/sci/ - Science & Math

somebody post the screen shot so we can wrap this up fast

>>10635918
A
Object at rest will stay at rest unless a force acts on it
Portals are not a force per se, but are merely changing the location of the object.
If you want a B outcome, throw the block into the portal.

>>10635918
its b because speed is relative and has to be conserved

>>10635918
>Can you science guys figure this one out?
What have you tried?

>thread gets deleted on /v/
>gets reposted to /sci/
like clockwork

>>10635918
Yes, we can. But this is still 4chan, so for every post that has figured it out there will be five posts with complete nonsense, so you will not be able to tell what is right and what is wrong from reading the thread unless you have already figured it out yourself.

>>10635930
Which screenshot?

>>10635930
>wrap this up fast
How? If /sci/ is anything like the rest of the boards on this retarded web site, you could post irrefutable proof of something and still get hundreds of replies from idiots who can't read or think. Good luck wrapping up a portal bait thread, of all things, without deleting it. These threads attract the kind of people who think inertial frames of reference are pseudoscience.

>>10635961
A detailed explanation on why the question is a meme and definitely doesn't have any decent physical answer

>>10635978
>a nonsense, unphysical problem has a solution
Good bait

>>10635976
If someone has it, I'd like to save it, assuming you're not referring to this: >>10635953

>>10635918
A

Reason: conservation of momentum. The portal is moving, not the block.
Also, consider the case where the portal only teleports half the block. If B is true, does the block’s momentum suck the other half of the block into the portal?

>>10635984
The portals featured in the video game Portal do not conserve momentum. "Speedy thing goes in, speedy thing comes out" is not what the law of conservation of momentum actually is. Momentum is a vector.

All we know from the games is that the magnitude of an object's momentum remains unchanged when passing through a pair of portals — or, more specifically, it maintains its speed when passing through a pair of portals which are not moving with respect to one another. But the direction of the object's momentum can be changed, and not in any way which agrees with how the law of conservation of momentum is supposed to work.

The game doesn't show us what happens when one portal is moving with respect to one another, but if portals facing different directions can change the direction of an object's motion in violation of the law of conservation of momentum, then it's not so absurd to assume that portals moving at different speeds can change the speed of an object's motion in violation of the law of conservation of momentum.

>>10635984
>cites the conservation of momentum in a system where the conservation of momentum does not hold
>>10635982
Im not. The gist is that the portals from the Portal games are in gross violation of the conservation of energy, the conservation of momentum, they violate causality, etc. The way they behave aren't even consistent in the games themselves. Therefore it is meaningless and a complete waste of time to argue and conject whether A or B is the right answer. The answer is whatever you want because is question is ill-posed. Anyone who feels strongly about one or the other is a physicslet.

>>10635994
>The portals featured in the video game Portal do not conserve momentum.
Yes they do.
>and not in any way which agrees with how the law of conservation of momentum is supposed to work.
Yes it does.

If you construct the reference frame in which the two portal surfaces are glued together back-to-back -- for which you need to use a weirdly warped space, but that's what portals seem to do -- then conversation of momentum applies to objects passing through the portal, *in that reference frame*.

This is the sense in which conversation of momentum legitimately applies to the Portal universe.

And if you apply that viewpoint the the problem in OP, answer B rolls right out.

>>10635994
>>10635995
>just believe in magic lol. I love GAYMING!

>>10635995
>Therefore it is meaningless and a complete waste of time to argue and conject whether A or B is the right answer.
For the record, I agree with this. I don't care whether it's A or B, although, from a /v/ perspective, I do believe that B would make for a more interesting gameplay mechanic.

To be honest, the only reason I post in these threads is not to argue A or B but rather to berate people who make claims which are provably false, such as that portals conserve energy.

>>10635918
What A fags can never explain is how the cube can pass through the portal in the first place. If the cube stops when it gets through to conserve momentum then how come individual particles within the cube don't follow the same rule?

Every single atom should stop the moment it passed through the portal, creating an extremely dense, atom thick sheet over the portal. But for some reason the atoms can pass through until the universe decides to stop them at some arbitrary point after they passed through the portal.

>>10635918
PhD = Piled High and Deeper....

>>10636006
Put two portals on walls that face each other. Throw a box into one of the portals and it will come put of the other portal with a momentum vector opposite of what it went into the entrance portal with. Ergo momentum isn't conserved.
>energy
Put a portal on the floor and a portal on the ceiling. Jump through the one on the floor and your body will accelerate indefinitely. Energy isn't conserved either.
>>10636007
Did you even read what I wrote? I explained why ViDeO GaEms aren't physics.

>>10636017
>Put two portals on walls that face each other
Shit. I meant put two portals on the same wall.

>>10636006
>If you construct the reference frame in which the two portal surfaces are glued together back-to-back
I concede that, if you do that, you can get the math to work out for one single object passing through a pair of portals. In your weirdly constructed frame of reference and coordinate system, the object basically moves in a straight line instead of changing direction, right? I mean, that's how it looks when you go through portals in first person. So I can totally understand the argument you just posted, and I can see how it could be used to justify B as an answer as well.

However, when you consider the total momentum of a system with multiple moving objects, and only one of those objects passes through a pair of portals as shown in the image I posted (>>10635994), I don't think you can construct a frame of reference in which the total momentum of that system hasn't changed. I mean, go ahead and try. I'm just not sure how it would work.

>>10636013
When you go through the portal, the whole universe moves the opposite direction. Think about it, the entry portal is essential the exit portal, but it’s in a different location. So if the entry portal is moving towards you, then so is the exit portal. Either the exit portal must also move, or the whole universe, except for you, of course. This is how momentum is conserved.

/thread

>>10636024
>ends his own post with "/thread"
newfag

There is no energy applied to object by other object so it will be A.

Portal is allowing to pass object from one place to another but it will not give any energy to cube.

But if portal will be down at the bottom and cube will fall into it then energy is applied by gravity and object will fly away like in case B.

it is clearly A, imagine it like dropping a box with a hole on something; it is in the box, but not because it had kinetic force, you just dropped the fuking box on it

>>10636029
>change the problem
>get different answer
wow no way

inb4 "portals are literally hula hoops"

This thread was pretty civil for a while but now the retards are arriving, so I think I'm out.

>>10636023
Not that guy but I'm pretty sure that's literally what the original post said. Conservation of momentum is broken overall but it can be explained locally from the reference frame of the portal.

>>10636024
How does that explain the problem in the port you replied to? What's true for the cube would necessarily also be true for any particle the cube is made of. What if I just apply the same logic to a single atom the cube?

>>10636013
What the fuck ?
This is game...

Something like this in reality would require to create miniwormhole that would break current space send object to higher dimension and send it to another linked wormhole.

>>10636017
>Put two portals on walls that face each other. Throw a box into one of the portals and it will come put of the other portal with a momentum vector opposite of what it went into the entrance portal with. Ergo momentum isn't conserved.
No, no. Momentum is conserved in the reference frame in which the FRONT of one portal equals the BACK of the other one. Which works out fine in your example, as in anything in the game.

>>10636034
shut up fag thats how portals work in the game

they are like a window to the other portal which in this case, you just dropped the fuking window on it

What's the final speed of the box?

>>10636028
>Portal is allowing to pass object from one place to another but it will not give any energy to cube.
If you'd played portal you'd know that this is blatantly false.

Put a portal on the floor, the other on the ceiling above it. Through a cube in the middle. That cube is gonna pick up more and more speed as time goes one but it'll never get closer to the ground. You're adding more energy to the universe.

It requires energy to warp space. Let’s say portal X and portal Y are 10 meters apart. From the perspective of an object entering portal X, the space between X and Y is non-existent. As you walk through X, you come out Y, as if space were compressed and the portals became linked together.

In order for one portal to move a distance away from the other, and still properly teleport an object, then either the portal must have more energy to warp a greater amount space, or the other portal must also move with it in the same direction and speed.

Answer B is right but only if you supply energy to the portal

>>10636029
>>10636051
Portals are not Hula hoops.

>>10636050
>dude just pick a reference frame in which there are TWO positive x directions

We’ve been thinking about it wrong the whole time.

PORTALS CAN’T MOVE.

When the portal is created, it is fixed to that subspace. The portal cannot be moved along with the machine that created it. Even if you were to suspend the machine in the air and let the portal + machine fall, the portal would remain fixed as the machine moves through it.

>>10636103
The earth moves you dibshit.

>>10636023
>In your weirdly constructed frame of reference and coordinate system, the object basically moves in a straight line instead of changing direction, right? I mean, that's how it looks when you go through portals in first person.
Right.

>However, when you consider the total momentum of a system with multiple moving objects, and only one of those objects passes through a pair of portals as shown in the image I posted (>>10635994), I don't think you can construct a frame of reference in which the total momentum of that system hasn't changed.
Oh, yes. In my view, portals maintain local momentum and local Newtonian physics in general, but *global* momentum and Newtonian physics go out the window. Everything in the game behaves as if physics is *locally* Newtonian, while not being globally Newtonian in any obvious way.

This is why I think people arguing conservation of energy and related notions on this problem are so misguided. Global conservation laws follow as a consequence from local behavior that keeps certain things invariant, not the other way around. Which means that when you analyze a universe with unfamiliar experimental local physics, you forget all global conservation laws you know, and you see which ones still apply under the new local behavior. You can't just assume that the generalizations you are familiar with still apply when the details have changed, that will just inevitably lead to contradictions.

>I don't think you can construct a frame of reference in which the total momentum of that system hasn't changed. I mean, go ahead and try. I'm just not sure how it would work.
I actually suspect it can be done, if you are willing to accept discontinuities in your topology. But that is well beyond my pay grade, and my argument is based on just accepting that the global viewpoints we are familiar with do not necessarily apply.

>>10636055
Gravity is adding force to the cube not the portal.
It's going to pick up more and more speed due to gravity no due to portal.

>>10636104
That’s why you make portals in outer space. Your video games are simply inaccurate, sorry.

mods should delete this thread every time it gets reposted, desu

>>10636134
Actually I think mods should just ban anyone who posts the wrong answer to >>10636052.

>>10636125
>Gravity is adding force to the cube not the portal.
What I think you meant to say is that gravity is applying a force on the cube which is correct.

However, when the cube passes through the portal it gains distance from the earth without loosing any momentum. In reality, in order to move an object away from an attractive force you need to use energy to do so. A portal allows you to move objects away from any attractive force without using any energy. That's how portals add energy into the universe.

>>10636125
You're really not grasping the concept of gravitational potential energy, are you?

>>10636111
(samefag)
>I actually suspect it can be done, if you are willing to accept discontinuities in your topology. But that is well beyond my pay grade, and my argument is based on just accepting that the global viewpoints we are familiar with do not necessarily apply.
Addendum: I think this can be done mathematically. But the game does not actually seem to behave as if space were bent in such a way. If it were, gravity would work in a completely different way from the way it does in the game -- you would feel gravitational pull towards a portal whose other end is on the ceiling, and a push *away* from a portal whose other end is on the floor. So while the mathematics might work out globally, Newtonian physics evidently does not. Unless you posit something ridiculous like "gravity ignores portals and the space-bending effects thereof but all other physics does not", in which case we might as well claim any phenomenon we damn well please as fundamental.

>>10636175
>gravity would work in a completely different way from the way it does in the game -- you would feel gravitational pull towards a portal whose other end is on the ceiling, and a push *away* from a portal whose other end is on the floor.
In terms of Portal gameplay, I think this would be a fun improvement.

>>10636187
It might be. I find it hard to imagine how this would work out in practice.

I can only imagine how horrible it will be to make the half-life engine pull off this shit, though.

A-fags... When will they learn?

>>10636220
“Portals can move” fags, when will they learn?

>>10636259
What do you call this fag?

>>10635918
HAMILTONIAN FLOWS IN PHASE SPACE ARE CONTINUOUS
STOP POSTING THIS FUCKING THREAD
FUCKING SAGED

>>10636272
>portals move along with Earth
Um no. Your games are wrong, sweaty

>>10636147
If you are talking about reality then yes but game engine works more simplistic i mean it calculates only vector of moving,gravity,friction(defined by material and mass),mass and i know there should be one more thing but i'm not sure if they really add air resistance into source engine.

>>10636143
-7m/s assuming a point mass of negligible width

>>10635918
Intuition says A, but B may be plausible for point mass. The image is misleading because classical physics (or at least most of our intuition for it) breaks down in the case of large objects.

Consider: What if the input portal stopped at a half-way point of the object? Naively assuming B, either (1) you'd have to argue how the object gets "sucked in" to the portal even after it had stopped moving, (2) or how momentum/energy or w/e aren't transferred until the object has fully passed through the portal (i.e. only when the solid has fully passed through A, it suddenly springs out of B). Either way you'd need to make axiomatic assumptions that don't easily reconcile with classical mechanics (or my admittedly rudimentary understanding of it).

But now imagine the input portal moving through air. It's not inconceivable to imagine that the faster the portal moves, the faster the air (wind) comes out of the output portal. And some small dust particle of negligible size in the air would probably behave the same way.

t. EEfag

B because momentum is conserved. Either way you look at it, after the block has gone through, the block is in the reference frame of the moving portal, hence it must have an initial velocity equal to that of the moving portal in relation to the reference frame.

Ok hear me out and tell me if I’m wrong

You are standing still in a room and 20 feet away is a huge piston facing you with a portal on it. You can clearly see through the portal to a long empty road where the exit portal is at on a brick wall on that road.

If the piston comes at you at 300 mph wouldn't the whole universe on that end be coming at you at that speed? Once you pass through you might as well be moving over an empty road at 300mph from an on looker on the other end and get jacked up making a lovely meat stain on the road.

If this is correct it can’t be possible for one end of the portals “universe” to be moving at a different speed than the side youre on.

Only makes sense if your dimensions hopping

Are no one questioning why the portals are two dimensional?

>>10636823
And what about the question raised in >>10636737?