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B for sure. Consider a long pole (stationary relative to the track) entering the portal at the front of the trolley, it would leave the portal at the speed the trolley is moving.
Yes but it wouldn’t be possessed of any momentum, it only appears to be moving because the train is moving. As soon as it cleared the portal it would drop straight to the ground.
But it gains the momentum when it exits. It’s moving at it exits the blue portal. Meaning it has momentum at the exit point.
Team B. If you looked through the blue portal you would see the people rocketing towards you. They would shoot out of the blue portal, but they wouldn’t accelerate up to speed because they’re already moving fast relative to the blue portal.
Dont they need to be hovering mid air for either to happen? I am trying to imagine how would a moving portal teleport a person laying down without teleporting the ground beneath him. I think neither a or b would happen, I think they would be draggen on the ground and splattered, but if I HAVE to choose, I say A is more likely. Because they are laying and not hovering I dont think they will be launched.
I agree, in the portal game they would be scraped/blended on the bottom of the support of the portal attached to the train. If they were in fact hovering in line with the portal I’m leaning towards, an object in motion will stay in motion. Given portal orange is moving and blue is stationary, objects entering the portal will exit at the same velocity and b would probably happen in game.
However, the portal is moving. So if we look at this relative to the portal, they would moving into the portal. I imagine they would get shot out along with the rails. Of course, they’ll eventually plop back down, so it really could be A if the trolley was moving quite slow.
B, but only their bellies; the portal is above most of their bodies, and their heads and ankles will get cut off for being off even the track.
B. Since there is relative velocity between the orange portal and the target, the momentum is conserved and they will launch.
In simpler terms, speedy thing goes in, speedy thing comes out
Except the people aren’t moving so aren’t speedy
No momentum goes in, no momentum comes out
The only way B is correct is if the people are launched as a pink paste from the forces resulting from the instant acceleration, and if the trolley also at least slows
Launched with a little more entropy.
A.
its the train that has velocity. The people who enter the portal will not be moving?
Its like that buster keaton clip where he stands still and the side of the house falls down around him(well… sort of)
The train has absolutely no velocity relatively to the orange portal. The people are moving relatively to the orange portal.
If the ground disappears from under your feet at 60 miles per hour, the moment you start falling are you falling at 60 miles per hour?
Yes, that is called running extra fast. And then falling, with the same momentum. Unless there are two grounds, with different relativities. Like with a treadmill: you run relatively to the treadmill, but you are stationary relatively to the ground under it, because you run at exactly the same speed as the treadmill moves in the other way (hopefully for you…).
This is all irrelevant, portals can’t be placed on moving objects.
In Portal 2 you place portals on moving surfaces to cut the neurotoxin pipes.
that is a game engine limitation, not an in-universe physics limitation.
Games and real life are the same! Now if you’ll excuse me I’m going to jump off a bridge then use an energy drink to heal my broken bones.
The earth is a moving object, so all portals are moving through 3d space at all times.
It’s probably dependent on the reference frame of the first portal, or the portal gun.
It can’t be the portal gun since you can shoot it while flying through the air.
There’s a reason why in the game you could never put a portal on a moving surface
Except when you use the laser tp destroy the tanks of neurotoxin. Always annoyed me.
I’ve seen this debate about the outcome of the moving portal. I’m pretty certain that because of inertia, and the people aren’t moving, they will just plop out the other side. Think of it like moving a hoola hoop through the people. That’s basically what the portal is.
The hoola hoop has inertia and is moving, but it doesn’t actually come in contact with the people, so it passes right around them. There’s no way for the people to have instant acceleration because the porta did, otherwise it’d be like them hitting a brick wall and they would probably explode
The problem with your hoola hoop example is that it keeps moving after you go through it so that you have the same relative velocity. However, in the portal example, the exit portal is stationary, so in order to stay the same relative velocity to it when you exit is to speed up yourself, as in B.
Momentum is relative.
If you say the portal is stationary, and the person is moving then B makes sense. However, this is just changing the frame of reference from following the tram to following the person.
Changing the frame of reference (from tram to person, or from person to tram) doesn’t change the velocity/momentum/energy (it’s just the person is moving towards the tram or the tram is moving towards the person).The acceleration the person would experience is likely similar to if the person just gets hit by the tram, however in Portals canon it is nonexistent.
Because, as you say, the person is accelerated. However, the acceleration when using the tram as the frame of reference is still 0 when you account for the rules of physics a portal would break. Even changing the direction of travel would be acceleration.
Like, if the in-portal and the out-portal were back-to-back where there was absolutely 0 distance between them, anything passing through the portal would experience 0 acceleration - no change in direction, it might as well be a standard hoola-hoop.
If the portals were side-by-side facing the same direction, anything passing through the portal would experience twice the acceleration of running into a wall - like bouncing a ball off a wall. Once going into the portal (forward motion) and once coming back (backwards motion), because the object has to completely reverse it’s velocity.And considering that things going into portals do not get damaged (and chel doesn’t lose health) it’s fair to consider that objects observe 0 acceleration.
But portals moving is outside of the Portals canon because it highlights that an object experiences acceleration when passing through a portal. And the acceleration is (or is near) instantaneous. And the object does not suffer from this.
How can it not be b? Every situation in the Portal games is already exactly like this, but with the portal fixed to a slab that moves with the rotation of the Earth, whereas in the drawing the portal moves as the sum of earth rotation + the movement of the train.
Because the rule that’s literally in the game
“Speed thing goes in, speedy thing comes out”
Something isn’t moving goes in, it won’t move coming out. A hole having momentum won’t transfer it to what passes through the hole.
Basic stuff
But, “speedy” relative to what? Relative to the walls of the room your are inside? What if you are in a falling elevator? Relative to the rotating surface of the earth? To the center of the solar system? “Relative to the portal” is the only answer to that question that makes sense.
Someone watched a YouTube video and think they know what they are on about…
Portals don’t transfer energy, there is zero energy transferred to the people they are simply moving from one space to another
But if we use coordinates relative to the orange hole, the whole world, including the rails and people on them, is moving, and the people are moving towards the hole with a speed of the train.
That YouTube video was wrong, doesn’t even make sense
It’s a hole, no energy gets transferred
I believe it should be A. People aren’t moving, and the portal doesn’t carry momentum. At most people would be appearing on the other side with very little delay between eachother resulting in the most recently teleported person violently pushing away the last one.
Of course the yellow/orange portal carries momentum. That’s why it should be B.
You can tell it’s been a long time since anyone played the game.
“Momentum, a function of mass and velocity, is conserved between portals. In layman’s terms, speedy thing goes in, speedy thing comes out.” -GlaDOS
Now it’s time for an all-out flame war with anyone who even took a moment to consider the utter nonsense that is A. ΔV goes in, ΔV comes out. And the bundle of wage slaves has velocity (and mass, therefore momentum) with respect to the portal.
Its just a hole though. If you have a tennis racket with no strings and swing it over something stationary the object doesnt move
With the tennis racket analogy both portals would be moving. In the thought experiment from the image just one is moving, resulting in an unaccounted for momentum, unless the people shoot out the blue portal
A if the trolley is going slow
B if the trolley is going fast.
Can portals exist on a moving object?
Not in the regular game, there are mods/fan games that allow it though.
The only way it could be B in this universe is if the train also decelerates equivalent to how the people accelerate. If the people accelerate and the train maintains velocity you’ve created energy in a closed system.
Portals don’t abide by the laws of physics. Portal above + portal below = infinitely falling object (and thus infinite kinetic energy)
Portals don’t abide by physics, but people still do. Even in the infinite fall scenario there isn’t infinite energy because the object accelerating is still subject to terminal velocity, and it’s change in momentum comes from gravity. For the people to change their velocity, there has to be energy imparted onto them. My theory is that the train would have to slow.
It needs to be 2. Otherwise all the people will materialize inside eachother. In fact, everyone will be deposited onto the 2-dimensional pane of the blue portal itself, like an infinitely thing coat of paint, absolutely smearing them.
Think about it. As your fingertips enter the orange portal, they materialize at the entrance of the blue portal. Then your wrist enters the orange portal, where does it materialize at the blue portal?
- If your fingers shift to make room, then that has imparted momentum and it’s option B.
- If you continue to materialize on the other side of the portal like a mirror image, then for all intents and purposes the blue portal is also moving at the same speed as the orange portal, even if orange ring appears still.
- If your fingertips don’t have momentum and your wrist materializes at the portal, then your wrist is occupying the same space as your fingertips. Congratulations, you’re now a paste.
For whatever reason I feel more willing to break conservation of momentum than I am to
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It’s two dimensional in the sense that the surface of the portal is a plane, through which things pass.
So as things pass through the portal, conservation of momentum is either preserved or it isn’t, with respect to a constant observer. What happens as they partly enter the portal in both of these situations?
If momentum is preserved, and they have zero momentum going in to the portal, then they are motionless as they exit the portal. There is nothing to cause your hand to move out of the way for your arm. Scaled down to the atomic level, you become a paste.
So you say that your hand moves out of the way because it is connected to your arm. The fact that it moves out of the way fast enough to make room for your arm means that it has velocity, and therefore momentum. The momentum means that it (and you) would get launched into the air, but conservation of momentum was violated.
There is no scenario where you exit the portal motionless but intact.
Good explanation.
This has the interesting implication that the relative speed between the portals is “added” to whatever goes through it.
Example: the blue portal is on a train running with the same speed in opposite direction. The people-bundle would instantaneously be accelerated to twice the speed of each of the trains. (This becomes a real headscratcher if you were able to put the portals in a particle accelerator)
Yeah I really think you’ve misunderstood some things. An infinitely thin coat of paint? Are you familiar with the mechanics of the Portal games?
It would be like dropping a hula hoop over a basketball. Regardless of how fast the hoop falls, the basketball still just sits there.
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Why?
Where does the energy even come from?
A hole/portal doesn’t create or generate energy it just passes things through.
Just think of it as a hole across space because that is exactly what a portal is.
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No energy is every transferred as a result of a portal
You fly in the air if you drop in one because you are carrying momentum downwards that suddenly translates to upwards
You are sat in the floor, a portal flies towards you. You are sat at the floor at the end, you had no momentum going in and no momentum going out
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Zero fast. There is no energy being transferred to the people, they would plop out and push into each other as they are forced through.
If you blocked the stationary portal then the portal moving would essentially just be a wall, no one would go though.
This whole relative thing makes no sense, energy isn’t just created because it’s observed by someone else, the door is moving not the people so them sitting there won’t suddenly be catapulted going through a moving portal, where is that energy created?
Your wind question is confusing.
I really think you didn’t read my full comment, because I explained the problem with this exact scenario.
First, in your hoolahoop example both sides of the hoop are moving with the same velocity (this is essentially option 3 I described). But the entire thought experiment is “what if the two sides didn’t move with the same velocity”
If you’ve played the game, you know that you don’t instantly teleport when you touch the portal, you can be half in the portal. This means that when something enters the portal, it is deposited on the surface of the other portal. So as your arm enters the portal, your hand needs to move out of the way to make space for your arm.
If your hand doesn’t move out of the way to make room for your arm (it is still because it has the same momentum that it had when it entered) then your arm will materialize in the same space as your hand. Now scale that down to the atomic level, if the atoms of your fingertips don’t move for the next atoms, everything will be deposited in a 1 atom thick film.
If your hand does move out of the way fast enough to make room for your arm, then it is moving at the same speed that the train was moving. Your momentum from that speed would fling you into the air.
In no scenario do you just pop out intact but motionless.
I just don’t agree that’s how it would work. You can’t gain momentum simply by passing through a portal. The portal cannot create momentum. The object passing through has no kinetic energy going in, it can’t have kinetic energy coming out. It would exit the portal at the velocity of the first portal, as the entry portal passes over the object, and then the object would drop to the ground.
There is no way that it works without breaking even more laws of physics than the game. So you’re right, you can’t gain momentum. Nor can you be deposited intact on the other side of the portal.
But of the options, the one you described seems the least likely. I keep telling you exactly how it wouldn’t work, and rather than addressing the concerns you just say “no”.
We can agree that you can partially enter a portal, so you can put your hand in and only your hand comes through the other side. So now tell me: how does your hand move out of the way for your arm to come through, without moving? Because if it moves, then it has gained momentum, which you’ve explicitly said doesn’t happen.
