How do we know that we are really living in 3 dimensional world?
We can draw 3D in a paper that is one dimension. So, maybe the world around us just looks 3D! how can we prove that we're living in 3 dimensional world not one dimensional?
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The simple proof is that you can tie your shoelaces.
This is a proof because you can only tie a knot in an (approximately) 1D object in three dimensions. In lower than three dimensions it's impossible because that would require the shoelace to self intersect. In higher than three dimensions it's impossible because there's always a way for the knot to untie itself.
Think what one dimension means: everything going forward or backwards in a line from -infinity to infinity.
1) A car would flatten you in one dimension, and there are billions of cars people etc in motion. As we exist there is an extra dimension. So we need two dimensions at least.
2) Walking in two dimensions you would hit your head at the first projection, the house would be on top of you. A third dimension is necessary.
This should be physical proof enough available to anybody that we live in at least three space dimensions.
There may be many more, as in string theories, but we live in a three dimensional space projection as far as our physics goes.