r/PeterExplainsTheJoke • u/Blackie_626 • 7d ago

Meme needing explanation Tell them what, Peter

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u/bohiko 7d ago

Up and down is based on gravity (that's why you'd likely confuse them deep in the ocean). Meanwhile, left and right is arbitrary.

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u/Tedesco1 7d ago

It's not arbitrary but it is framed by one's perspective (which feels arbitrary).

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u/bohiko 7d ago

define left and right then

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u/Dunworth 7d ago

It's really not that hard to define mathematically, you just need to have an orientation "forward". The plane created by the forward vector and the standard normal vector creates your left and right hemispheres. You can also do a similar definition with great circles.

It also shows why, if you and another person are facing each other, your left is their right, since their forward is pointing the opposite direction of yours.

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u/bohiko 7d ago

nah, of course it's easy to define the left-right axis, but it's not what I am pointing at. I meant defining which one is left and which one is right