B) The train transfers momentum to the things that pass through the portal. If it wouldn’t, the portal couldn’t exist since you need a certain amount of energy to displace the air on the other end.
I don’t agree. Inertia and momentum are not affected by a portal, even a moving one. If so, their legs would be stretched as they were partially through the portal till the body was being jerked away from the neck causing an even greated relative velocity compared to entering the portal.
Let’s say the train moves at 100mph, therefore your body needs to exit the other portal at 100mph. Otherwise it would be compressed. What happens to the energy of this movement if you just stop on the other end?
We also need to consider the air that is in front of the train as it moves forward. That air is going into the portal at the rate the train moves forward and therefore coming out the other portal at that rate.
My original idea for this involved two tracks (like the original trolley problem) and which track you chose (for minimum casualties) would depend on your interpretation of the physics problem.
Unfortunately it ended up super complicated and I made this simple one instead.
But adding the train on a treadmill is a great way to overcomplicate it further if I ever go for the complicated version.
Relative to the train, and by extension the portal, the people are moving towards it at the same speed as the train relative to the ground, since the people are tied to the ground. I’m gonna work with the definition of momentum that equals it to the velocity of an object times its mass, and with the assumption that the portals conserve mass and momentum of the objects during teleportation, or with negligible losses. Having found that the momentum stays constant, and given the mass before and after teleportation is constant, the velocities relative to the portal are gonna be constant too. (p1=p2 <=> mv1=mv2 <=> v1=v2). And since the velocity of the people relative to the portal is the velocity is the train relative to the ground, and the velocity of the train relative to the ground is far bigger than the velocity of the people relative to the ground, the answer is gonna be B, where the people shoot out of the portal with great speed.
If the people actually go into the portal and not under it that is.
If that is so, the train or portal would have to lose its momentum for the transfer to happen otherwise you’d be generating more relative velocity after the portal. I can’t imagine portals transfering monentum, only maintain it.
If you replaced the people with a pole on a roller, you wouldn't expect the pole to get sucked into the portal or to roll towards the tram as it advanced, right?
That is what would happen if people were launched out of the other side of portal. The part of the pole that has been launched would drag the remainder of the pole with it.
But that wouldn't happen.
The pole would just lay there until the tram passed it by, so the answer must be A. There's no momentum added to the pole as the tram passes it by. The only thing that changed is the location of the pole.
If the pole is entering the portal at the rate of 60 miles per hour, it must exit the portal at the same rate. After a minute, 1 mile of pole has entered the portal, and 1 mile has exited it. If it exits more slowly than it enters, where is the missing part of the pole?
And if it exits at the speed it enters, does it lack momentum despite clearly being in motion outside the second portal? Does it magically halt when all of it has passed through?
You almost arrived at the correct answer. The problem is that would happen. More specifically we know that four fundamental interactions can pass through the portals, e.g. a thing that is whole before passing through portals is still whole after passing through them, though for any pair of particles, atoms, neutrons and protons etc. there was a moment in time where they were separated by the portal. If you imagine the portal moving towards the pole at some speed and in the middle of it suddenly stopping, the momentum of the part on the other side would slightly pull on it, and the pole would still be moving at a reduced speed. The momentum of the second part cannot disappear and will pull on the first part. The only other reasonable option is that the pole gets split, but that obviously is not the case. So B it is
The front part of the pole wouldn’t pull the back part of the pole more so than in any normal contiguous space. If you send a pole flying from the front and catch it mid-flight from the back stopping its motion, you’ll have to apply a force opposite in direction to the motion of the pole, and by Newton’s third law (every action has an equal and opposite reaction) it’s gonna pull you towards the direction it’s moving by reactionary force while decelerating.
In the case if moving portals, it might be a bit confusing, but what it comes to teleportation through the portals, the portals are absolutely stationary the world around them moves. And in the case only one of the two portals move relative to the ground, not only does the world move relative to both portals, it also deforms in a non-euclidean manner. That is why the pole that was stationary relative to the ground suddenly started moving after coming out the portal. And yes, it would require massive amounts of energy for the portal to function like that and keep its own momentum relative to the ground after teleporting things, but tbh that’s a woe for Aperture science, not mine 🙂
I think it has to be A. You figure that if it were B, the people on the track would suddenly be traveling at a high velocity, but the train’s velocity wouldn’t be impacted at all, since there was no impact between the train and the people. Wouldn’t this mean that the portal had created energy, which is impossible?
This is how I always look at it. The portals don’t actually move what is behind them, they are just a portal to that place, so there is no momentum to impart
I mentioned this elsewhere but this line of reasoning may have a huge flaw, and that flaw is that energy has to be spent to maintain the portals operation. We do not currently know what the relationship is between the amount of mass that is moved through a portal and how much energy it takes to keep the portal operational.
So when you take into account the total entropy of the system you also have to include the entropy of the earth and the entropy of the power systems that maintain the portals.
As I said earlier, if you were to put a magnet inside of a vacuum tube that was welded to itself through the portal and then wrapped coils around that tube to drain the electromagnetic energy from the falling magnet, the energy that you were extracting from the system would come from either converting the mass of the planet into energy or it would be a total net loss as the amount of energy needed to maintain the portal would be greater than any amount of energy you could extract from the system no matter how fast the magnet inside of it was moving or how perfectly configured your coils were.
After all, as the magnet approaches the speed of light eventually its mass would be come equal to or greater than the mass of the planet, and that would cause the portal to lift the Earth towards itself.
However, coils on electromagnetics exert electromotive braking Force, and when you account for e that Force you can prevent the magnet from reaching luminal speeds, but I still don't think you're going to have an over-unity device.
No way, the portal displaces space meaning it just allows gravity to work unimpeded adding more kinetic energy to the object. The potential energy during a “falling cycle” is infinite but infinitely removed when the spacial disruption is broken.
By moving an object laterally into the portal falling loop, you would do no work and increase the potential energy of the object to effectively infinity. You would be creating energy.
I wouldn’t consider that the portal, itself, imparting the energy, though. It’s just facilitating an environment where an object can fall infinitely. The portal is outputting the same momentum that is inputted to it. The actual increase of energy happens while the object is falling between the portals.
The portal teleports an object to a position in space with high potential energy, while apparently spending no energy of its own. This action creates energy.
Think of a portal as a door, if someone brings an open door up to you (idk maybe it’s on wheels or something) and you go through it, you don’t suddenly fly through the frame.
If the door is moving 1 meter per second, you are relatively moving 1 m/s towards the door even if you are stationary on the ground. You pass and, although you are still stationary to the ground, you are still moving 1 m/s in the same direction relative to the door. The door is the frame of reference, not the ground.
But that would signify there is an impact? And that you are crashing at 1m/s, if you don’t enter in contact? If I’m in my house, I am not moving at 130km/h from the highway near my house?
If you are looking at someone through the portal, they will appear to be standing on a parade float. They are standing still on a surface, but that surface is coming at you.
You won’t feel any change in momentum as the portal passes around you, but the ground will be suddenly moving under you.
Yes but relative to you the door is moving away and you’re stationary. In this example of the portal coming towards you, therefore upon paasing through the other side of the frame, the other portal, is moving away from you.
In this diagram, it’s assumed that the person is the frame of reference, therefore I believe A to be the correct outcome.
Another violation is that they conserve speed, not velocity. Put 2 portals 90° apart. Travel into the first perpendicular to the surface. You’ll exit the second perpendicular to its surface. That means you accelerated to change direction, which takes energy. Portals don’t conserve momentum or energy.
The matter has to move through the portal at the speed of the train, and it won’t suddenly lose all momentum when it’s done being pushed through. B imo.
In classical physics you would be right, but in modern physics there is no standard frame of reference. It’s equally correct to think that the people are still and portal is moving as it is to think that portal is still and people go in it immn fast speed.
Regardless, people and portal have large speed difference going in, so there will be large speed difference going out.
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.
So if portals didn't have a distance maximum, assuming that they twist through some higher dimension or into an alternate universe and back or something like that, it would make sense that you could open a portal on Earth and on Mars and anything you push through that portal would maintain its velocity relative to Earth.
Which could result in some hilarious events where things basically detonate the instant they are pushed through as they are slammed into the surface of Mars at potentially ten of thousands of miles an hour depending on the Earths and Mars' relative velocities.
Despite that, there would also undoubtedly be times where their velocities synchronize due to their varying rotational locations and orbital velocities around the solar system, during which times you could conceivably quite easily step from Earth to Mars in a single go.
The safe thing to do though would be to decant from the Earth into a portal that is in orbit around Mars far enough away that at the worst you would experience some relatively gentle abrasion from the smattering of hydrogen atoms in the space surrounding Mars and then parachute down from orbit.
Hmm well if an object passed through that portal and it wasn’t moving ~2236mph relative to the surface of the moon, then I guess the question from the OP has been answered already haha.
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 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.
The issue with being able to get infinite amounts of energy out of a portal can be solved by thinking with entropy.
If you only look at the entropic system of the portal and the object falling through it, say for instance a magnet inside of a vacuum tube that is perfectly abutted to both ends of the portal, the energy that you are able to extract from the system using a set of coils would come from gravity, and that gravity energy would come from the Earth.
In that case, one of two things would have to happen, either the mass of the Earth would decrease by being converted into energy, or two, the amount of energy needed to maintain the portal would be equal to or greater than the amount of energy that you're capable of extracting from it with an infinitely falling magnet and coil.
I think that the tram would not have to slow down, and that there would be no additional momentum added to the victims as they pass through the portal, and any energy that is lost in those two equations would come from the energy needed to maintain the portals operation.
You see, shit like this is why I love theoretical discussions about impossible crap. Somewhere else in this thread we use the idea that a moving portal can impart momentum in combination with the idea that portals need to maintain a minimum energy level to explain why moving portals collapse in a way that would at least be satisfying to someone reading a sci-fi novel. It’s now my head canon.
Objects coming out of the portal in “a” have to have velocity coming out (they don’t magically appear outside of the portal, they move out inch by inch/ cm by cm). So in a you would actually have double the deceleration on the train because it has to accelerate people leaving the portal and then instantly decelerate them once they have fully exited the portal.
You still can’t filter reposts out of the feed without a browser extension to do it.
I go back every now and then, but my feed is full of everything but the music I actually want to hear from artists I follow.
And each track now takes up half the screen because it has to show off the album art in HUGE format, meaning even if I were willing to just scroll past reposts, scanning through the feed is a nightmare.
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
Yes, as I noted elsewhere in the thread, the part of the body exiting the portal will experience inertia as it enters into the space outside the second portal and it will be forcefully pushed by the next part of the body heading into the first portal and thus imparting momentum to the parts ahead.
If this momentum has to be taken from anywhere its from the portal itself and by extension the train.
Has the trolley come to a complete halt, or even showed down? If not, then either no energy has been transferred to the people and they just flop out, or we’ve just invented perpetual motion.
But the orange portal is moving. The game code works more like A (it bugs out and the object bounces off the portal surface, but it uses a world-fixed coordinate frame that would match A for behavior). A (Newtonian) relativistic coordinate system would match B. For everything with non-moving portals A & B are equivalent.
Yeah, most game engines like Portal’s uses absolute speed relative to the coordinate system (which doesn’t change when the coordinate values change), in addition Portal technically doesn’t actually implement “wormhole type” portals and instead superimpose a clone of the polygons near both portals behind the other (to preserve expected object collision behavior around the portal) plus doing tricks with virtual cameras, so if you fixed the bugs with moving portals then it would be A.
But if you implemented proper relativistic physics with proper wormhole type portals you’d get B.
The game code works more like A (it bugs out and the object bounces off the portal surface, but it uses a world-fixed coordinate frame that would match A for behavior).
Ah, I see what you are saying. They apply the velocity of the object again after teleporting rather than the difference between the velocities of the portal and the object. Thus the velocity of the train would be ignored. Well, B is wrong simply because the game engine doesn’t rotate characters in the teleport because that would ruin character physics. So B is wrong twice.
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