I rewrote Portal from scratch and solved the Portal Paradox
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- เผยแพร่เมื่อ 15 ก.ย. 2024
- The Portal Paradox has been the subject of a lot of debate online, but now it has been implemented by rewriting Portal with moving portals.
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Kinda cool that your de-make is now, at least in this particular regard, technically more advanced of a game than the actual original source version
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@@CBNST its* 🤓
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Not enough people have mentioned the god-tier move of making this video exactly how long it needed to be and that’s it. If any other creator covered this topic, this would’ve been a 14 min video at least. Bless you, sir. Subscribed.
One thing that sucks is he's wrong, but I do agree, 5 minute or less videos are the best 👌🏻
@@BalognamanforyaHow is he wrong though?
@nintardo2231 you can check my other comments to see the explanation, but here's a hint, it has to do with the conservation of energy 😉. This guys great at programming, but he's not so great at physics.
@@BalognamanforyaPortals already fundamentally break the conservation of energy regardless, so any further violations are a moot point.
@sharcc2511 no, they literally don't. Sure, if you look at it from a glance, it would seem like they do, but they don't.
It always amazes me what games were possible on the old consoles if only someone had thought to make them at the time.
Has always been like this in all the aspects of technologies
think about now, what's possible
The Ocarina of Time devs made portals back in the day, but they weren't implemented.
game design is its own technology
a lot of new things are possible on old hardware, just because of how much more we know about stuff like 3D rendering and programming now! back then stuff like this was POSSIBLE, but probably would've never happened
What would happen if you:
- Incrementally change how far down the moving portal moves, will the cube be "sucked" up and out the other portal?
- Both portals are moving in opposite directions, will the cube get the sum of the portals speed?
- Move the portals toward each other, having the object in the middle?
Just interjecting with my own thoughts:
1. Yes, the cube would be sucked up a bit. I think about it as a person that were standing and the orange portal slamming into me from the top. All the air above me has exited the blue portal at a high velocity, then comes my head, which has just entered another end of the world at a high velocity (this would be the same if the orange portal were stationary and I ran/fell head-first into it), so my head would definitely get tugged into the other end. Now if the portal stops midway, my head will retain the inertia and in the worst case, I'll be decapitated. Again, I think of it as jumping out of a moving train and the train immediately stopping to 0 when only my head is out of the door.
2. Logically, yes.
3. Depends entirely on how the atoms are recreated/phased on the other end. Ideally, they would either phase into each other or be in superposition. But logically, the atoms would layer/intertwine and you would end up with a fine Chell paste.
So the first question you had can be answered two ways, the previous commenter included velocity which is one of the ways to interpret it. I think you meant in a slower way as in how far would the portal need to go before it was sucked out. If the portals are both on a surface that faces the direction of gravity then it’s just when the center of gravity of the cube goes through that or would be “sucked” up and out. The second question is actually demonstrated in the video when he puts a portal through a surface and essentially it is the answer to your question. Its basically like if you were to drop a hula hoop over yourself, one side is moving (relatively) exactly at an opposite velocity of the other side. The third question is a bit harder to answer but I’d imagine it would be like trying to stuff the cube into a place with zero volume. In a real life scenario where we magically have portals to test this, I’d imagine that any object you put between the portals would make contact with itself and begin resisting whatever is pushing the portals together until it yields to the pressure.
This is the logical set of answers based on what the math is trying to simulate. What would actually happen in the N64 physics engine depends entirely on how James is simulating the "teleport."
1. Half the cube should appear on each portal face, at first. Gravitational forces on the Portal B side will immediately take effect on only the mass that is present on that side, and effect the whole cube as a calculation of the opposing forces on the other side, Portal A.
2. Yes, both logically, and according to the math.
3. It would look exactly the same as if there were no portals at all, and it was just two panels sandwiching the cube. Logically, the portals (or more accurately, the objects the portals are moving on) would either be forced to stop with the cube in the middle, or the opposing sides of the cube would crush the cube itself, depending on the force objects that the portals are painted on are exerting on the cube. It would be ultimately the cube crushing itself, but the force applied to the cube would be equal to the objects that the portal are moving on.
If we talk about just physic and not how he simulate the portal.
1. Think of it like the portal is grabing part of the box and throwing it like how you lift a box. So the answer is yes.
2. Since we are dealling with portal, we are dealing with relative position and velocity we have to take that into account. If you are talking opposite here as in from your POV in a room one go left and one go right with the direction facing the place they are heading. What would happen would be the velocity of the cube = the velocity of red portal + the velocity of blue portal. Imagine the slam experiment but the stationary one also moving forward. But opposite here mean how the portal is moved base on it orientation like one is going forward and one is going backwards then it will stay still like the hoola hoop example in the video.
3. The box will be destroy as it will try to exist in the same space. Imagine it more like slamming the middle box with 2 other box exactly the same down to the attom and the imperfection toward the middle one.
@@VarunGupta3009Yeah that phase/superposition answer doesn't really make sense, it's not like the portal instantly teleports an item into a different point in space, it lets the item "enter" that position from a specific direction, so the cube wouldn't have to phase into anything. The correct answer is what herewegoagain wrote: the cube would simply find itself in the middle of its own two sides crushing itself with the same force as the moving panels.
If you assume the portals to magically be unstoppable then sure, they would push until the cube disintegrates into atoms but you're just asking what would happen if you put the cube in an infinitely strong press.
“I could make you wait for it, but I value your time more than retention rate.” Mad respect for that.
I just told my friend about this project and his first question was if the ch_createairboat command will be in the de-make. 😂
Would be a sick easter egg if it also required the N64 keyboard to pull up the console!
@@VariaPrime the what now
I see no reason for this, unless he first made a de-make of half life 2 and was building his current project on top of it. But that would be... fuckin weird my dude
@@inanna8782 locale man has never heard of an Easter egg
@@inanna8782 How to make portal on N64:
Step one: Remake all of half-life 2
Step 2: Add portals
Step C: That's it. You win.
Test idea: what happens when you halt the piston mid-way through the box?
If the box is being treated as a point (with a 3D hit box built around it), I imagine the box won't "jump" out of the exit portal until the entrance portal has crossed the box's reference point. If you treat the box as a bunch of infinitesimal boxes rigidly bound to each other, perhaps more interesting stuff can occur, like having only half as much momentum when it leaves, or being dragged by gravity due to half of the box being affected by it in different directions.
That's actually a great question. My guess is that he will simplify the problem and make the mass point like somewhere at the centre of the object rather than having it distributed. It sounds to me that having a distributed mass might be computationally a bit too much for a 64. But as you point out that would lead to some edge cases not behaving with the correct Physics while for the majority (where that simplification works well) he's got it spot on.
if the portal stopped halfway through the box you'd simply have half the momentum and so half(i cant remember physics its either this or a fourth) the velocity it would have had if the portal went all the way
Wouldn't the force be cancelled by the stopping of the portal piston?
While the engine would likely require changes to account for this, I also think it would logically exit at half the velocity:
If the matter inherits the relative velocity of the portals, and only half of it exits the portal, half of its matter inherits the velocity. The affected matter would continue to shoot forward and either pull the rest of the object along - and as the rest of the mass has no relative velocity, the object would equalize to about half velocity - or it would tear itself in half. This would be entirely based on the structural integrity of the object. If the bonds are strong (like a block of metal) they will stay as a whole object, but if they are extremely weak (like jello) it would be torn apart.
There is no momentum on the box as the box never moves, it is the universe that is moving ... Its a stationary box on a moving universe...
If the universe stops relatively to the box mid way the box will appear to stop...
That would mean interestingly that if the portal would stop at any time in the period the box is in the air after "Jumping" out it woul lose its aperent lateral velocity.
Now another way to look at it is... It's more of an information teletransportation. In that case every particle on the box gets deleted and recreated in its state including relative velocity vector. In this case the box would probably be shred apart as an instantaneous stoppage of the portal would produce an infinite acceleration capable of riping the box at the bond level that separate a moving particle from a non moving one..
Now tell us what happens when you smash two portals together with something in between them. 🤔
my shot in the dark is that the object would crash with its own edges
In "reality" I think the object would be crushed, and if the force moving the portals isn't enough to crush the object then the portals would just stop moving.
THIS is the question. Using the box as the example, I agree with the others - it would collide with itself. But what is hard to answer is if the portal act as a window, with no physical connection with the box, will it be able to meet the other portal and create infinite force? Surely that's impossible? But so are portals, probably...
In game world I'm sure the box would just go flying or teleport to a random coordinate, probably out of any feasible range and crash the game.
OP can you try this with a long pole, but the pole is on an angle, if at the right angle, surely the portals could meet since the pole would never collide with itself.
This is as fascinating as playing Portal was for the first time, thank you to all cause that's all I've ever wanted to feel again.
Edit: After thinking about it, it wouldn't be infinite force, but just a lot of force, or enough to collapse any object down to what I would assume to be a micro black hole? Too much mass in a certain space - which actually happens with stars etc... That seems reasonable if we allow portals to exist. I'm content with this theory.
@@EldeNova So.... The EASY answer to that paradox is to realize that the cube doesn't have infinite rigidity. If it can exert force on itself through the portals, then that means it's under compression. It will immediately begin to heat up. Depending on the material properties of the cube, it could crumble, crack, deform, or crush. If it crumbles, then parts of the cube will be expelled from between the portals. If it cracks, the parts of the cube will slip relative to each other, again possibly being expelled as a result. If it deforms, then mass will squeeze out the sides, again being expelled. And if it crushes, it'll get hotter. If the cube melts or vaporizes, see "deforms". If something somehow prevents the mass of the cube from escaping, then eventually you're going to trigger nuclear reactions and the mass will turn into energy, escaping from the trap. And yes: if somehow THAT'S prevented from happening, welcome to Black Hole City, population Cube, though the moment the portals move apart again it'll instantly vaporize via Hawking radiation and kill everyone around.
The COMPLICATED answer to that paradox is that you have to figure out where the energy to push the cube into itself comes from. The answer to that gets into some... pretty complicated physics. The short version is that moving the portals relative to each other must necessarily require the input of energy because it changes the geodesics of spacetime. (That is, there's potential energy bound up between the portals just like there's potential energy bound up in a ball at the top of a hill.) A realistic implementation of the physics would mean that a surface without a portal would be easier to move than a surface with a portal attached to it. And where does the energy to move the portal come from? From the piston attached to the surface, of course! So that means that trying to push a cube into itself would cause it to become harder to move the portal by AT LEAST as much as it would take to crush the cube if the portals weren't there. If the piston isn't strong enough to crush the cube, it'll stop moving.
Welcome to the Hydraulic Press Portal! Today we are going to crush... cubes.
If the object could fit side by side with itself, it would push itself out of the way and sit next to itself, and the portals would get closer and closer until the object couldn’t repeatedly push itself out of the way anymore.
once the object is balanced on itself or cannot fit anymore next to itself, then it would lay against itself and the side of the portal. The portals would be forced a certain distance apart but could be shifted together after overcoming friction to pass over the object infinitely.
To bring the portals together would compact the object, causing pieces to fall from between the portals.
If you smack the portals together really hard, I bet the air would begin nuclear fusion and blast the portals apart. This brings the question of what would be made if an atom fused with itself? Would nuclear fission be forced to take place if the portals were separated? Strange stuff.
I always thought the portal paradox is what happens when you move one portal through the other.
I think there's a Veritasum video about it
I think you live under a rock 😂😂😂
Nothing happens. The one portal comes out the other, nbd
You tear the fabric of space-time and the universe implodes, only to create a super mass that explodes in a big bang that starts this whole reality all over again.
Its the momentum of the part of the cube that's already exited the portal that pulls the rest of the cube forward with it.
portal 2 contains moving portals. you have to cut the lines to the neurotoxin and you do it using lasers through moving portals. it's the only implementation of moving portals in the series.
Well, theres also the in motion add-on
They're only enabled in that one room, far away from the player or any physics objects, because the developers were never able to get them to work properly. Moving portals in the Source engine are very buggy, and will fling things around that aren't even touching them.
True. This is achieved by changing the config settings when the map loads. You can always allow this using the command “ch_allowmobileportals 1”. However, portals cannot slam down on stationary objects, as the game hasn’t been coded to do so
Yeah, but they only move parallel to the portal, not forward and back.
you just gave me the biggest mindf**k of the day. cause until this time I just thought that the in game universe doesn't allow moving portals for some reason. now it all doesn't make sense
So, important question, what happens if you don't slam the entrance portal all the way down, but instead stop halfway through the cube?
in game, idk
Using real world physics, my guess is the top/front half of the cube will have velocity, because it's already through the portal, but the bottom/back half won't, so it's just about whether that velocity is enough to overcome the cube's inertia and pull the rest of it through. I'm not sure of the exact numbers, but it should definitely move at least a little... probably.
A good guess would be it goes half as far, but I suppose it'd need a test, to be sure.
@@Bluhbearyou are 100% correct. Let’s say the piston stops half way through the cube, it depends on how much the cube weighs obviously and how fast the piston is moving. Just like you said if the top half overcomes the inertia of the bottom half then the cube will go through.
If the piston stop 1/4th of the way at the top leaving the other 3/4th on the bottom, you’ll probably get the cube to do a little “hop” but not go all the way through the portal.
oh damn, thats a good point
I'm going to say that all of the replies explanations so far are wrong, though the results may be similar. Imagine not the orange portal moving, but the floor instead. What happens if you stop the cube halfway through the orange portal is almost exactly the same as if you move it all the way through (minus the bottom half of the cube still being in a different gravity zone for longer without being pushed, if you push it halfway through). So if you slam the floor with cube onto the orange portal, the speed is the same as when you slam the orange portal onto the floor as explained in the video, and if you stop the slamming halfway through the cube (minus the small correction as written) because the "slam" speed was the same. Ofcourse this correction is going to have a bigger and bigger effect as you go to an infinitesimal part of the cube.
@@woud3404I'll point out a small potential flaw in your logic; (but props! I wouldn't have thought this through all the way without reading your post) just that slamming the portal down from above and the floor (with cube) up from below aren't quite equivalent. When the portal is moving down the floor and cube are stationary with one another. When the floor moves the cube up it imparts momentum to it, which is all fine and well until the floor stops moving up, which from the point if view of the cube is like it accelerating downwards away from it.
If we look at the portal-stops-halfway-down case one would lead the to top half of the cube having velocity relative to portal, and converting that velocity to momentum upon exciting. This would impart half the momentum of a full portal drop, it would pop out the exit portal at half speed as the top half yanked the bottom half through. Maybe slightly more, actually. Between the portal starting to clip the top of the cube and it's final position the cube should start moving as portions of it pull 'upward' on the rest, causing the relative velocity to increase. This would make a great word problem for calculus students.
In the floor-stops-halfway-up case the cube would be entering the portal at the regular full speed, and as the floor stops gravity would act to deaccelerate it, but only the back half is still in a gravity-down zone, the front half is experiencing gravity as 45 degrees off from 'forward' (direction of travel). This would nearly cancel, impart some spin, and let the momentum carry the cube the rest of the way through at nearly full speed. Again, calculus for the exact answer.
So if you throw a cube in a stationary portal while the other is travelling backwards at the same speed, you kill the momentum.
It looks very consistent to me.
No it wouldn't, the momentum would be kept. Rather, the distance traveled and trajectory would be altered.
@@Wild_Dice it's like jumping from the back of a vehicle at the same speed it is going forward
@@rogercruz1547 Yeah exactly, you inherit the *difference* of velocity (momentum and direction) between the portals.
@@rogercruz1547 exactly that!
I don't get it, the portal is just a link between 2 different places, it doesn't matter at which speed the portal is moving you remain unaffected by that, the only difference is that you get through the portal faster
The explanation at 2:02 made the first experiment make SO MUCH MORE SENSE. Amazing video
Except his explanation makes no sense when you understand that momentum is conserved between portals. Think of it like a baseball in a car. If you remove air, a car driving over a baseball will not move the baseball. Because before the car drove over the baseball, its momentum was 0. Therefore, after it drives over the baseball, the momentum would be 0. In the first clip where the cube goes flying, the car drives over the baseball and stops, then causes the baseball to go flying in the opposite direction as fast as the car had been moving, having never touched the baseball. Somehow, the car imparted momentum to the baseball, having never touched it.
@@trmerc7635 Except that's not really how this works. Imagine it from the perspective of the exit portal. The moment the entrance portal touches the cube it starts coming out the other end. This happens regardless of whether it falls into the portal or if the portal moves towards it. Assuming the velocity of the cube falling is the same as the portal moving towards it the cube is coming up out of the other portal at the same speed in either situation. And this is where the momentum plays a role. The exit portal does not care how the cube is coming through, all that matters is how fast it's coming through. Momentum doesn't just stop as soon as it's come through and plop down, it's going to want to keep moving in the direction it was coming out of the portal at. If actually look at the exit portal you can see the cube come closer and come through the portal. From the exit portal's perspective the entrance portal may as well have been static and instead the platform the cube is on got pushed upwards. This is why relative velocity is key here. All that matters is the relative velocity of the cube compared to the portal.
@@RNeeko It really is how it works. Instead of a portal, imagine a car. If you throw a baseball at a moving car and it goes through the open windows, does the ball get faster or slower? No. Because the ball did not interact with a physical object to impart momentum. The portals are just points in space that are connected. So is a long tube. If you throw a ball through a tube that is moving, as long as the tube doesn't touch the ball, it doesn't affect the speed of the ball. For some reason, people seem to think because it is a wormhole and not a physical tube, it somehow changes the laws of physics.
@trmerc7635 the cube has to leave the exit portal with the same speed it has entered the portal... thus giving it momentum. Witch causes the box to accelerate upon exiting the stationary portal.
I think you are misunderstanding how the portals work in the game. The portals are not physical objects that can move and interact with other objects, they are just openings in space that connect two locations. The velocity of an object that passes through a portal is relative to the portal, not to any other reference frame. This means that if a portal is moving, it will affect the velocity of an object that exits the other portal, even if the object itself is stationary.
To illustrate this, let’s use your analogy of a baseball and a car. Imagine you have a car with two open windows on opposite sides, and a baseball that is resting on the ground. Now, suppose you drive the car over the baseball, so that one window is above the baseball and the other window is on the other side of the car. If you ignore air resistance and friction, what will happen to the baseball? Will it stay on the ground, or will it fly through the car?
The answer is that it depends on how you look at it. From the perspective of someone standing on the ground, the baseball will stay on the ground, because it has no horizontal velocity and nothing is pushing it. From the perspective of someone inside the car, however, the baseball will fly through the car, because it has a horizontal velocity equal to the speed of the car in the opposite direction. This is because motion is relative, and different observers can measure different velocities for the same object.
Now, imagine that instead of windows, you have portals on opposite sides of the car. The portals are connected, so that anything that enters one portal will exit the other with the same velocity, relative to the portal. What will happen to the baseball now? Will it stay on the ground, or will it fly through the portals?
The answer is that it will fly through the portals, regardless of how you look at it. This is because the portals are not physical objects that can move and interact with other objects, they are just openings in space that connect two locations. The velocity of an object that passes through a portal is relative to the portal, not to any other reference frame. This means that if a portal is moving, it will affect the velocity of an object that exits the other portal, even if the object itself is stationary.
To see why this is true, let’s look at what happens to the baseball from different perspectives. From the perspective of someone standing on the ground, the baseball will enter one portal with zero horizontal velocity and exit the other portal with a horizontal velocity equal to the speed of the car in the same direction. This is because when an object enters a portal, it inherits its velocity relative to the portal. Since from this perspective, the portal above the baseball is moving with the speed of the car in one direction, the baseball will exit the other portal with the same speed in the same direction.
From the perspective of someone inside the car, the baseball will enter one portal with a horizontal velocity equal to the speed of the car in the opposite direction and exit the other portal with zero horizontal velocity. This is because when an object exits a portal, it preserves its velocity relative to the portal. Since from this perspective, the portal below the baseball is moving with the speed of the car in the opposite direction, the baseball will enter the other portal with the same speed in the opposite direction.
As you can see, both perspectives agree on what happens to the baseball, even though they measure different velocities for the same object. This is because the portals are not physical objects that can move and interact with other objects, they are just openings in space that connect two locations. The velocity of an object that passes through a portal is relative to the portal, not to any other reference frame. This means that if a portal is moving, it will affect the velocity of an object that exits the other portal, even if the object itself is stationary.
There ARE moving portal in Portal 2.
They're being used specifically in one scene in which you need to use a laser and a moving surface to cut through pipes.
Although I think I've heard there more of a hack and don't really work find with actual objects.
yeah, there is a command to enable them in any map, however he was talking about the original Portal, not Portal 2
those use hacks and mess up whenever theres an actual object
trouble is... those only move laterally, as soon as they rotate or extrude, portal's gone
All the portals are moving since earth and moon moove aswell
@@dopi3220 so true, god everyone’s dumb it’s like they don’t even consider the movement of the solar system relative to the Milky Way or the movement of the milky way relative to… ? on a daily basis lmao
Personally I'm not very into physics but I understand GLaDOS saying that the portals do not affect momentum to mean that my momentum will never be affected by the portals. Otherwise the forces acting on different parts of me might be so different as I pass through a portal, that I might conceivable be torn apart by a portal falling fast enough, as each part that enters the portal suddenly accelerates into the portal.
Thing is, momentum is relative to your reference frame. If the portal is moving towards the cube, from the perspective of an observer moving with the portal, the portal is stationary and the cube is moving, so the cube has momentum.
Also in-game portals already change momentum. Momentum has magnitude and direction and the portals in the game change the direction no problem.
That's only true when the falling portal changes its speed quite a bit or suddenly stops.
it's actually the opposite interpretation that has this problem.
Say you have an orange portal that's stationary, and a blue portal travelling sideways at 1000 m/s. If you stick your head into the orange portal, this game dev's logic states that your head should poke out of the blue portal at 1000 m/s- you'd move along with it, so the most you'd feel is a strong wind whipping your hair.
However, if you don't think your body should inherit the momentum of a moving portal, then sticking your head out of the moving blue portal would cause your head to emerge at 0 m/s, as the portal flies away- (low-speed head goes in, low-speed head comes out-) snapping your neck clean off.
@@NotaWalrus1If you have a drone flying stationary and put an open window on the back of a truck and drive at the drone will it pass through and not move or will it suddenly ping off into outer space
@@Xtv1234I feel if you came out the back end you'd be perfectly fine and would just drop but if you came out the front end it would just blow you back in.
A lot of people's theories seem to forget air exists and is real and we aren't just surrounded by empty space void of atoms. The air would be going through too. You wouldn't just put your head through and have it suddenly be 100% different
gosh, I remember this project when you were just testing out how much "depth" the N64 could render when looking at portals through a portal. this is amazing
I want to thank you.
1) giving the answer early, its why i stuck around for the rest of it, a sign of respect for a genuinely interesting video that gave a little more information and context to cement the findings presented
2) exactly how long it needed to be, tests, findings, results repeated tests with different settings and end. This earned a sub, if everything else on this channel is presented like this im going to be watching a lot
valuing the viewers time and immediately grabbing my attention by briefly explaining its an N64 demake was such a good way to start the video to keep me hooked, well written and well done.
Isn't long form media also valuing the viewers time? I feel like my time was just wasted by a guy saying "my engine proves I'm right now complain in the comments"
@@pappi8338 To be honest, somebody could make a perfect video that has no loopholes in the explanation and somebody will still want to be the underdog and go "yeah, but" and get 1K likes.
So, are you expecting him to debate himself to save you the time of doing it?
He has an opinion and a logical argument to back that opinion, and he doesn’t hide the fact that he created an engine to do what cannot be done with the original engine, based on physics and relative motion.
Your argument is more of a “because I said” than anything in the video.
So, lets say the portal lands on top of a human (really fast), but makes a sudden stop half way. Would then upper part of human (the part that has gone through the portal) be set in motion on other side of portal, and then pull lower part with it?
If speed of portal slamming down was fast enough, subject could be ripped in half. #Spagettification
Yeah, that is exactly what would happen.
@@james.lambert but would you get ripped in half though? If you think about it, the moment the first hair on your head enters the portal it's already pulling on your body. When your head is through, its already pulling your torso.
It's easier with "ticks" because you don't have to worry about individual atoms, but if you think about it an insanely fast portal might just rip you to shreds instead.
A portal stopping that fast might rip itself apart, too.
Yeah I always likened it to any changes in motion to a portal is like moving the entire universe on the other end of the portal. If you moved a portal (aka: accelerated a portal), you'd actually need to move/accelerate the whole universe along with it to match, unless the exit portal moved in a matching speed and direction to cancel it out. In "reality" you would be able to theoretically have a moving portal relative to its exit but it would have to continue moving in that direction and never change - absolutely no acceleration (no changes in direction or speed) would be possible as that would take infinite energy to do. Having the portal change direction or rotation would be akin to literally moving the entire universe on the other side of it. The reason is because of what you said, the person would get spaghettified if you went half way and then stopped. That's because the whole universe is suddenly 'stopping' (aka: instantly accelerating) on the other torso end of the portal relative to the other side of the portal that his legs are standing in.
Rotation of a portal is especially impossible; When you rotate a portal, the outer edges of the universe would be accelerating relative to your viewpoint at a rate of speed approaching infinity the further out you observe. If the universe is infinite then the rotation speed at the far corners of the universe also becomes infinite, and it would require not only infinite energy but also an infinite speed limit in the universe to move the whole universe on a swivel at infinite accelerations, as it must happen in order to conserve momentum between the two portals.
Also just to be technically correct, you can't have a moving portal anyway due to relativistic effects in spacetime. Spacetime is not uniform, so movements through it would not be a simple x universe moving relative to y universe, but rather you'd encounter shifting spacetime due to differing gravity at different points, and therefore even a totally uniform movement in one single direction relative to the exit portal would be varying all over the place, growing in differences the further out into the universe you look. For this same reason it would probably even disqualify a stationary portal just because of the immense energy required to reconcile the two reference frames - aka: the two 'universes' on either side of the portal.
Interestingly, the force between the two parts of the human would be directly caused by the portal's deceleration.
The next question would then be: What's the consequence of that?
Would a human/ an object that's halfway through a portal be able to hold the portal in place?
Would a heavy object sticking halfway through the portal increase the inertia of the object that the portal is attached to?
Would (as DeSinc conjectures) a moving portal have the inertia of the whole universe? I don't expect that: moving portals would not cause any effects, unless an object sticks through. But I would still not be 100% surprised if we figured out that portals that have objects sticking through would have infinite inertia while the object is sticking through; and in that case one _could_ argue that - since it's independent of the object - the cause isn't the object at all and all portals would have infinite inertia even when nothing is sticking through.
"So... why am I demaking Portal for the Nintendo 64?"
BECAUSE IT'S FREAKING AWESOME!!!!!!!!!!!! I've been following that little project for a while now! Absolutely fantastic work!!!!!
"We do what we must because we can"
¯\_(ツ)_/¯
...why aren't YOU demaking Portal for the Nintendo 64?
Science isn't about why. It's about WHY NOT!!
First of all, appreciate the video length. Secondly - test your solution with the piston stopping half-way through the cube.
The way physics should work, the half that's already flying out of stationary portal should pull the still stationary half from the other end, losing a bit of energy. But would be interesting to see how it would actually work in the physics you coded.
it would depend on the vector of the exit portal and the speed of the piston. it would need to be enough force to pull the cube out of its state of rest and then overcome gravity. you could write this as a physics equation easily enough.
@@adultdeleted True. I was writing that assuming the rest of experiment is same (angles and the speed of the piston).
Would be interesting to play around with different setups, though. Like what if exit portal is stationary on the ceiling, i.e. facing same direction as the entrance. Then depending on combination of speed and what chunk of it goes through the portal the cube would either remain stationary or get pulled through... This could be a fun toy like 4D Toys.
Probably (in the engine) the cube shoots out if its center is through and stays in place if it's not
Logically, the entrance portal is rushing down and then stopping, so the cube should rush out partway but then suddenly stop when the entrance portal stops.
I think the trick is that portals only conserve momentum relative to the portals, not relative to the room. So if the cube is going through the portal a force on the portal to make it stop moving is equivalent to a force on the cube to make it stop as well. The same would be true if the entrance portal is stationary halfway down the cube but you start moving the exit portal around, it should drag the cube with it.
Typically objects in physics engines don't have mass density fields, but rather are point objects with discrete momenta. So it will either jump or not jump, but not half jump.
Both examples shown feel so beautifully intuitive and natural. Love the work! Will there be a windows 98 port?
(let's start a chain of going to older and older versions)
Will there be a Windows 95 port?
@@tygical Will there be a Windows 3.1 port?
@@polorchen1592 will there be a Windows 2.0 port?
Why not DOS 3.3 with CGA, EGA, and VGA graphics options. Also don’t forget Roland MT-32, SoundBlaster, and pc speaker audio options?
A nes port??
I would say the issue with this discussion is the difference between momentum and velocity. If you're basing your coding on velocity, then the cube should move at the same relative speed as the slamming portal, but if you're basing on momentum, as the orange portal can't impart any energy to the cube, the cube should just fall out, based on the possible position of the blue portal.
Agreed, and I feel that the velocity is also a bit of a red herring, since it assumes both sides of the portal are the same frame of reference, which I don't think is a simple answer.
My thoughts exactly. His setup violates conservation of momentum. I reasoned it out slightly differently though. If we assume that slamming the portal down on the cube launches it through the other portal, then there must be some force applied by the portal to the cube. If this force is proportional to the speed of the portal and points through the portal in the opposite direction of its motion, then the hula hoop example will actually launch the cube into the air!
@@1925683 not quite, as I could be reasoned that in the same way the orange (down) portal imparts energy to the cube, it could be argued that the blue (up) portal could rob it of the energy, and that addition/subtraction of energy could be based relative of the two portals position in space/ velocity/momentum.
@@1925683 even stationary portals violate conservation of momentum. if you throw a cube down into a portal and it shoots out horizontally from a portal on the wall then momentum wasn't conserved
the hula hoop example is fine because you still have the cancellation of the motion of the exit portal and the cube being pushed through
Nope. e=mc² applies in both scenarios. Speedy thing goes in, speedy thing goes out. It does not matter how the relative speed came about. In fact, the portal paradox is nothing more than people arguing against relativity.
It does not matter if it's the cube moving towards the portal or the entire planet being lifted up to the portal by a piston. The difference in speed remains the same. The only argument there is room for is whether the game is programmed with realistic physics or inconsistent and arbitrary ones. And in my opinion, any portal mechanic that doesn't impart momentum in such a scenario has sloppy programming if momentum is supposed to be preserved between portals.
The hula hoop analogy and your explanation for how it worked was solid and earned my subscription!
also "i value your time more than my retention rate"
simply based.
Absolutely. I got about halfway through the video, sure that the answer was A, and spent about 30 minutes thinking about it, looking it up, and reading the comments before I understood why B makes more sense. Then I resumed the video and he answered it in 30 seconds lol.
Except it's wrong. We've actually demonstrated this as false as we've created "white holes" for qubits that instantly communicated information over distances and didn't impart any extra energy when doing so.
All you're doing is taking the outside of a window and moving it somewhere else. Just as if you had stuck your hand through a window you would not get flung through it, the location of the exit is all that changes. If you drop a hula hoop over yourself you are not flung out the other side.
Not only does he lack a basic understanding of inertial frames of reference and light cones, but he's asserting that the universe has an inherent "orientation", or an up and down locked to one position in the universe. This is a very stupid idea postulated by flat earthers, and has been debunked at every turn.
@@xelgodis80085 lmao, it must suck to be so conceited you can’t finish a video before rage commenting. You literally just used the hula hoop example that the video proves is different from the Portal Paradox.
@Scottish Cheese except both he and you don't understand inertial frames of reference. If his model held true, light itself would be accelerated through a portal, which is stupid to say the least. It's a white hole, and the laws of thermodynamics are conclusive about the effects of a white hole, and have been demonstrated in real lab settings.
That you lack the fundamental knowledge to begin understanding *why* you're wrong isn't my problem. Grow up.
as some kind of physicists I strongly support this interpretation, the velocity of the cube relative to the portal should be what counts
It just depends on how you define the portal. After all it's a fantasy concept.
I would define it so it doesn't jump. Because in this version the portal would have to exert some kind of force on the cube to accelerate it, which sounds wrong to me. Also the laws of constant momentum would break down.
@@0ntimetaiment921 In order to understand the forces acting on the cube try changing your perspective slightly. Imagine you are standing on top of a moving cart going at an incredibly high speed (somehow not being blown off by the wind), and suddenly that cart comes to a stop. You would fly forward off the cart, right? That is essentially what is going on here, but the portal moving at the cube is turning the entire WORLD into that cart that you are standing on. Going through the orange portal means that you are "Suddenly not moving" relative to your previous speed so it flies "forward" relative to the blue portal. Another way to imagine it is to simply think about how it would appear in the blue portal should the orange portal envelope it quickly. Imagine the blue portal was on the ground and the orange portal enveloped the cube quickly. The cube would rise from the blue portal equally as quickly right? The cube would be quickly moving upwards and then come to a sudden stop with no momentum in the model you suggested.
@@0ntimetaiment921 Well since it's fantasy and everything goes, I'll say that whenever you go trough a portal you speed up to match earths rotation... because reasons😅
@@VaanOtacon Nicely explained. The model you describe definitely has some merit. But again: It's a fantasy concept, so it's a matter of taste. In your model the cube would still suddenly have energy in the form of movement energy which comes from nowhere. In the the cart example you gave, the person already has that energy since it is moving. With the portal the energy must somehow be transferred from the portal to the cube. But since the portal itself has no mass that makes no sense to me. Worse still: The force on the cube would have to be infinite, since is goes from not moving to moving instantly.
In my model (which is of cause also breaking physics) the portal does not interact with the cube. It is simply a doorway. The cube remains in its relative state to the world instead of the portal. So yes if the portal moves quickly over it, it simply appears in the other without momentum at all. It rubs you the wrong way, since you say "it moves but then suddenly stops". In my interpretation it would not move at all though. You would simply move the "doorway" around it.
Neither model is completely satisfying, since portals are inherently against the laws of physics. I guess it's a matter of personal experience and taste what put's you off more.
@@BxPanda7 Actually I once wrote a fantasy story with portals. And one day I woke up and realized exactly this problem.
And yeah. I just "solved" it by saying "it just works in this magical world, ok?".
And I'm not ashamed of that. It's either that or never ever writing fantasy stories at all.
EDIT: It's all about pushing the absurd to a point where it bothers people the least. Most people do not think about the fact, that earth rotates and the moved around the sun at absurd speeds.
What bothers me about this problem and this solution is: what exactly gives the velocity to the cube?
From the cube's perspective, what pushes it away from the floor? Does it suddenly feel a force upwards and away from the portals? How does the Orange Portal transfer it's velocity to the cube if it never even touches it?
Say you place a portal on a ceiling and another on the floor and you drop a cube into it, allowing it to fall infinitely. As it passes through the portals it keeps picking up speed and if it wasn't for air resistance it would in fact pick up speed forever. Where is the energy coming from in that process? You might say gravity but no amount of height would allow you to fall at speeds reaching the speed of light within earth's gravitational field. No the portals themselves convey energy to objects that pass through them simply by their very nature of being able to transport objects to disparate points in spacetime.
But to give a more practical answer, the cube essentially pushes off of itself and the floor below it. Looking at purely the blue portal, what you would initially see in slow motion as the orange portal descends, is a small portion of the cube sticking out of the blue portal. Then a moment later more of the cube would be sticking out of the portal. But that would mean that the first portion of the cube would have to have moved out of the way in order for that to happen. Essentially the lower portion of the cube is pushing the higher portion forwards in order for it to exist the portal. And then the next portion does the same and so on and so on. By the time the cube fully exits, the entire cube is moving at the same velocity as the orange portal.
@@BlazeMakesGames No, it wouldn't keep picking up speed. The energy comes from gravity, that is a fact. You're in freefall, like jumping off a cliff, but you keep teleporting back up. The portals are doing absolutely nothing. The cube would reach terminal velocity and it would just keep falling at that same velocity. There is a limit to the speed. If we were in a vacuum, and you tossed a cube into portals that faced each other, the cube would keep the velocity you threw it at, because there are no other forces acting on it. If none moving portals did act on objects going into them, then everything would be shot out of stationary portals equal to the amount of force they exhibit. however, the portals do not interact in that way. They do not interact with objects going through them.
Portals are more like doorways. If a moving wall with an open doorway came towards you, and you go through, are you inheriting the wall's velocity? The difference here being the space on the other side, and how the forces on the other side interact with you, not the portal.
@@BlazeMakesGames By your definition, if you even touched a portal, it should suck you through it. On your gravity example, if you had infinite height, with a constant acceleration due to gravity, an object would speed up to its terminal velocity. This is what is happening in your example. This just can't happen outside of portals because A: get too far from earth and gravity decreases, and B: get too close, and the ground stops you.
The portals really just move one location in space to another, they don't pull objects through themselves (unless one is in space, sucking objects in because of the pressure difference).
@@ianwalsh3868 So portals work literally like doorways.
@@fantastikboom1094 Yes, that's my understanding.
“Moving portals aren’t implemented in portal”
That one random moving portal level in Portal 2: 👀
What level was this? I don't remember
@@LotharLivewhen you destroy the neurotoxin with lasers
Iirc, that’s a matter of just changing a single value to allow for it, but the logic required for the portal paradox isn’t implemented, as it was never intended to be used outside of that set piece.
So instead of either result happening, the box doesn’t go through. I may be wrong, this is just going off of what I remember.
@@MasterHyperionMC if the portal paradox was correct, moving a portal at a laser would accelerate the photons in a laser beyond c.
@@xelgodis80085 Ok? I feel like I’m the wrong person to say this to, given I didn’t actually express an opinion either way.
What happens if you stop the moving orange portal while the cube is only halfway through? Would the momentum of the cube coming out the blue portal make it so the cube gets sucked inside the the orange portal and out the blue? If it doesn't go fully through, would it at least jump up a little?
I wanted to see this too!
I think that the cube would stop moving when the portal stopped moving, that's almost entirely based on my own intuition though
here's my hypothesis (at least in a real-world physics sense, no idea about his engine): in the instant the orange portal stops, half of the cube has had the momentum transferred to it, while the other half hasn't. therefore, the cube will only receive half of the momentum! the non-moving part gets pulled along by the moving part, and the moving part gets slowed down by the non-moving part. so, it'll still be launched, but only half as far!
I think it would still get launched, just not as far, like if you threw a ball, but stopped your hand halfway.
in-engine, it will probably either move or not depending on which side the origin position of the object stops at. in the real world or a physically accurate simulation, the momentum would be imparted in proportion to the weight of the object on either side of the portal
@@axollyon Agreed. For completeness though, if the cube could deform, the resulting tension would actually _stretch_ the cube.
Funny thing about moving portals is that they are in portal 2 when you're using lasers to cut the neurotoxin tubes
And they are so frigging bugged
yeah they're also in the hydra DLC
They're not accelerating though. Earth is rotating at fixed speed so all portals are moving
@@pinwheelmotorbike Gravity is acceleration. So anything on earth IS accelerating as is everything else in the universe influence by gravity fields.
@Vaasref
I mean your conclusion is kinda right because relative to a fixed point in space earth is accelerating and so am I but saying gravity is acceleration is a gross oversimplification and the way you worded it implies that I am accelerating downwards regardless of the normal force from my chair right now… TLDR all motion is relative, including acceleration.
Portal 2 actually has _two_ examples of a portal on a moving surface. When we shoot a portal at the moon at the end of the game, it's easy to forget that the moon is actually moving substantially fast relative to the Earth. The moon portal is moving like 4000 km/h relative to the Earth portal, and yet when Chel and Wheatley enter it they aren't suddenly launched off the moon's surface at mach 3.5. The portals preserved their relative speed, as in this video.
Here’s the second example of a moving portal
th-cam.com/video/mCQiwhik8nc/w-d-xo.htmlsi=eNjSeNuZoeoGpVRC
@@ThePokeGod That's actually the one level in the entire game where they intentionally enabled the moving portals mechanic
Still: the movement is faked. It's just paralax, the moon does not actually move in engine
But that's an EXIT portal. The Entrance portal is "almost" stationary compared to Chell so there is no "speedy thing comes in" predicate. All checks.
surely they didn't actually model the relative orbital speeds of the Moon and Earth for that so that.
I actually appreciate you using the logic of conservation of momentum to solve the portal paradox. The portal moving over the cube at, say, 60mph, is no different from the cube moving into the portal at 60mph. This is very logically sound and I appreciate your approach
that's why it's not a paradox, it's solved by a fundamental law of physics lol
It is different, by the same logic a cube going 60mph not losing any speed from going through portal proves that portals have no mass, thus a portal colliding with a cube shouldn't increase its speed
I tried explaining this to my dad, he disagrees because the box didn't have energy to begin with. I told him to watch this video later, so hopefully I can win the argument through this video.
@@lasadaf5336 The portal is attached to a piston, which does have mass, therefore energy that can be passed to the cube.
@@lasadaf5336 Portals also create and destroy energy, so really they can behave however people want them to behave.
But you can also think of it that in order for the box to actually come out of the blue portal at all, each part of the box that comes out must be pushed out of the way by the next part of the box coming out behind it, and this will happen at the same speed that the orange portal moves over the box.
It's incredible what people can do, people would do such great lengths to make it possible, I love it every inch of it.
Yeah very cool, although one of original devs stated that should plop down rather than adding velocity.
Realistically wouldn’t a cube be stationary as if on a flat surface and only be affected by gravity, normal, and friction forces once out the other portal. I mean if you did that same thing but stopped halfway through the cube it would be odd for it to fly off the ground and gain speed from nowhere. Unless there are some unique portal physics I don’t know about. It’s a pretty cool video either way.
Portals aren't just doorways, but that completely redirect momentum for no cost. The only truth is that any velocity vector going in, is equal going out. To the Portals, an object moving towards the portal vs a portal moving towards an object looks exactly the same.
On the blue (exit) side, while the entrance side is halfway through, they see the Box emerging at speed. Once the entrance hits the ground, the box is still exiting at speed.
My theory is that a portal stopping half-way over a cube would cause it to partially fly off. Half the molecules of the cube would be stationary, half would be "moving", so the forces would balance out.
In-game, it would probably only matter if the object's origin or Center of Mass made it through the portal plane.
@@Appletank8 They redirect momentum but they don't create it. A portal is like a doorway, connecting two spaces in otherwise impossible ways
Portals do not thrust things out at specific velocities; they do to make the game work of course, but all they do is connect space
I do not see how he cube would gain any sort of momentum from a portal falling over it. The space through the orange portal is dictated by where the blue portal is. And even if that space is rapidly changing, there is no force causing the cube to move
@@100Darkspine technically going from a low portal to a high portal creates potential energy outta nowhere. that's why you can make perpetual motion out of a floor/ceiling pair.
Anyways, the only rule of portals is that if something enters the portal at speed, it will exit at speed. In order to exit a portal at all, you need some sort of velocity, otherwise nothing happens. From second 1 to second 2 of going through the blue portal, the box has a noticable change in position, therefore it now has a speed, Distance/time.
There is no way for the blue portal to tell the difference between the entire room moving at constant speed towards the portal, vs the portal moving at constant speed towards the box, so the results will be identical regardless.
@@100Darkspine
The portals are not creating the momentum. The cube already has momentum relative to the orange portal. Expecting it to stop once it leaves the blue portal is expecting its momentum to change for no reason.
Right when you talked about the "hula-hoop" analogy, it made sense. Everyone proposes the paradox when only taking in consideration the entrance portal, never the exit.
While they make a womehole while in tandem with one another they have their own unique positions in space, be it speed, or direction. Which does make a lot of sense.
My next portal paradox, is what if you do this across lateral direction, while moving?
So, imagine the portals are like the window of a car.
but, because the portals exist unconnected to two different inertial reference frames, then what occurs outside the blue portal, is not connected to what occurs outside the red portal.
So lets imagine you have a stationary red portal. And a moving blue portal.
If you stick your arm through the red portal then your scenario is best described like this.
Everything inside the car, is the red portal. The car is stationary and not moving.
Everything outside the blue portal is sticking out a car window. It is moving relative to the rest of the world. (Great - this explains that you will feel wind on your arm).
But what happens now, when the "blue portal" car stops. Well, in a normal car your entire body would feel a decelerating force and would struggle against it.
The parts of your body in "Red space" are in a stationary car, so those parts feel no decelerating force.
The parts of your arm in "Blue Space" now want to keep moving forward, while the blue portal entrance slows down. But, the tube of your arm in red space is connected physically to the tube of your arm outside the window in blue space.
So now, your arm in red space "Pulls" on your arm in blue space (in the direction of the deceleration the blue portal is undergoing). Your arm in blue space wants to keep going, but the blue portal is changing the acceleration, and applying that via the portal boundary.
Assuming the deceleration the blue portal is undergoing is low enough that it doesn't tear your arm off, you would decelerate your arm to the same relative velocity of the blue portal.
IE, in short, your arm in bluespace would "feel heavy" in the same way that your limbs feel heavy when you slow a car down. And your body (which is strapped in via seat belt or whatever) "pulls" your arms to the same relative velocity of the car. But in this instance, your body in redspace doesn't feel the deceleration, only the arm in bluespace does.
Haha thank you for clearing that up!
There's nothing applying force onto the cube itself...
Portals are basically wormholes... You're treating the ends of the portals as two separate entities, when they're one and the same.
If we're using the logic used for the angled portal, then it should have been shot out the top when it was in the hula-hoop orientation. Simply by adding rotation (180° rotation in the hula-hoop example), doesn't add velocity.
IF ANYTHING, what would occur if the portals were theoretically wide enough, is that you'd be stuck in a constant state of free-fall, until you gained enough momentum from the gravity and/or air pressure on the "stationary" end of the portal, to reach the edge of the portal.
Think of it like this. Assume you're floating in space. And both ends of the portal are 1km wide, and the orange end is moving at you at 100km/h. And the blue end is moving in the opposite direction at 100km/h as well. You'd be in a constant state of free-fall until you gained enough momentum to reach the edge of the portal. Remember, the portals are one and the same, the physical space between each end is arbitrary.
In this, the portals act like a small scale black-hole, requiring you to increase your momentum beyond that of the wormhole in order to escape. The wormhole isn't imparting momentum onto you.
@@notmyregret No, it isn't. But you already had momentum when you went in.
it always makes sense. its a easy physical behaviour. it was never paradox or a problem
You could show a case where the blue portal isn't directly above the yellow but is still moving down to show the effect as well.
Well, that's friggin cool. 😲
I'd also argue that in theory the orange portal should experience resistance when it hits the cube, such that it performs equivalent work to flinging the cube out of the blue portal. That conserves energy-though not momentum, because having portals facing different directions has already broken that permanently in this universe.
My position is that to properly use conservation laws through portals you must use the reference of the portal, in this case to conserve energy, velocity, relative to our reference, must remain constant at input and output (ignoring non conservative forces obviously) if we consider the portal as a system energy in must equal energy out… in any case energy is not conserved as potential energy can be increased with a portal eg perpetual motion machine using portal on floor and ceiling.
@@DracoTorment The object traversing the portals is ALWAYS the reference frame. Portals are only transformations of the vectors. If a person sat on the floor and the portal slammed down around them, they would feel acceleration and would fly out the exit. This is consistent with he person's interpretation; if they'd looked up, they would have observed the wall and ceiling careening toward them at speed, a sight consistent with them flying out the exit at speed. Further, we know the object's reference frame is the only view point we should examine because it is the object which possesses the momentum, velocity, and energy we are concerned with. The portals are just a boundary in space with an appropriate transformation that stitches space together at that boundary.
I've always wanted to know for sure what would happen if a person/object was between two moving walls, both with portals on the surface, as they move towards the person/object from either side.
My belief is the person/object would make contact with itself on the sides facing the portals and then crush itself - though the physics are hard to imagine, because if the portals went perfectly over them/it, then in theory there'd be no resistance placed onto the walls to prevent them from fully closing and having the person/object perfectly pancake themselves imbetween.
Others believe you'd somehow stumble into some kind of imbetween portal space, though I believe this doesn't add up, because they're portals and not wormholes - there is no space between one portal and the other which one has to traverse to reach the other side.
Generally in a case like this, any theory that violates physics is probably wrong. Sometimes a theory makes no sense but the math all checks out, and it turns out to be true. The mystery then is figuring out why it works that way. In this case, I feel like pancaking something between the portals is probably wrong, as is the in-between space, as neither seems consistent with what we know about physics. A more logical outcome is for the object to exert a force that prevents the walls from closing completely. How is anyone's guess, but it probably depends on how exactly portals work in the first place. Or something else might happen, which would lead to new discoveries in physics.
@@Greywander87 Perhaps some kind of force would be exerted on the walls when the two portals reach the edge of the person/object they're simultaneously closing in on - but that would rely on the portals themselves being receptive to resistance, and them then also transferring resistances onto the surface they're on - imo that doesn't add up logically.
E.g. if you had a portal on one unstable and loose wall (say an office wall tile) which someone is primed to run and jump through, and a portal on another wall which is solid, and then you seal that portal off by placing another solid and immovable object infront of the portal the person would be exiting from, the person moving through the entrance portal would be meeting that object blocking the exit portal, exerting force on that - both the portals and the walls they're attached to encounter no resistance or force.
Imo this is why a person stood between two portals moving towards them would simply be pancaked by themselves by a force that encounters no resistance from said pancaking - it would in theory work with infinite mass but relative velocity.
I feel like, it'd be the same as imagining that your left and right are copies of you, being pushed towards you, then my right shoulder gets pressed against the right copies left and vice versa. They keep pushing more, with deadly force and all 3 of us (tho we're all just 1) are squashed
I think the most intuitive way to answer these questions is to convert the problem into an equivalent one where the portals do not exist. If you were to instead have two people stuck between what is essentially a hydraulic press, then yes, they would be pancaked.
This technique helps solve the subsequent question of whether the portals would need to exert additional force to pancake the person - they would, since the press would. This conclusion is supported by the requirement of energy conservation, as energy must be expended to deform an object.
@@the1necromancer I think you're overlooking the fact that the portals are the whole point of the thought experiment though - they don't obey any known laws of physics, hence why it's so interesting to speculate how a portal (as depicted in the game) would function in ways beyond what is demonstrated - it's more about intuiting the information about how the portals work that we already know - they're not wormholes, they're seemingly without a physical presence themselves, they're simply magical doorways which can be dynamically relocated.
The moving walls with the portals on their surface would provide the velocity at which something is pancaked between them, but they don't tangibly interact with anything except the surface they're placed on (they stay relative to it) - the surface doesn't experience any resistance or impact or any sort of force from an object passing through a portal on it - therefore we have to assume if two portals simultaneously moved across either side of a person meeting in the middle of them, that the person would be crushed by themselves in a manner where no resistance is experienced by the walls (unless part of the person sticks out beyond the surface of the portal.)
Where does the energy to move the cube come from? Does the piston feel resistance as it transfers energy to the cube, so as to launch it?
What I find weird about it is that it implies when you move a portal, you're effectively moving the entire world towards the opposite end
but that's how relative speed works, doesn't it?
yes it doesn't make sense, the object should maintain the velocity relative to the plane
this is a big issue people are trying to solve about "how would a real wormhole act"
as it is simply a tunnel from one point to another based on general assumptions and maths - and by that, moving the tunnel, if it were to serve for instantaneous traversal, would likely yield a similar result
and the way a portal's function is described is not entirely dissimilar from a wormhole, and in fact, people study the idea that maybe portals if achieved like this in real life would actually be wormhole technology.
@@KingOfRedPlays I'm a bit curious. What is more realistic, a portal that is simply a hole and has an exit somewhere else? Or an actual tunnel with a bit of length to it?
@@amitbar5691 I don't know... For the cube to shoot out like that, it must have made a pretty big impact. And I mean, the impact doesn't have a limited range, after all, or does it? It has to be the entire universe colliding with itself, unless there's a logical error in my thinking. Maybe this is actually realistic given we accept the idea of portals, but it seems to give portals a ton of power that goes beyond traversal which doesn't seem to fit the use case they've been assigned in-universe
Then I think it also gets even weirder... because if it works like this, then the entire gravitational force of the planet must have an effect through the portal onto itself, so frankly, I can't imagine that it could possibly physically work like the way he coded this
i like how you showed the results first. it really hooked me and made me want to see the rest of the video. super interesting !
I'm actually really glad that you brought this question up because I decided to wrack my brain on this question as a serious question regarding what would really happen, suffice it to say that yeah, GLaDOS literally explained it, speedy thing goes in, speedy thing goes out, and that speedy thing is from the relative point of view of the portals which from their view are always stationary while everything else moves around or through them.
A fun side piece I realised though is angular momentum and forces acting through a portal, as well as a very interesting scenario of "What happens if the portal stops half way? Does it stop like nothing happened or what?", and the answer is "moment of inertia still exists, however much mass passed the portal will have inertia, pulling on the rest of the mass of the object through the portal like a harsh yank but through the entire intersecting plain.", which leads to very weird potentials of indirect forces acting on portal surfaces.
I don't remember everything on the matter off the top of my head as this was like a year and a half ago that I thought about this and logically approached it as, but there's a lot of weird and cool edge cases regarding physics and portals, I have the entire argument and logical set written down somewhere if anyone wants to chat about it as it's a very interesting extended problem.
I've also thought about these some time ago. iirc If you place the exit portal on a rail, facing a wall, and then start pushing a long stick into the entry portal, when the pole touches the wall, instead of stopping you from pushing further, the exit portal will start moving on the rail, even though it's not in contact with anything. super weird behaviour but that's what makes it interesting!
As much as I’d love to talk about this privately, I feel like it actually deserves a video of its own 😁
@@kantoros Ooh! Very interesting.
@@kantoros yeah, that leads into the whole "weird potentials of indirect forces" thing.
On the one hand, in theory, there shouldn't be any effect on the portals as they are not being contacted.
On the other hand, in theory, there _should_ be an effect on the portals due to their ability to impart moment of inertia.
And while I don't remember my original conclusion, I'm actually leaning toward the latter thanks to some recent physics concepts I came to know about recently.
The way it'd work would likely end up acting like an air spring or pneumatic piston with a pressure gradient leading to a "spooky force acting at a distance" to appropriately quote Einstein.
You're still applying force to the wall on the other side of the portal, but with it acting as a stopping, stationary force, the force will instead start being imparted on the portal as it effectively acts as an inverted form of the same effect that causes imparting of moment of inertia.
@@RonWolfHowl dude I would _love_ to make a video on this but I do not have the means to do so on my own, and it's kind of sad given there is an absolute ton of amazingly fun nuance to the brain breaking physics of this that would be amazing video content.
For example a visual representation of exactly what is going on with the other reply I just made would work wonders for explaining it better.
It also just sucks in general because if I had the means to making a video on this subject I'd also absolutely be working on the two portal 2 mod campaigns I've been writing up every now and then when inspiration strikes. Moving portals and their properties was going to be a thing I was going to attempt after having thought about them and their physics.
Sounds right. reminds me of Tom Scott's video on that unconventional auger wherein the tube and its openings are spun, but the auger itself remains stationary yet still elevates grain.
Also when you think about it, on a cosmic scale, all velocity is relative.
The Wuffle house has found it’s new host
Just a nitpick, the physics of the rotating auger aren't the same as the physics of the stationary auger with rotating shaft, I believe the grains will move in distinguishable ways and have a different stress distribution. This is because in Newtonian mechanics rotating reference frames are non-inertial and so aren't related by such a simple transformation. Fictitious forces such as coriolis forces and centrifugal forces appear in them. Read about Mach's bucket experiment. In an idealized Newtonian (non-relativistic) universe, spinning the entire universe around a bucket won't cause the water to form a parabolic curve on its surface.
unless its light, that speed is absolute
haha I love that all of my favorite niche projects wouldn't exist if talented people like you didn't just do it for no particular reason but to satisfy your passions/obsessions. And the world is a better place for it.
So this is basically the same as the "shooting a cannonball from a moving car" experiment from Mythbusters.
Id love to see a video on "shooting the cube in to a portal where the exit is moving the same speed as the shot cube but in the other direction (maybe for when you imolement the bouncy pads (if you haven't done that already))
this is sick! glad this got in my recommended, this sort of project is right up my alley. looking forward to more.
The portal shouldn't have velocity.
The experiment you showed at the start, at some point deletes the cube on the orange side and spawns a new one on the blue side. Portal allows you to put things halfway through a portal. What would the result of your experiment be if you stopped to orange portal 1/3 of the way through the cube? What about 2/3 of the way?
If I were remaking portal, I'd have two rooms. You can mirror all the object states in both rooms. Chel would not notice that there are two rooms because the object states are mirrored. When Chel goes through the portal she walks into the other room. In the case of our cube, when the Orange Portal interacts with our cube, it would come out of the Blue Portal in room 2, and the cube in room 2 would come out of the Blue Portal in room 1. Since the cube didn't have any movement it would still be resting on the surface of the floor. However that floor is at 45% at the Blue Portal position. At that moment, the force of the box is still 90% to the floor (where gravity was), but 45% to gravity (where it is now). This would cause the cube to begin spinning violently forward, as it normalizes those forces through rotational energy.
Basically, the object has the same velocity to appear in the other side but without momentum.
If the mass is uniform, you can assume a very proportional relationship between the resulting speed, and the distance the moving portal goes over the object.
1/2 the distance = 1/2 the exit speed
2/3 the distance = 2/3 the exit speed
and so on
I’m really torn on this, I may lose sleep over it, thanks for making it in N64 though, keep up the good work!
I love that you're just saucy enough for the people who are inevitably going to kludge together rebuttals to the really well-explained mechanisms you've posited.
My issue is that the hula hoop analogy is always how the portals work. They're just holes, the ends just happen to not physically connect. There's no reason for the energy of the portal to be conferred to the cube. Momentum is conserved between portals as well as the lack thereof. All of this with the caveat that I flunked out of high school. Regardless, loving the progress on the project, can't wait to see more!
I think if one portal moves, the other would have to move, too. The energy transfer from the portal to the cube seems to be a trick that gets around the space/occupation constraint on the other side.
Normally the entrance portal is static. This means forces acting on the cube have to push it through the portal. But if the portal moves, how is there going to be enough room on the other side, if the cube is not moving? I think the relativity trick is just a trick.
Or the portals are actually atom rematerializers.
@@user-zu1ix3yq2w I just assumed these things were like Loony Tunes holes.
Portals convey energy to what passes through them all the time. If you simply place a portal above another portal and pass an object through it, then it has just magically gained energy via passing through the portal. After all think about the times when you place a portal on the floor and ceiling of a room and fall infinitely. You continuously build up speed because the portals are in effect conveying energy to you by granting you more potential energy than should be possible.
Momentum is conserved through portals, but energy is not. Similarly if you go through a high portal to exit at a lower elevation, you will have effectively destroyed energy as well. Portals by their very nature allow you to create and destroy energy at will.
@@BlazeMakesGames In your example the energy isn't coming from the portals, it's coming from gravity. With nothing to slow an object down, gravity will cause it to accelerate through the portals until it's stopped. The energy is not magically gained. Momentum *is* energy, and is conserved through portals, but the portals themselves neither add nor take it away from the object.
wait but isn't the blue portal also moving relative to the cube when its stationary? because out the blue end is the orange end which is moving towards the cube, so those 2 should cancel out just like the hula hoop thing.
Correct, this guy is an amazing example of the dunning kruger effect.
Imagine looking through the stationary portal as the other one is going towards the cube in a void with no other point of reference, it's impossible to tell if the portal or the cube is moving since motion is relative, so the scenario with the portal moving has to behave the same as if it was the cube moving
@@heretichazel irl there are other points of reference like the level the portals are in, and especially the portals relative to each other, yourself looking through the portal and the cube. As well this is a video game meaning all speed is mostly objective with set numbers.
@@gdeveloper3309 I'm saying with no other points of reference just to get my point across, since the room existing doesn't change the physics of the situation
@@heretichazel well now that there are other points of reference, its easy to tell if the portal or cube is moving.
In both relative examples the cube and orange portal move closer to each other which makes sense, but i think its a different story once the other side of the portal/the blue end is taken into account.
Once the blue portal is taken as a point of view, anything that moves through the orange portal, winds up on the other side. Once the orange portal engulfs an object, it winds up on the blue side, and once an object is on the blue side, no portal or anything is moving to engulf it or transport it anywhere else. So any portal moving towards an object should just plop it to the other end, and once its on the other end, it just stops. If the object relative to the blue portal is moving, while the orange one is staying still, then it fires through the blue one.
The space between an object and the otherside of the blue portal is cut/gets closer the more the orange portal moves towards an object, but once the object is finally through the orange portal, there's nothing making the space closer to the other end of the blue portal imo.
As well, this version/solution to the portal paradox is a tiny bit easier to implement code wise because no properties of the portal change, except that they move now(anything that goes in, is on the other side). This would also solve stopping the portal halfway on a cube.
I think the correct version of the hypothetical would be if the blue and orange portal were back to back moving towards the cube, because then like the example was, it would be impossible to tell whether or not the cube or portals are moving, but it wouldn't matter because relatively the cube would still be flung on both ends (because then the blue end would also be traveling away from where it spits out the cube)
With a moving orange portal in your example, to me it always seems like the other end of the blue portal/whatever comes out of it is constantly moving away from the blue portal even if the blue portal is staying still
The stopping the portal is also a bit strange to me, in your hypothetical, since its impossible to tell if the cube or portal is moving and should therefore behave the same as if the cube were moving towards the portal, would stopping the portal stop the cube or does it fire through? if it stays still, it means there was never any momentum to begin with, if it keeps going, then that means everything relative to the stopped portal has to keep going towards the portal as well, unless there's some seemingly arbitrary rule that the speed effect only happens once you get through the portal which im really confused on
The other form of reasoning I use to come to the same conclusion is to try and think about the situation 1 frame at a time, for lack of a better term. When the Cube first has the moving portal coming down on top of it, then that portion of the cube is sticking out of the other portal. 1 Frame later the entrance portal has moved down slightly and thus more of the cube is now sticking out of the exit portal. But in order for that to happen, the portion that was already sticking out of the exit the previous frame had to have moved out of the way. It is essentially pushed by the previous portion of the cube trying to make room for itself. And the speed at which it was pushed would be equal to the speed that the entrance portal is falling down over the cube.
So while the portal is falling over the cube, the cube must be moving in order to physically move through the exit portal. But maybe it doesn't move beyond that point? Well that doesn't make much sense either. When the entrance portal finishes hitting the floor, the cube will have still just been moving due to it pushing itself through the portal, and inertia would still apply. So it still needs to lose all the energy that it just gained. There's nothing stopping it from moving other than gravity and air resistance. So it would slow down accordingly to those properties. Thus if the portal was fast enough to launch the cube, the cube will naturally fly out the other portal.
The other counter argument I've seen is that it doesn't make sense cause there's no clear source of the energy that propels the cube out of the other portal. but this is simply a fundamental property of portals as we see them. The simple act of placing one portal above another one creates energy from nothing. After all if you put a portal on a ceiling and floor and ran water through it, you could have a perpetual motion infinite energy device if you stuck a turbine in it. I mean you can do this in-game after all. So while I do argue that Newton's Laws still apply to the physics of portals, they do inherently break the fundamental law that energy cannot be created or destroyed. (similarly going from a higher elevation portal to a lower one effectively destroys energy as well)
Waitttttt that’s a really good explanation! I still didn’t get it after the video until I read this, but that makes sense to me! (Much more than some coding equation)
very good explanation
This is a fundamental misunderstanding of what a portal is. You assume that the cube is being moved through the portal, that it had to gain some energy to continue to push through threshold. This assumes that a portal is two separate objects. A portal is just a hole. For all intents and purposes, it's the exact same as dropping a hula hoop on a cube. The hula hoop represents a singular hole in space that is itself represented by two portals in this scenario. The entire hole is moving (which is NOT represented in the video, and why it only works when setting it up as a single moving hole in his engine). There is no force to overcome. When the moving portal has firmly stopped against the ground, the cube is still sitting on that ground. Any movement of an object that has a portal dropped on it is purely an illusion. The object has not moved. It is still sitting where it started. The only difference with an angled platform is that the axis on which gravity effects it would change and eventually drag it off the platform, provided the ground and cube themselves are not providing enough friction to counter that.
You also never create energy from nothing in Portal, nor do you destroy energy. The terminal velocity example you mention is simply providing an infinite corridor in which something can fall to reach terminal velocity due to gravity. You aren't creating any energy with the portals. As far as destroying energy, we don't do that either in the game and I'm not entirely sure what example you were trying to give for that.
@ChaoticNature portal above portal. place a copper coil around this collumn and drop a magnet through. boom- infinite electricity. how is this not creating energy out of nothing?
@@sydssolanumsamsys You're mistaking the conversion of one type of energy into another with the generation of energy. You're converting kinetic energy (gravitational and magnetic) into electricity. The portals themselves are making no energy, they're simply removing the work needed to reset the magnet to the top of the coil.
That's also not infinite as the coil would heat up, and beyond a certain point would melt and break down the system.
This video is absolutely correct in all regards.
The thing that people are missing about slamming down the portal that's blue on one side and orange on the other (the second experiment here) is that the orange and blue portals actually have the same velocities as each other, they're just also pointing in opposite directions. It's easier to think about the portals as having an in vs. out reference frame, rather than up vs. down or any other kind of reference frame.
If blue is stationary and orange moves toward the cube at 5 m/s, the cube will enter orange (in) at 5 m/s and exit (out) blue at 5 m/s. But in the experiment the "out" direction of blue is effectively moving at -5 m/s, not zero.
For another example, think about throwing a baseball. If you're on stationary ground and can throw a baseball at 20 mph, your throw makes it go 20 mph in whichever direction you threw. If you're on a train moving at 20 mph and throw it in the same direction as the train is moving, someone standing still will see a baseball moving at 40 mph. Conversely, if you throw it toward the back of the train (away from the direction of motion) a stationary observer would see the baseball stop and fall straight to the ground.
In all cases you have moved the ball in the same way relative to your own motion, but outside observers (us) see very different things.
To bring it back to the cube example, imagine instead that both portals are on vertical wall pieces, with the orange portal moving toward the cube which is sitting stationary on the ground. The blue portal is on a different section of wall and moving backward at the same speed that the orange portal is moving forward. Any motion conveyed by the orange portal running into the cube would be cancelled out by the backward motion of the blue portal.
The orange portal is essentially "throwing" the cube at 5 m/s, but it's on a moving train (the blue portal) and so it just stops and falls to the ground like the baseball.
This approach doesn’t quite work with the way I’ve always thought about portals, as doors. Is there a good analogy for this kind of approach?
Think of portals like double doors, but ignore the space in-between, and the doors can also move separately. If you throw a box through them, they may as well be normal doors. However, if you were to somehow pick up the first door, and then slam it around the box, then the box would be moving relatively fast as it inters the first door
And since it's connected, it would exit the second door with the dame relative speed too. But if the second door were moving, then you add lr subtract momentum, like when you throw a ball in the back of a truck.
Portals are basically kinetic energy / potential energy translations. If you have a velocity difference between them, it translates onto the object passing through. An object passing through a portal higher than another is just an object going through an instantaneous PE adjustment in the form of space displacement . A moving portal is basically a KE translation, which necessarily involves a velocity difference between frames of reference.
This is the best reasoning I found so far, nicely said!
why do we imagine that a portal separates spaces and if the portal moves, then its space moves? It always seemed to me that the portal only teleports objects while maintaining their kinetic force, only in the case of the game Portal this force rotates at the angle of inclination of the portal itself
@@TheDEFCHER If you put the portal at a higher altitude, you already have a change in potential energy, and if you consider that velocity also varies according to how far away it is from the center of Earth's rotation (or when faced on a completely different orbital body like the moon), it will also necessarily need to have a change in velocity which also requires a change in kinetic energy.
When you go out of the moon portal, you do not get flung at the speed difference between the orbital speed of the moon and the velocity of rotation of the Earth, which is a difference of several hundred kilometers per second.
There's really no argument, just unwillingness to see that potal physics would just be too inconsistent otherwise.
My question is what happens if the descending portal only descends half-a-box's height from the floor the box is resting on? The half below the portal is unaffected, but the part passing through gets momentum. I'm guessing the part passing through pulls on the part not passed through the portal and it comes out but with a slower velocity.
I was wondering something similar about the situation. Is the cube still affected by gravity?
the net velocity of the cube is zero as the two directions cancel until more than half the cube has moved through the portal. if the portal continues down it may eventually be overcome by gravity, otherwise it will only move maximally at the speed of the moving portal. energy in = energy out
Nobody knows the answer because we still don't know how it would look like in reality
@@realdragon i disagree, in the game and in real life it is just math. ask something like chatgpt or wolframalpha
@@JohlBrown You can rocketjump in games, it's just a math but I can assure you in real life it does not work like in games
No arguments from me. You are spot on. It's like being on a moving surface 10m long that goes at 10mph in one direction and you run along it at 10mph in the opposite direction. When you reach the end and the surface disappears beneath you there is no forward momentum. You will drop straight down because you will have been occupying the same lateral position in space at all times.
It's the same when you drop two back to back portals over a stationary object. It will enter the down facing portal at the same speed as it exits the upward facing portal. Both portals will also be moving downwards at the same speed as the object is travelling through the portals. The position of the object relative to the space outside the portals will remain the same. Exactly as if you dropped a hoola hoop over the object.
The problem with this implementation is that it doesnt take into considering the mass of the cube and its inherent inertia. Mass at a standstill resists being moved, instantaneous acceleration would logically not occur.
I like to imagine attaching cameras to different things
Like imagine a camera being on the cube, and a portal is hurdling towards you. Itd be weird to suddenly accelerate off the floor as soon as the portal passes through you.
But then attach the camera looking into the blue portal, youll see a cube hurdling towards you, but then it suddenly loses all of its momentum once it passes through the portal
Either way it doesnt make sense, but, I think it makes MORE sense if the cube gains the acceleration instantly, because its not like the cube can come out of the blue portal at a standstill anyways, since the top of the cube will be sort of pushed out of the way by the bottom of the cube.
Im still thinking about it though, I might change my mind
Why is instantaneous movement allowed between stationary portals but not instantaneous acceleration between moving portals? Energy is not conserved when going through portals.
@@asterpw Yeah exactly. I think glados even makes a reference to that in one of the portal levels, something like "observe how these portals conserve momentum, or to be more precisely, how they do not"
I’d love to see how your game engine handles the orange and blue portals both moving but at different velocities, i.e. the orange portal moves down onto the box while the blue portal is elsewhere moving at a different velocity than the orange portal (and perhaps even at different angles to see what affect gravity plays). Particularly if the blue portal is moving in the same direction as the orange portal, how does the cube handle going from one to the other when they’re different speeds?
He did it already! the first experiment that is shown is exactly that. as you can see, the angle of the blue portal is not the same as the orange, and both move at different speeds, all that will happen is the speed of the cube will vary in the exit following the equation he proposed
While both portals were moving at different velocities, one portal was _not moving_ at all.
@@DWal32 Mathematically that is just a different speed though. Going by the equations shown in the video, only the relative velocity of the portal and object matters, so varying the speed of the blue portal only changes the resulting speed of the cube as it flies (or plops) out of the blue portal, maintaining the relative speed between the cube+portal system.
@@DWal32 In terms of the math involved that really isn't important. Combining the two velocities and changing their vector would work the same way, just with different magnitudes of velocity input and thus different magnitudes of velocity resulting.
the implementation already handles that because it uses the relative velocities of both portals so you can work out what that would do very easily
I'm not sure if I agree with your solution for the portal paradox, but I'll accept it since you're the developer here.
In my own opinion I don't believe that the portal interacting with the box and shoving it through would change its velocity--- After all, portals in portal are more of a doorframe from one place to another. Instead, I'd believe that it would stay mostly relatively stationary, although it would likely fall through the portal once enough of it is through thanks to its new gravitational pull--- or simply fall through once the portal is flush with the floor.
But I can't say your solution isn't a nice one! I quite enjoy the thought behind it, and the idea of moving portals adding momentum is fun for gameplay reasons--- It has unique potential for puzzles!
yeah, the portal frames are just frames, maybe the portal itself is moving/stretching in another dimension, but i dont think this movement would translate into 3D velocity
I agree with this statement. Its a fantastic solution but does not sit right. For something to move, there has to be a direct force applied. Any object at all times has a bunch of forces applied so if you get moved the forces of that place would then apply, but seeing its, kinda, the same space, nothing would change.
Im not smart enough to even get a grasp on the mechanics of a portal but in my mind portals are less objects and more the same space connected. So the only thing the portal is doing is just changing the relative coordinate of the object entering. Like you said, a door frame.
Thank you for not making a 23 min video, talking about literally everything else before getting to your point. You’re a good dude
the portal paradox gets even weirder when you ask what would happen if the the portal were to accelerate as it moves towards the cube.
I mean, it does. The test shown when it drops is accelerating at -9.81 m/s^2. The blue portal is also accelerating in the opposite direction, so it cancels. Like Portal itself, there's still probably a terminal velocity limit, so it isn't uncapped acceleration. Where this still isn't completely resolved is if there is a delay in rematerializing something after it enters the orange portal. If there is any delay, then the cube will have a slightly slower exit velocity than as it was derezzed. That would cause it to be compressed... I probably don't want to be the first living thing to pass through an accelerating portal.
It kinda doesn’t get weirder. In-game it’s just the center of the cube that counts as either being in or out of the portal.
In real life, the cube would experience a “pulling” force (just like with the moving portal) but if the portal accelerates, the force just becomes bigger. As long as the structural integrity of the cube holds, it’s like picking it up with a vacuum hose around the cube.
I think it is introducing some dire consequences. If "cube" has some more traction with the surface (glued, welded, etc), there is potential to tear objects apart.
Also, normally, objects are getting momentum in some natural ways based on their structure/joints, but if the portal is the thing that you are getting momentum from - momentum passing to some 2d slice of an object with is potentially can break it internally.
This would of course be true regardless if the weld/glue/bolts/fasteners by any other name were too weak. That by itself though wouldn't necessarily prove this unsound. Would just mean that if something was weak enough to be moved, it would be moved. Portals rarely care about fasteners anyway, see GLaDOS about all the cameras I knocked off her walls
The issue is not in the cube though. This comes from the portal suddenly stopping after it slammed down.
If the cube were on a pillar the portal could continue downwards, with no damage to the cube. Only when the portal stops moving you introduce an acceleration between the two frames, potentially causing a break in the pillar.
The real issue is thusly not relatively moving portals, but relatively *accelerating* ones
You had me the moment you told me you valued my time more than your retention. Subscription inbound
Thats just not how physics work though. The cube would just follow gravity. Since it's not in motion. If you throw a hoolahoop ring over something, the object doesn't fly out on the other side of the ring. With your logic, a person would be flung out on the other side a portal whenever they ran into one. But they don't. They run through it keeping the same speed on the other end.
I always thought the portal paradox was solvable
MinutePhysics has a great video on the portal paradox. I recommend it, it's interesting!
Why would even someone call it a paradox if there is no conflicting math?
@@expioreris my thoughts exactly.
it aint a paradox if it's solvable
@@zeynaviegas thorough history there are paradoxes that became solvable with modern tech but still are called paradoxes, there's a video on the many types of paradoxes called "the five kinds of paradoxes" by jan Misali
@@expioreris Because there is conflict in math, box suddenly out of nowhere have energy
I like the explaination of the two portals attached to the same object. However I think there's some missing elements to the equation here.
The problem is the conservation of momentum. Say you have a portal (Portal A) attached to a platform which is falling (not powered, just falling due to gravity) towards a box resting on the ground. Portal B is stationary and pointing up. The falling platform has momentum caused by gravity, while the box has no momentum as it is at rest. When the platform reaches the box, in your current setup the box will gain enough momentum to fight gravity as it launches out of portal B, but the falling platform does not lose momentum, so where is this extra energy coming from?
My solution would be, that as portal A starts to envelop the box, gravity acting on the box as it comes out of portal B would cause an inverse force against the falling platform, slowing the platform's descent as it transfers its own momentum to the previously stationary box. This way, assuming the box and platform had approximately equal mass, the box would jump out of portal B at half the speed that the platform was falling, and the platform would slow to half its previous speed as the box is launched.
If the box was significantly heavier than the platform, it may not be launched fast enough to leave portal B entirely, and the platform would come to a complete stop before portal A could envelop the box. This would leave the platform seemingly floating because the gravity acting on the box as it pokes through portal B would be too much for the weight of the platform to overcome.
I'm not entirely sure of this answer, as I'm not sure how folding space would affect the setup. I'm no physicist, but the answer above at least made more sense to me as energy needs to be conserved somehow.
with portal 1, stationary portals, you can fall into a portal and exit through another farther up. You can also simply turn motion in one direction into motion in another direction, with no side-effects. So neither momentum nor energy are conserve in the original portals, meaning there's no reason moving portals should conserve them.
(to b fair, you could say the portals themselves store arbitrary amounts of energy which is used to offset this and that the facility is transferring the momentum differences through earth, but that also works in this implementation so long as the portals are rigidly attached to the facility)
@@user-sl6gn1ss8p Huh, I hadn't really considered that the argument was 'what mechanic fits best in the portal 1 game' as opposed to 'what would happen if portals were somehow real'.
My answer was based on the latter. Though to be fair, both examples you've given don't violate the conservation of momentum due to folding space. If you enter a portal and exit another that is farther up, your momentum is conserved because you aren't moving through the space between the portals. You would exit the second at the same velocity you entered the first, and any new forces acting upon you as you exit (different gravity, inherited inertia from the portal moving, etc.) would only act upon matter that has crossed to the other side of the portal (another explanation would be that there is no 'boundary' between the portals, and instead forces like gravity would cross through the portals as well and interact with things on the other side, but I doubt that matches the game mechanic).
The same goes for changing direction. According to the object moving through the portals, direction is arbitrary. Before and after moving through the portal, the momentum is unchanged, the direction according to an onlooker would be different, but there is no energy gained or lost so no laws are broken.
Yeah. If you wanted to conserve momentum that would make a lot of sense to have it come from the piston itself.
@@superplumpham @Hamish Williams "You would exit the second at the same velocity you entered the first"
you wouldn't though, because velocity is not a scalar: direction matters for velocity, and it absolutely matters for conservation of momentum. If it did not, than pushing something and being "pushed back" would actually break the conservation.
In the reference frame of the room, momentum is not being conserved, since the box changes direction with no associated force. In the reference frame of the box, it isn't being conserved either, since the room itself seems to change direction. That's supposing the portals aren't aligned, which in general they aren't.
Energy is not conserved either unless you postulate portals loose some forms of energy as stuff goes through or something like that, as I mentioned
@@james.lambert so long as you avoid free-falling portals : p
I've never even had N64, but I'm still impressed by this project. Keep up the amazing work! 👍
So appreciative of you not baiting us with the answer, that I watched again months later after having forgotten the solution.
I'm curious in an experimental way: What happens in your implementation, if the movement of the portal stops when the cube isn't completely through? Will the half of the cube that's already throug drag the other half through with half the final speed?
I think Valve had an approach to this where the entering portal had proportional magnetism such that the object would still find its way through in most circumstances. The further the object went in, the stronger the pull was on the exiting portal.
Consider slicing the block in half and doing this. As we've seen, the top half will fly through, and the bottom half will not (as it hasn't entered the portal).
Now connect the two halfs with cable: the top half will fly through, but will have its velocity decreased as it yanks the bottom half through with it. The cable is the same as a chemical bond, so this is what will happen to the block.
If the speed is great enough, the block will jump out the exit portal at a reduced speed. If it is not great enough (or the block is too heavy) then it will just stick out, with the block doing a tiny hop then settling on the ground.
to give the answer to the question - as in what happens in his implementation: Most likely it is done the same as in the original games and the same as nearly every other game.
Physical properties like position, velocity, mass etc are calculate for a single point - the center of mass - that normally is set smack in the middle of the object. So if the portal stops and the center has not passed the middle (so "only" 49.999% of the cube went through) it will just sit there and not move. If more than 50% passed the portal and the center is on the other side it would launch exactly like shown in the video.
However to be consistent with the physics the game tries to portrait you would need to think of objects not in terms of single entities but in terms of the one half that is on the blue side and the other half on the orange side:
If the portal moves exactly 50% down the cube and then stops that would mean that now half the cub has the full velocity relative to the blue portal, while the other one has 0 velocity relative to the orange portal. If the material is not insanely strong it would just rip the cube in half, otherwise it would be the moving part just yanking the stationary part along and it would move with roughly half the velocity.
Kinda like if you tried to grab onto a speeding car.
I guess it depends on how portals work. I always saw them literally as doorways or hula hoops so it would work the same way as literally just passing a cube through a hula hoop, meaning that the hoop has no effect on it at all?
Except for the part where you missed the point
@@DWal32be nice
@@DWal32says the guy who seems to have forgotten that the entire thing is a thought experiment and portals already break fundamental laws in physics, so OP’s interpretation is just as valid.
@@Scuuurbs says the guy who forgot that other fundamental laws of physics, i.e. gravity, still apply, thus this logic is flawed. Appling the same logic as the opening of a container to the openings of a wormhole is the only thing that makes sense.
Quick question: if there's nothing to push the cube how does it gain velocity? Won't it be something like a window that connects two distant places?
Portals already violate conservation of other forms of energy, and, axtually, while they preserve (as far as we know) kinetic energy, whenever two portals are not 180° apart, they violate conservation of momentum
@@pedroff_1they don’t in splitgate
Velocity is relative
The portal approaching the cube is the same as the cube approaching the portal
If you imagine yourself as the portal, the cube is approaching you and if you imagine yourself as the cube, the portal is approaching you
In either case, the cube gains relative velocity, which is translated through the other portal
@@dtstar331 He's asking what is the source of the energy imparted on the cube that allows it to fly out of the other portal. It was initially at rest, and upon exiting the blue portal, has significant kinetic energy.
@@GucciManeSaysBURR
Thing is, techincally the cube wasn't at rest; it was approaching the orange portal. I know, it sounds weird but that's more or less what relativity is about.
If you isolate the system with the orange portal and the cube, you can see they are approaching each other at a certain velocity. Therefore, there was kinetic energy in that system. And this energy was retained by the cube when it left through the blue portal. What changed was the relation between the cube and the portals. When it went through, it was moving away from the blue portal with the same velocity as when it was approaching the orange portal. And so it looked like it was shot out of there
EDIT: I'm bad at explanations, I know
I typically don't like or comment on videos, however I respect the fact the this guy got to the point and didn't drag out the video. I also find his solution to the moving portal questions to the best answer I've heard.
What happens if the portal stops when the cube is halfway through though? The original one should stay still but your teleported side needs to shoot out.
I would say the final velocity would be less than the entrance's original velocity.
You are completely correct in saying that half of the cube should stay still, and the other side should shoot out. But the side that's shooting out would pull on the side that is stationary. The stationary side is accelerated while the shot side is slowed down until both sides share the same speed.
Intuitively, I think it'd be the average of the bottom half's inertia and the top half's velocity (as inherited from the portal's velocity). If only 40% of the box is through, only 40% of the portal velocity is pulling on it.
If it's pulled halfway then stops, I could see the box pulling itself the rest of the way out of the portal then weakly tumbling to the floor; more air-time if the portal gets further down.
Basically 100% portal entry = 100% the portal's velocity; and it scales down proportionally from there. But even at 10% entry there would be 10% velocity trying to pull the box up.
If portal stops immediately, cube would break in hapf because there would be infinite force applied to uper half. If portal stops not immediately, then it depends on how fast the portal stops and how strong the cube is (if portal is stopping slow enough (or cube is strong enough) cube will fly out with half the momentum)
This is so weird to think from the cube's perspective, though. Like Imagine being in its place, you'd see the portal come toward you and then your feet would lift from the ground apparently without any force pulling you.
It would be functionally very similar to being hit by a moving object and having its velocity partially transferred over to it via the collision.
@@Celia_Dawn Eeeh... kinda, but not really. You wouldn't really have an object hit you and transfer its velocity, the portal is coming toward you and then you'd fly in the OPPOSITE direction of its velocity.
I think it's more similar to being in a car moving at constant velocity and not feeling its movement, then hitting a brick wall and flying out of the windshield and die after some agonizing pain because you weren't wearing a seatbelt. From your perspective you were stationary and the wall was coming toward you, then when it hits you you fly out of the car and into the outside reference frame.
...Actually now that I think about it IT IS pretty much just that!
@@KombatGod Portals don't transfer momentum themselves though, they are holes. The Hoolahoop analogy works well, the only different is the space fuckery of the top of the hoolahoop being somewhere else. It's still a hole.
For me I always saw it like a simple door. If you dropped an open door and the frame slammed down around you, you’d still be standing there. But if you went across the frame Mach 1, you’d just come out the other way with the same speed.
Since portals aren’t just doors tho, I can see how you’d carry its momentum into the other side. But it’s weird, because it’s as if the whole room, or the whole OTHER side of the portal was moving toward you. So when the portal slams down on top of you, it’ll be like the whole room was pushed down under your feet which results in you in the air. Same thing you the portal came at you from the side. You’d get through the portal as if the whole environment was moving on one side.
What a weird sensation that would be, one moment you're standing still the next you'd be at great speed but without having felt the acceleration of it. Suddenly being blasted by air from air resistance and seeing the room around you at speed heading towards you.
This is incredible man, original hardware running this feels like a miracle
The Wuffle hose has found it’s new host
@@CBNST the orphanage center has found it's new orphan
@@fran5678can I like the implications of this one
Relative speed is an incorrect logic in this frame of reference.
The cube does not have any force applied to it, therefore it can't suddenly break inertia. The portal moving towards it is akin to a doorframe moving towards you while you are standing still. If the door stops moving while you pass through it, you don't suddenly start moving yourself.
The fact one portal is moving and the other isn't, already breaks the law of physics (since the two portals are practically the same "doorframe", it can't be both moving and not moving at the same time).
Bro really just said that relative velocity is the same as conservation of velocity and then broke conservation of momentum. EPIC!
actually the conservation of momentum stays true because relative to the space outside of the exit portal the the cube is actually moving so as its coming out it gains momentum making it fly off
@@MommysGoodPuppy Couldn't you also say that the space relative to the exit portal is moving towards the cube? The global velocity of the cube is still 0 and relative motion only describes motion from a particular frame of reference
Don't forget that objects can also apply forces to the portal surfaces. If the blue portal is on the ground and the orange portal is on a free-falling panel that falls onto a very heavy object, what happens when the object tries to fall back into the blue portal? It might be strong enough to push the orange portal's panel back up off the ground a bit.
Or it may just hit the floor the other portal is pressed against and stop moving.
You can't apply force to the surface a portal is "placed" on through the face of another portal. If you go in the face of one portal, you come out on the front face of the other. The portal doesn't exist, so there's no way to apply pressure to it. It is just a visual metaphor for the warping of spacetime.
Portals are not affected by change of momentum of the objects that go through it. It's basically magic and never explained. If you think about it portals enable infinite energy generation with infinite vertical gravitational field.
All three of you should think - if you push against a wall through a portal, and the wall doesn't move, but the surface the portal is on is free to move, shouldn't the portal move instead?
@@LB_ No, because your scenario is functionally identical to "there is a wall with a hole in it, and behind it is a second wall. You push on the second wall through that hole and the wall doesn't move, but the wall the hole is in is free to move, shouldn't the hole move instead?"
Very cool! I'd argue that you have to take into account the relative velocity between the 2 portals. If your reference is the orange portal (it stays still) then the box AND the blue portal move up toward the orange portal at the same velocity. So the box enters the orange portal with some velocity, which has to be the same velocity as the blue portal. In that case, the velocity of the box would be added to the relative velocity of the blue portal, doubling the velocity of the box as it exits the blue portal, which is not consistent with another frame of reference.
I think it's less that speed is conserved, and more that energy (momentum) is conserved. In that case, there is no energy added to the box, so it can't change momentum, so it just falls out of the blue portal.
So much more well put then what I was gonna say, yeah no this is a pretty fantastic project and it is very impressive to reimplement portal’s mechanics this way. But yeah sadly I agree it’d be slightly lamer reality lol.
Yeah I agree, but there would be a rush of air throught stationary portal
I think gravity would be more of a factor than inertia. Arguably, the portal itself has no velocity, since it's just empty space. The platform has velocity, sure, but the portal might as well be a hole in the platform. Air would move freely through it, as if nothing were there. The same would apply to the box, no? The flaw in your code is that you designated the portal as an object, and one that has a velocity. The box would, thus, simply fall out of the exit portal, due to an inconsistent gravitational pull moving the center of gravity of the box.
With that stationary test, it seems like the part of the cube that has exited is moving relative to the exit portal. I'd actually expect that part of the cube to have a pulling effect on the rest of the cube (that is still on the other side of the portal). I wonder how far you'd need to extend the entrance portal down, before the rest of the cube is pulled out by this force alone. What do you think?
That's what I thought but as the entrance portal comes down on the object with the same speed the object is technically being pulled out the end while appearing to be stationary. If the entrance portal stopped before reaching the ground but after reaching the object, the object should be pulled out or (if it is not solid enough so not the cube for example) be stretched or teared off.
While, yes the part past the portal excerts a pulling force against the rest, it can not pull the rest through, since it also excerts an equal pulling force against the part past the portal, because of Inertia.
The only part of the force not negated is the effect of gravity.
The cube would fall if half the cube is through and the exit portal is pointing down, and slide to one side if the exit is not horizontal.
Now THIS is the real question.
I would imagine it depends on how fast the entrance portal stops.
If it can stop immediately with no "cooldown", it would probably shear the cube in half in real life depending on the material (in-game it is impossible as the game defines it as a single particle). This is cuz the half that enters the portal would have energy while the other side abruptly stops. It's similar to half of a stick being hit by a moving truck while the other half is anchored in a tree or something. If the material had a weak point, it would break at the weak point instead (as that's how energy travels).
Actually the cube never gains momentum. I don't know how a portal which does not itself transfer its momentum to objects that pass through it makes sense. The portal is a direct spacial link to a different location. It doesn't matter how fast the portal itself is moving.
I think the true "Portal Paradox" lies not in the clear, discrete time behavior of the system, but how the motion works in a slowed, more continuous case that probes that discontinuous boundary and mixed forces/momenta (gravity pulls 'down' on some volume of the cube yet the remaining volume has momentum in non-orthogonal direction). For example, a really tall, stretched rectangular cube and an accelerating portal. What happens in your implementation?
the cube would slide out slowly at first andthen faster ,as the moving portal sped up , out of the stationary portal before being thrown out like in this demonstration. i think
I was also thinking what would happen in the portal's velocity wasn't constant while an object was corssing it's boundary, since e.g. if we stop the portal, the parts of the object that were stationary relative to some other objects around it are expected to remain stationary, but the parts that got through are expected to retain momentum and start pulling on the rest of the object. I guess I kinda answered my question, but it would probably mean that a deccelerating portal would "suck" any object it comes into contact into itself.
As for this specific implementation, it seems to be using a very simple principle and the object is considered to be on one side right until it's center passes the portal, at which point it's teleported (unlike in Portal, where, if I recall correctly, the objects can actually smoothly transition through the portals).
An interesting quirk of this interpretation of portal physics is that if the cube is moving and the portal is moving, the cube will be sped up or slowed down by the portal its moving through which is quite strange and not how I think portals should work they aren't supposed to mess with the momentum of an object. If you just took the *entranceportalvelocity* out of the equation it wouldn't change much other than these strange momentum transfers from a portal to an object.
I think this scenario helped me actually understand what's happening in this video. From the blue portal's perspective it would be as though the cube would be moving towards it, so it would keep that momentum it has coming towards the orange portal
i think
So I guess it would be doing the same with a long cube? I... Assume it would be kinda stuck in place until it fully goes through the orange portal, and then when it exits the threshold of the blue portal it would keep the momentum from the orange portal and plop out? That's my best guess. But this hurts my brain and portal is black magic to me so I have no idea.
Since we're mixing gravity into the equation...would gravity not travel through the portal as well?
Portals are, what, connecting regions of spacetime? So any spacetime affect would be able to traverse the portal boundary, or...? And we know now that gravity travels at the speed of light, so it might propagate out of the portal...
I like to think of the portals in this game as doors
There is no delay whenever you teleport and you can see exactly what's on the other side with also 0 delay, so the portal isn't a physical object and more of a concept, a rip in the fabric of the space-time.
... If an open door comes at some object's direction at any speed it wouldn't be launched. the door's momentum wouldn't add up with the object's because they aren't even interacting.
Your "open door" idea is the same as the "holahoop" idea, but sideways, as shown the box did not move when it was hooped. The issue is one half of your door frame is moving while the other half is stationary, so spacetime shenanigans happen.
@@starburst98 "The issue is one half of your door frame is moving while the other half is stationary"
but in 3D space if you keep looking through the portals while they are moving they still act like a single stationary door, sure the FRAME is moving, but the portal (connection between both frames) isnt, the connection itself is static (in 3D space at least).
I think this movement would result into velocity in a 4th dimensional axis, but idk how it would translate into 3D movement
Correct! This is easily checked by placing two portals so that you can see yourself walking through.
Your explanation is spot on.
What this guy did, was to rewrite the Portal universe in a way that makes his hypothesis is the solution, essentially.
He didn't actually solve anything.
if you still have doubts, think about this: let’s say the cube is 1m long, and the orange portal is rushing towards it at 10 m/s. That means that in 0.1 seconds the cube will be through the orange portal. But think about the blue portal now, the cube should also exit the blue portal at the same speed it entered the orange one, obviously. So the cube will come out the blue portal in 0.1 seconds too. If a one meter cube moves through a hoop in 0.1 seconds then 1/0.1 = 10 m/s.
Great video.
A correction would be thay speed is relative within a inertial reference frame.
Lets determine the objects in our refence frame.
Intake portal carrier
Cube, aka mass
Exhaust portal carrier
In the reference frame, cube is stationary, intake portal carrier has a static velocity and exhaust portal carrier is also stationary.
When the cube passes through intake portal, no force is applied to it.
When no force is exerted. Inertia within the system shouldn't change so cube must be stationary relative to exhaust portal carrier and its relative velocity must not change relative to intake portal.
Thus it should be stationary when it exists the exhaust portal.
Reference frames relative to what though? I would say the reference frame is the other side of the exit portal.
Imagine a point in space a little bit outside of the exit, how fast is the cube moving compared to that stationary point.
In the first example the point approaches the cube at the velocity of the entrance portal, so in the frame of reference of the universe on the other side of the portal, the cube has momentum.
Now take the other example, again imagine a point, above the exit portal. When observed by the cube the entrance portal is approaching, but the exit portal is moving away from the point at the same rate, so the cube is stationary relative to the fixed point through the exit portal.
Looking at frames of reference is a good starting point, but you have to consider the space through the exit portal to be the authoritative frame of reference.
There are examples in the portal game, such as vertically aligned portals, that break conservation of energy, so appeals to that are invalid, infinite gravitational potential energy is trivial to achieve.
@@googlygoink why would you change inertial reference frames mid experiment?
There are no limits to inertial reference frames ? You can be in the same inertial reference frame even if you are on the other side of the universe. Just add a lot more objects to the frame
@@alqualonde2998 because through the portal is effectively another reference frame, the whole universe through the portal is moving towards you when the entrance moves towards you.
there is no consistent inertial reference when using portals like this, unless you consider everything on one side of the portal to be moving, and thinking about the cube's perspective on the exit frame of reference is easier.
In your explanation you say the cube has no momentum before, therefore has no momentum after, but you are neglecting that everything in the universe through the portal has a velocity relative to the entrance frame of reference, so even if the cube is still, the reality it enters is moving, so it ends up launched at the wall.
@@googlygoink ummm just no ?
The reality it's entering is moving ? Relative to what ?
It was still compared to cube before and after the teleportation.
The only thing that's moving is the intake portal carrier.
Movement is defined within inertial reference frames, not based on portals.
Your example also doesn't hold as cube itself has relative speed to itself. As it's part of the whole " moving" universe of the exhaust port.
You can't change inertial reference frames mid experiment they are not physical frames. They are abstract concepts we create that encapsulates all the variables withing the experimental. If you are changing reference frames, you are shifting to another experiment all together.
@@alqualonde2998 again going through the portal is not being teleported, a portal has no analogue in normal physics so instead let's look at a single static point in space.
Now if we take an inertial reference frame around that point.
Now if that point can observe itself through a portal, and the portal is moving, then the inertial reference frame breaks, we have a singular unique point of reference, that is approaching itself.
So you need to treat the point through the portal as being unique to the point we are observing from.
A reference frame cannot exist where a unique point moves relative to itself.
I'm glad you took relative velocity of the box and both of the portals. Everyone I've seen discuss the Portal paradox seems to neglect that. Speed and velocity are relative to objects in space. It doesn't really matter if the object is moving or the space around it is moving, because relative to the position of the object, it might as well be moving regardless
A portal does not _transfer_ its momentum to objects passing through it; a portal _preserves_ the momentum of things passing through it.
It's the same thing because momentum is relative. A portal moving towards an object is the same as the object moving towards the portal.
@@kremitthetaco8725 the way I picture it is the same as if you took a hollow box with a hole in the bottom and dropped it onto the platform with the cube. The box’s momentum would be absorbed by the platform and the cube wouldn’t move. Here, because the portal transports the cube to the slanted surface, to me the cube would slide off.
“Cube moving towards the portal is the same as the portal moving towards the cube” is valid as a way to explain conservation and is true given specific reference frames, but it disregards initial conditions. For example, depending on the reference frame me shoving you is the same as you shoving me, yet we both know there are more factors involved and in all likelihood the two actions would not yield equal results.
@@Scuuurbs Your analogy with the hollow box doesn't take into consideration that the cube already enters the portal before it touches the platform. What is absorbing the relative momentum of the cube from the moment it enters the portal to the moment the portal touches the platform? Let's say it takes 1 second to fully push the portal over the cube. That's 1 second of relative momentum basically pushing the cube through the portal until it stops.
If the cube truly had no momentum when leaving the portal, then the same would apply to every single particle the cube is made of, right? If every particle of the cube is static relative to the portal, they would all try to materialize on the same location on the surface of the exit portal Do you know what happens when you force 2 particles to exist in the same location? I don't. I don't think anyone does. But it probably wouldn't leave the cube intact.
The only thing which would stop that from happening is if the following particles push the preceding particles out of the portal, which would once again apply the relative momentum to the cube. So this also leads to the result shown in the video.
I'm also really not sure what "initial conditions" you're talking about. The entire point of the Portal games is that you're in a test facility for portals which exists particularly to eliminate external factors.
@@kremitthetaco8725The particles of the cube are "pushed" by the same atomic forces that maintain the cube's shape, irrespective of any qualities the portal possesses.
The only momentum that exists for the cube in this scenario is from the reference frame of the portal itself, which is unintuitive. Better to use the reference frame of an observer - in which case the momentum exists entirely in the piston/panel the portal is attached to, and its momentum is absorbed by the platform the cube was on, as well as whatever the piston is connected to.
@@Scuuurbs The laws of physics don't care much about what is perceived as "unintuitive" by some observer. If the camera was attached to the moving platform, your entire point of view on the experiment would change but the laws of physics remain the same.
The cube and portal have relative momentum to each other and that's the only thing that matters.
And if you're saying the particles of the cube are pushed through the portal, then they must have momentum when exiting the portal. And how fast would they be pushed? Is it some arbitrary number? Or is it simply the speed at which the cube is pushed into the portal?
bro the texture of the paint on the wall and his skin as well as his shirt and arms are literally so similar that I thought there was a static filter applied to the entire video.
watching this was trippy as all hell.
I wasn't onboard until you did the "hula hoop slam" and it changed my mind the instant you pointed out that the exit portal was also moving. Nicely done
You instantly got me to subscribe by prioritizing my time before your retentionrate. Hats off. TH-cam needs more creators like you.
Same.
i always thought of it as the total momentum of all three objects remaining consistent, so i figured the cube should stop, but admittedly i struggle to keep track of everything
I have the same idea. What happens to momentum here. The portal (or the object it is placed on) would decelerate giving it's momentum to the cube. But I cannot rationalize how that interaction would occur.
This was my thought too, but when I went to write out a comment about it explaining the math, I think I found the solution.
Newton's first law states that an object at rest stays at rest and an object in motion stays in motion, until acted on by an external force. But also, motion is relative. An external force acts on the platform to move it down towards the cube, so the cube is already in motion relative to the platform before it even enters the portal. When the cube goes through the portal, no additional external forces act upon it (aside from small ones like air resistance and gravity) so it retains the momentum relative to the portal.
This does seem completely illogical based on the laws of physics we know, but that's because our laws of physics don't allow for moving portals. If you imagine a similar situation in space, it might make more sense. If wormholes had no field of gravity, then an object entering a wormhole would come out the other side at the same speed it entered relative to the wormhole. It doesn't matter whether the wormhole or the object is moving, as motion is relative. No external force would have to act upon the object for it to retain its relative velocity.
@@mithrandireichner2667 The answer is basically that the cube doesn't actually accelerate and no additional momentum is required, so none is taken from the platform. The cube is already in motion relative to the portal as soon as the platform starts moving, it simply continues at the same relative velocity because no additional external forces act upon it to slow it down. It makes no sense with our current laws of physics, but, if wormholes area real (and traversable) our laws of physics are wrong anyway.
@@ayylith The way I see it, the system encapsulates the portals and the cubes. One side could argue that the *cube is moving* relative to the portals, but when discussing physics, or math, especially linear math, the discussion happens within systems. We could go on discussions about the properties of this system, but I'm going to ignore that for my comment. Assuming the system includes gravitation, that should logically include the exerting body of that gravitation. So the basis of this system is Earth, the cube and the portals. With both portals, gravitation is negative in both cases, so towards the basis ground of the system. This does not change regardless of any other factor. It is a fact, then, that the cube is resting relative to Earth and the portal is, in fact, the object that is moving. So it stands to reason to assume that the *portal is moving* relative to the cube.
So my interpretation of this problem more or less disregards the portals themselves as effect sources since the basis of the problem is the cube in resting position. The only thing that should really be affecting the cube is gravity, assuming the portals don't add, subtract, convert, transfer, etc in the process, and that itself is a question based in unrealized information of the *game's universe*, not ours.
@@mithrandireichner2667 From the cube's frame of reference the portal has velocity, but from the portal's frame of reference the cube has velocity. Relativity says whichever frame of reference you measure from the total energies involved are conserved (don't change over time), but that individual components of the system can measure different readings depending on the frame of reference you use. You can even use moving frames of reference such as the portal as long as you account for that movement.
We can simplify everything by measuring from the blue portal. And since when traveling through the portal the point in the middle of the orange portal is in the exact same place as the point in the middle of the blue portal (there is no spatial or time difference between them) We don't need to change to a different frame of reference, and therefore no adjustment is necessary (we'll call this point A).
The velocity of the box going into the portal, as measured from point A = the velocity of the box exiting the blue portal, as measured from Point A.
Thank you for respecting our time. just for that you got my like, subscribe, and loyalty to finish watching the video.
I am looking forward to your N64 Portal game. That sounds like lots of fun!!
Great job keep it up! We love your work!
Suggestion/Question: In your version, could you remake the demonstration done in this video from a few years ago?
th-cam.com/video/0TZd95BCKMY/w-d-xo.html
A portal sandwich type scenario is both a common thought, and is also not an easy thing to intuit, and I am curious if you would yield similar results as they did. I'm also not sure if their method (from Portal 2 which does allow moving portals in one level) would work for testing the portal paradox, but would be interesting to see if you could implement it and compare your results from this video.
th-cam.com/video/zDAE9A_1NA4/w-d-xo.html This minutephysics video gives a satisfying answer to the portal sandwich situation.
i imagine it would prevent the portals from getting closer to each other than the height of the cube, as I would think weirdly the two opposite sides of the cube would be pressed against each other. would be cool see if this actually happens though
Yes!
Please crush yourself between two portals.
It would simply be an unstoppable force vs unmovable object paradox, I'd think.
@@DrowGM exactly this. It's all about normal forces and inertial reference frames.
Great video, man. The first of yours I've seen. I like your non-sensationalist, calm approach to editing and content! Keep it up.
What kind of content do you watch that is sensationalist lol? You and I have two very different experiences on this platform
My only issue to consider is that the blue portal is facing (and therefore traveling) in the opposite direction of the orange portal, thus doubling the speed at which the cube motion should occur, not canceling it.
No, the object leaves the exit portal with the same relative velocity as the object had with the entrance portal.
If the portals were next to each other, facing the same way and moving together, the momentum would double in relation to the room because it goes from speedy portal and still object to speedy portal and speedy object.
This makes sense, scientifically speaking.
See, one might argue that, in order to move the cube, it needs energy, but the portal, since it doesn't come into contact with it directly, can't possibly give it any kinetic energy, which means it shouldn't move.
But here's the thing: we aren't dealing with normal spacetime here. These portals are wormholes.
It's like bending spacetime to "travel faster than light." You yourself, or the cube itself, doesn't move, but the space around it does. What the orange portal is doing is basically slamming space at and around the cube, which means, relatively speaking, it is moving. And since space is kind of our ultimate frame of reference, we can only ever experience this interaction as the cube moving in space, even though, technically, the cube is stationary and space is moving around it.
What happens to an object thrown in to a stationary portal while the exit portal moves forward relative to its face at the same speed. Awesome video it's got me curious.
The biggest argument to me against the moving portal paradox is the fact if it didn't shoot out the object would be forced to be squished when exiting, because otherwise the rest of it can't exit the portal
This is a really cool development, and it gave me some questions on the “science” of the portal paradox. What happens if you slam the portal down but suddenly stop halfway? Or 3/4 of the way? Would the cube bounce up through the portal, or is it still planted in place? I wonder if there’s a way to test this
It's all about relative velocity. It would be the same as if you were to, say, run really fast with a cube, then stop with the cube when it's partway through.
But of course, it seems counter-intuitive to a degree. Because if there was just a sliver of the cube that didn't go through the portal, then it would still theoretically remain stationary. But if it had moved one "sliver" further, it would exit at a velocity like in the video. So that's where we have to think about the physics of portals. If everything I've said here is indeed true, then it would seem that, while something is on both sides of the portal at the same time, it can be considered in "limbo". That is, "stuck" on both sides of the portal until it fully clears either portal. The exit velocity of the second portal would then be equivalent to the item's velocity at the exact moment when the final portion of the item completely clears the first portal. That would be my theory at least.
If you stopped the orange portal halfway down the cube, then there will be a half-cube leaving the blue portal with speed equal to the orange portal's previous speed. This will pull on the stationary half-cube, accelerating it through the orange portal (while decelerating the exiting half). Once the whole cube is through the portal, it will have half the speed it would have had if you hadn't stopped the orange portal.
The problem with the equations is the assumption that portals can have momentum. Portals are connections between regions in space. The cube doesn’t interact with the moving platform, it interacts with the portal *on* the platform. Since the portal cannot impart momentum and the cube is stationary, the cube simply drops as soon as it crosses the portal.