If the train drives slow enough that is takes 3s between when your head gets through and your feed are trough, it also needs to take 3s on the other side or you are ripped to pieces or squashed.
Now if it takes 0.1s, you also have to come out in this time and will have a velocity, the same as the train.
Yes, if the speed you go in wouldn’t the speed you go out, you’d be ripped apart.
In portal (the whole point of this joke), it happens instantly an works like walking through a door. If your hand is through, it’s at the other side and the rest of your body isn’t.
If you would travel at the same direction and speed of the train, you could step through and be stationary at the other side. If you stand still and the train travels to you, the only “logical” answer is that you fly out the other side or be ripped apart.
Suppose the blue portal is instead aligned parallel to and facing the ground. Maybe a 18" off the ground, a little higher than a person is wide. Additionally, the person is standing upright on the track.
In the above scenario, with the ground rushing at the person, does it suddenly “stop,” with the person gently falling onto the ground? This is the same problem, I suppose, but from a different perspective.
Now, what if that blue portal is instead only 6" off the ground? Is the person embedded in the ground, or does the universe crash?
I think you would collide with the ground like you were falling face-down, and is there isn’t room you’ll simply remain half-in half-out. At that point, your front half is still relative to the ground, but the back half is moving with the train, that way your velocity is zero in relation to both portals.
Discussed this with some friends and the view we came to is that your momentum relative to both the portal and your surroundings is preserved (which explains how you could portal to the moon and not get liquefied by the difference in rotational momentum between earth and the moon). The portal speeds you up or slows you down depending on local conditions on the other side to preserve your relative momentum. This would, logically, indicate that energy is created or destroyed depending on the difference, which (to me) means that ‘portals’ technically exist outside our universe as a concept and are therefore not subject to conservation of energy.
That’s already the case simply because you can go through a portal from the bottom of a cliff to the top of a cliff without doing work; this obviously lets you build a perpetual motion machine.
(Do gravitational fields pass through portals? If you try to go through a portal from earth to deep space, will Earth’s gravity pull you back?)
The train is not moving. The rest of the world is moving underneath it. Therefore, by the principle of “speedy thing go in, speedy thing come out”, the people will be launched.
Suppose the blue portal is sitting upright on the tracks facing directly into the orange portal (parallel to it) from some distance. We will of course neglect gravity and most physical laws.
Option B: The people shoot out of the blue portal, eventually reaching the orange portal again after a finite time (exactly halfway between the portals). At which point, their velocity relative to the train is double what it originally was, and they shoot out of the orange portal again twice as fast. Since the people are faster than the train, they will hit the train before it covers half of the remaining distance; and so this all happens again, with the people’s velocity now increasing to triple the initial value. And it happens again, and again, until relativistic effects take over and the velocity is no longer approximately additive. In other words, the people accelerate to an appreciable fraction of the speed of light, regardless of the starting velocity.
Option A: The people plop out of the portal and eventually get smashed between the train and the portal wall in a satisfying and physically plausible fashion.
Bonus Option C: In option B, it is unspecified if the resultant velocity of the people is equal to the velocity of the people relative to the train, or equal and opposite to the velocity of the train relative to the people. This difference becomes meaningful at the relativistic speeds we achieved, and I implicitly assumed the latter. In the former case, the people are eventually carrying ~100% of the energy of the system and therefore doubling it every time they pass through the portal, and time dilation be damned, for an instant they achieve infinite energy.
Now suppose the blue portal is just a centimeter behind the orange portal, opening the other direction, so anything that goes in one almost doesn’t even seem to have teleported. When the people pass through the orange portal, they appear on the other side; inside the train.
Option B: As the people pass into the portal, they instantly shoot backward, as if the train grabbed and threw them behind itself.
Option A: The people simply pass through the portal, as if it weren’t there at all.
Unfortunately, this isn’t testable in Portal because portals can’t be affixed to moving surfaces.
I would assume the people just plop out fine since they would retain their momentum (which is nil), and the portal’s own momentum wouldn’t be applied to them. But God damn it I wish I could just make a Portal map with a moving portal and see.
If we assume local relativity, their momentum, which would then be relative to the orange portal (the one which they will interact with), wouldn’t be “nil”. It is pretty clear to me that both portals have different relativities, and therefore, would clearly lead to case B.
Think of a portal like a doorway or just a frame of one. Stepping through it seamlessly puts you on the other side. If you were standing still, and the door went around you, would any force be exerted upon you, causing you to move? That’s why I think it would be A. Nothing is applying any force to you, you’re just basically teleporting. You may not even actually fully emerge from the portal, being trapped on the threshold, since no force is moving you beyond the point where the two ends meet.
Then I could imagine a sport where you have a racquet with a portal on it, and you swipe at a suspended ball, with a target somewhere beyond the other portal.
Considering that portals are quite literally linked in a spatial manner, it would make sense that they physically cannot move independantly. Moving the orange portal would also move the blue portal. Or from a different perspective: the portals are always fixed in space, but their surrounds can move.
But that does not make the question shown here untestable. It just means the output portal will have a velocity of it’s own.
How to test: place 2 portals next to each other on a wall. Then apply propulsion gel in front of the orange portal. And finally move yourself at high speed through the orange portal.
If your speed is unchanged after exiting the blue portal, but your velocity has been inverted with respect to the direction that the wall is facing, we can conclude option B must hold.
Trouble is even if you could, all that would show is what would happen under the developer’s implementation of the concept in their simulation, not what would happen if portals were real and you tried this which is really the spirit of the question.
EDIT: Actually mate, if you want to know what the game does with it, looks like a few people actually managed to experiment with this www.youtube.com/watch?v=S85nudR6D-Y ages back. Disappointing result, again it just shows what the game would do though.
Yes, that is called running extra fast. And then falling, with the same momentum. Unless there are two grounds, with different relativities. Like with a treadmill: you run relatively to the treadmill, but you are stationary relatively to the ground under it, because you run at exactly the same speed as the treadmill moves in the other way (hopefully for you…).
Enjoy over 30k hours of creative commons music, freely shared.
FunkWhale is another decentralized service like Lemmy or Mastodon. (It also runs on ActivityPub under the hood.) Most of the publicly available pods only share creative commons material, simply because it’s the easiest to share, but artists can share under whatever license works for them.
If you’re technically inclined, you can run your own pod and load whatever music you own onto it, and share it with others (I presume you’ll take care not to share beyond whatever license you have permits). Pods sharing pirated music exist, and they obviously should be avoided. Even if you’re not technically inclined, many pods allow you to upload some amount of music, you’ll want to double check the server’s rules to determine if that can be used for your personal library.
Thanks for the suggestion, but I was only using SoundCloud to listen to a friend’s new song.
Not only do I already have an account for Funkwhale, but I also have a formidable local collection of DRM-free music in the form of CDs and Ogg Opus. I also prefer to use Beatbump to stream music I do not yet own.
Yeah, since most of the public instances only make available creative commons stuff it’s better if you have a mood than particular artists. I suspect if most people switched they could find new artists to meet their tastes within a year.
My gut suspects that an artist with a good patron following probably has as much take home pay as a similar artist that signed a record deal. If true (and that’s definitely an if), why prop up up an industry that exists to siphon as much value away from artists as possible?
Except in that scenario both portals are moving if they act like a moving hole. Imagine a hula hoop, except it’s 2 portals connected back to back. If I passed a hula hoop over you, you’d be going into the bottom at the same velocity that you are coming out the top, therefore momentum is preserved. You’re moving at the exact same velocity in reference to both of the portals
This reminds me of when somebody set up the Trolley Problem for their toddler with those little wooden toy trains. The kid put the one guy on the track with the several guys and then plowed through all of them with glee.
But the orange portal is moving. The game code works more like A (it bugs out and the object bounces off the portal surface, but it uses a world-fixed coordinate frame that would match A for behavior). A (Newtonian) relativistic coordinate system would match B. For everything with non-moving portals A & B are equivalent.
Yeah, most game engines like Portal’s uses absolute speed relative to the coordinate system (which doesn’t change when the coordinate values change), in addition Portal technically doesn’t actually implement “wormhole type” portals and instead superimpose a clone of the polygons near both portals behind the other (to preserve expected object collision behavior around the portal) plus doing tricks with virtual cameras, so if you fixed the bugs with moving portals then it would be A.
But if you implemented proper relativistic physics with proper wormhole type portals you’d get B.
The game code works more like A (it bugs out and the object bounces off the portal surface, but it uses a world-fixed coordinate frame that would match A for behavior).
Ah, I see what you are saying. They apply the velocity of the object again after teleporting rather than the difference between the velocities of the portal and the object. Thus the velocity of the train would be ignored. Well, B is wrong simply because the game engine doesn’t rotate characters in the teleport because that would ruin character physics. So B is wrong twice.
sopuli.xyz
Hot