/pg/ - Portal General

[Anonymous No.14624610]

Let [math]P_\textbf{orange}[/math] come down on a stationary (i.e. [math]v_0 = 0[/math]) cube [math]C[/math] at the speed [math]v_p[/math] and let the cube exit the portal [math]P_\text{blue}[/math] at the speed [math]v[/math]. What is the exit velocity of the cube?

[eqn]A)\ v = 0\\ B)\ v = v_p [/eqn]

[Anonymous No.14624690]

[Anonymous No.14624799]

>>14624610
If the cube has zero velocity it ends up at zero height, smashed into a singularity. In order for the top half to exit the portal it must have velocity relative to it. If the top half has velocity relative to it, the bottom half does as well.

[Anonymous No.14624929]

>>14624610
The cube remains stationary as the whole universe is just moving relative to the portal, there is no kinetic energy to impart because the cube is stationary at all times

[Anonymous No.14625042]

>>14624929
Bringing kinetic energy into the discussion is completely pointless because portals already violate the conservation of energy.
Besides, kinetic energy doesn't have to be conserved between different frames of reference and the two ends of the portal are completely separate frames.

[Anonymous No.14625779]

>>14625042
Yes, but still, B-tards fail to explain why the rest of the universe doesn't rip through the portal since it's moving at the same velocity relative to the portals as the cube, since portals are a 0-dimensional instantaneous connection between two points in the universe then it only makes sense that the whole universe is moving around the portals rather than vice versa, no? In order for speedy thing go in speedy thing come out to apply the cube mustn't be at rest relative to the universe that surrounds it.

[Anonymous No.14625794]

the cubes will fly out

it doesnt matter that they're sitting on the ground.

they will exit the blue portal with a large velocity because they will be traveling relative to the exit of the blue portal

>b-bububbubbu-but

NO.

same reason a baseball flies away from your hand even though It'S StAtIoNaRy On YoUr hAnD wHeN yOu ThrEw it

lrn2relativity

[Anonymous No.14625905]

>>14625779
>only makes sense that the whole universe is moving around the portals
What is relativity?

[Anonymous No.14625906]

>>14625779
>at rest relative to the universe
What does that even mean?

[Anonymous No.14626383]

>>14625779
portals are two dimensional
as they move, they transport a three dimensional volume of stuff

[El Arcón No.14626393]

Ask what happens if you put blocks on the table so that the falling portal only half envelopes the cube before it stops. Is it going to tear the cube in half, suck the cube through, or not do anything?

[Anonymous No.14626415]

>>14626393
>if the entrance portal is moving fast enough relative to the exit portal
>if the entrance portal is moving slow/still relative to the exit portal, but there's sufficient force being applied to the exiting cube-half (ie gravity, rope, op sucking it off)
It gets sucked in.

>if any of the above, but you used some strong-ass glue to keep the cube stuck to the table
>if none of the above
The cube stays still

>if any of the above except both portals being still, but your cube is made of toilet paper
It gets ripped in half.

[Anonymous No.14626548]

>>14624610

[Anonymous No.14626563]

>>14624799
Hula hoop.
Now.

[Anonymous No.14626565]

>>14625794
The blue portal is moving the same speed relative to the orange as the cube is. Checkmate.

[Anonymous No.14626593]

>>14626548

[Anonymous No.14626653]

>>14625042
>pointless
Well, because Noether's theorems don't make much sense w/ portals, in this case translational/rotational symmetries, specifically, some conservation laws are broken. E.g. there is no more momentum conservation as a portal can cause mass to undergo an arbitrary change in velocity without having to transfer momentum to other masses. Time symmetry appears to be broken in the cases where an object is allowed to loop a path an arbitrary number of times, as there's no way to write a lagrangian for a path that travels over some potential gradient for a random interval. In cases where the portals do not form a loop, some sort of lagrangian with a piecewise potential function can probably be written down and solved, and this formulation leaves us with the conservation of instantaneous kinetic energy.

Regarding the energy of the portals moving through space, themselves: space is neither created nor destroyed, only reattached. I don't know what the latest physics has to say about the energy inherent in spacetime, itself (whatever that is), but I think "zero" is a safe bet here, too. Energy bends space according to GR, but space doesn't bend itself. Mass-energy and spacetime tensors are on opposite sides of the equation.

As a tangential problem, I'm thinking about how air would behave with a moving portal. It seems to me that it would remain still, even despite portal motion, as the pressure on either side of the portal is roughly the same in any given instant. In the case of opening one portal at the top of mount everest and another at the bottom of a deep canyon, we would see the violation in time/energy inherent in closed loop paths as the air rushed out of the high pressure region and into the low pressure region ad infinitum. The world would very eventually become a very windy place (or shed gas to space, more likely).

Suffices to say: instantaneous KE can be reasoned to be conserved, thus the box will roll/slide down the inclined plane.

[Anonymous No.14626658]

>>14626393
depends on the material of the red blocks, material of the cube, and mass of the cube. The red blocks being softer or harder makes the orange portal accelerate faster or slower (although "slow" is still every fast since its a collision). That acceleration * half the mass of the cube requires a force to pull the other half of the cube up to being the same speed. If that force is greater than the tensile strength of the cube, the cube will rip apart

of course, im using the B model. for the A model, it uhh... idk hoola hoops.

[Anonymous No.14626665]

>>14626563
What are you trying to say? Are you saying a hula hoop applies no load due to inertia?

[Anonymous No.14626682]

>>14626653
Another suggestion that instantaneous kinetic energy is conserved: in game, though the velocity of an object changes arbitrarily when it passes through a portal, the magnitude of the velocity doesn't, thus the momentum magnitude and (kinetic) energy are unchanged.

Another tangent: A (relatively slowly) moving portal probably doesn't provide enough of a tidal force (borrowing term from gravity and applying to my gut feeling on what would happen here w/ special relativity) on a co-moving object passing through it to overcome (or even significantly perturb) chemical, let alone atomic, bonds. If the object and portal were interacting relativistically, who knows? Is one option that the object is shredded into standard model foam as it crosses the spacetime discontinuity?

[Anonymous No.14626688]

>>14626665
No. I'm saying relative speed/motion doesn't matter because the portals connect space and are empty in between. The orange passes over the cube and the cube emerges from the blue at the same rate until the cube is all the way through, at which point it slides down the ramp due to gravity.

There's no reason to expect that there is resistance/energy needed to actually cover the distance between the portals.

[Anonymous No.14626712]

>>14626688
>There's no reason to expect that there is resistance/energy needed to actually cover the distance between the portals
I agree. I wondered about what sort of energy may be involved in moving the spacetime stitch of a portal pair above in >>14626653 but reckoned that it would be zero as far as the game physics go. In the real world? That's a question for the black hole folks I guess. Lots of energy, there. No experiments to be done...? Is there any overlap, there, with the particle folks at CERN? Upon further consideration of the game physics, the portal gun seems to be powered...

[Anonymous No.14626724]

>>14626653
There is no violation of conservation laws - the transition across the portal aperture is a non-inertial reference frame and all apparent violations are simply a consequence of pseudo-forces.

[Anonymous No.14626733]

>>14626688
Time speed distance.

Does the cube cross a distance over a time? If it does, then it has a speed.
In order to emerge from the portal it must cross one cube's height in the time it takes to emerge. That's its speed.

In order for the portals to be equivalent, the relative speed at which it enters one portal must be the relative speed it exits the other. If it enters one portal at one cube height per time t, it exits the other at one cube height per time t. The difference in the portal's velocity is made up by a difference in the cube's velocity.

[Anonymous No.14626758]

>>14626724
There is a violation. If everything moving into a portal exits a paired portal along a path not identical in direction to the initial path, linear momentum is not conserved. Momentum would then leak (unless everything going into the portal were necessarily complimented by an object/objects with opposite momentum going in the other direction.

Imagine a world in which all of the momentum is contained in bodies moving in a single line. Now place a portal in the path of theses bodies and place the output portal which is at a right angle to the first. All of the momentum along the initial axis will be transferred to an orthogonal axis. Momentum is a vector. This violates the conservation of momentum via symmetry theorem because symmetry is lost.

[Anonymous No.14626854]

>>14626758
>Imagine a world in which all of the momentum is contained in bodies moving in a single line. Now place a portal in the path of theses bodies and place the output portal which is at a right angle to the first.
Done. Oh look, you can travel on a single line and end up with a final coordinate momentum vector orthogonal to your initial coordinate momentum vector without any deviation in the direction of your proper momentum vector. One can travel 'northbound' through one aperture, experience no deviation in their apparent direction, yet find themselves travelling 'eastbound'.

If the relative positions, orientations portals change, the curvature changes.

Portals are simply expanding this concept to higher dimensions.

[Anonymous No.14626976]

>>14626854
You don't understand. Magnetic fields don't do work, themselves. To reverse the momentum of a particle requires work. Magnets which alter the momentum of charged particles are attached to something. Newton's second law applies.

Have you put time into studying physics?

[Anonymous No.14626997]

>>14626854
>>14626976
Forget earlier (76) reply. Cyclical acceleration in a magnetic field aligns with conservation of energy (which I agree with in this thought-experiment and have agreed with since my first post in the thread). It doesn't align with conservation of linear momentum (associated with translational symmetry). "Line" in this context doesn't mean "line in a circle". It means an ideal line in Euclidean space.

Momentum transfer via magnetic field is another topic. Might be worthwhile. Interesting if so.

[Anonymous No.14627019]

Steel pole 1 light year long meets portal traveling at the speed of light. Steel pole comes out of blue portal traveling at the speed of light.
6 months in, halfway down the pole, the portal stops. What happens to the pole?
The tip of the pole cannot instantaneously know what happened half a light year away.

[Anonymous No.14627049]

>>14626393
>Is it going to tear the cube in half
Pretty much.

[Anonymous No.14627051]

>>14626548
That's fucking retarded, if green sees purple's ceiling coming at him at great speed, he's not expecting A to happen, but B.

[Anonymous No.14627055]

>>14624610
It's A. Midwits get filtered by this hard.

[Anonymous No.14627088]

>>14624610
this is a good question for filtering sub-120 IQ "scientists" who probably thrive in fields that select for rote memorization ability and don't actually do any abstract thinking.
it's obviously B. if portals hypothetically exist and can move relative to each other it makes it like the whole universe through the portal is moving. e.g. if you put one on the front of a car driving down the road, wind would come blowing through the other portal, the air wouldn't just "change position without kinetic energy" or whatever the fuck until it was all the way through the portal and then suddenly become stationary.

[Anonymous No.14627101]

>>14624690
Is there an air, tho?

[Anonymous No.14627192]

>>14626653
>Suffices to say: instantaneous KE can be reasoned to be conserved, thus the box will roll/slide down the inclined plane.
Why? Actually, yes, it can be reasoned to be conserved, which is why the cube cannot slide down. The cube exiting the portal has some non-zero speed and is physically moving through space so why would it just stop once the whole cube is through? Why would all of its energy and momentum just disappear?

[Anonymous No.14627193]

>>14624610
Unironically, making a general might be the only way to make this shit die for good

[Anonymous No.14627200]

>>14624610
A, the cube has no momentum.

[Anonymous No.14627211]

>>14627019
Trivial. The pole rips at the intersection with the portal. It will happen at any speed if the acceleration of the portal is instantenous.

[Anonymous No.14627213]

>>14626854
>>14626976
>>14626997
What if the portals require to be placed upon a surface because they transfer the difference of momentum to the attached surfaces?

[Anonymous No.14627622]

>>14626976
>>14626997
Didn't say anything regarding magnetic fields. What is happening is not a proper momentum transfer to an object, but a manipulation of the coordinate space. If this was done in a zero-g vacuum environment the person going through the portal would experience no proper acceleration.

[Anonymous No.14627880]

>>14627211
Thus B.

[Anonymous No.14627903]

>>14627880
Yes, agreed

[Anonymous No.14627966]

>>14627051
are you stupid?

[Anonymous No.14627981]

>>14627966
Not at all, but thanks for pointing out that you are.

[Anonymous No.14627990]

>>14627966
Both of them see the one on the moving platform is approaching the ceiling at some speed so neither of them should expect to see A.

[Anonymous No.14628752]

>>14624799
the cube has velocity compared to the yellow portal, therefore it would have velocity compared to the blue portal when it comes out; it's B

[Anonymous No.14630092]

So, did anyone solve infinite force problem? I'm sticking my dick in it until they do.

[Anonymous No.14630230]

>>14625794
Imagine that the portal is just some delicate but 1km wide ring, and the object to be ported is a 1km monolith of lead.
Now lower the 1km (it's so light literally 4 men holding it at each extreme could do it) over the monolith. Better yet, imagine it falling at terminal speed.
Now, according to the b-tards and your retarded euthanasia-worthy claim, the monolith should fly out with the inverse speed of the ring falling, generating free energy.

[Anonymous No.14630234]

>>14630230
Rephrase your scenario in a way that can actually be understood. This is some literary vomit if I ever saw one.

[Anonymous No.14630236]

>>14630234
Embarrassing post

[Anonymous No.14630245]

>>14630230
If the portal is descending onto the object, the object has some velocity on the other side of the portal. If it doesn't fly out it means it magically lost all motion for no reason and that is a stranger scenario than it keeping its momentum in that frame of reference.
Not sure why you brought any sort of dimensions up. I fail to see how it helps to illustrate your example any better.
Portals already violate the conservation of energy and in-game portals already can generate free energy. Free energy is a problem whether A or B scenario is true so what is your problem here?

[Anonymous No.14630251]

>>14630245
>If it doesn't fly out it means it magically lost all motion for no reason and that is a stranger scenario than it keeping its momentum in that frame of reference.
It hasn't magically lost all momentum, it's simply that the momentum you think matters dissipates elsewhere (like the non-portalling edges of the portal: they slam onto the ground, generating heat), and A solution advocates think this supposed relative momentum does not matter because we are talking about a literal, classical tunnel in reality. If you enter a tunnel under a mountain, there is no further relative motion happening between the entrance and your car, besides the one already taking place. You have to imagine like such a tunnel.
>Portals already violate the conservation of energy and in-game portals already can generate free energy. Free energy is a problem whether A or B scenario is true so what is your problem here?
That may be the case, but I find the A solution much less egregious than the B solution. By the same token, we could imagine some C solution which is B but even worse in the free energy department (like also spawning 10 barrels of oil at your discretion to consume). Naturally, even if we are already talking about supernatural shit, I would still reject C before any other answer, as the most unreasonable option.

[Anonymous No.14630264]

>>14630251
The only way to move through space is to have momentum. The part of the object that already exited the portal has some momentum in that frame of reference and is physically moving through space. It no longer has any relation to the portal. The only solution for not including the portals' relative movement (which btw makes your tunnel analogy useless for illustration) is for the object to never have any momentum ever on either side of the portal which means that the object can't enter the portal in the first place (or be smushed into an atom thick pancake because the apparent motion through the portal is immediately cancelled).

[Anonymous No.14630321]

>>14630230
You know in-game portals generate free and infinite energy already, right?

[Anonymous No.14630345]

>>14630321
Speaking of conservation, A is even worse than B because A doesn't preserve momentum locally.

[Anonymous No.14630443]

>>14630264
What is a hula hoop?

[Anonymous No.14630511]

>>14630443
a portal whose apertures are aligned and separated by a negligible distance in 3-space

build me a hula hoop whose sides can move independently of each other while still allowing instantaneous and continuous motion across their aperture

[Anonymous No.14630538]

>>14630511
ok

[Anonymous No.14631384]

>>14630230
>ADVANCED hula hooping

[Anonymous No.14631660]

>>14630511
>>14630264
Anon already did.

[Anonymous No.14632342]

[Anonymous No.14632343]

>>14632342
this cube was moving at 0mph, then after the portals move over it, it is moving at 20mph

portals do not preserve momentum

[Anonymous No.14633692]

>>14632343
Portals don't preserve momentum even in the frame where they are stationary.