Ok, this is about 2d, not 4d, sorry.
But, I was reading about people in the second dimension. It says that a sphere would look like a circle growing then shrinking.
How is that possible? To see a circle, it must have width and must be perpendicular to the flat-creature, which would mean it was now 3d, not 2d.
Um, if that didn't make sense, read on, if it did, please answer how is that possible?
This is if we are looking upon the flatworld, like a picture.
If the flat creature always faces left, and this sphere comes along, according to the site, it says it will look like a circle growing, then getting smaller. It shows the flatcreatures field of vision to be 3d as well, as it has 2 lines on either side of the circle.
If it saw the sphere like we see a circle ( O) it would have to have depth as well as height, to us, so it would look like a line to us. |, as it is side on.
To the flatcreature, the page says it looks like a circle, which means it has to have width TO THE CREATURE. However, the width is already right-left, which means that it would have 3 dimensions, not 2.
How is this possible? This is really hard to explain.