this post was submitted on 18 Aug 2023
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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?
For whatever reason I feel more willing to break conservation of momentum than I am to
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.
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.
That is assuming both portals have speed. If the other portal was on the back of the train it would be like a hula hoop but if the other one is stationary you have the people going in really fast and coming out of the stationary portal at that speed.
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.
It's already established in Portal that energy can be created by changing elevation with portals. If the other portal is on the back of the train, you'd just fall out because you'd be shooting backwards at a speed that cancels out the speed of the back portal. If that portal were just sitting stationary you'd have to fly out at the speed you went in. The puzzle comes from people trying to apply ordinary physics to something that deliberately breaks them.
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
Exactly how fast do you think the people exit that portal? Train speed, less than train speed? What slows them down after they exit? If you blocked the stationary portal would you get hit by the people? If so, what force would cause that?
The people may be stationary relative to the area outside the first portal, but they already have velocity relative to the world outside the exit even before they go through
If there were no people on the track and you blocked the stationary portal, would you feel wind on your face?
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.
No, the dude is right - if they're moving "zero fast" upon exiting the portal, then that means they're either a 2 dimensional paste on the surface of the portal (dead), or they were entirely transported upon contact (cannot partially enter a portal) which is explicitly not how the portals in the game work.
This is because: if your hand goes into the portal and appears on the other side, it must move out of the way to make room for your arm. Because it is moving, it has velocity, which means it has momentum. If it doesn't move out of the way, then you're now 2 dimensional, and dead.
Also, in portal, energy is absolutely created. Every time you portal to a higher place, you gain potential energy that you didn't have before, without losing any of the other kinds of energy that you had.