Portal would fail due to being placed on moving object
this post was submitted on 18 Aug 2023
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Except for that one section in Portal 2 /s
Why the /s?
It's true. Obviously it makes for simpler puzzle design plus was easier to ignore the full capability (even the version in 2 seems to just work enough to allow the set-piece), so it seems silly to use developer limitation as a gotcha.
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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Speedy thing goes in, speedy thing comes out
E: I was just quoting GladOS..... Not really thinking about the actual physics!
Yeah but the thing isn't moving the portal is, and the energy has to come from somewhere if the portal makes the thing go fast.
The energy would come from the trolley. The people would launch out at approximately the same speed as the trolley interacts with them and the trolley would slow down in response to how much kinetic energy was transferred to the people.
This is correct. The motion of the people is relative to the Portal. It doesn't matter if the trolley is accelerating the Portal towards them or something is accelerating them towards the Portal. Therefore they accelerate out of the other side with some retained momentum. Technically it probably resembles something in between pictures A and B.
This reminds me of the experiment about whether an airplane could take off from a treadmill.
Only if you assume the people will experience friction against the portal.
If they would accelerate to the speed of the train within the time it takes them to go through it, they'd experience very high pressure change against the due to one part of body accelerating faster than the other. This would cause the bodies to explode out the portal
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B. Since there is relative velocity between the orange portal and the target, the momentum is conserved and they will launch.
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
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In simpler terms, speedy thing goes in, speedy thing comes out
B. Velocity is relative.
but relative to what? assuming portals work similarly to windows, if I take a hoop/window and place it quickly over an object, that object won't launch in the opposite direction
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Can portals exist on a moving object?
Not in the regular game, there are mods/fan games that allow it though.
There is one segment in Portal 2 where you need to cut some tubes that transport neurotoxin, and for that small segment only, the game allows moving portals. https://youtu.be/OrAHvenjZpA
it's specifically scripted for that though, normally the engine just freaks out
ITT: what I expected vs what I got
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.
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.
Unfortunately, this isn't testable in Portal because portals can't be affixed to moving surfaces.
I would assume the people just plop out fine since they would retain their momentum (which is nil), and the portal's own momentum wouldn't be applied to them. But God damn it I wish I could just make a Portal map with a moving portal and see.
If we assume local relativity, their momentum, which would then be relative to the orange portal (the one which they will interact with), wouldn't be "nil". It is pretty clear to me that both portals have different relativities, and therefore, would clearly lead to case B.
Then I could imagine a sport where you have a racquet with a portal on it, and you swipe at a suspended ball, with a target somewhere beyond the other portal.
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B.
Speedy thing goes in. Speedy thing comes out.
Although it kind of depends how fast the tram is going.
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There's a reason why in the game you could never put a portal on a moving surface
This platform deserves a community solely dedicated to trolley memes.
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Discussed this with some friends and the view we came to is that your momentum relative to both the portal and your surroundings is preserved (which explains how you could portal to the moon and not get liquefied by the difference in rotational momentum between earth and the moon). The portal speeds you up or slows you down depending on local conditions on the other side to preserve your relative momentum. This would, logically, indicate that energy is created or destroyed depending on the difference, which (to me) means that 'portals' technically exist outside our universe as a concept and are therefore not subject to conservation of energy.
This is my favorite post in a while.
Thank you!
Truthfully it was pretty low effort to make, but I appreciate it anyways.
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)
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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.
Fully disagree on concept. The thing with the portal is solid matter moves through at a constant rate.
If you have a portal moving towards you, at say 2 MPH and you are holding your arm out, From the other side of the portal, they would see your arm coming out at 2mph. Any other result would involve compressing or stretching your arm.
Lets say further here. a man dangling his legs off the back of a moving cart. Man is moving 20mph forward, portal trolley is chasing him at 22MPH. As his feet pass through the portal, they would start coming out the other end of the portal at 2mph.
As a result I concur that the only logical exiting of a portal. |travler velocity - Entry portal velocity| + exit portal velocity = objects exit velocity.
Now the real physics debate would be what happens if 2 portals were moving forward and someone was in the path of one. The only logical conclusion that fits my mind there, is instant compression
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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.
C. A train flies out of the blue portal
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.
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