Consider the proposed scenario in the attached image.
Assume that portals can have both velocity and acceleration without breaking (whatever physics of portals that might imply).
The top surface (with orange portal attached) moves towards the cube with non-zero velocity v.
The portal is not large enough to engulf the platform on which the cube is sitting, so when the two surfaces meet, the cube will pass through the portal but the platform will not, causing the upper surface to instantly decelerate to 0 (unless your answer requires realistic rates of acceleration, in which case elaborate in your answer).
For simplicity, assume that the environment is 0 gravity and a vacuum.
Will the cube be launched (i.e. move away from the blue portal at velocity v)?
Will resolve to the answer of a poll to be linked after the market close time. If there are arguments for a more appropriate resolution criterion, feel free to propose them in the comments and I will consider them.
I reserve the right to bet in the market (for as long as the resolution does not depend on my subjective judgment; if this changes, I will disinvest).
Update 2025-02-11 (PST) (AI summary of creator comment): Portal Relationship
The orange portal and blue portal are fixed relative to each other and remain directly adjacent.
As a result, if the cube moves away from one, it must simultaneously be moving away from the other.
1,000People are also trading
It would violate relativity if it was A, though right? For example, one of the important thought experiments of relativity is that if you are in a sealed room, you cannot identify whether or not the room is stationary or has some velocity.
But if portals worked like the way they do in A, couldn't you could devise an experiment? Suppose there are two scenarios, one where the room is moving with some velocity, let's say 1 m/s downwards that is orthogonal to the floor and ceiling. No gravity, no friction, etc. Then you can have two portals, one that is pointed orthogonal to the room's velocity (so, mounted on one of the walls), and another portal that is mounted on the ceiling. Then, hold a table with a companion cube on it like in the diagram in the post, and ram it upwards at a speed of 1 m/s so the cube goes through the portal in the ceiling.
Then if the room is moving, then the table you are holding is stationary, because the room is traveling downwards at 1 m/s and you are moving the table upwards at 1 m/s, so the cube would just plop out of the second portal with no velocity. But if the room was stationary, then the table you are holding is moving, so it would go out of the second portal at 1 m/s in an orthogonal direction. So you can tell if your room is moving or not based on that, whether or not the block plops out of comes out at velocity 1 m/s.
So it must be B, in both cases (table stationary and portal moving, or table moving and portal stationary) the cube must fly out at velocity v. This way, there is no difference. It could be interpreted as the moving portal transferring its momentum somehow to the block.
Of course, we are assuming principles of physics apply to a fictional portal that does not exist, so this might just be wrong.
@spiderduckpig I'm not sure I follow.
Then if the room is moving, then the table you are holding is stationary, because the room is traveling downwards at 1 m/s and you are moving the table upwards at 1 m/s.
The table would appear stationary to an external observer watching the room moving at 1 m/s, but neither of the portals fits that criterion, so I'm not sure why that frame of reference would be relevant.
If this question is going to be resolved based on a poll, then it will be disastrous because most people don't understand the correct answer. I suggest prolonging the market until there's a general consensus on the Internet.
@luvkprovider I don’t know that there will ever be a general consensus. I think the “correct” answer has been fairly well-argued elsewhere, but people always disagree. A poll is the only fair way I can see for this to ever resolve. Given that portals don’t actually exist, I’m fine resolving this in favour of whichever side makes the most convincing (and consequently generally accessible) argument.
@NBAP Now I agree with you that a poll is the best way to resolve this. I understand that there's never going to be an answer that will be accepted everywhere. Right now there are an equal number of YES bettors as NO bettors so it is fair. However, I think there is a bias in which people tend to favor the second answer in a poll over the first.
@luvkprovider Enough to be the deciding factor? I could use RNG to determine which option is listed first. If there’s a better way to account for this concern, let me know.
Guys it's obvious. The cube will be launched relative to the orange portal, but it will not be launched relative to the table or the blue portal. In this case, the table/blue portal (not the orange portal) is what we're assuming to be in a fixed position in space.
@luvkprovider The orange portal and the blue portal are fixed relative to each other (they are always directly adjacent to each other), so how could the cube be launched relative to one but not the other? If the cube is moving away from one, it must be moving away from both.
@NBAP The space below the orange portal and the space above the blue portal are two separate systems of space that are not fixed relative to each other. Therefore, if we wish to consider the vacuum/environment as a single system, then we have to accept that there can be points within that system that are not inside any space, or inside multiple spaces. The orange and blue portal are not fixed relative to each other in the vacuum/environment.
The space below the orange portal and the space above the blue portal are two separate systems of space that are not fixed relative to each other.
Hm, I hadn’t thought of it. Is this necessarily true regardless of the underlying portal mechanics? What if portals were just instant teleportation machines, rather than a wormhole or some such?
For what it’s worth, I’m a multiverse theorist, so I agree with you on this point, but I’m just not sure it’s true on every theory of portals.
Minute Physics videos on the topic.
The obvious YES argument is that by relativity, there should be no difference between the portal moving downward and the block moving upward.
@TimothyJohnson5c16 The obvious NO argument (though to disclose, I am a YES theorist) is that the block is currently sitting on the platform, and why should it suddenly fly off of the platform?
@StellarSerene The problem remains, though: the top of the cube has no momentum relative to the floor, and so how could momentum pull it off the floor? Otherwise put, should the velocity relative to the floor not also remain constant?
@NBAP Since the portal should keep the object continuous, the relative velocity of the two parts to the portal should be the same, so the part that have passed(the top of the cube) should have a non-zero velocity to the ground. The moment the portal stop moving, say it stop with the block being halfway through, will be when the bottom part have zero relative velocity to the portal which is not the same as the top part that have passed, so there will be a sudden exchange of momentum like a "pulling collision" between the two parts. The block's velocity to the floor does not remain constant despite no visible force is on it is because the portal is doing something here, interfering with its momentum and energy, otherwise the object will "break", which is the core here since there are many ways a portal might work but there should be no controversy that it should keep the object passing continuous. If the portal stop at the very bottom instead of in the middle, all of the block will have velocity.
@StellarSerene It's unclear to me exactly what you take "continuous" to mean. The cube has a frame of reference. From that frame of reference, at the outset of the scenario (before anything has passed through the portal):
The floor is stationary (the distance between it and the cube is not changing).
Everything on the blue side of the portal is moving with velocity v.
As the cube begins to pass through the portal, neither of these things should change:
Everything on the blue side of the portal will continue moving with velocity v (as evidenced by the fact that the cube is moving through the portal with velocity -v from the blue portal's frame of reference)
The floor will still be stationary (as evidenced by the fact that it is moving closer to the portal at the same rate as the cube, and would continue at that rate through the portal if it could fit).
I agree with your sentiment that the moment the portal stops moving is crucial, but before that point, I don't think anything weird happens and I think the physics are largely uncontroversial. I don't think it's right to regard the cube's velocity relative to the floor as having changed as it passed through the portal, rather than (potentially, if Theory B is true) at the moment that the portal stops moving.
@NBAP as the portal moves, the top part (passed) and the bottom part(remaining) of the cube will have different velocity to the floor since the relative (to the portal) velocity of it going into the portal and out of the portal should be the same, otherwise the cube will either be streched or compressed (not being continuous) due to the different rate of cube entering and leaving. But since the blue portal have zero relative velocity to the ground, this would require the top (passed) part having non-zero relative velocity to the ground (otherwise why is it coming out of a stationary portal at all?). The bottom part will remain still before portal stops. So if the portal stop midway the velocity difference will cause a collision and make the cube do v = (m2v2 / m1+m2).
as the portal moves, the top part (passed) and the bottom part(remaining) of the cube will have different velocity to the floor
They shouldn't, at least not until the two platforms collide and the cube (potentially) goes flying off the platform. When the cube is halfway through the portal (but the orange portal is still moving down), both halves of the cube have the same velocity relative to the floor of the platform, i.e. 0.
since the relative (to the portal) velocity of it going into the portal and out of the portal should be the same
Correct, it would be. The bottom half of the cube is moving into the portal with velocity -v, and the top half of the cube is moving out of the portal with velocity -v. They have the same velocity in both frames of reference (0 in the orange portal's frame of reference; -v in the blue portal's frame of reference).
But since the blue portal have zero relative velocity to the ground
To be clear, when I was previously saying "ground", I meant "platform", not the ground on the blue side of the portal. Going forward, I'll just say "platform" to refer to that surface, and "ground" to refer to the surface on the blue side of the portal. The blue portal has zero velocity relative to the ground, but it has velocity v relative to the platform.
this would require the top (passed) part having non-zero relative velocity to the ground (otherwise why is it coming out of a stationary portal at all?).
Yes, the top half of the cube has velocity -v relative to the ground, but it has 0 velocity relative to the platform. However, this is also true of the bottom (remaining) half of the cube: it also has velocity -v relative to the ground on the blue side of the portal.
I don't see there being any difference in velocity between any parts of the cube at any point in the process, and so the jump off the platform cannot be attributed to the velocity of one half transferring to the other half.
@NBAP If you consider both the left platform and the right slope stationary(zero relative velocity to the ground, since it's not specified that they are moving), then the two parts of the cube will easily have different velocity to the ground, so one stay on the stationary platform(v=0) and the other come out of the stationary blue portal(v!=0). And in this setting, if the portal stops in the middle of the cube, one half will pull out the other half. If the portal doesn't stops in the middle but finish its journey to the platform, it flys out in velocity v which can be seen as the whole cube pulling out nothing.
If you consider both the left platform and the right slope stationary(zero relative velocity to the ground, since it's not specified that they are moving)
The right slope is stationary relative to the ground, but the left platform is not: it is moving closer to the ground.
Yes, the platform the cube is sitting on is moving closer to the ground underneath the slope.
What is this?
What is Manifold?
Are our predictions accurate?
Why use play money?
Why use play money?People are also trading
What is this?
What is Manifold?
Are our predictions accurate?
Why use play money?
Why use play money?