Another Portal Paradox
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- Опубліковано 3 сер 2022
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What happens if you extend a piston through a portal? Or try to sandwich a cube between two portals? That's right, it's time to explore more portal paradoxes!
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Fun fact: there is actually one (and only one) instance in the games where a portal can move. It's in the neurotoxin generator room in Portal 2. They apparently just hard coded that one room's panels to work differently.
It's a command the game sets when you load that map so that you can place portals on moving surfaces, sv_allow_mobile_portals 1. If you load the neurotoxin map and exit without completing the level, the game won't reset the command and you can place moving portals in other maps without needing to enable sv_cheats.
Newest speedruns use these portals to achieve some fast runs. These portals behave very glitchy, like the stationary portal will suck in the player if it comes to close and gets horizontal momentum when it comes out the other side. But more importantly it allows speedruners to fly through walls for a short amount of time.
i literally learnt c# 3 days ago, please don’t let my brain explode lmfao
Yeah i saw that too
Technically there's a moving portal right at the end of the game as well
I love how you casually dropped at the end that one of these questions was posed to you directly by a portal developer. It's as if they were trying to get you to debug the concept.
So, Portal 3 confirmed?
@@UltimateJay1989 My thought exactly!
@@JM-us3fr Apparently, some dev(s) said that they would very much like to make a Portal 3, but the way Valve works as a company makes that really difficult.
@@nixel1324 valve is allergic to the number 3
Lmao
2:30 "Everything exists outside the portal, there is no place to hide." This sounds like a threat.
cuz it is
Why do you think G.L.A.D.O.S. just let Chell go?
I always imagined portals as a doorway. When you run through a doorway, you don't push the doorway, and likewise if the doorway was moving towards you, you wouldn't be pushed. Momentum can only be created outside of the system, since there is no "inside" of a portal, just how there isn't an "inside" of a two-dimensional doorway
Yes. That's also why the cube has momentum if a portal falls on it. Because "the other side" of the door is static. So the frame of reference changes. Think of it instead of the door moving towards you, you moving towards the door. So of course, you'd still be moving after existing the door. In a sense a door moving over you still moves past you and behind you, it's still getting farther away from you after you have gone through the door.
I think in that case you would simply be stationary in front of the static portal as while you may be moving relative to the moving portal, you're still stationary relative to the static one
I mean it's just a moving frame of reference
But if you look through the blue portal as the orange portal is moving you will see the cube moving toward you at the speed of the orange portal.
@@pjl22222 yeah, but that would be an issue of your perception. What you would actually be seeing is the portal moving toward the cube, not the cube moving toward the portal, but you can't perceive it that way. The momentum is in the portal (or, more accurately, whatever surface the portal is on), not in the cube.
Consider it like this: that cube is standing on the ground, yeah? The ground is, relative to your frame of reference, moving toward you at the same speed the cube is. That's because the portal is moving, not the cube. There is no momentum there. The "frame of reference" in this case is literally just a trick of your perception.
2:55
I've never thought of portals as anything like this. They're just tying two points of space together. So the idea of the portals ever moving by a force that's on the objects passing through is very strange.
But there are no points in space that aren't moving relative to SOMETHING :) I don't think it's absurd to say they're stationary with respect to each other, but that causes more issues I'm sure.
That's kind of how I always saw it. Granted, a "game" is able to make liberties that break its own [unspecified] lore (and obvious real world physics), but after Portal 2, I kind of assumed the surfaces are just what the portal was able to "stick" to... move the surface and the portal will collapse. When you're performing a theoretical maneuver such as folding space, that space is "theoretically" connected independently from the objects surrounding it (included the "sticky" catalysts that allowed for the portal to appear in the first place).
@@jacksonsmith2955 "I don't think it's absurd to say they're stationary with respect to each other, but that causes more issues I'm sure."
I disagree. If the portals always maintain a relative distance toward each other, then the frame of reference between the two portals will always be balanced out--even when you account for oddities moving at very fast speeds like in general relativity.
@@insidetrip101 I agree, it solves more if they are required by physics to be stationary in a shared frame of reference to work. If they move together the connection moves and the spacetime inside remains smooth. If they move relative to each other then the connected spacetime becomes fractured at the portal entrance and they close. Thus you couldn't squeeze something between portals because the moment they get closer it breaks the connection. Also answers the 'if the portal is moving' because once you translate to the portals frame of reference the cube is moving and we know what happens then.
Points in space are never fixed, but are affected by spacetime curvature and warping. On top of that, an object moving towards a point is relatively identical to the point moving towards the object.
I think a lot of the paradox comes from thinking of the portals as physical things (like a mirror) as opposed to a non-Euclidean connection in space. The portals should theoretically stay in a non-accelerating reference frame in space (but not necessarily spacetime) and are not exerting a force on anything passing through them-that eliminates any paradox that has to do with portals accelerating or decelerating. Of course that introduces other problems like what happens when one portal passes through another one-which I think the answer should just be it crushes anything between them, possibly explosively or to the point of a black hole, before the two portals cancel each other out.
I agree with the idea that the portals are just a "window" connecting one plane in space to another, but it can't be that they don't impart force on passing objects. When they redirect a moving cube they change its velocity, i.e. its momentum, so there must be a force hiding somewhere. Although it's a weird one that acts instantly and not continuously like ordinary forces do. I suppose one solution to conservation of momentum is to assign the portals infinite mass. That would also mean they cannot be accelerated after they form.
The more I think about it, the more it seems like the portals should just disintegrate anything that passes through them unless they have exactly opposite directions: as one end of the cube enters the portal, from one picosecond to the next the top layer of atoms must assume a vastly different velocity from the layer below. Essentially, the top layer of atoms experiences practically infinite force and gets ripped off, then the next layer of atoms, and so on until only a cloud of cold plasma emerges from the other portal. The only solution I can see is that portals can only form in opposite orientation, so that velocity remains unchanged when passing through.
I agree: a portal isn't a thing, it is a place where "here" connects to "there" instead of the typical "here" connects to "next to here." So a moving a portal is just different "heres" connecting to "there."
This arises the problem that as a new "here" is connected to "there" objects in the new "here" cannot be moved past the plane of the portal "there." So the moving "here" creates a tunnel of unmoved objects that cannot exit "there" but can be seen from "there" in their original location. From "here" you look into the portal and see the object sitting where it's momentum would leave it "there" - resting just in front of the portal. The object is in a super-postion: looking from "here" as if it is "there" and looking from "there" as if it is "here." The instant it is interacted with, the momentum imparted to it will push it into a discrete state at one or the other portal.
From a gameplay perspective I think if two portals are crushing an uncrushable object that the portals would have to fizzle (explode). A physical explanation rather than the object itself. A physics explanation at to why the portals would fizzle I can't think of, but it makes intuitive sense in my brain that they would.
@@emlun This has the fundamental issue of thinking that stationary portals *must* interact with objects that pass through them, because stationary portals don't. If I walk through a doorway, the doorway doesn't impart any force on me. If I step through a doorway facing north and exit facing east, it still wouldn't need to impart any force to do this, as the forces are the same as walking through a euclidean doorway.
Things only get weird when the portals move.
@@emlun if we think of the portals as non Euclidean 'windows' in space, then no changes in velocity are actually happening. from the cube's point of reference, it is just moving in a straight line through this window, and no change in velocity occurs. basically, the space around the cube is being folded into a straight line for it, so when it passes through the portal it looks like it's just made a turn, but it actually has just made one continuous movement in a straight line. if you look at some visualizations of non Euclidean geometry, I think you will see exactly what I'm talking about, where following a straight line can cause what seems like a rotation, or some violation of momentum.
During paradox 2, I would imagine that the portals have no physical interaction, that they simply displace two different points of space. The idea that they are affected by the forces applied by something between them seems to be incorrect. The portals should represent a closed system and therefore the forces of the piston would only be exerted on itself and itself alone. The idea that a portal can have a mass or momentum is interesting, as I think a portal isn't an entity in and of itself any more than a magnetic field. A portal would be induced by a device or phenomenon that causes the displacement of space itself, meaning that essentially the portal doesn't exist in the same sense as a physical object and that it requires no mass to exist. Another way to think about it is that a portal is simply a hole. A hole has no mass, and is somehow treated as a separate entity rather than as part of the ground. It has physical dimensions but no mass. A portal is a hole (rather, a tunnel) that is part of space and can therefore follow the same pattern. A portal therefore has no physical properties except for its dimensions. Interesting thoughts 🤔.
I think a portal gets its momentum from the stuff that it has to move through it. A portal in a perfect vacuum would have no momentum. A portal in atmosphere would have as much momentum as the air around it, and the air would act like friction on it if it was moving.
This paradox is actually solved in the games themselves. The portals are never free floating but instead always attached to a surface, so even if you assume the portals themselves have no mass or momentum the object surface they are on would. So the forces would be exerted on the surfaces.
I agree with you that something passing through a portal has as much affect on the portal as a rock dropped down a well. It is a hole. A strange hole but a hole nonetheless. A portal has no mass. It is a temporal rift physics does not apply to. Rather, a portal allows the physics of its surroundings to occur. This is why the portal end on the moon would create suction through the portal end on Earth. For Paradox 2 to push the portals in any way with equal and opposite reaction would have to be a force applied to the surfaces the portals are on.
TLDR:
Portals are holes. Objects passing through the portal don't affect the portal. If the portal is on a moving surface it has momentum.
The piston buckles/pushes itself. The box crumples as it is forced to exist inside of itself.
@@CadanL that doesn't solve anything, it just introduces more magic. If a portal is moving, whether attached to a "surface" (a human concept with no physical significance or meaning), the objects that go through it have some new, additional energy. This is energy coming from nothing, it breaks physics. It allows perpetual motion, etc etc. It's more impossible than the portal itself. That is, unless you imagine some reactive force on the portal.
Portals are not holes. If they are holes, you have to imagine they cannot move at all relative to each other, but that too introduces weirdness.
I think the root of the problem is that portals like in the game can't exist. Any real portal wouldn't have these paradoxes because it would be a real physical thing like a singularity, which has mass.
About your second "paradox" the portals are not connected to the object in anyway and the object would just crush itself.
That's why I was thinking Newton's equal and opposite law doesn't apply because the piston isn't pushing the portal at all for the same reason minutephysics gave in the video. There is no surface for the portal to be pushed because the portal is itself a tunnel, an infinitesimally small tunnel that connects to spaces that shouldn't be together. if the portals were closing towards each other, it does not matter how strong something is, it will get crushed because it is crushing itself with force that is greater than itself due to the portals not giving a shit how strong something is. So the closer together both portals get, the greater the force against whatever the object is, no matter the toughness, gets crushed at.
What I believe to be an unanswerable question is how it works if both portals are pressed perfectly against each other with something between them
Remember, portals are always attached to surfaces. So the crushing force depends on with what and how those surfaces are pushed towards each other. It's basically same as crushing the cube between 2 regular surfaces, even though with the portals, the point of contact becomes the cube itself.
You've just given me an idea of how the universe was pre - big bang. Space - time wrapping into a tiny sphere, crushing all of its contents against itself
Imagine the piston push in a circle, until it hit itself, what happens then?
It would be the result of a piston going through a portal against itself.
@@rtyzxc the counter force would be on the push piston itself, not the portals "teleporting" it.
I disagree with the notion that the piston pushes on the portal. You don't interact with a window by jumping through it. I'd argue that the "space between the portals" is simply reduced and when sandwiched by a portal you get crushed by space because there is not enough of it for you to exist in any longer.
I think what's implied by the video is that the portals aren't just passive doorframes, they're actively influencing the space surrounding them. Otherwise, portals moving relative to each other wouldn't be able to change the speed of an object.
Now changing an object's speed means exerting a force on it, which is why it's important to include Newton's third law in our thought experiments.
Personally, I don't think the portal itself is acted upon by the force in Newton's third law, since the portal isn't really a physical object and rather some weird (possibly quantum) phenomenon of space and time, but the portal's "host surface" should be able to feel the force the cube is pushed with and change its momentum accordingly. I'm imagining two portals on sheets of paper being stopped really easily by sandwiching a cube between them, and two portals on moving walls just crushing it.
I don't like these "window" analogies, because when you pass through a window, the other side of it can't be moving at a different pace. I think of it more like stepping onto a moving train, your stillness relative to the train station is now a high speed relative to the inside of the train, which thinks the entrance is standing still.
You do. It isn't much but you push and pull on the window as you pass by via gravity and electromagnetic forces.
@@Vexas345 true, but id say that's negligible
@@screwaccountnames one could look at the whole spacetime construct as the “object”. Its ability to do portal-y things is fully a consequence of its spacetime topology, which allows for such a localised flow of space in one and out the other.
In that way, the portal itself should be affected by the objects it carries, just as a mass’s gravity-well affects the space around it while also being affected by the topology of space.
The portals wouldn’t push apart very quickly though, or else your piston would run-out of power supply before you had enough juice to create a minuscule standing-gravity-wave between the two portals. (But that’s an example of what he meant by “if the portals are heavy”.)
3:50 Something worth mentioning here though, Portal 2 actually does have 2 cases in which portals are moving relative to one another. The neurotoxin sabotage has you use a static portal and moving portal to cut the neurotoxin pipes with laser. And at the end of the game you have one portal on Earth and one portal on the Moon.
So while they didn't have it as a more tangible element in the game, it is still possible in the game's setting, so these paradoxes definitely a thing to think about.
except "the moon" is just a room directly below the map because the easiest way to do that cinematic sequence and not worry about it too much was to cut a hole in the floor in the shape of the portal
fun fact you can shoot the wrong coloured portal and the game will auto adjust. I think here the moon portal is always orange, but there's a different case of that earlier in the game where you catch yourself with a funnel where it will change the colour of the other portal so you can't accidentally fall
I wander what would be the full physical description of portals if we account for all these game design quirks (also alighting and the gravity well mechanic)?
IMHO the short version of the full physical description would be some variation of "Argh, this makes no sense!" Especially if you consider scripted momentum.
(Scripted momentum is an intended game mechanic, primarily used to implement Aerial Faith Plates, but also used to "correct" the player's trajectory for some flings that would otherwise be difficult to precisely line up.)
@@malbacato91 while this is true mechanically in game, the Moon is not in a geostationary orbit in real life. I think its fair to consider this an example of moving portals.
@@haassteambraker9959 oh yeah, not discrediting it
I've never heard the point about the moon, that's genius.
I feel like some of these paradoxes only exist because we have different definitions and understandings of the concept of portals. Mine is more like a doorway. Like if someone moved a hula hoop over my head. I don't think it's that either of us are wrong though, since it's a fictional technology. If we knew how portals actually worked we would be having a very different discussion haha
hoopy the hoop (is a lie)
Lol I just saw your comment check out what I wrote it's basically what you said
Ok so I think of portals like a hoop which is completely different from how you think and like you said it's fictional we are all right. So this is my idea it is just a Hola hoop the if slam the portal over the block it wouldn't move because it I only a door/gate it's sole purpose is to allow objects to go through it. I do like you idea it is definitely better for a vid
@@Bubbashinif you move a hula hoop over a block then the block does move, relative to the hula hoop's reference frame. In physics, there is no such thing as stationary. If you are the hula hoop, then the block(and the floor it's sitting on) is flying towards you. "Stationary" is just an arbitrary reference frame we take. As a human, it's most natural for you to say that the room you're in is the "stationary" reference frame, but there's nothing fundamentally true about that, it's just an arbitrary choice.
Imagine a ball and a hoop, in space. The ball going through the hoop, and the hoop moving over the ball are the same thing, it just depends on whether you are looking from the perspective of an observer moving at the same speed as the hoop, or an observer moving at the same speed as the ball. If you're level with the ball, the hoop is moving, if you're matching the hoop, the ball is moving.
One part of the hoop is moving while the other part is still though.
Portals irl wouldn't even be oval shaped, or even circular in 3D space, they would be spherical which introduces entirely new problems like "enter a portal that is too small and get ripped apart on the other end" and "the portal kissing point crushing anything between the portals against itself"
Not sure if this has been mentioned, but in season 4 of Stranger Things they also played with the idea of gravity pulling both sides of the portals between the regular world and the Upside Down by way of a suspended rope hanging directly between. I think that would make a great video as well!
Game theory on portal
That'd techincly work but wouldn't work as soon as something touches it or if it was slightly unbalanced, the force would slightly off at one spot.
Some of these scenarios get into whether portals have their own mass. I always thought of them like a "hole" within the universe that connects around, but if they have mass to them, where an object entering them move them around, then that would change the physics of how they work.
Don't forget that portals have to be opened on specific surfaces, so moving them should be possible only by moving an object they were projected onto. Portals are less of an separate object and more of the state of matter it is placed on. So all mass calculations should be build around plates that portals can be placed on. And in the game portal plates are quite heavy and are connected to heavy pistons so it actually can make sence why they dont recoil when we pass through them, despite receiving our momentum
I say there are no forces acting on the portal - the object going through it cannot push them apart, because it isn't touching the portal at all. Imagine a ring suspended inside a hollow loop. Moving the ring causes the ring to rotate, but the loop doesn't move still! The same way, objects in portals never tough the "portal" .
Conservation of energy does not apply to portals, so why would the forces transfer to the portals? It makes more sense to presume the object would be squished out the sides as though it were in a hydraulic press.
Correct... Portals are space, not objects... It would be like an infinite-force hydraulic press or trash compactor... Where the center would be a few microns thick or whatever distance there is between the portal entrance thresholds when they're held against each other, with the excess mass being squished to the outside edges of the portal.
You're also not using the cube, to crush the cube, you're using SPACE ITSELF to crush the cube, via dimensional folding, which is why the the object the portals are anchored to, wont feel any of the force... You could anchor a pair of portals into the palms of a human, and they would be able to crush a titanium cube into mush with their bare hands... You need no force whatsoever, only movement, because only the space around the cube is under pressure.
Would be the greatest trash compactor/hydraulic press to ever exist. xD
I agree, i don’t think these portals would have mass at all
@@ThomasTheThermonuclearBomb Not only are they ostensibly massless, but have no apparent surface on which force could be applied, save perhaps the backside that adheres to the surface of a flat solid object.
The argument is that portals would transfer force to the object they're sitting on. This makes sense if you assume portals conserve momentum; the momentum needs to go _somewhere_ when speedy thing goes in and comes out at a different angle.
Does it make sense to assume that non-conservation of energy implies non-conservation of momentum? No; the two are largely unravel. Now, I also can't argue _for_ momentum being conserved, but I consider that the null hypothesis in most scenarios.
Why do you think it doesn't apply? Kinetic energy is concerved, since speed stays the same, it's gravitational potential energy that isn't. But gravitational energy conservation is already broken by space expanding, so why wouldn't it be allowed to break for a weird topology of space (given that it's stabilized somehow?)
As I understood it, the portal just bridges two spaces. Like something going through goes through with only ITS momentum. So the portal doesn’t change the momentum of the object at all.
I personally think of it like walking through the moving portal you are still moving the same speed and so would exit at the same speed only in a different place.
Not sure if this really is understandable but it is just my interpretation of the quote “Speedy thing goes in, speedy thing comes out.”
exactly what I was thinking
But its only happen to static portal. If portal moves toward you which is not moving, how did you stay not moving in another portal?
You should "come out" from another portal which mean, you are the one who move in another portal
If an open Windowframe falls around the stand still Me, am I ejected from the ground? No, I Do not think so.
Keep in mind that momentum is a vector quantity ( p = m ⋅ v ) so in may cases, portals DO change the momentum of objects passing through them.
@@shosuke1991 a window frame is a different situation. With a portal, one portal is stationary and the other is moving towards you so that when you go in, you would have whatever momentum the portal had (I think)
I don't think that the portals would move in the piston instance. Portals act like a hole in a wall. If the piston is pushing through a hole in the wall the wall is unaffected, it does not matter how hard the piston is pushing, or if it overcomes whatever it is pushing on, the hold in the wall is unaffected. As for the sandwiching paradox, it is about how strong the wall the the portal is on is pushing. If the wall the portal is on is pushing with enough force it will crush the item with itself, if the wall is coming towards the item at a force that is too weak, it will stop when the item hits itself.
For paradox 1, I'd argue by relativity that the cube stops. For the relative analogy, instead of the portal approaching the cube and stopping half way, we have the cube approaching the portal and stopping half way. A force was exerted to stop the movement of the cube (or the portal). If there's no force required to change the momentum of the portal, then all relativity breaks down.
Exactly, his ideas on the original paradox and the stopping portal seem to contradict each other. If you think about it there really is no force that exists that would continue to suck the cube through the portal
In defense of the relativity perspective, pushing the portal onto the cube will be met with resistance to accelerate the cube as a whole. Trying to push the portal down once in contact with the cube is like trying to pull the it out from the other side. How the two forces are connected depends on how portals work in the first place: arbitrary sci-fi mumbo jumbo.
There is part of the cube on the other side.
But you're not stopping the entire cube, you're stopping half the cube, because the other half has gone through already.
Agreed, the deceleration of the portal isn't being taken into account in the example. If the portal decelerates to zero, then there's no momentum left to push (or pull?) the cube through, regardless of how far the cube has gone through it. That said, since it's already science-fiction, we can imagine a portal that stops to zero with no deceleration at all, and that would indeed theoretically transfer the momentum into the cube.
1. For the orange portal to stop halfway, there has to be a force of deceleration effecting it. The same force can be applied to the object, making it stop halfway through.
2. An object going through a portal can't put force on the portal. The force just gets tunneled to the other end/portal (still okay for newtons law i guess). And Therefore sandwiching a cube between two portals is the same as sandwiching two cubes without portals (crumble, if the force is sufficient)
2. Object not putting any force on the portals means there's no counter-force to stop you from moving the portals closer together. That creates a system that can squeeze the object no matter how rigid it is - creating an infinite force.
The version in the video seems more realistic
@@splytrz there is a counter force it's just from the base of the piston is it not?
@@splytrz "Object not putting any force on the portals means there's no counter-force to stop you from moving the portals closer together. That creates a system that can squeeze the object no matter how rigid it is - creating an infinite force."
Precisely, the thing is, that makes sense, when you're folding dimensions.
You're not crushing the cube, with itself, you're crushing the cube with SPACE ITELF, you're using space to crush the crube via dimensional folding... Neither the portals, nor the objects they're achored to, will feel any effect of the crushing, the cube will be crushed into a pancake that is a few microns thick (however far away each of the portal thresholds are from each other when held against each other), it will be dense as all hell, crush enough materials into the same microns thick pancake, and you got yourself an object with immense density/gravity... sorta like the singularity inside a black hole, keep doing that, an eventually it actually becomes one.
The fact that black holes exist, means that this infinite crushing force, is definitely possible. Whether or not we can achieve that with portals, is a different matter entirely, but... If portals work the way they do in this instance, that's an infinite-force compactor you're looking at, 100%.
The video doesn't seem realistic because there's no reason for the portals to magically be repelled by each other, just because there's an object between them... There's no direct contact between the object being crushed, and the object the portals are anchored to, and the portals aren't objects, they're dimensions, they're space, a direction in space.
@@MyouKyuubi Well it all comes down to how we think portals work. Your comment is the first one i upvoted that I disagree with btw.
The way I see it, the kinetic energy of the object moving out of the portal has to come from somewhere. If the portals are stationary, and the object is moving into the portal, of course that same kinetic energy can be applied when it exits without issue. But if the object is stationary and it's the portal that's moving, then the energy has to come from the portal. That's why I think a force is applied to the portal. As the portal is moving over the object, it will either slow down, or whatever is pushing it needs to overcome that force, and the energy from this is what's being transfered to the kinetic energy on the other side. So if that's how portals work, then the video is correct.
But your explanation seems just as valid as far as I can tell (I'm of course not a physicist, I haven't done any physics after high school).
@@xway2 "But if the object is stationary and it's the portal that's moving, then the energy has to come from the portal."
Actually, it doesn't, because you're not applying crushing force to an object, space around the object, is simply shrinking... And the crushing of the object is just a sideffect of that. :P
We're dealing with dimensions here, we're outside the confines of 3dimensional space, rules work differently in this case.
For a lot of these, it's easier to think of the "next thing over" as you'd look through the portal. When the portals are closing in on the cube, just imagine all of those other cubes, suspended in air over one another, slowly closing that distance until they're stacked atop one another. Move the portals any closer, and you're forcing matter into a space already occupied with matter, and that's probably the end of the world or something.
3:26 that's voice crack hurt me
the portals should *sTop*
The piston has no way to assert force onto the portal. It just asserts the same force into itself, so it can block itself (Edit: THROUGH the portal), but not move the portals at all.
Yeah, I don't buy the idea of "applying a force to a portal". I don't see portals as phyiscal objects, but rather (in theory, if they existed) as phenomena emerging from unusual topologies of spacetime.
But that means that the portals violate conservation of momentum.
To avoid this and get Physics at least compatible to our own, you have to assume that when a body traverses a portal, it transfers momentum to it.
@@RafaelSCalsaverini I don't think you do, it's a hole. So the force is all sent through it to the piston
Law of Momentum. The momentum has to go somewhere. If there's nothing else, then it has to go to the portal.
Then again, portals *_are_* impossible. So their existence might meant a corollary violation of this very law.
@pyropulse if a something enters a portal with moving in one direction and leaves it moving in another direction, the momentum of that object changed. This is inevitable.
For the global momentum to be conserved, something else needs to move in the opposite direction to the difference between the velocities.
The only "something-elses" in the picture are the portals.
3:52 There are moving portal surfaces in portal 2 that are usable, but the player doesn't have control of the surface movement. The player is to shoot a laser beam through the static portal, so that the laser beam shooting out of the movoing portal can cut something.
(You can type in YT search: "Portal 2 Neurotoxin Generator Implosion" to see the sequence Im talking about).
they also only move in the plane of the portals surface, if you put a portal on a surface that gets moved to the normal of that surface the portal disappears
But those are moving laterally, so it's not what's described in the video.
It could just be a rule of portals that they can't move relative to one another.
Or more precisely, the planes of the portals can't move relative to one another
A script activates a special flag in the engine just for this one room. There are speedrunning glitches where you can cause this flag to stay active afterwards (basically by skipping the trigger to disable it again), which creates all kind of glitchy behavior.
1:12
The relative speed will only afect one half of the item, but since the other half is part of the whole object, it will move as well
It is like grabbing a bottle by its cap
The whole thing will move, even if the force applied is only applied to a specific section of the object
Would that movement = the speed of the moving portal though. Considering gravity pulling on one half down, and side way on the other.
I think the video missed something important, for the portal to stop halfway on an object the portal would need to slow down at the same rate as the object is going through the portal, so it wouldn’t get sucked through, it would decelerate and stop, the rope example mentions fragility which would lead to it breaking half way if the deceleration of the portal/object is high enough but in all instances where it doesn’t break the cube should stop
Honestly the "very trippy and non physical" reaction from the game seems more "realistic" than your solution.
I definitely get how you arrived at that conclusion and it makes sense too, and like you said, they aren't real so on some level it's pointless to worry about.
That said, I think you're ignoring the fact that objects passing through a portal don't convey any forces on the portal itself. A portal isn't pushed back by something thrown through it. So an object blocked on the other side wouldn't be able to stop the movement of the portal. I'd assume the object would be crushed to a smaller space and higher density. That or like it was handled in the game the object folds over itself recursively which would work like we see for rendered textures in the game. It was actually right. It's just a real physical object occupying space can't do that. It would just go flat and maybe spark some fusion reaction or insane state of matter like a neutron star. I'd assume as you approach infinitely close all matter is converted to energy and blown out the sides.
I agree with his theory that portals would receive an equal but opposite force for everything going in, as the physical theories for energy conservation have to apply somehow. But your counter theory is probably the best I've seen. Most people just seem to not grasp the problem at all, which is unsatisfying even if they were to be right. But your idea that portals are beyond the theory of relativity and thus can exert unlimited energy, to the point of obliteration of the object being transported is interesting. We just have to assume that all objects going through the portals are subjected to this energy, which makes sense if the portals are essentially wormholes anyway, and that this energy exertion is just insanely balanced so that anything going through stays in one piece under normal circumstances.
@@nolanjenson4785 yeah, I think you have to at least consider the fact that forces aren't conveyed normally when stuff goes through them. I don't move a door when I walk through it.
But yeah like your said that doesn't actually explain how it would be able to create the every to crush something like that. Maybe that's why they can't exist with our physical laws lol. Still very cool to think about though.
I think the portals have to feel some reactive force when they're moving, since the stuff coming out the other end is accelerated. So it would be harder to move a portal over something more massive (like it would feel as if you physically were pushing the block), but even moving the portal would have friction in an atmosphere as it accelerates the air out the other end. And in that way, the portals coming together with a block halfway through would have to feel a force just like if two blocks ran into each other. It wouldn't be infinite because the blocks aren't perfectly rigid.
Of course, none of this explains how the force is transferred to the portals from the objects moving through, as you say. But nothing really explains that in real life with other fields either, it just is. There are fields, shrug.
The thing is, real life physics seems to allow wormholes although there are a lot of unanswered questions about how they work (or how they would be created in the first place). As you say, maybe this thought experiment is a hint that actually they can't exist.
@@1three7 The option that you missed is space being created between the portals outside of “normal space.” This would be akin to the “neck” of a wormhole that the two portals are the entrances to.
@@TheJohnreeves You are talking about “moving space” which is more like compressing or expanding space like the space between distant galaxies expanding isn’t actually accelerating galaxies away from each other.
An object wouldn’t compress relative to itself IF the SPACE that it occupies is being compressed. The only way to perceived compressed space is from a higher dimension of existence where you can perceive space “moving.”
This video had made me realize I have very strong opinions on how the portals in Portal work.
I always thought of them as essentially a window. The center is empty and just connects 2 points in space. So in my mind in the case of a piston pushing itself through the portals the portals wouldnt be affected by the pressure from the piston as its passing through the window in the center and not pushing against the portals.
i feel like the game also backs this up since you can look through the portal just like you would a window
That's not "very string opinions" that's just basic logic.
@@blade7y156 well the “basic” logic in your eyes has been pointedly misunderstood by the uploader of the video. So it’s not like there’s no room for discussion
They're like a window, if one side of the window can have a speed relative to the other side.
Next time, think before you type.
@@MrStarman926 He didn't misunderstand anything. You did.
The portals dont do anything to am object that passes through them, they just connect space, so that solves all of your paradoxes. A portal stopping halfway on an object would have the same effect as a hula hoop stopping half way on an object, no effect at all.
The only thing I can think of is maybe if the other portal is at a weird angle, gravity might pull on the object, but not the portal itself
precisely my thought!
Well he did start with "if a cube moving towards a portal keeps it's momentum upon exiting, then a portal moving towards the cube will have the same effect" (-1 or 2 words). So he just made some rules himself and presented the solution to these paradoxes following his rules.
I would say that the affirmation is wrong because it doesn't really make sense to transfer the speed of a gate on an object. Just like you passing through a loop, just because it goes towards you, doesn't mean you will magically get the object's speed.
So if a portal stop midway then the object going through the portal will A- be affected by gravity according to the percentage of body that went through the portal, B- it will stay because it's stopped by friction.
You're all not getting it. It's not the portal that's "pulling" the cube through it, or anything like that. It's the other side of the cube pulling the rest along.
@@gavinwilson5324 the cube isn't moving. Neither is space itself moving. All that is moving is the link between two locations in spacetime. There is no momentum to keep half of the cube moving.
I didn't think to type it out but you resolved the first paradox exactly how I was imagining it would go
The second paradox feels weird in my mind though
1:01 I’d say C.
Since the portal is halfway, and we’re using the theory from last time which is it’d shoot out the other end, it’d be as if half of the cube was being launched. Since by common sense that the half that is in the portal is connected to the half that is not (as they are the same object), it’d just pull itself back through the portal, but at half the speed it would’ve if it were to go in all the way. If the cube were weak af, then it’d probably split in half, but that’d just be boring.
Edit: I was right. The vid said so.
Edit2: 3:09 I don’t like this one. The portals don’t have the weight, it’s the wall that they are on that has the weight, portals were never meant to just float in the air. Portals have no mass, they’re completely two dimensional, and they’re more like the empty space between two rooms. But, if that empty space where to be moved and no longer connected logically, the destination would still be the same, therefore, still connected.
Extra edit 4 about this one: Portals are meant to be placed of surfaces, so it’s more like the walls the portal is on would break (or slide if they weren’t inserted into the ground very well) because it’d be like the piston is pushing in two directions into the wall.
Edit3: another way of thinking about 1:01 is that there is a propeller attached to the cube and it is going through the portal. The propeller *pulls* the cube through. Or, there is a bunch of mini helium balloons inside the cube. The balloons would float to the top at normal speed, but when they reach the top, they’d be forced to float at a much slower pace. If the cube were weak, it’d break in half and the balloons would continue pushing the top half. If it were strong, the cube would do as said earlier in this paragraph. I’d also say that the one with the rope was a much better way of explaining this but it doesn’t hurt to have multiple examples.
Speedy thing goes in, speedy thing goes out
-Glados
@@titan1umtitan half of a speedy thing goes in, speedy thing at half speed comes out.
-me who just ripped that idea straight from GLaDOS.
@@edex59 but the cube is not a speedy thing, it be stationary, considering the portal is simply a quantum tunnel
@@titan1umtitan speedy portal absorbs cube, speedy cube comes out. The video didn’t cover how this is exactly but it seemed that the whole solution kinda revolved around that assumption.
@@edex59 yeah, but we must go off of game logic, first and foremost, it’s like putting an end of a bendy straw over the cube
Wait why would the portals move? A doorway doesn't move when you walk through it. The floor is the only thing that gets pushed back when walking. Their also isn't a interaction between the edge.
Imagine the portals are mounted on walls with rails. Several of the test chambers are shown to be constructed by mobile panels Glados controls.
@@Appletank8 Yes, but the portal never exerts a force on the cube, so the cube wouldn't exert one back on the portal (or the surface the portal is attached to). Walking through a portal is just like walking through a door. You don't exert any force on an open doorway when you walk through it.
So the cube would just keep exerting more and more force on itself as the portals got closer to one another. It might, at that point, shatter, or be flattened, or otherwise fall apart.
think of it like this, either the piston crumbles or the wall behind the portals crumbles/move
Because doors don't redirect momentum like portals do. You can argue that Portals just completely bypass those physical laws in some way, but that's the idea behind the explanation.
@@Crossfire024 I think idea behind this video is the premise that since a portal is able to change the momentum of an object (when it maintains momentum through a portal its momentum changes from a broader reference frame), then it is applying some force - by definition. The alternative would be that portals just totally undermines our real world notions of force and momentum, which is just as likely to be fair. But still, this video assumes the former for sake of exploring the idea.
1:12 My thoughts: You argued that having the orange portal moving towards the cube is equivalent to the cube moving towards the orange portal. I agree with this notion. Now, in the current question, having the portal stop half way means that it must decelerate to a stop (relative to the cube) during its encounter with the cube. Per the aforementioned notion, this is equivalent to the cube moving through an orange portal at rest, and decelerating to a stop (relative to the portal) during its encounter with the portal. Per established game mechanics, it seems obvious that this would cause the cube to be half-way in one portal and half-way in the other, with a relative speed of 0. Thus, option A seems best.
That's what I thought too, they seemed to focus on the outside perspective, but if you imagined looking through the portal coming at you and it suddenly stopped, you would just end up part way through, like running into a portal.
I disagree that "Portal stops half-way through the cube entering it" and "The cube stops half-way through entering the portal" are equivalent.
In the first case the portal is deccelerating, while in the second case the cube is deccelerating.
A more accurate change in perspecive for the first case would be "When the cube is half-way through the portal, the Portal accelerates to match the velocity of the cube"
This doesn't apply any acceleration to the half of the cube that has already exited the other side of the portal, so the half the is moving (relative to the portal) and the half that is not average out at half the original velocity.
@Manabender THIS. I thought this too. They forgot about their own first statement of how this would work. As did Tachrayonic.
Like Tachrayonic said, those two ate not equivalent. In the case of a decelerating portal, only half the cube is affected, but in the case of a decelerating cube, the whole cube is affected.
Imagine if instead somehow only a half of the cube decelerated to 0, while the other half was still moving at 2m/s. This is the same scenario as in the video: Either the cube tears itself apart, or equalizes the two velocities and continues at 1m/s
right, but that only applies to the half of the cube still outside of the entry portal, does it not? the other half would have its velocity unchanged, pulling the remainder of the cube with its momentum. for a rigid body, the end result would be a cube moving at half of its initial speed relative to the entry portal.
My thoughts: I would agree if the portals were connected to the objects being pushed through, but they are just holes in wall of space and time. Think fluids being pushed onto themselves because the space between them is being changed, not the walls themselves. The Walls moving mean the objects inside push themselves, not the portals (objects and portals cannot be connected)
This is so interesting, the law of conservation of momentum and other laws work even under impossible conditions, I think this will help to better understand ordinary situations.
Paradox 1 is actually really interesting if you think about it. I wish you'd explored option A a bit more because when I was imagining the scenario in my head I was imagining the portal slowly moving downward and the box staying put, this isn't one of the options you presented though so I began to wonder why this was my initial conclusion. Turns out if you account for the speed in which the orange portal moves downwards and compare it to the force of gravity holding the cube in place you might get different results. If the orange portal doesn't reach a certain speed, the momentum the cube gets that is shot out of the blue portal might not be strong enough to combat the force of gravity so it won't lift at all, unless it snaps in half of course. I believe when making the video you might have imagined the portal moving a bit faster than I did, thereby demonstrating how the entire cube would most likely shoot out of the portal entirely if it's stable enough.
I think the assumption on frame of reference is incorrect. The orange portal is what has momentum, not the cube itself and the portal doesn't physically interact with the cube Anything passing through a portal would conserve it's current velocity so a stationary cube would still be stationary until the forces of the other side interact with it. In the case of a moving cube the cube itself has momentum so it keeps moving after passing through. In the case of a falling portal it would be like dropping a hulahoop over a cube, except gravity on the other side would probably pull the cube to the bottom of the blue portal if enough mass passed through to overcome friction on the orange side floor.
@@franwi1722 interesting approach but I can't say I agree. If you move the portal to the cube the cube will still be transported through the portal gradually over time regardless of how you image momentum to transfer. Coming out of the exit portal the cube would be moving at the same speed it entered, at the very least because there is more of the cube pushing from behind as the entrance portal continues to move. Unless you think all parts of the cube will be transported to the exact same location relative to the portal, forming a compressed 2 dimentional version of your cube on the exit portal. The rate at which the cube is covering distance over time should be the exact same as that of the portal transporting it there. Undeniably it moves a certain speed. After it is fully moved through the portal there isn't any force in particular that would slow it down so why should it suddenly stop?
@@copycalico I'm thinking of it in the sense of if I take a broom and push it through a window, the bedroom has momentum on both sides, if I move the entire window around the broom the broom itself hasn't and doesn't have speed itself. There is no force on the cube at the orange or blue sides of the portal, we just moved the window.
Thinking about the forces on the cube at the orange side. The cube wound need the orange portal to impart a pull on it as it passes over for the cube to have any force act on it. The portal itself would have to some kind of suck to lift the bottom half of the cube up. Nothing is actually in motion other than the orange portal, both the blue and cube are stationary, the orange portal just brings the blue side world around the cube.
@@copycalico I think the difficult concept to accept is that if the cube is "pushing" out of the right portal that it must have rightward momentum. But if we repeat this same thought but rotate the the right portal so it faces up, it reinforces fran wi theory of the hulahoop.
@@AbolishedShadow I think it's bc the cube appears to have momentum on the blue side but I believe that's just an illusion. The portals are intersections of two separate places that don't interact with the environment around them, so moving the orange portal is equivalent to moving the entire world outside of the blue portal. The cube isn't passing through the orange portal, the orange portal is bringing blue around the orange.
I like to think of the portals as doorways. Yes they're a bit more quantum in nature, however I just think of them as doors. For me personally that would lead to the scenario of paradox 1 having a cause of essentially just walking through a moving door. An object without motion acted upon it should not move.
in the case of physics, if we consider portals wormholes, then yes moving something through a portal is the same as making the portal move through that.
Thing is, if the door is moving, then you're also moving relative to it
@@LineOfThy Which is the same as being on a moving walkway that goes through a doorway. Are you implying that the doorway applies a force on you as it moves past you?
@@josephcoon5809 The issue is that the two doorways (the entrance and exit) are on the same reference point. That's like portals that aren't moving. We are talking about when one portal is moving and the other isn't. So your point is moot.
@@LineOfThy Energy does not appear out of no where though. In order for the cube to shoot out the portal would have to slow down or show some kind of resistance and then transfer its kinetic energy to the cube.
For the portal stopping halfway through, I think it depends on how the portals are setup. If the exit portal is facing down, it will have gravity pull it the rest of the way down. If the exit portal facing up, then it will stay put. If the exit portal is facing left or right, it will really depend on which direction the enter portal is facing. It may be affected by gravity, or may continue moving.
For portals to work with the physics we know, space has to be compressed around it.
This means a few things:
- Portals can't be oriented at an angle since that would curve space around it. This solves many problems we have at thinking about portals.
- Portals can't be moved vertically. If they did, it would cut everything passing through it. Imagine an open elevator where you stand in the middle of the open door while the elevator moves up. You won't be thinking about portal paradoxes anymore.
- You can't hit yourself when going through a portal since it's simply a straight tunnel from one place to another. Space is compressed around your 'doorway' while the portal itself won't change your appearance. Forces therefore have no play in this theory.
1. It depends on the inertia gained by the 1st half. If the force is strong enough to pull the rest of the cube then it will shoot, if the material is too weak it will break.
2. Image a circular piston that can push itself. I agree with the idea that the piston can crumble itself if it's too seak. For newton's 1st law to be applied (if I am not wrong) both objects need to have mass, do portals have mass? I say no. Thus I think that the cube "disappears" a.k.a get flattened in a 2D plane that is the portals themselves.
I think it makes more sense to interpret the 'flattening' physically, so the cube gets crushed with massive pressure and explosively squishes out molten cube materials to the side.
My initial thought on the first paradox was a variant option A because I was focused on the non-portal forces acting on each half of the cube [Orange half is pulled away from the portal so cube doesn't go through, blue half is pulled to the side of the portal so the cube "falls" and stops on the "edge" unless the floor's friction was high enough] but I do agree with your proposed solution as long as the portal's speed is high enough to keep the orange half's gravity from fully decelerating the cube before it goes through.
[This assumes that the blue portal is angled perpendicular to gravity, if the blue portal is angled "down" then no movement towards the portal's "edge" happens and the blue half's gravity will instead aid in pulling the cube through, lowering the speed requirement, but a blue portal angled "up" would result in in the direct interpretation of option A.]
My thoughts on the second paradox are that it's the same as the falling tile part of the first paradox video, in that a fixed amount of matter is being compressed by itself (or infinite copies of itself in the cube's case) so the cube would break apart until A) the rubble that falls outside the portal's area jams whatever mechanism is moving the portal surfaces or B) The material is broken into molecules or atoms that would be small enough to fit between the two surfaces if the portals weren't there.
I think that both problems that have been shown here aren't problems at all. I consider the way through the portal like going through a door or any other opening but with the difference that the way in and out aren't physically connected and tied to the same place...
This way of thinking automatically poses that a flat portal always has to be an a surface which has matter, like walls. Therefore: The portal stopping at half way is (from my perspective) correct. The end that went through the portal experiences the normal way of traveling through a window of sorts where it flies away and pulls at the other end of the cube that doesn't experience that. Both halves of the cube must now be considered as two objects that pull on each other in a way like the one described in this video.
The other problem is easier to solve if the initial condition is applied, which states that there has to be a surface for the portals. If you now put two portals on ceramic plates and set one facing up on the ground, then a cube on it and then the other portal facing down on the cube, it would look like the plate would just lay ontop of cube. It would be like the portal isn't letting the cube through. However, if you lift up the top portal just by a tiny bit, the cube would start to infinitely fall through the portals.
Exactly what I was thinking. Also used this kind of thinking for his first video, let's say a door is zooming towards you, then magically stops once your through, you won't be pushed with the same speed as the door, you'll simply stop. Now of the door keeps zooming, then you will continue to move away from the door relative to it. When it comes to portals, if the portal continues to move, more particles are being pushed through the door in a certain speed making you move at that speed, until ofc other forces start to take effect or if its air being pushed, until it disperses and isn't pushing you anymore
You finally menaged to get the final piece I needed for my understanding of portals, especially 2 portals moving into each other. Basically whatever is in between will experience infinite falling, or differently, will experience only the inside of the portal.
2 portals on top of each other is basically a pocket dimension, where one could (theoretically) store an infinite amount of matter and once you lift one of the portals will start falling (based on current gravity orientation?) And if you were to re-place the top portal somewhere else, then with terminal velocity all that matter would be launched, similar to the infinite falling setups.
This has some serious implications though. What of you break both portals simultaneously? You would "lose" all that matter in a different dimension/universerse/what have you. Lol
@@theknight1573 There is something wrong in your comment, sorry. There is no "inbetween". If you were to place an item on top of one portal and the other portal on top of the item, the item will stand on itself because there is not inside.
@@azubilp right, but if you were to move the portals closer, would that not result in some sort of dimensional shift? Or do you think this would destroy the cube as stated in the video?
@@theknight1573 If you move the portals closer, you automatically push the item against itself resulting in either squishing the item or being resisted by it so that the portals wouldn't move closer to each other...
So I got something to add to this paradox. In Portal, you can put one portal on the ground, one on the ceiling, and they'll be aligned the same way if you're facing the same way when you shot both portals. But what if you shoot one portal, go around to the other end, turn to where you would be facing in the direction of that portal, and then shoot the other one? Because in the game, they would be aligned differently.
Now in the case of using a box, yeah, the result is the same if the two portals come together, or try to. But what if you had something that could be at one end of a portal?
To try to be clear, suppose you could have the portals face horizontally and you could shoot one of them upside down, so that when you go through the portal that is right side up, you end up upside down. So what if you had a small box that could be at one end of the oval-shaped portal, since it would be on the opposite end of the other portal?
If Portals could move, wouldnt there be a wind, because of the air-particels?
It would depend. if both surfaces are in the same air pressure, I dont see it doing much. But if one is at a higher pressure than the other it would move the air from the higher pressure to the lower pressure(like the ending of portal 2 with the moon)
@@MyAramil the way I see it is there'd be a bit of a draft if the other portal is moving slower or is stationary
When thinking about the first portal paradox I concluded portals shouldn't preserve speed regardless of frame of reference. Static portals don't even do that.
Consider the situation where (in a static frame of reference) a box moves at a speed v down into the blue portal and comes out at a speed v right out of the red portal.
In the frame of reverence moving at a speed v/2 right the box moves down left into the portal but comes out straight right. But this isn't how portals redirect speed.
I imagine moving portals like a moving door frame. The door frame moving very quick passed you doesn't means you'll suddenly be moving very fast on the other side (except if you are ex pushed by all the air passing through the portal).
I asked this exact question (paradox #1) on r/portal about a year ago, and I had the same conclusion. Thanks for finally confirming it.
When you talked about the two portals sandwiching the cube I immediately thought of Gmod physics and the sound of objects clipping against each other super fast
3:22
(1) The problem (for me) arises because of the 'fact' that i don't see any correlation/connection between the object and the event horizon (where one spot on the right become a spot on the left); like a open window and a stick, not physically connected (other then some negligent micro gravity, air displacement etc).
(2)However there should be some connection because when pushing the portals at the same speed (etc) toward each other would suggest that they can't move any closer, but why; since there appears that there is no connection between the object and the portal. Uhg.
I think that portals require a rule that says "portals can't move relative to each other"
Or more specifically "the plane a portal is in can't move relative to one another"
I'd say that by moving the portals towards each other, one is contracting space itself. The cube would then crumple and not affect the portal in any way. The portals would act like a hydraulic press with "infinite" force, as they aren't affected by the cube.
There isn't an event horizon because the portal (singular) doesn't have one, any more than an open doorway has one. You can draw an imaginary line that signifies when you are no longer in the hallway, and now you are in your bedroom, but the actual doorway is unecessary in that scenario, since you can accomplish the same net effect by drawing a line on the floor of an open room and say "I am now in the bedroom".
The portal (again singular) is nothing more than an open doorway that just happens to go from one place to another that can be anywhere. It is a single portal with an orange side and a blue side. It is two-dimensional and massless (otherwise it would affect stuff like the momentum of objects passing through it)
@@FlesHBoX With event horizon i mean the hypothetical center or inner part of the circle / the "doorframe". Just like with a blackhole, it's not something physical, just referring to a location where something happens.
I got to it being singular, but that doesn't solve for what happens to the cube if the open sides, facing each other, with a infinitely strong cube 50% in/out each side, goes toward each other perfectly..
>What would happen to the cube; where does it go, does it even go anywhere since it's not affected by the frame? (or is it?)
>If it's full stop not affected, then where does it go when the portals touch, since it doesn't break the approach of the portal(s)(sides)..
@@hockdudu It's not contracting space itself, (it can escape to the sides,) the problem is where does the cube go since the portal has (that's an assumption) no grip/influence on the cube other then the obvious of being a window to an other location.
In this thought experiment it's completely indestructible.
The portal either has or has not got any connection to the cube, if it has not, then it (the portal) should be able to go until it touches it self (that's an other problem, forget that).
But logically the front of the cube touches the back of the cube and pushes itself (an other problem) but has no where to go; When to portal almost touches it self the cube has the be somewhere but the right side IS the left side with zero width (when the portals touch) There is no 'inside' of the portal, only the separate windows to the same place/location.
I imagine a portal as a door between two rooms. It might have a visible frame to mark the position of the portal, but not in the sense of a wooden door frame that you can touch to accelerate or decelerate while you are moving through it. To change your motion relative to the portal you have to interact with the room you are in. So if there is a road, you can walk or drive if there is a vacuum you should have at least a rocket motor and a space suit. If you see water or lava coming out of the portal it might not be the right portal to go through if you are just walking home from the pub. If nothing suspicious is moving through the portal you can try to go through. If you manage to stop within the frame of the portal you are partially in both rooms. If the other room is not filled with 10^^33 tons of compressed dog food or other things you cannot easily pass, you can try to move forward. But don't try to apply Newton's or other's laws to fantasy objects like portals. So better don't say: 'This fantasy object must behave this way, because otherwise it would violate Thomas Schmidt's Spin Compensation Law'. Even if you are able to 'construct' an object without any inconsistencies with known laws, that does not mean that this kind of object may occure in reality. OK, Higgs proposed a boson this way, and fifty years later it has really been found. But there were much more things proposed and will maybe never be found. So we are free to integrate portals into funny stories without solving so difficult questions like 'What happens with a portal if the two rooms are accelerated related to each other?' or 'Which conservation law may be violated in that particular definition of a portal?'.
For moving portals:
I think velocity of both portals have to be linked to each other which means when red portal is moving to the right at velocity |v| then blue portal is moving to the left with that same velocity |v|.
When the red portal hits/eats an object then that object flies through the blue portal with velocity |v| but in the opposite direction of the blue portal
|v| - |v| = 0 so the objects exiting velocity will be 0
yea I was just thinking this!
I agree, but the portal is clearly orange
What a lot of people aren't taking into account here is that for portals as they are portrayed in the game to exist and physics to still work, spacetime itself has to be capable of applying forces to objects, as otherwise, me stepping through a portal facing north at 1kph and coming out facing west at 1kph, in a stationary observer's frame of reference, would involve me undergoing an acceleration without a force. This breaks the laws of motion and would allow for stuff like free energy, so a force must have acted upon me to change my velocity from 1kph north to 1kph west. The only thing that could've applied that force to me is the portal itself, which if we're treating as a connection between two points in space, means space itself is applying a force to me, and I must apply a force back. Portals aren't like ordinary doors, stepping through a portal not oriented back-to-back with another changes your velocity, so they must be able to apply forces, or F=ma breaks down.
A buddy and I have been spending the last three hours discussing the calculations I did last night. I love when I get to explore physics like this 🎉💖
I think the piston system could have a result in pushing itself.
Love these, by the way. :)
Take on paradox 1.
A moving portal I believe can ruin the object that it passes through, since a portal will also transfer not only the main object but also the atmosphere and pressure depending on the speed. You can maybe look at it like the thing that kids use to make bubbles, there will be resistance so the object might appear stretched once it appears on the other portal.(I say so since the object hasn't adapted perfectly on the condition in and out of the portal.)
Or maybe the portal is so light that it doesn't really affect the air around it. Kinda like the void. Then the object will not be affected in any way, it will only be displaced and transferred to the output portal.
Thoughts on paradox 2.
Since the object appears on the side where it should appear it will definitely squish the object.
Btw the piston one didn't make sense, a portal can't be pushed since it is almost like a ripple in space-time, it might be weightless, the only logical thing that would happen is that once the piston reaches itself it will only pressure itself like it will push a wall until it breaks.
For the first question, I believe the speed of the portal doesn't matter because it doesn't give any energy to the object. For example, if a doorframe came towards you and you went through it, you wouldn't be yanked out the other side but the doorframe will continue it's trajectory, now for portal it's like one side of the doorframe doesn't move so one end would go over you and then it would be like standing in the doorframe.
Same for the piston question, there shouldn't be any transfer of energy between the object and the portals, as you can't push a hole unless you push the wall, you shouldn't be able to push a portal (unless they are magnetic or something).
I like to think of the "event horizon" of the portal being immovable relative to where it is placed. Then when 2 portals move in to each other the object in the center would just be crushed no matter how hard it is and no matter how lightly we press the portals together. Maybe the event horizon are also so massive that its absolutely impossible to pass through another portal, no matter how hard we press them.
Ironically what you are referring to at the start of the video, in regards to maintaining momentum when exiting from a portal, or wormhole if it fact curves time as well as space, was also covered in one punch man recently, and was a pretty interesting paradox in itself!
Box entering orange portal exits blue portal inheriting both boxe's and portal's orientation, speed, acceleration and so on.
Here is one thing you Forgot:
Box is halfway portals. Orange portal moves, what happens?
Orange portal moves away from the box?
Orange portal moves towards the box?
Orange portal moves sideways to the box?
Orange portal spins in place?
Now if human was halfway standing what would happen if you turn yourself, blue portal or orange portal? How about if you flip, pull or push one of the portals how it will effect you?
Like i said in the first portal video.
I believe if the lovely companion cube is moving and so is the portal.
It should come out disfigured.
As it is coming out its essentially changing on how its going in.
I believe it would be half a staircase as its first half comes through and as its shifts its centre of mass and becoming more disfigured coming out the more it would spin or change how it is moving through the portal.
So cube = half staircase other half obliod ? Maybe curved like half of a yinyang but jagged.
No clue with the pistons.
I always imagined them as an unstoppable force that would reduce the amount of space between them if pushed closer together.
from your previous portal paradox video, The portal moving to the cube would just see the cube pop out, as opposed to being thrown, as the cube itself has no momentum.
and for this one. A cube suspended between 2 portals would just sit between two portals, as per what we can see in game
I would have to disagree on that one :)
I would think that momentum is conserved when an object passes through the portal, as it makes the most sense logically to me (which seems to be a popular opinion). An object’s momentum relative to one of the portals would be equal to its momentum relative to the other portal, and it would be like passing through a window. So if the portal were moving towards you, you would come out the other end at the same speed
@@Bluzigo but aren't the portals just tunnels in space? they don't even 'exist', like how an event horizon doesn't exist
to say a static cube would get flung by a moving portal is like saying a sci-fi ship deactivating its warp bubble would keep moving at ludicrous speed. the space it's INSIDE OF is 'moving' (more accurately, being shifted)
the object is not moving, space is moving around it, giving the illusion of moving the object-and if the space stops, the object stops. if a portal were to envelop it entirely, it'd just fall out the other end unceremoniously, because the space it occupies was 'moved'.
that's as far as i'm aware, anyway
@@ponponpatapon9670
(Apologies for the long response lol)
TL;DR: for anyone reading, imagine looking through a “stationary” portal to the other side, in which the other portal is moving, so the whole world on the other side would move at you.
So to respond: I definitely see where you’re coming from, and that does make sense. I’d say, though, that “space moving around an object” would, from the perspective of the portal, mean that the object does have momentum.
For example, if you’re in a moving car, space moves around you. While yes, the car is propelling itself, from your perspective everything inside the car has no momentum, but from the outside it looks like the car and everything in it does have momentum.
I think of a portal like a window, where relative to itself an object just passes through both ends at the same speed. So if you were to throw a window at a stationary floating basketball, the basketball would “move” through the window, in and out, at the speed you threw it (relative to the window) but relative to you, the basketball wouldn’t move at all. So if the window were replaced by a portal, then with these rules, you could say by throwing the portal at the stationary basketball that the basketball would come out the portal at the same speed you threw the window at.
If that’s a little confusing, imagine looking through the “stationary” portal to the other side looking at the basketball, sitting there stationary to the world it’s in. But since the portal is moving, it appears that the whole world through the portal is moving, including the basketball, so that when the basketball does pass through the portal, it keeps its momentum relative to YOUR portal and flies out the same speed the other portal was moving.
I really appreciate your guys’ input though, this is a super interesting question that I love working to uncover :))
No, it HAS to come out fast. Think about it - the speed of the edge emerging from the portal has to be fast enough to allow the rest of the cube room to come through behind it. Otherwise it's somehow being compressed in "portal space" (which doesn't exist). The cube has to "get out the way" of itself - therefore, it emerges from the portal at a fast speed. Therefore it's moving (fast) as it exits the portal. That momentum doesn't just disappear.
I was thinking along the same line as you, I just didn't think of the string point. The top half of the cube is given the momentum but the bottom isn't so the top half applies force to the bottom half for it to fall out of the blue side slower.
About the portal stopping halfway: First of all, moving the orange portal towards the cube should not make the cube exit the blue portal at any speed, if the cube itself is stationary. There is no inertia in the cube. Hence the gravitational forces should in that case combine, depending of the volume percentage on each side, and that would determine the direction and the velocity of the cube when "stuck" between two portals. So basically, if the blue portal is set just like in the first example (standing upright), the lesser part of the cube exited the blue portal, the slower it will start falling there. And yes, that would move the cube on the orange side as well, since the combination of gravitational pulls would work on both sides.
As for the one with the ropes - again. There is no inertia. So same as above.
Now, if the cube is very fragile: it may still remain whole. Let's say that the orange portal is moving towards it at a constant speed, and stops instantly at exactly 50%. From the blue portal's side, the cube will NOT accelerate immediately, nor constantly. Instead, it will start falling with the speed increasing from 0.000...001m/s to half the gravitational pull (9.81 m/s divided by 2), then continue falling at that speed. Now it's only a matter of how fragile the cube really is, and if it can withstand this speed increase. But it definitely has more chances of exiting in one piece than it appears in the video - again, due to lack of inertia.
Onto the paradox number 2, part 1. This is purely hypothetical, though, as I'm no physicist. But it gets very chaotic, and interesting, for me at least.
It's basically similar to trying to make perpetual motion with regular magnets. For which we know that it doesn't work. If you put a magnet in front of an iron vehicle, and attach it to that same vehicle, the magnetic force will have no effect on the vehicle's movement. Same principle should apply here. The piston won't push itself at all, since the force attempting to move the object is connected to that same object.
Now for part 2, where portals are moving towards each other. Let's ask this question first: what happens to the matter between the two portals first? Let's say we have a closed cylindrical tube, and circular portals on both ends of the tube are moving towards the cube in the middle. While the portals are approaching the center, they're also transporting air on both sides, making it more dense. If we take the cube out of the equation, portals connecting this way would basically created solid air, by condensing it to an unmeasurable amount. Now, this is only possible because air is a gas, and it lets its molecules mix easily. That doesn't apply for solids, though... so what can we do?
Let's come back to inertia. The air compressed this way also had no inertia when being swallowed by the moving portal. Which means, it is also affected by gravity the same way. Except that we cannot apply the percentage like with the solid cube here, because gases are basically only "solid" on a molecular level (?). Again, I'm no physicist. But would this mean that the percentage of the molecule itself would determine, for each molecule separately, how fast would it move when exiting the portal?
If that's true, and the portals are both moving at the same, constant speed towards the center, that would start making a wall of air on both portals. Since the portals themselves here have inertia, as soon as a molecule of air enters one portal and exits the other, it re-enters the portal and exits the first one, creating a loop. The reason would be that the speed and the inertia cause the portals to be ALWAYS faster than the initial acceleration speed of a singular molecule, which is the minimum possible speed.
And now, let's try to incorporate all this into the cube. How would this back-and-forth bouncing of gas work on a larger, solid object? I think the only explanation is that the portals connecting would break the molecular structure of the solid, turning it into dust, and similar to air, create a wall of dust made of the solid cube's molecules.
Ultimately, when the two portals would get so close to each other, and make this mixture of air and dust so dense, that it would be impossible to push the portals further, without one of the two being destroyed. So basically, depending of the portals' structure, if they're sturdier than this supercondensed mixture, they would try to destroy the mixture. But as matter cannot be destroyed, this mixture then has to go elsewhere. In this case, it would be squeezed out of the portals and break the tube holding them there. Then, when they connect, since they have the same structure, they'll stop each other, glued together with nothing between them. The portals then stop working, as they start sharing the two dimensions each of them had. You can still pass through the fusion of the two portals, I guess, but nothing would happen. If the mixture has a stronger structure than the portals, however, the portals would be forced to stop there.
And yes, I love wasting my time on useless stuff :D
"Everything exists outside the portals.
There's nowhere to hide."
*That's a threat if I've ever heard one.*
This is actually my favourite game, especially the community chambers, brain bending stuff sometimes!
First question: Each can be true dependent on the mass and structure of the cube. Cube can have different mass in different parts of it. Speed is a big factor too.
A - if the mass of the cube that has come through the portal has not enough energy to move the other half of the cube and structure of the cube is strong enough to hold. This however needs a friction for it to work this way.
B - if the mass of the cube that has come through the portal has not enough energy to move the other half of the cube with enough speed and structure of the cube is not strong enough to hold.
C - if the mass of the cube that has come through the portal has enough energy to move the other half of the cube and structure of the cube is strong enough to hold.
For paradox 2 part 2, the opposite reaction is on the stationary end of the piston, right?
Regarding paradox 1, just imagine pushing the cube through an ordinary door. Stopping halfway would never tear the cube apart. Portals are just that. An ordinary door, where entry and exit are not on the same coordinates, every other physics is exactly the same. (Except gravity maybe if the portals do not have the same orientation but gravity would also not tear a box apart)
If we go with portals working regardless of frame or reference, the first one (portal stopping halfway through the cube) is indeed the same as moving the cube toward the portal. and whatever "pulling" as described in the video, is just the inertia of the moving cube. If it's moving with a constant speed, it keeps that constant speed. if there's enough force to stop it, it just stops there.
But the 2 sides of the door are moving in relative to each other, which tears apart your imagination. To have the same effect, in addition to the cube suddenly stopping, the blue portal needs to move too. This makes the part of the cube that will go through the portal after has momentum while the part that has gone through the portal before the change does not, effectively replicating the conclusion in this video.
@@quananhmai5701 You need to add the third frame of reference to your imagination. It is not just the two sides of the portal, but rather the complete portal (entry and exit point) is a third complete frame of reference.
But let's say you don't stop. What is causing the cube to continue moving? That force has to still act on it even if you stop halfway through, the only difference is that then you also have some force holding it back. I agree the cube probably wouldn't break because there's proabably not that much force acting on it, but if it was extremely weak (yet heavy so there still is a decent amount of force in that momentum) it definitely would break.
@@xway2 the frame of reference it has. It’s not that the frame of reference has changed, it’s that there were always two frames of reference-one from each portal. Each portal still “sees” it locally as having the same reference frame it always had. The real cool part is how you can “accelerate” the cube from an outsider’s perspective by passing it forth continually from one portal in a different frame of reference from the other, even without gravity or another source of potential energy
1:45 When the portal stops halfway, then how the block gets the force to accelerates forwards
From the cube that went in. If you are talking about the cube that went in, well the video is treating a moving portal going through a cube as if the cube was moving through the portal. The momentum from the portal carries out to the cube because the other portal isn’t moving relative to it.
The way I imagine it is that the vector relative to one portal is maintained with the other portal on the way out.
So if a portal quickly is lowered stopping halfway through a cube, then the part of the cube is accelerated through, and while the rest of the cube isn't since it isn't held in place, its pulled along by the other half of the cube that was accelerated. To be fair, if you push a cube, you're only pushing one side, but atoms push atoms and the whole box moves. This scenario would be the same but look really weird since the cube would appear to be sucked through the portal suddenly.
As for sandwiching the cube between portals, the cube would just collide with itself.
One of the key assumptions the game made is that momentum must be conserved through a portal. I think this assumption can be rephrased as, two different (but linked) portals must necessarily be the same frame of reference. A portal's movement relative to the cube is the same as the cube's movement relative to the portal. Both portals' perspectives are linked, so the orange portal's movement relative to the cube is the same as the blue portal's movement relative to the cube when viewed from blue cube's perspective, meaning that if the orange portal sees the cube moving towards it, the blue portal sees the cube moving towards it too. This is also the same as the cube's movement relative to the blue portal - when the cube sees the orange portal moving towards it, it's also seeing the blue portal moving towards it, just from the other side. So, when the portal has moved past the closest face of the cube and is decelerating to a stop in the middle of the cube, the portion of the cube that has already moved through the orange portal, starts decelerating relative to the orange portal too. Which means it also starts decelerating relative to the blue portal, since they are the same reference point by nature of being portals, and it is all the same deceleration. So, when the orange portal comes to a rest in the middle of the cube, the portion of the cube that has moved past the orange portal comes to a rest as well, meaning, everything comes to a rest with half of the cube coming out from the orange portal and half of the cube coming out from the blue portal.
In the case of the two cubes joined by the rope, the same thing happens. After the orange portal moves past the first cube, it starts decelerating. The first cube starts decelerating relative to the orange portal -- that means the first cube starts decelerating relative to the blue portal, since they're the same reference point. As the orange portal comes to a rest, the first cube comes to a rest outside of the blue portal as well.
What about gravity? The second assumption I'm making here (I can't remember if it was addressed in the game) is that force fields don't work through portals, they only work up to the portal itself and they die out past the portal. In this way, each side of the portal has its own fields of forces, even though they may have the same source, like gravity. For example, if you open the orange portal facing the ground and the blue portal upright, anything on the blue portal's side wouldn't feel the sideways gravity coming from the ground in the orange portal -- they'll only feel the downwards gravity coming from their own ground, as if the orange portal never existed. With this assumption, going back to the two-cubes-one-rope problem, if the first cube comes out of the blue portal in mid-air, gravity starts pulling on the first cube the moment it crosses the blue portal's threshold. The first cube decelerates relative to the orange portal, meaning it decelerates relative to the blue portal too, so it stops moving sideways, but starts accelerating downwards due to gravity, eventually pulling upon the rope and hence the first cube. If both the orange and blue portals are in mid-air, it'll be as if the cubes were hung up by the rope in mid-air like a pulley.
As for the piston problem, it isnt the orange portal itself that is pushing the piston out of it, it's whatever's originally pushing the piston in the first place, i.e. itself, since it's self-extending. When it hits itself through the blue portal, it's the same as if it hit a ceiling, or a wall. It experiences a contact force that opposes its expansion, coming from its own arse. If it starts pushing with even more force, it experiences that same increased force upon itself as the contact force, due to Newton's Third Law. The more it tries to extend itself, the more it actually compresses itself, because that same force is actually acting on itself, until eventually, it shatters from the compression.
I always imagined that the portals crushing a cube with its self paradox would essentially result in a 0 resistance way to crush things, so if you put a cube between two portals you could walk a panel with the blue portal by hand toward the orange portal and crush the cube by hand without even feeling the cubes presence, whether that be the cube crushing its self and flattening and splintering off in all directions until it's paper thin, or alternatively the pressure from it crushing its self would generate a lot of heat and melt it like putty from the pressure. The portals themselves don't interact with the objects in them so having them space themselves apart from a piston wouldn't really make sense, not to mention they're fixed on a wall and literally cannot float so how could they move away?
I'm not sure why you're so adamant that portals can't interact with the surfaces they sit on. Would you mind explaining?
@@timothymclean Nothing is interacting with the portals to interact with the walls, it's empty space. The portals themselves are the thin rims of glowing ovals that sit on panels and spread space apart inside of them. There's nothing special about the hole its self so it'd still work like empty space. It has no structure, it's a lack of structure, a hole.
@@chaoschaoful You think that empty space can't have an effect on matter? Do you want me to try explaining general relativity and gravitational waves, or do you want to admit you just hadn't thought about it from that angle?
@@timothymclean Cringe.
I agree with a lot of the comments saying that in 1) the cube would just stop in the middle.
I don't consider there being any connection between the portal and the object to substitute a collision. A portal is just that, a portal, a gate, a window.
If you stop your hand halfway through moving through a window it just stops in the window. And if you swung your hand with immense force and violently stopped it you might dislocate your shoulder. The cube, if fragile, would break because of that reason along some fault line unrelated to the portal.
A portal is a window of 0 thickness and no mass. With the property that both sides of it do not have to be connected.
What if both of the portals are facing down? Would gravity pull it from both sides? What if the orange portal stays down, but the blue portal is vertical? Would gravity from the blue portal pull it "down" from that frame of reference and towards a side of the orange portal?
@@RealDanteS01 gravity is unrelated to the problem at hand. Gravity when dealing with portals is messy and complicated, but the problem that was proposed is not about gravity, it's about inertia. But to answer your question, gravity would act differently on different parts of the cube depending on what side of the portal the part of the cube is on.
The third option for the cube crushing paradox is impossible, because forces applied through a portal do not apply to the portal itself. A portal is essentially a doorway: in the same way that moving through a doorway will never cause the doorway itself to be moved (besides negligible gravitational effects), moving through a portal will never cause the portal to move.
The cube crushing paradox can be reframed as an infinite series of identical doorways, each with an identical cube in between them. Each cube always remains in the middle of its pair of doorways (held in place by some arbitrary force that we can assume is probably electromagnetism), regardless of how the doorways move. In this circumstance, pushing the doorways closer together will eventually result in either every cube being crushed, or the doorways no longer being able to move towards each other, depending on how the strength of each cube exceeds the force applied to each door. There is no circumstance where the cubes all get pushed together and the doors start to move apart.
I’d like to take the paradox of pushing 2 portals torwards a cube and explain it in the way I thought of it:
Imagine that the portals each lead to another room on the side that are the exact size from one wall (portal) to another as the middle room. each of these rooms have a cube in it as well, and you can do as many rooms as you would like. If you shrink the middle one, the other ones match it. So, if you half the distance of the middle room, the rest each half, and the cubes become closer to each other. If you keep shrinking the room, eventually you’ll see that once the rooms become the size of the cube, they all hit each other and there’s no room for the cubes to go to. If you try to keep shrinking the room, you’ll have to compress the cube as well to do that, so either the cube would be crushed or the rooms would stop becoming smaller.
As for moving portals, there is one level in portal 2 where portals move with the panel , it's where the laser cuts through the pipes - those who have played it will know what I mean!
If you go halfway through a portal or run to it while holding a cube, what'll happen is it'll just stop. I would argue the same would happen if the portal is what's moving. the way I visualize it is the portal is like a door and the other end of the portal is what's on the other side. if you had a wall with an opening shoot towards you and stop midway through your body you wouldn't jump off, you'd just stay in place.
Stop relative to what? The portal would look like a hole in a wall *but* the floors and air on each side of the wall are moving at different speeds. "Stationary" has a different definition on each side of the portal as you're looking through it.
If you immediately stop, then you'd get crushed. You're whole body can't exit a stationary portal without moving. However, you entered by moving the portal over yourself. You or the portal MUST move to safety travel. So the question remains, what if one portal is moving but the other isn't?
The hoolahoop or door analogy is flawed because you are assuming that the two ends of the portal are moving at the same exact velocity, when infact they are moving relative to eachother.
@@JWQweqOPDH It doesn't matter if the portal moves over the cube and stops, or the cube moves into the portal and stops. It's a change in momentum for the half of the cube that's still outside the portal/in your hands, but it's a solid object and doesn't get torn apart, just because you change its momentum.
You're not defining where the ends of the portals are, if they are moving or not. Are you saying that there is a distance from entering one portal before you exit on the other side?
Nope, you’re thinking about standing on the ground. Think about if both you and the door were falling straight down. If the door if falling faster than you, then if you look from the doors frame of reference, once you go through the door, you have the same velocity away from the door as the velocity you had going towards the door. The door here is the portal. If it stops partway through, you’d still have the same relative velocity until the moment that it stopped. In physics terms, you’d have half the velocity. But I don’t think you’d really move at half the speed.
Paradox 1 : What if the speed is so slow that its not even enough to fully propulse the cube out of the blue portal
Moving portals are used in one level in portal 2 in the level neurotoxin sabotage, but you cannot reach these portals normally and only a laser enters them. If you do go through the portal, if you go through a portal connected to a moving one, you get sucked inside it. If you enter a moving portal, you get accelerated out of it. Moving portals were a broken mechanic never properly finished.
4:02 What happen if portal enter another portal like in the draw ?
He made a vid already 😉
Portals are two teams of nanoscopic Keebler elves. One team dismantles the incoming object and telegraphs the assembly instructions to the other team that assembles the object. Both teams do it really fast. I may be wrong about the Keebler elves, they may in fact be faerie princesses or nanoscopic My Pretty Ponies.
Thank you for the chuckle :P
What if you look at the portals like a wormhole or a doorway? Like they are just openings, where there is no force acting on the portal by the objects moving through it? That would be true if they were just space being bent and pinched so 2 different coordinates on a 3D space grid were touching, and the portal is a hole connecting the 2 spots.
The piston pushing on itself would be like having a radius shaft, starting at one side of a doorway, that comes around and meets the back on the other side of the doorway.
Pushing the portals together, collapsing the space between them, would be like space itself forcing the radius of the piston arm in the doorway to shrink without removing or making material smaller.
Theoretically you could push 2 portals together flat with any object in between, and crush it to an infinitely flat 2D shape without feeling any additional force beyond the force of moving the portals while nothing is passing through.
Maybe the object would act like its being crushed like the hydraulic press videos, and squish its contents outside the edge of the gap between the portals. That would prevent the portals from ever getting infinitely close together with matter inbetween.
So on the first example it depends on gravity based on where the object is coming from. Potrals aren't exacting anything on the object, it's just a gateway.
For example 1: as the orange one goes down half way and it come soit the blue one horizontally, the more it comes out the blue the more gravity is exerted on it downwards. As more gravity is exerted on the one side than the other it will eventually just fall out.
In the second example: nothing would happen to the portals. It's like a hydraulic press pressing on itself almost. It goes in one portal and comes out the other and it hits itself in the back. Assuming it's not attaches to anything it will just keep pushing itself. If it is attached to something and it isn't strong enough to break it, it'll stop.
The portals aren't exerting any force on the objects. All the force comes from an outside source.
The portals are doorways. A doorway doesn't inherit the momentum of people passing through them. It's a non-paradox.
3:38 no way, that video is where I got my profile pic from
Your Picture is from Portal
It would be interesting to have a more complicated and real-world-physics-accurate sandbox version of portal that coded in moving portals. Would be fun to mess around with
stargate's writers struggled with this a lot.
Sometimes a person could put a hand through the event horizon, and pull it back. Jack O'Neill does this once just to hold the wormhole open, so people on the entry end couldn't dial out before being blown away by the enemies on their side.
sometimes you got pulled in. A couple times, a stationary object or dead body has been just barely inserted, and then it got pulled the rest of the way.
Most of the time, the relative speeds of the gates with respect to one another doesn't mean a thing -- and this applies between any combination of gate locations: planets, planetary orbits, black hole orbits, ships. It acts just like Portal. Your speed relative to the gate is all that matters. But in the first episode of stargate universe, a planet-to-ship event accelerates people forward. They explain this by noting the special nature of one-of-a-kind ship, travelling faster-than-light without entering subspace.
There’s one sequence in the game involving a moving portal, the one where you destroy the neurotoxin generator
That's the one I was thinking of!
We need a 3rd portal game with moving portals
For the first problem, I would say the part that had traveled through the portal already, thus having momentum imparted to it in the process, would drag the other half through the portal at a reduced speed (as force, and therefore acceleration, would be applied opposite the direction of movement for the moving half in order to accelerate the previously unmoving half.) This of course assumes that the initial movement speed was great enough to overcome the inertia/gravity on the unmoving side.
on the second one, what if the cube is touching itself then welded to itself, what would happen if you pull the portals?
You've effectively welded the portals together
Then it would depend on what is stronger, the force through which the portals are pulled apart or the weld holding the cube together. Unless you meant to only pull one of the portals, then it would potentially move the whole contraption if there is no stronger force holding it in place.
There's actually only one instance where portals move, and it's the neurotoxin sabotage puzzle.
I remember my first time playing that thinking: THEY MADE MOVING PORTALS!
When you shoot a portal to the moon isn't that a moving portal?
@@androkguz In real life, it would be, but if you stop before shooting that portal and just wait in-game (with any necessary cheats to disable a countdown to death if there is one - it's been a while since I last played), I would be very surprised if the moon moves at all (relative to the Aperture Science facility) even if you leave the game running for days (not that the game has a day-night cycle either)
It's moving relative to Aperture Science, yes. Also, if you put a portal on a wall and run by it, then it's a moving portal relative to you.
I think the assumption that the cube would shoot out the other side of a portal, if said portal was dropped onto, it is an inaccuracy based on the model used for the portals.
A portal is essentially an infinitely short tube, connecting two places in space. In the physical world, an object passing through a portal is the same as an object passing through a hoop. The only difference is in the case of portals, the other side of the hoop is a different location. The portal itself is not an object that interferes with the thing being transported. It's a tunnel.
When you drop a hoop over a box, it does not move unless they touch each other, and in these examples, the edge of the portal never touched the object. Therefore, the cube would remain in place. For the moments that the portal was moving, it would appear the cube was being shot out the other side, but once the portal had fully transported the cube, it would become apparent that the portal was moving, not the cube.
This same thing happens if you stop halfway. In both cases the cube is never being given momentum. Its coordinates are simply changing, which means for it to gain momentum from nothing breaks the laws of physics.
If this is the way the model works, it must mean that the portal and cube must be non-interactive systems - I don't know the correct terminology for this but essentially the hoop and cube in the before example do not interact and therefore they both experience their own events without ever sharing a frame of reference. In the same way, a portal dropped onto a cube will not interact with the cube. The transportation of the cube is a coincidental consequence of the portal moving downwards, and the cube itself only experiences a coordinate change.
With this understanding as a basis, the last paradox actually gets a bit more complex.
As the portals move closer together (we'll assume they're moving at minutely different speeds to make for ease of modelling) the cube begins passing through them and emerging out the other side. As the side of the cube emerging from the other portal approaches the back, they begin to press against each other. However, as the portal and cube do not interact, this means that no matter how much force the cube is experiencing, being pressed against itself in reverse, the portals are unaffected and will not stop. Eventually, the portals will be touching face to face. The cube, in this instance, is very crushed, as it was applying more and more force to itself until eventually it was applying infinite force.
This happens because there is no space inside a portal. Therefore the space left between the portals can be visualised as the space between two walls. As those two walls close in, the space decreases, until eventually there is less space available than what the cube occupies, which will either cause the cube to crush itself, or some whacky quantum phsyics stuff, but that's above my pay grade. Something something quantum superposition probably.
I believe this not to be a breach of the portal model in relation to physics, but rather a demonstration of one of the reasons why portals are impossible. A cube in space will not simply start exerting infinite force on itself, but, the portals closing in on each other does in fact cause this. I would say the most comparable phenomanon to this is likely spaghettification due to place holes, but perhaps directly inverse, but to explain that is another couple paragraphs and I'm okay thanks
I think the portal stuck halfway scenario demonstrates how B is problematic. Trying to conserve momentum in one room will necessarily cause you to violate it in the other. The question is in which frame of reference can momentum be violated? The answer lies in whether the FOR is moving or not. Imagine driving, you wouldn't freak out because the trees and roads are moving past you even though no forces have been applied to them. Hence, in a moving FOR, momentum does NOT have to be conserved. Objects can move and stop without any applied forces.
In the case of the portals, if you peer into the room from the exit portal, everything seems to be moving. So that's like when you're in a moving car peering out.
In other words, the exit portal is the moving (non inertial) FOR relative to the first room and the first room would be the stationary (inertial) FOR, which means the box can't get sucked out the exit portal because momentum has to be conserved in the first room, not the second one. The answer should be A instead.
A more intuitive way to think of it is a truck with a hole in the back backing into a cube stuck on a wall, you wouldn't expect the cube to get sucked into the back of the truck, would you?
Now if the portal adds energy to objects passing through it then I guess it would shoot the box out but that then becomes problematic even when the portals are stationary. What if you step halfway through the portal? Would you get sucked through the exit portal? Would it pull your leg apart because velocity through the exit portal must be maintained? I always see the portals as just holes between two dimensions that doesn't add any energy to the objects passing through.
In the game, portals effectively act as doorways to perfectly identical copies of the current room, just in different orientations. In the same way that you can run up to an open doorway and skid to a stop right on the threshold, you can run full speed into a portal and skid to a stop while you're halfway inside, with no ill effects (disregarding the usual grocery list of negative side effects associated with all Aperture tech).
For scenario one, I think the assumption that the portals would enact a force onto an object is wrong. The portals are just connecting two points of space, moving them at different speeds would just change the rate at which you transition from one space to another. The only force on the cube in this scenario is gravity. The object resting on a platform has a portal coming from above and is connected to a portal facing right. In theory the cube should not move until the portal extends past the halfway point and the new "downward" gravity force is enough to overcome the original gravity force plus static friction (determined by the objects weight, texture, ext) . At which point it will begin to slide and tumble out of the second portal at a normal fall rate. Changing the speed of the portal would just change the rate at which the two forces increase/decrease but shouldnt amplify them. Coming out of the right portal the object should never have any rightward momentum regardless on how fast it goes through the portal because the only forces acting on it at the time are pushing left (original gravity force) and down ( new gravity force.) To envision this better flip the second portal so it faces up, so gravity never changes direction and repeat the thought. Moving the first portal back and forth rapidly would just have it pop back and forth out of the second portal rapidly.
For the second scenario theres two ways to think about it. One, portals themselves are physical objects that have mass in which case id agree with your assessment that they would either crush or get pushed back depending on if their mass is greater or lesser than the object, but that introduces a host of other questions like how they can be effected by the objects forces but not forces such as gravity. Or two, the portals have no mass and moving them closer together would ALWAYS squish the object because the only forces involved would be the pressures of the object pushing on itself until the portals touch and its squished until the last of it slips out at sub atom particle thickness. That also has a fun thought experiment like sandwiching an indestructible object (in theory which is impossible to exist) between the portals and closing them, but thats just the unstoppable force and immovable object loopyty loop.
"In theory the cube should not move until the portal extends past the halfway point"
This theory is entirely impossible though. Either the cube is moving at the static exit portal, or the cube isn't entering the moving portal at all. In order for the portal to extend halfway over the cube, half the cube must be outside one portal, and the other half of the cube must be outside the second portal. The portals from the Portal video game series that these paradoxes are based on do *not* have a magical hammerspace to hold the exiting half of the cube until it is arbitrarily ready to exit. Edit: the video reiterates this fact when giving the second example. There's no space between portals *AT ALL*.
Also, given the portal on the moon and the moving portals utilized during the neurotoxin sabotage both in Portal 2, how moving portals behave when connected to static portals (or simply portals moving in a relatively different direction to their partner) is actually a canonical concern to have.
@@haassteambraker9959 So this assumes that portals must follow the laws of conservation of energy, but what if thats not necessarily true. The cube would be "pushed" out of the second portal at the same rate as the moving portal, but as its going through the cube itself doesnt actually have any forces imparted onto it, other than what i theorized so it would behave as such. (What if the blue portal is just not moving relative to us and the universe, but the universe and the blue portal is being dragged over the cube at the same rate as the orange portal.[added edit]) Keep in mind we're talking about fictitious portals that can transport matter which in itself break a lot of our known laws.
I've never thought of the portals as "being something". They have no weight, there is no pushing or pulling involved, it's just a fold in space. Moving through a portal is no different than moving next to it.
Sure but if a portal moves, it is as if it connected to a whole universe that was moving relative to it
1:11
It could apply half of the speed to the object since it only half engulfs it if we are considering the portal/block passing though interaction as some sort of collision i.e. option C. Think what happens when an object deflects off of a larger one colliding with it. So then we would have to consider inertia, gravity and create a force chart based on the speed and amount of the object that passes through.
if we consider that a portal doesn't actually apply force which I think it doesn't in the game, it is simply that current vector of the object is maintained until say gravity changes it on the other side of the portal. Basically a portal moving down doesn't matter the force is applied by gravity on the other side of the portal in which case half ingulfed by a piston moving down and coming out of a ceiling portal means no movement until 50.0000~1% of the block is engulf in which case the force of gravity acting to hold it to the ground is less then that pulling it from the ceiling on the other side of the portal, assuming of course that the Block is perfectly balanced and not say bottom heavy and the surface of the floor is not sticky or otherwise bound to the cube.
0:35 aren't the blue and orange portal part of the same "structure"? I always assumed they were rigid and so you'd need to move both portals relative to the object you're sending it through instead of just one.
They actually aren't! In Portal 2 when you sabotage the neurotoxin tanks you utilize a static portal and a moving portal to cut the pipes with a laser. Additionally, at the end of Portal 2 there's a portal on Earth, and a portal on the Moon, and the Moon is absolutely moving in reference to something on Earth's surface.
I have stood in portals in walls before. It is absolutely possible to reposition one of them without being ripped apart or falling off.
But the most interesting thing about the portals is, they can act as perpetuum mobile for infinite energy. One portal at the top, one at the bottom, a turbine in the middle, then pour water in the bottom portal.
A portal moving over a object would not "pull" on an object, but instead cause the object to compress itself. If we are talking a stack of papers, as the portal moves down the stack, the first sheet moves through and occupys the space on the other side of the portal, then the second sheet goes through with each piece pushing on the other accordingly, since they are both trying to occupy the same space. If both portals were moving equally, no compression would be exerted. So any force would be a difference in the "speeds" of the two portals. This means a portal moving backwards (with negitive speed) would result in pulling a near stationary object from the other side.
With two forward moving portals, such as when moving towards an object as in this video, the object would be crushed, not (just) because its trying to move into itself when it collides with itself, but because its moving into itself at the event horizon of the portals.
3:52
Technically, in Portal 2 they did and you can glitch it in a way that you can use moving portals anywhere. There is one level in the game with moving portals and if you leave the level at a certain time you can just keep the moving portals in other levels.
If I remember correclty it breaks the game.
What does make sense to me is that the portals just get stuck, and that would be it. They attach to the object and then stay there.