What is the opposite of a circle?

Answer 1

Based on circle definition, all points are equal distance from centre.

the opposite of circle will be spiral.

I do not believe circle is something which has an opposite. In order to have an opposite, something must have quantifiable features of which there are contrary features to be found in something else. While some of the features of a circle, such as being the two-dimensional shape with the greatest area for its perimeter could be opposed by something like a line, which has no area and infinite perimeter, there are other features of the circle which are not opposite.

The only answer I can give beyond "there is no opposite" would be elcric.

A circle is represented visually in 3D space, meaning it is bound by the constructs of space-time and dimensionality. The opposite of the "circle" would be the form the concept takes after compressing it back through the dimensions of the universe. Since this is impossible to do experimentally, with any type of matter/shape/concept - it's likely we'll never "know" what the opposite of a circle really is. Mathematically though, a well-versed quantum physicist with a heavy background in dimensional calculations may be able to help clarify what would happen to that circle on the other side. Geometrically, though, the opposite of a circle is an identical circle existing in negative space.