Ok so I just read somebody else’s question on dimensions and that prompted me to ask this question. It is kind of hard to explain my thought process but I’ll do my best.
So we often think of 2 dimensional objects as being flat, but I feel like a truly flat object would be as un-perceivable as a 4d object to us. So if we imagine a cube made of paper we have a 3d object.
Now if we squish the cube down and flatten it we have a “2d” object, a square. But in reality that square isn’t flat because the thickness of the paper still exists. So how do we make the paper truly flat? We can cut it in half to make it thinner and flatten it out, but there is still depth. No matter how much we “flatten it” there will still be some depth. Even if it’s 0.00^ to the trillionth degree.
So my thought is for something to be truly flat it must be completely non-existent in our universe. So how can we know that it’s flat? Once we can perceive of a truly 2d object wouldn’t you also perceive an entirely new plane of existence that we can’t even fathom?
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You gave this the physics tag, but you’re actually talking about mathematics.
It’s flat because of mathematics. Mathematics is used to model the universe in which we perform physics, and that’s why you’re starting to witness the model “breaking down” when you take it to the literal extreme such that a “flat” object still has some thickness.
OP, we live in the 3D world. Nothing is 2D to us. Only can we simulate 2D objects via computers, possibly even simulating 4D objects if I’m not wrong. Of course, in our world, the thinnest thing still has thickness to it and, therefore, isn’t 2D. (Someone mentioned atoms are 3D)
However, 2D and 1D still exist, along with higher dimentions. Hopefully, someone can eli5 this better heh
The piece of paper is 3d, as you rightly say, because it has depth.
The *surface* of the paper is 2d (assuming it’s completely flat). Like one face of a cube is 2d, while the cube is 3d.
We see two dimensional projections in three dimensional space all the time – they are called shadows. Just turn on a light or stand outside, and the object created from the projection of your three dimensional body on any surface will be a 2 dimensional version of you.
Aside from projections, yes, anything that has mass in a three dimensional space must be three dimensional.
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