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.
The only way it could be B in this universe is if the train also decelerates equivalent to how the people accelerate. If the people accelerate and the train maintains velocity you’ve created energy in a closed system.
Portals don’t abide by physics, but people still do. Even in the infinite fall scenario there isn’t infinite energy because the object accelerating is still subject to terminal velocity, and it’s change in momentum comes from gravity. For the people to change their velocity, there has to be energy imparted onto them. My theory is that the train would have to slow.
The issue with being able to get infinite amounts of energy out of a portal can be solved by thinking with entropy.
If you only look at the entropic system of the portal and the object falling through it, say for instance a magnet inside of a vacuum tube that is perfectly abutted to both ends of the portal, the energy that you are able to extract from the system using a set of coils would come from gravity, and that gravity energy would come from the Earth.
In that case, one of two things would have to happen, either the mass of the Earth would decrease by being converted into energy, or two, the amount of energy needed to maintain the portal would be equal to or greater than the amount of energy that you're capable of extracting from it with an infinitely falling magnet and coil.
I think that the tram would not have to slow down, and that there would be no additional momentum added to the victims as they pass through the portal, and any energy that is lost in those two equations would come from the energy needed to maintain the portals operation.
You see, shit like this is why I love theoretical discussions about impossible crap. Somewhere else in this thread we use the idea that a moving portal can impart momentum in combination with the idea that portals need to maintain a minimum energy level to explain why moving portals collapse in a way that would at least be satisfying to someone reading a sci-fi novel. It’s now my head canon.
Objects coming out of the portal in “a” have to have velocity coming out (they don’t magically appear outside of the portal, they move out inch by inch/ cm by cm). So in a you would actually have double the deceleration on the train because it has to accelerate people leaving the portal and then instantly decelerate them once they have fully exited the portal.
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.
You still can’t filter reposts out of the feed without a browser extension to do it.
I go back every now and then, but my feed is full of everything but the music I actually want to hear from artists I follow.
And each track now takes up half the screen because it has to show off the album art in HUGE format, meaning even if I were willing to just scroll past reposts, scanning through the feed is a nightmare.
I think B and maybe it’s easier to explain my reasoning with a more dramatic example. instead of people on a track, maybe the trolly is heading towards a 50 foot horizontal pole. when the trolly comes to the pole at 90mph, the pole is not moving. but after the trolley’s portal has “swallowed” 40 feet of the pole, all 40 feet of that pole are exiting the portal at 90mph, being pushed by the 10 feet of pole that the trolly is still “swallowing”, so the momentum of 40feet worth of pole would continue to launch the remaining mass of the pole out of the portal and it would be launched out instead of flopping to the ground.
if we go back to our people on a track example, I think this would also kill them as for people on either side of the portal, it would feel like they’re being ran into at 90mph by the people on the other side of the portal.
Yes, I also thought of the pole example. It would feel like a wave of gravity suddenly shifting around them. I do think it would be less dangerous than a direct collision at the same speed, but only by a little - the danger with sudden deceleration isn’t the fact that it’s sudden, but that it is almost always uneven, it rips things inside you apart or collapse them together. But the portal would be a very clean uniform wave of pressure moving over you, so it could still cause damage by compression over one dimension (in the direction of portal movement) but most other forms of impacts will be missing
I have considered the repercussions of importing Japanese honeybees (which are able to defend themselves against Asian hornets), but I don’t know enough about bees to see if it would be a good idea.
B) The train transfers momentum to the things that pass through the portal. If it wouldn’t, the portal couldn’t exist since you need a certain amount of energy to displace the air on the other end.
I don’t agree. Inertia and momentum are not affected by a portal, even a moving one. If so, their legs would be stretched as they were partially through the portal till the body was being jerked away from the neck causing an even greated relative velocity compared to entering the portal.
Let’s say the train moves at 100mph, therefore your body needs to exit the other portal at 100mph. Otherwise it would be compressed. What happens to the energy of this movement if you just stop on the other end?
We also need to consider the air that is in front of the train as it moves forward. That air is going into the portal at the rate the train moves forward and therefore coming out the other portal at that rate.
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