When you ask for directions and someone tells you "go straight", what do you do? I think you follow the directions. Do you stop and think about the 1D shape "line" that can't exist in our 3D world? No. You just walk along a straight line.
I don't think your question has anything to do with the real world and thickness. That's not involved in the bit of the video you picked out. There, we're considering ideal, geometrical points in space. Points have no size. But if you pick any three points, there is one plane that passes through all of them. That's the plane mentioned in the video.
You have just proven my point about your not understanding concepts in geometry. A point has no dimension. A line has no dimension. A plane has no dimension. You seem to think of dimension as something like thickness. But thickness is not a basic geometrical property.
What about it?
(pretend there are arrows to show that it is going endlessly). So, after this, Sal connects the points, creating a triangle ON the plane (So the triangle is stil in the second dimension, but the plane itself is in the third is in the third dimension).
Yes, the plane is 'endless'. Yes, the triangle is on the plane. No, the triangle is not in the second dimension and the plane is not in the third. They both are in 3d space. They both have zero thickness.
I mean to say the plane is in the second dimension. But, if the triangle and (maybe) plane are not 2 dimensional, and they exist in the 3d space, then what are they?
Let's consider the number line and the point 3.7 on it. I hope you would agree that this point exists on the number line. Yet, this point has zero length. Do you see this as a contradiction?
The connection is that you think "zero thickness" 2d shapes can't exist in 3d world.
They can exist in the mathematics 3D space, but not our 3D world (physically).
I’m not sure I follow you. A wall is a model that represents a plane, but you’re saying a wall is represented by a plane. I thought that the physical objects themselves are models of the mathematical models (ie. a physical cube represents a mathematical cube, not that a mathematical cube represents a physical cube)
It works both (actually 4) ways. We can create a math model of physical object (use sphere as a model of a planet). Physical model of a math object (edge of a ruler is a model of a straight line). And we can create math models for math objects (simplified formula to convert Celsius to Fahrenheit) and physical models of physical objects (toy cars).
Ok, I understand a lot more than before this thread. Thank you all. No need to further discuss. Thanks!!!