/sci/ - Science & Math

>>10682754
I think it depends on which side of the portal is the cubes reference frame. We don't know enough about portals to make that judgement. Actually, i think someone recreated that experiment in the portal 2 level editor, so if you want an in-universe answer it's whatever the result of that was.

>>10682754
Portals break reality. There is no answer.

>>10682754
It would be at rest on the slope unless the friction was low enough for it to slide to the bottom, so the first one is more correct. It should not matter how quickly the portal envelops an object since portals do nothing except connect two disconnected areas of space; in other words, no matter how fast the cube emerges from the other end, it is still stationary. Furthermore, the diagram depicts the portal as being smaller than the platform the cube is on, so only the cube would be transported but it would remain on the same flat surface unless gravity pulls it down the slope.

>>10682795
/thread

>>10682754
For the TREE(3)th time:

Hamiltonian paths in phase space are continuous. Portals are as nonphysical as you can get.

But what particularly gets me is this version of the image. Creator clearly has no idea what Einstein's relativity actually is and that Galilean relativity would already "account" for the option B ("account" in quotation marks since, as I already said, portals are physically inconsistent and reference frames don't offer any solution).

>>10682754
If the cube will exit blue at the same rate it enters orange, It's B.

>>10682754

>>10682754
Both are wrong since portals break conservation of energy but B is less wrong since it respects relativity while A doesn't.

wtf is this some kind of forced meme or something

also I'm INTJ and B is obviously correct since the frame of reference through the portal would see the whole world as moving when that portal is moving

the portal would sink into the angled platform at the same rate the cube exits so that there is net zero force imparted to the cube

>>10682999
>frame of reference

>>10683008
Not him but how is that wrong? From the reference frame of the portal, the cube is moving towards it.

>>10683012
The reference frame of the portal is completely undefined. It is physically nonsense.

>>10683015
only brainlets just default to "SYSTEM ERROR - DOES NOT COMPUTE" instead of using their imagination

>>10683015
Look, we all know that portals are physically impossible but we can still draw some logical conclusions from it.

>>10683023
>dude what if we ignore everything we know about reality, then what is the solution?
>>>/v/

>>10683025
How? If we can't use the tools of newtonian or relativistic mechanics, please explain what we use to draw "logical" conclusions from it. The only way we draw ANY conclusions is by looking at how the source engine handles portals. So it isn't science or math.

>>10682754
>portals can move

>>10683033
Well we know one thing about portals. "Speedy thing goes in, speedy thing comes out". More formalised, portals conserve the magnitude of momentum of any object passing through (though obviously not the direction or the total momentum of the system).

This is already a concrete law of the portal universe.

>>10683033
Just because some aspects of physics break down with portals doesn't mean logic itself gets torn apart. Since portals demonstrably create free energy, we just have to assume that they get that energy from "somewhere".

>>10683043
>This is already a concrete law of the portal universe
Yeah, and another one is that portals can't be placed on moving surfaces. The point is, literally the only way to answer OP is to test it in source engine. Go back to your video game board.

>>10683047
You can't solve "physics" problems with pure logic, moron.

>>10683026
>apply known laws to a situation with one impossible factor
>ignore everything we know about reality
you can't answer a math story problem involving kawaii anime girls?

>>10683040
the earth is moving

>>10682754
If you animate this it becomes obvious which one is correct. The box appears out of the portal at the same rate it is inserted therefore B is the only answer that makes any sort of sense.

>>10683051
>>10683054
Suppose for a second that portals could move, as is shown in the OP. Then all we know is that a postal must conserve the magnitude of momentum. Wouldn't you say that you could logically conclude that the object would have the same velocity before and after it passes through the portal.?

>>10682754
>>10683076

>>10683051
>>10683078
you guys didn't play portal 2? there's a part where you have to shine a laser through the portal and put one on a moving platform to cut some pipes off a gas container. also you shoot a portal onto the moon at the end of the game.
they just didn't program the physics to work with moving portals so it breaks if you do it in a mod

>>10683082
This animation is wrong tho, it doesn't appear out of the portal but just 'pops' into existence already on the other side.

>>10683106
That's just an artifact of the fact that it's an animation with a limited number frames.

>>10683110
No it's not, it's an artifact of the animator not knowing what they where doing and deciding not to depict the crucial moment when the box was partially inserted.

>>10683120
It's literally only crucial if you slow down the gif and analyse each frame individually which, funny enough, kinda undermines the ultimate purpose of the animation.

Besides, what were you hoping to see? A slightly blurry image of cube halfway through the portal?

>>10682961
You know how you can't move around a tear on a piece of paper? You can only move through it or warp the plane itself. But that's two dimensional and not schitzo.

Say we pull up graph theory for this. We have point x,y,z and point a,b,c. We use incredible amounts of energy to punch a singularity in x,y,z that only exists temporarily and to link with the second, nearest singularity, or else it'd travel through space looking for some other singularity (luckily there are no nearby black holes). The second "portal" punches through point a,b,c. Those two points link. Either they collapse into two entry points to a black hole, or entropy forces the energy outward from that point and builds a tunnel from x,y,z to a,b,c.

Damn that's good schitzo.

>>10683126
Think about it in terms of what you see from the far end of the exit portal. I made this animation to illustrate my point.

>>10683257
I don't understand why the teapot would continue to move, it isn't accelerated by the portal hitting it.

>>10683277

>>10683277
>I don't understand why the teapot would continue to move
It is already moving, why would it stop?

>>10682754
Let's start at the bottom of even beginning to get to an answer to this question: Is there any symmetry that isn't broken in a metric with portals in it? I'm pretty sure Lorentz symmetry gets fucking mangled by it, but is there a less general symmetry that sticks around?

>>10683289
just because you change the frame of reference doesn't mean it moves. There's no energy to accelerate it

>>10683296
>just because you change the frame of reference doesn't mean it moves.
Do you not know what a reference frame is?

>There's no energy to accelerate it
It's already moving you don't need to accelerate it.

>>10682754
Portal universe is known to violate conservation laws.

>>10683296
>just because you change the frame of reference doesn't mean it moves.
Do you literally not understand what a reference frame is?

>>10683277
It exits the portal at the same rate it is inserted into the portal. It's already moving coming out of the portal, it stays in motion because it would take a force to stop it from moving, it requires no force for it to keep moving at the velocity it's already moving.

>>10683257
youre thinking about it from one frame of reference. what about the other frame?

>>10683257
you can't make an animation like this since you don't know the physics of a portal.
If you were to stand still, and have a hula hoop drop on your head, it wouldn't look like your jumping through it either.

>>10683304
how is it moving, looks like it standing still from here

>>10683309
It's moving from the reference frame of the portal.

>>10683308
For fucks sake this has been said a hundred times. PORTALS. AREN'T. HULA HOOPS.

>>10682754
okay, I made a gif simulating this the other day, but 4chan says no audio streams are allowed when I try to upload it. There is no audio in the webm, how tf do i upload it? I don't want to convert it into a gif.

>>10683309

>>10683316
sorry bro ur retarded. You move backwards in the frame of reference of a car when ur standing still, but when it passes you, you don't suddenly speed up in the opposite direction LOL

>>10683316
>It's moving from the reference frame of the portal.
from the reference frame of the plateau it isn't

>>10683306
>what about the other frame?
The other frame doesn't matter because it is stuck on the other side of the portal.

>>10683309
On both sides of the portal it looks like the entire world on the other side of the portal is coming towards you.
What is moving and what is still depends on what side of the portal you're on. If you're half way inside the portal you are standing still and moving at the same time.
If the portal slammed to a stop with you half inserted you would feel the part of you already on the other side pulling at the part of you that still haven't entered.

>>10683340
>you would feel the part of you already on the other side pulling at the part of you that still haven't entered.
actual in game physics prove you wrong

>>10683345
>actual in game physics prove you wrong
No they don't.

>>10683316
>PORTALS. AREN'T. HULA HOOPS.
exactly, you have no clue what it is. So stop making stupid animations about something you don't understand.

>>10683289
I just don't understand how it's moving
t. never had Physics in school

>>10683345
>The in-game physics argument
Moving portals in the game don't even work, if you're going by that standard the answer is C: The cube is pushed through the platform, glitching through the surface and falling into the void, forever.

>>10683324
You're still using hula hoop logic. You maintain the same relative velocity to the car obviously, which is analogous to the cube retaining the same relative velocity to the portal.

>>10683325
Are you trying to say that a portal isn't an inertial frame of reference?

>>10683352
First, I didn't make the animation.

Second, we know how portals operate. Speedy thing goes in, speedy thing comes out, i.e. portals conserve the magnitude of momentum. All the animation demonstrates is that the object is moving relative to the portal and will retain that movement.

>>10683361
The portal REALLY, REALLY ISN'T an inertial frame of reference. It absolutely is not that. It fucks with the very concept of a reference frame even when standing still, because these two special flat areas in space are now connected in a way that fucks with angles, maps distinct regions of space on top of each other, just generally fucks up everything.

>>10683372
Well I mean, if you can "just" accept that conservation of energy doesn't exist in the portal universe, I don't see how a portal couldn't be considered an inertial frame of reference.

>>10683377
The fact that energy (and momentum) isn't conserved is actually a major hint towards portals fucking with inertial reference frames. Energy-momentum conservation (4-momentum in relativistic language) comes from Lorentz symmetry by Noether's Theorem, and Lorentz symmetry is the basic symmetry of Special Relativity. No 4-momentum conservation MEANS that there's fuckery going on at the fundamental level of "Are all reference frames equivalent?"

>>10683368
>Speedy thing goes in, speedy thing comes out, i.e. portals conserve the magnitude of momentum.
Speedy thing go in, speedy thing come out. Portal speed itself doesn't give inertia to an object once it closes over it.

>>10683387
>Portal speed itself doesn't give inertia to an object
Of course not, no one said that. The object already had inertia from the reference frame of the portal.

>>10683386
We're basically going full circle and coming up with more elaborate reasons why portals make no sense in reality.

Now how about this case?

>>10683407
>Of course not, no one said that. The object already had inertia from the reference frame of the portal.
so it's answer A

I just realized that inertia not being conserved solves the terminal velocity/infinite potential energy problem when an exit is placed above its own entrance.

>>10682754
I think it should be B
let's say the cube is 1m tall and the portal moves towards it at 1m/s, the cube moves through the portal at 1m/s, and therefore should shoot out of the blue portal and fly a couple meters.

>>10683413
How do people even arrive at A.? The alternative to B. from where I'm standing isn't A. but C. that you must be Crushed by a fast moving portal, since you will collide with yourself on the other side if you're not translated so you're exiting it at the same rate you're entering.

>>10683417
Yeah, if one replace the idea that 'portals conserve momentum' and replace it with the idea that 'portals translates whatever goes into them to the other side'
you can make them work conceptually on any kind of moving surfaces.

Actually coding them to work for a game is prob a lot more difficult than what they had to do to make the static ones work from a pure technological standpoint.

>>10683412
Option 1 is correct.

>>10683428
the whole point is that the cube isn't moving, so there is nothing to translate

>>10683504
That just confirms his point. If that's what you believe then you'd have issue with the fact that the top part of the object continues to move for a short while after it's passed the portal. In reality according to your logic it should just end up as an ultradense atom thick sheet.

>>10683524
Why should we assume that the falling portal is being accelerated to c?

>>10683524
it's just *plop*ing down due to gravity and not because of the top moving, if that's what you mean

>>10682754
This problem can't be solved, because it is an invalid problem. For the following reasons:
>The portals always need to be stationary in relation to each other.
>You cannot freely switch between frames of reference, since the cube's and portals' frames of reference aren't inertial in relation to each other. This means that either the cube moves and the portals are stationary, or the portals move(with the same velocity, always in the same direction) and the cube is stationary.

Only idiots try to do solve invalid problems

what if it was a pole, instead of a box?

>>10683599
Drop something circular over a rod or a pen stood on its end, does it jump?

>>10683599
>>10683421
now the cube is just taller, doesn't change anything

>>10683599
When do we get to account for acceleration, both due to gravity and not?

>>10683609
you understand that the velocity of the pole coming out the blue portal must by definition be the same as the velocity going into the yellow portal

>>10683622
that's exactly what he says tho?
Apart from all of you being retards see >>10683582

>>10683582
>The portals always need to be stationary in relation to each other.
No they don't you can put a portal on the moon.
>You cannot freely switch between frames of reference
Yes you can the portals connect two surfaces without regard to inertial frames.

>>10683582
Just because it's not part of our reality doesn't make it an invalid problem. We can create simulations where it's possible and play with the physics of it and trying to get it to work consistently. If you for example set out to make Portal 3 or write some sci-fi these are things you'd might wanna resolve. Thinking seriously about non serious topics isn't harmful for the quality of one's entertainment.

>>10683684
>No they don't you can put a portal on the moon.
yeah, if they weren't you'd literally tear spacetime idiot

>>10683694
>t. I haven't even played the game.
Get the fuck out.

>>10682754
Actual solution here
https://youtu.be/S85nudR6D-Y

>>10683700
>>10683702
works great in game, doesn't it?

>>10683706
Yeah it does.
https://www.youtube.com/watch?v=DAn87KyNjJ0

>>10683710
moon is stationary though, unless you'd say that the other portal isn't stationary because the earth moves

>>10683694
>>10683684

The portal on the moon obv work different from the ones typically depicted in the game since it's a scripted story event.
Playing the game it's quite clear that the way the portals are meant to work lore-wise is quite different from what is possible for them to depict with the source engine.

Obsessing over how the portals work inside the games is staring one self blind on technical limitations.
I'm sure valve would've loved to use moving portals if they could've made them work.

>>10683724
>moon is stationary though
Turbo brainlet detected.

>>10682754
There's no such thing as a global inertial reference frame. This makes arguments that rely on conservation of momentum and conservation of energy easy to get tripped up by.
To explain: 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 space-time 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, in particular, 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. To be specific, 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" (i.e., 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.

portals break newtonean mechenics if you thinks about it sorta speak

The answer is B, since the situation is equivalent to the plate with the cube on it shooting up into a stationary portal. At the instant that the whole cube is through the portal it maintains its momentum and so shoots out. Of course A could be right if the cube goes through very slowly but based on the number of s p e e d lines its going at some speed.

You can try it yourself by holding something in your hand, moving your hand up rapidly and then stopping your hand, the thing will continue upwards. For bonus points, set up a camera at 45° to your hand for a view of the second portal

>>10684433
no the answer is A, because portals conserve only the momentum of the object moving through it.

some anons have disagreed, but i think it literally is a hula hoop which joins two points of space.

as such A is correct.

So when you consider it as a hula hoop, you see that if the table is pushed up you get situation B

but if the portal is pushed down you get situation A.

>>10684482
If the cube must come out with the same speed that it came in, how do you handle >>10683412 ?

>>10684482
no the answer is B, even with your hula hoop the cube is still moving through the portal with speed and its momentum is conserved

>>10683412
this is the real million dollar question

>>10684525
portals can't be placed on moving surfaces m8

>>10684525
easy

>>10684492
if the exit node has a velocity, then that is transfered to the cube to conserve the inertia(ie set v2 to zero and its the same as the previous post), so would have velocity v2.

in the case of the table pushing up to the portal, then you would have case v1+v2

make sense?

its al least internally consistent with the intial posts
>>10684482
>>10684486

>>10683728
moving portals can work. you just have to make a decision on how you want them to work. A or B

>>10684525
https://www.youtube.com/watch?v=0TZd95BCKMY

>>10682754
>Im driving at 20 miles an hour
>I see a box moving past me at 20 miles an hour
>I immediately break

>THE BOX KEEPS GOING AT 20 MILES AN HOUR ON THE OPPOSITE DIRECTION

>>10682810
Smart man.

To all the brainlet plop fags out there. At what velocity does the cube exit the portal? If the speed is greater than zero then why does it stop moving? If the speed is zero then how is it a cube and not a flat plane?

>>10682754
Why the fuck would the portal magically impart momentum to the box?
Whoever chooses B is a literal retard.

>>10684562
So the speed of the blue portal matters for the movement of the cube, but for some reason the orange portal doesn't? It's either the v1+v2 case, or the V0 case. Pick one.

>>10684584
so basically >>10684560

>>10684606
If you immediately braked, you’d go flying out the window due to 1st law. When flying out you see the cube still moving at 20mph past you in your frame of reference.

The box has two different speeds in the same refference system.
This problem cannot be solved.

>>10684651
I have seat belts, it turns out. The car scenario is just for visualization, the abstraction is that I'm breaking and the box stops moving.

>>10684525
It depends on the structural integrity of the cube.

>>10684633
It depends on the cube's speed relative to the blue, destination, portal. The orange portal is treated as just a hole.

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Consider for a moment, my dear brainlets, that an object can't appear on onside of the portal slower than it disappear on the otherside. Therefore it has to leave one side at the same speed as the other.

>>10684674
you didn't even read 5% of the comments before you wrote that retarded shit, right?
Answer is right here >>10683745

>>10684525
the cube would block itself halfway thru and the surfaces cannot close

>>10684584
wow thats awesome. is it real in engine?

>>10684641
ok ill try to explain. imagine the exit portal was in a car and the first one was stationary. you jump in and immediately you are in the car. how fast would you be going? you would be going as fast as the car.

>>10684641
what im trying to say is that there are different internally consistent explanation depending on your initial assumptions. if normies were arguing for A i would be arguing B

>>10684716
yeah i thought that. it would crush itself.

>>10684726
https://steamcommunity.com/app/620/discussions/0/343787920123988466/
From video description
"For the record: Portals can move. In Chapter 5 (The Escape) at the thirty-third level of the game, you have to place portals onto moving panels to cut neurotoxin generator tubes by using a laser - https://youtu.be/B2gBNwT6aqU?t=2m11s - This gameplay mechanism is not activated by default, so a special command was used to achieve the experiment (sv_allow_mobile_portals 1)."

itt

>>10682795
based

>>10683023
retarded

A. people, please explain this to me.

If the portal is coming down ontop of you at 100km/h we all agree you are disappearing into the portal at a rate of 100km of you per hour right?
We all agree that on the other end you are coming out of the portal, but at what rate?

1) If it's the same rate you are inserted to the portal you're appearing on the other side already going 100km/h.
If so, what force would instantly bring you to a halt and make you go 'pop' once you are fully inserted?

2) If your 'momentum is conserved' you are coming out of the portal stationary so you are appearing on the far side of the portal going 0km/h.
But this means you are now colliding with yourself since you're still being inserted into the portal at 100km/h but the far end is already occupied by non moving mass.
In this case you wont go 'pop' unless you are made out of some marvel universe super material, you would sorta mushroom into a mush at the interface of the portal.

How do you A. people resolve this to get the 'pop' thing and somehow gently fall off intact?

>>10684820
Butthurt

>>10684844
>If so, what force would instantly bring you
This is not an argument since it can be applied for both cases: if I consider the cube as speeding out of context, then looking at the first(orange) portal, if I stop this portal mid-way, in other to preserve the speed and momentum on the exit portal, the cube will lift itself from the ground with an imaginary force and go upwards into the orange portal.

>you are coming out of the portal stationary
Stationary relatively to the exit portal at the original distance, that is, the cube is not moving before he enters the portal according to an observer at the blue portal.

>>10682754
Alright A fags, riddle me this. Since the cube has 0 velocity when exiting the blue portal, you would have absolutely no problem placing your head just above the blue portal. It can't smack your head backwards since since the cube has no momentum right?

>>10682754
Alright A fags, riddle me this. Since the cube has 0 velocity when exiting the blue portal, you would have absolutely no problem placing your head just above the blue portal. It can't smack your head backwards since since the cube has no momentum right?

>>10682810
This. The portal exerts no force on the cube. Any momentum or force the portal platform had is transferred to the platform the cube is standing on upon impact. As per the game rules.

>>10684929
lol good job my retardo man u forgot the image

>>10684902
> if I stop this portal mid-way, in other to preserve the speed and momentum on the exit portal, the cube will lift itself from the ground with an imaginary force and go upwards into the orange portal.

Not an imaginary force, the moving part would still be moving and pulling at the stationary part that still haven't entered and vice versa. Depending on the velocity and the strength of the object it might rip in two case that happened, it'd be a violent yank.

You did not address the key points tho, how do you resolve it?

>>10684955
So you don't actually have an answer to the question, gotcha.

>>10684983
Is it possible there isn't any A. people and they all be trolling us?