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Message: <blockquote data-quote="MerakSpielman" data-source="post: 1168742" data-attributes="member: 7464">Your hand in this instance would not exist in any definable sense as far as anything in that universe is concerned.  Let's stick to the sheet of paper 2D universe. The sheet of paper is infinite in all directions. As a 3D person, we see a 2D creature as a flat thing moving on the flat surface of it's universe. The vision of the flatlander <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f642.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt="(:" title="Smile    (:"  data-smilie="1"data-shortname="(:" />)) is limited to his plane - he can't see us. No matter how far he travels in any direction he can never reach us. To him, we exist is a mythical place that can only be theorized and never interacted with. To him, we might as well not exist at all. We could poke the piece of paper, bending it, folding it, whatever, and the Flatlander wouldn't percieve a thing because his universe is being manipulated in ways that are invisible to him. Maybe we, as mysterious creatures from the Third Dimension could take his universe, and fold it so that one layer was parallel to the other. Then, using Universe Scissors, we cut a strip from one layer and tape it to the end of a strip from the other layer, creating a bridge between two remote locations in Flatland. This would look very odd indeed from the perspective of the Flatlander, who could now magically travel from one place to another instantly (though horrible things would happen should he wander off the edge of the strip while traversing it). This is essentially what sci-fi writers propose we do for space travel - except we use the fourth dimension (assuming it's a spacial dimension, not "time") and connect two distant points of physical space so that we can travel instantly across far distances without breaking any rules about the speed of light. Nobody has any idea how to go about doing this. This is also where the term "parallel universes" comes from. If we're a Flatlander, perhaps there are other "sheets of paper" universes, also infinite in all directions, but existing in the mystical 3rd Dimension and parallel to ours, so they never intersect. Perhaps there are infinite numbers of these. All the Flatlander examples (pretty much stolen from the book Flatlander) are supposed to be analogies to try to try to understand the 4th dimension (if it exists). It's easy to imagine parallel, infinite plane-universes, but hard to imagine parallel, infinite sphere universes. More fun with dimensions: If we can see all sides and the inside of a 2D creature, then a 4D creature would be able to see all sides and the inside of us, all at once. If a sphere were to pass through a 2D universe, the confused flatlander would observe a circle, expanding rapidly from a single point, and then contracting again (more accurately, he would "see" a line, but assuming he has some sort of depth perception, he would realize it was a curved surface and assume a circle). Thus, if a hypersphere (a 4th dimensional sphere) were to pass through our 3D universe, we would see a sphere, expanding rapidly from a single point, and then contracting to a single point again and vanishing. Seeing a 4th dimensional creature would be strange indeed, since we would only be able to see and interact with the portion of it that was currently in our universe, really only a tiny "slice" of the whole creature.</blockquote>

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