I just published this paper that PROVES the answer is B:

Wow, this is brilliant!

I bet one day this research somehow becomes useful for science/particle physics. It may seem like it only applies to portals, but maybe the math can be used for even more applications!

Most brilliant thing I've ever read on Veeky Forums!

Cringe

Well done Veeky Forums, you actually did something.

Should moving one portal cause the other to move?

What kind of retard names a law after himself?

what kind of retard says he published a paper when it got no peer review?

what kind of retard DIRECTLY uses wikipedia as a source in a said paper?

b r a i n l e t

That's a really interesting question.

I don't know the answer, yet.

If you put one portal 500m above another, do you get a cyclone from the pressure differences ?

Its not a solution, it doesn't adress any of the problems with the senario.
As an example:
Newtons laws doesn't hold if you stop the portal half way over the cube. The 2 halfs of the cube will be experiencing a force pulling it up through the portal. If the change in velocity is big enough it could even tear it self apart without anything acting on it. This makes it obvius that your solution isnt the only answer.

The only source is the portal video game wiki you fuggin ass hat

You're right that this is a problem.

Right now it's a special case.

I need to work out the general case where the piston can accelerate/decelerate. If the piston were to have non-constant velocity, the reference frame sticking out of the portal would be accelerating! And then it couldn't be an inertial frame. Hmm I need to think about this.

I wouldt think too hard on it. Portals will always break conservation of energy in some ways. No matter which solution you pick it wont be concistant with all physics and every refrence frame. You have to pick and chose for it to make sense, but overall, It can never be a total solution.

They might break conservation of energy, but they shouldn't break newtons laws. You can only derive conservation of energy from newton's laws if you assume a flat, unbroken space.

>shouldn't break newtons laws
What makes you say this. The half way example shows it pretty clear that this is not the case. Its also not the case in the normal example, but slightly more subtle.

I'm gonna read this paper tomorrow. Don't let this thread die before then.

>open link
>"JOURNAL OF Veeky Forums"

and why the fuck does the face in the A/B problem have to be tilted diagonally?

Do you guys think the jerk on the cube would be constant?

Imagine instead of the piston stopping suddenly, it is moving at a constant velocity. If the jerk is constant I can solve it.

>The 2 halfs of the cube will be experiencing a force pulling it up through the portal
what force? the portal only serves to reposition an object, not impart any force onto it

The cube's velocity would be changing in any given reference frame.

So there's a force acting on the cube

>The cube's velocity would be changing in any given reference frame.
no, it's "A" m/s in the x direction, regardless

So according to you, if the portal stops half way, the cube will still move at full speed?

>the cube will still move at full speed?
no.

So the cube will be moving full speed, and then some time later not be moving at full speed?

the portal will be moving at full speed, and then the portal will at some time later not be moving at full speed, at which it will be stopped at the centroid of the cube

*at which point

Guys my computer is taking a shit right now so I can't write out the full math today, but I solved the problem of a portal passing over the cube at a constant velocity instead of a constant velocity.

You need to add a fictitious force.

But I am not sure if the jerk of the cube is constant. I think it might not be constant! But if it is constant:

Then I can find the x position using this equation of motion:

X = x_0 + v_0*t + (1/2)*a_0*t^2 + (1/6)*j*t^3

Where j is the jerk. We know that the initial acceleration is a_0 (acceleration of the portal) and the final acceleration is 0, because after the cube passes through the fictitious force is 0.

I've found the solution assuming constant jerk. But I don't think the jerk is constant... What do you guys think?

>solved the problem of a portal passing over the cube at a constant velocity

* constant Acceleration

>You need to add a fictitious force.
no

When the portal is accelerating, the reference frame is also accelerating. This makes it a non-inertial frame, so you have to account for the fictitious force.

en.m.wikipedia.org/wiki/Fictitious_force

>When the portal is accelerating
there is no mention of acceleration
the portal is moving with constant velocity.
this isn't reality, and if it were, there is no solution, because it violates the rules of the game.
fucking sperg

Ugh. I'm solving a different problem, the problem where the portal IS accelerating over the cube.

WHERE IS YOUR GOD NOW?

No but really, how the HELL do you solve this?

what the FUCK LOL

in that picture it is ALWAYS travelling at the same velocity v, or -v, not both

Ill repost in this thread too. You need GR and 4 dimensional spacetime geometry to really get a good explanation for this.
---

But lets start simpler, see my amazing drawing.
You have 2 cars "a" and "b" both traveling at the same velocity down the highway. Their relative velocity Is 0.

Car "b" suddenly fucks off through a portal and has now changes its direction. Car b still has the same momentum, but their relative speed has increased. Fucking portal magic.

>but user, in the problem, car "b" velocity would have to increase along the its starting direction too.
Okay calm you tits for a second. This is where GR comes in.

If we instead imagine the road as its path through spacesime (i.e. 4D) The change in direction is instead an analog to a change along its time axis. Its momentum HAS now changed, but the car(cube) will not experience any acceleration, its sounds strange maybe depending on how good your intuition for GR is, but this isn't anything that strange in the world of GR, Falling objects do this exact same thing everyday because of a curve in spacetime, we call it gravity.

>but user, what happens if the portal stops before the cube has gone all the way through.
Oh Jesus common. If we go back to the car example, this would be comparable to the two half's of the car getting sent though different portals in different directions. They would then experience the change in velocity as a force pulling itself apart.
>bullshit
Nah man, this also happens everyday close to backhole event horizons as objects pastaficate. The top part of the object will be on a slower path through spacetime than the lower.

>So is it solved then?
Fuck no, I'm making assumptions about how portals work, in order to make it work.

>GR
>GR
>GR
>GR
What are you on about?

General relativity

Why would you need general relativity?

General relativity breaks down the same way Galilean relativity breaks down. You have to use sterling relativity.

Its an explanation for where the momentum is coming from. You're going to need general relativity if you want a full explanation.
Too bad that solving for it isn't going to happen here on this board.

And how about you go more in depth about your sterling relativity. Your example seems pretty limited.

We'll you're saying that the relative speed of the two cars changes after the car passes through the portal.

I'm saying the relative speed of those two cars to each other does not change when you have your reference frame follow the path through the portal.

If you take the reference frame of the right car, shift the reference frame through the portal, then have that reference frame measure the speed of the left car, it would be zero (zero because the two cars are going the same speed).

I haz a question

Is this accurate?

Does the object stop when hitting the portals like a wall? does it get split in half?

Does splitting object into parts via portals require enough force to overcome the force required to tear the object?

This would suggest that trying this at insufficient velocities would cause the object to stop, as if hitting a wall of sorts.

is this correct?

>then have that reference frame measure the speed of the left car, it would be zero (zero because the two cars are going the same speed)
In the car example, the cars do have a relative speed between them after the portal, even though they are traveling at the same speed along their roads.

Not sure I'm getting you here..

If we use GR, the portal would have to be a sharp shift in its time axis causing the spacetime interval to change. The same way objects traveling along a curve in spacetime(a gravitational well) also get shifted.

I see your point.
I can't say for sure, but I don't think the cube's bonds holding it together could slow it down as its going through the portal. The forces on it seems to be to be limited to internal stress, as I see it.

I agree it would slow down the object if indeed the object had enough velocity to cause its internal bonds to break.

Seemingly, if the portal's boundry line were thin enough this would be like trying to passing thru a razor. if the boundry lines are thick enough this would be more like hitting a solid object

I also believe that if the object were travelling at insufficient speeds it would not manage to overcome it's own internal bond strength, ie the object wouldnt rip in half, rather it would come to a stop without managing to traverse either of the two portals.

>, if the portal's boundry line were thin enough this would be like trying to passing thru a razor.
After thinking about it some more, I agree. The more curved the geometry is around the portals, the more chance the cube has to curve back together, out of the curvature leading into the portal, not alowing it to pass.

I'm not sure how this "curving of time" would work :/

Here is my picture. The velocity relative to the red frames would be the same, since you are just shifting a fixed amount, so this doesn't affect velocity. From the red frame, both objects would be traveling the same speed in the same (positive x) direction.

forgot pic

>both objects would be traveling the same speed in the same (positive x) direction.
I see, sure, but I don't think the initial post disagrees with this either.
>Car b still has the same momentum, but their relative speed has increased
>I'm not sure how this "curving of time" would work :/
Its just general relativity, with some assumptions about how a moving portal would work.

Think about it like this. If you are traveling along a an axis in 3D space, if you change your direction along that same axis, you can't do that without influencing how fast you are traveling along at least one of the other 3 axis.

Now; we live in a 4D world where we are traveling along the time axis at some speed. So if you increase your speed along one of the 3D axis, we know the "time axis" speed would have to be the one that change with it, because at least 2 axis change together.

So if we instead do it the other way around, where we change the speed along the "time axis" then you could also add speed to one of the spacial axis. This is why we get timedialation and a gain in momentum in a gravitational well.

>he still hasn't addressed the partially descended portal issue

Dude just stop

I'm working on it right now.

It involves differential equations. I'll post the results when I finish.

If both portals velocities have an affect on the block, then what happens to the block here?

If the block enters the blue portal at a reference of V and is ejected from a still orange portal at V, then what happens when the orange portal is moving at 2V and its velocity is acting opposite (same direction, opposite orientation) to the blue portal?

I think if we are going by B being the answer, then the cube would have to be coming out the orange portal at V, but the orange portal is also going away from the top layers of the cube that have gone through, so the cube will experience a force pulling it up through the portal.

It gets similar to the piston stopping half way problem, only here there aren't 2 half's, here every new layer of the cube exiting will experience the same stress pulling it apart.

By the way, if we do say it does exit the orange portal at 2V, then you get the exact same problem, only on the opposite end.

From the orange's perspective, the box is moving up at v.

The the camera's perspective, the orange portal is moving down at 2v.

v - 2v = -v

So from the camera's perspective, the box is moving down at speed v.

Can you draw a diagram?

Here is a simplified space/time diagram of what is happening.

There are 2 axis, one is the development over time, and the other is just a 1 dimensional representation of space.

The the portals and cube and are drawn as vectors.

In normal portal physics(in the game), most agree that momentum will carry through at the same angle it entered the portal. a rotation in the portal rotates the in going momentum too.

If we say the portal can also rotate the incoming time-axis as well, to carry it through, then we know the answer is "B"

If it doesn't then it will be "A" (Here the portal ends up pushing itself through)

Personally i think "B" is more consistent with the rest we know from the game.

According to the game, you should.

As long as the motion of the portals remains constant, the cube will not experience any pull from anything. It will simply go through the portal at a relative velocity of V.

That's called ''''''''''RELATIVE'''''''''' velocity.

This can't be, unless the cube would actually stretch out as its passing the portal.

Notice how the cube gets stretched out along the axis of the portals in the first example. This is happening because once the top of the portal has passed the portals, there will be a difference in velocity between the two half's. The top will want to continue faster then the lower half.

The second example is closer to what would likely happen where the lower half accelerates into the portal when the top enters, and the top is deceleration as its pulling on the lower half. The acceleration angles of the cube would of course match on both sides of the portal if I did it properly, and they would be curved, I guess.

>This is happening because once the top of the portal has passed the portals, there will be a difference in velocity between the two half's. The top will want to continue faster then the lower half.
This is true, but only from a certain frame of reference, that is someone looking at both portals at the same time would perceive the cube to be stationary on one end and flying out the portal on the other. The object actually passing through the portals experiences both of these as the same velocity, though. It will only feel the deceleration as gravity and wind resistance take hold. This is, in fact, the only way to prevent stretching the cube. If the upper half undergoes acceleration relative to the lower half it would pull itself apart. It would also mean that it is actually exiting the portal faster than it is entering.

So unless the portal itself changes its velocity before the cube is entirely through, the cube will not be pulling itself.

I think you forgot to flip the V of the piston. The total relative velocity when the cube exiting the orange portal is 3V (Btw. do you think A or B is correct?)

The timings totally gets messed up if you do this.
The top and bottom of the cube wont be exiting and entering at the same time then, unless the cube has stretched or the cube has accelerated. It just doesn't work.

>The total relative velocity when the cube exiting the orange portal is 3V
That would make no sense. The cube is going the opposite direction from the portal, so you don't add them, you subtract them.

It's B btw

Sorry, yea you're right about that. I'll think about it some more.

I have been rethinking it and, you're right of course. The velocity of the orange portal should just be ignored, because it will be considered a rest frame as the cube is exiting. Should just be a single constant angle. The whole stretching problem also goes away too now.
Fuck, too easy to get mixed up thinking about this stuff.