intuition behind this is the following:
Consider you are in a box moving at constant velocity. You feel no force. If the box decelerates to a stop, you are suddenly thrown against a wall of the box - this is a fictitious force due to the acceleration of the reference frame. Please read: https://www.ux1.eiu.edu/~cfadd/1350/06CirMtn/AccFrames.html if this is still confusing.

Simple calculations show that this fictitious force is exactly the force required to prevent the box from having ANY velocity as it exits the portal.

If portals is too complex, think of not a portal, but a ring being dropped down onto the box. The box doesn't fly upwards after the ring lands.

The real answer is that portal entrances and exists can not move relative to one another and must be oriented spatially the same direction or else they break the laws of physics.

If you only care about a video game then the answer is whatever the game programmers programmed the answer to be.

>>8919305
>the cube isnt moving

The cube is moving relative to the reality on the other side of the blue portal. The blue portal is moving the entire universe behind it. If the blue portal went around you, you would see everything moving relative to you.

>think of not a portal, but a ring being dropped down onto the box

But it's not a ring. It's as if you had an opening on a train, and that train was travelling at a certain speed. See this image:
>>8916903
No force is acting on the box. If you were in the box, it would just feel like you weren't moving. But the reality on the other side of the portal IS moving in relation to you.

>>8919321
You are wrong. From what we know about how portals work we can logically construct how things will behave. It doesn't matter if it breaks the laws of physics, as long as it is predictable.

>>8919328
>It's as if you had an opening on a train, and that train was travelling at a certain speed. See this image:
As soon as the box is fully inside the train the train abruptly stops. Suddenly the box doesnt move relative to the inside of the train.

>>8919368
Are you asking what would happen if the blue portal suddenly stopped after the cube went through?

The orange portal has no way of knowing what the blue portal did. The cube will keep moving as if nothing happened.

If you are not asking that, tell me what.

File: BTFO.gif (116KB, 507x347px) Image search: [Google]

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"A" FAGS BTFO

LMAO DEMOLISHED BY NEWTON'S FIRST LAW

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>>8919348
>It doesn't matter if it breaks the laws of physics

how is this any better than pic related?

>>8919416
So you are saying that the entire train analogy is bullshit? Interesting to see ppl calling their own arguments bullshit.

>>8919433
>So you are saying that the entire train analogy is bullshit?
When did I say that the train ever stops? You came up with that.

No, It's not bullshit as long as the relative velocity between the two portals doesn't change. Of course it's not the exact same as portals because it's not portals.

You still haven't told me in your example, are you saying that the blue portal stops after the cube already went through.. or what?

File: Boring Tunnel Hyperloop Train Sled.png (31KB, 363x391px) Image search: [Google]

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>>8919433
Ok, If you wanted to extend the train analogy you would need a train within a hyperloop. The blue hyperloop would have to start moving the same speed (relative to the tunnel) as the orange train so that the speed between the orange and blue is zero. Then it would look like this

>>8919429
>how is this any better than pic related?
It's not, you can get free energy from portals. e.g. put one portal on ceiling, put one on ground, have an infinite waterfall.

can aportal go throught another one?

Everyone in this thread who EITHER says A or B don't belong here. They are BOTH equally wrong for the same reason.

>>8919422
Both are equally wrong because they both break causality in some reference frames. If you consider you gif, only from blue's perspective, then it totally makes sense that the cube stopped, (It wasn't moving in the first place, so why would it start moving from a portal going over it). But go to Orange perspective and it doesn't make sense again. Orange says, no, the cube is moving towards the portal, it shouldn't just stop when it comes through.

>>8919219
It doesnt in the animation. That's the problem. From the blue portal perspective, the entire floor is moving towards it, not just the cube.
>>8919210
What I'm arguing is that relative to the blue portal, the distance between the orange portal and cube is constant.

Initially the blue portal is some distance y from the cube. When the blue portal moves down, or the floor moves up, y becomes less. But the height distance between the cube and the orange portal remains constant no matter how you look at it. So when the cube enters the blue portal, the cube AND the orange portal have 0 velocity or the same non zero velocity depending on what frame you initially viewed. Either way, it comes out to a.

>>8919697
Nigga you don't see how fast as fuck that prism is going boi? It's fast as fuck.

>>8919738
So according to you this >>8919422 would happen, correct?

>>8919995
No.

The statement that the object suddenly stops for no reason is misleading. In that frame of reference, it was never moving to begin with, so there would actually be a violation if it were.

If you look at it from the blue portal frame , both the cube and the portal move towards the blue portal with the same velocity. B-lievers seem to think that only the cube moves in the blue portal frame, which is just wrong.

>>8920061
but it has to move in respect to the orange portal too, since it comes out of it. what exactly is stopping it from moving afterwards?

>>8919422
/thread

>>8920061
>In that frame of reference, it was never moving to begin with,
Nigga you seriously can't see that prism moving fast as fuck? It's moving fast as fuck boi you can't see that?

>If you look at it from the blue portal frame , both the cube and the portal move towards the blue portal with the same velocity.

Yea, if you fix your frame on the blue portal, the cube and the orange portal are moving. And if you throw a cube into a portal, it come out of that portal at the same speed. But if you throw a cube and the exit portal is already moving, the resulting speed of the cube is [math]v_1 + v_2[/math] (speed of the cube + speed of the exit portal)

So with the cube thrown at the portal at speed V, and the orange portal moving up at speed V, the total speed of the cube after it exits is 2V, relative to the blue portal. And you can see that the cube, does indeed go at 2V relative to the blue portal. From orange's perspective the cube is moving up at V and the blue portal is moving away at V. So that's why it's 2V relative to the blue portal.

File: SECON ROUND.jpg (110KB, 1500x636px) Image search: [Google]

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here is a gift.

File: every portal thread ever.png (119KB, 661x953px) Image search: [Google]

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>237 posts
Good job /sci/ we almost solved it. Maybe in the next few dozen threads we might even agree upon a solution.

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>>8920343
Portals don't interact with matter so orange portal will just fall through... is what I would say I was an A brainlet.

>>8917559
See pic related

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>this is what A fags actually believe

>>8920362
I love you

>>8918648
The difference is in the cube's inertia. The cube has resistance to a change in acceleration. If the cube's speed were to change, then some force would have to change it. 10m/s cube at portal, would follow a parabolic trajectory through the portal and continue along the same trajectory after passing.
10m/s portal around cube would not affect the cube's inertia at all, so the cube would continue sitting there after the portal passes around the cube. I theorize that the portal has no interaction with the cube, therefore no change in momentum can occur.

>>8920412
>I theorize that the portal has no interaction with the cube,

The "interaction" is that the cube is moving relative to blue portal. Imagine if the blue portal was sitting still in the middle of space and you threw a cube at it. It is the same thing as if your camera was fixed to the cube the whole time and the blue portal was moving towards it. You can't even say these situations are different, according to Newton and Einstein these are actually the same exact thing.

There is no "inherent" inertia of anything. From any object's perspective, it is moving at a speed of zero.

>>8920343
I think the answer is B

It's counter intuitive, because the piston is not touching anything at all. But in order for the piston to move down any farther, the pole would have to be take up less space with the same matter. If you were pushing hard enough it would be A.

Someone convince me one way or the other. I can't really think of an analogy to this situation.

File: 1437867194139.gif (303KB, 400x300px) Image search: [Google]

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>>8920412
>10m/s portal around cube would not affect the cube's inertia at all, so the cube would continue sitting there after the portal passes around the cube
Uh, so, if the cube was moving 1km/s it would continue moving 1km/s after the portal passes around the cube at 1m/s?

I would think either answer is correct depending on the properties of the portal itself.
If the portal is nothing, simply an entrance into another part of the room, then I think the answer is A. The cube makes no contact with the portal because there is no portal to come into contact with.
If the portal gateway does have some mass and directly strikes the cube, then we could say the cube is hit with a force of x newtons. In this case I think the answer would be B.

File: THIRD ROUND.png (86KB, 1834x498px) Image search: [Google]

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>>8920455
>>8920343
Now what?

>>8920519
Definitely B.

At first I shat myself, but it's just the first question in reverse.

The part sticking out of the blue end starts to move backward, because the orange portal makes it start moving from the orange side's perspective looking in.

A doesn't even make sense, look at the portals lol.

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This thread is abhorrent. I want /sci/ to leave.

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But what if the piston stops when the cube is only halfway in?

File: Screenshot_38.jpg (29KB, 373x218px) Image search: [Google]

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>>8912828
Think of it like this. If you slammed down a giant piston on a cube but the piston had a hole that the cube fit through on the stamping end, the cube has never even interacted with the piston at all. Assuming that the portals are a seamless hole in a surface which teleports you to the other portal I don't see how the cube would have any energy added to it's system.

Any argument for B implies that the portal defies physics in a mysterious way which is less grounded in reality than A, and if you are talking about how portals work it makes sense to go with the most logic situation.

If we aren't making arguments based in reality why not say that due to unknown portal forces the energy passing through the portals is what keeps them open, and when a large amount of energy passes through them they absorb it to charge their mysterious portal batteries (not pictured).

>>8920731
Addition to this argument - I think that B is based on the idea that the entire platform that the piston is sitting on is coming through with it. The piston getting stopped by the cube's platform creates a very different scenario than the entire piston going through the portal.

>>8920731
I'm dying to see your answer to this question:

>>8920391 (see image)

Tell me what would happen in this two scenarios, /sci/:

1. The piston moves down at a set speed but only envelopes half of the cube

2. The piston moves down at a set speed and envelopes both the cube and stand the cube was on

Surely in the second scenario it would appear, beyond the second portal, that the cube was ejected at the same speed it went in? It would look like the stand was pushing the cube out at whatever speed it came on.

The question is unanswerable.

>>8920343

Either A: Portals can exert force and crush the pillar or B Portals can excert force and keep the plate aloft.

Therefore portals CAN exert force, meaning the fucking box will go out flying.

>>8911783
From the perspecive of the orange portal that means the cube quickly exits the orange portal before losing all momentum. If nothing else you should be able to tell that the momentum already achieved from being ejected from the orange portal would "pull" the orange cube out, but you didn't because you're 89IQ

>>8912467
>loss.jpg

>>8912568
>>8915039
>>8916863
>>8916882

Momentum isn't conserved in this system. Spatial translation symmetry is broken, so by Noether's theorem the corresponding current isn't conserved.

Any answer that relies on "momentum conservation" in any form is wrong.

>>8911770
Depends on how portals work. When the blue portal collapses onto the block, does it carry the entire universe (i.e. what's past the orange portal) with it? If it does then it]'s scenario B. If it doesn't then it's scenario A.

>>8920731
No.

See: >>8913724

Stanford Physics here.

It's A. What shitty state school do you have to go to to think it's B?

File: portalspacecurve.png (14KB, 403x651px) Image search: [Google]

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>>8911770
You can draw the same room like this, so A without breeze

>>8920731
But the cube doesn't need any additional energy to start moving, it's already moving out of the orange portal. In fact, you're going to need additional energy to stop it from moving afterwards for A to work.

>>8921391
Scenario A and B have the same problem. Its just about what frame of reference you are in. If you really a physics student, you should ask for your money back, if you can't see why that is.

People who say A are thinking from Blue point of view, while people who say B are thinking from Orange point of view.

neither because portals cant move relative to one another and must be oriented the same direction in space.

if you don't care about breaking the laws of physics, to a greater extent than a portals mere existence already does, then the answer is whatever you want it to be, and who cares because you're just making up impossible shit anyways.

b

>>8921391
retard

>>8921391
>not considering the rate of emergence of the cube from orange exit portal.

File: dancer.gif (2MB, 320x240px) Image search: [Google]

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This is like the black blue dress or the rotating dancer. It can be discussed infinitely without coming to an agreement because there are 2 frames of references involved, and neither A or B matches both of them, so there are 2 equally valid ways of viewing this. If you are convinced it must be one way, try stepping back and looking at it from the other perspective.

>>8920731
Only the part of the cube that hasnt yet gone through the portal is not moving. For that part your comparison is valid. The part that has gone through the portal (the whole cube at some point) is moving and has inertia, thus can not just suddenly stop for no reason.

>>8921408
>>8921526
it's like it's in the same room just the gravity direction changes

>>8911783
>>8911787
Forget where the cube is coming from, look at the orange portal. Dont you think the first half of the cube exiting the orange portal at n miles/hr has any momentum? Lets assume orange is a stationary point of reference, before the cube is even all the way out the first half of it is already moving relatively fast. Where does the velocity go? Heat? Fuck outta here A plebs.

>>8921572
Forget where the cube is going, look at the blue portal. Dont you think the half of the cube on the platform sitting there at 0 miles/hr has any inertia? Lets assume blue is the platform is a stationary point of reference, after the cube exiting the portal nothing has pushed it off the platform. Where does this velocity come from? The platform? Fuck outta here B plebs.

>>8921538
>thinking gravity is actually relevant in this problem
dumbass

>>8917554
This implies everything behind the orange portal is moving relative to the cube and suddenly stops. Which would still lead to the cube shooting out of the portal, just lke things jolt backwards in a car when you brake (from your perspective). So no matter how you turn it around, it is always B.

>>8921593
>thinking there is a problem
gravity is the only thing that chnges

>>8921595
What about the cube suddenly shooting of the platform without anything touching it? You're dumb if you still cant see that neither is valid. It takes the same energy to stop something as making it move the same speed, so its the same fucking problem with A and B.

>>8921474
>People who say A are thinking from Blue point of view, while people who say B are thinking from Orange point of view.

Both are the same...

From the blue portal's perspective, the cube is moving in relation to the portal. The cube has momentum relative to the portal.


>>8921500

All speed and momentum are relative. Relative to the "ground", the cube is not moving. So people think the answer is A. But the assumption they make is that the ground is not moving relative to the portal.

The real, correct question is "what is the cube's speed relative to the orange portal?" and the answer to that question will be the same answer to "what is the cube's speed relative to the ground?" WILL ONLY BE THE SAME ANSWER IF AND ONLY IF the portal is not moving relative to the ground. We can see that the orange portal does not move with the ground, ok good. But we see that the BLUE portal is moving in relation to the ground. And since both of these portals are actually the same points connected instantaneously, then we can say that the portal is moving relative to the ground. So we can not substitute the ground as a reference point for the portal, because they are moving at different speeds, and thus, THESE ARE NOT THE SAME FRAME OF REFERENCE.

"But no, the portals are two different things!" No, they are the exact same point. If you had a person standing in the middle of a portal, both portals on the wall, it would look like there was two people, but no it's only one person.

>>8921619
>Both are the same...
I fucking know, which is why i copied his comment, only from the other perspective...... .. . . .

>>8921602
Woops i phrased that wrong, the part of the cube that went through the portal would of course also be moving. Then, when the whole cube has gone through and, from the point of view that gif is made from, the whole room would have to suddenly stop.

>>8921474
>People who say A are thinking from Blue point of view, while people who say B are thinking from Orange point of view.
Not true at all. It seems more like people who say B are thinking in terms of relative velocities and momenta, whereas people who say A are thinking in absolute velocities (which do not, in fact, exist).

>>8921627
meant to reference
>>8921595

>>8921602
>What about the cube suddenly shooting of the platform without anything touching it?

Why exactly does the cube need to touch anything?

When you throw a ball at a portal, it comes out the same speed that you put in. The ball doesn't need to touch anything to maintain this speed.

>>8921602
conversation of energy is no more with portals anyway

>>8921645
*conservation
lol

In the game, portals clearly preserve velocity *relative to the portal surface* but not velocity *relative to the fixed earth*. For example, if you have a blue portal on the north wall and an orange portal on the east wall, if you throw an object into the blue portal (north), it comes out the orange portal moving west -- not moving north, as would be the case if portals preserved velocity (which includes direction, remember) relative to earth.

Scenario B does exactly this. Scenario A does not, and therefore directly contradicts the game. Why are we still talking about this?

>>8921629
The cube still has a relative velocity to the platform retard. Try to argue otherwise, I'd love to see how you can twist reality around to fit your personal answer.

>>8921644
It maintains its relative speed to the platform. Something needs to push on it to change that. But its the same for Orange, the cube should maintain its relative velocity to the orange exit and something needs to push on it to stop it. They are the same.

>>8921645
So, you still need to decide which of the 2 relative velocity the cube is going to keep. Conversation of energy is broken in both scenarios.

>>8920362
This is fucking gold. saved.

>my curved portal idea is in it
no-one else will ponder that. feels bad, man.

>>8916041
no, entering and exiting 10 m/s. no acceleration

>>8920598
If (A) the cube would suddenly stop

If (B) the half of the cube that went through would have momentum and the cube would either levae the portal completely with less momentum or tear into two pieces.

>>8920343

(A) if the rod itself is really weak. (B) if the rod isn't weak.

>>8920519

Again, it depends on the strength of the materials.

>>8921669
>It maintains its relative speed to the platform. Something needs to push on it to change that

Yes it does, and if the blue portal kept going, it would also be the platform emerging out of the orange portal just like the cube.

>the same for Orange, the cube should maintain its relative velocity to the orange exit and something needs to push on it to stop it

I agree. What is the cube velocity relative to the orange portal? Well the orange portal is right on the other side of the blue portal, and the blue portal is moving the orange portal around the cube.

>>8921695
>Again, it depends on the strength of the materials.

Have a reeeeeally close look at A.

>>8921703
I think that if you took the rod and connected it at the ends, (B) would likely happen. If you took two half-rods, connected them and the ends and welded the two halves together, (A) could happen.

>>8921699
>Yes it does, and if the blue portal kept going, it would also be the platform emerging out of the orange portal just like the cube.

This doesn't change anything, you're basically just saying: >what if the ball was longer.
It still has a relative velocity to something that wont be maintained as its exiting the portal. So you can arbitrarily just say that the ball maintains its relative velocity to the orange exit, and that will work, but nothing in the animation suggest that, and no psychics can help you prove it either. So pick a side, and either way you are half wrong and right.

>>8921715
>This doesn't change anything, you're basically just saying: >what if the ball was longer.

Yeah it doesn't change anything.

>So you can arbitrarily just say that the ball maintains its relative velocity to the orange exit

Ok. let's make this easier. What would you say if I asked you this question:

Tell me, how fast is the cube moving relative to the blue portal?

>>8921408
how stupid are you all, this is the right answer

>>8921745
no one cares about the gravity, nerd, it's irrelevant

>>8921739
>Tell me, how fast is the cube moving relative to the blue portal?
You still don't think I understand the argument for B? Are you being deliberately dense? Its the same as the orange exit. Is that what you are fishing for?

Still doesn't change the fact that the cube will have to suddenly change its relative momentum so something as its going through the portal. If that is the portal, or the earth doesn't matter, its just depends on the way you decide the portal works.

>>8921688
You can't give only half of an object momentum. If it gained any moment at all, it would have the possibility of "jumping" through the blue portal, inverting gravity in its original position - which has never been how portals worked.

And yet, if the blue portal crashed down on both the stand and the cube at the same time at, say, 10m/s it would appear as though the stand ejected the cube out of the orange portal at 10m/s.

It's a paradox. My argument is flawless. This cannot be answered.

File: nani.jpg (541KB, 2560x1440px) Image search: [Google]

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>>8921791
>You can't give only half of an object momentum.
>Objects are indivisible
>My argument is flawless

okay then.

>>8921500
The rotating dancer's shadow gives her away. This meme needs a better gif.

>>8921756
yes, but everything else is also irrelevant, the picture isn't about the gravity, how stupid are you

>>8921799
What, do you think it would split apart - one bit would fly straight out while the other stayed on the ground? You really think you can use a portal to split things apart like that? There is absolutely zero precedent for it.

>>8921821
portals don't real, there's no precedent for them doing anything

>>8921825
Exactly. Both instances are paradoxical - i.e. they cannot be answered.

>>8921821
>Objects are indivisible and point-mass mechanics applies perfectly to the physical world.
You realise that different parts of an object can be subjected to different forces, causing different movement from if the forces were all in the same point, right?

Like if I force the ends of a rod one way but the middle of the rod the other way, that rod will bend or break in the middle.

Or if I accelerate one portion of an object but not the other, the part I didn't accelerate will be carried with the part I did accelerate or be broken from it.

>>8921843
If the piston with the portal on it was movie really, really fast and suddenly stopped halfway, the piece of cube on the other side would appear as though it was being ejected at great speed. Yet, on the other side, the cube would have to stay perfectly still lest it violate the law of gravity. I'm assuming the cube can't stretch like taffy.

>>8921858
Where does gravity play into this?

>>8921780
Oh, I know MY answer. I just want to hear YOUR answer.

Can you please clarify for me, how fast is the cube moving relative to the blue portal?

I apologize if you already answered this but I want to hear what you think.

How fast is the cube moving relative to the blue portal? What is your answer??

>>8921863
It's what keeps the cube below the blue portal and on top of the stand. The cube cannot move upwards unless there is a force accelerating it in that direction.

Where is that new force coming from? The other portal? Why?

>>8921867
>The cube cannot move upwards
Move upwards relative to what, exactly? This should be good.

>>8921866
Some non-0 speed. Same speed as the piston. You want an exact number, or what?

>>8921869
The stand it's resting on. If it moves upwards without being fully enveloped by the portal, or experiencing suction from the other side, it is defying gravity.

>>8921879
Okay GOOD! So the cube enters into the blue portal at some non-zero speed. Let's say speed "V".

So the cube enters the portal at speed V. Now answer this question:

What speed does the cube exit the portal?

>>8921880
>The stand it's resting on.

Bingo. We aren't trying to calculate the cube's speed relative to the stand. We are trying to calculate the speed relative to the portal.

*mic drop*

>>8921885
I understand the argument for B you literal retard. Can you actually read?
See:
> for Orange, the cube should maintain its relative velocity to the orange exit and something needs to push on it to stop it.

My first fucking comment to you. Why are you replying if you are not going to read what I say?

>>8921898
Ok, tell me, in no uncertain terms, if you agree with these two satements:

1) The cube is moving at V speed relative to the blue portal

2) Objects entering a blue portal will exit the orange portal at the same speed they entered. Speed is conserved.

One of these two must be wrong, because it can only lead to this conclusion:

3) Cubes entering the blue portal at speed V will exit the orange portal at the same speed V.

>> for Orange, the cube should maintain its relative velocity to the orange exit

Right, and the cube's velocity it V relative to the surface of the portal.

In order for you to be right, there must be something wrong with 1), 2), or the logical step that gets us to 3). So tell me, in no uncertain terms, which is wrong? Is it 1), 2) or 3)?

>>8921913
Sure, Ill give you your answer just, answer me this first.
What side do you think I'm arguing for?

>>8911770
Would scenario B be correct if part of the stand went through the portal with the block? Then it would seem as though the cube was being pushed out of the orange portal at high speed... right?

>>8911770
If you were in freefall, you could stand on the piston and it would look like the cube was being pushed towards you and not the other way around. What's up with that?

>>8921920
I think you're trying to say there is no answer, when 1) 2) & 3) logically show that the answer is B.

>>8921966
And by "you" I mean the portal, which you would be standing above.

>>8922006
Okay then.

2) is wrong.

Depending on what you are measuring the
speed relative too, the speed isn't conserved.

>>8922099
>2) is wrong

Except GlaDOS says in the actual game "Momentum, a function of mass and velocity, is conserved between portals"

And no, GlaDOS is not wrong.

>Depending on what you are measuring the speed relative too

Lol no it doesn't matter one single bit. If you measure the speed relative to, let's say the platform it's sitting on (0 m/s), and the blue portal doesn't stop, and then say it passed through the portal and you measure the speed again, (again relative to the platform) you will see that it the cube is still travelling at 0 m/s.

The cube goes through the portal same speed as it come out.

Relative to the platform, this is 0m/s and 0m/s.

Relative to the portal, this is V and V.

So it doesn't matter how you measure, as long as you keep measuring the same way.

>>8911783
/bread

>>8922207
You dingus. The cube has plenty of momentum. The cube is moving relative to the blue portal.

>>8922192
>And no, GlaDOS is not wrong.
Except momentum is relative. So just saying it is conserved doesn't solve the issue, momentum will not be conserved in all frame of references. You are picking the portals frame arbitrarily and saying the portal is the only one that matters. If it is, then sure, you are right, but I don't see anything in the problem that suggests that the portals reference frame is special in any way.

And you don't need to keep explaining relativ motion to me in every post, like that solves the issue, it is issue. All reference frames don't agree on the momentum of an object, but they do agree on causality. But causality brakes when an object suddenly gains relative motion to object without anything acting on it. And this happens in both scenario A and B.

>>8921590
If the blue portal is stationary the cube has velocity before it even touches the portal. Checkmate athiests.

>>8911770
It's coming out at a finite speed in both instances. What are these speeds?

>>8922214
Yeah but that doesn't have any significance. It doesn't get any momentum relative to the ground.

>>8922438
So how fast does the cube come out? Why does it come out at the speed it does?

>>8922282
Ok then, give me one frame of reference where momentum is not conserved across portals.

>>8922806
The platform, The earth, or you know; the rest of the universe.

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>>8922686
Assuming portals do not alter any Newtonian and classical mechanics, the cube is not accelerated at all by either portal. Simply going through the portal does not change your velocity, acceleration, or jerk; rather, it only changes your position via teleportation. Thus, the infinitesimal slices of the cube (since it has to pass through the portals) are placed instantaneously in the location of the orange portal's center. The cube then accelerates at that point due to the force of gravity acting on the block's center of mass.

Please ignore that I assigned the portals a letter to be called by when I didn't use it, I thought I was going to write more. Here is the acceleration of the block instead of speed. If you truly want the speed, I can integrate my answer for you, just ask.