this post was submitted on 18 Aug 2023
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[–] Yadaran@feddit.de 2 points 1 year ago

The Portal can't move front or back, only "to it's sides"

[–] reverendsteveii@lemm.ee 2 points 1 year ago (7 children)

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.

[–] Fubarberry@sopuli.xyz 2 points 1 year ago

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.

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[–] Zithero@lemmy.world 2 points 1 year ago

A, the people are traveling towards the portal, not the other way around.

If they were falling/running at the portal it would be different.

Here the portal is moving forward towards them, they have no momentum.tk travel through the portal.

[–] kogasa@programming.dev 2 points 1 year ago* (last edited 1 year ago)

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.

[–] NoFood4u@lemm.ee 2 points 1 year ago* (last edited 1 year ago) (1 children)

a portal is supposed to be like a hole that you go thru except you end up somewhere else, if i pass a hole over you, would you feel anything? A

[–] sulfate7016@lemm.ee 1 points 1 year ago

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

[–] zakobjoa@lemmy.world 1 points 1 year ago (1 children)

A

No, I will not elaborate. Fight me.

[–] And009@reddthat.com 1 points 1 year ago* (last edited 1 year ago)

boom pow crack

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