If you think about it in a different reference frame, the portal moving toward the cube is essentially the same as the cube moving toward the portal, so the same physics would apply.
See this is exactly how I visualise it and don't understand why it isn't explained in this way more. A portal pushing into the cube is exactly the same as the cube pushing into the portal because - depending which portal you're looking at - both are occurring.
But there is another equally valid reference frame where the cube is not moving, and then later it is, without any force having acted on it. It always loops back around to "portals are impossible".
Yeah, that's exactly how he solved the problem in the last video, seems like the most sound explanation to me and the most simple to explain too, and this whole thing with particles and bonds seems to follow that.
@@SnakebitSTI Which reference frame? From the reference frame of the seal of the portal (the entrance/exit "surface") the cube is moving towards it (as already said). We cannot describe the movement of the cube from its own reference frame, so you are implying another reference frame.
The idea of the material fracturing because of a sudden change in portal momentum is scary. If the portal surface was indefinitely thin a sudden change of momentum or position could act as a kinetic “knife” changing the inertia at an infinitesimal plane thinner than a razor. Makes me wonder what might happen if an earthquake or seismic event happened while a person or living thing went through. Worst case could be just as bad as a portal closing mid-transfer… Thanks for helping us think about yet another disaster that could come of this innocuous-looking technology!! 😅
I don't think that would be like a knife under normal conditions or even earthquake . I think that only if portal stops at infinite speed that would be a problem. maybe edge of the portal could be like a knife tho
I always figured the portals were two ends of a wormhole. The path between any two portals is actually a null geodesic. Therefore there is no violation of energy or momentum conservation. It's like how the moon orbiting the earth changes its velocity constantly despite no energy input yet we know this is not a violation of conservation laws, rather it happens because the conservation laws hold.
My main problem with this is that it suggests that gravity should be able to travel through portals, and as such gravity would be able to pull you _up_ through a portal above you if the exit was lower. This would prevent the terminal velocity setup from working, instead making it a 0g zone between the portals.
@@angeldude101 It would not make it a zero G zone necessarily as you still get the gravitational influence from all the ground around the lower portal. You should still pick up speed and hit terminal velocity albeit at a slower rate.
@@ragingfred By necessity of the conservation of energy, you couldn't gain any speed by travelling from a point A to the same point A, even if your path goes through the portal. An object at the point A would always have the same potential energy, so you couldn't get any kinetic energy unless you include an energy source exterior to gravity (even including the Earth's gravity). You can't invent a perpetual motion machine, even in a world with portals. Technically, a free falling closed path that goes through the portal would by necessity sum up to zero gravity. Or if you want to be more precise, the integral of the gravity field throughout the path would sum up to zero, just like the moon does during its orbital path around the Earth. That doesn't mean that the gravity stays at zero G throughout, but it does mean that you can't gain speed between two cycles of a free-falling scenario ; since the integral of an acceleration force throughout the path corresponds to a speed difference, the speed would necessarily be exactly the same at the same point between two cycles. While the Earth does have an influence on the system and does still have a gravity pull, it only has a real influence as you move away from the system. Functionally, the two ends of the wormhole would probably act for gravity in a similar way as the two ends of a magnet act for electromagnetism, where the gravity influence near the wormhole is so intense that the Earth's influence is negligible in comparison. As you approach the system, you only feel the portal's gravitational influence, just like a compass gets fully influenced by a nearby magnet, but as you get away from it, it loses its influence and you can start feeling Earth's gravity again, just like your compass starts pointing North again as you escape the magnet.
I'm so glad you called out the fact portals merely existing already break several laws of physics. Great video! Edit: I really wish commenting this didn't result in further debates in the replies lol people need to chill and just enjoy things more
A portal on a moving surface can only take you to world that looks identical - but where the walls are moving and the piston is static. Two observers in the two worlds give different numbers for objects moving in their worlds - they can't agree on velocities - so I guess we just pick one.
@@JohnnyWednesday Arguably we don't just "pick one", the scenario is defined as the piston moving, so we know which reference frame we're in. It's not that important that another reference frame can come up with another value. Both would see the cube shoot out, at whatever speed it approached (ish), though how that is expressed can change. Consider both portals moving, along the same axis and facing opposite directions. The cube would almost certainly just plop out the other side given the negative velocity of the exit portal, even though it had positive velocity from the input. From the cube's reference frame, it doesn't look too exciting, mostly a teleport. And from the moving portals' perspectives, it does what it always does, and just keeps the speed it had.
@@JohnnyWednesdayYeah, two different observers with two different frames of reference would give you different results. That has nothing to do with the portals though, that's just how motion works
The cube has to move to conserve momentum in one frame, and it has to stay still to conserve momentum in another frame. That's a contradiction and proves the situation is impossible. You can do the same with energy conservation. All frames of reference being equally valid does not mean that what happens in one is irrelevant to what happens in another. Special and General Relativity describe how different frames of reference relate to each other. If you're talking about real physics, the correct answer is "mu". It's a meaningless question due to false premises. If you're talking about a game engine, as mentioned in the video it's a question of how the game engine works. It should be noted that the canonical answer in Portal is also that it's an invalid question due to false premises, as a portal cannot exist on a moving surface relative to the frame of reference of the room/a point on Earth's surface.
@@SnakebitSTI *except for the very notable instance in 2 where this is shown to not actually be an inherent property of portals. Also, what is the frame of reference where the cube with a portal slamming down over it must stay still to conserve momentum? Can the portal itself not be acting on the cube to change its momentum? Bc clearly its momentum _is_ changing, so instead of saying that change came from nowhere and defies physics, why can't we say it came from the portal?
8:12 It's probably important to note that this isn't necessarily a clean cut along the plane of the portal. The portal isn't acting as a knife, it's the object pulling itself apart.
i love how this starts out as a chicken and the egg situation and then James goes to prove the point by stating simply "where do you think the chicken came from", making everything else seem relatively obvious in the process. thank you for finally creating a well made solution to this lol
@@urlhnd An almost-chicken. Eggs are eggs, but egg laying animals may or may not be chickens. So an animal that was nearly a chicken laid an egg, from which hatched a chick that grew into a chicken. Egg came first.
@@messymessr exactly, chicken or egg first only seems interesting to people unfamiliar with basic science, educated people understand that the egg came first.
@@SuppaflyZSM Educated people understand that the question is supposed to be understood as "Which came first, the chicken or the chicken egg?", which is impossible to answer because we have no single coherent definition for either of those things when viewed on an evolutionary scale, similarly to how it's impossible to say where one color ends and the other begins on a gradient scale.
@@Lernos1 The "gradient" in this case only advances when new life is created, i.e. the egg. Assuming that 1) When something is born it either is or is not a chicken, whatever that definition is, and 2) that a pre-chicken cannot randomly mutate from radiation or cellular decay into a chicken... Then the chicken egg came first due to random genetic mutations during breeding. If it were possible to say there were a "first" chicken, then whatever that designated chicken is came from an egg.
I agree, thats how I've seen this problem all along. But it doesen't apply to the conservation of energy. Never had I considered the infinite portal fall, his example really fucks with my head.
It makes slightly more sense if you assume that the portals are "smart" and "powered" and can somehow - while the momentum of the object imparts some energy upon the surface they're placed - impart appropriate energy on objects moving in/out of them. If I'm understanding this correctly, it's pretty much the only explanation for how they can work at all. I think he had this same thought, and he pretty much says it, but not expressed in much detail. People genuinely arguing about something from a work of fiction that is a physical impossibility in our universe is a pretty silly exercise in futility obviously, but I think this video and what's been said here is the closest approximation to how it should/could work, and I think that's pretty cool lol
To me that would then mean the cube pushes back on the portal as well, so must at least be effectively slowing the portal on the piston down, or requires the piston to push with progressively more force
@@Haps_q I guess it makes more sense when I think about it now. Just the inherent fact of teleporting something to a higher place is an issue, because you're taking an "energy shortcut" when compared to the energy required to lift that object up normally. I agree with the video, there's probably no way to make this consistent with physics without handwaving the energy requirement away like "the portals are powered" or "the portals harvest energy from somewhere else" etc.
That's a force not an energy, and the problem is that in the example with a piston all the energy is already accounted for yet somehow the cube is imparted a force, and thereby given energy proportional to the speed of the piston. This only makes sense if pushing a portal creates a resistance equal to the kinetic energy imparted onto the mass moved through the portal, a lot like air resistance.
It's nice seeing your reasoning behind this. It almost convinces me that this is the way it should work. The way I see the portals are two sides of one thing. You can't have one without the other. One portal on a wall is not a portal. So it's more like, if a hula hoop fell around you, you wouldn't shoot out the other side.
Except from the perspective of the hula hoop, you DO infact shoot out the other side. It's only from your perspective that you're stationary, just like how the entire earth is moving at extreme velocities yet we are stationary relative to it.
On the problem of conservation of energy where you get infinite kinetic energy from this 8:57 scenario, I think you could apply this 6:00 to it. If the portals are stuck on a rigid surface, then that pushback would be felt entirely by you instead of the portals moving. Essentially, the portals would absorb your movement kind of like how a magnet falls slowly through a copper pipe or like a non-newtonian fluid. The faster you move through the portal, the more resistance to motion you feel. Of course, this kills all the fun of many if not all puzzles in Portal, so maybe we wouldn't want to implement it.
Love your videos on the Portal demake, but these videos are also great! Big fan of educational RU-vid channels like VSauce, MinutePhysics, Veritasium, etc. You did a great job in this video of combining two types of content I enjoy. Keep up the great work. Excited to see more from you in the future!
To figure out where portals get their energy from, there's some information that is relevant: 1. Moon rock is excellent at sustaining portals 2. Other materials can support portals (aperture had portal surfaces before they bought the moon rock) The most promising energy source in moon rock is Helium-3, an isotope of helium that can be used in nuclear fusion reactors. As other nuclear fusion fuels exist, this explains how old aperture panels could support portals, and as there's a limited ammount of Helium-3 in moon rock, it explains why the auto-portals in the early levels turn off (to preserve power), and even why the moon portal closes; The higher energy required to reach and match speed with the moon, combined with unpurified moon rock, results in a portal that only lasts a few seconds. Sure, it's nowhere near enough power, but that's a much smaller handwave than portals just being magic
There were so many people viciously arguing this problem in multiple reply threads over what seemed like hundreds of comments on the original short. There was one guy I remember specifically who was jumping into every thread to call everyone else an idiot and typing out multiple essays of manic physics mumbo jumbo, and ANOTHER guy who was doing the same thing(more politely though) rose to battle the first man. It was wild to see, highly reccomend reading through the comments on that video
My two cents on the conservation of energy problem is that portals fundamentally violate it. There's something called Noether's theorem which shows that symmetry and conservation are equivalent. For example, conservation of momentum is true because of translational symmetry, and vice-versa. Similarly, conservation of energy is due to time invariant symmetry. If portals were to exist in reality as they're shown in the game, you could violate causality by instantly transmitting messages (not a GR expert by any means, but there are some physics stackexchange posts where they explain this better). If you can violate causality, you break time symmetry which breaks conservation of energy. So even if crossing portals used energy, as long as you can break causality, conservation of energy can't be true Fun fact: conservation of energy isn't even true in reality because of the expansion of the universe (also because of Noether's theorem). It just appears to be true at our scale
I'm glad to see you did a follow up to this topic honestly, there's still some intricacies that you're missing, as I had mentioned in my previous comments on the other paradox video, but I'm thrilled to see you came to the same conclusions I did for the most part! I ended up writing down effectively a small essay from when I first sat down to think about the portal paradox and knowing some funky physics points regarding portals given their being based on wormholes and I'd honestly love it if I could sit down some day and have a chat with you on this some time! Especially given there is enough weirdness left to cover regarding the paradox on offer that you could actually make a third video, one thing I'll share adamantly though, all interactions should be considered from the reference point of the portals where the world always moves around them and that they are from their perspectives always static, makes understanding "Speedy thing goes in, speedy thing goes out" a lot easier for the weirder side of the physics, also puts more plainly the moving portal interactions true nature imparting moment of inertia. Please do let me know if you're open to having a chat regarding this given I had a lot of fun breaking down a ton of weird and at times in words of Einstein, spooky interactions and would love to properly share them in a form more readable than a youtube comment.
The answer to the last question is that portals - either as depicted in the games, or as imagined in an attempt to make those depictions physically consistent - inherently violate the laws of physics in some way. As portrayed in the games, and as popularly imagined, the portals connect two regions of space in such a way that the space is completely continuous. However, in the real world, gravitational fields propagate through continuous space, so a "real" portal would also cause gravitational fields to propagate. To make it obvious, imagine the scenario of one end of a portal on Earth, and the other on the Moon: you will of course get a massive flow of air at first, but even faster than that (at the speed of light in fact) you'll also get the Earth's gravitational field propagating through the portal. Needless to say, this is going to do *weird* things if you work through the consequences, e.g. I suspect that the portal ends moving relative to each other would generate gravitational singularities, at least in some circumstances.
One thing that's interesting about portals is that gravity doesn't seem to pass through them. You don't get pulled by the earth on the other side of the portal until you actually move to that side of the portal. I wonder if having gravity work through portals would solve all the infinite potential energy shenanigans, or if they would just make portals incredibly violently destroy their surroundings, as earth starts being pulled by itself through both ends of the portal.
A possible theory to where the energy comes from is if portals themselves had a mass. Considering the portal funnel effect, this could vaguely support the idea that they have their own gravitational pull. As objects enter and exit the portal its mass would change. In the case of infinity falling through portals, I guess one of the portals would collapse once too much mass is moved through.
About conservation of energy - in the case of the cube shooting out of the other portal - it would definitely have to come from whatever force pushes the portal in the first place. in the case of teleporting up - I think the obvious solution would be that you *should* need equivalent amount of kinetic energy to even go into such portal in the first place, and you just wouldn't fall into it when stationary, so when you fall through a portal and go up - the needed energy is taken from your kinetic energy, just like when moving up normally. Same with going down - such a portal would "suck you in" (this would require carefully thinking about how air pressure would work but I'm sure it would eventually equalize to *something*).
Actually, thinking about the air pressure thing more - my idea would *fix* air pressure issues, without this you would naturally have air being sucked from a portal below to a portal above, infinitely. This would provide a mechanism to prevent it. I think this would make portals completely physically consistent. But practically may result in some insane tidal forces when a portal goes between places at vastly different heights... so spaghettification by portal? And they would be so much less fun in a game
For the piston pushing against the portal, my intuition also tells me that it would come out shooting. The energy could come from the piston's kinetic energy (i.e. slow it down). For the infinite portal drop, it is a bit trickier because you are basically connecting two points in a potential field (gravitational in this case) you would need to penalize the energy somehow (e.g. subtract the potential delta between the portals from the kinetic energy of the object everytime it crosses) I think this is basically a weird discontinuous potential field where the potential increases a constant amount in an infinitesimally thin layer. That would mean you could stand over the portal on the floor, because you have not enough kinetic energy to even cross that layer (boring lol). It would also mean that you would get sucked into the ceiling portal if you crossed a single hand, and you would come out shooting to the same height you were before (that's why I mean the energy is conserved if you have it like this) Other interesting "paradoxes" would arise in virtually all other fielsd of physics. For example in electromagnetism, there are also very important potential fields like the electric field. To put it simply, you could just connect a battery to itself in series infinitely, and you would have the same exact problem/paradox as the infinite falling. For the record I am a physicist, so I should know what I am talking about even if I really don't. Maybe we just cant have portals in real life lol
I think the gravitational field would evolve over time after the portal is formed(you know, gravitational waves, whatever) and result in a stable, continuous boundary through the portal. If you placed a portal on the floor and on the ceiling, you might experience weightlessness and float at some point in between the two portals. Either way, there is necessarily a force from the change in gravitational potential. Otherwise, the portal the portal must effectively transport you to a parallel world where the gravitational potential is offset by a constant value. Because of gravitational time dilation, this means that falling infinitely down portals would mean travelling back in time. Canonically, interdimensional teleportation has been acheived by Black Mesa, and time travel is "_illegal anyway and strictly regulated by time cops_". Aperture Science very much dislikes following regulations, so I think this is somewhat plausible. (ignoring a number of paradoxes) Btw, I am not a physicist, and I have no real understanding of the math behind GR. I've been recently learning some differential geometry and geometric algebra motivated by a (remarkably relevant) problem relating to a bubble with discontinuous curvature, and I hope to someday be able to apply it to portals and spacetime curvature. Honestly extremely rewarding to find connections and apply math to things I genuinely wonder about.
Well the fact that the edges of the portals are fiery could help your explanation on the conservation of energy. Maybe the portal gun shoots a goo that burns slowly, and the burn rate adjusts based on the energy needs of what goes in and out of it, but it's always lit, like a pilot light of some sort. But now we're really getting into the weeds of scifi technology. We'd probably need to crossreference it with Half Life Lore and get Xen Magic Space Rocks involved
The cube is moving with respect to the portal it is entering, therefore shooting out is correct. For stopping halfway, once the cube starts to go through, it is now ALSO moving with respect to the exit portal. When the entry portal stops moving, the cube will continue, but with its momentum halved. It would then slow down thanks to gravity pulling more directly against the entry portal (assuming this exact diagram), so probably wouldn't shoot out, but would come to rest on the bottom edge of the exit portal.
Conservation of Energy is probably a bit easier to deal with. On the infinite portal fall, you're speeding up because gravity is pulling you down. But, your mass too is pulling the source of gravity towards you (the earth presumably in this case), since you have mass you too have your own (very extremely weak) field of gravity. And it's just building up with each loop through the portal. I have to wonder if there would be some sort of multiplication factor with the gravity pulling you through the portal. Since gravity is thought along the lines of warping space, that warp would extend up to the ceiling where the exit portal is, go through the entrance and back up. My instincts tell me it's unlikely to be a continual escalation of gravity build up, but it may have a sort of "higher gravity tube" between the two portals. Buuuuuut, I'm not sure if that would be the case. As for momentum itself, momentum is a bit weird. It could be considered having stored energy, but, from my limited understanding, that energy is more of a differential between two reference points. Like how in a car that is going a constant speed you don't really feel momentum until you come to a sudden stop. You don't actually have actual energy built up in you, but the act of speeding up or slowing down will change your vectors to make you feel like it. So with that in mind, when it comes to portals that are side by side facing the same direction, you can think of it like something along these lines. First imagine a wall between the two portals that don't even let the fabric of space and time to seep through. Then imagine a "space-time grid", with coordinates on it, and it intersects the first portal while one of the axis coordinates increment higher the closer it gets. One of the lines are colored red goes straight through the portal. On the other portal, the space time grid would push through it, and the axis coordinate is now increasing as it gets further from the portal. Now place an object on that line, and launch it forward, it's coordinate on the axis grows and grows as it reaches the portal. And when it exits the otherside, the coordinate continues to grow. Basically, think of it as the reference point the object is, is not in relation to the universe, but to the portal. And after this long write up, I thought of another way to think of the coordinates, think the coordinates for both portals, regardless where they are, as being [0,0], and the object is at [0,10], and moving towards portal A. It's coordinates decrease till it hits [0,0], and when it comes out of Portal B, the axis is now going into the negative numbers till it's at, say, [0,-10]. Even if Portal B was at [100,100] from the perspective of Portal A, from the object's perspective it's only [0,-10], despite being at [100,110] from Portal A. and with that rambling done I think I should leave this comment off here before I ramble more.
For the question of "How is energy conserved?": What if, it's the gun that provides the initial energy to open the portal, and as it's used, the energy in the 'wormhole' is removed. And then we can explain that the magical portal gun is smart enough to know and measure the current portal locations and puts more energy into those spots to keep it open.
I feel like relativity would solve all of the problems. The direction is relative to the portal, the speed is relative to the portal, and the kinetic energy would also be relative.
I liked this video a lot as someone that intuitively agreed with you, and agreed with your argument in the previous video, but it still didn't make sense as to why in my own head. Showing the two boxes made it instantly click. Thanks for all these wonderful videos.
I think the platform you're smashing into the cube is transferring it's energy into the cube through the portal. as you said, because the target portal is stationary while the other is moving, the first portal must be essentially pushing/pulling the object to the other side, and the only reason it's doing that is because it's being moved by the platform. so if this were reality I would expect that the piston encounters resistance similar to the momentum the object is gaining on the other side
how it is tansfering it since it is not touching it? and if it was magnetised than same energy that was pulling it towards portal would pull it backwards towards orange
@@klawypl I view the portal as a rigid membrane that warps light and matter upon contact to the matching membrane, so yes it is touching it otherwise it wouldn't be "going through" the portal
I think the best way to get over the conservation of energy is to state that it actually requires energy to travel through the portal. This energy can come from whatever is powering the portal itself. Which is still unknown from the game. Like, a portal which has nothing traveling through it is consuming 'x' amount of energy, but once an object travels through it, the energy consumption increases proportional to the work required to alter the objects momentum (plus a little more for entropy sake). While I'd love to draw the free body diagrams and do the calculations, I'm literally procrastinating studying for my physics midterm as I type this.
I think in most interpretations I have seen of portals they are seen more as doorways. They don't reconstruct you on the other side, they don't teleport your particles, etc. You literally move through them as though you move through a doorway. What the portals do is they contort spacetime so that the two portals are directly on the other side of each other spatially. Essentially imagine the universe is a piece of paper, they severely bend the paper back on themselves and then poke a hole, you as the player traverse through the hole. Momentum is conserved in that case, since you did actually walk through a door in the same direction. If you were to draw a line and then have the line"fall down the hole" spatially it's a straight line however, from our perspective it is not. It's the portal equivalent of a straight line on a curved surface does not look straight on a flat surface. If you look at it from this way and it is the idea of a door frame just falling on a cube, things start to make a little more sense.
You are forgetting the major reason for the breaking of conservation, its the frame of reference, relativity. the portals allow the change in reference frame for the object from one side to the other. with the piston example: * the stationary cube is accelerating constantly at 1g, but the platform is pushing back with an equal force (ie the ground) so it is stationary *as the piston drops the section of the cube passing through has its reference frame altered to that of 45 degrees local gravitational constant, so now the top half has an acceleration pulling the top of the cube to the side at that 45deg *also the mass of the top of the cube is is being accelerated by the emerging lower section of the cube (which you explained, but forgot the next bit) which is being pushed upwards by the stationary platform. THIS is where the momentum comes from for the emerging cube, the stationary platform is pushing the cube through the moving portal (the moving change in reference frame) with the opposing portal example the momentum is conserved because the reference frame of the cube (from the cubes perspective) doesn't change, from the observers perspective the reference frame itself of the cube changes when passing through the portal. So to be clear, the cube is in a box (its reference frame) the box has no mass or energy cuz is a reference to space time relativity of the objects within it. so from the cubes perspective the universe flips around 180deg and it just continues as it was without any force being applied to it. when playing with portals you need to remember that the frame of reference is the thing that is altered when passing the event horizon and not the object, and if the net forces on an object do not match the resulting net forces of the object on the other sides frame of reference than there will be an change in acceleration imparted proportional to the moment of inertia (mass) on either side of the portal.
The most generous approach to conservation of energy with portals would simply say that creating an infinite-falling loop would just result in some sort of anti-gravity effect between the two portals, although this gets way more complicated depending on the circumstances. The anti-gravity effect has to be dependent on the energy required to enter the portal, meaning that a simple vertical setup has zero gravity if you're exactly above the portal and more gravity the further you are from it, and/or the faster you're moving horizontally relative to it. It's a big mathematical headache that's not really fun for a video game.
My portal theory is going through a portal is invisible to the matter other than the physics on the other side of the portal once your matter gets there. The world on the other side of the portal is not yours but is simulator in every way other than your not in it yet. And you basically enter the world and leave the world just before you brake physics. The portals just are able to find a parallel universe where this extremely unlikely thing is happening just at this moment since at quantum physics level particles come in and out of existence randomly. And aperture science found a way to tame that. I also don't think portals can move but instead have a really short life, so short you don't even notice it. As you said the earth is moving all the time. I think they keep getting spawned and die so fast that it seems like it's one thing. They are still science fiction but it's some of the fun ideas I had :)
A portal is just a hole, where the other side of the hole is somewhere else. If you have a cube on a table, cut a hole in a piece of paper and put the paper on the table with the cube going through the hole, the cube doesn't just shoot up.
Instead of thinking about the piston at all, for a second think of the diagonal portal as a regular hole with a piston and a cube attached to it; flinging it out the other end. If the piston portal from the example were to stop halfway, the cube would have no sufficient momentum to pull it through leaving it on the ground with the other half poking through the exit portal.
As for where the energy comes from, a cool in universe explaination would be that portals absorb energy from their surroundings and then use that energy to apply momentum. Like if you did that ceiling trick for long enough eventually the room would be freezing temperature und till there is no energy left to absorb and it collapses. Could be a cool mechanic for a game where you have to be carefull not to use the portal to much. If you do it to much youd freeze to death but before that the floor would get slippery and it'd be more challenging. Or you could route lasers to a location to transport heat there and allow for more portal uses
In my head canon, a portal is just a device that very rapidly analyses every particle entering it, absorbs the particles into some hidden physical storage medium, and sends some information to the exit portal describing those particles, which '3D-prints' them on the other side from some hidden source of matter. From this perspective, the exit portal is effectively functioning as a sort of rocket engine so it makes total sense that the cube going through the portal imparts momentum upon it due to Newton's second law.
RE: Conservation of Energy Obviously portals aren't actually possible in reality, which means at some point we have to concede that portals are breaking some law or laws of physics. We'd rather it be as few laws as possible so it's as real as possible, but *something* still has to be broken. It obviously must be breaking conservation of energy. And there's no real explanation for that because... it's not real. It's where you need to apply suspension of disbelief and just don't worry about it. Intuitively I don't like the swinging portals thing. But also does that explanation even work if the portals aren't facing the same direction? Like if you put two hanging portals in a V shape (but with enough room to swing freely) and shoot a cube straight in to one of the portals. The entrance portal being pushed back still could make sense, but the exit portal would basically have that momentum applied sideways, even though the cube comes straight out. Or if the exit portal is still just pushed back like your explanation, I don't see how that's conserving momentum since it's a different direction. It seems more like portals just don't conserve the direction part of momentum, just the value. Edit: actually, direction is relative just like speed. So it still keeps the same direction relative to the portal the whole time just like it does with speed. Is that not conservation of momentum?
For me I think it will do both of your solutions: - imagine your first area contain water and the other simply air, then pushing piston in water would make the water flay off and flow, then replace the water with honey, a sandcastle, a rope or soft bread. For me the first part would gain inertia and with that inertia would pull the second part, but if bond are too weak then it would break, the breaking wouldn't be uniform but would depend on local weakness of bond Here a way to demonstrate: You have a pile 4 cube named from top to bottom A,B,C,D. You weld B and C, then you put honey between A and B then between C and D. What would happens when you stop halfway ? A and B would get inertia but not C and D, A would easily detach from B but like with the rope, There would be a mutual transfer between A and B, so A will not be at full speed, but B would have more speed D would also easily detach from C, but there would be a mutual transfer between D and C, so D will not be completely immobile, but B would have less speed B and C, having a strong binding would not break but maybe stress it if it's the weakest point, you can stil consider that they would totally share their energy and for me they would go about half the full speed
What if the platform with the portal coming down over the cube isn't being pushed, but is free-falling? As the platform with portal falls over the cube, the part of the cube already through the portal pulls on the part that is still on the other side, which is being kept back by gravity. With the right combination of weights (cube and platform) and falling speed, could it happen that the platform stops falling midway over the cube as the forces equal out? This could also change in interesting ways by making the cube bottom- or top-heavy. The one could make the falling platform stop higher up the cube, while the other could make the cube shoot out as soon as its heaviest part is through the portal.
Correct me if I’m wrong but the infinite falling trick works because when you put a portal on the ceiling and the floor, what you’ve basically done is create an infinite stacked building. just imagine you have a building with a bunch of floors and a hole in each and you dropped a cube all the way down but with the case of the portals it just drops forever That’s how I imagine it
I'd like to think of portals like the star trek transporter: The input portal destroys us slice by slice(like a material emancipation grill) , the output portal reconstructs(extrudes) us from a 2D surface. Something about the heisenberg compensators, let's just hope we don't get a Tuvix - or a ChElDoS.
since it isn’t expanding the capacity of the room in any way, it should maintain the same exact state even after putting portals top and bottom. or you know what actually, gravity is still pulling all water to the bottom, with the bottom having the greatest amount of pressure. i imagine it to be an endless loop of having the pressure constantly try and equalise coming through the hole in the bottom and pushing against the water in the top. nah bro idk it’s too late at night for this
Note that, if the cube must impart momentum to the portals if they reverse its direction (or change it by any angle, generally), there must be a corresponding _pressure_ upon the attached wall, as the cube passes. The cube too, ...maybe? I think it is best to think of the portal itself as a magical modifier upon the attached wall. The portal has, maybe not zero thickness, but arbitrarily small let's say, and in that thickness, magic happens. And that's "magic" in the most literal sense: we shall make this the singular, egregious conceit in our sci-fi world, and build everything around it as reasonably as possible otherwise. With this framing, we can understand the portal as a matter-teleporting front layer, and a force-reacting back layer. What should the force be? If we wish to conserve momentum as shown, then clearly it must be in relation to the amount of mass flowing through each point of the portal. The matter disappears instantaneously in one location, and thus its momentum is absorbed; and reappears instantaneously in the other location, to the same effect. It's identical to the cube hitting each wall: an elastic collision, simply bouncing off overall, but with a discontinuity in the trajectory. What about the piston case? The cube gains momentum, but this is no different from an angle change; magnitude or angle alone doesn't matter, different is different. We take the relative momentum between respective portal supports and the cube; the piston has to push the portal onto the cube to fling it. In these cases, we can simply teleport the cube (or its atoms as the case may be) with whatever force we like (since that's part of the conceit). Presumably the force should be zero (so the portal feels like an extension of normal space), and presumably there should also be reciprocal forces i.e. anything pulling/pushing through the portal gets transmitted in kind; so the cube doesn't fall apart as it passes, but retains cohesion, i.e. it sticks to itself through the portal. The important insight here is we need to transmit force to the teleporting object in such a way that it holds together, but this force isn't necessarily related to the force on the attached surface. This works fine for unaccelerated frames, but what about acceleration then? What if we stop the piston midway? If we suppose the above remains true before and after the acceleration, then we have the case where half the cube is given momentum, and half is at rest; as long as the force doesn't exceed the breaking strength of the cube, it continues on its way at half the piston velocity. Notice we've gone from a situation where the cube feels nothing, to one where suddenly it's being torn apart from the inside! The portal is accelerating away from the cube (it's moving towards, then stopped), and it's induced a tension force in it. Portal acceleration induces a proportional pressure on the object, at the portal plane. Accelerating away from an object causes negative pressure (tension), and vice versa. Consider the elastic collision case: suppose we have the face of a wall, with two adjacent portals, and the wall is accelerating toward the cube. We expect a cube to bounce off the wall, imparting an additional momentum due to its velocity at the moment of impact (acceleration doesn't factor in, aside from what velocity the wall had at the instant of impact). Here, velocity increases as the cube passes, and thus it's being compressed. We can also consider the static acceleration case: two portals on the ground, with gravity. In that case, there is a compressive internal force when passing through (which makes sense, both halves of the cube are pushing against each other by their relative weights). These cases are mostly pretty straightforward, but we could read the stopping piston case as something quite peculiar: the act of accelerating the piston away from the cube almost seems to _suck it up_ -- a force that neither camp anticipated! :)
I don't know if its like a question of right or wrong... As someone else has commented, portals don't exist in reality (as far as we know; and if we did we could look to that for reference lol). But in the case of this paradox, I always visualized it in my mind in the same way that if you take a piece of paper, and cut a hole in it, then take a book and place a crumpled up piece of paper on it (making sure the crumpled up piece of paper could fit through the hole of the first sheet of paper). Now take your sheet of paper and place it directly above the book/crumpled ball. Now quickly move the piece of paper down so that the sheet is flat with the book's surface, but the crumpled ball is untouched by the sheet of paper (kind of like threading the ball through the hole, but by moving the sheet only). The ball won't magically shoot up into the air. However, if you instead have someone hold the sheet of paper in the air, and you take the book+crumpled ball and move them just as quickly towards the sheet (by holding the book only), but stop immediately when you touch the sheet, then the ball WOULD keep going upwards. So in the portal paradox, I see the piston being more like the first scenario, where you bring the sheet of paper down. It isn't the stationary column + cube (book + crumpled ball) that moves up. It would essentially be more that the block, once through the portal, is now on an angled plane, so it tumbles or slides down the "ramp". Either way, its a simulated world, so you get creative license to make it whatever you want. Love your work btw!
Counter argument: I interpret the portals as like a window, where each side of the window is on a different surface. If i stand inside a house and throw a cube out the window, the window had no effect on the physics of the cube. If I take a window and slam it over a cube, nothing happens becuase I haven't effected the cube in any way. I think the portals are like if you cut a window in half. There's no barrier for particals to come out of
My personal theory is that the energy needed to allow for conservation of energy is simply coming from the portals themselves. Or by extension the portal gun.
Since the gun is connected to the portal and actively maintaining it, the gun must be supplying SOME energy, so it's a fair assumption that it's the source of all energy. But the gun isn't necessarily the source of its own energy. By the nature of the technology being very non-local and the fact that we only ever see the gun used inside the Enrichment Center, the power source could be massive and external with the gun only serving as a tool for directing it.
If you take a real life object and put down a hula hoop around it, it doesn’t cause the object-or stacks of objects-to suddenly accelerate upwards and jump merely by nature of having a closed loop surrounding them. The impact of the loop can cause the surface the object is sitting on to jump, but no matter how hard or fast that loop is going it doesn’t directly impart velocity into the object. Relative to the cube’s perspective, this is what’s happening. As soon as it completely exits the portal any new gravity takes effect. But even if there’s an infinitesimal sliver the cube is still anchored to its original ground. You can argue that all motion is relative, but that is a solved problem. Whether the portal moves down onto the cube or the platform and cube move up into the portal causes different effects. In the second case, the cube gets inertia if it goes fast enough. In the first case, stopping the portal halfway causes it to stay there. The portal, to the cube’s perspective, is just an empty volume of air like any other. In the second case, it’s behavior is dependent on how much inertia it has and can be modeled accordingly
I don't see any problem with the violation of conservation of energy. Portal 2 put an exit portal on the *moon*; the portal gun either breaks symmetry or is able to draw an arbitrarily large amount of energy from "somewhere off camera" to pay for its shenanigans. Probably alternate universes or something, if Half-Life is anything to go by.
Two things. 1. When you set portal to floor and ceiling the air starts to fall trough the portal causing updraft from portal above which pushes the air down harder and the gravity is now pulling air trough the portal on the floor which is pushing the air under the portal at the ceiling. This should cause the air to start fall and generated air current downwards? 😅 You basically made ceiling fan. Also all that carbon dioxide on the floor is now gonna fall down first from the ceiling, while it wont do anything in small amounts it is interesting topic. 2. The cube going trough a portal moving a constant speed leaves the other portal with same speed -> the cube didn't accelerate! That means you can send space ship to warp speed with 0 acceleration! The only thing that feels the G forces is the piston, the portal and the air going trough the portal while the portal is accelerating but once it stops accelerating and moves constant speed is also the point you can go trough the portal without feeling acceleration. Tough you might have to worry about hitting the air on other side if you are going too fast which might cause Sonic Boom from braking the sound barrier.
The entire portal thing breaks down as soon as you bring energy into the equation, because they'd already hypothetically take an astronomical amount of energy just to open...
By your logic, if you have a portal moving through our atmosphere, the stationary portal would have air blowing out of it (the air would be moving like a fan blowing it). I think most consider portals to be like a window frame or simpler, a hula hoop. If you move a hula hoop through the air, the air inside the hula hoop doesn't move. It doesn't care about one side of the hula hoop or the other. I think most believe that the portal itself imparts no collision with any matter, just like the opening in a window doesn't either.
I address the hula hoop argument in the first video I made about this subject. To accurately represent the hoola hoop you would need a flat surface with a portal on both sides. Since both portals in this situation are moving in the same direction the velocity from entering the portal cancels out the velocity of the exit portal.
I think we can wave away the seemingly breaking of conservation of energy by just saying that the portals are some hyper-dimensional connection along what can only be assumed to be hyperbolic space, such that there is no energy loss... which basically just equates to "magic science did it" now that I think about it :p
The main assumption is that cubes are appearing and the portals are not being treated like a regular hole, if you slam a hula hoop over two cubes nothing happens. Though I do understand the nature of the regular paradox. If the portals worked like Scenario A there is no issue of the cubes launching each other
I suppose technically, the energy pushing the cube through the portal is coming from the combination of the piston moving into the cube, and the relative direction of gravity on the other end of the portal. The cube would more likely jump simply from the impact of the piston against the metal plate below it, before gravity takes hold of the cube on the other side of the portal and forces it back down towards the planet, relative to its new location in space. Not accounting for the flow of air through the portal as the piston travels (which would likely result in a sort of breeze as the air is forced through into a new location), I feel all of the energy is accounted for, even if it doesn't necessarily transfer 1-to-1 through the portal itself.
you're transforming spacetime, even if its a moving reference frame, vector space can be transformed continuously. but portals wouldn't shoot off into space anyway because there is no absolute reference frame. instead, they would just fall into the earth if they weren't confined to a surface they wouldn't fly off tangentially either, since orbits are also gravity based spacetime deformations... but you are right about the rotation of the earth, that is a momentum, not a spacetime interaction
Here's some experiments you can try to help you visualise this problem a bit more: From their top ends, hold a pole in one hand and a slinky in another. Now drop them at the same time. Put a cube on an adjustable ramp. Going from a flat angle to a 45° angle, see how the speed of adjusting from one value to the other affects how much the cube moves 🤔
Also for the bit at the end about where the energy is coming from when you reach terminal velocity from having 1 portal directly above another portal, the answer is Gravity. Gravity pulls you down, then you hit the portal. You conserve your momentum, and you're still in free fall, so gravity pulls you down more until you reach terminal velocity
I don't think the portal would add momentum. I think the portal simply partitions the mass of the object between two points in space. So, the physics should be calculated as a combination of the gravity of both sides of the portal. So, basically, of you can calculate the percentage of volume on side A and side B, then add the two vectors together, weighted by the percentage of mass on each side, that would be your answer. In your example, portal B is on a slope, meaning gravity would be pulling it at an agle. So, as the cube passes through, it gradually becomes more and more influenced by gravity on side B. Effectively, you need to calculate physics twice and divide it by the percentage of each side. So, in your example, the cube would stay stationary initially, but as it passes further to the other side, the gravity of side B will eventually make it tumble. If side B had the exact same global transform and down was down, it would just sit still no matter how hard the piston slams, as the piston doesn't add momentum, it simply partition's the object's mass, and re-orients the object's velocity relative to its own rotation relative to the other side. This would solve your conservation of energy, as no new energy is created or destroyed, the object's influence of gravity is just calculated based on how far it is between each gravitational field from the respective sides.
Hey I think I missed the confusion. The piston portal will lay flat against the floor, this “floor” will be just in front of the piston portal. The other portal will make that floor show up effectively making the portal moot. It does not “stop” or “fly out” it simply suddenly finds itself on an incline and slides off. Hope this helps the conversation.
I like to look at it in a way I personally can understand. You could see the portals as a door. If that door moves towards you, you don't gain the velocity it built up. (Yes that's my whole argument lmfao)
There is conservation of energy if you consider relativity. Moving one portal applies the same force to the other portal. The speed of the launch will always be equivalent to the speed of the moving portal. It's like if you're in a car and get hit. You don't just stop, you fly through the windscreen. Same as if the portal randomly stops, like you do when teleporting to the stationary portal.
This is not even a question to stop and consider as long as you see the whole picture. Looking through the portal on the slant, you see the cube getting closer, but this is because the portal is moving closer to the cube, not vice versa. This means that the cube is motionless until the gravity from the slant acts upon it. Once it is slightly out of the portal, gravity combines with gravity from the other side, causing the cube to slid downwards until it hits the edge of the portal. I hope that made sense.
if you perfectly place a cube with equal mass distribution halfway into one of two floor portals, would it just sit there suspended with two equal and opposite forces of gravity pulling it? that’s rad ngl
0:45 the cube isn't "stopping", it never moved to begin with. the portal is moving space around the cube, not the cube through space. since the piston has the portal on it, it never touches the cube, so why would the cube move at all? so what would actually happen is: once the piston is fully down, the weight of graving pulling sideways on the cube would make it slide down, which until that point wasn't moving at all.
One more possible outcome for the portal stopping halfway, to go along with the other two possibilities. If the piston is moving slow enough, there won't be enough momentum to shoot the cube out, but maybe just give it a little jolt where it partially will hop through before falling back down. In this case, it would move the cube slightly on the original plane after falling back down before being stuck by the initial gravity with no additional momentum.
I don't really understand the first point he makes in the video. How would the cube receive energy seemingly out of nowhere and shoot out? From what I understood, the video (2:25) makes it seem as if the top box is already on the tilted platform, before a bottom box "knocks it" forward. Though my idea of portals is that the top box would not be considered on the platform, but rather would still be considered on top of the bottom box, as a form of continuation. It's like as if you had two boxes stacked on top of eachother and took a flat plane with a hole in it. As you move the plane down so the boxes would go through the hole, the top box wouldn't magically shoot up, they would stay still. I believe, at least in the context of the portals in the game, the portals would act just like this - a continuation, not a destruction/creation.
When you remove the floor with a portal, you are just allowing the object to follow the curve of space time. The 'energy' is already there in the object as that is what is making it 'stick' to the floor?
my favourite portal based game is actually now frame:portals on steroids, found the game while trying to find a puzzle game somehwere between squishcraft and a normal puzzle game, still love portal 2. this isn’t too relevant but yeah halfway gives it like half momentum and all the way shoots it off with the momentum i think the biggest issues with portals are stuff like atomic disassembly and failure to properly re-arrange, also you can drop portals in that portal game.
Actually it should just cause things to collapse. Since it is sending matter to X point while the Y point it is being sent from changes. So it should cause the matter to become as compact as possible eventually leading to a blackhole or outright making one due to matter being in matter or something along the lines of atoms exploding.
If an object was to fall on an infinite loop cenario, wouldn't it be stuck in mid air as the gravity fields coming from the Earth on the portal above would cancel out with the Earth bellow you? But most importantly, what about the gravity fields themselves, now wouldn't they fall in an infinite loop creating like a black hole pillar between the two portals as there would be an incountable number of fields in the same place?
I'm laughing at how you kept so tightly to the theme of cubes. I think some of this would be more intuitive if you asked "what if you accelerated a portal into a pool of water?"
The piston never touches the cube and force is never applied. If you had a moving piston with a hole the cubes would stay in the same place as the piston goes around. The portal is just a hole that ends up in a different location. They're not holes in space they're s hole in an object thats tethered. Portals wouldn't work how they do in the game because they would require an insane amount of mass (to bend space time)which would slow the moving objects and have their own gravitation pull
I personally do not think the cube would either stop _or_ fly out of the stationary portal. I think the cube would simply become violently crushed by the moving portal. The portal gun is described as a quantum tunnelling device. I really just think what will happen is that each particle will be teleported to the other portal, And without the particle having its own intrinsic momentum, It will just stay still on the other side while the other particles get sent through, Leading to violent destruction of the object as molecular bonds are destroyed and the particles fly off all over the place. I think it is a mistake to think of the portal as a physical object with momentum. Instead it's more like a field which changes the position of particles which enter the field.
Cubes aren't being pushed. They are always stationary. Moving them through the portal is just effectively changing where they are in the world, but not their velocity. If they were at rest before going through the portal they will stay that way. And if they were moving they will keep moving. Portals aren't applying any forces to the cubes, but rather changing their position and orientation.
I think that for the falling portals, if portals could exist (which they cannot), I think that the net gravitational force on an object between both portals should be zero. Meaning it would actually be impossible to fall forever through two portals as it would be impossible to fall, period.
I would argue it's the same thing as shoving a cardboard box with a hole in the bottom of it over a cube. I don't think it would fly out. It would only move because of the shift in gravity on the other side.
but it does fly through it, relative to the surrounding cardboard boundary, until the cardboard accelerates in a way that makes its velocity match that of the cube.
@@drdca8263 I feel like just because the portal moves fast around the cube wouldn't make the cube suddenly fly through it. I feel like the logic is flawed here. How exactly is the portal affecting the cube if it doesn't even touch it?
@@drdca8263 Since portals are just that, portals, imagine that the blue portal is on the immediate other side of the orange one on a suspended platform. Having what is essentially a hoop pass over the cube wouldn't just make it fly upwards, right? Is this really so different from having the blue portal be stationary? Edit: Okay yeah it IS different, because having the blue portal be stationary makes it so that it would fly out because of the pushing explained in the video You're right!
@@pierson9905 what do you mean when you say it doesn’t touch it? The cube goes through a surface with boundary the boundary of the portal. (Now, which surface you associate with it might be a choice.. maybe you don’t have to pick the taut surface connecting to the edge, but could choose some other surface, as long as you pick corresponding surfaces on both sides (would different such choices have the exact same consequences? I feel like maybe, but maybe not), but, there’s still something that the cube passes through at some point, else, if it never interacted with the portal, it would just be hit by the moving object?)
This is my understanding as a non-physicist nerd: Potential energy and kinetic energy don't exist. They are a useful tool to calculate predictions about motion, but there isn't a container inside an object that holds different levels of each energy and the levels change as an object moves through space. An object has a current state of motion which is given by the average velocity of the particles. The particles keep hitting each other and bouncing around in "random" directions. The velocity of these particles represents their temperature, but the average motion also represents the velocity of an object. The object as a whole appears to move in a cohesive direction because the particles are bound together by the nuclear forces -- when a particle would try to escape, if it doesn't have enough energy it gets pulled back toward the rest of the of the object. When an object gets accelerated by another object, the particles bump against the particles of the other object, and reorient their average motion while exchanging some of the heat. Gravity meanwhile, is just a distortion in space. Under the influence of gravity the line you follow that we call momentum, which is really just a consequence of the average of the wiggle of the particles, this line curves toward the gravity well such that "moving forward" becomes "falling". So, if a portal as seen in the Portal game existed, it would cause this metaphorical "line of momentum" to get interrupted and continue at the other end of the portal, with no exchange of energy necessary. The average wiggle of the particles would naturally change as the particles go from one end of the portal to the other, so the momentum would have changed, without any interaction between the object going through the portal, and the portal itself.
The conservation of energy problem was actually researched by Google X. They spent a few mil trying to make portals and then came to the conclusion that "they're impossible because they violate several fundamental laws of physics." 😂
Using portals actually converts your bone marrow directly to energy in a process that is reasonably efficient. Broken bones, however, are not part of the testing experience and should be immediately reported to your designated testing official.
What about 2 portals moving together, sandwiching a cube? In that case the portals can't touch each other, otherwise the cube would just vanish. So objects entering and exiting the portals exert force on the portals (and vice versa).
I'm not sure that this proves that the objects exert forces on the portals themselves - what would prevent the two portals from coming together in that situation is that one side of the object would begin to collide with its own opposite side.
I don't think the argument "portal would just fly out becuase the Earth is moving in space" works because there is no stationary system in the universe. We always count with what a certian observer sees relative to him
There is no energy created because what actually happens is that the Earth is pulled towards the ever faster falling object loosing its potential energy to the kinetic energy of the object.
Isn't it the case that conservation of energy doesn't even apply when it comes to manipulation of spacetime? I could've sworn there's something in general relativity that says something along those lines, like how the universe's expansion doesn't need to obey CoE.
was already thinking it would just pull the object through or at least start pulling it through before dropping it back down, another thought I had was if the object the portal was moving toward wouldn't fly out wouldn't it just crush the object? if it doesn't keep the relative momentum then it seems like the portal would act like a solid surface and crush whatever object it was pressed against, probably missing some information but that was my best guess.
