Passing A Portal Through Itself

portals those magnificent sci-fi devices where you step into one end and are immediately

transported somewhere else portals are just begging for us to ask

what happens if you pass a portal through itself

because anything going into the orange portal comes out of the blue portal

so when the Blue Portal goes into the orange portal

it should come out of itself

which is that even possible

yes I'm going to show you how

and it's weird to make things easier we'll start with a portal in 2D

space which is basically a line

we'll imagine these work just like portals in 3D

when an object enters a portal it exits at the same position relative to

the other portal the idea is that if you put two portals back to

back you can't tell there's a portal at all and then you keep that

same relative Behavior no matter where you move or how you Orient the portals

so an object entering near the bottom of the orange portal exits near the

bottom of the Blue Portal

and so on and if the Blue Portal itself starts to pass through the

bottom of the orange portal portal and we'll try to keep it clear where

the front and back and top and bottom of the portals are so you

can tell how they're oriented

if the top of the Blue Portal enters the bottom of the orange portal

it will emerge out of the bottom of the Blue Portal with the same

relative orientation which looks weird

but it's what logically should happen

if we just keep pushing the Blue Portal in the portal will crash into

itself and we won't be able to keep going

and it's the same if we flip it and put the bottom of the

Blue Portal in near the top of the orange

but if we put the top end of the Blue Portal into the top

of the orange portal

it comes out of itself closer to the top until the part coming out

of itself goes back into the orange portal again and comes out of the

blue portal farther down it's the portal coming out of itself coming out of

itself it's all a bit confusing to keep track of but it's may be

slightly easier if we add numbers along the Blue Portal so you can keep

track of which part of it is where

because you should be able to keep track of the entire Blue Portal

there's no inside of a portal since anything that passes through one portal is

immediately outside the other end

so 100% of the Blue Portal must remain visible and in existence

at all times that is we should always be able to account for the

full length of the Blue Portal no matter how weirdly recursive

the situation becomes and it can be very

very weird and pretty

but definitely weird anyway to get the blue portal to go all the way

through the very end of the Blue Portal has to finish coming out of

itself as it simultaneously

disappears into the orange portal

which seems impossible unless the portal is infinitely

thin otherwise it's going to get stuck on itself or get squeezed or something

but if we allow ourselves a little flexibility

a 2d portal passing through itself

looks like this or

this or this and in 3D

it's similar but slightly more confusing because of the multiple rotations needed to fit

the portal through itself

here's one way a portal can pass through itself where I've colored the back

side of the portal black and kept the front side a solid color and

here's the same thing with a grid on the portal so you can keep

track and really confirm that it is always 100% outside

even as it's passing through itself

but of course you probably want to be able to look through the portals

as this is all going on which looks something

like this to be honest I was kind of surprised that it's as possible

as it is to pass a portal through itself

but when we follow things through to their logical conclusions

sometimes the universe even a madeup one

can surprise us and while it may not surprise you to learn that I

made the animations in this video using visual effect software I also had to

use a fair bit of computer coding as well computer coding sneaks in everywhere

these days even video editing and that's why you should check out nebula classes

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